CN209313424U - A kind of zero-sequence current protection circuit - Google Patents

Abstract

The utility model discloses a zero-sequence current protection circuit, which comprises a high-voltage switch tripping contactor for protection. The high-voltage switch tripping contactor is connected in series with a normally open contact of a time relay to form a first control circuit. The first The two ends of the control loop are respectively connected to the positive and negative poles of the power supply; the coil of the time relay is connected in series with the normally open contacts of the zero-sequence voltage relay and the normally open contacts of the zero-sequence current relay to form a second control loop. Both ends of the two control loops are respectively connected to the positive and negative poles of the power supply; the voltage input contacts of the zero-sequence voltage relay are connected to the zero-sequence voltage transformer, and the zero-sequence current relay is connected to the zero-sequence current transformer. The utility model has the advantages of: judging whether there is a grounding fault through the two parameters of zero-sequence voltage and zero-sequence current, and more accurately judging the fault and then tripping when the single-phase is grounded, thereby avoiding misoperation and improving the accuracy of the action .

Description

A zero-sequence current protection circuit

technical field

The utility model relates to the field of power grid systems, in particular to a zero-sequence current protection device for distribution network lines.

Background technique

The neutral point of the 10KV system is grounded with a small resistance. When the line cable is single-phase grounded, the zero-sequence current protection directly acts on the trip. When the two-way power supply A and line B of the substation are closed, the zero-sequence current protection section II of the switch trips by mistake. The wave recording of the protection device shows that the three-phase voltage is normal, the three-phase current waveform is stable, and the zero-sequence current amplitude reaches twice 2A (more than 40A once) exceeds the action setting value of the zero-sequence protection stage II, and it is judged to be caused by excessive three-phase unbalanced current during ring closing. Subsequently, the circuit breaker contacts and contact resistance of the switch cabinet were checked, and the line cable heads were processed and polished, but the unbalanced current generated when the two lines were closed still could not be eliminated. If the protection action setting value is further increased, the influence of unbalanced current can be avoided; however, when the single-phase grounding of the cable actually occurs, the amplitude of the zero-sequence current may not reach the protection action setting value, the protection will not operate, and the fault cannot be removed . Therefore, how to prevent the zero-sequence current protection device from malfunctioning when the two power supply lines are closed without increasing the setting value of the zero-sequence current protection action is a problem to be solved by our invention.

Contents of the invention

The purpose of the present invention is to overcome the deficiencies of the prior art and provide a zero-sequence current protection circuit, which can improve the accuracy of zero-sequence current tripping protection.

In order to achieve the above object, the technical solution adopted by the present invention is: a zero-sequence current protection circuit, including a high-voltage switch trip contactor for protection, and the high-voltage switch trip contactor is connected in series with the normally open contact of the time relay to form the first A control loop, the two ends of the first control loop are respectively connected to the positive and negative poles of the power supply; the coil of the time relay is connected in series with the normally open contacts of the zero-sequence voltage relay and the normally open contacts of the zero-sequence current relay to form The second control loop, the two ends of the second control loop are respectively connected to the positive and negative poles of the power supply; the voltage input contact of the zero-sequence voltage relay is connected to the zero-sequence voltage transformer, and the zero-sequence current relay is connected to the zero-sequence current relay. Sequence current transformer connections.

In the second control loop, a tripping outlet switching pressure plate is arranged in series.

The present invention has the advantages of: judging whether there is a ground fault through the two parameters of zero-sequence voltage and zero-sequence current, more accurately judging the fault and then tripping when the single-phase is grounded, thereby avoiding misoperation and improving the accuracy of the operation. Simultaneously, the structure is simple and the realization is convenient, and it can be realized by adopting the normally open and normally closed contacts of the most commonly used relays.

Description of drawings

The content expressed in each accompanying drawing of the description of the present invention and the marks in the figure are briefly described below:

Fig. 1 is the schematic diagram of the first control loop of the utility model

Fig. 2 is the schematic diagram of the second control loop of the utility model;

Fig. 3 is a schematic diagram of the zero-sequence voltage and current relay of the present invention.

Detailed ways

The specific implementation manner of the present invention will be described in further detail below by describing the best embodiment with reference to the accompanying drawings.

In the 10KV neutral point small resistance grounding power supply system, when one phase is grounded, the zero-sequence voltage can reach up to 100V (metallic grounding). The technical solution of the invention is to use the zero-sequence voltage criterion as an auxiliary criterion for the action of the composite zero-sequence current protection device to realize the correct tripping function of the zero-sequence current protection. The protection action logic of this composite zero-sequence current protection device adopts two criteria of zero-sequence current and zero-sequence voltage: when the zero-sequence current is greater than the "single-phase grounding value", the zero-sequence voltage is greater than the , the protection device trips; when the zero-sequence current is greater than the "single-phase grounding value" and the zero-sequence voltage is less than the "zero-sequence voltage setting", the zero-sequence current protection is blocked. In this way, the composite zero-sequence current protection device can protect and operate reliably when the line is single-phase grounded; and the line does not appear single-phase grounded, and the protection device will not malfunction when there is a large unbalanced current in the ring closure of the two lines.

As shown in Figure 1-3, a zero-sequence current protection circuit includes a high-voltage switch trip contactor TC for protection. The coil of the high-voltage switch trip contactor TC is connected in series with the normally open contact of the time relay to form the first control loop , the two ends of the first control loop are respectively connected to the positive and negative poles of the power supply; the coil of the time relay is connected in series with the normally open contacts of the zero-sequence voltage relay and the normally open contacts of the zero-sequence current relay to form the second control loop. The two ends of the control circuit are respectively connected to the positive and negative poles of the power supply; the voltage input contacts of the zero-sequence voltage relay are connected to the zero-sequence voltage transformer, and the zero-sequence current relay is connected to the zero-sequence current transformer.

