Objective
This procedure explains the methods for testing lightning arresters or surge arresters used to protect electrical distribution lines & substation equipment. This procedure relates to:
- Metal Oxide (Zinc Oxide) Gapless Arresters
- Gapped Silicon Carbide Arresters
The primary purpose of this testing is to check arrester integrity, discover internal faults and assure dependable system protection.
Definitions
Metal Oxide Type (ZnO)
Metal Oxide Type (ZnO) utilizes zinc oxide blocks for optimal performance.
The arrester starts and stops conduction at specific voltage levels, providing accurate system safety.
Gapped Silicon Carbide Type (SiC)
Gapped silicon carbide (SiC) has strong nonlinearity.
A gap is used to prevent thermal failure due to leakage current. Spark-over happens when the gap voltage threshold is surpassed.
Test Equipment
- Double Insulation Power Factor Test Set and
- AC High Potential (Hi-Pot) Test Set
AC High Potential (Hi-Pot) Test Set
Importance of Testing
Visual inspections cannot reliably detect arrester problems. Electrical testing is necessary to detect
- Internal element damage,
- Moisture Ingress,
- Severe lightning strike consequences and
- Incorrect arrester ratings.
These tests confirm that the arrester is reliable and the system is safe.
Safety Precautions
- Caution is advised before carrying out any tests that involve high voltage.
- The lightning arrester that is being tested should be isolated and disconnected.
- Unplug the equipment and circuits that are next to one another in order to avoid induced voltages.
- Make sure that the testing equipment is properly grounded.
Test Setup
AC Hi-Pot Test Arrangement
- When you are in the test area, position the HV module.
- Put the control cabinet approximately 20 feet away from the high-voltage module.
- Connect the power cables and the coaxial cables that are used for interconnection between the HV module and the control cabinet.
- Put the high-voltage probe on the toroid, and then connect the coaxial wires to the ports for the high-voltage supply and the voltmeter.
- Using the diagram provided by the manufacturer, connect the ground and return leads.
- Connect a wire with a gauge of 12 AWG between the toroid of the HV module and the arrester terminal.
- 230 V alternating current should be used to supply power to the control cabinet.
Testing Procedure
1). Spark-Over Voltage Test (Gapped Arresters)
- Set the current meter to its maximum range.
- Put the kV meter in the range of 0–50 kV.
- At the output voltage control, make sure it is set to zero.
- After turning the HV on, the indicator lamp is supposed to light up.
- The output voltage should be gradually increased until the arrester spark-over phase occurs.
- In the “as found” value, the spark-over voltage should be recorded.
- Bring the voltage control back down to zero.
- When the HV switch is turned off, the indicator lamp should go out.
- Completed the test.
2). Leakage Current Test (Gapless Arresters)
- Set the current meter to its maximum range.
- Put the kV meter in the range of 0–50 kV.
- Check that the voltage control is set to zero.
- After turning the HV on, the indicator lamp is supposed to light up.
- The voltage should be increased until it reaches the Maximum Continuous Operating Voltage (MCOV) of the arrester.
- Low range (0–1 mA) should be selected on the current meter.
- Record the leakage current at the MCOV.
- Bring the voltage control back down to zero.
- Turn off the high voltage.
- Completed the test.
3). Power Loss (Watts Dissipation) Test – Using Double Insulation Power Factor Test Set
The Double Insulation Power Factor Test Set measures power loss (watts dissipation).
Instrument Setup
The test set should be grounded to the station earth.
The HV test cable should be connected from the test set to the arrester terminal.
Create a connection between the control console and the transformer casing using the control cable.
Make sure that all of the switches are set to their initial settings:
Voltage: 0
Current Multiplier: Maximum (100 mA)
Watts Multiplier: Maximum (1 k)
Interference (Icc): OFF
Selector Switch: CHECK
Provide 120/240 V AC to the test set. Confirm that the power indication light is on.
Test Procedure
- HV test wire should be connected to the arrester terminal.
- To activate the test circuit breaker, press the HV button (which will turn the indicator on).
- Raise the voltage gradually until it reaches 10 kV.
- The meter scales should be adjusted to 100 divisions.
- Please select the proper range for the current multiplier.
- The current reading should be recorded (first position).
- Alternate the position of the switch responsible for reversing.
- Record the second reading of the current.
- Determine the average value at the moment.
- Set the selection to the Watts Multiplier setting.
- The minimum watt reading on the proper scale should be adjusted.
- Set the value of the watts.
- Put the polarity in reverse and take another measurement.
- Compute the average measurement of watts while taking into account the polarity.
- The final recorded value is equal to the Watts of loss dissipation of the arrester.
- Make sure the controls are set to zero, and turn off the test set.
Completion
Each and every recorded value needs to be compared to the standards provided by the manufacturer.
If the findings of spark-over, leakage current & watts dissipation are outside of the permitted limits, this indicates that the arrester has failed (or) is deteriorating.
The test report should include the measured values, conditions * specifics about the equipment.