Explain on-load tap-changers (OLTC) in power transformers and their effect on voltage regulation.

Explain on-load tap-changers (OLTC) in power transformers and their effect on voltage regulation.

• A. OLTCs adjust the transformer turns ratio in steps to regulate the secondary voltage, maintaining bus voltages within limits; switching can cause voltage step changes and wear.
• B. OLTCs only regulate frequency, not voltage.
• C. OLTCs automatically disconnect feeders during faults.
• D. OLTCs are used to increase transformer rating without changing voltage.

Answer: (A)

On-load tap-changers let a transformer adjust its turns ratio while the system is energized, so the secondary voltage can be kept within desired limits as load and source conditions change. They do this by stepping through taps on the winding, controlled automatically or manually. Each tap change produces a small, discrete change in the bus voltage, which is how the regulator maintains voltage within a specified band. This approach improves voltage stability across the network, but it comes with wear on the contacts and insulation and some switching transients each time a tap is changed. OLTCs do not control frequency, they do not automatically disconnect feeders during faults, and they are not used to increase rating without changing voltage; their purpose is to regulate voltage by altering the transformer turns ratio in steps.

On-load tap-changers let a transformer adjust its turns ratio while the system is energized, so the secondary voltage can be kept within desired limits as load and source conditions change. They do this by stepping through taps on the winding, controlled automatically or manually. Each tap change produces a small, discrete change in the bus voltage, which is how the regulator maintains voltage within a specified band. This approach improves voltage stability across the network, but it comes with wear on the contacts and insulation and some switching transients each time a tap is changed. OLTCs do not control frequency, they do not automatically disconnect feeders during faults, and they are not used to increase rating without changing voltage; their purpose is to regulate voltage by altering the transformer turns ratio in steps.