Classification of Transformer

Main classification

Transformers are divided into two categories: voltage transformers and current transformers. Voltage transformers can be used for voltage and power measurement in high-voltage and ultra-high-voltage power systems. Current transformers can be used for the measurement of exchange current, the measurement of exchange power, and the protection of electric drive lines.

Voltage transformer

According to purpose

Voltage transformer for measurement or measurement winding of voltage transformer: Provide grid voltage information to measurement and metering devices within the normal voltage range;

Voltage transformer for protection or protection winding of voltage transformer: in the state of power grid failure, provide power grid fault voltage information to relay protection and other devices.

According to the insulation medium

Dry-type voltage transformer: It is insulated by ordinary insulating material impregnated with insulating varnish, and is mostly used at and below low voltage levels;

Pouring insulation voltage transformer: It is cast and molded from epoxy resin or other resin mixed materials, and is mostly used at voltage levels and below;

Oil-immersed voltage transformer: insulated by insulating paper and insulating oil, it is the most common structural type in our country, and it is often used for voltage levels and below;

Gas-insulated voltage transformer: Mainly insulated by gas, mostly used in higher voltage levels.

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

According to the number of phases

Most of the products are single-phase. Because the voltage transformer has small capacity and small body volume, the internal and external insulation requirements between the three-phase high voltage bushings are difficult to meet, so only 3-15kV products sometimes use three-phase structure.

According to the principle of voltage conversion

Electromagnetic voltage transformer: According to the principle of electromagnetic induction, the voltage is transformed. The principle is completely similar to the basic structure and transformer, and it is mostly adopted in my country at and below the voltage level;

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

Photoelectric voltage transformer: The voltage conversion is realized through the principle of photoelectric conversion, and it is still under development.

According to the conditions of use

Indoor voltage transformer: installed in the indoor power distribution device, generally used at and below the voltage level;

Outdoor voltage transformer: installed in outdoor power distribution devices, mostly used at voltage levels and above.

According to the operation status of the primary winding to the ground

Voltage transformer with grounded primary winding: the end of the primary winding of a single-phase voltage transformer or the neutral point of the primary winding of a three-phase voltage transformer is directly grounded;

Voltage transformer with ungrounded primary winding: both terminals of the primary winding of a single-phase voltage transformer are insulated from the ground; all parts of the primary winding of a three-phase voltage transformer, including the terminals, are insulated from the ground, and the insulation level is The rated insulation level is the same.

According to magnetic circuit structure

Single-stage voltage transformer: The primary winding and the secondary winding can have multiple secondary windings wound on the same iron core as required, and the iron core is at ground potential. Single-stage type is used in my country for voltage levels and below;

Cascade voltage transformer: The primary winding is divided into several units with the same number of turns and connected in series between the phase and the ground. Each unit has its own independent iron core, with multiple iron cores, and the iron core carries high voltage. The secondary winding can be provided with multiple secondary windings as the last unit connected to the ground. This type of structure is commonly used in voltage levels in my country;

Combined transformer: The transformer combined with a voltage transformer and a current transformer is called a combined transformer. There are also transformers produced in conjunction with combined electrical appliances as a combined transformer.

Current Transformer

According to purpose

Current transformer or measuring winding of current transformer for measurement. Provide current information of the power grid to measuring and metering devices within the normal working current range;

Protection current transformer or protection winding of current transformer. In the power grid fault state, provide power grid fault current information to relay protection and other devices.

According to the insulation medium

Dry-type current transformer: common insulating material is dipped in varnish as insulation;

Cast-in current transformer: a current transformer molded with epoxy resin or other resin mixed materials;

Oil-immersed current transformer: insulated by insulating paper and insulating oil, generally outdoor type. Our country is commonly used in various voltage levels;

Gas-insulated current transformer: The main insulation is composed of gas.

According to the principle of current conversion

Electromagnetic current transformer: a current transformer that realizes current conversion based on the principle of electromagnetic induction;

Photoelectric current transformer: A current transformer that realizes current conversion through the principle of photoelectric conversion is still under development.

According to the installation method

Through-type current transformer: a current transformer used to pass through the screen or wall;

Pillar current transformer: It is installed on a plane or pillar and serves as a current transformer for the primary circuit conductor pillar;

Bushing type current transformer: a current transformer that does not have a primary conductor and primary insulation, and is directly sheathed on an insulated bushing;

Bus-type current transformer: A current transformer that has no primary conductor but primary insulation and is directly used on the bus. [2]

The characteristic of the active electronic current transformer is that the primary sensor is an air-core coil, and the high-voltage side electronic devices need to be powered by the power supply to work.