E – 1672 Voltage Transformers

There are two types of voltage transformers, magnetic voltage transformers (VT) and capacitive voltage transformers (CVT). The magnetic voltage transformers are most economical for voltages up to about 145 kV and the capacitive voltage transformers for voltages higher than 145 kV. A CVT can also be used together with the Power Line Carrier (PLC) devices that are used for communication over the high voltage transmission circuits. Voltage transformers are together with current transformers known as instrument transformers. Voltage transformers are in most situations connected between phase and ground. The standard that describes voltage transformers in details is IEC 186. The main functions of voltage transformers are:

• – To transform voltages from high value to a value that can be easily handled by protection relays and instruments
• – To insulate the metering circuit from the primary high voltage.
• – To give standardization possibilities for instruments and protection relays to a few rated voltages