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The difference between voltage transformer and current transformer

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The difference between voltage transformer and current transformer

Date of release:2018-06-11 Author:Compson Technology Click:

Voltage transformer

Current Transformer


The voltage transformer (pt) and the current transformer (ct) are identical in principle. They all use the principle of electromagnetic conversion. The difference is that the magnetic circuit is different, and the magnetic flux of the primary and secondary flows of the voltage transformer The pass is the same, the potentials on both sides are proportional to the number of turns, so the voltage transformer made according to this principle can measure the voltage, the voltage transformer is at the voltage to be measured, and the corresponding voltage can be induced twice. The voltage ratio and the turns ratio are reciprocal; and the current transformer is such that the current to be measured flows through the inside of the coil of the transformer, so that the corresponding current is generated twice, the primary current * the number of turns = the secondary current * the second number of turns, according to The magnetic flux can be analyzed that the voltage transformer can not be short-circuited, the short circuit returns to generate overcurrent, the current transformer can not open, and the open circuit will generate high voltage. The voltage transformer has various voltage levels of 220kv/110v, 110kv/110V, 10kv/100v, etc. There are two types of current transformers, 1A and 5A, such as 100/5, 100/1, 200/1 and so on.


The secondary winding must be reliably grounded to prevent the high voltage on the primary side from jeopardizing personal safety due to insulation damage.

It is absolutely not allowed to open the road. When the circuit is open, the transformer becomes unloaded. The magnetic flux is much higher than the rated time (1.4-1.8T). In addition to generating a large amount of iron loss and damaging the transformer, it also induces dangerous high voltage in the secondary winding, endangering personal safety.

When installing a current transformer, the accuracy level should be considered. High-precision measuring instruments with low precision for protection. Care should be taken when choosing.

When installing the current transformer, pay attention to the polarity (the same name end), the terminals on the primary side are L1, L2 (or P1, P2), and the primary side current flows from L1 and flows out from L2. On the other hand, the terminal on the secondary side is K1, K2 (or S1, S2), that is, the terminal on the secondary side flows out from K1 and flows in from K2. L1 and K1, L2 and K2 are of the same polarity (the same name end), and must not be mistaken. Otherwise, if the meter is connected, the meter will be reversed.

The primary winding of the current transformer has a single turn and a multiple turn, and the LQG type is a single turn. When using the LMZ type (through-the-heart type), pay attention to whether there is threading data on the nameplate, and if so, wear the required number of turns as required. Note: The number of piercings is based on the number of roots passing through the hollow, not the number of turns in the periphery (otherwise the error will be one).

The secondary winding of the current transformer has one winding and two windings. If there are two windings, one of the windings is used for high precision (small error value) and the other is low precision (error). Larger value) is generally used for protection.

The current transformer connection line must be connected by a 2.5mm2 copper core insulated wire. Some electrical industry departments must use a 4mm2 copper core insulated wire, but generally there is no such necessity (except in special cases).

Current transformer connection

Current transformers mainly have the following four wiring methods:

(1) Full star connection.

(2) Two-phase two relays are not completely star-connected.

(3) Two-phase one relay current difference wiring.

(4) Delta wiring.

(5) Three-phase parallel connection to obtain zero-sequence current.

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Key word:Voltagetransformer,CurrentTransformer,Transformer

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