1. Requirements for resistance value of metal oxide lightning arrester
1.1 Voltage above 35kV: Use a 5000V megohmmeter with an insulation resistance not less than 2500M Ω;
1.2 Voltage of 35kV and below: Use a 2500V megohmmeter with an insulation resistance not less than 1000M Ω;
1.3 Low voltage (below 1kV): Use a 500V megohmmeter with an insulation resistance of not less than 2M Ω.
1.4 Voltage 4-17kV and below: Use a 2500V megohmmeter with an insulation resistance not less than 1000M Ω;
2 Test steps and methods
2.1 Check and confirm that the connection between the test object and the lead has been disconnected, with obvious disconnection points, and meets the test conditions.
2.2 Place qualified temperature and humidity meters in a shaded and ventilated area.
2.3 Fully discharge the high-voltage end of the test sample, and wear insulated gloves to discharge first through a resistor and then directly. Ground the low-voltage end of the test object to the base.
2.4 Use a dry, clean, and soft cloth to wipe off the dirt on the external insulation surface of the test object, and if necessary, wash it off with an appropriate cleaning agent.
2.5 Copy the nameplate of the test object and record the weather conditions, environmental temperature, and humidity.
2.6 Select a suitable megohmmeter (2500V or 5000V) based on the voltage level of the test object, and check the certificate of conformity and validity of the megohmmeter.
2.7 Check the megohmmeter (using BL2672 as an example): Turn the function knob to "BATT CHECK", press the "PRESS TO TEST" button, and the megohmmeter pointer should be on the right side of "BATT GOOD" to indicate sufficient power; Stabilize the megohmmeter horizontally, turn the function knob to "M Ω", press the "PRESS TO TEST" button, and momentarily short circuit the "LINE" and "EARTH" terminals with a wire. The pointer should point to zero, and when there is an open circuit, the pointer of the megohmmeter should point to "∞", indicating that the megohmmeter is qualified.
2.8 Connect the "EARTH" end of the megohmmeter to the ground wire of the test object, turn the function knob to "M Ω", press the "PRESS TO TEST" button, connect the "LINE" end of the megohmmeter to the high voltage end of the test object, and start timing. After 60 seconds, read the insulation resistance value. After reading the insulation resistance, first disconnect the connecting wire to the high voltage end of the test object, then release the "PRESS TO TEST" button and turn the function knob to "OFF". When measuring under high humidity conditions, equipotential shielding can be applied to the surface of the test object. The shielding ring of the test object should be close to the pressurized live wire and away from the grounding part to reduce shielding leakage to the ground and avoid overload of the megohmmeter. The shielding ring can be made by tightly winding a fuse or soft copper wire for several turns.
2.9 Remove the low-voltage grounding wire of the test object and measure the insulation resistance of the base according to the above steps.
2.10 Wear insulated gloves and use a well grounded discharge rod to fully discharge the test object.
2.11 Record the test data, tester, test date, as well as the name, model, number, and manufacturer of the instrument used.
2.12 Remove all wiring, restore the test object to its original state, and place the test instrument back in its original position.
2.13 Check if the grounding wire has been removed and if there are any remaining objects on site.
