1 The problem is that in the power system, the secondary circuit plays a very important role in ensuring the safe operation of the system. In the normal operation of the system, in order to ensure the safety of the person and equipment, the "Safety Work Site Safety Regulations" stipulates that an electrical connection of the secondary circuit of the current transformer must have a reliable grounding point. At the same time, in order to ensure the correct operation of the relay protection and automatic device, the current loop is required to be grounded at one point. However, the substation current secondary circuit connection equipment is numerous, and the extension range is wide. Often, due to artificial wiring errors or some unavoidable natural laws, such as insulation aging, etc., multiple points appear in the secondary circuit of an electrical connection. Grounding, and the secondary circuit of the system is mostly outside, the probability of insulation damage is large, and multiple points of grounding cause incorrect operation of protection, resulting in large-scale blackouts occurring frequently in the system. The two points are grounded as follows:
(1) The main control room control screen and the protection screen are grounded separately, causing two points to be grounded.
(2) The 10kV switchgear is connected to the circuit breaker casing when it is shipped from the factory. In the installation, the switchgear is connected to the grounding grid. It is grounded and grounded in the control room, causing the current loop to be grounded at two points.
(3) In the transformation of the substation, the grounding point is connected to the control room to unravel the grounding point of the outdoor terminal box, but due to human negligence, the current loop is grounded at two points.
(4) The current secondary circuit insulation damages the grounding, causing the current loop to be grounded at two points.
2 Two-point grounding hazard (1) The current secondary circuit is connected by cable. When there is short-circuit current or lightning current on the grounding network, the current in the shielding layer may flow due to the difference in potential between the two points of the cable shielding layer, which may burn out. Shield. When current flows through the shield, an interference signal is generated for each core.
(2) In the current secondary circuit, if there is a grounding point on both sides of the relay current coil, on the one hand, the parallel circuit formed by the two-point grounding point and the ground will short-circuit the current coil, so that the current passing through the current coil is large. To reduce. In addition, in the event of a ground fault, a ground potential difference will be generated between the two grounding points due to the zero-sequence current of the ground grid, which will generate a large extra current in the current coil. For these two reasons, the current through the relay current coil and the fault current of the current transformer can be greatly different, which will cause incorrect operation of the protection and cause inaccurate measurement.
3 Solution In order to eliminate the hidden danger of two-point grounding, the AC current flows into the A phase on the primary side of the current transformer, and the current secondary circuit uses the clamp-type ammeter to monitor the A phase and the N line. If the A phase and the N line current are equal, the current loop One point is grounded, and the correctness of the wiring is also checked. If the N-line current is about half of the A-phase current, the current loop is grounded at two points, and the two points of the main control room and the switch field are grounded. If the N-line current is less than about one-half of the A-phase current, the current loop is also grounded at two points, and the two points in the main control room are grounded (the protection screen and the control panel are grounded separately). For example, the current transformer ratio is 300/5. In the first phase A flow 60A, the current secondary circuit is monitored as 1A in the A phase, and the secondary circuit N point is also 1A, which is a point grounding; if the current secondary circuit A The phase is about 1A, and the secondary circuit N point is about 0.5A, then the main control room and the switch field current are grounded at two points; if the current secondary circuit A phase is about 1.23A, the secondary circuit N point is about 0.77A, Then the main control room control screen and the protection screen are grounded separately, causing the current to be grounded at two points. The above method is equally applicable in the neutral point indirectly connected to the grid or in the direct grounded grid, or in electromagnetic protection or microcomputer protection. It can solve the multi-point grounding problem of the AC secondary circuit in the long-term troubled power system of the power system, and can find the multi-point grounding of the AC secondary circuit in time, avoiding the protection misoperation and refusal caused by the AC secondary multi-point grounding, ensuring the protection. Safe operation of the grid.
4 Conclusion In the substation's new investment protection, as well as the substation protection and transformation work, the above method is used to ensure that the current secondary circuit must have only one ground. Practice has proved that this method can not only check the multi-point grounding problem, but also check the correctness of the current loop wiring.
KNBL1-32 Residual Current Circuit Breaker With Over Load Protection
KNBL1-32 TWO FUNCTION : MCB AND RCCB FUNCTIONS
leakage breaker is suitable for the leakage protection of the line of AC 50/60Hz, rated voltage single phase 240V, rated current up to 63A. When there is human electricity shock or if the leakage current of the line exceeds the prescribed value, it will automatically cut off the power within 0.1s to protect human safety and prevent the accident due to the current leakage.
leakage breaker can protect against overload and short-circuit. It can be used to protect the line from being overloaded and short-circuited as wellas infrequent changeover of the line in normal situation. It complies with standard of IEC/EN61009-1 and GB16917.1.
KNBL1-32 Residual Current Circuit Breaker,Residual Current Circuit Breaker with Over Load Protection 1p,Residual Current Circuit Breaker with Over Load Protection 2p
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