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Cable megger test insulation resistance values table.
For good insulation the resistance usually reads in the megohm range.
The first thing to check is the cable testing environment and cable preparation.
B kv is the rated machine terminal to terminal voltage.
A megger is an ohmmeter that measures resistance in the megohm scale.
The megger insulation tester is a small portable instrument that gives you a direct reading of insulation resistance in ohms or megohms.
Figure 4 typical record of insulation resistance of a mill motor.
1k v 1 mω minimum 1kv 1 mω 1kv.
Since 80 of electrical maintenance and testing.
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.
Reverse side of card at right is used to record the test data.
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.
The procedure of insulation resistance test or megger test are given below.
It s also known as an insulation tester.
The minimum acceptable insulation resistance value is calculated using the following formula.
Ansi neta mts 2015 table 100 11 insulation resistance test values rotating machinery for one minute at 40 c.
One meg ohm rule for ir value for equipment.
Comparing this result with the correct row of table 2 shows that our cable passes the insulation resistance test.
The megger insulation tester is essentially a high range resistance meter ohmmeter with a built in direct current generator.
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.
Curve b shows same values corrected to 20 c see page 22 giving a definite downward trend toward an unsafe condition.
Curve a shows test values as measured.
L insulation r v rated 304 8 1 where.
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.
First we will disconnect all the line and neutral terminals of the transformer.
Based upon equipment rating.
As per ie rules 1956.
Megger leads are connected to lv and hv bushing studs to measure insulation resistance ir value in between the lv and hv windings.
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.
Figure 3 typical scale on the megger insulation tester.
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