Gas Insulated Substation (GIS) Method Statement

Scope

GIS AC Voltage Withstand Test – The test procedure entails applying voltage in increasing levels to each phase while connected to ground and holding for the required times until the complete test voltage is reached.

Objective

This is to ensure that the requirements of electrical individual test procedures are consistent with the codes and contract specifications. To ensure that the work is completed with acceptable workmanship and adheres to the requirements outlined in the quality manual.

Reference

1. Reference Manual.
2. Manufacturers’ Manuals and Standards
3. Contract specifications & construction drawings.
4. GB Standard 50150-2006 specifies the hand-over test for electrical equipment installation engineering.
5. Installing an on-site AC voltage test system with variable frequency allows for withstand voltage testing at GIS (4.5). The test system runs in the frequency range of 20 to 300 Hz and meets the criteria of IEC 60517 & IEC 62271-203.

Risk & Safety Precautions

• All construction workers must wear helmets and use safety belts when working at heights.
• The high voltage testing area must be surrounded by a rail and a warning board, with a designated watchperson.
• If any abnormalities occur, testing should be halted and strengthened to ensure safety.
• Ensure that all tools & instruments are clean and that any changes to wires are properly repaired after testing.

Test Category

• Visual Inspection
• Insulation Resistance Test
• AC voltage withstand Test

Test Procedure

Visual Inspection

Conditioning before testing.

All compartments are filled with SF6 gas at the rated pressure.

All components of the circuit being examined are in the closed position.

All earing switches of the circuit under test are in the open state.

All nearby portions are insulated & grounded.

If VTs are built for GIS test voltage, one side of the secondary winding must be connected to earth, and the cabling to the local cubicle must be disconnected.

If VT’s not intended for GIS testing are removed (or) insulated by opening a disconector.

The secondary winding of any current transformer should be shorted & grounded.

Surge arrester / lightning arrester are disconnected from GIS.

Power transformers are disconnected from the GIS substation & connected to the ground.

All work on the substation is paused, and the team is notified that a test will be carried out.

AC voltage Withstand Test

Precaution

SF6 pressure should be maintained at minimal levels across all compartments, & SF6 must be in good condition.

Test Voltage (Specification)

1. Test Voltage: 270 kV AC (phase to ground).

2. Test Frequency: 20–300 Hz.

3. Test Duration: 1 minute.

Voltage Sequence

Ensure insulation does not breakdown when applying voltage.

Application / Test Circuit

One phase is under test, while two other phases are connected to the earth.

Test Point

Bushing

Test Sheet

TRANSFORMER AC VOLTAGE WITHSTAND TEST

Location-

Station Name-

Equipment-

Manufacture-

Model / Type-

Operating Voltage-

Insulation Level-

Nominal Current-

Year-

Test Record

Circuit Section	Phase	Applied Voltage (KV)		Time		Charging Current (mA)	Remark	Result
1	R	86,67 (KV)		5 minute
		270 (KV)		1 minute
2	Y	86,67 (KV)		5 minute
		270 (KV)		1 minute
3	B	86,67 (KV)		5 minute
		270 (KV)		1 minute
	Tested By		Witnessed By				Incharge
Signature
Name

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