VFD line reactor question

[peoplehouse]

Hello fellows, can anyone explain what a line reactor for VFD's actually does? I just had one burn up and don't quite know enough about them. Could it be to prevent exessive current or smooth out the frequency? I have one installed on about a 400ft run of 12awg wire for a small 1 HP motor. When I bypassed the burnt line reactor the motor starter OL would trip.
Any tips would be very welcoming
Thank you,
Jeff

 

[504bloke]

It cancels out some of the capacitance of the cable ie its an inductor. Normally only needed on long cable runs. Most drive manuals give a max length of cable run and list a reactor in mH that is required above this.

 

[DickDV]

Line reactors are simply high frequency filters. On VFD motor leads, blocking the high frequency components of the drive output pulses from running down the leads toward the motor helps to reduce ringing thus protecting motor insulation from overvoltage damage, helps to reduce the RFI/EMI radiation from the motor leads into the surrounding environment, and helps to reduce capacitive coupling of the output pulses into the ground system where they can create all kinds of havoc with sensitive instrumentation.

When used on the drive input leads, their primary purpose is to block high frequency current harmonics from passing backward into the power supply network causing problems with other electronic loads and overheating the supply transformer.

 

[jawolthuis]

You said:

"When I bypassed the burnt line reactor the motor starter OL would trip."

Are you sure that the motor is not burned up? This could be what caused your line reactor to burn up in the first place. Put an amp meter on the line with the motor running and compare it with the nameplate rating.

 

[peoplehouse]

Hello jawolthuis. The first thing I did was check the OL device, contactor, motor and megged the conductors from contactor to motor. Then I discovered the line reactor was smoked. On an A/B powerflex 70 I was getting an F041 fault-excessive current between U & V. I've found out that the line reactor was installed because of the all the nuisance tripping on the OL. I replaced the reactor and it's running like a champ. DickDV's explanation is really good.
Always good to learn something new. Thanks for the responces.
Jeff

 

[rwy34ils]

Just to clarify...if it is installed before the VFD then it is called a line reactor. If it is installed between the VFD and motor then it is called a load reactor.

 

[DickDV]

Looking further into the OP, since this is a 1hp VFD with 400ft leads to the motor, the most likely reason that the drive is faulting on OL is due to the high frequency coupling of the output pulses into ground.

Whatever current that couples into the ground originates in the drive and causes the drive to read that current as if it was flowing to the motor. This makes the OL calculation in the drive wrong and causes faulting when the motor is not actually overloaded. I have seen this demonstrated by disconnecting the motor at the motor junction box and then reading output current on the drive. At 400ft of motor lead length, I would expect to see somewhere around .6amps flowing out of the drive. It must be going to ground since the motor isn't connected.

If this leakage current is well balanced, the drive may not fault on ground fault. If it's imbalanced, the ground fault may occur faster than the OL fault.

The reactor or, in even worse conditions, a dv/dt filter is exactly the right solution to this problem.