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WO2004088338A1 - Apparatus and method for evaluating underground electric power cables - Google Patents

Apparatus and method for evaluating underground electric power cables Download PDF

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Publication number
WO2004088338A1
WO2004088338A1 PCT/KR2003/001545 KR0301545W WO2004088338A1 WO 2004088338 A1 WO2004088338 A1 WO 2004088338A1 KR 0301545 W KR0301545 W KR 0301545W WO 2004088338 A1 WO2004088338 A1 WO 2004088338A1
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WO
WIPO (PCT)
Prior art keywords
cable
temperature
current
measuring means
conductor
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
PCT/KR2003/001545
Other languages
French (fr)
Inventor
Seok-Hyun Nam
Su-Kil Lee
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
LS Corp
Original Assignee
LG Cable Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by LG Cable Ltd filed Critical LG Cable Ltd
Priority to AU2003257711A priority Critical patent/AU2003257711B2/en
Priority to NZ538181A priority patent/NZ538181A/en
Publication of WO2004088338A1 publication Critical patent/WO2004088338A1/en
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/50—Testing of electric apparatus, lines, cables or components for short-circuits, continuity, leakage current or incorrect line connections
    • G01R31/58—Testing of lines, cables or conductors
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/22—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for distribution gear, e.g. bus-bar systems; for switching devices
    • H02H7/228—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for distribution gear, e.g. bus-bar systems; for switching devices for covered wires or cables
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
    • G01K7/00—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements
    • G01K7/02—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using thermoelectric elements, e.g. thermocouples
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B29/00—Checking or monitoring of signalling or alarm systems; Prevention or correction of operating errors, e.g. preventing unauthorised operation
    • G08B29/02—Monitoring continuously signalling or alarm systems
    • G08B29/06—Monitoring of the line circuits, e.g. signalling of line faults
    • H02J13/1323—
    • H02J13/36—
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J13/00—Circuit arrangements for providing remote indication of network conditions, e.g. an instantaneous record of the open or closed condition of each circuitbreaker in the network; Circuit arrangements for providing remote control of switching means in a power distribution network, e.g. switching in and out of current consumers by using a pulse code signal carried by the network
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y04—INFORMATION OR COMMUNICATION TECHNOLOGIES HAVING AN IMPACT ON OTHER TECHNOLOGY AREAS
    • Y04S—SYSTEMS INTEGRATING TECHNOLOGIES RELATED TO POWER NETWORK OPERATION, COMMUNICATION OR INFORMATION TECHNOLOGIES FOR IMPROVING THE ELECTRICAL POWER GENERATION, TRANSMISSION, DISTRIBUTION, MANAGEMENT OR USAGE, i.e. SMART GRIDS
    • Y04S40/00—Systems for electrical power generation, transmission, distribution or end-user application management characterised by the use of communication or information technologies, or communication or information technology specific aspects supporting them
    • Y04S40/12—Systems for electrical power generation, transmission, distribution or end-user application management characterised by the use of communication or information technologies, or communication or information technology specific aspects supporting them characterised by data transport means between the monitoring, controlling or managing units and monitored, controlled or operated electrical equipment
    • Y04S40/124—Systems for electrical power generation, transmission, distribution or end-user application management characterised by the use of communication or information technologies, or communication or information technology specific aspects supporting them characterised by data transport means between the monitoring, controlling or managing units and monitored, controlled or operated electrical equipment using wired telecommunication networks or data transmission busses

Definitions

  • the present invention relates to an apparatus for evaluating underground electric power cables included in electric power transmission equipment, and more particularly to an apparatus and method for evaluating, in real time, the conductor temperature and allowable current of an underground electric power cable to efficiently calculate the transmission capacity of the electric power cable.
  • the transmission capacity of an electric power cable is determined based on a temperature range in which the insulating performance of an insulator surrounding the electric power cable is maintained.
  • the conductor temperature of an electric power cable Upon determining the conductor temperature of an electric power cable, it is important to determine heat sources. To be taken into consideration for such a determination are Joule loss caused by current flowing through the cable conductor, insulation loss caused by high voltage applied to the cable conductor, Joule loss caused by Eddy current generated at the sheath of the cable and sheath circulating current, the thermal condition around the cable, etc.
  • the transmission capacity of an underground electric power cable is calculated by evaluating the conductor temperature and allowable current of the under ground electric power cable. The evaluation of the conductor temperature and allowable current is achieved using a method recommended by an international Standard, for example, IEC 287 or JCS 168.
  • LEC 287 is an international Standard established by the International
  • Electro-technical Commission (LEC). This LEC Standard includes standards for ships, electrical installations, electric power cables, high-frequency cables, windings, etc.
  • JCS 168 is a Standard established by JCS for standardization of electric wire products.
  • conventional transmission capacity determining methods aim to secure an increased stability, they calculate the transmission capacity of a cable by setting the worst temperature condition without taking into consideration an actual temperature variation occurring at the cable due to a variation in the environmental condition around the cable. For this reason, the transmission capacity of the cable is calculated, based on a limited static transmission capacity and a limited emergency operation condition, so that the calculated transmission capacity provides unnecessarily high security.
  • the conventional methods propose a transmission capacity considerably lower than a practically-allowable transmission capacity.
  • Most national key underground electric power transmission networks in, for example, Korea are installed in electric power cable tunnels. In such a case, the temperature of each electric power cable tunnel is simply prescribed to be 40°C.
  • each electric power cable tunnel is typically maintained at a temperature of 30 to 35°C even in the summer season exhibiting the highest temperature.
  • a direct measurement is not known.
  • emergency power transmission is typically carried out when an accident occurs.
  • allowable current is set, based on a fixed transmission time stipulated in the international Standard.
  • this method is inefficient because electric power can be transmitted only in a transmission capacity fixed based on the fixed transmission time, in spite of the fact that a higher transmission capacity can be given when the emergency power transmission time is shorter than the time stipulated in the international Standard.
