HK1190791A - Detection system and method for detecting impedance variation in a neutral conductor, transformer station comprising such a system - Google Patents

Description

System and method for detecting impedance change of neutral conductor and transformer substation comprising system

Technical Field

The invention relates to a system for detecting an impedance change of a neutral conductor of a polyphase Alternating Current (AC) network, wherein the network comprises P phase conductors and one neutral conductor, wherein P is an integer larger than 1.

The detection system comprises a set of P voltage sensors, each voltage sensor being adapted to measure the voltage of a respective phase conductor with respect to the neutral conductor, and a supervision device connected to each voltage sensor via a data link.

The invention also relates to an electric power substation to be connected to a polyphase AC grid, the substation comprising P phase conductors, a neutral conductor and such a system for detecting impedance changes at the neutral conductor.

The invention also relates to a method for detecting impedance changes in a neutral conductor of a polyphase AC grid using such a detection system.

Background

Document US2007/0258175a1 discloses a detection system of the above-mentioned type. The detection system includes: means for measuring a voltage unbalance between the first conductor and the neutral conductor on the one hand and the second conductor and the neutral conductor on the other hand. The system is suitable for two-phase circuits. The detection system comprises means for comparing the voltage unbalance with respect to a predetermined threshold value. The system comprises: means for generating an alarm if the measured voltage imbalance is greater than or less than any predetermined threshold. In this way, by measuring the voltage of the two power phase conductors and comparing this value with a predetermined threshold, the system enables an alarm to be generated in the measurement circuit, such as a consumer board, regarding the opening of the neutral.

However, such detection systems do not provide information about the state of the power grid off-board the consumer.

Disclosure of Invention

It is therefore an object of the present invention to propose a detection system suitable for detecting impedance variations on the neutral conductor of an electric network and locating the neutral variations along the electric network.

To this end, the invention relates to a detection system of the above type, characterized in that:

-the system further comprises (N-1) other groups of P voltage sensors, where N is an integer greater than 1, the N groups of voltage sensors being arranged at different locations along the grid, and characterized in that

The supervision device is adapted to detect a change in voltage of a given phase conductor relative to the neutral conductor between two successive sensor groups in order to detect a change in impedance of the neutral conductor and a change in impedance positioned between two successive sensor groups.

According to a further advantageous aspect of the invention, the detection system comprises, in isolation or according to any technically feasible combination, one or more of the following features:

-each voltage sensor comprises means for sending an alarm message to a supervising device if an overvoltage or undervoltage is detected for at least one phase conductor;

-each voltage sensor comprises means for comparing the measured voltage with predefined overvoltage and undervoltage thresholds to detect overvoltage or undervoltage;

the supervision device comprises means for comparing the measured voltage received from the corresponding voltage sensor with predefined overvoltage and undervoltage thresholds to detect overvoltage or undervoltage;

the supervision device comprises means for communicating with each voltage sensor, adapted to send a query to each voltage sensor in order to receive in response the voltage measured by each voltage sensor;

the supervision device comprises a calculation unit adapted to compare the measured voltage of each phase conductor with predefined overvoltage and undervoltage thresholds.

The invention also relates to an electrical substation to be connected to a polyphase AC grid, the substation comprising:

a first board comprising P power input conductors adapted to be connected to the grid, where P is an integer greater than 1,

-a second board comprising at least one output of P power conductors and one neutral conductor,

-a transformer connected between the first board and the second board and adapted to convert an input current having a first AC voltage on an input conductor into a current having a second AC voltage, an

-a detection system for detecting impedance changes in the neutral conductor, characterized in that the detection system is a detection system as defined above.

