Question 01 The voltage designation 7200V12470VY is used for

Question 01: The voltage designation 7200V/12470VY is used for the primary winding of a single phase distribution transformer. Make the choise below that best fits the above designation.

a) The winding can be connected between two phases if the feeder line-to-line voltage is 7200 V or it can be connected between a phase and the neutral (ground) if the feeder line-to-line voltage is 12470 V.

b) The winding can operated at a minimum of 7200 V and at a maximum of 12470 V.

c) The winding can be used in multiple connections depending on the feeder voltage (7200 V or 12470 V L-L).

d) The winding can be connected between two phases if the feeder voltage is 7200 V Line-to-Line.


Question 02: Power losses in the transformer are due to the following (select all that apply)

a) Winding resistance
b) Eddy current loss
c) Hysteresis loss
d) Dieelectric loss

Question 03: The secondary current of a single-phase 15 kVA 7200V-240 V is 50 A. Compute the pu value of the current. (use 2 digit precision)

Solution

Q1)

The answer is C)

Because the voltage rating of the given transformer is V1 : V2 = 7200 : 12470 ;

If feeder line to line voltage is 7200 V the primary i.e low voltage side of a transformer is connected to a feeder, Similarly if feeder line to line voltage is 12470 V then secondary or high voltage winding can be connected to a feeder.

Q2)

The answer is option A)

The power losses depends on conductor resistance of winding. Winding are made of conductor which has neglagibleresistance, so power is lost.

Power loss are given by Ploss = I² R

Q3)

Consider base Voltage V2 = 240 V and Base Power P = 15 kVA

Base current is given by Ibase = P/V2 = 15000/240 = 62.5 A

PU value Ipu = Iactual / Ibase = 50/62.5 = 0.80 PU