The megger insulation tester is essentially a high range resistance meter ohmmeter with a built in direct current generator.
Cable megger test insulation resistance values table.
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 a shows test values as measured.
The first thing to check is the cable testing environment and cable preparation.
Based upon equipment rating.
B kv is the rated machine terminal to terminal voltage.
First we will disconnect all the line and neutral terminals of the transformer.
The megger insulation tester is a small portable instrument that gives you a direct reading of insulation resistance in ohms or megohms.
Figure 3 typical scale on the megger insulation tester.
Curve b shows same values corrected to 20 c see page 22 giving a definite downward trend toward an unsafe condition.
One meg ohm rule for ir value for equipment.
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.
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.
For good insulation the resistance usually reads in the megohm range.
As per ie rules 1956.
Ansi neta mts 2015 table 100 11 insulation resistance test values rotating machinery for one minute at 40 c.
Comparing this result with the correct row of table 2 shows that our cable passes the insulation resistance test.
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.
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.
Megger leads are connected to lv and hv bushing studs to measure insulation resistance ir value in between the lv and hv windings.
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.
Figure 4 typical record of insulation resistance of a mill motor.
It s also known as an insulation tester.
Values based on ieee std 43 2013.
The minimum acceptable insulation resistance value is calculated using the following formula.
Since 80 of electrical maintenance and testing.
Reverse side of card at right is used to record the test data.
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A megger is an ohmmeter that measures resistance in the megohm scale.
L insulation r v rated 304 8 1 where.
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