How to Adjust the Tap Position of an On-Load Tap-Changer

The operation of an on-load tap-changer (OLTC) can be performed automatically via remote control (from the main control room monitoring system or the transformer’s measurement and control panel with OLTC controller). The steps for on-load tap-changing operation are as follows:

Voltage Raise Button: In manual operation mode, press the “Raise” button to initiate the voltage-raising operation of the on-load tap-changer.

Voltage Lower Button: In manual operation mode, press the “Lower” button to initiate the voltage-lowering operation of the on-load tap-changer.

Stop Button: In any mode, pressing the “Stop” button will halt any ongoing raise or lower operation of the on-load tap-changer.

Inspection of the On-Load Tap-Changer

The voltage indicated by the tap-changer should be within the specified deviation range;

The power indicator light on the controller should display normally;

The tap position indicator should show the correct position;

The operation counter should function properly, accurately recording the number of tap changes.

Precautions for Operating the Main Transformer’s On-Load Tap-Changer

(1) When adjusting multiple tap positions in one operation, proceed step by step with sufficient time intervals. Each adjustment should be spaced at least 1 minute apart, while closely monitoring changes in tap position, voltage, and current. Abnormal conditions such as resetting to zero, sudden jumps, or no changes should not occur. The tap position indicator and operation counter should reflect corresponding changes.

(2) During operation, observe the readings of the voltmeter and ammeter. Abnormal phenomena such as resetting to zero, sudden jumps, or no changes are not allowed. The tap position indicator and counter should show corresponding changes. After operation, verify that the tap position indicated on the OLTC matches the tap position shown in the computer system diagram.

(3) If loss of control or sliding between taps is observed during the voltage adjustment process, immediately press the “Stop” button to halt the operation. Do not resume until the cause has been identified and resolved.

(4) Record the operation time and changes in tap position for each voltage adjustment. After adjustment, monitor changes in the station service voltage.

(5) Avoid performing tap-changing operations during peak load periods. Do not adjust taps when the main transformer is overloaded or when the tap-changer is faulty.

(6) Prohibit switching the main transformer’s on-load tap-changer under the following abnormal conditions:

The main transformer is overloaded;

Frequent signals from the OLTC’s gas protection device;

The number of tap changes exceeds the specified limit;

The tap-changing mechanism exhibits abnormalities;

Unintended continuous tap-changing (runaway) occurs;

The power system is experiencing oscillations.