Testing of High Voltage Isolators

Type Tests of Isolators as per IS 9921 (Part 4) – 1985

The type tests of isolators are conducted to ensure that the isolators meet the performance criteria under standard operating conditions. According to IS 9921 (Part 4) – 1985, the type tests of isolators can be broadly categorized into the following:

1. Dielectric Tests
   These tests verify the insulation strength of isolators under different conditions. The dielectric tests are performed to ensure that the isolator can withstand the rated power frequency voltage without any disruptive discharge.
2. Temperature-Rise Test
   This test is conducted to prove that the temperature rise in any part of the isolator does not exceed the specified limits during its operation.
3. Short-Time Withstand Current and Peak Withstand Current Tests
   These tests verify the capability of the isolator to carry the rated peak withstand current and the rated short-time withstand current. The tests are conducted with the isolator in a closed position to ensure it can handle high currents without any damage.
4. Short-Circuit Making Performance Test for Earthing Switches
   For isolators that include earthing switches, the short-circuit making performance is tested to ensure the switch can safely handle the rated short-circuit current.
5. Mechanical Operation and Endurance Test
   The mechanical endurance test is performed to verify the durability of the isolator’s moving parts. This test involves repeated operation cycles to simulate long-term usage. The test ensures that the isolator can operate without failure over a specified number of cycles.
6. Operation Under Ice Conditions (Special Request)
   In certain cases, a type test of isolators is carried out under icy conditions to ensure their performance in cold environments. This test is typically performed on special request from the user.
7. Radio Interference Measurement
   This test measures the level of radio interference caused by the isolator during operation. It ensures that the isolator does not emit radio frequencies that could interfere with communication equipment.
8. Tests for Minimum and Maximum Ambient Temperatures (Special Request)
   Isolators may be tested to confirm their performance at extreme temperatures, both minimum and maximum, as specified by the user.

These type tests of isolators are essential for proving the reliability and safety of isolators in various operational environments. All test results are recorded and documented to verify compliance with the standards set by IS 9921 (Part 4) – 1985​

Routine Tests of Isolators as per IS 9921 (Part 4) – 1985

As per IS 9921 (Part 4): 1985, titled “Alternating Current Disconnectors (Isolators) and Earthing Switches for Voltages Above 1000 V – Part 4: Type Tests and Routine Tests,” the specified routine tests for high voltage isolators are:

1. Power-Frequency Voltage Dry Withstand Tests on the Main Circuit:
   • This test verifies the dielectric strength of the main circuit by applying a power-frequency voltage under dry conditions. The standard voltage for this test are listed as follows

   Nominal Voltage	Rated Voltage	Power Frequency withstand Voltage
   400KV	420KV	520KV
   220KV	245KV	460KV
   132KV	145KV	170KV
   33KV	36KV	70KV

   These power frequency withstand voltages are to apply between conductor and earth part of the isolators. The duration of application of the voltage is 1 minute as per standard.

   Here to be noted: Since the only insulation between the conductor (or live side) of an isolator and the ground (or earth side) is provided by insulators, it is important to note that these insulators are typically procured from external manufacturers. As a result, the power frequency withstand test for the isolator may be excluded from routine testing. Instead, the routine test certificates provided by the insulator manufacturer can be accepted as proof of the isolator’s compliance with the routine power frequency withstand test requirements.

   The test is performed not only between the conductor parts and ground parts of an isolator but also to verify the power frequency withstand capability between the terminals of the isolator when it is in an open condition. The test voltages in this case slightly differ from the power frequency withstand voltages applied between the conductor and ground.

   Nominal Voltage	Rated Voltage	Power Frequency withstand Voltage
   400KV	420KV	610KV
   220KV	245KV	520KV
   132KV	145KV	315KV
   33KV	36KV	80KV

2. Voltage Tests on Control and Auxiliary Circuits:
   • These tests assess the insulation integrity of control and auxiliary circuits by subjecting them to specified voltage levels.
3. Measurement of the Resistance of the Main Circuit:
   • This involves measuring the electrical resistance of each pole in the main circuit to ensure it is within acceptable limits, indicating proper conductivity.
4. Mechanical Operating Tests:
   • These tests confirm the mechanical functionality of the isolator by performing a series of operations to ensure it opens and closes correctly without any mechanical issues.

These routine tests are essential to ensure that high voltage isolators meet the required safety and performance standards before they are commissioned into service.

For detailed procedures and acceptance criteria for each test, please refer to IS 9921 (Part 4): 1985.

Note: IS 9921 (Part 4): 1985 has been withdrawn and is no longer active. It has been superseded by updated standards. For the most current testing procedures and requirements, please refer to the latest applicable standards.

Factory Acceptance Tests (FAT) of Isolators

The Factory Acceptance Tests (FAT) of isolators are a set of tests conducted at the manufacturer’s facility before the isolators are shipped to the customer. The purpose of these tests is to ensure that the isolators meet the required specifications and function correctly under normal operating conditions. The FAT ensures that the isolator is ready for installation and operation in the field. The following are the key Factory Acceptance Tests (FAT) of isolators:

1. Visual Inspection Test
   To check the isolator’s physical appearance and ensure that there are no visible defects, damage, or missing components.
2. Mechanical Operation Test
   To verify the smooth operation of the isolator and its operating mechanism.
3. Contact Resistance Test
   To measure the resistance of the isolator contacts and ensure that it is within acceptable limits.
4. High Voltage Dielectric Test
   To ensure that the isolator can withstand the rated high voltage without any insulation failure.
5. Insulation Resistance Test
   To verify the insulation strength between the phases and between the phases and ground.
6. Functional Test of Auxiliary Circuits
   To verify the correct operation of auxiliary circuits, including control, alarm, and indication circuits.
7. Verification of Dimensions and Clearances
   To ensure that the isolator’s dimensions and clearances meet the specified design requirements.
8. Interlocking Test (if applicable)
   To ensure that the interlocking system of the isolator functions correctly to prevent unsafe operations.
9. Verification of Nameplate and Documentation
   To ensure that the isolator’s nameplate information is correct and matches the specifications.

These Factory Acceptance Tests (FAT) of isolators are crucial to ensure that the isolator meets all design and safety requirements before supply.