NH3 Industrial screw compressor motor selection

[RANGER1]

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

[seanf]

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?

[mbc]

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 )

[RANGER1]

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?

Seanf 2200 rpm, but amps still to high, that matches high side compressor mass flow.

[RANGER1]

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 )

MBC,
Mostly on VSD amps set 10% above name plate to avoid unnecessary current limiting.
But each situation different.
This one set 10% name plate.

Apparently, this compressor has worked okay in the past
Same oil as other machines

[seanf]

Seanf 2200 rpm, but amps still to high, that matches high side compressor mass flow.

Is that mass flow measured with a flow meter, or calculated with know comp speed and slide valve position?

[seanf]

MBC,
Mostly on VSD amps set 10% above name plate to avoid unnecessary current limiting.
But each situation different.
This one set 10% name plate.

Apparently, this compressor has worked okay in the past
Same oil as other machines

Does it have a data logger/trend you could look back on and see how it was running?

[RANGER1]

Is that mass flow measured with a flow meter, or calculated with know comp speed and slide valve position?

Through OEM advice slide 100% & set speed maximum in drive.

[RANGER1]

Through OEM advice slide 100% & set speed maximum in drive.

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.

[seanf]

Through OEM advice slide 100% & set speed maximum in drive.

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?

[seanf]

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.

Does site have any manually taken logs?

Seen smaller motors put on a few high stage machines, but fixed speed and the economisers were always kept closed.

Is it you on site, or is it the sites engineers telling you what they've found?

[RANGER1]

Does site have any manually taken logs?

Seen smaller motors put on a few high stage machines, but fixed speed and the economisers were always kept closed.

Is it you on site, or is it the sites engineers telling you what they've found?

seanf,
I think something else going on, like motor torque issue.
Booster is a 399 with 220 kw motor, not 316 as first stated.

[seanf]

seanf,
I think something else going on, like motor torque issue.
Booster is a 399 with 220 kw motor, not 316 as first stated.

Do you have access to enough info on the motor and on the comp, to check their matched up correctly for running at the 2200rpm high stage, and maybe give rough running values to expect?

[mbc]

MBC,
Mostly on VSD amps set 10% above name plate to avoid unnecessary current limiting.
But each situation different.
This one set 10% name plate.

Apparently, this compressor has worked okay in the past
Same oil as other machines

Hi
Full Load Amper is showing by FLA Is a Max. Ampers for Electro Motors .
For more safety we go %5 to %10 under FLA .
What I do
Set %15 Under FLA. For Stop Raising capacity
%10 under FLA. reducing capacity
% 5 under FLA. For Stop Running .

[RANGER1]

Hi
Full Load Amper is showing by FLA Is a Max. Ampers for Electro Motors .
For more safety we go %5 to %10 under FLA .
What I do
Set %15 Under FLA. For Stop Raising capacity
%10 under FLA. reducing capacity
% 5 under FLA. For Stop Running .

MBC have found this inadequate when using VSD drive
Full load amps & if necessary + 10%.
Teco advises okay.
Full load amps can run long term in my opinion, thermistors will protect it.
Ideally in perfect world give everything easy life.

[cricri]

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

[RANGER1]

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

[cricri]

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?

[RANGER1]

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?

Okay,
Thanks set slide to 80% maximum, then in speed control & seems to manage at the moment.
-40/-10/35 C
Unusual one for me.
Be interesting if installer had to work it out on commissioning.

[GrantD]

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.

[RANGER1]

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.

Thanks GrantD for information,
I think installer new what they were doing, as it would have possibly fitted it to a specification requested by a consultant (guessing).
Plant is so oversized it’s not funny, but swing is hybrid, could have just been another Frick 222.

[NH3LVR]

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!

[Tycho]

MBC have found this inadequate when using VSD drive
Full load amps & if necessary + 10%.
Teco advises okay.
Full load amps can run long term in my opinion, thermistors will protect it.
Ideally in perfect world give everything easy life.

I have been told that electromotors, at least Lönne and ABB can run with FLA +10% continuously without taking damage.

[Tycho]

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

[RANGER1]

Tycho, more like Horden 255193, that was the weird scenario