Powerfactor Improvement

We are using 2 mva 33KV/ 690 V Delta Star 11 (DY11) transformer feeding an Induction Generator , this Load is Drawing 35 % of RKVAH Power fromgrid to Give the power output ( 35 KVARH for generating 100 KWH )

The Supplier is not allowing to put the AUTOMATIC POWER FACTOR IMPROVEMENT System By Switching the Capacitor Steps .

So we are going to put a sensing circuit in the 33 Kv bus in the Incoming and with that sensing we are going to instal a 33kv /690v0lt 800Kva transformer in the same 33 kv bus . we want to inject the capacitance effect from the secondary of 33Kv/690volt 800 Kva transformer by only adding the pure capacitance load .

Wether it will improve the capacitance in the 33 kv bus ?

Which type of Transformer is required (DY 11 Or DD 11) are any specific type transformer is required for this?

What will be the Impact in the 800 KVA 33Kv 690 Volt transformer if we Load 400 to 500 KVAR capacitor load alone ?????

reply

1. it will improve P.F.

2. DY11 Transformer can be used. But it is better to have a single transformer having territiary winding of 400 or 440V. Induction generator is connected to 690V winding and capacitors of appropriate voltage in the 400/440V territiary winding with sensing CT at 33kV side. Votage to P.F. relay may be taken from secondary side if transformer is Y-Y. If delta star primary to secondary vector has to be considered. In my opinion atransformer Y-Y transformer is better for this. Other wise E/F protection at 33kV side has some problems. 33kV/690V/440V Y-Y-Y trnsformer is preferred. Additional capacitors with APFC relay required for P.F. compensation of induction generator. This may be connected in 690V winding with sensing CT at 690V side. Capacitors in 440V side is for P.F. compensation of transformer and line inductance.

Dear Sir

Thank you for your reply . The system is already functioning with normal transformer . Now we have to go for another transformer as i have narreted . Please reply .

Thanking You

I. Dhanaraj Lazarus

better to provide another transformer of 33kV/440V for P.F. compensation of transformer and line. Capacitors may be provided at 440V side with APFC relay. Sensing CT may be provided at incomer of 33kV bus. For compensation of P.F. of Induction Generator seperate capacitor banks with APFC relay to be provided at 690V side. Its sensing CT may be at 690V side. As transformer is of 2MVA, taking %Z as 5% total capacitance required is approximately 100kVAr. Hence a 250 kVA transformer is adequate For P.F. compensation (33kV/440V).This transformer may be Delta-star. While setting APFC, vector difference between delta side and star side to be considered.

Have you tried changing the taps for the 2 mva transformer (or is it auto tap change)? You must have much more load on the 690v bus if the induction generator is only 100kw (i.e. 2000kva transformer - if that's all the load on that transformer, it's no wonder they don't want any more capacitance!). Also if you calculate the pf, it is only .94 (cosine of 19.3 degrees), normally the convention is .8 for pf before penalties. Does your auto pf correction system use series or shunt capacitors, is it in the high or low side of the system? What is the actual voltage of the 33kv line and are you considered a radial feed? Your idea will work (voltage will go up), but if the power company doesn't want more capacitance then you're still out of luck. If you do use your 800kva transformer with pure capacitive load your temperatures will shift away from the normal monitoring points so be sure before you order your equipment that you let them know how you plan to use it. If you answer my questions, I can give a much better answer. Good luck.

Dear sir

I mentioned 100 kw as an Examble but machine Generated 1500 Kw Transformer is with the OFF Load TAp Changer . We have to addanother Transformer to add Capacitive reactance to Improve the Power Factor ofthe Wind mill + Its Transformer .

Thanking You

With Regards

I.Dhanaraj Lazarus

Hello sir,

I take it that your generator (motor?) is consuming 35 KVR/HR per 100 KW/HR, well then the angle 19.3 degrees remains constant at 1500 KW and 525 KVR (i.e. tan-1 of 525/1500 = 19.3 degrees). The cosine of 19.3 degrees is .94 (i.e. pf). Can you tell me what your pf is? What is your supply votage to the transformer and what is your voltage on the 690v side (with all equipment running)? Now if you have a 2,000 kva xfmr, the apprent load is 1592 kva which is < the 2 mva. What tap do you have set on your power transformer? If you can tolerate a lower voltage (not much) you can boost power factor by loading the transformer a little bit more (with the tap changer). I'm willing to bet you can make .96 pf, just by adjusting the tap changer. What is your utility's pf limit? Does the utility penalty justify the expense of another transformer and capacitors? You mention a windmill, is this the induction load or generator that's causing your problem? Are the capacitors with the pf correction device in shunt (parallel) with the 690v line? Maybe the power company just doesn't want reactive load switched in and out of the line continually. What if you made the capacitors (from the pf device) static, i.e. permanently tied to the line? The utility company would never know they're there because the reactive load would be supplied by the capacitors (actually they would be happy - they would be getting paid for all the current they generate). Just select sufficient capacitive reactance to reduce the 19.3 degree angle to get the pf that you want. When your equipment goes off line you will have to switch off the capacitors to keep everybody happy. You can email me at hughes838@yahoo.com if need be.

Dear Huges

You have wrongly understood the Explanation I will attach the Month wise Yearly Generation report & KVARH drawl it is comming as an Average of 37 % annually . Grid Supplier ( Utility ) company will Put Penelty for Excess VAR Drawel from Utility . So Pf isvery less . Please adviseme .

Regards

I.Dhanaraj Lazarus

Dear Sir,

You are right, I don't understand. I will wait for your generation report before I make any further comments. It is hard to believe that your pf is < .37 annually!

Best regards,

hughes838