2. Electrical Safety
• Electric shock
• Over current
• Thermal hazard
• Safely procedure
3. Electrical instrument
Electrical Instrument • Measuring instruments
• Analogue • Ammeter
• Digital • Voltmeter
Measurement • Ohmmeter
-voltage • Multimeter
-Current • Insulation tester
- Resistance • Wattmeter
- Power • Watt-hour meter
• Power factor meter
• Frequency meter
• Voltage indicator
• Phase sequence indicator
• Earth loop tester
• Earth resistance tester
• Phase stick tester
4. Meter specification
• Types of meter
• Max measuring value
• Accuracy
• Operating temperature
• Resolution
• Types of supply (AC or DC)
• Connection method
• Percentage error
• Maximum surge current
• location
5. Continuity test
• to check condition of current path
• Correct condition
• Condition of circuit and equipment
• For ie cable, coil, winding
-ohmmeter test
Good- low ohm reading
Malfuntion- high or infinit ohm reading
-buzzer test
-lamp test
6. Resistance test
• To check condition of equipment winding or
coil
Good- small resistance- 3 phase expected to have
equal resistance value
7. Insulation resistance test
• Check condition of insulation material
Types-
Hand cranking
Battery operated
Acceptable values of output
250V DC - extra low voltage – 0.5 M- Ohm
500V DC - <500V - 0.5 M- Ohm
1000V DC – 1000V – 1.0 M-Ohm
8. Test procedure
• For equipment - Remove equipment from circuit
• Testing
-1 phase- between coil or winding to ground or body
-3 phase- between winding to winding or pole to pole
-Between each winding
For cable or circuit
Remove cable /circuit from supply and load
Testing
1 phase- between phase to neutral, phase to earth and neutral to
earth
3phase- between phase to phase, each phase to neutral, each
phase to body or earth, neutral to earth
9. Current injection test
• Primary injection
CT ratio, connection, polarity
Stability and sensitivity of protection
• Secondary injection
• To check relay performance- operating current
at various TMS and PMS using injection tester
10. Pressure test
• Insulation property of HV
• - 2 times voltage is supplied for 1min of AC,
and 10min of DC
11. Earthling testing
• Test earthing system items earth loop
independence, earth electrode resistance
