CN201146385Y - Discrimination and protection device for eliminating single-phase ground fault in neutral point non-effectively grounded power grid - Google Patents

Abstract

The utility model aims at the misunderstanding of the single-phase ground fault judgment of the neutral point non-effective ground system, and discloses a judgment and protection device for neutral point non-effective ground grid to eliminate single-phase ground faults. The method is based on the zero sequence voltage and The relationship between phase voltage and phase voltage is used to distinguish the fault phase, which provides a basis for accurate grounding protection. Grounding protection is to directly ground the faulty phase busbar through the reactor. This method not only retains the advantages of the neutral point ungrounded method, but also makes up for the The ungrounded single-phase grounding arc is easy to reignite, and the internal overvoltage multiple is high; it is unique in the protection of high-impedance grounding faults. The device has the advantages of simple and reliable method and structure, small occupied area and low comprehensive cost.

Description

Discrimination and protection device for eliminating single-phase ground fault in neutral point non-effectively grounded power grid

technical field

The utility model relates to a method and protection device for discriminating and protecting a power grid for eliminating grounding faults, in particular to a discriminating and protecting device for eliminating single-phase high-resistance grounding faults for a neutral point non-effectively grounding power grid.

Background technique

In the power system, single-phase grounding is the main fault form in the operation of the power grid, accounting for more than 60% of the total faults in the entire power grid, and a considerable part of interphase short-circuit faults are developed from single-phase grounding faults. The safety and reliability of the power system, when other conditions are the same, only depends on the working mode of the neutral point of the power system. To study the grounding mode of the neutral point of the power system, it is mainly to correctly understand and deal with the most common single-phase ground fault problem.

The types of single-phase ground faults can be divided into: arc ground, high resistance ground and metal ground. According to the statistics of the power system, the vast majority of single-phase ground faults are arc grounding and high-impedance grounding. Single-phase arc-flash grounding is the most harmful. In the 6-66kV medium-voltage power grid, the neutral point is not grounded. As more and more distribution lines are cabled, the grounding capacitor current also increases. Once grounding occurs, it cannot be extinguished automatically, and high intermittent arc overvoltage will be generated, which will endanger the insulation safety of electrical equipment. It will often develop into phase-to-phase short circuit in the cable line, and even cause the bad consequences of "burning and burning". In addition to mechanical damage, most lines have a process of insulation aging or insulation damage before an arc ground fault occurs, and a high-impedance grounding state appears during this process.

High-impedance grounding is one of the most common faults in single-phase grounding, such as the hanging of tree branches in overhead lines, disconnection, damp and aging of cable insulation in cable lines, etc., all present the characteristics of high-impedance grounding. The grounding resistance varies in a large range and is unstable, and the fault state is the most complicated. When the grounding resistance is large enough (such as >1.5kΩ), the fault characteristics are different from common ones, and the fault information is very weak, so that it becomes a problem in protection and line selection. a difficult problem. Therefore, when a high-resistance grounding fault occurs, there are reports of accidents caused by protection malfunction or refusal to operate: for example, if the transmission line breaks and falls on the concrete ground, the protection refuses to operate, causing personal injury or death; Fires, cable blasts, and more. Most protection products have misjudgment, misoperation or refusal to operate high-resistance grounding protection. The reason is not only weak fault information, but also misunderstandings in understanding. Since the voltage analysis of the single-phase grounding of the ungrounded system is usually done according to the typical metal grounding, the grounded phase voltage is zero at this time, the unconnected phase voltage rises to the line voltage, and the neutral point shifts to the grounding point. The zero-sequence voltage is equal to the pre-fault phase voltage in the opposite direction. As a result, there is a generally accepted conclusion: the ground phase is the phase with the lowest amplitude among the three-phase voltages, and most of the ground fault protection products that use voltage as the criterion also judge the ground phase according to this conclusion. In fact, this is only true when the grounding resistance is less than a certain critical value. When the grounding resistance is greater than this critical value, this conclusion is wrong. In other words, in the range of high-impedance grounding, when the grounding resistance is large enough, the grounding phase is not the phase with the lowest voltage amplitude. Adhere to the aforementioned conclusions will inevitably lead to misjudgment and misoperation of protection in high-resistance ground faults. In addition, the ground fault protection products based on current as the criterion refuse to operate because the zero-sequence current is very small when the ground is high-impedance; the line selection products cannot be selected for this reason.

