OLTC Service

As the only moving parts in a typical power transformer, on-load tap changers (OLTCs) are among the most susceptible components, their regular testing and maintenance is an important part of transformer asset management. Visual inspection can be used to detect the degradation of accessible OLTC parts at regular intervals. However, many mechanical parts are not easily accessible for inspection, and it is recommended to perform additional tests to establish the OLTC condition. It is therefore important to be able to assure the best of tap-changers as efficient and reliable as possible. 

On-Load Tap Changer

The on-load tap changer is majorly used to alter the tapping connection of the transformer winding to change the voltage ratio while the transformer is still in service without interrupting the load. 

How does OLTC Work?

OLTC comprises two major components, the tap selector and diverter switch. 

The tap selector selects the tapping and its electrical contact is designed to carry the rated current of the transformer but not to make or break this current. The diverter switch, however, needs to be designed to carry, make and break the load current in circuits previously selected by the tap selector switch. During the operation of the diverter switch, the transition resistors bridge the tap in use and the tap next to be used, thereby limiting the circulating current due to the inter-tap voltage. The OLTC motor drive mechanism is used to control the OLTC to increase or decrease the tap operation, it consists of a motor, reduction gearbox, planetary gearbox, and motor drive panel.