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Instrument transformer

Instrument transformers are used in power systems as signal sources for circuits such as measurement, control, indication, and relay protection. It can insulate instruments and relays from the circuit under test with high voltage and high current, and can make the specifications of instrument and relays much smaller and uniform in specifications than those used in directly measuring high voltage and high current circuits. Instrument transformer is mainly used when measuring high voltage and high current, also known as instrument transformer.

Description

Usage:Current
Phase:Single
Coil Structure:Toroidal
Coil Number:Autotransformer

Definition

Instrument transformer refers to a special purpose transformer. It has two main purposes: one is to expand the range of AC electrical instruments, and the other is to isolate high voltage and high current and make it low voltage and small current. Later, as a signal for relay protection, automatic devices and control circuits.

Features

1.Three built in fixing methods: panel/din rail/busbar

2.Built in hinged terminal cover

3.Compact design

4.Primary current from 5A to 3000A

5.A range of compact plastic case current transformer.

6.Its volume is much smaller than general model.

Function and role

1. The instrument transformer secondary provides a lower voltage, which can reduce the insulation requirements for the measuring instrument and make the measurement operation safer.

2. The power supply line can be isolated from the measuring instrument through the instrument transformer.

3. The measuring instrument can be led from the instrument transformer to other places with wires in order to achieve long-distance measurement.

4. The secondary voltage or current of the transformer can be standardized (usually 110V or 5A) so that the measuring instruments can be replaced with each other.

Instrument transformers are used in power systems as signal sources for circuits such as measurement, control, indication, and relay protection. It can insulate instruments and relays from the circuit under test with high voltage and high current, and can make the specifications of instrument and relays much smaller and uniform in specifications than those used in directly measuring high voltage and high current circuits. Instrument transformer is mainly used when measuring high voltage and high current, also known as instrument transformer.

Classification

Instrument transformers are divided into current transformers and voltage transformers.

Current Transformer
The structure of the current transformer is similar to that of ordinary double-winding transformers, and it also has iron cores and windings, but it has a small number of primary winding turns, only one to several turns, and the wires are thick and connected in series in the circuit under test. Over the measured current, the magnitude of the measured current is determined by the user load.

The secondary winding of the current transformer has a large number of turns. It is connected in series with the current coil of the ammeter or power meter as a closed circuit. Since the impedance of these coils is very small, the secondary side is approximately short-circuited.

The current transformer has the following working characteristics.
(1) The primary side input and secondary side output of the transformer are both currents, and the voltage is almost zero, which is different from ordinary transformers, indicating that it transmits and changes current instead of voltage.
(2) The transformer works in a short circuit state, that is, the total magnetic flux generated by the secondary side current and the primary side current is almost zero, so the secondary side cannot be opened. Once opened, the magnetic potential balance is broken and the total magnetic potential is not Zero, the magnetic circuit will be severely saturated. Because the primary current is large and does not change with the change of the secondary side, a strong magnetic flux is generated in the iron core. This magnetic flux generates a high voltage on the secondary side, which can reach hundreds of volts or even thousands of volts. It will endanger the safety of the instrument and personnel, and also cause the core to overheat and age the insulation. Therefore, the secondary side of the current transformer must not be allowed to open.

Voltage transformer
The principle of the voltage transformer is exactly the same as that of the ordinary step-down transformer, except that its transformation ratio is more accurate; the primary side of the voltage transformer is connected to a high voltage, and the secondary side is connected to a voltmeter or other meter (power meter). , Electric meter) voltage coil.

The voltage transformer converts the high voltage in a proportional relationship into a standard secondary voltage of 100V or lower for protection, metering, and instrumentation. At the same time, the use of a voltage transformer can isolate high voltage from electrical workers. Voltage transformers Although it is also a device that works according to the principle of electromagnetic induction, its electromagnetic structure relationship is exactly the opposite of that of a current transformer. The secondary circuit of a voltage transformer is a high-impedance circuit. The magnitude of the secondary current is determined by the impedance of the circuit. When the load impedance decreases, the secondary current increases, so that the secondary current automatically increases by one component to meet the electromagnetic balance relationship between the primary side and the secondary side. It can be said that the voltage transformer is a limited structure and use form Special transformer.

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