Reactive power compensation for 11 kV motor 1

[SA07]

Hi
We have installed capacitor banks in our plant on the 400 V and 690 V panels to reduce our utility bills. However we have an 11 kV 970 kW motor for which we have not compensated the reactive power. We would like to know if capacitor bank is commonly installed on such motor and how this is done? Is it automatic or fixed capacitor bank? We have a problem of space on our 11 kV busbars to install another 11 kV switchgear. Plz see attached measurement of energy meter for the motor during normal operation. This is a boiler feed pump motor. We are a power plant. However when we stop for maintenance or trip, we import power from the utility grid. We have to pay for the max. kVA demand for 6 months. The capacitor banks is more important as the start up of the plant. Do you know any company which can provide the supply and installation of the 11 kV capacitor bank? Thks

 

[RRaghunath]

It is possible to have a capacitor bank connected to motor terminals, probably at the 11kV switchgear BFP feeder cable connection.
Since the pump is not working at full capacity during start-up, a smaller capacitor (and fixed one) should do.
There are many PFCC vendors and your switchgear vendor should be able to advise.

 

[waross]

More important than the motor power factor is the power factor at the point of common coupling. (The revenue meter)
Nonetheless there are several good reasons to connect the capacitors to the motor terminals.
1. They will reduce the starting current of the motor.
2. If the motor capacitor bank is left connected when the motor is not operating you may have overvoltage issues.
3. If the motor capacitor bank is left connected when the motor is not operating you may be penalized for a leading power factor.
Based on the picture of the meter, which is the only information that we have, I suggest 350 KVAR of capacity connected to the motor terminals. The connection may be made anywhere between the load terminals of the motor starter and the terminals at the motor.
In some jurisdictions PFC capacitors will be protected by internal fuses and may be connected to motor terminals without the need for further protection.
They will be protected by the motor protection.
How does your utility measure PF and apply the penalties?
It may make a difference.
Some utilities use a monthly average.
Some utilities sum the 15 minute averages.
Some allow 0.9 PF before applying penalties.
Some are more punitive.

Check your cost of installation versus the sum of the penalties for 6 months.


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

 

[Kiribanda]

1)At 600V & 400V level: It looks like you have already compensated the pf.Therefore, there cannot be penalty issues.
2)At 11kV Level: From your meter reading the motor is running at 92% pf. That means you are done and in therefore
I am in the opinion that you donot need to do any further compensation. (Pl. note that the Utility is not charging you for the boiler feed pump
starting in-rush).
As waross pointed out you should measure the operating PF at the point of common coupling (PCC).
Could you please upload your SLD indicating the PCC and a snap shot of the P,Q, S & PF meter reading at the PCC?

 

[waross]

Kirbanda;
Not all utilities use 0.9 as the cutoff for power factor penalties.
When I first started doing PF correction, the utilities took a monthly average PF based on the monthly KWHrs and the monthly KVARHrs.
However over the years it has come to my attention that some utilities use a much more punitive method of calculating PF for the purpose of applying penalties.
When I see a user wanting to correct a PF of 0.92 I do not assume that the user does not understand PF penalties.
I accept that he has been paying penalties and ask:

How does your utility measure PF and apply the penalties?

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

 

[jraef]

Is this a high speed motor? Because if not, I would consider using a synchronous motor instead. And if it runs all the time, at that size you might be able to utilize that synchronous motor as a synchronous condenser to correct the power factor of your other loads. 970kW is not a trivial size load to deal with.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[cuky2000]

Consider to include In the cost/benefit analysis the secondary beneficial effect of connecting a capacitor to the motor not only to improve the PF but also to increase the surge protection to the winding insulation by reducing the steepness of wavefronts applied to or reflected within the motor windings as shown in the graph below.

>>>>>

[link Do you know any company which can provide the supply and installation of the 11 kV capacitor bank?]Link[/url]
Try Eaton, ABB, Northeast Power Systems, Inc., etc.

Take advantage of the free calculator available from one manufacturer web site.

 

[SA07]

Thks for info provided
The utility in Mauritius takes the average over 15 min.
Plz see attached a copy of our utility bill for a month for your info. Rate of change USD-Rs = 44.15
Since we installed the capacitor bank panels in 2018, we saved on our bills 2015 compared to 2019 around 10450 USD.
The motor is switched on/off by an 11 kV circuit breaker Siemens. It is DOL.
Should we connect the 11 kV capacitor bank directly to the motor terminals or install another 11 kV switch that closes after the motor has started?

 

[waross]

OK, you are not being charged a PF penalty.
You want to reduce your KVA hrs.
You can't reduce your KVA below your kW.
Your motor is drawing 885 KVA.
Your motor is drawing 809 kW.
The most that you can reduce your KVA on that motor is 76 KVA.
That will be a saving of 76 KVA x 6 month x 136 Rs = 62,016 Rs or $1,404.67.
Note that your demand is a maximum.
The charge will be the same whether the motor runs for 30 minutes or for 30 days.
Connection:
My preference is to connect the capacitors to the motor.
This may be done at the load terminals of the motor starter or at the motor itself.
The deciding factors may be available space to mount the capacitors and protection from physical damage.
Your motor current will be reduced by 8.6%.
You may wish to adjust your protection setting accordingly.

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

 

[SA07]

Thks a lot for the advice