CN202649370U - PT (potential transformer) secondary loop multipoint grounding online monitor - Google Patents

Abstract

The utility model relates to a PT secondary circuit multi-point grounding online monitor. The utility model is composed of a one-point grounding connection line (1) of the control room of the PT secondary circuit, a lightning arrester F, a milliampere meter A, a small knife switch K and a sliding wire rheostat R; the one-point grounding connection line (1) of the control room is connected to Between the zero-phase N600 of the control room of the PT secondary circuit and the secondary equipotential ground network B; the milliampere meter A, the small knife switch K and the sliding wire rheostat R are connected in series in sequence and connected to the control room at one point ground connection line (1 ) in parallel; the arrester F is connected between the zero-phase N600 in the control room and the secondary equipotential ground network B. The beneficial effect of the utility model is that under the premise of ensuring that the running PT secondary circuit does not lose the grounding point and does not affect the normal operation of the protection equipment, it can accurately determine the hidden dangers of multi-point grounding, and provides technical support for the investigation of relay protection hidden dangers .

Description

PT secondary circuit multi-point grounding online monitor

technical field

The utility model relates to a PT secondary circuit multi-point grounding online monitor.

Background technique

At present, there have been many examples of protection misoperations caused by multi-point grounding of the PT secondary circuit in the substation. The multi-point grounding of the PT secondary circuit is caused by the reconstruction and expansion of the substation. To solve this problem, the existing LT-N600 PT The multi-point ground fault locator needs to add an electrical signal to the PT secondary circuit to detect the change of the signal to determine whether a multi-point ground has occurred in the PT secondary circuit. The electrical signal will interfere with the running protection equipment and affect its normal operation. Operation may cause malfunction and refusal of protective equipment. Therefore, there is a need for an online monitoring device for multi-point grounding of the PT secondary circuit that can ensure that the running PT secondary circuit does not lose the grounding point and does not affect the normal operation of the protection equipment.

Utility model content

The technical problem to be solved by the utility model is to provide a PT secondary circuit multi-point circuit that can accurately determine the hidden danger of multi-point grounding under the premise of ensuring that the running PT secondary circuit does not lose the grounding point and does not affect the normal operation of the protection equipment. Grounding online monitor.

The utility model is aimed at the technical scheme that its technical problem adopts:

The utility model is composed of a one-point ground connection line of the control room of the PT secondary circuit, a lightning arrester F, a milliampere meter A, a small knife switch K and a sliding wire rheostat R; the one-point ground connection line of the control room is connected to the control Between the zero-phase N600 of the room and the secondary equipotential ground network B; the milliampere meter A, the small knife switch K and the sliding wire rheostat R are connected in series and then connected in parallel with the one-point ground connection line of the control room; the arrester F is connected to Between the zero-phase N600 in the control room and the secondary equipotential ground network B.

The arrester F is a low voltage zinc oxide arrester with a breakdown voltage of 380V.

The resistance range of the sliding wire rheostat R is 0-10Ω; the accuracy of the milliampere meter A is 1mA, and the range is 0-100mA; the rated voltage of the small knife switch K is above 220V, and the rated current is above 20A .

The beneficial effects of the utility model are as follows:

On-site simulation experiments in substations are feasible. Under the premise of ensuring that the running PT secondary circuit does not lose the grounding point and does not affect the normal operation of the protection equipment, it can accurately determine the hidden dangers of multi-point grounding, which provides technical support for the investigation of hidden dangers in relay protection. .

Description of drawings

Figure 1 is the circuit schematic diagram of the PT secondary circuit multi-point grounding online monitor.

Figure 2 is the equivalent circuit diagram of one point grounding of the PT secondary circuit.

Figure 3 is the equivalent circuit diagram of the two-point grounding of the PT secondary circuit.

In Figure 1-3, 1 is the one-point ground connection line of the control room of the PT secondary circuit, F is the lightning arrester, A is the milliampere meter, K is the small knife switch, R is the sliding wire rheostat, and C is the PT secondary circuit cable pair Ground distributed capacitance, U ₁ is the PT secondary equivalent voltage, O is the grounding point of the substation PT secondary circuit in the control room, F is another grounding point of the substation PT secondary circuit except the one point grounding point O of the control room, U ₂ is the potential difference between the ground point O and the ground point F on the secondary equipotential ground network, and R _f is the cable resistance between the ground point O and the ground point F.

Detailed ways

As can be seen from the embodiment shown in Figure 1, the utility model is composed of a point grounding connection line 1, a lightning arrester F, a milliampere meter A, a small knife switch K and a sliding wire rheostat R in the control room of the PT secondary circuit; The ground connection line 1 is connected between the zero-phase N600 of the control room of the PT secondary circuit and the secondary equipotential ground grid B; One point ground connection line 1 is connected in parallel; the arrester F is connected between the zero-phase N600 in the control room and the secondary equipotential ground network B.

The arrester F is a low voltage zinc oxide arrester with a breakdown voltage of 380V.

The resistance range of the sliding wire rheostat R is 0-10Ω; the accuracy of the milliampere meter A is 1mA, and the range is 0-100mA; the rated voltage of the small knife switch K is above 220V, and the rated current is above 20A .

