Maintenance & Care of Transformer

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Regular Maintenance of Transformers should be carried out and logged

  1. 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

  1. Permit-to-Work should be Issued
  2. Transformer should be disconnected from power supply
  3. 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

  1. 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

  1. Replace Screens, Protective Girds and Top Cover
  2. All Terminals should be Tightened
  3. 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