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01-01-2023, 10:30 AM #1
NH3 Industrial screw compressor motor selection
NH3 2 stage plant
Have situation where swing compressor on VSD drive.
Normally would run as a booster, but can run as high side.
Motor for swing compressor was selected to run as high side, but was selected with smaller motor to match normal high side compressor capacity.
Booster motor 150kw Frick 316
High side motor 330kw Frick 222
swing machine 330kw Frick 316 (normally for high side 510kw).
To match high side compressor capacity the swing machine could possibly run at a lower speed.
In this situation motor amps extremely high & forced to reduce speed.
Any suggestions, all checks out electrically.
Thanks
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01-01-2023, 12:18 PM #2
Re: NH3 Industrial screw compressor motor selection
When the swing comp is running high stage. Are the extremely high motor amps coming from when its trying to run the drive motor at its max speed, or is it when the comp is being driven at reduced speed to try and match the capacity that the Frick 222s give?
Last edited by seanf; 01-01-2023 at 01:55 PM.
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01-01-2023, 04:00 PM #3
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Re: NH3 Industrial screw compressor motor selection
Hi
To run compressor we have low and high limits for RPM .
The best set for current in electic motor %10 Under the max. Ampers.
Also sometimes we use ECO. in both type (booster and high )
To chang them from system to other systems we should reset ECO. Setting for new one .
Also if they use different types of oil in the booster and high system should look and have a good attention for that .( Normally we use one type of oil )
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01-01-2023, 09:37 PM #4
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01-01-2023, 09:59 PM #5
Re: NH3 Industrial screw compressor motor selection
Last edited by RANGER1; 01-01-2023 at 10:01 PM.
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02-01-2023, 11:36 AM #6
Re: NH3 Industrial screw compressor motor selection
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02-01-2023, 11:38 AM #7
Re: NH3 Industrial screw compressor motor selection
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02-01-2023, 06:19 PM #8
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02-01-2023, 06:25 PM #9
Re: NH3 Industrial screw compressor motor selection
That would have been possible, except multiple Quantum panel components died.
Slide valve & Vi recalibrated.
Cannot say I have seen this scenario before with a motor selected to match smaller machine.
Obviously saves a lot of money on massive motor & drive.
Basically limiting compressor to suit motor.
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02-01-2023, 08:22 PM #10
Re: NH3 Industrial screw compressor motor selection
When running high stage. Is the output power of the drive at the set reduced speed shown to be opertaing at the 330kw?
Are all the measuring instruments reading correctly? CT, voltage in and out, pressure transducers...
Are the other VSD settings changed for running low and high stage, or just max speed?Last edited by seanf; 02-01-2023 at 08:29 PM.
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02-01-2023, 08:26 PM #11
Re: NH3 Industrial screw compressor motor selection
Last edited by seanf; 02-01-2023 at 09:19 PM.
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02-01-2023, 11:16 PM #12
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03-01-2023, 10:20 AM #13
Re: NH3 Industrial screw compressor motor selection
Last edited by seanf; 03-01-2023 at 10:36 AM.
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03-01-2023, 06:25 PM #14
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Re: NH3 Industrial screw compressor motor selection
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04-01-2023, 08:16 AM #15
Re: NH3 Industrial screw compressor motor selection
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04-01-2023, 02:54 PM #16
Re: NH3 Industrial screw compressor motor selection
Hello Ranger,
Compressor and motor are both operating at constant torque when sat suction and discharge temperature are fixed.
This mean that your swing compressor require a 510 kW motor to operate the compressor at high stage.
when you reduce the speed of the motor its capacity is also reduced.
In your case the swing compressor has to be used at reduced capacity by the slide valve instead of speed.
Qvb 222/ Qvb316= 0.65 slide valve position
let's try
222 / -10+35°C 2960tr/mn= 1169 kW 315.5 abs.=> motor 330 kW is 5% oversised....
316 / -10/+35°C 2960tr 1692.2kW 455 abs.=>ok for 510 Kw
316/ -10/+35°C 2000tr/mn 1119 kw 303,5 abs
your motor 330 kw at 2000tr/mn has a capacity of approx 330/2960 * 2000 = 223 kw to short at max slide valve position!
using 316 at 70% slide valve, 2960 tr/mn; result is 1184 kw 354,8 kW abs. motor is to short again.
