To evaluate the insulation integrity of an arrester, measure the power loss (watts-loss or dissipation factor) at a specified voltage and compare it with previous measurements on the same or similar arrester. Measurements on a surge arrester should always be performed at the same or recommended test voltage since nonlinear elements may be built into an arrester. When using this test set, all measurements should normally be made at 10 kV. Except for the specific purpose of investigating surface leakage, the exposed insulation surface of an arrester should be clean and dry to prevent leakage from influencing the measurements. Some types of arresters show substantial temperature dependence, while others show very little dependence. Temperature correction curves for each arrester design should be carefully established by measurement, and all measurements should be temperature corrected to a base temperature, Usually 20°C. The temperature measurement should be based on that at the arrester surface. The air temperature should also be recorded. The surface of the arrester should be at a temperature above the dew point to avoid moisture condensation . Test under IEC 60099 . In substations, surge arrestors appears on two types 1. Single arrester unit 2. Multi-unit arrester stacks.
It is recommended that tests be made on individual arrester units rather than on a complete multi-unit arrester stack. A single arrester unit can be tested by the normal ungrounded specimen test (UST) in the shop; however, it can only be tested by the grounded specimen test (GST) when mounted on a support structure in the field.
1. Single arrester unit: Surge arresters which contains single unit tested by Insulation resistance test, Capacitance test by tan delta equipment and leakage current monitor test. Insulation resistance test: Insulation resistance test must be carried out at the surge arresters through Insulation resistance tester such as Megger. Insulation resistance test must be carried out between the conductor of bushing and ground of the bushing. By applying 5KV to the Surge arrester for 1minute, record the value of insulation resistance with atmospheric temperature. Capacitance and Dissipation power factor test: Surge arrester with single unit must be subject to capacitance and dissipation power factor test by applying 10 KV through Tan delta equipment with the GST (Ground Specimen Test) mode. The temperature must be noted at the time of testing and the values measured must be compensated to 20°C. The below table show the connections on single unit. The results must be match with factory reports for their integrity. TEST NO
SURGE ARRESTOR SYMBOL INSULATION TESTED
LOW VOLTAGE CONFIGURATION TEST MODE
SA
GST
MEASURE
TEST CONNECTIONS TO SURGE ARRESTOR
GROUN D
RED
GAURD
BLACK
1
RED
5
BLUE
REMARKS
Leakage current monitor test: For every phase of the surge arrester the leakage current monitor is available. The monitors must be calibrated and tested by injecting milliamps current by sverker. Record the calibrated values with standard values and its error must be within the limits of respected manufacturer.
2. Multi-unit arrester stack: Surge arresters which contains multi-unit tested by Insulation resistance test, Capacitance and dissipation power factor test by tan delta equipment and leakage current monitor test. For the Insulation resistance and leakage monitor test the above mention procedures in single unit can be followed. For the capacitance and dissipation power factor the following procedures must be used. Table below shows the recommended test procedure for testing installed multi-unit arrester stacks. When testing in the field, disconnect the related high-voltage bus from the arrester .
Surge Arrester Test Connections TEST NO
SURGE ARRESTOR SYMBOL INSULATION TESTED
LOW VOLTAGE CONFIGURATION TEST MODE
MEASURE
GROUN D
TEST CONNECTIONS TO SURGE ARRESTOR GAURD
BLACK
RED
BLUE
1.
SA-A
UST
BLUE
RED
2
3
1
2.
SA-B
UST
RED
BLUE
2
3
1
REMARKS
TERMINAL 3 GROUND TERMINAL 1
GOUND 3.
SA-C
UST
4.
SA-D
GST
RED
BLUE RED
Note: Apply 10KV for each injection
Typical Multi-Unit Arrester Stack
4
3
4
3
TERMINAL 3 GUARDED
Record the values as per the requirements and standards with the temperature at the time of testing. These recorded values of Dissipation power factor must be corrected to 20°C.
