The voltage transformer in the distribution network is used to isolate high voltage and convert high voltage into low voltage for relay protection, automatic device (protection) and measuring instrument (metering) to obtain the primary side voltage signal. According to the working principle, voltage transformers can be divided into the following two types:

1. Electromagnetic voltage transformer (PT)

Electromagnetic type, the principle is similar to that of power transformers (electromagnetic induction), suitable for 6kV ~ 110kV systems. According to the insulation method, it is also divided into oil-immersed type (mostly outdoor type) and dry type (epoxy resin casting type).

2. Capacitive Voltage Transformer (CVT)

Capacitive voltage divider type, composed of capacitor voltage divider, compensation reactor, intermediate transformer, damper, etc., is suitable for 110kV ~ 500kV system, and 35kV system has a small amount of applications.

According to the national standard GB1207-2006 "Electromagnetic Voltage Transformer", "ungrounded voltage transformer" (full insulation) and "grounded voltage transformer" (semi-insulated) are defined. When the grounding terminal (N terminal) of the primary winding of the semi-insulated voltage transformer is designed, it is close to the secondary winding, and the voltage of the main insulation between the primary winding and the secondary winding and the ground is very low. GB1207-2006 stipulates 6/10kV voltage mutual inductance The power frequency withstand voltage of the device is only 3kV, and the 35kV voltage transformer has a power frequency withstand voltage of 5kV.