Contents of the invention

The purpose of this utility model is to design a single-phase grounding fault detection method for the existing single-phase grounding fault discrimination method is not comprehensive, there are misunderstandings, and it is easy to cause misjudgment or missed judgment of high-resistance grounding faults and cannot provide protection for eliminating faults. Comprehensive fault identification and protection device.

The technical scheme of the utility model is:

A protection device for eliminating single-phase grounding faults in neutral point non-effectively grounded power grids, which is characterized in that it is mainly composed of four single-phase high-voltage switches ZA, ZB, ZC, ZD, reactor L, current transformer CT, and three-phase Voltage and zero-sequence voltage voltage transformer TV and microcomputer controller, the three-phase power lines of the system bus are respectively connected to the upper contacts of the normally open main contacts ZA1, ZB1, and ZC1 of the three single-phase high-voltage switches. The lower contacts of the normally open main contacts ZA1, ZB1, and ZC1 of a single-phase high-voltage switch are connected together and then connected to one end of the reactor L, and the other end of the reactor L passes through the primary winding of the current transformer CT and then grounded , the secondary winding of the current transformer CT is connected to the analog input terminal of the microcomputer controller; the normally open main contact of the other single-phase high-voltage switch ZD1 is connected to the middle tap of the reactor L and the three single-phase high-voltage switches Between the parallel contacts of the lower contacts of normally open main contacts ZA1, ZB1, and ZC1, the line packs ZA, ZB, ZC, and ZD of the four single-phase high-voltage switches are respectively connected to the corresponding output terminals controlled by the microcomputer to collect the three-phase voltage and The voltage transformer TV of zero-sequence voltage is connected between the system bus three-phase power line and the corresponding sampling input terminal of microcomputer controller; The output circuit 4 and the switching value input circuit 5, the input of the sampling filter circuit 2 and the voltage sampling circuit 6 and the current sampling circuit 7, its output is connected with the corresponding input terminal of the single chip microcomputer 1, and the output terminal of the switching value input circuit 5 passes through a photoelectric isolation circuit 3 is connected to the input terminal corresponding to the single-chip microcomputer 1, the input terminal of the single-chip microcomputer 1 is connected to the input terminal of the relay output circuit 4 through the photoelectric isolation circuit 3, and the relay output circuit 4 is respectively connected to the corresponding four single-phase high-voltage switches ZA, ZB, ZC, ZD is connected. The voltage transformer TV is a voltage transformer using a three-phase five-column connection method, one end of its three-phase primary winding is connected between the three-phase power line and the ground using a Y-type connection method, and the six terminals of the voltage transformer TV Three of the two secondary windings are connected between the phase voltage sampling input terminal of the microcomputer controller and the ground in a Y-type connection, and the other three secondary windings are connected to the zero-sequence voltage of the microcomputer controller in an open delta connection. Between the input end and ground, between the control output end of the microcomputer controller and the power supply, there is a harmonic elimination relay package JX, the normally open contact JX1 of the harmonic elimination relay is connected in series with the harmonic elimination resistor RX, and then connected across the voltage transformer TV The opening of the winding in which the open delta connection is adopted.

The single-chip microcomputer 1 is also connected with a keyboard 8 and a display 9 .

The beneficial effects of the utility model:

The utility model reveals the law of the single-phase ground fault in the neutral point ungrounded system, finds out various characteristics of the high-resistance ground fault and the discrimination and protection method, no matter how the ground resistance and fault characteristics change, the fault can be accurately judged And fault phase, the implementation of effective protection.

The utility model realizes full-range effective protection for single-phase grounding faults in the neutral point ungrounded system, especially can distinguish weak signals that are difficult to detect high-impedance grounding faults, and eliminates faults in the bud.