The invention also relates to a method for detecting an impedance change in a neutral conductor of a polyphase AC grid, the grid comprising P phase conductors and a neutral conductor, where P is an integer greater than 1, the method comprising the steps of:

-measuring the voltage of each phase conductor with respect to the neutral conductor at a given location of the grid by means of a set of P voltage sensors,

-transmitting the measured voltages from the set of voltage sensors to a supervising device,

the method is characterized in that during the measuring step, the voltage of each phase conductor with respect to the neutral conductor at different positions along the power network is measured by N groups of P voltage sensors arranged at said different positions, and in that the method further comprises the steps of:

-detecting, between two consecutive groups of sensors, a variation in voltage of the conductor with respect to the neutral conductor at a given phase, so as to detect a variation in impedance of the neutral conductor and a variation in impedance positioned between the two consecutive groups of sensors, the detection step being carried out by a supervision device based on the measurement voltage transmitted by each of the groups of voltage sensors.

According to a further advantageous aspect of the invention, the method for detecting a change in the impedance of the neutral conductor comprises the following features:

-after receiving an alarm message from a given group of voltage sensors when a voltage anomaly, such as an overvoltage or undervoltage, is detected for at least one phase conductor, the supervision device sends an inquiry to the given group of different voltage sensors in order to receive the voltages measured by the given group of sensors;

after receiving the voltages measured by the sensors of a given group, the supervision device checks whether an overvoltage with respect to one phase conductor and an undervoltage with respect to the other phase conductor are both detected;

after receiving the voltages measured by the sensors of a given group, the supervision device checks that the detected voltage anomaly is not caused by a loss of any phase of the network or by a load imbalance between the phases of the network;

-after receiving the alarm message from the voltage sensors of a given group, the supervising device also sends a query to the different voltage sensors of the groups adjacent to the given group;

the supervising device determines the group of sensors detecting the voltage anomaly and the group or other groups not detecting the voltage anomaly and determines the zone of variation of the impedance located between the final group of sensors not indicating an anomaly and the first group of sensors indicating an anomaly.

Drawings

These characteristics and advantages of the invention will emerge from reading the following description, provided purely by way of non-limiting example and with reference to the accompanying drawings, in which:

figure 1 is a diagrammatic representation of an electrical substation connected to a three-phase AC power grid, wherein the substation comprises a system for detecting changes according to the invention;

FIG. 2 is a large-scale view of region II of FIG. 1;

fig. 3 is a flow chart of a method for detecting a change in the impedance of the neutral conductor of the power grid.

Detailed Description

In fig. 1, a substation 10 connected to an AC power grid 12 includes a first medium voltage board 14, a second low voltage board 16, a transformer 18 connected between the first board and the second board, and a system 20 for detecting impedance changes in a neutral conductor 22.

The substation 10 is adapted to convert a current output by the network 12 and having a first alternating voltage into a current having a second alternating voltage.

The grid 12 is a multi-phase ac network comprising P phases, where P is an integer greater than 1, such as a three-phase network. In other words, in the described embodiment, P is equal to 3.

The grid 12 is a medium voltage network, i.e. a network whose voltage is greater than 1000 volts and less than 50000 volts. The first three-phase voltage is thus a medium voltage.

The first board 14 includes a plurality of inputs 24. Each input 24 comprises P power input conductors 26, where P is an integer greater than 1, and includes a disconnector 28.

The first board 14 includes an input breaker 30 connected between the transformer 18 and the input 24.

The second board 16 includes a plurality of outputs 32, each output 32 being adapted to provide a second AC voltage and including P power output conductors 34 and the neutral conductor 22.

The second board 16 includes an output breaker 36 connected between the transformer 18 and the output 32.

The transformer 18 is adapted to convert a current having a first AC voltage from the grid into a current having a second AC voltage supplied to the second board 16. The transformer 18 includes a primary winding 38 connected to the first board 14 and a secondary winding 40 connected to the second board 16.

The detection system 20 is adapted to detect impedance changes in the neutral conductor 22 along the conductor.

