What is the five-protection interlock of high-voltage switchgear？

Definition of Five-Protection Interlocking

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High-voltage switchgear is a critical piece of equipment in power systems. To ensure safe and stable operation, it must have five-proof interlocking features. These five features include:
1. Preventing the opening and closing of disconnectors while under load. During power system operation, disconnectors isolate the high-voltage power supply to ensure the safety of maintenance personnel. Operating disconnectors while under load can cause arcing and short circuits. Therefore, high-voltage switchgear must have a function to prevent the opening and closing of disconnectors while under load to ensure safe operation.

2. Preventing the accidental opening and closing of circuit breakers, load switches, and contactors. In power systems, the operation of equipment such as circuit breakers, load switches, and contactors requires caution. Improper operation can cause equipment damage or system failure. High-voltage switchgear must have a function to prevent the accidental opening and closing of these equipment to avoid unnecessary accidents.

3. Preventing the closing of circuit breakers, load switches, and other switches while the grounding switch is in the closed position. The grounding switch connects the equipment to the ground during maintenance to ensure the safety of maintenance personnel. If other switches are closed while the grounding switch is in the closed position, a short circuit may occur, potentially leading to an explosion. Therefore, high-voltage switchgear should be equipped with features to prevent this type of operation error.

4. Preventing the accidental closing of the grounding switch while energized. In power systems, the function of the grounding switch is to ground equipment during maintenance, ensuring the safety of maintenance personnel. Accidentally closing the grounding switch while energized can cause a short circuit or even a fire. Therefore, high-voltage switchgear should be equipped with features to prevent this type of operation error.

5. Preventing accidental entry into energized compartments. Compartments within high-voltage switchgear may contain high voltages. If maintenance personnel mistakenly enter these areas, they could suffer electric shock. Therefore, high-voltage switchgear should be equipped with features to prevent accidental entry into energized compartments to ensure the safety of maintenance personnel.

Interlocking requirements for removable and fixed high-voltage switchgear

 Interlocking requirements for removable high-voltage switchgear
1) The trolley may be withdrawn or inserted only when the circuit breaker, load switch, or contactor is in the open position.
2) The circuit breaker, load switch, or contactor may be opened or closed only when the trolley is in the working position, test position, disconnect position, grounding position, or removable position.
3) The trolley may be moved to the working position only when the grounding switch is in the open position.
4) The grounding switch may be closed only when the trolley is withdrawn to the test position or later.

Interlocking requirements for fixed high-voltage switchgear
1) The disconnector can only be opened or closed when the circuit breaker, load switch, or contactor is in the open position.
2) If the disconnector itself has a grounding switch, interlocking must be implemented to ensure the sequence of their operation. At the same time, whether they can meet the insulation level requirements during movement must also be considered.
3) The circuit breaker, load switch, or contactor can only be operated when the disconnectors on both sides of the circuit breaker, load switch, or contactor are in the closed, open, or grounded state (if any).

Other Interlocking Requirements

1. When handling components within a compartment, ensure they are de-energized and grounded. Only in this state can the compartment door or cover be opened safely. If installing an interlock is inconvenient, a padlock can be used as an alternative. This ensures operator safety and prevents accidents caused by electric shock.

2. If the short-circuit closing capacity of the grounding switch is less than the rated dynamic stability current of the circuit, additional safety measures are required. One feasible method is to install an interlock between the relevant disconnectors. This prevents the disconnectors from automatically closing even in the event of a short circuit, thus preventing damage to the equipment caused by excessive current.

3. Special protective measures are required for main circuit components that could be damaged by misoperation, or for establishing isolation points to ensure safe maintenance work. In these cases, a locking device should be installed to prevent misoperation. This ensures normal equipment operation and reduces the risk of accidents caused by misoperation.

4. During the design process, mechanical interlocks should be given priority. This is because they are highly reliable and operate stably in a variety of environments. In addition, mechanical interlock is relatively simple and easy to use, and can meet the safety requirements of most equipment. By using mechanical interlock reasonably, we can greatly improve the safety performance of the equipment and protect the life safety of the operators.

Contact Us

If you need further communication or consultation on specific issues regarding the five-protection interlocking of high-voltage switchgear (such as design, operational failures, selection, etc.), you can contact me in the following ways:

Email:pannie@hdswitchgear.com.

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