Transformer FAQ
What is the difference between OLTC and OCTC?
An OLTC changes transformer taps while energized and carrying load, while an OCTC is operated only when the transformer is de-energized.
Direct answer
An on-load tap changer provides voltage-ratio adjustment without interrupting service and is used where operating voltage must be regulated during normal system operation. An off-circuit tap changer provides a simpler adjustment method but requires the transformer to be isolated and de-energized before changing position.
OLTC
OLTC systems add switching equipment, drive mechanisms, controls, protection and maintenance requirements. They are common on grid and substation transformers requiring active voltage regulation.
OCTC
OCTC arrangements are simpler and are commonly used where tap settings are selected during commissioning or infrequent maintenance outages.
Specification points
Confirm tap range, number and size of steps, winding location, automatic voltage control, parallel operation, control supply and required monitoring.
Related transformer questions
Continue with questions that usually come up next in the same specification.
Apply this to a project.
The final transformer design is confirmed against the complete load, site and standard requirements.