Voltage is equal to the ratio of the high voltage winding turns divided by the high-pressure side of the low pressure side of the winding turns, that is, the voltage ratio is equal to the turns ratio. The current transformer primary side coil turns put little general is a wire, put a lot of turns on the secondary side, so from the principle of voltage transformers up analysis, if one senses a low voltage, then the secondary side if induction into the open, they would have a very high voltage and the voltage on the secondary side is not more than 2000V, so the secondary side is determined not open circuit. Will, because the primary and the secondary are connected in series circuit formed from the other side, so that the primary side to the voltage induced on the primary side equal to the resistance of the current flowing *, the secondary-side current is equal to the secondary side induction voltage divided by the resistance to the secondary side, the primary side when a large current flows when, because of a side of the sensed voltage is equal to the resistance of the primary side current flowing *, so the primary voltage is increased, the primary voltage by large secondary sensed voltage increases, and the secondary-side current is equal to the voltage divided by the secondary-side resistance, so induced to the secondary side of the current also increases.

Many voltage transformer wiring, common are the following:

1. With a single-phase voltage transformer to measure a relative voltage or phase voltage wiring.

2. With two single-phase transformers connected in incomplete star, also known as the V-V wiring, used to measure the voltage between the phases, but can not be measured relative to the voltage, widely used in 20KV following ungrounded or grounded by the discharge coil the grid.

3. With three single-phase three-winding voltage transformer constitute YN, yn, d0 or YN, y, wiring form d0 widely used 3 ~ 220KV system, the secondary winding is used to measure the relative phase voltage and voltage, the auxiliary secondary winding connected as open triangles, for access to AC power meter and insulation monitoring relays used. With a three-phase five-column instead of the three single-phase voltage transformer wiring voltage transformer winding consisting of three, in addition to the core, its form and Figure 3 is basically the same, generally used only for 3 ~ 15KV system.

4. Connection type capacitor voltage transformer.

Ungrounded neutral point or arc suppression coil grounding system in order to measure the relative voltage, PT primary winding must be connected to a star grounded way.