The one-point ground connection line 1 of the control room of the PT secondary circuit is a multi-strand annealed copper wire of ^4mm ; the function of the lightning arrester F is to prevent the secondary equipotential The potential of the ground grid B rises, which endangers the safety of people and equipment. After the lightning arrester F breaks down, the PT secondary circuit is connected to the secondary equipotential ground grid B again, thereby ensuring the safety of people and equipment; the function of the milliampere meter A is Measure the current in the branch circuit.

The usage method of this embodiment:

Connect one end of the sliding wire rheostat R to the secondary equipotential ground network B, connect one end of the mA meter A to the zero-phase N600 in the control room, close the knife switch K, and disconnect the one-point ground connection line of the control room of the PT secondary circuit 1. Adjust the resistance value of the sliding wire rheostat R to change between 0-10Ω, observe the current on the sliding wire rheostat R, that is, observe the change of the current value of the milliampere meter A, if the current value of the milliampere meter A changes then Indicates that there is a multi-point ground, otherwise there is no multi-point ground.

When the zero-phase N600 of the control room of the PT secondary circuit is grounded at one point (see Figure 2), the distributed capacitance C of the PT secondary circuit cable to the ground, the PT secondary equivalent voltage U ₁ and the control room of the PT secondary circuit are grounded at one point The connection line 1 forms a loop. The distributed capacitance C is very small and presents a high impedance. The capacitive reactance of the capacitance C and _U1 determine the size of the loop current I. Connect the sliding wire resistor R in parallel at one point grounding connection line 1 in the control room. After disassembling the one point grounding connection line 1 in the control room, because R<<(1/jwC), change the resistance value of the sliding wire resistor R (less than 10Ω), does not affect the loop current I, and the size of I remains unchanged.

When the zero-phase N600 in the control room of the PT secondary circuit has multi-point grounding (take two-point grounding as an example for analysis, see Figure 3), the PT secondary circuit of the substation has a grounding point F in addition to one point O in the control room. , there is a potential difference U ₂ between the two grounding points on the secondary equipotential ground grid B, and the cable resistance between the grounding point F and the grounding point O is set to R _f , and the resistance value of R _f is in the range of 1-5Ω; at one point in the control room The sliding wire resistor R is connected in parallel at the ground connection line 1; after disassembling the ground connection line 1 at one point in the control room, it can be obtained from Figure 3: I=U ₂ /(R+R _f ). When R=0Ω, I=U ₂ /R _f , when R=10Ω, I=U ₂ /(R+R _f ), since the resistance range of the sliding wire rheostat R is 0-10Ω; therefore, the sliding wire When the rheostat R is adjusted from 0Ω to 10Ω, the current I will decrease significantly.

It can be seen from this that it is theoretically feasible to judge whether there is multi-point grounding through the influence of the change of loop resistance on the current value.

On-site verification of this example: Dongsi Station is undergoing comprehensive renovation recently, and simulation tests can be carried out in combination with the complete stop of 10KV II section. Add 0.05V voltage to the zero-phase N600 at the PT cabinet, connect the zero-phase N600 to the secondary equipotential ground network B at the 10KV562 shunt PT secondary circuit, and connect the millisecond of the utility model to the 10KV public test screen One end of the safety meter A is connected to the zero-phase N600 in the control room, one end of the sliding wire rheostat R is connected to the secondary equipotential ground network B, close the small knife switch K, disconnect the one-point grounding connection line 1 of the control room, and connect the sliding wire rheostat R Adjusted from 0Ω to 10Ω, the current value changed from 50mA to 5mA. At this time, there are other grounding points besides the one point grounding of the control room; disassemble the grounding connection line at the secondary circuit of the 562 shunt PT, and slide the rheostat R From 0Ω to 10Ω, the current value is almost zero and does not change, which means that there is no multi-point grounding. The experiment was carried out many times, and the results were uniform.

Claims (3)

1. A PT secondary circuit multi-point grounding online monitor is characterized in that it consists of a point grounding connection line (1) in the control room of the PT secondary circuit, a lightning arrester F, a milliampere meter A, a small knife switch K and a sliding wire rheostat R Composition; the one-point ground connection line (1) of the control room is connected between the zero-phase N600 of the control room of the PT secondary circuit and the secondary equipotential ground network B; the milliampere meter A, the small knife switch K and the sliding wire rheostat R is serially connected in parallel with the one-point ground connection line (1) of the control room; the arrester F is connected between the zero-phase N600 of the control room and the secondary equipotential ground network B. 2. The PT secondary circuit multi-point grounding online monitor according to claim 1, characterized in that said arrester F is a low voltage zinc oxide arrester with a breakdown voltage of 380V. 3. The PT secondary circuit multi-point grounding online monitor according to claim 1, characterized in that the resistance range of the sliding wire rheostat R is 0-10Ω; the accuracy of the milliampere meter A is 1mA, and the range 0-100 mA; the rated voltage of the small switch K is above 220V, and the rated current is above 20A.

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