The detection system 20 includes N sets 42A,42B, … …,42N of voltage sensors, where three consecutive sets 42A,42B, 42C are shown in fig. 1, and where a large scale set 42A can be seen in fig. 2. Each of these N groups includes P sensors, such as 56A,58A,60A of group 42A, for measuring each voltage of the P phase conductors relative to the neutral conductor 22. In the embodiment depicted in fig. 1, each group 42A,42B, 42C is made up of P voltage sensors 56A,58A,60A, 56B,58B,60B, 56C, 58C, 60C.

In this way, N voltage sensors are distributed along each output conductor 34 and are adapted to measure the voltage of each phase conductor 34 relative to the neutral conductor 22 at N different points. This is the case, for example, when the voltage sensors 56A, 56B, 56C are used for voltage measurement of the first phase.

The detection system 20 includes a supervisory device 61 connected to each voltage sensor 56A.

Each output 32 is a low voltage output, i.e., an output where the voltage is less than 1000 volts. Thus, the second three-phase voltage is a low voltage.

Each phase conductor 34 carries power to a load 63 of a customer located along the grid. Some of these loads, particularly those that include electronic circuitry, are susceptible to grid voltage variations.

Each voltage sensor 56A,.. 60N includes a processor 64 and a memory 65 associated with the processor 64. The memory 65 is adapted to store first communication software 66 and first computing software 68.

In one embodiment, each sensor 56A, 60N includes a radio transceiver 70 adapted for bidirectional communication with the supervisory device 61, with each data link 62 being a radio data link in this case.

Alternatively, each sensor 56A, 60N includes a PLC transmitter (not shown) adapted for bi-directional communication with the supervisory device 61, and each data link 62 is a data transmission link via power line communication.

The supervisory device 61 of the detection system 20 is adapted to communicate with the voltage sensors 56A, 60N and with the control center 72.

The supervising device 61 comprises a processor 74 and a memory 76 associated with the processor 74. The memory 76 is adapted to store second communication software 78 and second computing software 80.

In this embodiment, the supervisory device 61 includes a radio transceiver 82 adapted to communicate with each sensor and with the control center 72. In this embodiment, the control center 72 further comprises a transceiver (not shown) adapted to communicate with the supervising device 61. In addition, the above-described communication uses a data transmission link via power line communication.

The first communication software 66 is adapted to establish communication between each voltage sensor 56A.., 60N and the supervisory device 61. The first communication software 66 is particularly adapted to send an alarm message to the supervising device 61 in the event that an overvoltage or undervoltage is detected on the at least one phase conductor 34 by the first calculation software 68.

The first computing software 68 is adapted to detect a measured over-voltage or under-voltage based on predefined over-voltage and under-voltage thresholds by a given voltage sensor 56A. The first calculation software 68 is particularly adapted to compare the measured voltage with predefined overvoltage and undervoltage thresholds to detect said overvoltage or undervoltage.

Alternatively, the voltage sensor 56A,. -, 60N transmits the measured voltage directly to the supervising device 61, wherein the supervising device 61, using the second calculation software 80, is adapted to determine the voltage sensor 56A,. -, 60N measuring an over-voltage or an under-voltage with respect to a predefined threshold.

The two pieces of software 66 and 68 are adapted to communicate together. In this manner, the detection of a voltage anomaly by the first computing software 68 causes an alert to be sent by the first communication software 66 to the supervising device 61.

The second communication software 78 is adapted to establish communication between the supervisory device 61 and the various voltage sensors of the network 56A.., 60N, as well as between the supervisory device 61 and the control center 72. The second communication software 78 is adapted to send queries to each of the voltage sensors 56A.., 60N in order to receive the voltage measured by each of these sensors in response.

The second computing software 80 is adapted to determine an under-voltage or an over-voltage that is abnormal above a predefined over-voltage threshold or under-voltage threshold based on data communicated by the voltage sensors 56A.

