After dc overpotential test is completed the insulation resistance test is done again to assure that the cable has not been damaged by the hi pot.
Insulation resistance test standard for cable.
The test measures the insu lation resistance between the phases and or between phase and ground.
Table 100 22 minimum radii for power cable.
Historically many field electricians use the somewhat arbitrary standard of 1 megohm per kv.
If insulation resistance of the cable is found between 1000 and 100 kω km at buried temperature the subject cable should be replaced urgently within a year.
The megger insulation tester is a small portable instrument that gives you a direct reading of insulation resistance in ohms or megohms.
Minimum acceptable insulation resistance for 600 v cable from 100 to 1000 feet.
When overpotential testing cable its common practice to conduct the insulation resistance measurement first and then proceed with the dc overpotential test if acceptable readings are achieved.
For cables rated 600 v the minimum acceptable insulation resistance values for cable lengths from 100 to 1000 feet would be as shown in the following table from ieee 525.
If during periodical testing insulation resistance of cable is found between 5 and 1 mω km at buried temperature the subject cable should be programmed for replacement.
Developed early in the 20th century the insulation resistance ir test is the oldest and most widely used test for assessing the quality of insulation.
Insulation resistance testing purpose.
It is commonly used in the industry for acceptance testing prior to energizing the cable and for maintenance testing programs.
Power cables with extruded insulation and their accessories for rated voltages from 1 kv um 1 2 kv up to 30 kv um 36 kv part 1.
Insulation resistance testing is a non destructive test procedure.
Insulation resistance test data may be used to establish a trending pattern.
The international electrical testing association neta specification maintenance testing specifications for electrical power distribution equipment and.
Also acceptable values of insulation resistance depend upon the equipment you re testing.
Principle of insulation testing and influencing factors insulation resistance measurement is based on ohm s law.
Test results are dependent on the temperature of the insulating material and the humidity of the surrounding environment at the time of the test.
Insulation resistance decreases in temperature or moisture.
Deviations from the baseline information permit evaluation of the insulation.
The insulation resistance test consists in measuring the insulation resistance of a.
With a little record keeping and common sense however you can get a good picture of the insulation condition from values that are only relative.