  • the ambient temperature of the cable may be considerably higher than the ambient temperature applied to a standard for calculation of transmission capacity.
  • transmission of electric power in a transmission capacity calculated in accordance with conventional methods may cause a dangerous situation.
  • conventional methods cannot cope with such a dangerous situation. In severe cases, a cable accident may occur.
  • sheath circulating current is taken into consideration, they simply calculate the sheath circulating current as a certain ratio to the current flowing the cable conductor, without actually measuring the sheath circulating current in a state of taking into consideration the ground type of the cable.
  • sheath circulating current corresponding to 2% or 5% of conductor current is applied in accordance with the JCS 168 Standard.
  • sheath circulating current of up to 10% of the conductor current may often flow.
  • the internal temperature of the cable may be erroneously calculated.
  • the transmission capacity calculated based on the sheath circulating current corresponding to 2% of the conductor current is applied to an actual transmission operation, there may be a great danger.
  • the present invention has been made in view of the above mentioned problems, and an object of the invention is to provide an apparatus and method for evaluating, in real time, underground electric power cables, which can measure, in real time, the sheath circulating current and cable temperature of an underground electric power cable in order to calculate the conductor temperature of the cable to be basically used for calculation of a transmission capacity, thereby providing accurate information for calculation of a transmission capacity, not only in a general transmission operation, but also in an emergency electric power transmission operation carried out when a cable accident occurs or a peak load is generated in the summer season, while being capable of reflecting, in real time, an external thermal variation, so as to cope with the external thermal variation, so that the allowable transmission capacity of the current transmission line can be accurately calculated, in order to efficiently transmit electric power.
  • the present invention provides an apparatus for evaluating, in real time, an underground electric power cable, comprising: cable current measuring means for measuring current flowing through a conductor of the cable; sheath current measuring means for measuring current circulating through a sheath of the cable, thereby acquiring actual data about the sheath circulating current; cable temperature measuring means for measuring a temperature of the cable; and a communication unit for connecting the cable current measuring means, sheath current measuring means, and cable temperature measuring means to a main computer; and the main computer connected to the communication unit, and adapted to calculate, in real time, a conductor temperature of the cable based on data received from the cable current measuring means, sheath current measuring means, and cable temperature measuring means, and to calculate a transmission capacity of the cable, based on the calculated cable conductor temperature.
  • the present invention provides a method for calculating and evaluating, in real time, a transmission capacity of an underground electric power cable, comprising the steps of: inputting an installation condition including a cable installation length and a cable installation type when current begins to flow through the cable; calculating a thermal constant, based on the inputted installation condition along with respective thermal conductivities and respective specific heats of inner and outer materials of the cable, and a structure of the cable; measuring conductor current and sheath current of the cable, calculating Joule heat generated at a conductor of the cable, based on the calculated conductor current and the electrical and thermal characteristics of the cable conductor, calculating insulation loss based on a voltage applied to the cable conductor and characteristics of an insulator of the cable, and calculating sheath Joule heat caused by sheath
  • the method may further comprise the steps of: determining whether or not the difference between a measured temperature of a temperature-measured cable portion on a cross section of the cable and a calculated temperature of the cable portion is less than a predetermined temperature difference, after execution of the step of calculating, in real time, the conductor temperature of the cable; calculating an allowable transmission capacity, based on acquired data when the difference between the measured and calculated temperatures is less than the predetermined temperature difference; and informing a line operator of the conductor temperature of the cable and the calculated allowable transmission capacity.
  • the method may further comprise the step of adjusting the thermal constant and the correction coefficient of the heat source when it is determined that the difference between the measured and calculated temperatures is not less than the predetermined temperature difference.
  • the method may further comprise the steps of: comparing the calculated conductor temperature with a predetermined temperature, after execution of the conductor temperature calculating step; sending an alarm to a line operator when the calculated conductor temperature is not less than the predetermine temperature, thereby informing the line operator of generation of an abnormal temperature.
  • the calculation of the conductor temperature may be carried out using a method in which the conductor temperature is calculated using the temperature of a temperature-measured cable portion on the cross section of the electric power cable as a temperature boundary, or a method in which the conductor temperature is calculated using the temperature of the measured cable portion as a feedback value.
  • the feedback method comprises the steps of: calculating respective temperatures of all layers of the cross section of the cable under the condition in which the surrounding temperature around the cable is set as an ambient temperature; comparing the temperature of the measured cable portion with the calculated temperature of the same layer as the temperature-measured cable portion; and determining the calculated result to be reliable when the difference between the calculated temperature and the measured temperature is less than a predetermined temperature difference.
  • the method may further comprise the steps of: informing the line operator of the calculated and measured temperatures when it is determined at the comparison step that the difference between the calculated temperature and the measured temperature is less than the predetermined temperature difference; calculating an allowable transmission capacity, and informing the line operator of the calculated allowable transmission capacity.
  • the method may further comprise the step of generating an alarm when the calculated conductor temperature is not less than the predetermine temperature, thereby informing the line operator of generation of an abnormal temperature.
  • Fig. 1 is a block diagram illustrating the configuration of an apparatus for evaluating, in real time, an underground electric power cable in accordance with the present invention
  • Fig. 2 is a flow chart illustrating a method for evaluating, in real time, an underground electric power cable in accordance with the present invention.
  • Fig. 1 is a block diagram illustrating the configuration of an apparatus for evaluating, in real time, an underground electric power cable in accordance with the present invention.
  • Fig. 2 is a flow chart illustrating a method for evaluating, in real time, an underground electric power cable in accordance with the present invention.
  • the underground electric cable evaluating apparatus shown in Fig. 1 is applied to, for example, an electric power cable 2 installed in an electric power tunnel 1. As shown in Fig.
