Figure 3 typical scale on the megger insulation tester.
Cable megger test insulation resistance values table.
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.
For good insulation the resistance usually reads in the megohm range.
The minimum acceptable insulation resistance value is calculated using the following formula.
Figure 4 typical record of insulation resistance of a mill motor.
As per ie rules 1956.
Based upon equipment rating.
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.
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.
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.
Since 80 of electrical maintenance and testing.
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.
B kv is the rated machine terminal to terminal voltage.
Reverse side of card at right is used to record the test data.
Curve a shows test values as measured.
The procedure of insulation resistance test or megger test are given below.
The megger insulation tester is essentially a high range resistance meter ohmmeter with a built in direct current generator.
The megger insulation tester is a small portable instrument that gives you a direct reading of insulation resistance in ohms or megohms.
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.
1k v 1 mω minimum 1kv 1 mω 1kv.
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.
L insulation r v rated 304 8 1 where.
Values based on ieee std 43 2013.
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.
Megger leads are connected to lv and hv bushing studs to measure insulation resistance ir value in between the lv and hv windings.
Comparing this result with the correct row of table 2 shows that our cable passes the insulation resistance test.
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.
/You-got-the-power;-With-PowerDB-lite/pdb2.gif)
