The Basic Knowledge and Safety Common Sense of Current Transformer September 9,2022.

           In our daily life, we can often meet some problems about circuit aspects, these professional problems often ask for help from electrician and other professional personnel. Among the professional tools they use is a current transformer, which can measure the amount of current. It uses the principle of electromagnetic induction, the power generation, transformation, transmission, distribution and electricity lines in the difference of the current unified conversion into ampere-level easy to measure the current, and through the electrical insulation function to isolate the voltage on the line, in order to protect the safety of staff.

        

The current transformer consists of a closed iron core and two windings. The number of turns of the primary winding is small, and in series in the measuring line, all the current of the line will pass through it, and it will be converted into a smaller value of the secondary current. The number of turns of the secondary winding is relatively large, and the measuring instrument and the protection circuit are connected in series, and the circuit is always closed. When the current transformer is working, the current transformer will form a short circuit state due to the minimal impedance of the series coil of the measuring instrument and the protection circuit.

There are many types of current transformers, as follows:

I) Bush-type current transformer:

A current transformer fitted directly to an insulated bushing without a primary conductor or insulation.

II) Pillar type current transformer:

A current transformer mounted on a flat surface or on a pole that doubles as a primary conductor pole.

III) Busbar type current transformer:

A current transformer that has no primary conductor but primary insulation and is installed directly on a bus.

IV) Through-through current transformer:

A current transformer used to pass through a screen or wall.

Each type has its own role, and there are many precautions when using current transformers, so be sure to pay attention to safety.

I) Pay attention to connection polarity

When the current transformer is connected, pay attention to the polarity of the terminals of the first and secondary side coils. The polarity is marked with "±" or letters on the terminals of the primary and secondary coils of the current transformer. In our country, the primary coil end is indicated by L1 and L2, and the secondary coil end foot is indicated by K1 and K2. L1 and K1 have the same polarity, and L2 and K2 have the same polarity. The so-called "same polarity", that is, at the same instant these two ends are both high potential or low potential. For example, if L1 is more positive than L2, K1 is more positive than K2 at the same instant. As a current transformer, in terms of current direction, if the primary current 11 flows from L1 to L2 at a certain moment, the secondary current 12 flows from K2 to K1. This polarity labeling method is also known as "reduced polarity" labeling method. Therefore, when using current transformer wiring, we must pay attention to its polarity label. Otherwise, the secondary side of the instrument, relay through the current, is not normal current, serious will cause accidents.

II) One end of the secondary side should be grounded

One end of the secondary side of the CT must be grounded to prevent the high voltage on the primary side from crossing to the secondary side when the insulation between the primary and secondary coils breaks down, endangering the safety of people and equipment.

III) The secondary circuit of the current transformer should not be open

The secondary circuit of the current transformer must not be open during operation, because the current of the secondary side is zero when the secondary side is open, so the magnetic flux cannot be generated to offset the effect of the primary side magnetic flux. However, the secondary side can induce a voltage of about 1000V, which endangers the safety of people and equipment. And the core of the current transformer itself will be seriously hot. Therefore, when disassembling the instrument, it is necessary to short-circuit the secondary coil of the CT first.


We manufacture various precision current transformers and voltage transformers, which are widely used in electric power, energy, telecommunication, railway, industrial control and other fields.

If you have any needs, pls be free to contact us, we welcome customers to customize.

Email: sales008@mycoiltech.com

Sales engineer: Bob Bao

Tel: +86 551 6291 5885

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