  • the underground electric cable evaluating apparatus includes a cable current measuring means 3 for measuring current flowing through a conductor of the cable 2, a sheath current measuring means 4 for measuring current circulating through a sheath of the cable 2, a cable temperature measuring means 5 for measuring the temperature of the cable 2, a cable surrounding temperature measuring means 6 for measuring the surrounding temperature around the cable 2, and a communication unit 7 for connecting the cable current measuring means 3, sheath current measuring means 4, cable temperature measuring means 5, and cable surrounding temperature measuring means 6 to a main computer 9 which is also included in the cable evaluating apparatus.
  • the main computer 9 is connected to the communication unit 7, and adapted to calculate, in real time, the transmission capacity of the cable 2 based on data received through the communication unit 7, and to inform a line operator of the calculated transmission capacity.
  • the main computer 8 also sends an alarm to the line operator when the temperature of the cable conductor is not less than a predetermined cable conductor temperature or when the temperature of the electric power tunnel is not less than a predetermined tunnel temperature.
  • the cable current measuring means 3 is installed such that it surrounds the cable 2, in order to measure current flowing through the conductor of the cable 2.
  • each current transformer may be used, each of which serves as a current measuring sensor.
  • each current transformer has a measuring range of 0 to 2, 000 A. Since the same current flows through all transmission lines, only one current transformer for the cable current measuring means 3 is installed on each transmission line.
  • the sheath current measuring means 4 is installed to measure current circulating through the sheath of the cable 2.
  • current transformers may be used, each of which serves as a current measuring sensor, as in the cable current measuring means 3.
  • the current transformers for the sheath current measuring means 4 are arranged at respective grounding points on the transmission lines.
  • each current transformer for the sheath current measuring means 4 has a measuring range of 0 to 500 A.
  • the cable temperature measuring means 5 is installed on an insulator sheath, sheath layer, or armour layer or jacket, where the cable temperature measuring means 5 does not damage an insulator of the cable, or outside the cable, in order to measure the temperature of the cable 2.
  • resistance temperature detectors may be used, each of which serves as a point temperature sensor.
  • thermocouples may be used.
  • the resistance temperature detectors or thermocouples may be installed on the cable 2 while being uniformly spaced apart from one another in the longitudinal direction of the cable 2 by a distance of 1 to 50m.
  • the resistance temperature detectors or thermocouples are arranged at intervals of 10m, taking into consideration economical purposes and cable characteristics.
  • fiber optic distributed temperature sensors may be used which are adapted to acquire longitudinal temperature data.
  • Such a fiber optic distributed temperature sensor employs a single optical fiber as its sensor medium.
  • This sensor can utilize the temperature dependency of Raman scattering and Brillian scattering. Where optical fibers are used, it is possible to achieve lightness and miniaturization. It is also possible to easily measure the temperature of the entire portion of an object without any influence of electromagnetic noise.
  • the cable surrounding temperature measuring means 6 may be used in order to measure the surrounding temperature around the cable 2.
  • the cable surrounding temperature measuring means 6 is preferably installed in the electric power tunnel 1.
  • the cable surrounding temperature measuring means 6 is preferably installed on the wall surface of the pipeline or in the earth around the pipeline.
  • the cable surrounding temperature measuring means 6 may be installed in the earth while being spaced apart from the cable by a certain distance.
  • the present invention has been described as being applied to the case in which the underground electric power cable 2 is installed in the electric power tunnel 1, it may be applicable to other cable installation types, for example, the case in which the cable is installed in a pipeline, or the case in which the cable is directly embedded in the ground, by appropriately installing the cable surrounding temperature measuring means 6.
  • the communication unit 7 preferably uses a programmable logic controller
  • the main computer 9 connected to the communication unit 7 calculates, in real time, the conductor temperature of the cable, based on data received from the current measuring means 3 and 4 and temperature measuring means 5 and 6, thereby calculating the transmission capacity of the cable, based on the calculated conductor temperature.
  • the main computer 9 subsequently informs a line operator of the calculated transmission capacity. Also, the main computer 9 sends an alarm to the line operator when an abnormality in the power transmission of the cable occurs.
  • the main computer calculates, in real time, the transmission capacity of the underground electric power cable, so that it appropriately operates the underground electric power cable.
  • This method includes: an installation condition inputting step 110 for inputting an installation condition having high influence on sheath circulating current, such as a cable installation length and a cable installation type; a thermal constant calculating step 120 for calculating a thermal constant, based on the inputted installation condition along with respective thermal conductivities and respective specific heats of the inner and outer materials of the cable, and the structure of the cable; a current measuring and heat source calculating step 130 for measuring the conductor current and sheath current of the cable, calculating Joule heat generated at the conductor of the cable, based on the calculated conductor current and the electrical and thermal characteristics of the cable conductor, calculating insulation loss based on the voltage applied to the cable conductor and the characteristics of an insulator of the cable, and calculating sheath Joule heat caused by sheath circulating current in accordance with the inputted installation condition; a longitudinal cable temperature measuring step 140 for measuring a temperature of the cable varying in a longitudinal direction of the cable; and a conductor temperature calculating step 150 for calculating, in real
  • the calculation of the conductor temperature based on the measured temperature may be carried out using a method in which the conductor temperature is calculated using the temperature of a measured cable portion on the cross section of the electric power cable as a temperature boundary, or a method in which the conductor temperature is calculated using the temperature of the measured cable portion as a feedback value.
  • the temperature of the measured cable portion is used as a feedback value
  • respective temperatures of all layers of the cross section of the cable are calculated under the condition in which the surrounding temperature around the cable is set as an ambient temperature.
  • the temperature of the measured cable portion is then compared with the calculated temperature of the same layer as the measured cable portion. When the difference between the calculated temperature and the measured temperature is less than a predetermined temperature difference, it is determined that the calculated result is reliable.
  • the method of the present invention may further include step 160 for determining whether or not the difference between a measured temperature of a cable portion on the cross section of the cable and a calculated temperature of the cable portion is less than a predetermined temperature difference, after execution of the step 150 of calculating, in real time, the conductor temperature of the cable, step 170 for calculating an allowable transmission capacity, based on the received data when the difference between the measured and calculated temperatures is less than the predetermined temperature difference, and step 180 for informing a line operator of the conductor temperature and the calculated allowable transmission capacity.
