What are the capacities of voltage transformers? What is the difference?

Voltage transformers - according to the principle is divided into electromagnetic induction type and capacitor partial pressure type. According to the purpose, the voltage transformer is divided into two categories: measurement and protection.

1. Electromagnetic induction type voltage transformer. The working principle is the same as that of the transformer. The basic structure is also the core and the primary and secondary windings. The characteristic is that the capacity is small and relatively constant, and it is close to the no-load state during normal operation. The voltage transformer itself has a small impedance. Once the secondary side is short-circuited, the current will increase sharply and the coil will be burnt. For this reason, the primary side of the voltage transformer is connected with a fuse, and the secondary side is grounded to prevent the primary side and the secondary side from being damaged, and the secondary side is exposed to a high potential to cause an accident. The equivalent circuit of the electromagnetic induction type voltage transformer is the same as the equivalent circuit of the transformer.

2. Capacitor voltage divider voltage transformer. Made on the basis of a capacitive voltage divider. Capacitive voltage transformers are often used in conjunction with coupling capacitors for power system carrier communication to simplify the system and reduce cost. At this point, it also needs to meet the requirements of communication operation. Voltage transformers are classified according to structure, and are oil-filled, dry, and three-core and five-column.

By purpose

Measuring star windings for measuring voltage transformers or voltage transformers: providing grid voltage information to measurement and metering devices within the normal voltage range;

Protective windings for protection voltage transformers or voltage transformers: In the event of grid faults, grid fault voltage information is provided to devices such as relay protection.

According to the insulating medium

Dry-type voltage transformer: Insulating varnish is impregnated by ordinary insulating material, and is used in low voltage grades below;

Casting Insulation Voltage Transformer: Casting from epoxy resin or other resin mixed materials, used in and below the voltage level;

Oil-immersed voltage transformer: Insulation paper and insulating oil as insulation, is the most common structure type in China, and is often used for the following voltage levels;

Gas-insulated voltage transformer: It is mainly used for gas insulation and is used at higher voltage levels.

The low-voltage transformers usually used for measurement are dry, and high-voltage or ultra-high-pressure sealed gas-insulated (such as sulfur hexafluoride) transformers are also dry. The cast type is suitable for voltage transformers of 35kV and below, and the products of 35kV or above are oil immersed.

By number of phases

Most products are single-phase, because the voltage transformer has small capacity and the body size is small. The internal and external insulation requirements between the three-phase high-voltage bushings are difficult to meet, so only 3--15kV products sometimes adopt three-phase structure.

According to the principle of voltage conversion

Electromagnetic voltage transformer: According to the principle of electromagnetic induction, the voltage is changed. The principle is completely similar to the basic structure and the transformer. The voltage level is used in China and below;

Capacitive voltage transformer: It consists of capacitor divider, compensation reactor, intermediate transformer, damper and carrier device protection gap. It is used in neutral grounding system for voltage measurement, power measurement, relay protection and carrier communication. use;

Photoelectric voltage transformer: Through the principle of photoelectric conversion to achieve voltage conversion, it is still under development.

According to the conditions of use

Indoor voltage transformer: installed in indoor power distribution equipment, generally used in the following voltage levels;

Outdoor type voltage transformer: installed in outdoor power distribution equipment, used in and above voltage level.

The main method of voltage transformers is mainly these, you can combine the actual use of various types of products for comparison.