Transformer Voltage Regulation SOP

 Transformer Voltage Regulation SOP


1. Purpose

To maintain the secondary voltage of a transformer within the desired range, ensuring safe and efficient operation of connected equipment.

2. Scope

Applicable to all power and distribution transformers with either on-load or off-load tap changers.

3. Responsibilities

  • Operators: Follow SOP, monitor voltage, record operations, and report anomalies.
  • Maintenance Team: Service tap changers and verify voltage regulation equipment.
  • Shift Supervisors: Authorize voltage adjustment and ensure safe operations.

4. Safety Precautions

  1. Only trained and authorized personnel may operate tap changers.
  2. Wear PPE: insulated gloves, helmet, safety shoes, and face shield.
  3. Confirm no live faults before operation.
  4. Avoid operation during maintenance work on transformer or feeder.
  5. Use lockout-tagout (LOTO) when doing physical maintenance.
  6. Maintain minimum safe distance from live components.

5. Pre-Operation Checks

1.. Visual Inspection:

      1.      Inspect transformer, bushings, tap changer, and connections for damage or leaks.
2.      Check oil level and temperature (for oil-filled transformers).

2.. Metering and Protection:

      1.      Verify voltage meters and tap position indicators are functional.
2.      Ensure protection relays are enabled and operational.

3..Environment:

      1.      Ensure no water accumulation, dust, or debris around the transformer.
2.      Verify proper grounding.

6. Transformer Voltage Adjustment Procedure

6.1 Off-Load Tap Changing

  1. Switch transformer OFF (de-energized).
  2. Open incoming and outgoing circuit breakers.
  3. Move the tap changer to the desired tap position.
  4. Close circuit breakers and energize the transformer.
  5. Record tap position, input voltage, and output voltage in the logbook.

6.2 On-Load Tap Changing (OLTC)

      1.      Check OLTC mechanism status and ensure it is functional.
2.      Verify load current and voltage readings on HV and LV sides.
3.      Monitor voltage change and load stability after each step.
4.      Record tap position, input voltage, output voltage, and load current.
5.      Adjust the tap changer gradually to maintain target secondary voltage.
6.      Most OLTCs have automatic regulation—manual intervention only if required.

7. Monitoring During Operation

  • Continuously monitor:

  1. Secondary voltage
  2. Load current and power factor
  3. Transformer temperature
  4. Tap changer operation status and position indicator

  • Ensure voltage remains within ±5% of nominal value (or as per site standard).

8. Fault Handling

Tap changer failure:

     1).. Isolate transformer using circuit breakers.
     2).. Do not operate transformer manually until maintenance is done.

Overvoltage or Undervoltage:

      1).. Check incoming supply and load conditions.
      2).. Adjust taps gradually if needed.

OLTC motor or diverter switch malfunction:

       1).. Stop operation immediately.
      2)..  Call maintenance team.

9. Shutdown Procedure

  1. For off-load tap change, ensure transformer is de-energized.
  2. For OLTC, leave transformer in normal operating tap position.
  3. Record final tap position and voltage readings.
  4. Inspect tap changer and transformer for any anomalies.

10. Maintenance

  • Monthly: Check tap changer contacts, oil level, and indicators.
  • Quarterly: Test OLTC mechanism and perform functional check.
  • Annually: Full preventive maintenance including contact cleaning, oil testing, and mechanical inspection.

11. Documentation

  • Logbook: Date, time, operator, tap position, voltages, load current.
  • Fault reports: Description, action taken.
  • Maintenance records: Scheduled and completed work.

12. Best Practices

  • Never switch taps under heavy fault conditions.
  • Avoid rapid or frequent tap changes.
  • Always coordinate with control room and downstream systems.
  • Follow manufacturer instructions for tap changer operation.

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