  • step 160 for determining whether or not the difference between a measured temperature of a cable portion on the cross section of the cable and a calculated temperature of the cable portion is less than a predetermined temperature difference, after execution of the step 150 of calculating, in real time, the conductor temperature of the cable, step 170 for calculating an allowable transmission capacity, based on the received data when the difference between the measured and calculated temperatures is less than the predetermined temperature difference, and step 180 for informing a line operator of the
  • the method of the present invention further includes step 210 for adjusting the thermal constant and the correction coefficient of the heat source when it is determined at step 160 that the difference between the measured and calculated temperatures is not less than the predetermined temperature difference.
  • the method of the present invention may further include step 310 for comparing the calculated conductor temperature with a predetermined temperature, after execution of the step for calculating the conductor temperature, and step 320 for sending an alarm to the line operator when the calculated conductor temperature is not less than the predetermine temperature, thereby informing the line operator of generation of an abnormal temperature.
  • step 310 for comparing the calculated conductor temperature with a predetermined temperature
  • step 320 for sending an alarm to the line operator when the calculated conductor temperature is not less than the predetermine temperature, thereby informing the line operator of generation of an abnormal temperature.
  • the present invention it is possible to alert the line operator of an abnormality by measuring, in real time, the current and temperature of an underground electric power cable, and comparing each measured value with an associated calculated value. Also, the currently allowable transmission capacity can be accurately calculated, based on the measured values. It is also possible to output one or more allowable transmission capacities respectively calculated in association with transmission periods desired by the line operator. For example, it is possible to calculate respective transmission capacities allowable for 2 hours, 4 hours, 6 hours, 12 hours, 24 hours, 100 hours, etc., and to inform the calculated allowable transmission capacities, thereby allowing the line operator to efficiently manage the transmission capacity of the electric power cable.
  • the currently allowable transmission capacity can be calculated and evaluated in real time, even in an emergency transmission operation caused by an accident, irrespective of the span of the restoring time. That is, the cable sheath circulating current is not calculated, based on its ratio to conductor current, but calculated in real time, and the calculated value is used for calculation of transmission capacity. Accordingly, it is possible to accurately evaluate Joule loss caused by sheath circulating current generated due to an erroneous grounding work or unbalance of cable installation distance.
  • the real-time evaluating apparatus and method for underground electric power cables can measure, in real time, the temperature and current of an underground electric power cable to calculate the transmission capacity of the cable.
  • the present invention is useful and effective in that it is possible to calculate, in real time, the transmission capacity allowable for a desired period, thereby efficiently operating transmission of electric power.

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Computer Security & Cryptography (AREA)
  • Laying Of Electric Cables Or Lines Outside (AREA)
  • Electric Cable Installation (AREA)

Abstract

Disclosed is an apparatus for evaluating underground electric power cables. In order to evaluate, in real time, the conductor temperature and allowable current of an underground electric power cable, and thus, to efficiently calculate the transmission capacity of the electric power cable, the apparatus includes a cable current measuring means (3), a sheath current measuring means (4), a cable temperature measuring means (5), a cable surrounding temperature measuring means (6), and a communication means (7) for connecting all the measuring means to a main computer (9). The main computer (9) calculates, in real time, the transmission capacity of the cable, based on data received from all measuring means via the communication means. The main computer (9) informs a line operator of the calculated transmission capacity and conductor temperature, and sends an alarm to the line operator when an abnormality in the power transmission of the cable occurs.

Description

APPARATUS AND METHOD FOR EVALUATING UNDERGROUND ELECTRIC POWER CABLES
Technical Field
The present invention relates to an apparatus for evaluating underground electric power cables included in electric power transmission equipment, and more particularly to an apparatus and method for evaluating, in real time, the conductor temperature and allowable current of an underground electric power cable to efficiently calculate the transmission capacity of the electric power cable.
Background Art Generally, the transmission capacity of an electric power cable is determined based on a temperature range in which the insulating performance of an insulator surrounding the electric power cable is maintained.
In the case of some electric power cables, in particular, cross-linked polyethylene (XLPE) cables, their cable conductor temperature is limited to 90°C. In the case of oil filled (OF) cables, their conductor temperature is limited to 85°C.
Practically, it is very difficult to measure the conductor temperature of an electric power cable because the electric power cable is in a state in which high voltage is applied.
Upon determining the conductor temperature of an electric power cable, it is important to determine heat sources. To be taken into consideration for such a determination are Joule loss caused by current flowing through the cable conductor, insulation loss caused by high voltage applied to the cable conductor, Joule loss caused by Eddy current generated at the sheath of the cable and sheath circulating current, the thermal condition around the cable, etc. In this regard, the transmission capacity of an underground electric power cable is calculated by evaluating the conductor temperature and allowable current of the under ground electric power cable. The evaluation of the conductor temperature and allowable current is achieved using a method recommended by an international Standard, for example, IEC 287 or JCS 168.
LEC 287 is an international Standard established by the International
Electro-technical Commission (LEC). This LEC Standard includes standards for ships, electrical installations, electric power cables, high-frequency cables, windings, etc. On the other hand, JCS 168 is a Standard established by JCS for standardization of electric wire products.
However, conventional methods according to such international Standards cannot take into consideration a temperature variation in the conductor of a cable and a variation in the internal temperature of the cable in practical cases. That is, they utilize a static heat transfer system taking into consideration only the thermal conductivity of the core material of the cable. In such conventional methods, the heat transfer system of the cable is modeled as a static system on the assumption that when the transmission current flowing the cable varies, the internal temperature of the cable varies immediately without any time difference, for calculation of the transmission capacity of the cable.
