Short Answer:

An isolator and a circuit breaker are both switching devices used in power systems, but they serve different purposes. A circuit breaker is used to automatically switch off the power during faults like short circuits or overloads. It can operate under both normal and fault conditions and is designed to break the circuit with a load.

An isolator, on the other hand, is a manual switch used to disconnect a part of the system during maintenance. It is only operated when the power is already off and cannot break the circuit if current is flowing. Isolators ensure safety by providing visible disconnection.

Detailed Explanation:

Difference between an isolator and a circuit breaker

In electrical power systems, many different devices are used to ensure safe operation, maintenance, and protection of equipment. Among these, isolators and circuit breakers are two common devices, often found in substations, switchyards, and control panels. Although they both help in opening or closing a circuit, they are designed for different tasks and operate in different ways.

Understanding the difference between them is very important for ensuring the safe design and operation of electrical systems.

What is a Circuit Breaker?

A circuit breaker is an automatic protection device. It can:

• Operate during normal and fault conditions.
• Open or close a circuit when the current is flowing.
• Detect faults like short circuits or overloads.
• Interrupt high fault currents safely.
• Be reset and used again after operation.

Circuit breakers are available in many types (like air, oil, SF₆, and vacuum breakers) depending on the voltage level and application. They are used in both low and high-voltage systems for fault protection.

What is an Isolator?

An isolator is a manually operated mechanical switch. It is:

• Used only to disconnect a part of the system for safety during maintenance.
• Operated only when there is no current flowing through it.
• Not designed to break the circuit under load or fault condition.
• Provides visible disconnection so that workers can safely carry out repairs.

Isolators are usually installed before or after circuit breakers to ensure safe handling of power equipment like transformers or feeders during shutdown.

Key Differences

1. Function:
   • Circuit breaker: Protects the system by breaking the circuit during faults.
   • Isolator: Ensures safety during maintenance by isolating equipment.
2. Operation:
   • Circuit breaker: Can operate automatically and under load.
   • Isolator: Operated manually and only in no-load conditions.
3. Fault Handling:
   • Circuit breaker: Interrupts fault currents safely.
   • Isolator: Cannot break fault currents.
4. Usage Time:
   • Circuit breaker: Works during both normal and abnormal conditions.
   • Isolator: Used only when the system is already de-energized.
5. Location in System:
   • Circuit breaker: Installed on live lines.
   • Isolator: Installed before or after the breaker for safe disconnection.

Example Use Case

Suppose a transformer needs maintenance. First, the circuit breaker is opened to stop current flow. Then the isolator is opened to safely disconnect the transformer, ensuring that no accidental flow of electricity can occur while maintenance work is done.

When the work is complete, the isolator is closed first (without load), then the circuit breaker is closed to restore the power.

Conclusion

The isolator and circuit breaker serve different but complementary purposes in power systems. A circuit breaker is an automatic protective device that can safely interrupt current during normal and fault conditions. An isolator, on the other hand, is a manual switch used to isolate equipment from the system for safe maintenance. While the circuit breaker protects the system, the isolator protects the people working on the system. Both are essential for safe and reliable power operation.