The comprehensive protection device controlled by the microcomputer of the utility model not only retains the advantages of the neutral point non-grounding method: the grounding current is small, the power supply reliability is high, and it also makes up for the single-phase grounding arc of the non-grounding method, which is easy to reignite and the internal overvoltage. High multiples and other disadvantages; especially in the protection of high-impedance ground faults have unique features. It is safer than direct grounding and large current grounding with small resistance grounding using the grounding grid of the substation. Its arc suppression performance and the limitation of arc overvoltage and resonance overvoltage are more effective than arc suppression coils, and its structure is simple and reliable. , small footprint and low overall cost, it is a grounding protection device worthy of popularization and application.

Description of drawings

Fig. 1 is the method flowchart of the present utility model.

Fig. 2 is an electrical schematic diagram of the discrimination device of the present invention.

Fig. 3 is the functional block diagram of the microcomputer controller of the utility model.

Detailed ways

Below in conjunction with accompanying drawing and embodiment the utility model is described further.

As shown in Figures 1, 2, and 3.

A discriminating and protecting device for eliminating single-phase high-resistance grounding faults in a neutral point non-effectively grounded grid, mainly composed of four single-phase high-voltage switches ZA, ZB, ZC, ZD, reactor L, current transformer CT, and three-phase Voltage and zero-sequence voltage voltage transformer TV and microcomputer controller, the three-phase power lines of the system bus are respectively connected to the upper contacts of the normally open main contacts ZA1, ZB1, and ZC1 of the three single-phase high-voltage switches. The lower contacts of the normally open main contacts ZA1, ZB1, and ZC1 of a single-phase high-voltage switch are connected together and then connected to one end of the reactor L, and the other end of the reactor L passes through the primary winding of the current transformer CT and then grounded , the secondary winding of the current transformer CT is connected to the analog input terminal of the microcomputer controller; the normally open main contact of the other single-phase high-voltage switch ZD1 is connected to the middle tap of the reactor L and the three single-phase high-voltage switches Between the parallel contacts of the lower contacts of normally open main contacts ZA1, ZB1, and ZC1, the line packs ZA, ZB, ZC, and ZD of the four single-phase high-voltage switches are respectively connected to the corresponding output terminals controlled by the microcomputer to collect the three-phase voltage and The voltage transformer TV of zero-sequence voltage is connected between the corresponding sampling input end of system busbar three-phase power line and microcomputer controller; Described microcomputer controller (as shown in Figure 3) comprises single-chip microcomputer 1 (model can be: TMS320C600, or DSP563X X, etc.), sampling filter circuit 2 (can be realized by integrated block or common textbook circuit), photoelectric isolation circuit 3 (can be composed of photocoupler and peripheral circuit), relay output circuit 4 and switch input Circuit 5 (can be realized by integrated block or common textbook circuit), the input of sampling filter circuit 2 and voltage sampling circuit 6 (can be realized by integrated block or common textbook circuit) and current sampling circuit 7 (can be realized by Manifold block or common textbook common circuit to realize), its output is connected with the corresponding input end of single-chip microcomputer 1, the output end of switching value input circuit 5 is connected with the corresponding input end of single-chip microcomputer 1 through photoelectric isolation circuit 3, the input end of single-chip microcomputer 1 The photoelectric isolation circuit 3 is connected to the input terminal of the relay output circuit 4, and the relay output circuit 4 is respectively connected to the corresponding four single-phase high-voltage switches ZA, ZB, ZC, and ZD. The single-chip microcomputer 1 is also connected with a keyboard 8 and a display 9 for Parameters are adjusted, entered and displayed. The voltage transformer TV is a voltage transformer using a three-phase five-column connection method, one end of its three-phase primary winding is connected between the three-phase power line and the ground using a Y-type connection method, and the six terminals of the voltage transformer TV Three of the two secondary windings are connected between the phase voltage sampling input terminal of the microcomputer controller and the ground in a Y-type connection, and the other three secondary windings are connected to the zero-sequence voltage of the microcomputer controller in an open delta connection. Between the input end and ground, between the control output end of the microcomputer controller and the power supply, there is a harmonic elimination relay package JX, the normally open contact JX1 of the harmonic elimination relay is connected in series with the harmonic elimination resistor RX, and then connected across the voltage transformer TV The opening of the winding in which the open delta connection is adopted.

