POWER FACTOR-CORRECTION

[kumar250688]

SIR;
now i had worked in transformer side ,please improve the power factor from 0.97 to 0.999,so please help to give the solution for arresting the transformer losses,lt side improved the power-factor 0.99 by capacitor banks. but ht side 0.97 has only,please tell it as bring to high level power factor
33kv feeder Ht side Lt side
33kv /11kv transformer(oil cooled) 0.965 _
11kv/400 transformer(fan cooled) 0.97 0.989
11kv/400 transformer(fan cooled) 0.965 0.975
11kv/400 transformer(oil cooled) 0.989 0.984

 

[kumar250688]

please give must reply

 

[cranky108]

Because of load type mixtures, we would expect the power factor to change with load levels. So a simple answer may not be possible.

 

[LionelHutz]

You've posted twice on this forum and now you're demanding that someone "must" give you an answer?

The capacitors required can be calculated using variations of these 2 simple formula.

W = VA * PF
VA^2 = sqrt(W^2 + VAR^2)
where
PF = power factor
W = true power
VA = apparent power
VAR = reactive power
^2 = squared.

If you can't figure out what you need from this information then you simply shouldn't be doing the project you're working on.

If you have a good power meter then there is an even easier way to determine the required capacitance that should be very obvious.

 

[jraef]

I still think that trying to attain a .99 PF using bulk capacitors is a hopeless exercise.

"Will work for (the memory of) salami"

 

[sibeen]

I still think that trying to attain a .99 PF using bulk capacitors is a hopeless exercise.

+ brazillion.

 

[LionelHutz]

I still think that trying to attain a .99 PF using bulk capacitors is a hopeless exercise.

Yes, especially if this is being done to save energy and I already explained in the last thread by the OP.

 

[waross]

If you are being charged a PF penalty on a PF of 0.965 then the answer is a power factor controller with CTs and PTs to monitor and correct the high side to 0.99 PF. Although the monitoring may be on the high side, the correction capacitors may be on the low side.
If this is for school, then ask your professor for more information. There is not enough information given to calculate an answer.

I still think that trying to attain a .99 PF using bulk capacitors is a hopeless exercise.

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

 

[jraef]

I have heard* that some power utilities insist on PF being .99 without penalty. In my opinion this is essentially just a use tax disguised as a penalty. It might even have been originally lobbied by the PF correction capacitor industry in collusion with the regulating authorities! If there is even the SLIGHTEST variation in mechanical load or electrical supply, the PF is going to deviate from .99. I do not believe it can be effectively accomplished with capacitors unless you have an incredibly small incremental capability.

The only way I can see to do this effectively would be by using synchronous motors for the largest loads, or possibly even unloaded as synchronous condensers. Monitor the PF as warps said, then use that as a feedback loop into a PF controller that adjusts the excitation to create leading (or lagging) PF.

* This issue of PF penalties based on .99 PF has been mentioned in various Internet forums in which I participate, but consistently seems to come from posters in India.

"Will work for (the memory of) salami"

 

[squeeky]

YOu don't give kVA ratings of these transformers.

If you are doing this to reduce your energy costs, please spend some time at looking at the kVAr costs to go from 0.80 to 0.90 then 0.90 to 0.95 and finally 0.95 to unity. You will find the cost increases greatly and there is actually a formula where the most cost effective kVAr rating (pf) can be calculated.

If you get the LV side to unity, there is still the inductance of the transformer. Running your LV side in a leading state is not cost effective and could be dangerous. So you will end up with HV capacitors. These along with the control gear is very much more expensive and can only really be justiifed if you have many transformers on the same bus system.

 

[kumar250688]

oil-cooled transformer kva rating-33/11kv transformer(5500kva rating)
dry type distribution transformer 1-11kv/400 volt transformer(2000kva rating)
dry type distribution transformer 2-11kv/400 volt transformer(2000kva rating)
oil cooled type distribution transformer 3/400 volt(1250 kva rating) ups having 160 kva,the same is connected across the load 26(160x26).its also reducing the losses from Lt side
i am added the capacitor from Lt side 1100 kvar,after that i need to installed ups in cnc machines,each
company demand is 4500 kva ,i had not utilize the power 110 kva because transformer losses,so please how to improve the pf transformer side,somebody told like as introduce the capacitor parallel to the transformer it compensate ht side at the same time you observe the harmonics,its not going to above unity ,please give a tips for that particular side.

 

[waross]

I doubt that you will be successful correcting to within 1% with bulk correction. VAR consumption in an industrial plant is too variable.
For many years the PF penalties in North America were based on a monthly average and 0.9 PF.
It was something of an art to select KVAR values of correction capacitors and connection points to raise the monthly average above 0.9 PF.
When a plant was running full out, the PF may be below 0.9.
When the plant was idle at night and on week ends the PF would be above 0.9, putting KVARHrs "in the bank" to correct the monthly average.
You may correct the high side of a transformer with capacitors on the low side, but don't over correct.
We need a little more information;
How are your PF penalties determined?
Where is your revenue metering connected? (If the metering is on the low side then capacitors on the high side are pointless. The correction will not be seen by low side metering.)
You may correct large motors to unity by capacitors connected to the motor leads. Don't forget to adjust the motor protection settings.
You may correct each transformer to unity by permanently connected capacitors which will be switched with the transformer.
You will probably need a PF controller to do the remainder of the correction.
Hint: Back in the day, with bulk correction, it was often economical to accept the occasional penalty of 1% or 2%. The cost of correcting for the odd small penalty was often more than the penalty.

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

 

[squeeky]

I am not a fan of correcting each load with the load. I do believe that modern power factor correction controllers are able to give you a very close control. Using round figures for ease of explaination. Most people would look at teh required correction of 150kVAr and their 5 step controller and then connect 5 only 30kVAr capacitors, allowing all five steps to be used. The problem is that anything in between each step is uncontrolled. Only 30, 60, 90, 120 and 150kVAr correction values are availible.

Now consider this. if you find youe smallest step correction to be say 10kVAr you would not get any correction until your load requirement reached 30kVAr. Using the doubling rule you make your steps 10, 20, 40 and 80kVAr. In the set up of the controller it requests your smallest step. It then asks you for the mulitple of that value for each step. If you require 10, step 1 comes in. If you require 20, step 2 comes in and step one drops out. Require 30, step 1 and 2 are active. require 40 only step 3. 50 Step 1 and 3 and so on. YOu now effectively have 15 steps each of 10kVAr and able to give finite control.

If you are willing to pay for the correction to 0.99 then this will ensure that you stay very, very close to it.

 

[davidbeach]

But to do that you've got to be willing to switch back into a cap that may not have had a chance to fully bleed off since the last time it was switched out.

 

[waross]

If you correct the major loads with direct connected capacitors, the balance of the correction may be done with a PF controller with smaller steps and closer control. I am not a fan of jumping between steps on a PF controller but that's just me. I may disagree with you but still respect you. Different strokes etc.

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