The zero-sequence voltage relay and the zero-sequence current relay conduct the action according to the preset voltage and current. There are preset voltage thresholds and current thresholds. When the zero-sequence voltage detected by the transformer is greater than the set value, the zero-sequence voltage relay acts, the coil is energized, and its normally open contacts are closed; when the transformer detects that the zero-sequence current is greater than the set value When the value is fixed, the zero-sequence current relay acts, and its coil drives the normally open contact to close after being energized. When the normally open contacts of the zero-sequence current relay and the zero-sequence voltage relay are closed, the first control loop is turned on at this time, and the coil of the time relay TJ is energized, so that the normally open contacts of the time relay in the second control loop Closed, the TC coil of the high-voltage switch trip contactor is energized, and the contactor disconnects the fault line, thereby achieving the protection function.

In the second control loop, a tripping outlet switching pressure plate QT is set in series, which is used to start or stop the zero-sequence current protection circuit.

A composite zero-sequence current protection device includes: IJO is a zero-sequence current relay, YJo is a zero-sequence voltage relay, QT is a trip outlet switching pressure plate, TJ is a trip outlet time relay, and TC is a high-voltage switch trip contactor coil.

When single-phase grounding does not occur in the high-voltage cable line of the neutral point small resistance grounding system, the zero-sequence voltage is lower than the set value. At this time, even if the unbalanced current (zero-sequence current) caused by factors such as ring closure is greater than the set current threshold, The contactor TC of the protection device will not trip at the outlet; if the line is single-phase grounded, the zero-sequence voltage is greater than the set value, the zero-sequence current is greater than the set value current threshold, and the two conditions meet the requirements at the same time, then the time relay can Power-on action, the contactor TC of the protection device can be energized to trip the outlet.

1. The connection relationship of the circuit:

(1) The zero-sequence current relay IJO is connected to the zero-sequence current output terminal of the zero-sequence current transformer, and the two ends of the zero-sequence voltage relay YJo are connected to the two ends of the zero-sequence voltage transformer. When the input zero-sequence current of the zero-sequence current relay is greater than the set value, the coil is energized and the normally open contacts are closed; when the zero-sequence voltage relay is input with the zero-sequence voltage greater than the set value, the coil is turned on. Normally open contacts are closed. Its zero-sequence voltage relay and zero-sequence current relay can be realized by selecting a relay whose conduction voltage and conduction current meet the conditions according to actual needs, or choose an electronic relay that can set conduction parameters, and manually set the conduction voltage and conduction current.

(2) This scheme has two control loops, one is used to control the conduction of the time relay, and the other is the high-voltage switchgear trip control loop. In the control loop of whether the time relay is on or not, the positive power supply K+ is connected to The first end of the zero sequence current relay IJO normally open contact, the second end of the IJO normally open contact is connected to the first end of the zero sequence voltage relay YJo normally open contact, the second end of the zero sequence voltage relay YJo normally open contact The two ends are connected to one end of the tripping exit switching pressure plate QT, the other end of the tripping exit switching pressing plate QT is connected to one end of the tripping exit time relay TJ, and the other end of the tripping exit time relay TJ coil is respectively connected to the negative power supply K- of the control circuit.

(3) The positive power supply KT+ of the trip control circuit of the high-voltage switchgear is connected to one end of the normally open contact of the trip outlet time relay TJ, and the other end of the normally open contact of the trip outlet time relay TJ is connected to one end of the coil TC of the high voltage switch trip contactor , the other end of the high-voltage switch trip contactor coil TC is connected to the positive power supply KT- of the high-voltage switch cabinet trip control circuit.

2. The working process of the protection device

(1) When the power supply line is single-phase grounded, the zero-sequence current is greater than the operating current of the zero-sequence current relay, the normally open contact of the zero-sequence current relay IJO is closed, and the normally open contact of the zero-sequence voltage relay YJo is closed. When the trip outlet switches the pressure plate QT, the trip outlet time relay TJ is energized, the normally open contact of the trip outlet time relay TJ is closed, and the coil TC of the high-voltage switch trip contactor is energized, the high-voltage switch starts the trip circuit, and the switch trips and cuts off the single-phase grounding fault line.

(2) When the two power supply lines are closed and the line is not single-phase grounded, the zero-sequence voltage relay is in the disconnected state because it does not meet the operating conditions, and the zero-sequence voltage relay YJo normally open contact opens. The balance current (zero-sequence current) is large, the normally open contact of the zero-sequence current relay IJO is closed, and the relay TJ will not be energized when the trip exits, and the switch will not trip, which prevents the zero-sequence protection from closing the two lines Misoperation.

Apparently, the specific implementation of the present invention is not limited by the above methods, as long as various insubstantial improvements are made by adopting the method concept and technical solutions of the present invention, they all fall within the protection scope of the present invention.

Claims (2)

1. A zero-sequence current protection circuit, comprising a high-voltage switch tripping contactor, is characterized in that: the normally open contacts of the high-voltage switch tripping contactor and the time relay are connected in series to form a first control loop, and the first control loop of the first control loop The two ends are respectively connected to the positive and negative poles of the power supply; the coil of the time relay is connected in series with the normally open contacts of the zero-sequence voltage relay and the normally open contacts of the zero-sequence current relay to form a second control loop, and the second control loop The two ends of the zero-sequence voltage relay are respectively connected to the positive and negative poles of the power supply; the voltage input contacts of the zero-sequence voltage relay are connected to the zero-sequence voltage transformer, and the zero-sequence current relay is connected to the zero-sequence current transformer. 2. A zero-sequence current protection circuit according to claim 1, characterized in that: a tripping outlet switching pressure plate is arranged in series in the second control loop.