Starting large motor 2MW with captive transformer using temporary transformer

[15484]

Dear all,

I need some advices regarding to start large motor cooling water pump 2000kw, 3.3kV(detail info is listed below) using captive transformer 3500kVA (13.8kV/3.3kV).
And IMHO, captive trafo is supplied from temporary transformer 3000kVA (20kV/3.45kV) which sufficient to deliver starting motor 2000kW (I think), but not bigger than the captive tranformer 3500kVA,
This captive trafo also through using backfeed transformer 10MVA, 3.3kV/13.3kV (normal is step down Dyn-11, 13.8kV/3.45kV) which I have proposed ground protection transformer or zig-zag trafo for delta side of the 10MVA trafo.
With this starting scheme, is it sufficient to make start of this motor?

Motor data:
Pump driven for motor cooling water: 2000kW,
BHP: 1760kw, spee: 600rpm, poles :10
LRC motor: 500%
PF motor at starting : 0.2
Voltage: 3300kV, 3phase, 50Hz
Full load amp: 458Amp
temp rise:B
Efficiency and pf: 95.5% and 80%at 100%

I have calculated that it can work with using captive trafo 3500kV with detail below:
Voltage: 13.8kV/3300kV
Amp: 146.43/612.34
short circuit impedance: 4
Vector group: Dyn-11

This motor should be normal operated using STG 19MVA,13.8kV
But within start up comm this captive trafo will be fed from backfed tranformer 10MVA,with detail data below:
Voltage: 3450V/13.8kV
Amp: 1673.48/418.37
short circuit impedance: 8%.
Vector group: Dyn-11

This trandformer is also energized from temp trafo 3000kVA, with detail below:
Voltage: 20000kV/3450kV
Amp: 86.6/502.04
short circuit impedance: 7%.
vector group: YNyn-6
The utility system is using 20kVA, with short circuit impedance 500MVA,

Do you have any experience this scheme, and other advices will be welcome.

Thank you,

Athan

 

[jraef]

Wow, that's a LOT of transformers in series! Why?


"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington

 

[15484]

yes,

I could not avoid this since this scenario happen when DEG is run out (2 fail), and when this start-up commissioning, this alternative is just only our option,

hope you can give us some advices,

Thx,

At

 

[7anoter4]

IMHO the voltage drop will be more than 50% and I never heard an induction motor starting D.O.L. in this conditions.