However, a considerable time is required for the cable to vary in temperature by virtue of the specific heat of the core material of the cable in practical cases. For this reason, it is possible to transmit, through an electric power cable, a larger quantity of electric power than a calculated transmission capacity of the electric power cable, for a certain short period of time (for example, up to about
100 hours).
Furthermore, since conventional transmission capacity determining methods aim to secure an increased stability, they calculate the transmission capacity of a cable by setting the worst temperature condition without taking into consideration an actual temperature variation occurring at the cable due to a variation in the environmental condition around the cable. For this reason, the transmission capacity of the cable is calculated, based on a limited static transmission capacity and a limited emergency operation condition, so that the calculated transmission capacity provides unnecessarily high security. In other words, the conventional methods propose a transmission capacity considerably lower than a practically-allowable transmission capacity. Most national key underground electric power transmission networks in, for example, Korea, are installed in electric power cable tunnels. In such a case, the temperature of each electric power cable tunnel is simply prescribed to be 40°C. However, the temperature of each electric power cable tunnel is typically maintained at a temperature of 30 to 35°C even in the summer season exhibiting the highest temperature. Although it is possible to achieve an increase in the transmission capacity of a cable by directly measuring the thermal condition of the cable, there is no conventional method to which such a direct measurement is applicable. Meanwhile, emergency power transmission is typically carried out when an accident occurs. For such an emergency power transmission, allowable current is set, based on a fixed transmission time stipulated in the international Standard. However, this method is inefficient because electric power can be transmitted only in a transmission capacity fixed based on the fixed transmission time, in spite of the fact that a higher transmission capacity can be given when the emergency power transmission time is shorter than the time stipulated in the international Standard.
On the other hand, where a new heat source such as a steam pipe is arranged around an underground electric power cable as it is embedded under the ground around the underground electric power cable due to an erroneous pipe installation work, the ambient temperature of the cable may be considerably higher than the ambient temperature applied to a standard for calculation of transmission capacity. In this case, transmission of electric power in a transmission capacity calculated in accordance with conventional methods may cause a dangerous situation. However, conventional methods cannot cope with such a dangerous situation. In severe cases, a cable accident may occur.
Where an increase in ground resistance occurs at an electric power cable due to an erroneous cable grounding work, excessive sheath circulating current may flow through the electric power cable, thereby causing Joule loss. Such Joule loss causes an abrupt increase in the internal temperature of the cable. However, conventional transmission capacity calculation methods cannot calculate the sheath circulating current. For this reason, there is no method of coping with the problem caused by the sheath circulating current.
Although there are conventional methods in which sheath circulating current is taken into consideration, they simply calculate the sheath circulating current as a certain ratio to the current flowing the cable conductor, without actually measuring the sheath circulating current in a state of taking into consideration the ground type of the cable.
For example, in the case of a grounding method using cross bonding of an aluminum sheath, which is frequently applied to national underground electric power cables in, for example, Korea, sheath circulating current corresponding to 2% or 5% of conductor current is applied in accordance with the JCS 168 Standard. In such a cross bonding system, however, sheath circulating current of up to 10% of the conductor current may often flow. In this case, the internal temperature of the cable may be erroneously calculated. In the worst case in which the transmission capacity calculated based on the sheath circulating current corresponding to 2% of the conductor current is applied to an actual transmission operation, there may be a great danger.
Disclosure of the Invention
The present invention has been made in view of the above mentioned problems, and an object of the invention is to provide an apparatus and method for evaluating, in real time, underground electric power cables, which can measure, in real time, the sheath circulating current and cable temperature of an underground electric power cable in order to calculate the conductor temperature of the cable to be basically used for calculation of a transmission capacity, thereby providing accurate information for calculation of a transmission capacity, not only in a general transmission operation, but also in an emergency electric power transmission operation carried out when a cable accident occurs or a peak load is generated in the summer season, while being capable of reflecting, in real time, an external thermal variation, so as to cope with the external thermal variation, so that the allowable transmission capacity of the current transmission line can be accurately calculated, in order to efficiently transmit electric power.
In accordance with one aspect, the present invention provides an apparatus for evaluating, in real time, an underground electric power cable, comprising: cable current measuring means for measuring current flowing through a conductor of the cable; sheath current measuring means for measuring current circulating through a sheath of the cable, thereby acquiring actual data about the sheath circulating current; cable temperature measuring means for measuring a temperature of the cable; and a communication unit for connecting the cable current measuring means, sheath current measuring means, and cable temperature measuring means to a main computer; and the main computer connected to the communication unit, and adapted to calculate, in real time, a conductor temperature of the cable based on data received from the cable current measuring means, sheath current measuring means, and cable temperature measuring means, and to calculate a transmission capacity of the cable, based on the calculated cable conductor temperature. The main computer of this apparatus informs the line operator of the calculated cable conductor temperature and transmission capacity, and sends an alarm to the line operator when an abnormality in cable transmission occurs. Thus, this apparatus provides convenience to the line operator. In accordance with another aspect, the present invention provides a method for calculating and evaluating, in real time, a transmission capacity of an underground electric power cable, comprising the steps of: inputting an installation condition including a cable installation length and a cable installation type when current begins to flow through the cable; calculating a thermal constant, based on the inputted installation condition along with respective thermal conductivities and respective specific heats of inner and outer materials of the cable, and a structure of the cable; measuring conductor current and sheath current of the cable, calculating Joule heat generated at a conductor of the cable, based on the calculated conductor current and the electrical and thermal characteristics of the cable conductor, calculating insulation loss based on a voltage applied to the cable conductor and characteristics of an insulator of the cable, and calculating sheath Joule heat caused by sheath circulating current in accordance with the inputted installation condition to calculate a heat source; measuring a temperature of the cable varying in a longitudinal direction of the cable; and calculating, in real time, a conductor temperature of the cable, based on information acquired in the calculations carried out at the above steps, and the measured cable temperature.
