The function of generator current transformer is to convert the primary current with large value into the secondary current with small value through a certain transformation ratio for protection, measurement and other purposes. What problems should be paid attention to when using the generator current transformer?
1. The wiring of current transformer shall comply with the principle of series connection: the primary winding resistance shall be connected in series with the circuit under test, while the secondary winding resistance shall be connected in series with all instrument load current transformers.
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 at the primary side from entering the low voltage side of the secondary once the insulation is damaged, causing personal and equipment accidents.
3. Open circuit is absolutely not allowed at the secondary side, because once open circuit occurs, all the current at the primary side will become magnetizing current, resulting in over saturation magnetization of the iron core. The heating is serious or even the coil is burnt.
At the same time, the error increases after the magnetic circuit is supersaturated and magnetized. When the current transformer works normally, the secondary side is nearly short circuited. If it is suddenly opened, the excitation electromotive force changes from a small value to a large value, and the magnetic flux in the iron 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, which can reach thousands or even tens of thousands of volts, threatening the safety of staff and the insulation performance of instruments.
In addition, the open circuit on the primary side makes the secondary side voltage reach hundreds of volts, which will cause an electric shock once touched. Therefore, the secondary side of the current transformer is equipped with a short circuit switch to prevent open circuit at the primary side. In the process of use, once the secondary side is open circuit, the circuit load shall be removed immediately, and then the vehicle shall be stopped for processing. It can be reused only after everything is handled.
4. In order to meet the needs of measuring instruments, relay protection, circuit breaker failure judgment, fault filtering and other devices, 2-8 secondary winding current transformers are set in generator, transformer, outgoing line, bus sectionalized circuit breaker, bus circuit breaker, bypass circuit breaker and other circuits. For high current grounding system, three-phase configuration is generally adopted. For small current grounding system, it shall be configured as two phase or three phase according to specific requirements.
5. The installation site of current transformer for protection shall be set to eliminate the unprotected area of main protection device as far as possible. For example, if there are two groups of current transformers and the position is allowed, they should be set at both sides of the circuit breaker to make the circuit breaker in the cross protection range.
The above are the precautions for the use of generator current transformer that Guangxi Dingbo Power Equipment Manufacturing Co., Ltd. has arranged for you. I hope it will be helpful to you.
Founded in 2006, Guangxi Dingbo Power Equipment Manufacturing Co., Ltd. a wholly-owned subsidiary of Guangxi Dingbo Power Group, is one of the earliest manufacturers of generating sets in China. Over the past 10 years, the company has won the recognition of users by relying on advanced testing equipment, modern production technology, professional manufacturing technology, perfect quality management system, strong R&D technology strength. For more details, please contact us with email@example.com.