Detection and Marking of Current Transformers

1. Detection of current transformers

Current transformers play the role of current conversion and electrical isolation. It is convenient for the secondary instrument measurement to be converted into a relatively uniform current to avoid the danger of directly measuring the current transformer line. The detection method of the current transformer has the following aspects.

1) Transformer comprehensive tester: measure the error between the standard transformer and the tested transformer, and display the working current.

2) Standard current transformer: It is used as a standard in transformer verification, and its accuracy is generally more than two levels higher than the measured one. It is designed with multiple variable ratio taps to adapt to the verification of different transformers.

3) Voltage regulator: It is used to adjust the test current. Generally, it is installed in the same console with the protection and switch. There are two voltage regulators for coarse adjustment and fine adjustment to meet the adjustment fineness. When measuring below the rated current of 2500A, it can be made by a combination of 10KVA general-purpose voltage regulators. Larger currents must be specially made, generally 30~6OKVA.

4) Current booster: Cooperate with the voltage regulator to generate various required test currents. Its capacity and cost increase with the increase of current.

5) High-current connection cable: Connect hundreds or thousands of amperes, and the price of the cable cannot be ignored.

6) Load box: simulate the actual working state of the current transformer under test.

2. The marking of current transformers

1) The model of the current transformer consists of the following parts, and the characters and symbols of each part indicate the content.

The first letter: L-current transformer.

The second letter: F-air pressure type; M-bus type (through the heart type).

The third letter: C-Porcelain Insulated ; Z-Pouring.

Fourth letter: B-protection; D-gap.

Fifth letter: number - voltage level (kV).

For example, LMZ-0.66 represents a core current transformer 0.66kV injected with epoxy resin.

Rated working voltage, mutual inductor allows long-term operation of the same voltage RMS.

The rated primary current is the primary current value as the performance standard of the transformer.

The rated secondary current, as the secondary current value of the mutual inductance performance standard, is generally 5A or 1A.

Rated current ratio, the ratio of rated primary current to rated secondary current.

Nominal load, the load value upon which the correct level of the mutual inductor is determined. The circuit impedance other than the secondary K1 and K2 terminals of the current transformer is all the load of the current transformer. Usually, it is seen as power volt-ampere or impedance ohm.

Rated power factor, the ratio of the effective part of the secondary rated load impedance to the rated impedance.

Accuracy level, under the specified conditions of use, the error of the mutual inductor is within the limit specified by the level to measure power engineering, and the commonly used levels are 0.2, 0.5, 0.2S, 0.5S, etc.

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