Difference between OLTC and Off Circuit Tap Changer
A transformer tap changer is used to adjust the effective turns ratio of a transformer and maintain the required output voltage. Depending on the application, transformers may use an On Load Tap Changer or an Off Circuit Tap Changer.
What is an OLTC?
An On Load Tap Changer, commonly called OLTC, allows the transformer tap position to be changed while the transformer remains energized and supplying the load.
The OLTC changes the effective number of turns in the winding to regulate the output voltage without interrupting the power supply.
An OLTC generally consists of a tap selector, diverter switch, motor drive mechanism, transition resistors or reactors, and associated control and protection components.
OLTC systems are commonly used in power transformers where continuous voltage regulation is required, particularly in transmission and distribution substations.
What is an Off Circuit Tap Changer?
An Off Circuit Tap Changer, also known as an Off Load Tap Changer, changes the transformer tap position only when the transformer is de energized.
The transformer must be isolated from the electrical supply before changing the tap position. After selecting the required tap, the transformer can be re energized.
This type of tap changer has a simpler construction and is generally used where voltage variations are relatively small and frequent voltage adjustment is not required.
OLTC vs Off Circuit Tap Changer
OLTC operates while the transformer is energized, whereas an Off Circuit Tap Changer operates only when the transformer is de energized.
OLTC provides continuous voltage regulation during transformer operation. An Off Circuit Tap Changer requires an outage or isolation before the tap position can be changed.
OLTC has a more complex mechanism and requires additional control, switching, and maintenance arrangements. Off Circuit Tap Changers have a simpler construction and generally require less maintenance.
OLTC is commonly used for power and distribution transformers where load voltage must be continuously controlled. Off Circuit Tap Changers are suitable for applications where the transformer voltage ratio can be adjusted occasionally.
Why is Tap Changing Important?
Transformer loading and system conditions can cause the voltage to vary. Tap changing allows the transformer ratio to be adjusted so that the required voltage can be maintained within the specified operating range.
OLTC is particularly useful where voltage regulation must be performed without interrupting the load. Off Circuit Tap Changers are more suitable where tap adjustments are infrequent and the transformer can be safely isolated.