Cable Megger Test Insulation Resistance Values Table

A megger is an ohmmeter that measures resistance in the megohm scale.

Cable megger test insulation resistance values table.

Figure 4 typical record of insulation resistance of a mill motor. 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. 1k v 1 mω minimum 1kv 1 mω 1kv. First we will disconnect all the line and neutral terminals of the transformer.

The megger insulation tester is essentially a high range resistance meter ohmmeter with a built in direct current generator. A rated line to line voltage for three phase ac machines line to ground voltage for single phase machines and rated direct voltage for dc machines or field windings. It s also known as an insulation tester. Based upon equipment rating.

Curve b shows same values corrected to 20 c see page 22 giving a definite downward trend toward an unsafe condition. To test a cable with a megger you connect one probe to the outside of the cable and with the power turned off you touch the probe to the conducting wire at the point of connection. Figure 3 typical scale on the megger insulation tester. L insulation r v rated 304 8 1 where.

Comparing this result with the correct row of table 2 shows that our cable passes the insulation resistance test. The megger insulation tester is a small portable instrument that gives you a direct reading of insulation resistance in ohms or megohms. Megger leads are connected to lv and hv bushing studs to measure insulation resistance ir value in between the lv and hv windings. Ansi neta mts 2015 table 100 11 insulation resistance test values rotating machinery for one minute at 40 c.

For good insulation the resistance usually reads in the megohm range. If the cable does not pass if a cable does not pass the test the cable still may be good but additional cable evaluation should be per formed. 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. Since 80 of electrical maintenance and testing.

One meg ohm rule for ir value for equipment. The first thing to check is the cable testing environment and cable preparation. Reverse side of card at right is used to record the test data. B kv is the rated machine terminal to terminal voltage.

The procedure of insulation resistance test or megger test are given below. Go no go minimum acceptable insulation resistance value go no go testing is performed on new cable installations to determine if the insulation has been damaged during installation. As per ie rules 1956. Values based on ieee std 43 2013.

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