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How to use the current transformer correctly?
Proper use of current transformer

1. The connection of current transformer should obey the principle of series connection: the primary winding resistance should be in series with the circuit under test, and the secondary winding resistance should be in series with all instrument loads.


2. according to the magnitude of the measured current, choose the appropriate change, otherwise the error will increase. At the same time, one end of the secondary side must be grounded to prevent the high voltage of the primary side breaking into the secondary low voltage side once the insulation is damaged, causing personal and equipment accidents.


3. The secondary side is absolutely not allowed to open circuit, because once open circuit, the primary side of the current I1 all become magnetized current, resulting in a sudden increase in PHIM and E2, resulting in excessive saturation magnetization of the core, heating serious and even burning the coil; at the same time, the magnetic circuit after excessive saturation magnetization, so that the error increases. When the current transformer is working normally, the secondary side is close to short circuit. If the secondary side is suddenly opened, the excitation EMF will suddenly change from very small value to very large value. The magnetic flux in the core presents a seriously saturated flat-top wave. Therefore, the secondary side winding will induce a very high peak wave when the magnetic field passes through zero, and the value can reach thousands. Up to 10000 volts, endangering the safety of the staff and the insulation performance of the instrument.

In addition, one side open circuit causes the two side voltage up to several hundred volts. Once it touches, it will cause electric shock. Therefore, there are short circuit switches on the two side of the current transformer, so as to prevent the primary side from opening. In the process of using, the circuit load should be removed immediately after the two side of the circuit is opened, then the car will be stopped. Everything is handled well before it can be reused.


4. In order to meet the needs of measuring instruments, relay protection, circuit breaker failure judgment and fault filtering, 2-8 secondary winding current transformers are installed in generator, transformer, outlet, bus segment circuit breaker, bus circuit breaker, bypass circuit breaker and other circuits. For large current grounding system, it is generally arranged in three phases; for small current grounding system, it is arranged in two or three phases according to specific requirements.


5. The installation location of the protective current transformer should be set according to the non-protective area of the main protective device. For example, if there are two sets of current transformers, and the position permits, should be located on both sides of the circuit breaker, so that the circuit breaker in the cross protection range.


6. In order to prevent bus failure caused by bushing flashover of pillar current transformer, current transformer is usually arranged on the outlet line of circuit breaker or transformer side.


7. In order to mitigate the damage caused by internal faults of the generator, the current transformer used in the automatic regulating excitation device should be arranged at the outlet side of the generator stator winding. In order to facilitate the analysis and find the internal fault before the generator is merged into the system, the current transformer used for measuring instruments should be installed at the neutral side of the generator.
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Measuring current transformer
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Leakage (residual) protection device
The zero sequence current transformer
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How to use the current transformer correctly?
Introduction to installation specification of current transformer
Technical problems easy to appear in transformer test
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