We are going to run a three phase 400V 50HZ 2900RPM induction motor of feed water pump through a star delta starter. Is this way of starting is suitable while the short circuit level of this station is about 65KA?

Regards
Shaheed
[email protected]

 

Shaeed... what is the motor size?

Phill Corso ([email protected])

 

Sir,

size of motor is 600KW 1050A 400V 50HZ and 2900RPM. we are trying to run by star delta starter.

Regards
Shaheed

 

Shaheed...

I will use my Gi.Fi.E.S. method (pronounced Jiffy’s) for an approximate solution. Gi. is for “Given”; Fi. for "Find"; E. for "Equation"; and S. for "Solution!"

A) Given: 3-phase source of infinite power having a voltage, Vb = 400V; Short-circuit fault-current, Isc = 65,000A; and a SCIM motor whose rated capacity = 600kW, and rated current, Ir = 1,050A. For simplicity, assume Starting-current to Run-current ratio, Is/Ir = 6.0!

B) Find: The Motor’s Terminal voltage for two conditions: a) DOL Starting; and b) Y-D starting!

C) Equation(s): Infinite means no intentional impedance between the 400V bus and its source:<pre>
o kVAsc = Sqrt(3)xVbxIsc
o Motor Run, kVAr=Sqrt(3)xVbxIr
o Motor Strt,kVAs=(Is/Ir)x kVAr
o DOL Vdrop=100x kVAs/kVAsc,%
o Y-D Vdrop=0.577 (not 0.500) of DOL%

D) Solution:
o kVAsc = Sqrt(3)x400x65,000=45,000kVA
o kVAr = Sqrt(3)x400x1,050=727.5kVA
o DOL, kVAs=6.0x727.5=4,370kVA
o Y-D, kVAs=0.577x4,370kVA=2,520kVA

Part a) DOL Vdrop=100x(4,370/45,000)= 8.7%
Part b) Y-D Vdrop=0.577x8.7= 5.0%</pre>
Regards, Phil Corso ([email protected])

 

Sir

Thank you for useful informations.

Regards
Shaheed