The method may further comprise the steps of: determining whether or not the difference between a measured temperature of a temperature-measured cable portion on a cross section of the cable and a calculated temperature of the cable portion is less than a predetermined temperature difference, after execution of the step of calculating, in real time, the conductor temperature of the cable; calculating an allowable transmission capacity, based on acquired data when the difference between the measured and calculated temperatures is less than the predetermined temperature difference; and informing a line operator of the conductor temperature of the cable and the calculated allowable transmission capacity.
The method may further comprise the step of adjusting the thermal constant and the correction coefficient of the heat source when it is determined that the difference between the measured and calculated temperatures is not less than the predetermined temperature difference. The method may further comprise the steps of: comparing the calculated conductor temperature with a predetermined temperature, after execution of the conductor temperature calculating step; sending an alarm to a line operator when the calculated conductor temperature is not less than the predetermine temperature, thereby informing the line operator of generation of an abnormal temperature. The calculation of the conductor temperature may be carried out using a method in which the conductor temperature is calculated using the temperature of a temperature-measured cable portion on the cross section of the electric power cable as a temperature boundary, or a method in which the conductor temperature is calculated using the temperature of the measured cable portion as a feedback value. The feedback method comprises the steps of: calculating respective temperatures of all layers of the cross section of the cable under the condition in which the surrounding temperature around the cable is set as an ambient temperature; comparing the temperature of the measured cable portion with the calculated temperature of the same layer as the temperature-measured cable portion; and determining the calculated result to be reliable when the difference between the calculated temperature and the measured temperature is less than a predetermined temperature difference.
When it is determined at the comparison step that the difference between the calculated temperature and the measured temperature is not less than the predetermined temperature difference, adjustment of the thermal constant and the correction coefficient of the heat source is carried out, and respective temperatures of all layers of the cable are calculated again, based on the adjusted thermal constant and correction coefficient. Based on the resultant calculated temperatures, the comparison step is carried out again. Thus, it is possible to increase the reliability of the conductor temperature calculation.
The method may further comprise the steps of: informing the line operator of the calculated and measured temperatures when it is determined at the comparison step that the difference between the calculated temperature and the measured temperature is less than the predetermined temperature difference; calculating an allowable transmission capacity, and informing the line operator of the calculated allowable transmission capacity.
The method may further comprise the step of generating an alarm when the calculated conductor temperature is not less than the predetermine temperature, thereby informing the line operator of generation of an abnormal temperature. Thus, convenience is provided to the line operator.
Brief Description of the Drawings
Fig. 1 is a block diagram illustrating the configuration of an apparatus for evaluating, in real time, an underground electric power cable in accordance with the present invention; and Fig. 2 is a flow chart illustrating a method for evaluating, in real time, an underground electric power cable in accordance with the present invention.
Best Mode for Carrying Out the Invention
Now, preferred embodiments of the present invention will be described in detail with reference to the annexed drawings.
Fig. 1 is a block diagram illustrating the configuration of an apparatus for evaluating, in real time, an underground electric power cable in accordance with the present invention. Fig. 2 is a flow chart illustrating a method for evaluating, in real time, an underground electric power cable in accordance with the present invention. The underground electric cable evaluating apparatus shown in Fig. 1 is applied to, for example, an electric power cable 2 installed in an electric power tunnel 1. As shown in Fig. 1, the underground electric cable evaluating apparatus includes a cable current measuring means 3 for measuring current flowing through a conductor of the cable 2, a sheath current measuring means 4 for measuring current circulating through a sheath of the cable 2, a cable temperature measuring means 5 for measuring the temperature of the cable 2, a cable surrounding temperature measuring means 6 for measuring the surrounding temperature around the cable 2, and a communication unit 7 for connecting the cable current measuring means 3, sheath current measuring means 4, cable temperature measuring means 5, and cable surrounding temperature measuring means 6 to a main computer 9 which is also included in the cable evaluating apparatus. The main computer 9 is connected to the communication unit 7, and adapted to calculate, in real time, the transmission capacity of the cable 2 based on data received through the communication unit 7, and to inform a line operator of the calculated transmission capacity. The main computer 8 also sends an alarm to the line operator when the temperature of the cable conductor is not less than a predetermined cable conductor temperature or when the temperature of the electric power tunnel is not less than a predetermined tunnel temperature.
The cable current measuring means 3 is installed such that it surrounds the cable 2, in order to measure current flowing through the conductor of the cable 2.
For this cable current measuring means 3, current transformers may be used, each of which serves as a current measuring sensor. Preferably, each current transformer has a measuring range of 0 to 2, 000 A. Since the same current flows through all transmission lines, only one current transformer for the cable current measuring means 3 is installed on each transmission line.
The sheath current measuring means 4 is installed to measure current circulating through the sheath of the cable 2. For the sheath current measuring means 4, current transformers may be used, each of which serves as a current measuring sensor, as in the cable current measuring means 3. The current transformers for the sheath current measuring means 4 are arranged at respective grounding points on the transmission lines. Preferably, each current transformer for the sheath current measuring means 4 has a measuring range of 0 to 500 A. The cable temperature measuring means 5 is installed on an insulator sheath, sheath layer, or armour layer or jacket, where the cable temperature measuring means 5 does not damage an insulator of the cable, or outside the cable, in order to measure the temperature of the cable 2.
For the cable temperature measuring means 5, resistance temperature detectors may be used, each of which serves as a point temperature sensor.
Alternatively, thermocouples may be used. The resistance temperature detectors or thermocouples may be installed on the cable 2 while being uniformly spaced apart from one another in the longitudinal direction of the cable 2 by a distance of 1 to 50m. Preferably, the resistance temperature detectors or thermocouples are arranged at intervals of 10m, taking into consideration economical purposes and cable characteristics.
In place of the point temperature sensors, fiber optic distributed temperature sensors may be used which are adapted to acquire longitudinal temperature data.
