Five-Prevention Functions: The Safety Line of Defense for High-Voltage Switchgear

In power systems, high-Voltage Switchgear serves as the "nerve center" connecting the power grid to electrical equipment. Electrical operations in power systems require specific procedures, each step being fixed and non-skippable. Therefore, to ensure the safety of electrical operators and prevent accidents caused by improper operations, the interlocking mechanism of "Five-Prevention" has been established.

The "Five-Prevention" in high-voltage switchgear refers to:

1、Preventing incorrect opening or closing of the circuit breaker, ensuring that the circuit breaker does not open or close due to misoperation under normal operating conditions.

2、Preventing the opening or closing of the disconnector under load, avoiding equipment damage caused by arc discharge when the circuit is energized.

3、Preventing the connection of grounding wires to live equipment, avoiding short-circuit accidents.

4、Preventing the closing of the circuit breaker with grounding wires attached, ensuring that the circuit breaker cannot close when grounding wires are present, thereby preventing short-circuit accidents.

5、Preventing unauthorized entry into live compartments, ensuring the safety of operators by preventing accidental access to energized equipment areas.

The design principle of anti-misoperation devices is that any high-voltage electrical equipment potentially prone to misoperation should be equipped with anti-misoperation devices and corresponding anti-misoperation electrical interlocking circuits. Common anti-misoperation interlocking methods mainly include four types: mechanical interlocking, procedural locking, electrical interlocking, and electromagnetic locking.

Below are the working principles of the "Five-Prevention":

1、Preventing incorrect opening or closing of the circuit breaker: This operates on a principle of dual interlocking protection. Mechanical interlocking binds the operating handle to the circuit breaker position, with the handle locked by a latch when not in the "Test/Operational" position. Electrical interlocking involves connecting a position sensor in series with the closing circuit, cutting off the control power if the position is incorrect. Before operation, confirm the indicator light (green light for Test/Operational position), turn the handle vertically with force, and stop immediately if resistance is encountered for inspection.

2、Preventing the opening or closing of the disconnector under load: This works on an operation sequence locking principle. A mechanical baffle physically blocks the disconnector operating hole when the circuit breaker is closed. Electrical interlocking connects the circuit breaker’s auxiliary contacts in series with the disconnector motor power supply, cutting off power when the circuit breaker is closed. Operations must strictly follow the procedure: "First open the circuit breaker (green light for open position), confirm the baffle has retracted, then operate the disconnector."

3、Preventing the connection of grounding wires to live equipment: This relies on live detection and interlocking. Front-end sensing: The outgoing line side’s voltage indicator monitors voltage in real-time; when live, the red light flashes and locks the grounding switch. Dual verification: Both "no voltage detected by the tester" and "green light on the indicator" must be satisfied for the grounding switch lock to unlock. Before connecting the grounding wire, first use a voltage tester to confirm no voltage, align the lock hole vertically with the operating rod, and avoid tilting to prevent damage to the lock core.

4、Preventing the closing of the circuit breaker with grounding wires attached: This operates on a state linkage interlocking principle. Mechanical blocking: When the grounding switch is closed, a baffle rises on the circuit breaker trolley track, preventing it from entering the "Operational" position. Electrical cut-off: The grounding switch’s auxiliary contacts are connected in series with the closing coil, cutting off power when the grounding switch is closed. Before closing, observe the grounding switch lock hole color (green for open, red for closed) and ensure the trolley moves without resistance before operation.

5、Preventing unauthorized entry into live compartments: This involves triple isolation protection. First, mechanical interlocking: The rear door is individually locked with the grounding switch; the lock core can only rotate when the grounding switch is closed. Second, electrical warning: A red warning light inside the cabinet automatically illuminates when live, and reflective warning labels are attached to the door handle. Third, key control: Special keys require authorization through the "power off, voltage test, grounding" safety confirmation process. To open the cabinet door, the grounding switch must first be closed. For multi-person operations, implement a key custody system with dual-person supervision.

The Five-Prevention design is indispensable in high-voltage switchgear. At Hangbian Electric, we strictly adhere to these principles during production, prioritizing operator safety. For more information, feel free to inquire.