The testing apparatus only goes between 500 and 1,000 volts, which is low. On account of the voltage, some punctures in insulating material go unnoticed. It generally provides the amount of deterioration, moisture and winding faults in addition to information concerning the leakage current and whether insulation areas have moisture or excess dirt. Higher excellent option are available which are easy to use and very secure.
Insulation resistance quality of an electric system degrades with time, environment condition i.e. temperature, humidity, moisture and dust particles. The equipment essentially use for verifying the electric insulation level of almost any apparatus such as cable, motor, generator winding, etc.. This is a evaluation being carried out since long back. Not necessary it reveals us region of puncture but shows the total amount of current and amount of moisture inside electrical equipment/winding/system.
Different Types of Megger
This can be divided into mainly two classes:
1. Electronic Type (Battery Operated)
2. Manual Type (Hand Operated)
Construction of Megger
1. Deflecting and Control Panel : Connected parallel to the generator, mounted to each other and keep polarities in a way.
2. Permanent Magnets : Produce field to divert pointer.
3. Pointer : One conclusion of this pointer linked with coil another end deflects on scale from infinity.
4. Scale : A scale is provided from range ‘zero’ to ‘infinity’, enable us to read the value in front-top of their megger.
5. D.C Battery or generator connection : Testing voltage is made by hand operated DC generator for guide operated Megger. Battery voltage charger is supplied for automatic kind Megger for purpose.
6. Pressure coil resistance and coil resistance instrument from any damage because of low electrical resistance under evaluation.
Voltage for testing controlled megger in case of kind by turning crank, there can be a battery used for electronic tester. 500 Volt DC is for performing evaluation on gear enough range around 440 Volts. The control coil is connected across the circuit. Where as in type that is electronic megger battery are used to generate the testing voltage.
With a increases of present pointer raises and deflection of pointer’s deflection decreases as the voltage increases in circuit. Therefore, resultant torque is proportional to voltage and inversely proportional to current. When circuit is open, torque due to voltage coil will be maximum and pointer reveals ‘infinity’ means no shorting through the circuit also has maximum immunity within the circuit under test. When there’s short circuit pointer reveals ‘zero’, meaning ‘NO’ resistance within circuit.
Work doctrine based on ohm-meter or ratio-meter. The deflection torque is produced as a result of magnetic field created by voltage and current with megger tester, similarly such as ‘Ohm’s Law’. Torque of this megger changes in accordance with V/I, (Ohm’s Law :- V = IR or R = V/I). Electrical resistance is connected and in string. If present supplied to the coil torque that is produced will probably be in reverse direction.
– High resistance = No present :- No current will flow via deflecting coil, in case immunity is extremely high i.e. infinity standing of pointer.
– Small resistance = High current :- If circuit measures small resistance allows a high electrical current to pass through deflecting coil, i.e. generated torque make the pointer to place at ‘ZERO’.
– Intermediate resistance = current that is varied :- If immunity is intermediate, generated torque align or set the pointer between the range of ‘ZERO’.