The AC withstand voltage test is very important test to mantain GIS (gas-insulated substation). To ensure the safety and effectiveness of the test, the specific steps are as follows;
1. Confirm the status of the subject
Installation integrity
The GIS equipment should be completely installed, and all connecting parts (such as casing and air chamber) should be properly sealed without mechanical damage or looseness.
SF6 gas state
SF6 gas should be filled to the rated density, and the leak test should be completed to ensure that there is no leakage.
The moisture content of the gas should meet the standard (such as ≤150ppm) to avoid affecting the insulation performance due to humidity.
Completion of basic test
Before the voltage test, complete basic items such as the main circuit resistance measurement and insulation resistance test to ensure that there are no remaining defects
2. Non-test equipment isolation
The range of devices to be isolated
High voltage cables, overhead lines, power transformers, and electromagnetic voltage transformers (if the test circuit may cause magnetic saturation, they need to be isolated; If the frequency modulation series resonant device is used and the voltage standard is consistent, it can be retained).
Overvoltage protection devices such as lightning arrester and spark gap protection.
Extension treatment
If a voltage test is performed on the GIS extension, power off the adjacent existing devices and ground them reliably to prevent breakdown risks.
3. Test loop construction
Pressure mode planning
The test voltage should be applied between each phase conductor and the housing (phase-by-phase test), and the non-test phase conductor should be grounded.
Priority pressurization through inlet and outlet bushings to ensure that all components are subjected to at least one test voltage
Stage test condition
If the overall power capacity of the GIS is too large (for example, a long bus bar or a complex structure), perform voltage withstand tests in different sections to avoid device overload
4. Safety and protection measures
Environmental inspection
The test area shall be set up with fences and warning signs, and non-test personnel shall not enter.
Ensure that the grounding system is reliable and that all ground cables on the cover are securely connected.
Equipment status check
Check the frequency conversion resonance device, voltage divider, protection resistance, and other equipment status is normal.
If you need to perform fracture withstand voltage (such as a disintegrated circuit breaker), you need to plan a separate test scheme.
5. Test procedure presets
Advanced purification preparation
Although it is an experimental phase, a "sophisticated purification" procedure (removal of internal conducting particles by a gradual increase in voltage) 1 needs to be configured in advance.
Parameter setting
Set the test voltage value, boost rat,e and duration according to the GIS rated voltage (such as 35kV, 72.5kV).