The use of line reactors and load reactors confuses a lot of people. Sometimes, it is hard to figure out which reactor should be installed for protecting the drive and which is better to use for protection of the motor. So, in this blog, we will discuss when to use a line reactor and a load reactor.
To make things easier, first, you should know that a line reactor is also known as an input reactor and load reactor as an output reactor. Both input and output reactors serve different purposes. While an input reactor is designed for protecting the drive, an output reactor is used for protecting the motor. But, to determine their accurate application, you should know about other details too.
Line Reactors a.k.a. Input Reactors:
These reactors are built to safeguard a variable frequency drive (VFD) from input power line disturbances responsible for nuisance tripping or damage to the drive. Besides, it also helps in reducing the harmonics that the VFD produces back onto the line.
Their size is determined on the basis of HP and voltage ratings of the drive in use. Usually, most drive manufacturers use 3% or 5% reactors. One can use these reactors in the following circumstances:
- When the input power line is prone to disturbances such as spikes, surges, transient current, etc.
- When power of the supply line is very high (greater than 10 times the kVA rating of the connected VFD)
- When harmonic distortion is an issue
Line reactor should be connected only in series between the input source and variable frequency drive controller and it should be mounted as close as possible to the drive.
Load Reactors a.k.a. Output Reactors:
If the wiring distance between variable frequency drive and the motor is very long, an output reactor is required to be installed so that the motor can be protected. A high frequency PWM three-phase output is produced by the drive when in function and noise spikes are generated on the leading edge of the signals. When the cable length is long and it has additional capacitance, these noise spikes get amplified. As a result, the voltage can exceed the motor’s peak voltage rating and cause insulation breakdown.
You should remember just a simple thing that an output reactor installation is required when the motor wiring is 100 feet; however, this value varies depending on the motor. If the motor meets NEMA MG-1 Part 31 standard, one can have around 300 feet of cabling without the need for output reactor and if not, it is best to consider 100 feet as the maximum cable length, exceeding which reactor installation becomes necessary.
By now, you must have a clear understanding of when and where you should use a line reactor and a load reactor. So, next time, you need to install one, don’t make a mistake.