Current Transformer

A current transformer is an instrument that converts a large current on the primary side into a small current on the secondary side for measurement based on the principle of electromagnetic induction.

A current transformer consists of a closed iron core and windings. Its primary side winding has few turns, and it is connected in the line of the current that needs to be measured.

Therefore, it often has all the current of the line flowing through it, and the secondary winding has a large number of turns. It is connected in series in the measuring instrument and the protection circuit. 

When the current transformer is working, its secondary circuit is always closed, so the measurement The impedance of the series coil of the instrument and the protection circuit is very small, and the working state of the current transformer is close to a short circuit.

The current transformer is to convert the large current on the primary side into a small current on the secondary side for measurement, and the secondary side cannot be opened.

Introduction

The principle of current transformer is based on the principle of electromagnetic induction.

A current transformer consists of a closed iron core and windings.

Its primary winding has a small number of turns, and it is connected in the line of the current that needs to be measured, so it often has all the current of the line flowing through it, and the secondary winding has a large number of turns. 

When the transformer is working, its secondary circuit is always closed, so the impedance of the series coil of the measuring instrument and the protection circuit is very small, and the working state of the current transformer is close to a short circuit.

Working principle

In the lines of power generation, substation, transmission, distribution and consumption, the current varies greatly, ranging from a few amperes to tens of thousands of amperes.

In order to facilitate measurement, protection and control, it needs to be converted into a relatively uniform current. 

In addition, the voltage on the line is generally relatively high, such as direct measurement, which is very dangerous. 

The current transformer plays the role of current transformation and electrical isolation

For pointer-type ammeters, most of the secondary currents of the current transformers are in the ampere level (such as 5A, etc.).

For digital instruments, the sampled signal is generally at the milliamp level (0-5V, 4-20mA, etc.). 

The secondary current of the miniature current transformer is milliampere, which mainly acts as a bridge between the large transformer and the sampling.

Similar to the transformer, the current transformer also works according to the principle of electromagnetic induction. 

The transformer transforms the voltage and the current transformer transforms the current.

The winding of the current transformer connected to the measured current (the number of turns is N1) is called the primary winding (or the primary winding, the primary winding); the winding connected to the measuring instrument (the number of turns is N2) is called the secondary winding (or secondary winding). winding, secondary winding).

The current ratio of the primary winding current I1 to the secondary winding I2 of the current transformer is called the actual current ratio K. 

The current ratio of the current transformer when it works under the rated current is called the rated current ratio of the current transformer, expressed by Kn.

Kn=I1n/I2n

Current transformer, referred to as CT for short, is used to convert a primary current with a larger value into a secondary current with a smaller value through a certain transformation ratio, which is used for protection, measurement and other purposes. For example, a current transformer with a ratio of 400/5 can convert an actual current of 400A into a current of 5A.

Current Transformer Kit RJ45

Power Measuring System 8 pin RJ45 connector

Accessories for low-voltage current transformer 

Split-core current transformer RJ45 Plug adaptor

Adapter Connector RJ45 Male Terminal Block 8 pin

RJ45 Plug adaptor for measuring split-core current transformer