When we talk about limiting faulty current, the most common component used in the power industry is a quality power reactor. It is mainly used for avoiding faults involving high fault currents and impedance. However, for this purpose, there is also another component called as resistor that is quite popular too. So, how to know what component should be used for current limiting purpose – a resistor or a reactor? To make you understand this concept, I will discuss the pros and cons of resistor and reactor. In this way, you will be able to determine which one is suitable for your application.
Pros of reactor and resistor:
Reactor:
- A quality power reactor utilizes the inductive reactance of coil to create impedance for fault current. It is used on power lines to bring down the short circuit current to a safe zone. Since it uses inductive reactance, it is essentially a combination of many inductors but with some extra mechanical linkages.
- It is most suitable for the applications which require thousands of amperes of current to flow within it for a short period of time.
Resistor:
- A resistor uses the actual resistance of the material from which it is designed to control the fault current.
- It can be universally applied without any limitation.
Cons of reactor and resistor:
Reactor:
A reactor is well-suited only for the systems where you need to limit 25% to 60% of the three-phase fault current. If the ground fault current is smaller than 25% of three-phase fault current then neutral winding can be subjected to transient over-voltages ( when voltages are not allowed to discharge, thereby the arc re-fires and charge is continually build to create over-voltages). Transient over-voltages are capable of damaging the neutral winding of the transformer. In that case, you need to install a surge resistor along with the reactor to achieve the desired reduced fault current. This will prevent transient over-voltages.
Resistor:
The only disadvantage of a resistor is that it is very expensive. It must possess sufficient mass and weight to absorb large fault current energy. Thus, as the fault current value and time rating increases, the price also increases.
A tip to make your decision easy:
For controlling fault current of very low magnitude, a resistor should be chosen. However, where you need to limit the fault current of magnitude of thousands amps, you must choose a quality power reactor. You can use a reactor in either case as it is more economical and also suitable. Just remember that I am discussing the shunt air core reactor in the transformer neutral as series reactor is also expensive and neutral ground reactor’s price increases with the increase in continuous current, time and impedance rating.
After considering all pros and cons and the tip given below, you can easily decide what is suitable for your application.