Evaluating Retrofit Energy Saving Devices, (PF improvement type)
Evaluating Retrofit Energy Saving Devices, (PF improvement type)
(OP)
Dear All,
I'm evaluating a Energy Saving Device (powerliner) based on power factor improvement. This unit manly consists of capacitors which are installed near the motor.
Already in this forum there is a lot mentioned about such units. Most of the savings consist of power line savings which is logical and can be explained.
The manufactor claims to have high savings, up to 5 or 6%. From my point of view, that's not realistic.
To do further investigation, we've done some measurements on a motor (application: water pump)
We've installed 2 measuring points. 1 at the power cabinet, 1 near the motor, just before the energy saver connection.
Normal measured load is appr. 150 kW. As expected we see a large variation in Q (kvar) but we see also a slight decrease in P (kW) power when the unit is switched on. Even near the motor we see a decrease of approximately 8 kW = 5%.
At this point we can not explain this variation. It was not possible to do torque measurment on the motor shaft. But in generally, such a passive device can nog influence the motor output power, can it?
Does anyone know how to explain this variation, or has some experience with these type of devices?
Thanks for your answer,
Kind regards,
Rob van Heur
(The Netherlands)
I'm evaluating a Energy Saving Device (powerliner) based on power factor improvement. This unit manly consists of capacitors which are installed near the motor.
Already in this forum there is a lot mentioned about such units. Most of the savings consist of power line savings which is logical and can be explained.
The manufactor claims to have high savings, up to 5 or 6%. From my point of view, that's not realistic.
To do further investigation, we've done some measurements on a motor (application: water pump)
We've installed 2 measuring points. 1 at the power cabinet, 1 near the motor, just before the energy saver connection.
Normal measured load is appr. 150 kW. As expected we see a large variation in Q (kvar) but we see also a slight decrease in P (kW) power when the unit is switched on. Even near the motor we see a decrease of approximately 8 kW = 5%.
At this point we can not explain this variation. It was not possible to do torque measurment on the motor shaft. But in generally, such a passive device can nog influence the motor output power, can it?
Does anyone know how to explain this variation, or has some experience with these type of devices?
Thanks for your answer,
Kind regards,
Rob van Heur
(The Netherlands)





RE: Evaluating Retrofit Energy Saving Devices, (PF improvement type)
If you had bigger wire you would see a smaller improvement.
The real savings of this type of device is if you are penalized for PF. If you aren't then the payback is much longer.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Evaluating Retrofit Energy Saving Devices, (PF improvement type)
The problem I have with these things is more in the way the purveyors sell them, basically implying that they will ALWAYS get that much, or more! It's way too situational to make those kinds of generalizations. They find and document applications like this and use that as "proof" that it works, then allow potential customers to believe it will happen for them too. It's just not that simple, but simple sells.
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RE: Evaluating Retrofit Energy Saving Devices, (PF improvement type)
RE: Evaluating Retrofit Energy Saving Devices, (PF improvement type)
Imho, it is not worth the time and energy spent to "evaluate" such gizmos. And yes what is the device "near" the motor? Where is the "far" from motor meter?
Rafiq Bulsara
http://www.srengineersct.com
RE: Evaluating Retrofit Energy Saving Devices, (PF improvement type)
I've been thinking about this a bit more. If your metering equipment is out a bit - say a phase shift error between current and voltage - then it would see a slight portion of the reactive current change as a change in real power.
The power into the motor can not go down if the load hasn't changed. The capacitors are not perfect and they have some losses, typically up to 0.5W per kVAR. You probably installed 30kVAR of capacitor which could have a 15W loss. I would expect this loss to easily counter any gain due to lower current in the conductors.
So, it really makes no sense that the power input could go down.
RE: Evaluating Retrofit Energy Saving Devices, (PF improvement type)
thanks for your answers so far! The answers seem compelteley logical to me. What is strange in tis case, that we measure the kW power decrease near the motor. The cable length between RESD (retrofit energy saving device) connection point and motor terminals is only a few meters. Therefore it's really strange because at this measuring point the cable losses should me really small. The power difference between both measuring points is about 1 kW which can be explainded by cable losses. (Appr. 200m cable, but not fully loaded)
I've uploaded some measuring data / graphs. See:
http
LioneHutz, can you explaine a bit more about the meting equipment? If the euipment is out a bit, but the connection or meter isn't changed when the RESD is switched on/off, will there still be a measuring fault?
Kind regards,
Rob
RE: Evaluating Retrofit Energy Saving Devices, (PF improvement type)
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Evaluating Retrofit Energy Saving Devices, (PF improvement type)
The comment I'll add today is that if you're involved with a company that is selling a power factor correction capacitor as a "retrofit energy saving device" then these particular capacitors also likely cost way too much and can be sourced through normal channels much cheaper.