Line Reactor for VFD

[tom baker]

I have a VFD installed to operate a 60 HP 460V vertical motor, the motor is 25 ft from the VFD. The VFD is sized for a constant torque load.
The location is at a pumping station, 600 Ampere service with 3 other across the line 40 hp motors. This location can have power outages and phase failures.
There have been two VFD failures at this location, where the SCR and IGBT's fail.This location does not have a line reactor on the input to the drive, or TVSS on the incoming power.

Question: Would a 5% line reactor help protect the VFD?
Should a line reactor and TVSS be installed as a good practice?

 

[charlie tuna]

Re: Line Reactor for VFD

toshiba will double the warrentee time if you install reactors on the line side of their drives. does that tell you anything? larger drives have them built into their design. remember the drive you have nearly doubles the incoming voltage applied to the motor. think what happens on a power bump where your spike is seventy or eighty volts above normal. the igbt's can't handle it and the motor doesn't neither! the cost of a reactor is about $300.00 ans simple to install---i never figured a drive without including a reactor............

 

[petersonra]

Re: Line Reactor for VFD

VFDs do not much care about phase failures or power outages. They are fairly well protected against these kind of problems.

Many have built in surge suppression, at least in smaller sizes.

Line reactors were often necessary to reduce the source impedence and thus the available short circuit current, but again many more modern VFDs either have them built in or do not require them.

Best bet is to call the tech support line for the VFD manufacturer. The sales weenies are of little help in this regard and will just waste your time and give you bad info. Go to someone who can actually help you.

Some VFDs require terminations at the motor. This is dependant on a number of factors, length of wire being the most obvious.

 

[steve66]

Re: Line Reactor for VFD

What does the VFD do when there is a power or phase failure? Does it wait to make sure the motor is stopped, or does it immediately try to restart the motor? I think that can cause problems, and some VFD's have automatic "in-phase" restarting for motor loads. Even then, you might not want the motor to restart until any water hammering is over.

Also, I assume the motor has a clutch on it so it doesn't spin backwards as the check valve closes.

Steve

Steve

 

[petersonra]

Re: Line Reactor for VFD

many vfds have ride through capability where the drive stays on for some short period of time on a power failure (usually some fraction of a cycle).

usually they also have auto restart capability, again selectable. i think most of the time it has some time delay before restart is allowed.

 

[tom baker]

Re: Line Reactor for VFD

A phase monitor prevents drive operation on a phase fail or undervoltage.
A ratchet on the motor prevents reverse operation
What I think has happened is the driver board (it controls the IGBT's) went bad and caused the IGBT's to short. The driver board is solid state.
The IGBT's are $1,000 each, there are three.
We have a motor terminator at the motor to absorb the high voltage ringwave.
Last fall the drive developed a noise, similar to a bad fan. I called tech support they said it was normal. After the drive failed, a second tech support person said the noise was due to the driver board failing, causing the diode bridge to fire incorrectly.
I will call tech support and discuss with them.

 

[BAHTAH]

Re: Line Reactor for VFD

Series Line Reactors are typically used to reduce harmonics on the AC line. Because you have three additional 40hp motors which I assume are commonly coupled to the same bus, depending on their frequency of operation and if they start across the line as opposed to soft-starting you may be getting Transient Voltage Spikes that are effecting your AFD over time. The drives I work with for water pumping have oversized DC Link filters built into the drive to protect against hight potential spikes and can withstand a spike of about 2.3 times the rated voltage but as with most electronics if you hit it enough times something is going to give. I would suggest placing a high-speed recorder on the system so you can see what is hitting your drive. I think there are companies where you can rent these recorders. That way you can get an actual printout and see what is happening.

 

[John Valdes]

Line reactors are cheap and effective insurance. Line reactors change the line impedance and will knock down spikes in current and voltage. I have witnessed this many times with a scope. When a solenoid or some other induction load (motor) energizes you can clearly see the spike. With the reactor you can see the reduction or elimination of the spike. Also, if this verticle motor is a pump it is not a constant torque load. It is variable torque load. Check the settings in the parameters and see if the drive is set for variable. The diode bridge does not fire anything. The bridge is to convert ac to dc. The IGBT's (transistors) are what fires in chorus to create the simulated sign wave.
Always try the reactor first. It's easy and inexpensive to install. The distance from the motor to the VFD is of no concern (25'). Now, a reactor will not protect against lightning strikes or other major power issues. You need to find out what the impedance is that you have. Then you can select the proper % of impedance needed. I just always put a 3% in. Since I can get them same day. Check with (TCI) Trans-Coil Inc. They are leaders in this area.

 

[kc8dxx]

As others have pointed out, power quality detectors are good engineering practice when you are at a facility where you KNOW you have problems. It's hard to argue with a customer that you knew of a potential problem and wouldn't spend $ to put a simple protective device in your $$$$ system.

Line reactors are SOP in my VFD designs, sized per OEM requirments. RF Line Filters are added between the SS/GF Fuse/CB and the line reactors when needed for Euro-land requirements.

Failing internal parts may mean that your branch circuit devices were supposed to be semiconductor rated for drive I*I*T protection. Doublecheck that OEM manual.

It's been my experience that VFD failures are caused by one of three things: missing line reactor, missing OEM-required grounds, and wrong fuses. At least that's what I've had to fix in the school of hard knocks, :roll: your mileage may vary!

 

[John Valdes]

Kc.....Good point on the semicondutor fusing. I left that out on my previous rant....lol

 

[John Valdes]

"A ratchet on the motor prevents reverse operation" True but:

VFD'S are not phase sensitive. Reversing of line conductors will not change motor rotation. However, reversing load side conductors will change motor direction.