Insulation Resistance Test Standard For Motor

Figure 3 typical scale on the megger insulation tester.

Insulation resistance test standard for motor.

As per ie rules 1956. At a the insulation resistance decreases due to aging and dust accumulation. Minimum ir in megohm kv 1 example 1. 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.

The international electrical testing association neta specification maintenance testing specifications for electrical power distribution equipment and. Set the voltage. Curve a shows test values as measured. Since 80 of electrical maintenance and testing.

Ansi neta mts 2015 table 100 11 insulation resistance test values rotating machinery for one minute at 40 c. Also acceptable values of insulation resistance depend upon the equipment you re testing. Historically many field electricians use the somewhat arbitrary standard of 1 megohm per kv. B kv is the rated machine terminal to terminal voltage.

1k v 1 mω minimum 1kv 1 mω 1kv. For 11kv equipment mi. 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 a 440v motor minimum ir between phase and ground 440 1000 1 1 44 megohm example 2.

The measurement of insulation resistance is carried out by means of a megohmmeter high resistance range ohmmeter this is how the test works. Minimum insulation resistance ir value is depend upon rated line voltage of equipment. Figure 4 typical record of insulation resistance of a mill motor. A if the insulation resistance of a new cleaned or repaired motor that has been stored for some time is less then 10 mω the reason might be that the windings are humid and.

Curve b shows same values corrected to 20 c see page 22 giving a definite downward trend toward an unsafe condition. Reverse side of card at right is used to record the test data. For a three phase motor insulation resistance is usually measured between each motor winding or phase and between each motor phase and motor frame earth using an insulation tester or megger. Dc voltage of 500 or 1000 v is applied between the windings and the ground of the motor.

Regular checks of motor insulation resistance the key to prolonging the life of any electrical device is periodic checks maintenance the insulation resistance of stored and active motors should be checked regularly. During the measurement and immediately afterwards some of the terminals carry dangerous voltages and must not be touched. Z 5 date of test r eading in megohms the graph below shows an example of the insulation resistance readings on an electric motor. Values based on ieee std 43 2013.

One meg ohm rule for ir value for equipment. Ground insulation test of a motor.