What is voltage ratio on a transformer?

The voltage ratio of a potential, or voltage, transformer (PT or VT) depends upon the primary voltage to which it is connected. Accordingly, its voltage ratio varies considerably, as there is huge variety of system voltages throughout the world.

Typically a VT's secondary voltage is standardised at 110 V which will match the full-scale deflection of a voltmeter connected to it (although it can also supply protective relays), while its primary voltage is then matched to the voltage of the system to which it is connected: in the UK, for example:

• 11-kV:110 V
• 33-kV:110 V
• etc.