What precautions should be taken when using miniature current transformers?
2022-06-14
Miniature Current Transformer What are the precautions for use?
Miniature current transformers are classified into many types, each with its own function. There are also many precautions for using miniature current transformers; safety must be ensured.
(1) Correct use of miniature current transformers
When connecting the current transformer, pay attention to its polarity markings. Otherwise, the current through the meters and relays connected to the secondary side will be abnormal, and in severe cases, accidents may occur.
2) One end of the secondary side should be grounded.
One end of the secondary side of the current transformer must be grounded to prevent high voltage from the primary side escaping to the secondary side in case of insulation breakdown between the primary and secondary coils, thus endangering personnel and equipment safety.
3) The secondary circuit of the miniature current transformer cannot be opened.
The secondary circuit of the current transformer must not be open-circuited during operation, because its current is zero when the secondary side is open-circuited, so it cannot generate magnetic flux to counteract the effect of the primary side magnetic flux, and a voltage of about 1000V can be induced on the secondary side, endangering personnel and equipment safety.
Moreover, the iron core of the miniature current transformer itself will generate serious heat. Therefore, when disassembling the instrument, the secondary coil of the current transformer must be short-circuited first.
(2) Types of miniature current transformers
1) Bushing miniature current transformer:
A miniature current transformer without primary conductor and primary insulation, directly fitted on the insulating bushing.
2) Column-type miniature current transformer:
A current transformer installed on a plane or column, used as a conductor column for the primary circuit.
3) Busbar miniature current transformer:
A current transformer without primary conductor but with primary insulation, used directly on the busbar.
4) Through-type miniature current transformer:
A miniature current transformer used to pass through panels or walls.
(3) Connection methods of miniature current transformers
Miniature Current Transformer The wiring should follow the series principle: the primary winding should be connected in series with the circuit being measured, and the secondary winding should be connected in series with all meter load current transformers.
1) In order to meet the needs of measuring instruments, relay protection, circuit breaker fault judgment and fault filtering devices, 2-8 secondary winding miniature current transformers are installed in the circuits of generators, transformers, outgoing lines, bus section circuit breakers, busbar circuit breakers and bypass circuit breakers. The installation location of the miniature current transformers for protection should be set as far as possible to eliminate the unprotected area of the main protection device. For example, if there are two sets of miniature current transformers, if the location permits, they should be located on both sides of the circuit breaker respectively, so that the circuit breaker is within the cross-protection range.
In order to prevent busbar faults caused by flashover of column-type current transformer bushings, current transformers are usually arranged at the outlet of the circuit breaker or on the transformer side.
2) In order to reduce the damage caused by internal faults of the generator, the miniature current transformers used for automatic excitation control devices should be arranged on the outlet side of the generator stator winding. In order to facilitate analysis and find internal faults before the generator is connected to the system, the current transformers for measuring instruments should be installed on the neutral point side of the generator.
3) According to the measured current, select the appropriate change, otherwise the error will become larger. At the same time, one end of the secondary side must be grounded to prevent high voltage from the primary side escaping into the low voltage side of the secondary side once the insulation is damaged, causing personal injury and equipment accidents.
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