Alternatively, when the voltage sensor 56A. -, 60N directly transmits the measured voltage to the supervisory device 61, the second computing software 80 compares the measured voltage received from the voltage sensor 56A. -, 60N to predefined over-voltage and under-voltage thresholds to detect over-voltage or under-voltage.

The impedance change 84 on the neutral conductor 22 is shown in fig. 1. The impedance change 84 includes, for example, a neutral wire disconnection, or a neutral wire contact degradation.

The operation of the detection system will now be described with reference to fig. 3. Fig. 3 shows a flow chart of the steps of the detection method implemented by the detection system 20 (which comprises N groups 42A.., 42N of voltage sensors distributed along the output conductor 34) and by the supervision device 61.

In fig. 3, during a first step 100, a voltage sensor (e.g., sensor 56B) detects the presence of an overvoltage on one of the phase conductors 34. For example, the detected overvoltage corresponds to a voltage measured between the phase conductor 34 and the neutral conductor 22 which is 10% higher than the nominal voltage of said phase conductor 34 with respect to the neutral conductor 22, i.e. a nominal voltage of 110%, i.e. about 260V in the example of the embodiment of fig. 1.

Upon detecting an overvoltage on either phase conductor 34, the voltage sensor that detects the anomaly sends an alert to the supervisory device 61 during step 110.

Upon receiving the alarm, the supervisory device 61 interrogates the two voltage sensors 58B,60B, which belong to the same group 42B as the sensor 56B that detected the anomaly.

During step 130, the supervisory device 32 checks that the overvoltage detected on any of the voltage sensors (such as sensor 56B in the example of FIG. 1) occurs in parallel with the undervoltage measured on the other two voltage sensors (such as sensors 58B and 60B) of the group 42B. In the case of a three-phase network and a predetermined overvoltage threshold equal to 110% of the rated voltage, the supervision device 61 checks for at least 5% of the undervoltage observed by either of the voltage sensors 58B,60B associated with the two other phase conductors. In other words, the supervisory device 61 checks that at least one voltage sensor 58B,60B from the same group 42B as the sensor 46B detecting the overvoltage measures a voltage that is less than 95% of the corresponding nominal voltage, i.e. 228V in the example of embodiment of fig. 1.

After step 130, step 140 includes checking that the detection described above does represent an impedance change, such as a neutral break. In other words, step 140 includes locating potential false alarms. In particular, the supervisory device 61 checks that the voltage anomaly detection is not due to a loss of any phase of the medium voltage network, so that an overvoltage event occurs on the second low voltage board 16 at any phase conductor 34, while the other two phase conductors have an undervoltage in 50% of the area.

In some cases, the presence of decentralized coordinated co-frequency power production, for example by photovoltaic panels, causes an overvoltage in 10% of the area on one of the phases of the grid. In contrast, in some cases, the presence of a significant load on any one phase of the grid causes an undervoltage in the region of 5% to 10% on the other phases of the grid. In one embodiment, the supervisory device 61 measures the current flowing on each phase, and all the power generated or consumed on the same phase. It can therefore distinguish between voltage anomalies due to decentralized production and the presence of one or more significant loads on the grid and those due to degradation of the neutral conductor. Furthermore, the degradation of the neutral conductor is characterized in that it causes sudden changes in the network phase voltage.

After detecting a voltage anomaly representative of a change in impedance of the neutral line 84 in step 140, step 150 is intended to determine the final sensor 56A that is not indicative of a change in impedance and the first sensor 56B that is indicative of a change in impedance.

For this purpose, after measuring a voltage anomaly on any phase conductor 34, and after warning the supervising device 61 by means of the voltage sensor 56B, the supervising device 61 queries the group of sensors 42A, 42C adjacent to the sensors 56B,58B, 60B. If no anomaly is measured by any of these sensor groups (such as group 42A), then supervisory device 61 infers that the location of the impedance change is between the group 42B where an anomaly was measured and the queried group 42A where no anomaly was measured.