The discriminating device of the utility model adopts the mode of inputting a reactor to be grounded on the busbar of the fault phase for protection, and has functions such as line selection, fault tripping, and communication. This device not only retains the advantages of the neutral point ungrounded method: the grounding current is small, and the power supply reliability is high; The ground fault protection is unique.

The working process of the microcomputer integrated protection device of the present utility model is as follows:

The microcomputer controller always detects the three-phase voltage and zero-sequence voltage of the system and their frequency, and makes a judgment. When the system is running normally, the four high-voltage switches are all in the breaking state, and the device does not have any impact on the system; once it is judged that a single-phase ground fault occurs in the system, the microcomputer controller immediately drives the device for protection (see Figure 2):

If the fault parameter is in the fault characteristic area 1, the microcomputer controller drives the high-voltage switch of the phase with the lowest voltage to close; if the fault parameter is in the fault characteristic area 2, the microcomputer controller drives the high-voltage switch of the fault voltage phase to close; if the fault parameter is in the fault characteristic area 3 , the microcomputer controller drives the high-voltage switch of the second-lowest phase to close. The results of the three protection actions are that the reactor L is connected in parallel between the bus bar of the fault phase and the ground, resulting in the following effects: 1) clamping the voltage of the fault phase to approximately zero, and limiting the voltage of the non-fault phase to be less than the line voltage. 2) For arc grounding, transfer 100% of the fault current; for high resistance grounding, transfer more than 98% of the fault current; for metal grounding, transfer more than 90% of the fault current. Its effect is to eliminate or suppress the fault, and protect the personal and equipment safety at the fault point.

For transient faults, the high-voltage switch will be disconnected after a few seconds to eliminate the fault without affecting the continuity of power supply; for permanent faults, the high-voltage switch will be delayed for tens of minutes, according to the prior selection, or the faulty line can be cut off by manual tripping. Or cut off the faulty line by the action of the trip box of the device. If the fault parameter is in the alarm range, the device will accurately alarm the fault type and line.

Specific examples are as follows:

example 1.

When single-phase grounding occurs in a 6kV neutral point non-effectively grounded grid system, the measured zero-sequence voltage is 2kV, while the normal phase voltage of the system is 3.6kV. It can be seen from the discrimination method described in claim 1 that the single-phase The ground fault satisfies the condition of characteristic area 1, therefore, it can be judged that the lowest phase of the three-phase voltage is the fault phase at this time, and immediately put into ground protection on the busbar of this phase (ground protection can be grounded through a reactor, or grounded in other ways) ), for instantaneous faults, the grounding protection will be disconnected from the busbar of the phase after a delay of several seconds, and the fault can be eliminated; for permanent faults, the grounding protection will be delayed for tens of minutes. Line, or cut off the faulty line by the action of the trip box of the device.

Example 2.

When single-phase grounding occurs in a 6kV neutral point non-effectively grounded power grid system, the measured zero-sequence voltage is 1.8kV, while the normal phase voltage of the system is 3.6kV. It can be seen from the discrimination method described in claim 1 that the single The phase-to-ground fault satisfies the conditions of characteristic area 2. Therefore, it can be judged that the phase voltage lagging behind the zero-sequence voltage by 90° at this time is the fault phase, and immediately put into ground protection on the busbar of this phase (ground protection can be grounded through a reactor, or grounding in other ways), for instantaneous faults, the grounding protection delays for a few seconds and disconnects from the phase bus to eliminate the fault; for permanent faults, the grounding protection delays for tens of minutes, according to the prior selection, or manually Cut off the fault line by tripping, or cut off the fault line by the action of the trip box of the device.

Example 3.

When single-phase grounding occurs in a 6kV neutral point non-effectively grounded grid system, the measured zero-sequence voltage is 1.2kV, while the normal phase voltage of the system is 3.6kV. It can be seen from the discrimination method described in claim 1 that the single The phase-to-ground fault satisfies the conditions of characteristic area 3, therefore, it can be judged that the second lowest phase of the three-phase voltage is the fault phase at this time, and the grounding protection is immediately put into use on the busbar of this phase (the grounding protection can be grounded through a reactor, or other mode grounding), for instantaneous faults, the grounding protection will be disconnected from the busbar of the phase after a delay of several seconds, and the fault can be eliminated; for permanent faults, the grounding protection will be delayed for tens of minutes, according to the prior selection, or by manual tripping Cut off the faulty line, or cut off the faulty line by the action of the trip box of the device.

