Interlocks are safety mechanisms used in electrical substations and switchgear to ensure the safe and proper operation of various components, including circuit breakers, isolators (also known as disconnectors or disconnect switches), and earth switches. These interlocks help prevent dangerous conditions and human errors that could lead to electrical accidents. Here’s how interlocks can be implemented between these components:
Circuit Breaker-Isolator Interlock:
- Circuit breakers are used to interrupt the flow of electrical current in the event of a fault or for maintenance purposes.
- Isolators are used to physically disconnect a section of the electrical circuit for maintenance or isolation purposes.
- An interlock between a circuit breaker and an isolator ensures that the isolator cannot be closed unless the associated circuit breaker is in the open position.
- This prevents the possibility of accidentally closing the isolator while the circuit breaker is still conducting current, which could be dangerous.
Isolator-Earth Switch Interlock:
- Earth switches (also called grounding switches) are used to provide an electrical connection to the earth (ground) for safety purposes when working on a disconnected circuit.
- An interlock between an isolator and an earth switch ensures that the earth switch cannot be closed unless the isolator is in the open position.
- This prevents the dangerous situation where the circuit is grounded while the isolator is still in a closed or conducting position.
Circuit Breaker-Earth Switch Interlock:
- In some cases, there may be an additional interlock between the circuit breaker and the earth switch.
- This interlock ensures that the earth switch cannot be closed unless the associated circuit breaker is in the open position.
- It adds an extra layer of safety to prevent grounding a circuit that is still connected through the circuit breaker.
Interlocks can be implemented using various mechanisms, including mechanical, electrical, or electronic systems. These mechanisms can include physical keys, mechanical linkages, or sensors that detect the position of the components and control their operation accordingly. The goal of these interlocks is to enforce a sequence of operations that ensures the safety of personnel working on electrical equipment and prevents electrical accidents.
Proper training and understanding of these interlock systems are essential for the safe operation of electrical substations and switchgear. Violating interlock sequences can lead to hazardous conditions and should be avoided at all costs.