Cable Megger Test Insulation Resistance Values Table

B kv is the rated machine terminal to terminal voltage.

Cable megger test insulation resistance values table.

Figure 3 typical scale on the megger insulation tester. A megger is an ohmmeter that measures resistance in the megohm scale. 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. Based upon equipment rating.

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. The procedure of insulation resistance test or megger test are given below.

1k v 1 mω minimum 1kv 1 mω 1kv. The first thing to check is the cable testing environment and cable preparation. Hands down without a doubt one of the most universally searched topics on ec m s website from a historical perspective is insulation resistance testing as a result some of our most popular evergreen articles like understanding insulation resistance testing continue to top the charts when it comes to most popular content. For good insulation the resistance usually reads in the megohm range.

The minimum acceptable insulation resistance value is calculated using the following formula. Curve a shows test values as measured. Values based on ieee std 43 2013. It s also known as an insulation tester.

The megger insulation tester is essentially a high range resistance meter ohmmeter with a built in direct current generator. Reverse side of card at right is used to record the test data. 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. 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.

Curve b shows same values corrected to 20 c see page 22 giving a definite downward trend toward an unsafe condition. At a pressure of 1000 v applied between each live conductor and earth for a period of one minute the insulation resistance of hv installations shall be at least 1 mega ohm or as specified by the bureau of indian standards. 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. L insulation r v rated 304 8 1 where.

As per ie rules 1956. First we will disconnect all the line and neutral terminals of the transformer. Ansi neta mts 2015 table 100 11 insulation resistance test values rotating machinery for one minute at 40 c. Figure 4 typical record of insulation resistance of a mill motor.

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.