What is the function of current transformers?
1. The role of current transformers
A Range conversion function
Convert the primary side high current (such as 1000A) into standard secondary current (usually 5A or 1A) in precise proportion, solving the problem of difficulty in direct measurement of large current. For example, a 500/5 transformer can convert 400A primary current into 4A secondary current for instrument measurement
B Electrical isolation
Through core magnetic coupling, the primary and secondary circuits are electrically isolated to avoid high voltage direct contact with the measuring instrument and ensure the safety of operators.
C Standardized interface
Provide unified secondary side parameters (such as 5A or 1A) to facilitate access to various measuring instruments and relay protection devices, realize equipment miniaturization and wiring economy.
D Protection and monitoring
Provide signal source for relay protection and automatic devices, such as zero-sequence current detection or differential protection.
2. Precautions for use
A It is strictly forbidden to open the secondary side.
When the circuit is open, the magnetic flux increases sharply, which may generate thousands of volts of high voltage, endangering equipment and personal safety. Short-circuit the secondary side before disassembling the instrument.
B Reliable grounding The secondary circuit needs to be grounded at a single point (usually the distribution cabinet grounding busbar is selected) to prevent high voltage from entering the secondary side when the insulation is broken. C Load and capacity matching The secondary load impedance must meet the error requirements. Excessive capacity will lead to increased measurement errors or protection malfunction. D Transformation ratio and polarity verification The transformation ratio selection must take into account the maximum load (not exceeding 2/3 of the nominal value) and the minimum short-circuit current resolution. The polarity of the differential protection circuit must be strictly checked to prevent protection refusal/malfunction. E Other key requirements (1) Avoid overload operation that affects accuracy or damages equipment. (2) Residual magnetism management: The protection-level CT needs to test the residualmagnetism coefficient to prevent transient saturation. (3) The primary winding is connected in series with the circuit under test, and the secondary winding is connected in series with the instrument.
LZZBJ4-35 current transformer produced by Shaanxi West Power Tongzhong Electrical Co., Ltd. is a kind of sensor used to measure large current, mainly used in substations, power systems and electrical equipment, etc. The transformer adopts magnetic core type DC current transformer, which is characterized by high linearity, strong anti-interference ability, small volume, simple structure, etc., and it is a kind of very high cost-effective current transformer.
1.Convenient equipment standardization
The current transformer can convert large current into standard small current signals (such as 5A or 1A), unifying the specifications of secondary instruments, relays and other equipment, which is conducive to the standardized design and production of these equipment, reducing the production cost and maintenance difficulty of the equipment.
2.Easy to realize automatic monitoring and control
The standard signal output by it is easy to connect with various automatic monitoring and control systems, and can realize remote monitoring and automatic control of power systems and industrial equipment, improving the intelligence level and operation management efficiency of the system.
