High Voltage Gas Insulted Substation (GIS) Routine Tests According to IEEE C37.122

Routine tests, often referred to as production tests, are performed to ensure that each GIS operates as it has been designed and type-tested for. The routine tests are performed for each GIS after assembly and marks a major quality gate before the GIS leaves the factory. The test parameters are based on the type test results, which means that, within certain tolerances, the routine tests need to reflect the type test data.

The following sections describe briefly Routine Tests included in IEEE C37.122 standard:

1. Dielectric Tests:The dielectric tests are done after the mechanical routine testing and demonstrate the dielectric performance of the GIS, ensuring the correct assembly, correctly manufactured parts from a dielectric point of view, and the absence of particles and other contaminants

1. 1. Power frequency dielectric test: For routine tests, the dielectric test is a power frequency withstand voltage test. Impulse testing, such as lighting and switching impulse, is not typically part of the routine testing. At minimum functional SF6 pressure, the following conditions are tested: phase-to-ground, phase to-phase (in the case of three phases in one enclosure design), and across open switching devices. Successfully withstanding the one minute withstand level without a disruptive discharge is the main criteria to mark that the test passed successfully.
   2. The measurement of partial discharges: shall be performed to detect possible material and manufacturing defects.The measurement of partial discharges shall be performed with dielectric tests after mechanical routine tests. The test shall be carried out on all components of the gas-insulated switchgear.
2. Measurement of the Resistance of the Main Circuits:Typically, the voltage drop or resistance of main circuits are measured using a DC current of 100 A.this test. The test data should be within a 20% tolerance band compared with the type test data.
3. Tightness Tests:Using devices such as SF6 piping, adaptation of SF6 leakage detectors, all areas of enclosures assemblies, SF6 gauges, and SF6 density monitoring will be checked for leaks.

4. Pressure Tests of Enclosures:After complete machining of enclosures, pressure tests are made at 1.3 times the design pressure for welded aluminum and welded steel enclosures and at 2 times the design pressure for cast enclosures. Automated test stations facilitate the inclusion of a tightness test using helium after the pressure test of the enclosure. The standard test pressure shall be:

• • 1.3 times design pressure for welded aluminum and welded steel enclosures.
  • 2 times design pressure for cast aluminum and composite aluminum enclosures.

The test pressure shall be maintained for at least 1 min. No rupture or permanent deformation should occur during this test.

5. Mechanical Operation Tests :Mechanical operation tests include all devices of the GIS that will be mechanically operated, such as a circuit breaker, disconnect switches, ground switches, and high-speed ground switches. The tests include a certain number of operation cycles at different control voltage levels and the correct function of the related auxiliary equipment; for example, auxiliary switches to indicate the position of the circuit breaker and switches.
6. Tests on Auxiliary and Control Circuits:These tests confirm that, during manufacturing, all wiring has been done correctly according the related circuit diagrams. Auxiliary and control circuits shall conform to the schematics, wiring diagrams, and technical data provided by the manufacturer. Technical data may include the number, class, type, capacity of available contacts, and electrical power of shunt releases (other than auxiliary and control contacts, electrical power of shunt releases, etc.). This test have following sections:
   1. Functional tests:A functional test of all low-voltage circuits shall be made to verify the proper functioning of auxiliary and control circuits in conjunction with the other parts of the switchgear. The test procedures depend on the nature and the complexity of the low-voltage circuits of the device.
   2. Verification of protection against electrical shock:Protection against direct contact with the main circuit and safe accessibility to the auxiliary and control equipment parts liable to be touched during normal operation shall be checked by visual inspection.
   3. Dielectric tests on auxiliary and control circuits:Only power-frequency withstand voltage tests shall be performed.All control wiring associated with current and linear coupler transformer secondaries and potential device secondaries shall receive a power-frequency withstand test of 2500 V for one minute. All other control wiring shall receive a power-frequency withstand test of 1500 V for 1 min or 1800 V for 1 sec.
7. Pressure Tests on Partitions:Partitions are gas tight insulators that separate one gas compartment from the other. They allow full pressure on one side and vacuum on the other. Each partition has to be tested to twice that of the design pressure. It has to be ensured that the weakest mechanical direction of the device is being considered for the test. This test verifies that the partition has been manufactured correctly to withstand the pressure the partition is designed for. Partitions will also be tested to the dielectric withstand capability and a sensitive partial discharge measurement.Pressure tests shall be made on enclosures after complete machining. Each partition shall be subjected to a pressure test at twice the design pressure for 1 min in the weakest direction. For the pressure test the partition shall be secured in exactly the same manner as in service. The partition shall not show any sign of over stress or leakage.

References:

• IEEE Standard for High Voltage Gas-Insulated Substations Rated Above 52 kV :IEEE Std C37.122.
• Gas Insulated Substations Book by Edited by Hermann Koch.
• IEEE C37.122-1 (2013) Guide for Gas Insulated Substations Rated Above 52 kV.
• High-voltage Tests and Measurements during the Life Cycle of GIS article from SIEMENS company Authors: U. Schichler E. Kynast
• High Voltage Testing of Gas (SF6) Insulated Substation article by John De Britto C

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