What is the purpose of changing taps on transformers during operation when there is an over or under voltage?

Purpose of Changing Tap Settings When Overvoltage or Undervoltage Occurs in Transformer Operation

When a transformer experiences overvoltage or undervoltage during operation, the purpose of changing tap settings is to adjust the transformer's output voltage and bring it back to the normal operating range. Here is a detailed explanation:

Function of Transformer Tap Settings

Transformer tap settings are a mechanism used to regulate the output voltage of a transformer. By changing the position of the tap settings, the turns ratio between the primary and secondary windings can be adjusted, thereby altering the output voltage. Tap settings are typically located on the primary side (high-voltage side) of the transformer, but they can also be found on the secondary side (low-voltage side).

Overvoltage and Undervoltage Conditions

Overvoltage:

• When the grid voltage is higher than the rated value, the transformer's output voltage will also increase, potentially leading to overload or damage to connected equipment.

• Excessively high voltage can also cause aging of insulating materials and increase the risk of system failures.

Undervoltage:

• When the grid voltage is lower than the rated value, the transformer's output voltage will decrease, potentially preventing connected equipment from functioning properly and affecting performance and efficiency.

• Low voltage can also cause difficulties in starting motors and reduced brightness in lighting fixtures.

Purpose of Changing Tap Settings

Maintain Stable Output Voltage:

• By adjusting the tap settings, the turns ratio of the transformer can be changed to bring the output voltage back to the normal operating range.

• For example, if the input voltage is too high, the tap setting can be switched to a lower position, reducing the number of turns in the primary winding and thus lowering the output voltage. Conversely, if the input voltage is too low, the tap setting can be switched to a higher position, increasing the number of turns in the primary winding and thus raising the output voltage.

Protect Connected Equipment:

• Maintaining a stable output voltage helps protect the equipment connected to the transformer, preventing damage or performance degradation caused by voltage fluctuations.

• For sensitive equipment such as electronic devices and precision instruments, a stable voltage is particularly important.

Optimize System Performance:

• Appropriate voltage levels can improve the efficiency and reliability of the entire power system.

• For example, motors operate more efficiently at the correct voltage, and lighting fixtures perform better with the right voltage.

Operating Steps

Measure Voltage:

Use a voltmeter to measure the input and output voltages of the transformer to determine if there is an overvoltage or undervoltage condition.

Select Appropriate Tap Setting:

• Based on the measurement results and the tap setting specifications on the transformer's nameplate, select the appropriate tap setting.

• Typically, tap settings have multiple positions, each corresponding to a specific voltage ratio.

Switch Tap Settings:

• Turn off the power to the transformer to ensure safety.

• Manually or using specialized tools, switch the tap setting to the selected position.

• Re-measure the voltage to confirm that the adjusted voltage is within the normal operating range.

Record and Maintain:

• Record the time and position of the tap setting change for future reference and maintenance.

• Regularly check the contact condition of the tap settings to ensure good connectivity.

Conclusion

The purpose of changing transformer tap settings is to adjust the output voltage and keep it within the normal operating range. This helps protect connected equipment, optimize system performance, and enhance the reliability and safety of the power system.