vfd to motor 100 ft?
vfd to motor 100 ft?
(OP)
What kind of problems should I expect with installing a vfd 100 ft from my motor that is 25hp 480v 33.7a w/ an Allen Bradley power flex 70 vfd. The conductor size I came up with is 3 - #6 thw-2 and a #10 grnd. Any suggestions on better condutors? I also came up w/ a 90a inverse time trip breaker ahead of the vfd any other opinions?





RE: vfd to motor 100 ft?
As to the sizing of the circuit breaker, make sure you read and understand the NEC sections specific to this, somewhere around 430.52 (I don't have my version here with me). The breaker must be sized according to the VFD input current, NOT the motor current. 90A seems a tad large for that size drive, unless your VFD is a lot larger than necessary for a 25HP motor.
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RE: vfd to motor 100 ft?
A good paper on the subject is:
http://l
Quote from Allen-Bradley Publication 20A-UM001M-EN-P – May, 2009 which is the Powerflex 70 User Manual:
Motor Cable Lengths:
Typically, motor lead lengths less than 30 meters (approximately 100 feet) are acceptable. However, if your application dictates longer lengths, refer to "Wiring and Grounding Guidelines for Pulse Width Modulated
(PWM) AC Drives" for details.
Per the following Allen-Bradley document "Wiring and Grounding Guidelines for Pulse Width Modulated
(PWM) AC Drives":
http://l
A 25HP inverter duty motor (1600V insulation rating) is good for 600 ft without additional termination devices. However, this spec also requires the use of an appropriate cable, i.e., a shielded/unshielded cable designed for inverter use (an improperly designed cable can have capacitive charging currents that can cause nuisance overcurrent trips at long motor lead lengths).
I would recommend an inverter duty motor and a VFD rated shiedled cable and you should be fine.
With respect to the drive overcurrent protection:
For a 25HP Standard Duty Powerflex 70 drive (Model 20AD034), I would use a Bulletin 140M (part number 140M-F8E-C45) motor protection device. The devices are listed for use with the Powerflex drive and are typically cheaper than a UL489 breaker.
The previous information can be found in the following document (Powerflex 70 User Manual):
http:
As jraef stated the circuit conductors are sized at 125% of drive rated input per NEC 430.122(A).
(FYI: NFPA standards including NFPA 70 2008 (the NEC) can be viewed online at NFPA.org)
Per Allen-Bradley a 25HP 480V Normal Duty drive has an input rating of 31.2A so 31.2A * 1.25 = 39A. Based on Table 310-16 a #8AWG @ 75 degC conductor is good for 50A so unless your branch circuit supply is far from the drive (voltage drop) a #6AWG is a bit of overkill. A #10AWG ground is ok.
RE: vfd to motor 100 ft?
Keith Cress
kcress - http://www.flaminsystems.com
RE: vfd to motor 100 ft?
I don't know whose recommendation that is but it is totally out of sync with general industry practice and experience. At 460V, a 25hp MG1P31 (inverter duty) motor starts being at risk right around 100 feet, just as jraef suggests.
Actually, the need for reactors, etc. is dependent not only upon motor lead length but also motor hp. Everyone seems to do the derate a little different but, the rule I use is "at 10hp or less lead length can be up to 60 feet, at 250hp or more the lead length can be up to 250 feet, and use linear extrapolation between those points".
But 600 feet at 25 hp, no. Brace yourself for trouble at that rate!
RE: vfd to motor 100 ft?
Muthu
www.edison.co.in
RE: vfd to motor 100 ft?
See Rockwell Knowledgebase Answer ID 34253.
A quote from the following drive system sample specification:
http:
REFLECTED WAVE
A software algorithm to limit the reflected wave due to long cable lengths to a maximum of
2.25 times the bus voltage or 1600V, whichever is less, up to cable lengths of 600 ft (183m).
Hardware designs also limit peak voltages on the motor.
Please note the motor must have 1600V insulation and the drive output cable must be VFD rated for this spec to stand.
I would contact my local Allen-Bradley rep for a consultation.
RE: vfd to motor 100 ft?
You may think that if you wish!
RE: vfd to motor 100 ft?
http://www
Also, Marathon Motors specifies their Max Guard insulation system (which includes the Blue Max and Black Max series of motors) for use on PWM Inverters at any distance. Quote from Page 10 of the following document:
h
"Motors that employ the MAX GUARD® system can be operated at
any cable length and/or carrier frequency. MaxGuard® surpasses the requirements of NEMA MG1-2003, Part 31, Section 4.4.2."
Is it possible our rules of thumb need updating? Is it possible a properly specified drive, carrier freq, motor cable, and motor can withstand the standing wave overvoltage and CIV (corona inception voltage) problems at 600ft for an acceptable mean time before failure?
On a related note, when installing 600ft motor leads, I would think voltage drop should be considered.
RE: vfd to motor 100 ft?
Anyone else care to comment of what constitutes a good rule for protecting MG1P31 motors on drives?
RE: vfd to motor 100 ft?
Neil
RE: vfd to motor 100 ft?
I was at one site and there was about 10' of cable. The 3% motor reactor caused a lot of extra ring-up which disappeared when it was removed. There was a case posted here where a sinewave type output filter caused neutral and/or ground current which then caused voltage problems. So, reactors or filters aren't always the solution.
RE: vfd to motor 100 ft?
This is the law.
Where it is not the law, it doesn't mean you do not need to worry about it!
RE: vfd to motor 100 ft?
So far, we have widely diverse claims which lack specific application.
Or, is my claim of snake oil being verified here?
I, for one, think 600ft without protection is wildly risky especially for small motors.
RE: vfd to motor 100 ft?
It'd be interesting to hear from people who actually qualify every installation or who have tested different combinations.
RE: vfd to motor 100 ft?
Neil
RE: vfd to motor 100 ft?
The cable size is ok and as MAGtiger points out, inductance and capacitance are factors of any load from a VFD but at this cable length and cable size then you should still be driving the motor and not just the cable.
Assuming the motor insulation is suitable for VFD use, this should be ok.
I wouldn't have a problem as long as there are no other factors not mentioned; i.e. this is not 100ft down a borehole running a submersible pump etc.
RE: vfd to motor 100 ft?
http://www.yaskawa.com/site/dmdrive.nsf/link2/MHAL-6C3MQ2/$file/AN.G7.01.pdf
http://www.controleng.com/article/265495-Focus_on_PRODUCTS_Three_level_inverter_improves_motor_drive_performance.php
(Please copy and paste the links as the TGML was rendering the first link incorrectly so I turned TGML processing off. Thanks!)
RE: vfd to motor 100 ft?