Such a fiber optic distributed temperature sensor employs a single optical fiber as its sensor medium. This sensor can utilize the temperature dependency of Raman scattering and Brillian scattering. Where optical fibers are used, it is possible to achieve lightness and miniaturization. It is also possible to easily measure the temperature of the entire portion of an object without any influence of electromagnetic noise. In addition to the cable temperature measuring means 5, the cable surrounding temperature measuring means 6 may be used in order to measure the surrounding temperature around the cable 2. For an electric power cable installed in an electric power tunnel 1, the cable surrounding temperature measuring means 6 is preferably installed in the electric power tunnel 1. On the other hand, for an electric power cable installed in a pipeline, the cable surrounding temperature measuring means 6 is preferably installed on the wall surface of the pipeline or in the earth around the pipeline. Also, for an electric power cable directly embedded in the ground, the cable surrounding temperature measuring means 6 may be installed in the earth while being spaced apart from the cable by a certain distance. Although the present invention has been described as being applied to the case in which the underground electric power cable 2 is installed in the electric power tunnel 1, it may be applicable to other cable installation types, for example, the case in which the cable is installed in a pipeline, or the case in which the cable is directly embedded in the ground, by appropriately installing the cable surrounding temperature measuring means 6.
Meanwhile, the current measuring means 3 and 4 and temperature measuring means 5 and 6 are connected to the communication unit 7 via communication lines or in a wireless manner so that they are connected to the main computer 9. The communication unit 7 preferably uses a programmable logic controller
(PLC). In particular, where the communication unit 7 using such a PLC is used, it is possible to transmit data without any influence of the high- voltage electric power cable, in so far as optical communication transmitting/receiving equipment and communication lines 8 made of optical cables are used. The main computer 9 connected to the communication unit 7 calculates, in real time, the conductor temperature of the cable, based on data received from the current measuring means 3 and 4 and temperature measuring means 5 and 6, thereby calculating the transmission capacity of the cable, based on the calculated conductor temperature. The main computer 9 subsequently informs a line operator of the calculated transmission capacity. Also, the main computer 9 sends an alarm to the line operator when an abnormality in the power transmission of the cable occurs. Thus, the main computer calculates, in real time, the transmission capacity of the underground electric power cable, so that it appropriately operates the underground electric power cable. Now, a method for evaluating an underground electric power cable by calculating the conductor temperature of the cable in accordance with the present invention will be described. This method includes: an installation condition inputting step 110 for inputting an installation condition having high influence on sheath circulating current, such as a cable installation length and a cable installation type; a thermal constant calculating step 120 for calculating a thermal constant, based on the inputted installation condition along with respective thermal conductivities and respective specific heats of the inner and outer materials of the cable, and the structure of the cable; a current measuring and heat source calculating step 130 for measuring the conductor current and sheath current of the cable, calculating Joule heat generated at the conductor of the cable, based on the calculated conductor current and the electrical and thermal characteristics of the cable conductor, calculating insulation loss based on the voltage applied to the cable conductor and the characteristics of an insulator of the cable, and calculating sheath Joule heat caused by sheath circulating current in accordance with the inputted installation condition; a longitudinal cable temperature measuring step 140 for measuring a temperature of the cable varying in a longitudinal direction of the cable; and a conductor temperature calculating step 150 for calculating, in real time, the conductor temperature of the cable, based on information acquired in the calculations carried out at the above steps, and the measured cable temperature. The calculation of the conductor temperature based on the measured temperature may be carried out using a method in which the conductor temperature is calculated using the temperature of a measured cable portion on the cross section of the electric power cable as a temperature boundary, or a method in which the conductor temperature is calculated using the temperature of the measured cable portion as a feedback value.
In the feedback method in which the temperature of the measured cable portion is used as a feedback value, respective temperatures of all layers of the cross section of the cable are calculated under the condition in which the surrounding temperature around the cable is set as an ambient temperature. The temperature of the measured cable portion is then compared with the calculated temperature of the same layer as the measured cable portion. When the difference between the calculated temperature and the measured temperature is less than a predetermined temperature difference, it is determined that the calculated result is reliable.
On the other hand, where it is determined at the comparison step that the difference between the calculated temperature and the measured temperature is not less than the predetermined temperature difference, adjustment of the thermal constant and the correction coefficient of the heat source is carried out, and respective temperatures of all layers of the cable are calculated again, based on the adjusted thermal constant and correction coefficient. Based on the resultant calculated temperatures, the comparison step is carried out again. Thus, it is possible to increase the reliability of the conductor temperature calculation.
Meanwhile, the method of the present invention may further include step 160 for determining whether or not the difference between a measured temperature of a cable portion on the cross section of the cable and a calculated temperature of the cable portion is less than a predetermined temperature difference, after execution of the step 150 of calculating, in real time, the conductor temperature of the cable, step 170 for calculating an allowable transmission capacity, based on the received data when the difference between the measured and calculated temperatures is less than the predetermined temperature difference, and step 180 for informing a line operator of the conductor temperature and the calculated allowable transmission capacity. In this case, it is possible to calculate, in real time, the allowable transmission capacity, and to inform the line operator of the calculated allowable transmission capacity.
The method of the present invention further includes step 210 for adjusting the thermal constant and the correction coefficient of the heat source when it is determined at step 160 that the difference between the measured and calculated temperatures is not less than the predetermined temperature difference.
For convenience of the operation, the method of the present invention may further include step 310 for comparing the calculated conductor temperature with a predetermined temperature, after execution of the step for calculating the conductor temperature, and step 320 for sending an alarm to the line operator when the calculated conductor temperature is not less than the predetermine temperature, thereby informing the line operator of generation of an abnormal temperature. Thus, it is possible to immediately inform the line operator of generation of an abnormal temperature.
In accordance with the present invention, it is possible to alert the line operator of an abnormality by measuring, in real time, the current and temperature of an underground electric power cable, and comparing each measured value with an associated calculated value. Also, the currently allowable transmission capacity can be accurately calculated, based on the measured values. It is also possible to output one or more allowable transmission capacities respectively calculated in association with transmission periods desired by the line operator. For example, it is possible to calculate respective transmission capacities allowable for 2 hours, 4 hours, 6 hours, 12 hours, 24 hours, 100 hours, etc., and to inform the calculated allowable transmission capacities, thereby allowing the line operator to efficiently manage the transmission capacity of the electric power cable.