Example 4.

When single-phase grounding occurs in a 10kV neutral point non-effectively grounded power grid system, the measured zero-sequence voltage is 4kV, while the normal phase voltage of the system is 6kV. It can be seen from the discrimination method described in claim 1 that the single-phase grounding The fault satisfies the condition of characteristic area 1, therefore, it can be judged that the lowest phase of the three-phase voltage is the fault phase at this time, and the grounding protection is immediately put into use on the busbar of this phase (the grounding protection can be grounded through a reactor or in other ways) , for instantaneous faults, the grounding protection will be disconnected from the phase bus after a delay of several seconds, and the fault can be eliminated; for permanent faults, the grounding protection will be delayed for tens of minutes, according to the prior selection, or the faulty line can be cut off by manual tripping , or cut off the faulty line by the action of the trip box of the device.

Example 5.

When single-phase grounding occurs in a 10kV neutral point non-effectively grounded grid system, the measured zero-sequence voltage is 3kV, while the normal phase voltage of the system is 6kV. It can be seen from the discrimination method described in claim 1 that the single-phase grounding The fault satisfies the condition of characteristic zone 2, therefore, it can be judged that the phase voltage lagging zero-sequence voltage by 90° at this time is the fault phase, and the grounding protection is immediately put into use on the busbar of this phase (the grounding protection can be grounded through a reactor, or other methods grounding), for instantaneous faults, the grounding protection will be disconnected from the busbar of the phase after a delay of several seconds, and the fault can be eliminated; for permanent faults, the grounding protection will be delayed for tens of minutes, according to the prior selection, or cut off by manual tripping Faulty lines, or cut off the faulty line by the action of the trip box of the device.

Example 6.

When single-phase grounding occurs in a 10kV neutral point non-effectively grounded grid system, the measured zero-sequence voltage is 2kV, while the normal phase voltage of the system is 6kV. It can be seen from the discrimination method described in claim 1 that the single-phase grounding The fault satisfies the condition of characteristic zone 3, therefore, it can be judged that the phase with the second lowest voltage among the three phases is the fault phase at this time, and the grounding protection should be put into operation immediately on the busbar of this phase (the grounding protection can be grounded through a reactor or in other ways) ), for instantaneous faults, the grounding protection will be disconnected from the busbar of the phase after a delay of several seconds, and the fault can be eliminated; for permanent faults, the grounding protection will be delayed for tens of minutes. Line, or cut off the faulty line by the action of the trip box of the device.

Example 7.

When single-phase grounding occurs in a 35kV neutral point non-effectively grounded grid system, the measured zero-sequence voltage is 12kV, while the normal phase voltage of the system is 21kV. It can be seen from the discrimination method described in claim 1 that the single-phase grounding The fault satisfies the condition of characteristic area 1, therefore, it can be judged that the lowest phase of the three-phase voltage is the fault phase at this time, and the grounding protection is immediately put into use on the busbar of this phase (the grounding protection can be grounded through a reactor or in other ways) , for instantaneous faults, the grounding protection will be disconnected from the phase bus after a delay of several seconds, and the fault can be eliminated; for permanent faults, the grounding protection will be delayed for tens of minutes, according to the prior selection, or the faulty line can be cut off by manual tripping , or cut off the faulty line by the action of the trip box of the device.

Example 8.

When single-phase grounding occurs in the 35kV neutral point non-effectively grounded grid system, the measured zero-sequence voltage is 10.5kV, while the normal phase voltage of the system is 21kV. It can be seen from the discrimination method described in claim 1 that the single-phase The ground fault satisfies the condition of characteristic area 2, therefore, it can be judged that the phase voltage lagging behind the zero-sequence voltage by 90° at this time is the fault phase, and immediately put into ground protection on the busbar of this phase (ground protection can be grounded through a reactor, or other mode grounding), for instantaneous faults, the grounding protection will be disconnected from the busbar of the phase after a delay of several seconds, and the fault can be eliminated; for permanent faults, the grounding protection will be delayed for tens of minutes, according to the prior selection, or by manual tripping Cut off the faulty line, or cut off the faulty line by the action of the trip box of the device.

