Please suggest me about my idea for power transformer 2

[amphan]

Hi;
My factory worked since 1992, I check the power circuit of power transfermer and found a point of loss as this follow.
:-----------: :------------:
: 100 : : 72 :
: MVA : ------> Series reactor ---------------->: MVA :
: 115/22 : : P 22 kV:
: kV : Voltage drop 2.5kV : Sec 900: V
:-----------: at I 2000A :------------:

1992: Short cct level at line incoming 1600 MVA
2004 ;-------------------------------------------; 10000 MVA

I know the series reactor used for protected the transformer and breaker when the breaker swtich to 'on' because the inrush current very high and long time (0.5 s). My idea want to bypass the series reactor when inrust current down to 0 A and before permissible to take load. I ask many expert in power system and
every person says, it's very good idea but cann't do because may be transformer damaged from other effects. I don't understand because i show my calculation it's clear ,same condition except when the transformer start to take load it havn't series reactor.
Please every body suggest me what and how to solve this problem for possible to do.

Best regards;
ast.

 

[Bung]

It is probably to reduce the fault level on the 22kV busbar to a value inside the interrupting cpacity of the circuit breakers, or the fault capability of some other 22kV equipment. I don't think it is there for transformer inrush problems.

What are the transformer impedances - you will find it on the nameplates? I presume the fault levels are at the 115kV busbar.

Bung
Life is non-linear...

 

[amphan]

Hi;
Thank you for your answer; At power tr 100 MVA Imp= 12 %
and Power tr 72 MVA Imp = 10-12 % depend on OLTC tap select.

Best regards;
ast

 

[RalphChristie]

I tend to agree with Bung. The reactors are normally used to limit short circuit current (fault current) from rising to values dangerous for the equipment and not to limit inrush currents.
See:

http://www.power-capacitors.com/current-limiting-reactor-reactors.htm

If you have some problems with voltage drops, you can use a current limiter in parallel with the reactor. See the following site for more details:

http://www.abb.com/global/seitp/seitp328.nsf/pp/2932573B3EB7A508C1256DCE004D1EF7-6

Regards
Ralph

 

[amphan]

Hi;
Thank you to Ralph, So I contact to ABB's representator in the next time. Yes I worry very much about volatge drop on series reactor because my process need the voltage and power for increase the pocess time but not need change the transformer.
Before I post this problem , I check the circuit between my factory and main power supplier(the bigest in country) not found the series reactor, I read the ABB Substation handbook it said the reactor should not exceed 6 % of system and used for protect cable, swithgear breaker, other part that damaged from braeker switch ON
, I asked ABB technical sale manager and Siemens representator (In my country) how to reduced the loss but no anwser for me, I contact to the main contractor for solve this problem they suggest me replace the new technology system that very high cost and long time to payback.
So in my idea only need bypass the series reactor after close the breaker 0.5 s , before to take load when occured the fault short circuit in this time , I think my protection relay shoud be active , I check the time trip = 30 mS. Please you consider my idea what wrong or must be consider the other point that I forget it.

Best Regards;
ast

My factory produce the steel.
Thailand is the my country.

 

[prc]

I think in your case the series reactor must have a specific need .It may not be to limit the short circuit current ,eventhough that is the normal purpose of it .It will not reduce the inrush at all as in rush current depends on the trf characteristics and point of switching on. Your plant must be arc furnace,aluminium smelter etc,Some times series reactor is provided as a third harmonic filter.Dont bypass the reactor with out first knowing why it was put in first instance.

 

[amphan]

Hi;
Thank you to prc, Yes, My plant have an arc furnace and my system have the SVC system for 2'nd, 3'rd,4'th harmonic filter total power = 100 MVA and now I used only 2'nd,3'rd and have pf=0.9957
So I think the 3'rd harmonic should be a SVC's Function.


Best regards;
ast

 

[prc]

Amphan,In your case then it may be a case of limiting short circuit currents in the furnace trf.When the electrodes arc with the metal in the furnace, it is a dead short on the trf and usually this short circuit current is limited below 2-2.5 times rated current to avoid too much stress in trf.This additional reactance to limit current is provided by the series reactor.Normaly this is an iron cored reactor with 10-20% MVa of furnace trf.In your case what is the rating and % reactance of the reactor ?

 

[amphan]

Hi;
I don't know %reactance of the reactor but I calculate from voltage drop, it's about 10% of system.
Specification of reactor:

I 1870 A
L 4.8 mH


Best Regards;
ast