Regular Maintenance of Transformers should be carried out and logged
- Keep the Transformer Well Ventilated, Clean & Dry
Area around the transformer should not be used for storing spares, etc
Transformer is naturally are cooled (natural air circulation) – improper ventilation will cause overheating
- Permit-to-Work should be Issued
- Transformer should be disconnected from power supply
- Measure the Insulation Resistance between Phase Windings & Earth using Megger
If Value is Low- It indicates presence of Dirt/Dust /Moisture
Cleaning & Heating is required to remove Dirt/Dust & Moisture
Remove the Top Cover
Remove & Clean the Protective Grids and Screens
Dirt/Dust should be removed using a Brush/Vacuum Cleaner
Compr. Air should not be used since it will Force the Deposits into the Insulation
Moisture can be removed by Heating
- Measure Insulation Resistance between Phase Windings using Megger
If Value is Low – It indicates Short Circuit of the Windings
Visually inspect for signs of burning or damage
Apply Varnish and Heat it
- Replace Screens, Protective Girds and Top Cover
- All Terminals should be Tightened
- Measuring Instruments – Measures the electrical quantities and Indicate their values by deflection of a pointer on a graduated scaleVarious Electrical Quantities that are measured:
Current (A)
Voltage (V)
Power (W)
Insulation Resistance (Ω), etc
Types of Measuring and Indicating Instruments:
PMMC (Permanent Magnet Moving Coil) Type (Only DC applications)
MI (Moving Iron) Type (DC & AC applications)
Electrodynamometer Type (DC & AC applications)
Electrodynamometer Type Measuring Instrument
Instrument works on dynamometer principle
i.e. Mechanical force exists between two current carrying conductors or coils
Interaction between the currents (magnetic fields) of the two coils causes mechanical movement (deflection) of the coils
Instrument consists of a Two Fixed Coil and One Moving Coils
A shaft is attached to the Moving Coil. A Pointer is mounted on the Shaft
When Moving Coil moves – Pointer moves (moves over a graduated scale)
Current /Voltage/Power to be measured is fed to both Fixed and Moving Coils
Both the Fixed Coils and Moving Coils gets Energized
Both the Coil produces their own Magnetic Fields
Both these magnetic fields interact causing a movement/deflection of the Coils
Since the fixed coil cannot move, moving coils moves / deflects
This causes the pointer to move (moves over a graduated Scale)
Meter Reading can be read from the graduated Scale