It'll be difficult to solve
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04-01-2023, 06:47 PM #17
Re: NH3 Industrial screw compressor motor selection
Cricri,
Good to hear from you, has been awhile.
This plant was put in by others & sounds like they have a few tricks in set up.
The swing is only used as back up high side normally, or in the past to get some hours on it.
Has worked, so will limit slide to see how it goes.
They may have calibrated slide at lower point which would show example 70 %, but on screen 100 %.
Currently high side cruises, so it has a lot of spare capacity anyway.
Does not sound like very efficient design, but who knows what circumstances were.
Client oblivious.
Regards Ranger1
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04-01-2023, 09:46 PM #18
Re: NH3 Industrial screw compressor motor selection
Ranger,
for exemple LP 316 can produce 702 kW / 106.6 kw abs at -35/-10°C
if you run the swing comp 316 at -35/+35°C (without éco) production is 530 kW / 324.6 kW abs.
its better. 75% coverage of needed capacity.
PS: I dont know the operating conditions...what was sold?
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05-01-2023, 05:31 AM #19
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07-01-2023, 11:39 AM #20
Re: NH3 Industrial screw compressor motor selection
Hi Ranger,
The motor is undersized for the machine however the machine is oversized for the load. I am of the opinion the installer missed an important fact regarding VSD driven motors. It seems you have found the sweet spot for now but probably the best way to run the package is at full motor speed and reduce the slide valve however the C.O.P will drop off badly...
See below extract copied off the web for you:
A variable speed drive operating an induction motor directly controls two variables: frequency and voltage. Speed is proportional to frequency. Torque capacity is proportional to the V/Hz ratio. That is, at half of the motor’s design frequency, if the voltage is also reduced by half, the motor is capable of producing its full rated torque. 0.5S x T = 0.5P, so at half of rated frequency the motor can produce half its rated power while drawing its full rated current. Again, P = V x A, so if the voltage is reduced by half and current is kept constant: 0.5V x A = 0.5P.
A variable speed drive is not a gearbox. Reducing the motor speed does not increase its torque capacity. If your load requires constant horsepower, you have to design for the worst-case torque condition, which in this case is the minimum operating speed. Then, as the speed increases the torque requirement decreases and the power remains constant.
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07-01-2023, 06:52 PM #21
Re: NH3 Industrial screw compressor motor selection
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07-01-2023, 09:07 PM #22
Re: NH3 Industrial screw compressor motor selection
Have been following this with great interest. Novel idea, but nothing I have ever seen. A real problem for those who have to work on it if the original motor setup information is gone!
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Re: NH3 Industrial screw compressor motor selection
Not sure where to begin
330kw motor on a Frick 316, for the pictures it looks to be in the ballpark of an XRV204?
What is the VFD manufacturer?
The biggest issue I've had with VFD's on screw compressors over the years is the issue of "overcurrent", especially since I have had a lot of RSW plants where the starting temperature is often waaay outside the design parameter.
The Ampere you are reading from the VFD is a fantasy number that has been made up by the VFD
Don't use that for anything.
An experiment I did some 15 years ago on an RSW plant.
Compressor kept reducing slide load because of overcurrent, but it was within the design limits for suction and discharge and should have been going at full load.
I changed the minimum speed from 2400 rpm to 3000 rpm and all of a sudden it was running at 100% slidevalve and 40 amps below the limit.
Took some self educating and a new automation engineer in the office that were willing to listen.
At frequencies below 60Hz, the output voltage from the VFD is below the line voltage. Since VIin = VIout (or Powerin = Powerout, Pin = Pout), the output current must be higher than the input current. That is, at half speed, the output voltage is half, so the output current is double.
We have changed all our regulators to now read the power (kW) from the VFD, because power in = power out
So probaly you need to change some parameters in the VFD and maybe the PLC-Cheers-
Tycho
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09-02-2023, 11:04 PM #25
Re: NH3 Industrial screw compressor motor selection
Tycho, more like Horden 255193, that was the weird scenario