**DC Loop Operation: Key Safety Procedures for Substation and Power Plant Operators**
DC loop operation is a critical task commonly performed by substation and power plant operators. This procedure involves checking the grounding point in the DC system when a fault occurs, as well as managing the activation or deactivation of relay protection and automatic devices. While essential, DC loop operations carry certain risks. If not executed properly, they can lead to malfunctions in protective systems. Therefore, strict adherence to safety procedures is vital.
1. **Operation of DC Control Fuses (i.e., Circuit Breaker Fuses)**
(1) When removing a DC control fuse, always remove the positive terminal first, followed by the negative terminal. When reinserting, start with the negative terminal and then the positive one. This sequence helps prevent parasitic loops and unintended tripping of protection devices. The fuses should be installed quickly without repeated on-off cycles. There should be a minimum interval of 5 seconds between removal and reinstallation.
(2) When deactivating the DC power supply for an active protection device, it is crucial to disable the protection outlet connection piece before cutting off the DC circuit. The reverse order should be followed during recovery.
(3) For bus differential and failure protection systems, the outlet connection piece must be disabled before removing the DC fuse. After reapplying the DC power, ensure the entire system functions correctly. If necessary, use a high-impedance voltmeter to check the voltage across the connection piece before reactivating it.
(4) During breaker power-off operations, the control fuse should only be removed after the circuit breaker has been opened and appropriate safety measures—such as grounding wires or insulating covers—have been applied. Removing the fuse too early may result in accidental closing of the circuit breaker, which could cause serious issues if the breaker fails to trip.
(5) When performing power transmission operations on a circuit breaker, the control fuse should be installed before removing the safety measures. This allows for a quick check of the protection device and control circuit functionality. If any issues are detected, they can be resolved while the safety measures are still in place. Additionally, having the protection system ready ensures that it can respond promptly in case of any unexpected events. Installing the fuse after the isolating switch is closed could lead to dangerous situations if the circuit breaker fails to trip.
2. **Operation of Circuit Breaker Closing Fuses**
The closing fuse refers to the fuse used in electromagnetic operating mechanisms. When a circuit breaker is being powered off, the closing fuse should be removed only after the circuit breaker has been disconnected. This prevents accidental closure due to external factors. If the fuse is removed after the isolating switch has been opened, there is a risk of accidentally closing the circuit breaker while the isolating switch is open, leading to a load-related fault.
Similarly, during power transmission, the closing fuse should be installed after the isolating switch has been closed, but before the circuit breaker is operated. This ensures the system is properly prepared and reduces the likelihood of faults caused by improper sequence.
By following these detailed procedures, operators can significantly reduce the risk of errors and enhance the overall safety and reliability of the DC system. Always double-check the sequence of operations and ensure all safety precautions are in place before proceeding.
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