VFD causing High current 6

[Alij23]

We have got couple of VFD controller for our Cooling fans, fans are 600V motors, when we run them locally (bypassing the VFD) the voltage and current is normal (600V and 90Amps) but whenever we use our VFDs we are getting 480V and 120Amps therefore the controller gets hot, some times it causes alarm, any body has any idea why does it happen? What can we do to eliminate this problem?

 

[waross]

Not mad, but a little frustrated.
Forget the meter, it probably is NOT giving you the right value anyway, but.
CHECK YOUR DEFAULT SETTINGS TO SEE IF IT IS SET FOR A 480V INCOMING LINE INSTEAD OF A 600V INCOMING LINE AS JRAEF SUGGESTED.
If you need help with that, ask and one of the VFD experts may help be willing to walk you through it.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[edison123]

Alij

Did you read and try to understand any of the responses posted above ?

If you did, then all your questions were already answered. If you didn't, then Bill is right.

 

[itsmoked]

The VFD can and will display everything you ask about, and correctly! You may need to find the manual and look up how to select the various displays. But it WILL show you the DC bus voltage, the supply voltage selected, the correct current value, that is being sent to the motor, etc., etc. ,etc. ,etc. ,etc. ,etc..

And do forget your meter!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[LionelHutz]

OK, unless the meter is a high quality true RMS unit then throw it away and quit using it. The cheap meters most electrical people like to purchase are useless when measuring voltage and current on a VFD. I would recommend you purchase a higher end Fluke model, such as a Fluke 87 or better, that states it's true RMS and expect to pay $300+ for it.

A couple of people posted that you need to post details of the equipment you used and you ignored them.

Also read what itsmoked just posted. The VFD will display the outut voltage and current internally and it will do it correctly.

If the frequency is 55Hz then the output voltage should be 527V. Your measurement of 480V makes either the meter or the VFD settings very suspect.

Two other settings you must get right are the motor voltage and the motor frequency (sometimes called the knee frequency).

 

[Alij23]

thanx guys , i did not know enough about VFDs ,i did read some about them and i got it .

 

[rcw retired EE]

Gentlemen - Ali is working with me trying to puzzle this drive issue out.

The drive is a GE AV300i Model 3150, 157 A IEC 146 class 1 rated output, 575V +/-10% input. It is programmed for the motor nameplate data: 575V, 125 HP, 119 FLA, 900 rpm and for 575V Mains Input Voltage. The motor characteristic data was gathered using the drive's auto program features. There are 35 identical units acting the same way.

Ali's meters are Fluke 87 or better. All readings match the GE drives' readout for voltage, motor amps and input amps and the readings from high end analyzers. It is unlikely that it is a metering problem.

The drives have no speed feedback signal and use "sensorless" vector control software to estimate/control the output speed. Speed follows a 4-20 MA input signal from the plant DCS. The drive says the input signal is calling for 820 rpm (55 Hz)output and the output is about 55 Hz, output speed is within a few rpm of setpoint. The 450-480 V drive output is less than expected for 55 Hz (55 x 575/60 = 527V).

The drives all have bypass contactors so the motors can be operated at rated voltage and frequency. When on bypass, the motor currents are under the FLA (depending on ambient air temperature). On VFD, the motor amps are at or above FLA.

Will a vector drive back off the output voltage to minimize torque and save energy? Is that even possible?

We will recheck the drive programming and see if we missed something that did get reset to 480V. The high temperature alarms got cleared for now by activating the room ventilation and cleaning the drive cooling fan filters.

The supplier for these drives almost went bankrupt on the job and will not supply support. Their technical expertise was lacking after their engineer left. GE no longer distributes or supports these Italian made AV drives.

At my suggestion, Ali went on this web site and asked for some help trying to understand how these drives could be working correctly. (I was busy elsewhere.)

We need to take a unit down and do a full check on the programming parameters.

