Five Prevention Interlocks of Medium Voltage Switchgear

Why we need Five Prevention Interlocks in medium voltage switchgear

As the power system continues to develop, Medium voltage switchgear is being increasingly applied within power systems. The five prevention interlocks of medium voltage switchgear serve as crucial measures to ensure the safe operation of power systems, making it essential knowledge for every electrical technician. This article will provide a detailed introduction to the five prevention interlocks of medium voltage switchgear to help electrical personnel better understand and master this important knowledge.

1, Definition of Five Prevention Interlock

Medium voltage switchgear is a critical piece of equipment in power systems. To ensure its safe and stable operation, it should possess “five prevention” functions. These five prevention functions include:

• Preventing Load Switching of Isolating Switches: In power system operations, the role of the isolating switch is to isolate the high voltage power supply to ensure the safety of maintenance personnel. If the isolating switch is operated under load, it will cause arc burning and lead to short circuit faults. Therefore, high voltage switchgear should have the function of preventing load switching of isolating switches to ensure safe operation.
• Preventing Misoperation of Circuit Breakers, Load Switches, and Contactors: In power systems, the operation of circuit breakers, load switches, and contactors must be cautious. Misoperation can lead to equipment damage or system faults. High voltage switchgear should have the function of preventing misoperation of these devices to avoid unnecessary accidents.
• Preventing Switching of Circuit Breakers, Load Switches, etc., When the Grounding Switch is Closed: The role of the grounding switch is to connect the equipment to the ground during maintenance to ensure the safety of maintenance personnel. If other switches are operated when the grounding switch is closed, it can cause short circuits and potentially lead to explosions. Therefore, medium voltage switchgear should have the function of preventing such erroneous operations.
• Preventing Closing of Grounding Switches When Live: In power systems, the role of the grounding switch is to ground the equipment during maintenance to ensure the safety of maintenance personnel. If the grounding switch is closed when live, it will cause short circuits and potentially lead to fires. Therefore, medium voltage switchgear should have the function of preventing such erroneous operations.
• Preventing Entry into Live Compartments: The compartments inside medium voltage switchgear may contain medium voltage(10KV-35KV). If maintenance personnel mistakenly enter these areas, it can lead to electric shock accidents. Therefore, medium voltage switchgear should have the function of preventing entry into live compartments to ensure the safety of maintenance personnel.

SPRING MECHANISM OF SIS

2, Interlock Requirements for Withdrawable and Fixed Medium Voltage Switchgear

• Interlock Requirements for Withdrawable Medium Voltage Switchgear

The truck can only be withdrawn or inserted when the circuit breaker, load switch, or contactor is in the open position.

Circuit breakers, load switches, and contactors can only be operated when the truck is in the working position, test position, disconnected position, grounded position, or removed position.

The truck can only enter the working position when the grounding switch is in the open position.

The grounding switch is only allowed to close when the truck is withdrawn to the test position or beyond.

• Interlock Requirements for Fixed Medium Voltage Switchgear

The isolating switch can only be operated when the circuit breaker, load switch, or contactor is in the open position.

If the isolating switch itself has a grounding switch, there should be interlocks to ensure the procedural operation of these switches and to ensure they meet insulation level requirements during movement.

Circuit breakers, load switches, and contactors can only be operated when the isolating switches on both sides of these devices are in the closed, open, or grounded state (if present).

3, Other Interlock Requirements

When handling components in a compartment, we must ensure they are de-energized and grounded. Only under these conditions can we safely open the compartment doors or covers. If installing interlocks is inconvenient, we can use padlocks as an alternative to ensure the safety of operators and prevent electric shock accidents.

If the short-circuit closing capacity of the grounding switch is less than the rated dynamic stability current of the circuit, additional safety measures must be taken. One feasible method is to install interlocks between the relevant isolating switches. This way, even if a short circuit occurs, the switch will not close automatically, avoiding damage to the equipment due to excessive current.

For main circuit components that may be damaged by misoperation or for isolation breaks used to ensure safe maintenance, special protective measures need to be taken. In these cases, locking devices should be installed to prevent misoperation. This ensures normal operation of the equipment and reduces the risk of accidents caused by operational errors.

During design, priority should be given to using mechanical interlocks due to their high reliability and ability to operate stably in various environments. Additionally, mechanical interlocks are relatively simple and easy to use, meeting most equipment safety needs. By rationally using mechanical interlocks, we can greatly improve the safety performance of the equipment and ensure the safety of operating personnel.

The above content provides a detailed introduction to the five prevention interlocks of medium voltage switchgear and their interlock requirements. It is hoped that through this introduction, electrical personnel can better understand and master this important knowledge, thereby ensuring the safe and stable operation of power systems.

Thanks for reading.