If the query set also measures anomalies, the supervisory device 61 further queries the neighboring sets upstream and downstream from the previous query set. In this manner, after multiple queries, recursive queries from sensor groups located upstream and downstream of the first set 42B of measured anomalies are appropriate to locate the first set 42A of sensors that did not measure voltage anomalies.

Finally, during step 160, the impedance-change zone is located by the area between the final sensor 56A, which is not indicative of a voltage anomaly, and the first sensor 56B, which is indicative of a voltage anomaly.

Once the location has been discovered by the supervisory device 61, the abnormal location information is sent to the control center 72 to enable scheduled maintenance on the network.

Thus, the detection system according to the invention is not only suitable for detecting impedance changes (such as neutral line disconnection), but also for locating the areas of impedance changes along the low voltage network due to the N groups 42A, 42N of voltage sensors arranged along the low voltage network.

Further, the communication between each voltage sensor 56A, 60N and the supervisory device 61 is adapted to distinguish between voltage anomalies associated with the structure of the medium voltage network 12 and voltage anomalies due to impedance changes 84 that require maintenance.

The system and method according to the invention are therefore suitable for detecting deterioration of the neutral conductor before it is disconnected, enabling preventive maintenance on the network.

Intervention of the low-voltage network then takes place before a complete disconnection of the neutral line 22 occurs and damages or damages the loads 63 connected to the low-voltage network. This helps to prevent degradation of these loads.

The use of such an apparatus and such a method may also enable the use of voltage sensors 56A, 60N, including radio transceiver 70, thus avoiding the need for the worker to make readings.

Such a device and such a method are also suitable for, after locating a fault 84 of the power network, generating an alarm from the supervising device 61 to the control center 72, together with location information associated with said fault 84. The control center 72 then sends out a maintenance team to check the connection status of the neutral conductor 22 in the determined target and previously located area.

Thus, the repair team optimizes the availability of its resources to maintain the impedance change zone. This optimization is achieved because the maintenance operator can go directly to the impedance change zone without wasting time locating the zone.

It can therefore be envisaged that the voltage monitoring of the detection system according to the invention via the power grid is not only suitable for detecting, but also locating impedance changes on the network, such as neutral line disconnections.

Claims (13)

1. A detection system (20) for detecting an impedance change (84) in a neutral conductor (22) of a multi-phase Alternating Current (AC) grid, the grid including P phase conductors (34) and one neutral conductor (22), where P is an integer greater than 1, the system comprising:

-a set (42A) of P voltage sensors (56A,58A,60A), each voltage sensor (56A,58A,60A) being adapted to measure the voltage of a respective phase conductor (34) with respect to the neutral conductor (22), and

a supervision device (61) connected to each voltage sensor (56A,58A,60A) via a data link (62),

characterized in that the system further comprises (N-1) other groups (42B, … …,42N) of P voltage sensors (56B, 58B,60B, …,56N,58N, 60N), where N is an integer greater than 1, the N groups of voltage sensors (42A, …,42N) being arranged at different locations along the grid, and

characterized in that the supervision device (61) is adapted to detect a change in voltage of a given phase conductor (34) with respect to the neutral conductor (22) between two consecutive groups of sensors (42A,42B) in order to detect a change in impedance (84) of the neutral conductor (22) and said change in impedance (84) positioned between the two consecutive groups of sensors (42A, 42B).

2. A detection system (20) according to claim 1, characterised in that each voltage sensor (56A, …,60N) comprises means (66) for sending an alarm message to a supervision device (61) when an overvoltage or undervoltage is detected for at least one phase conductor (34).

3. A detection system (20) according to claim 1 or 2, characterized in that each voltage sensor (56A, …,60N) comprises means (68) for comparing the measured voltage with predefined overvoltage and undervoltage thresholds to detect overvoltage or undervoltage.

