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Current transformer is an instrument which converts the large current at the primary side into the small current at the secondary side according to the principle of electromagnetic induction. The current transformer consists of a closed core and windings. Baoding Daheng Electric introduces the correct use of current transformers. 1. The wiring of the ct should follow the principle of series connection: the primary winding resistance should be connected in series with the circuit under test, while the secondary winding resistance should be connected in series with all instrument loads 2. Select the appropriate change according to the measured current, 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 from jumping into the secondary low voltage side once the insulation is damaged, resulting in personal and equipment accidents 3. Open circuit is absolutely not allowed on the secondary side, because once open circuit, the current I1 on the primary side all become magnetization current, causing a sudden increase of φ M and E2, resulting in over-saturation magnetization of the core, serious heating and even burning coil; At the same time, the error increases after over-saturation magnetization of magnetic circuit. Current transformer in normal work, the secondary side is akin to short circuit, if all of a sudden make its open circuit, the excitation electromotive force by the numerical small change value of great value in the core flux present serious saturation flat wave, therefore the secondary winding through zero in magnetic induction out high steeple wave, its value can reach thousands or even tens of thousands of volts, Endanger the safety of the staff and the insulation performance of the instrument. In addition, the primary side open circuit makes the secondary side voltage up to several hundred volts, once touched will cause electric shock accident. Therefore, the secondary side of the CT is equipped with a short-circuit switch to prevent the primary side from opening. In the process of use, once the secondary side open should immediately remove the circuit load, and then stop processing. Take care of everything before you can use it again. 4. In order to meet the needs of measuring instruments, relay protection, failure judgment and fault filtering devices of circuit breakers, 2-8 secondary winding current transformers are installed in the circuits of generators, transformers, outgoing lines, bus section circuit breakers, bus circuit breakers, bypass circuit breakers and so on. For large current grounding system, generally according to the three-phase configuration; For the small current grounding system, according to the specific requirements of the two phase or three phase configuration 5. The installation site of the current transformer for protection should be set according to the non-protection zone where the main protection device is eliminated as far as possible. For example, if there are two sets of current transformers, they should be placed on both sides of the circuit breaker so that the circuit breaker is in the cross protection range 6. In order to prevent busbar failure caused by flashover of busbar of pillar ct, ct is usually arranged at the outgoing line of circuit breaker or transformer side 7. In order to reduce the damage caused by the internal failure of the generator, the current transformer used for automatically regulating the excitation device should be arranged at the outgoing side of the stator winding of the generator. In order to facilitate analysis and find internal faults before the generator is integrated into the system, the current transformer used for measuring instruments should be installed at the generator neutral point side. |
