Capacitor bank requirement

[rajapon]

Hi everyone,

I am Raja, i have some technical doubts ,i am working in 33/11 KV substation with 3 20 MVA(33/11.5KV) transformer

1) 11KV SWG SEC-A,SEC-B & SEC-C (three incomer & 2 Bus section scheme)

2) 5 MVAR capacitor bank for each 11KV SWG( SEC-A,SEC-B & SEC-C)

My doubt when incomer-1 in off condition bussection-1 closed and incomer-2 feeding the load of SEC-A & SEC-B ,so in this condition for power factor correction capacitor bank -2 is enough to connect in the bus or capacitor bank-1 also need to be connected to the bus?


please clarify the above issues


Thanks & Regards

Raja.P

 

[crshears]

Hello Raja, I'm trying to understand your question but I'm having difficulties with it. Do you have a drawing or drawings of the system you could post to clarify what it is you wish to know?

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[Marmite]

There isn't a simple answer. It depends on the amount of reactive compensation you require in the form of capacitance. If you have too much capacitance in service you will get voltage rise issues on your 11kV busbar that might be beyond the range of the tapchanger to control. The voltage rise will be made worse by the reduced fault level caused by losing an incomer.

Make sure your switchgear has been type tested and assigned a rating for back to back capacitor bank switching. Not all manufacturers type test for that duty.

Regards
Marmite

 

[crshears]

Hi Marmite, I'm glad someone else understood the question...maybe it was the terminology I couldn't get my head around...

CR

"As iron sharpens iron, so one person sharpens another." [Proverbs 27:17, NIV]

 

[jghrist]

If two banks of capacitors (10 Mvar) are needed for compensating reactive load of SEC-A and SEC-B, then they would be needed if they are served by two transformers or by one transformer.

As noted by Marmite, there may be problems when one bank of capacitors is switched on when the other is already on (back-to-back switching). Energizing the second bank will create a switching surge that may exceed the capabilities of the switch (or tie breaker - whatever is energizing the second bank).

You also may be creating a resonant harmonic condition by putting both banks on one transformer.

These things need to be investigated.

 

[rajapon]

Thank you guys for your reply.........here i will attach some of the drawings

Capacitor bank Auto Power Factor Controller CT input selection
1) Capacitor bank-1
a) If I/C-1 CB closed R-phase of the CT will come to summation CT of APFC
b) If I/C-1,B/S-1 & I/C-2 closed R-phase of I/C-1 & I/C-2 will come to summation CT of APFC
c) If I/C-1 open and B/S-1 & I/C-2 closed R-phase I/C-2 will come to summation CT of APFC
d) If I/C-1 & 2 open B/S-1 ,B/S-2 & I/C-3 closed R-phase I/C-3 will come to summation CT of APFC
e) If I/C-1,2,3,B/S-1 &B/S-2 closed R-phase CT I/C-1,2 &3 will come to summation CT of APFC

 

[rajapon]

Hi Guys

I need your attention on the drawing which i sent u in the above attachment

Incomer-1 ,Incomer-2 & Incomer-3 R phase CT they connected to the capacitor bank-1 Auto Power Factor Controller through auxiliary contact multiplication with the condition of Bus section & incomer combination.

Incomer-1 ,Incomer-2 & Incomer-3 Y phase CT they connected to the capacitor bank-2 Auto Power Factor Controller through auxiliary contact multiplication with the condition of Bus section & incomer combination.

Incomer-1 ,Incomer-2 & Incomer-3 B phase CT they connected to the capacitor bank-3 Auto Power Factor Controller through auxiliary contact multiplication with the condition of Bus section & incomer combination.


Please comment your advice regarding the above scheme is reliable or not?

 

[ScottyUK]

Have you even registered the comments above about equipment capability and system resonances?

 

[rajapon]

Dear ScottyUK


the following are the details i have in the drawing


Rated output =5MVAR
Nf Stages =5
Stepsize =1
Rated voltage =11500V
Insulation level =28KVrms

Each capcitor stage contains the following

Air cor damping reactor 250uH,53A
6 no's 201.7KVAR,7303volt internally fused capacitors connected in UN-grounded double star