Synchronous Motor as Reactive Power Source 1

[eaaf]

Hello.
I have a 3000 KW Synchronous Motor. Made by KATO. I replace this motor with a wound rotor motor. I'm thinking to install the synchronous motor as a Reactive Power Source, in order to improve the PF. The plant is a big consumer, almost a 42 MW, The incoming has two transformers and its feeders, seven in each one, one for each section. I'm thinking to install the motor after one of these feeders. We have the biggest induction motors downstream of one of the principal transformer.
Do you have any thoughts about it? I'll appreciate if any of you could give some ideas about to implement it or if you have some experience about the topic.
Regards.

 

[dpc]

Do a search for synchronous condenser. It can be done - it is just a matter of determining what the payback will be. The motor will have losses that you will be paying for, so that has to be factored in, along with the installation and maintenance costs.

 

[roydm]

Where I served my apprenticeship we had a synchronous motor running no load for just that reason, mind you our power factor was really bad 0.3 in places. We had a lot of pre-WW2 open type motors. Running the motor had a significant effect on our KVA demand and the utility bill.
Roy

 

[eaaf]

Thanks a lot.
DPC. We have this motor out of services, and I expect that the improvement in the PF will be a benefit. This motor has sleeve bearings, and when it had been loaded, it didn't need to much maintenance. Just checking the air filters, changing the oil time to time when the analysis said that it begins to get degraded. I have measurements that when the motor has no load it has 100 KW.

Roydm. What kind of control or equipment do you had been used to control the excitation of the motor, I'm thinking about a Basler equipment.

Any idea will be appreciate.

Regards.

 

[itsmoked]

Is there currently a penalty for you that paying for the operation/installation will reduce/eliminate?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[eaaf]

Itsmoked.
Actually there is a penalty over the bill of energy, if we have a low PF. I'm not have the exactly value, but it is below 0.75 lag or so. We have almost this value, due to the inductive motors that we have. So I'm looking for a solution, but I don't like the idea to use capacitor, because in some time we don´t have all the plant running, and in some time we have to many motor running so the PF get below 0.75.
The installation of the motor could be a great solution, using a Basler o other controller, that sense the PF of the line, and controls the reactive power that the motor produce.

Regards.

 

[roydm]

"What kind of control or equipment do you had been used to control the excitation of the motor"
This was over 40 years ago, the starter and exitation were strictly manual and our pf was so bad we couldn't have enough correction.
The motor was 100 HP and could be coupled to a compressor by flat belt drive.
I expect it was dated from the 40s
Roy

 

[waross]

I would try to put the sync motor on the same transformer as the large motors. That will avoid passing the reactive current through the transformers with the resulting reduction of capacity and I^2*R losses.

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

 

[ScottyUK]

If the PF is as bad as 0.75 then a static capacitor bank would possibly be a better long-term solution with no active power losses and minimal maintenance requirements. The payback period of installing a cap bank compared with continuously running a 100kW load may not be that long. If the synchronous machine can do some useful work as well as PF compensation then that is a very different situation.


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If we learn from our mistakes I'm getting a great education!

 

[itsmoked]

Is there any chance your PoCo would actually pay you for that much available correction? I remember the Sacramento Municipal Utility District having two large synchronous condensers on Power In Road. Could they be interested in your correcting more than just your plant? Hence cover the actual power it uses?

Would that ever happen Scotty?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[ScottyUK]

Hi Keith,


Not sure - distribution ain't really my field. Generators are certainly paid for their reactive capability. Someone like David Beach will hopefully comment.

42MW at a 0.75pf is a pretty awful load and adding 3MVAr isn't going to improve it by much, only to about 0.78 or so.


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If we learn from our mistakes I'm getting a great education!

 

[davidbeach]

To my knowledge, we have no synchronous condensers connected to our system. Also, to my knowledge, a customer subject to power factor penalties is subject to the same penalty for leading pf as for lagging pf. I have no exposure to the commercial aspects of generator interconnection (nor do I want any) and don't know if we would be willing to pay someone for kVAr production. My guess is that we wouldn't, that we'd prefer to use our cap banks that we have already paid for.

 

[eaaf]

Thanks a lot for your comments.
We consider the use of a back of capacitors. But right now we would like to get almost the reactive power that the motor gave to us, when it was installed.
It would be installed downstream the transformer that have the largest motors.

 

[ScottyUK]

I'm curious: why did you replace the synchronous motor with a wound rotor type if the synchronous machine is still fit for service?


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If we learn from our mistakes I'm getting a great education!

 

[eaaf]

ScottyUK.
We replace the synchronous motor for a wound rotor motor, because the inrush current and for the torque of the load, a vertical mill. So with the wound rotor motor, we can manage the inrush current. With the synchronous motor, we have the problem that the principal transformer is near of its capacity, and we have to put our emergency generators online, to manage the voltage line. And the torque of the synchronous motor are pretty low for the application. So we decide to replace the motor, and one of the options is a wound rotor motor from Siemens. But this options increase the reactive power that we need. Siemens is trying to put a bank of capacitor for this motor, to compensate the reactive. And we obtain fron the synchronous motor more that the siemens motor needs.

Regards.

 

[itsmoked]

I have found this to be a most informative thread - greatly aided by eaaf's great clear replies.

Thanks all!

Keith Cress
kcress -

http://www.flaminsystems.com

 

[burnt2x]

Scotty, I think you missed some figures in your earlier post. 3 MVAr is just enough for eaaf's plant to be over the penalty zone PF. I computed 27.78 MVAr with 42 MW @ 0.75 PF. Reducing the MVar by 3MVAr improves the plant PF to 0.86 lagging.
new MVAr = 27.78 - 3 = 24.78;
new MVA = sqrt(42^2+24.78^2) = 48.76 MVA
And the new PF = 42/48.76 = 0.86
I guess most utilities penalize plants operating below 0.85, depends on the area though.

 

[ScottyUK]

Quick check - bearing in mind that it is 0550hrs here - gives:

42MW at 0.75 PF = 56MVA = 42MW + 37MVAr.

42MW + (37 -3)MVAr = 54MVA

54MVA = 42MW at 0.777 PF

One of us is wrong!


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If we learn from our mistakes I'm getting a great education!

 

[davidbeach]

Scotty's numbers appear correct.

 

[cunin]

old rule of thum of mine is to correct power factor at the sorce of low power factor. Check your motors for low pf. On low pf motors, add a power capacitor to correct the pf. Tie cap and motor together after starter. Will not work with vfd starters. This small measure will reap large benefits upstream.