The main reasons why the secondary side of a current transformer (CT) cannot be open-circuited are as follows:
1. Working Principle
The current transformer converts the large current on the primary side into a standard small current (5A or 1A) on the secondary side. Compared to the secondary load, the primary internal resistance impedance of the current transformer is very high, and can be regarded as an infinite internal resistance current source. However, during a short circuit, due to the high short-circuit current on the primary side, the magnetic flux density increases significantly, sometimes even far exceeding the saturation value.
2. Analysis of potential problems that may arise from open circuit of the secondary side
The magnetic flux generated by the secondary current has a demagnetizing effect on the magnetic flux generated by the primary current. The excitation current is very small, and the total magnetic flux in the core is also very small.
This causes a significant increase in the magnetic flux within the core, making the core operate in a highly saturated state. According to the law of electromagnetic induction, a very high voltage (even up to several thousand volts) will be generated at the ends of the secondary winding.
3.Solutions
(1) It can be equipped with open-circuit protection devices;
(2) Develop relevant preventive measures for opening up.
4.Preventive Measures
The secondary circuit of the current transformer must not be equipped with fuse or other short-circuit protection devices.
(1) If they must be used together, the measuring instruments should be connected through an intermediate current transformer.
(2) The terminals of the secondary circuit of the current transformer should be equipped with test terminals.
(3) The connection wires of the secondary circuit of the current transformer should be ensured to have sufficient mechanical strength.
In conclusion, during the future operation and maintenance process, when it is necessary to carry out maintenance or calibration of secondary instruments for the equipment, the secondary windings or circuits of the current transformers must be short-circuited first. Work can only be carried out under the premise of taking corresponding safety measures.
LVZW-35 current transformer produced by Shaanxi West Power Tongzhong Electrical Co., Ltd. is a sensor used to measure large current in 35kV system. It is mainly used in substations, power systems and electrical equipment. The transformer adopts magnetic core type, which is characterized by high linearity, strong anti-interference ability, small size and simple structure. It is a current transformer with very high cost performance.
Product Advantages
LVZW-35 current transformer offers numerous advantages:
Safe and reliable
Electrical isolation: The current transformer can effectively isolate the primary circuit of high voltage and high current from the secondary measurement and protection circuit of low voltage and low current, avoiding direct contact of operators with high voltage current, greatly reducing the risk of electric shock, and ensuring the safety of personnel.
Strong anti-interference: Its working principle is based on electromagnetic induction, which will not affect and interfere with the measured circuit, ensuring the accuracy and reliability of the measurement results, and can work stably in a complex electrical environment, providing a strong guarantee for the safe operation of the power system.
High measurement accuracy
The output signal accuracy can reach 0.5, 0.2 or even higher, which can meet the application occasions with high requirements for current signal accuracy. Whether in the normal operation state of the power system or in the transient process when a fault occurs, the current can be accurately measured to provide accurate data support for relay protection, metering, monitoring, etc.
Wide measurement range
It can be applied to different voltage and current levels, and can meet the needs of various power systems and industrial application scenarios. Modern current transformers usually have a multi-speed adjustable measurement range. By adjusting the transformer ratio, it can adapt to current measurements of different sizes, and has strong versatility and flexibility.
Shaanxi West Power Tongzhong Electrical Co., Ltd.
Contact: Ms.Grace Liu (Director of Sales Department)
Tel: +86 917 3661109 Fax: +86 917 6739416
Mobile: +86 18091765882(WhatsApp/Wechat/skype )
Website:https://www.xdtzelectrical.com
