Q6
(a) With the aid of delta and star connection diagrams, state the basic equation from which the delta-star and star- delta conversion equation can be derived.
(5)
(b) Three identical coils are delta connected to a 3 ph, 440 V, 60 Hz supply and consume a total power of 9 kW at a power factor of 0.8 lag.
(i) Calculate the resistance and inductance of EACH coil.
(5)
(ii) If the same three coils are now connected in star to the same supply, calculate the current in each line if:
(1) one coil is short circuited;
(2) one coil is open circuited.
(9)
Reference Answer
### Part (a): Delta-Star and Star-Delta Conversion #### Concept The fundamental principle for deriving the conversion equations between a Star (Y) connected network and a Delta (Δ) connected network is based on the concept of **network equivalence**. For the two configurations to be equivalent, the impedance (or resistance, for a purely resistive circuit) measured between any two corresponding terminals must be identical, regardless of the configuration. The third terminal is considered open-circuit during this measurement. Let the three terminals be A, B, and C.
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