Example 9.

When single-phase grounding occurs in the 35kV neutral point non-effectively grounded grid system, the measured zero-sequence voltage is 9kV, while the normal phase voltage of the system is 21kV. It can be seen from the discrimination method described in claim 1 that the single-phase grounding The fault satisfies the condition of characteristic zone 3, therefore, it can be judged that the phase with the second lowest voltage among the three phases is the fault phase at this time, and the grounding protection should be put into operation immediately on the busbar of this phase (the grounding protection can be grounded through a reactor or in other ways) ), for instantaneous faults, the grounding protection will be disconnected from the busbar of the phase after a delay of several seconds, and the fault can be eliminated; for permanent faults, the grounding protection will be delayed for tens of minutes. Line, or cut off the faulty line by the action of the trip box of the device.

The parts not involved in the utility model are all the same as the prior art or can be realized by adopting the prior art.

Claims (3)

1, a kind of neutral non-effective grounding electrical network is eliminated the protective device of single phase ground fault, it is characterized in that it is mainly by four single-phase high voltage switch ZA, ZB, ZC, ZD, reactor L, current transformer CT, gathering the voltage transformer TV and the microcomputerized controller of three-phase voltage and residual voltage forms, the bus of system's three phase mains respectively with three single-phase high voltage switches often open main contacts ZA1, ZB1, the upper contact head of ZC1 is corresponding to link to each other, three single-phase high voltage switches often open main contacts ZA1, ZB1, after interconnecting, the following contact of ZC1 links to each other with the end of reactor L, the other end of reactor L passes ground connection behind the winding of current transformer CT, and the secondary winding of current transformer CT connects the analog quantity input of microcomputerized controller; The main contacts of often opening of another single-phase high voltage switch ZD1 is attempted by the centre tap of reactor L and also between the contact of the following contact of often opening main contacts ZA1, ZB1, ZC1 of three single-phase high voltage switches, the line bag ZA of four single-phase high voltage switches, ZB, ZC, ZD connect micro-processor controlled corresponding output respectively, and the voltage transformer TV that gathers three-phase voltage and residual voltage is connected between the correspondence sampling input of system busbar three-phase power line and microcomputerized controller; Described microcomputerized controller is by comprising single-chip microcomputer (1), sampling filter circuit (2), photoelectric isolating circuit (3), relay output circuit (4) and switching value input circuit (5), the input of sampling filter circuit (2) and voltage sampling circuit (6) and current sampling circuit (7), its output links to each other with the corresponding input of single-chip microcomputer (1), the output of switching value input circuit (5) links to each other with single-chip microcomputer (1) corresponding input end by photoelectric isolating circuit (3), the input of single-chip microcomputer (1) links to each other with the input of relay output circuit (4) by photoelectric isolating circuit (3), relay output circuit (4) respectively with four corresponding single-phase high voltage switch ZA, ZB, ZC, ZD links to each other.

2; neutral non-effective grounding electrical network according to claim 1 is eliminated the protective device of single phase ground fault; it is characterized in that described voltage transformer TV is the voltage transformer of an employing three-phase and five-pole connection; one end of a winding of its three-phase adopts wye connection to be connected between three-phase power line and the ground; three windings in six secondary winding of voltage transformer TV adopt wye connection to be connected between the phase voltage sampling input and ground of microcomputerized controller; other three secondary winding adopt open-delta connection to be connected between the residual voltage input and ground of microcomputerized controller; between the control output end of microcomputerized controller and power supply, be connected to harmonic elimination relay line bag JX, be connected across the winding opening part that adopts open-delta connection among the voltage transformer TV behind the normally opened contact JX1 serial connection harmonic elimination resistance R X of harmonic elimination relay.

3, neutral non-effective grounding electrical network according to claim 1 is eliminated the protective device of single phase ground fault, it is characterized in that described single-chip microcomputer (1) also is connected with keyboard (8) and display (9).

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