4. A detection system (20) according to claim 1 or 2, characterized in that the supervision device (61) comprises means (80) for comparing the measured voltage received from the corresponding voltage sensor (56A, …,60N) with predefined overvoltage and undervoltage thresholds to detect overvoltage or undervoltage.

5. A detection system (20) according to any one of the preceding claims, characterised in that the supervision device (61) comprises means (78) for communicating with each voltage sensor (56A, …,60N), which are adapted to send an inquiry to each voltage sensor in order to receive in response the voltage measured by each voltage sensor.

6. Detection system (20) according to any one of the preceding claims, characterized in that the supervision device (61) comprises a calculation unit (80) adapted to compare the measured voltage of each phase conductor (34) with predefined overvoltage and undervoltage thresholds.

7. An electrical substation to be connected to a polyphase AC grid (12), the substation comprising

-a first board (14) comprising P power input conductors (26) adapted to be connected to the power grid (12), wherein P is an integer greater than 1,

-a second board (16) comprising at least one output (32) of P power conductors and one neutral conductor (22),

-a transformer (18) connected between the first board (14) and the second board (16) and adapted to convert an input current having a first AC voltage on an input conductor (26) into a current having a second AC voltage, and

-a detection system (20) for detecting an impedance change (84) in the neutral conductor (22),

characterized in that the detection system (20) is a detection system according to any one of the preceding claims.

8. A method for detecting an impedance change (84) in a neutral conductor (22) of a multi-phase AC electrical network, the network comprising P phase conductors (34) and the neutral conductor (22), where P is an integer greater than 1, the method comprising the steps of:

-measuring the voltage of each phase conductor (34) with respect to the neutral conductor (22) at a given location of the grid by means of a set (42A) of P voltage sensors (56A,58A,60A),

-sending the measured voltage from the set (42A) of voltage sensors to a supervising device (61),

the method is characterized in that during the measuring step, the voltage of the phase conductor (34) relative to the neutral conductor (22) at different positions along the power network is measured by N groups (42A, …,42N) of P voltage sensors (56A, …,60N) arranged at said different positions, and

the method is characterized by further comprising the following steps:

-detecting, between two consecutive groups of sensors, a variation of the voltage of the conductor (34) of a given phase with respect to the neutral conductor (22), in order to detect an impedance variation (84) in the neutral conductor (22) and said impedance variation (84) positioned between the two consecutive groups of sensors (42A,42B), the detection step being carried out by a supervision device (61) based on the measured voltages sent by each of the groups of voltage sensors (42A, …, 42N).

9. The method of claim 8, wherein: after receiving an alarm message from a given group (42B) of voltage sensors (56B) when an over-voltage or under-voltage anomaly is detected for at least one phase conductor (34), a supervisory device (61) sends an inquiry to different voltage sensors (56B, 58B, 60B) of the given group (42B) to receive the voltages measured by the sensors of the given group (42B).

10. The method of claim 9, wherein: after receiving the voltages measured by the sensors (56B, 58B, 60B) of a given group (42B), the supervision device (61) checks whether both an overvoltage with respect to one phase conductor (34) and an undervoltage with respect to the other phase conductor (34) are detected.

11. The method according to claim 9 or 10, characterized in that: after receiving the voltages measured by the sensors of a given group (42B), the supervision device (61) checks that the detected voltage anomaly is not caused by a loss of any phase of the network or by a load imbalance between the phases of the network.

12. The method according to any of claims 9 to 11, characterized by: after receiving the alert message from the voltage sensors of a given group (42B), the supervisory device (61) also sends a query to the different voltage sensors of groups (42A, 42C) adjacent to the given group (42B).

13. The method of claim 12, wherein: a supervisory device (61) determines a group of sensors (42B, 42C) that detected a voltage anomaly and a group (42A) or other group that did not detect a voltage anomaly, and determines an impedance change zone located between a final group of sensors (42A) that did not indicate an anomaly and a first group of sensors (42B) that indicated an anomaly.