Type Tests for a 36kV Class Vacuum Circuit Breaker (VCB)
As per IS: 13118, these type tests include:
- Dielectric Tests – Lightning voltage and power frequency withstand voltage tests are conducted. However, the switching impulse voltage test is not performed, as this test is generally required for circuit breakers rated above 300 kV. It is not applicable to vacuum circuit breakers (VCBs) since they are normally rated up to the 36 kV level.
- Temperature Rise Tests – Under rated current conditions we need to measure the temperature rise of different parts of VCB mechanism and check whether the VCB complies with specified temperature limits to prevent overheating.
- Measuring the Resistance of the Main Circuit – The DC current of 100A is injected to the closed main circuit of the VCB and voltage drop across the VCB terminals is measured. The values are usually in the range of millivolts (mV) due to the low resistance of the circuit. For a 36kV vacuum circuit breaker, the typical contact resistance (i.e. measured mV drop by injected 100A) is in the range of 30–200 micro-ohms (µΩ).
- Short-Time Withstand Current and Peak Withstand Current Tests – Verifies the ability of the VCB to carry the rated short-circuit current of 31.5kA without damage for a specified duration (3 seconds).Tests peak withstand capability for short-time fault conditions. This is 31.5kA X 2.5 = 78.75kAp.
- Mechanical Endurance Test – Validates the mechanical reliability of the circuit breaker under a high number of operating cycles (e.g., 10,000 operations or more as specified).
- Making and Breaking Capacity Test – Verifies the VCB’s ability to interrupt the rated symmetrical and asymmetrical short-circuit current.
- Electrical Endurance Test – Assesses the VCB’s ability to withstand repeated electrical operations at rated current and voltage to ensure the operational reliability under normal working conditions.
- Capacitive Current Switching Tests – Evaluates the VCB’s performance when switching capacitive loads (e.g., capacitor banks or cables). Checks for voltage transients or restrikes during operation.
- Magnetizing and Small Inductive Current Switching Tests – Evaluates the VCB’s performance when switching for voltage transients or restrikes during operation.
These tests are intended to ensure that the circuit breakers perform reliably, safely, and efficiently under various operating conditions.
Routine Tests for a 36kV Vacuum Circuit Breaker (VCB)
As per IS: 13118, the routine tests include the following:
Power Frequency Voltage Withstand Test
- Main Circuit: Verifies the insulation of the main circuit under power frequency voltage conditions. Conducted at specified test voltage levels (70KV) for a duration of 1 minute.
- Control and Auxiliary Circuits: Tests the insulation of control and auxiliary circuits at a lower test voltage (typically 1 kV for 1 second).
Measurement of the Resistance of the Main Circuit
- Measures the contact resistance of the main circuit using the current-voltage method.
- Ensures the resistance value is within permissible limits, typically in the micro-ohm range.
Mechanical Operating Tests
- Verifies the proper functioning of the operating mechanism.
- Includes multiple operations such as:
- Open and close operations at different control voltages (e.g., 70%, 85%, and 110% of the rated control voltage).
- Measurement of operating times for closing and tripping.
Final Factory Acceptance Tests on a Outdoor 36KV VCB
Measurement of Contact Resistance of the Main Circuit
- Ensures low resistance at contacts for efficient current flow.
Power Frequency Dry Withstand Test on Auxiliary Circuit
- Test Voltage: 1 kV for 1 minute.
- Validates insulation integrity of the auxiliary circuits.
One-Minute Power Frequency Dry Withstand Test on the Main Circuit
- Conducted in both open and closed conditions to ensure insulation reliability.
Mechanical Operation Test
Includes the following:
- 5 closing and 5 opening operations at:
- 110% of control voltage
- 85% of control voltage
- Rated control voltage
- 5 opening operations at:
- 70% of control voltage
- 5 closing-opening operations at 100% control voltage.
- 5 opening and 0.3-second closing operations at 100% control voltage.
Tripping and Closing Time Measurement
- Ensures proper timing for opening and closing operations.
Visual and Measurement Tests
- Visual Inspection for Completeness – Verification of assembly and components.
- Verification of Paint Shade – Ensures the paint coating matches the specified standard and provides adequate protection.