Also, the currently allowable transmission capacity can be calculated and evaluated in real time, even in an emergency transmission operation caused by an accident, irrespective of the span of the restoring time. That is, the cable sheath circulating current is not calculated, based on its ratio to conductor current, but calculated in real time, and the calculated value is used for calculation of transmission capacity. Accordingly, it is possible to accurately evaluate Joule loss caused by sheath circulating current generated due to an erroneous grounding work or unbalance of cable installation distance. Although the preferred embodiments of the invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims. For example, although the present invention has been described in conjunction with an embodiment implementing a real-time evaluating apparatus and method for underground electric power cables, it is not limited to such an embodiment.
Industrial Applicability
The real-time evaluating apparatus and method for underground electric power cables can measure, in real time, the temperature and current of an underground electric power cable to calculate the transmission capacity of the cable.
Accordingly, it is possible to achieve calculation of the transmission capacity within a certain tolerance, and verification of the calculated transmission capacity.
Also, it is possible to rapidly detect generation of an abnormal temperature caused by a variation in the conditions of the cable and surroundings, and to cope with the detected abnormal temperature. An actual variation in temperature occurring at the cable can be expected, taking into consideration the thermal conductivity and specific heat of the cable. Such a temperature variation is also monitored in real time, taking into consideration the influence of the surroundings.
Accordingly, stable transmission management can be achieved. Thus, the present invention is useful and effective in that it is possible to calculate, in real time, the transmission capacity allowable for a desired period, thereby efficiently operating transmission of electric power.

Claims

Claims
1. An apparatus for evaluating, in real time, an underground electric power cable, comprising: cable current measuring means for measuring current flowing through a conductor of the cable; sheath current measuring means for measuring current circulating through a sheath of the cable, thereby acquiring actual data about the sheath circulating current; cable temperature measuring means for measuring a temperature of the cable; and a communication unit for connecting the cable current measuring means, sheath current measuring means, and cable temperature measuring means to a main computer; and the main computer connected to the communication unit, and adapted to calculate, in real time, a conductor temperature of the cable based on data received from the cable current measuring means, sheath current measuring means, and cable temperature measuring means, and to calculate a transmission capacity of the cable, based on the calculated cable conductor temperature.
2. The apparatus according to claim 1, wherein: the cable current measuring means comprises first current transformers each serving as a current measuring sensor, the first current transformers being installed on respective transmission lines; and the sheath current measuring means comprises second current transformers each serving as a current measuring sensor, the second current transformers being installed at respective grounding points on the transmission lines.
3. The apparatus according to claim 1, wherein the cable temperature measuring means is installed in a longitudinal direction of the cable outside an insulator of the cable.
4. The apparatus according to claim 1, wherein the cable temperature measuring means comprises resistance temperature detectors each serving as a point temperature sensor.
5. The apparatus according to claim 1, wherein the cable temperature measuring means comprises thermocouples.
6. The apparatus according to claim 4 or 5, wherein the resistance temperature detectors or thermocouples are installed to be spaced apart from one another by a distance of 1 to 50 m in a longitudinal direction of the cable.
7. The apparatus according to claim 1, wherein the cable temperature measuring means comprises fiber optic distributed temperature sensors.
8. The apparatus according to claim 1, wherein the main computer informs a line operator of the calculated transmission capacity, and sends an alarm to the line operator when an abnormality in cable transmission occurs.
9. A method for calculating and evaluating, in real time, a transmission capacity of an underground electric power cable, comprising the steps of: inputting an installation condition including a cable installation length and a cable installation type when current begins to flow through the cable; calculating a thermal constant, based on the inputted installation condition along with respective thermal conductivities and respective specific heats of inner and outer materials of the cable, and a structure of the cable; measuring conductor current and sheath current of the cable, calculating Joule heat generated at a conductor of the cable, based on the calculated conductor current and the electrical and thermal characteristics of the cable conductor, calculating insulation loss based on a voltage applied to the cable conductor and characteristics of an insulator of the cable, and calculating sheath Joule heat caused by sheath circulating current in accordance with the inputted installation condition to calculate a heat source; measuring a temperature of the cable varying in a longitudinal direction of the cable; and calculating, in real time, a conductor temperature of the cable, based on information acquired in the calculations carried out at the above steps, and the measured cable temperature.
10. The method according to claim 9, wherein the step of calculating, in real time, the conductor temperature of the cable comprises the step of calculating the conductor temperature of the cable, using a temperature of a temperature- measured cable portion on a cross section of the cable as a temperature boundary.
11. The method according to claim 9, further comprising the steps of: determining whether or not the difference between a measured temperature of a temperature-measured cable portion on a cross section of the cable and a calculated temperature of the cable portion is less than a predetermined temperature difference, after execution of the step of calculating, in real time, the conductor temperature of the cable; calculating an allowable transmission capacity, based on acquired data when the difference between the measured and calculated temperatures is less than the predetermined temperature difference; and informing a line operator of the conductor temperature of the cable and the calculated allowable transmission capacity.
12. The method according to claim 11, further comprising the step of: adjusting the thermal constant and the correction coefficient of the heat source when it is determined that the difference between the measured and calculated temperatures is not less than the predetermined temperature difference.
13. The method according to claim 9, further comprising the steps of: comparing the calculated conductor temperature with a predetermined temperature, after execution of the conductor temperature calculating step; sending an alarm to a line operator when the calculated conductor temperature is not less than the predetermine temperature, thereby informing the line operator of generation of an abnormal temperature.
PCT/KR2003/001545 2003-04-04 2003-07-31 Apparatus and method for evaluating underground electric power cables Ceased WO2004088338A1 (en)

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