 

[jraef]

I was a bit confused, because all of the information I could find on that drive at first stated that the maximum voltage is 460V. But I found a manual with reference to their having a 575V version for Canada, so that cleared things up from a logistic standpoint, but I still have my suspicions (see below). Something is amiss here and the evidence presented in this thread still points to the motor being under-fluxed. So I have to theorize based on what I can see in the available literature. Here are my working theories;

1) The drive is set for V/Hz mode of operation and someone turned on the "Variable Torque" mode. Most vector drives I have encountered will not allow you to put a drive in Auto-tune unless you have the control method set to Vector, but this drive doesn't seem to state any such restriction. That means you may THINK you are setting the motor tuning by doing an Auto-tune, but if someone left Fn 321 at setting 3, which is V/Hz mode (default) and 712 to a setting of 3 which is Variable Torque, the motor will still be providing less voltage at a given speed in an attempt to save energy. If the load needs constant torque then it will slow down, increase slip and draw more current.

2) Someone, at some point, got themselves messed up with programming of this drive and reset to the Factory Defaults. UNFORTUNATELY, the factory default values may in fact be for 460V motors, even on the 575V version of this drive! Here's my evidence, pasted from the 575V manual:

5.3.2.2. Setting Motor Parameters
The AV-300i drive is factory set for use with 4-pole standard motors, either for 400V or 460V, to be operated up
to the nominal speed. Enter nameplate data recorded for the connected motor to ensure satisfactory performance.

Then later:

The BASIC MENU provides the parameters required for the initial commissioning of the drive. The data that is factory set for the default motor concerned refers to a four-pole machine for either 400V or 460V). The motor data in the DRIVE PARAMETER menu should be changed accordingly if different motors are used.

Now if I look at Fn `161, the Motor Voltage setting, it says in this manual that the default setting is in fact 575V. But being that the fact that the 575V version of this drive appears to be an afterthought in their product line (because there is no other literature saying it even exists), it's entirely possible that the mfr messed up and allows the Set to Factory Defaults function to reset the drive to 460V, the original design voltage. Just a hunch, but one based on my experience with other mfrs that attempted to sell 575V drives into Canada. Some of them just "tweak" a 480V design and call it good, and when you do that, nasty little details get missed.

If neither of those conditions exist, it also appears that this drive has something called a "dynamic regulation margin" (Fn 889) that artificially limits voltage above a certain speed. Here's how they describe it:

Example 2
Use of a standard motor 575 V / 60Hz
Application requiring total immunity from torque disturbances due to main voltage fluctuation.
Base voltage 575 V -15% = 490 V
Base frequency 60 Hz -15% = 51 Hz
The motor works at nominal flux until 51Hz (85% of the nominal speed), supplying full torque.
Over this frequency the voltage is regulated constant regulated, the flux is weakened and the motor supplies
constant power equal to 85% of the nominal (rated) power

If that is enabled, that would cause what you are describing if your load is demanding full torque at that speed.

God I love forensics, I shoulda been a detective... it's just not as satisfying when I'm not in front of the drive though.


"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[edison123]

Jeff - You are hereby renamed Lieutenant Colombo.

 

[rcw retired EE]

jraef-You are the detective and the engineer!

We checked everything we could in the software, all appeared to be OK, except the motor amps was programmed as 136 instead of tne nameplate 119 amps. We checked voltage and speed on several units and caculated the V/F ratio (actually the V/rpm ratio).

In all cases it was about 0.52 = 460 Volts/886rpm.

It should have been 0.65 = 575 V/886 rpm.

You are correct that it looks like something in the firmware defaulted the drive to the 480V version.

 

[jraef]

You know what they say, if it looks like a duck, it quacks like a duck and it floats on the water, it's probably a duck...




"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> faq731-376

 

[itsmoked]

Are you saying you float?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Awesome jraef.




Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[DayB]

Try using a low pass filter inbetween the meter amd terminals. Is the DC link in good condition and if so, is the drive output clamped at 480 via a parameter.

 

[damiens]

Try TCI filters. We use them all the time with ABB drives.

http://www.clrwtr.com/TCI-Trans-Coil.html