1. Product Overview

The power branches of various electrical equipment such as transformers, mutual inductors, capacitors, etc. in the power system have a small current under normal working conditions. However, once a short circuit occurs, the impedance of the circuit is small, resulting in a particularly large short-circuit current, which will cause great difficulties in selecting disconnect protection equipment; At the same time, the traditional disconnection protection equipment has a disconnection action time of several tens of milliseconds, which cannot quickly and effectively limit the amplitude of short-circuit current. The extremely large short-circuit current will cause impact damage to the insulation of electrical equipment such as generators and transformers; In addition, higher requirements have been placed on the dynamic and thermal stability of other equipment in the system, which inevitably increases equipment investment and is unsafe.
Based on the above issues, Shanghai Songbang Electric Co., Ltd. has developed and produced a FURB high-capacity high-voltage current limiting fuse combination protection device with independent intellectual property rights. This equipment is specifically designed to solve the problems of insufficient ability to break large short-circuit currents, slow time, and lack of overvoltage protection function of traditional fuses and circuit breakers

2. Product Usage and Performance
The FURB high-capacity high-voltage current limiting fuse combination protection device is mainly suitable for circuits with large short-circuit capacity in 3-35kV power systems, such as excitation transformers, plant transformers, isolation transformers, voltage transformers, and capacitors; It can withstand frequent connection and disconnection of normal working current, and can automatically limit current and quickly and reliably disconnect and protect against overvoltage for extremely large short-circuit currents. It can also be used as phase to phase short circuit protection and backup protection for power circuits.

3. Main features of the product
The FURB high-capacity high-voltage current limiting fuse combination protection device consists of a specially designed high-voltage high breaking capacity current limiting fuse, a specially designed high-voltage high-energy zinc oxide overvoltage protector connected in parallel at both ends, and a limit signal switch combination. Once a short circuit occurs in the circuit, the high-voltage current limiting fuse quickly melts within 2mS, immediately cutting off the short-circuit current. At the same time, a specially designed high-voltage high-energy zinc oxide varistor connected in parallel at both ends of the high-voltage current limiting fuse operates to limit the operating overvoltage generated when the fuse is disconnected within the specified value, and absorbs the magnetic field energy that decays the cutoff current to zero in the system, further improving the energy absorption safety margin of the fuse; At the same time as the high-voltage current limiting fuse is opened, the limit signal switch sends an action signal, which can be connected to the load switch (or circuit breaker) for linkage or to the control room for maintenance and fault finding.
Due to the inherent ampere second characteristic of high-voltage current limiting fuses, there is no need for any external mechanical or electrical protection equipment to operate them. Therefore, the reliability of high-voltage current limiting fuses is extremely high, and there will be no refusal or misoperation. Moreover, the operating speed of high-voltage current limiting fuses is much higher than that of mechanical circuit breakers. The short-circuit current is cut off before it rises, and the current amplitude can be limited to about 15% less than the expected transient peak of the short-circuit current, with a time not exceeding 2mS. This ensures that electrical equipment such as transformers, voltage transformers, and capacitors are no longer affected by the peak short-circuit current, avoiding damage to electrical equipment caused by several cycles of high current impact; Due to the current limiting and fast nature of high-voltage current limiting fuses, I2t is very small, which can ensure that electrical equipment such as transformers, voltage transformers, and capacitors do not explode, and the busbar connection does not need to consider dynamic and thermal stability issues.

4. Main working principle of FURB high-capacity high-voltage current limiting fuse combination protection device
The high-voltage current limiting fuse combination protector mainly uses the arc voltage of the continuous current arc at the moment of fuse melting to limit and cut off short-circuit current and provide overvoltage protection. The higher the arc voltage, the better. Excessive arc voltage is a type of overvoltage that can damage the insulation of electrical equipment and expand accidents. For this purpose, we have parallel connected a specially designed high-voltage high-energy zinc oxide varistor FR at both ends of FU, and its volt ampere characteristics are shown in Figure 2. As shown in the figure, when the voltage at both ends of FR rises to the set value, FR automatically switches from cutoff to conduction, limiting the overvoltage of FU and preventing it from damaging the equipment insulation. At the same time, FR conduction reduces the energy absorbed by FU through shunt. In short, parallel FR makes the operation of the protector safer and more reliable.

Figure 1 Schematic diagram 2 Voltage current characteristics of zinc oxide varistor

FURB high-capacity high-voltage current limiting fuse combination protection device