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Q: Star transformer, 3 phase system ( No Answer,   1 Comment )
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 Subject: Star transformer, 3 phase system Category: Science > Physics Asked by: pkuanko-ga List Price: \$5.00 Posted: 14 Aug 2006 18:16 PDT Expires: 03 Sep 2006 17:50 PDT Question ID: 756034
 ```A 66kV/11kV 10MVA star transformer with impedance of 0.06p.u. is connected to a solid voltage source of 69 kV. A delta connected balance load of impedance R = 60 ohms. Determine the total power to the load by (a) converting all elements to single phase equivalents (b) convert impedance to per unit (c) solve for current/power single phase per unit (d) convert to 3 phase MVA. Please give me full working, I will give you a good tip.```
 ```Perhaps I can help by translating some of the abrieviations: 66 kv = 66,000 volts primary voltage, applied to each of the 3 points of the star = Y. This is the design specs of the transformer, which is likely three separate transformers inside a box 11 kv secondary voltage. More transformer design specs including: 10MVA = 10,000,000 volt amperes = volts times amps: divide by 11,000 = 910 amps but that is not exact as the 3 phases add vectorally at 120 degrees of phase shift. Impediance is normally measured in ohms resistive and ohms reactive. I have no idea of the meaning of 0.06p.u. 60 ohms is likely the resistance connected to each of the three points of the delta, so there are 3 separate resistors (more likely it appears as if it is three separate resistors of 60 ohms each) We can assume the power factor of the load is 100% since no reactive power is suggested, unless it is suggested by p.u. p.u. may mean per unit which could refer to the 3 units of the load or to the 3 separate transformers in the Star transformer box MVA = megavolt amps which is likely about 1/4 of the star transformer rating of ten million VA = 2.5 MVA This is because slightly more than the rated input voltage is applied, but the load is only about 1/5 of the Star transformer rating. Sorry I do not know how to get the correct answers. Neil```