Problem 97-1
Source: Adapted from example 2-55 - page 189 -
SAHDEV, S. K. - Book: Electrical Machines - 1st edition - Cambridge University Press - 2018.
A 500 A load with PF = 0.8 lagging and a terminal voltage of 400 V is supplied by two
transformers connected in parallel. The equivalent impedances of the two transformers,
referenced to the secondary side are 2 + j3 and 2.5 + j5, respectively.
a) Calculate the current and powers supplied by transformer a.
b) Calculate the current and powers supplied by transformer b.
c) What is the power factor at which each transformer is operating?
Problem 97-2
Source: Adapted from example 2-55 - page 189 -
SAHDEV, S. K. - Book: Electrical Machines - 1st edition - Cambridge University Press - 2018.
Taking into account the results of the previous problem, find:
a) The load impedance.
b) The value of the voltages E1 and E2, that is, the voltages of the transformer secondaries.
Problem 97-3
Source: Example 2-56 - page 189 -
SAHDEV, S. K. - Book: Electrical Machines - 1st edition - Cambridge University Press - 2018.
Let two single-phase transformers be connected in parallel supplying a current of 1,000 A to a load that has
PF = 0.8 lagging. For each transformer, the secondary EMF in open circuit is 3,300 V. The secondary impedances are 0.1 + j0.2
and 0.05 + j0.4, respectively.
a) Calculate the current supplied by each transformer to the load.
b) Calculate the real power delivered by each transformer.
Problem 97-4
Source: Adapted Example 2-59 - page 191 -
SAHDEV, S. K. - Book: Electrical Machines - 1st edition - Cambridge University Press - 2018.
Consider a transformer "A" that has an open-circuit EMF of 6,600 V
with a secondary-referenced impedance of 0.3 + j 3. This transformer is connected in parallel with a
transformer "B" that has an open-circuit EMF of 6,400 V and a
secondary-referenced impedance of 0.2 + j.
a) Find the current supplied by each transformer to a load 8 + j6 Ω.
b) What is the real and reactive power supplied to the load?
Problem 97-5
Source: Adapted Example 2-58 - page 191 -
SAHDEV, S. K. - Book: Electrical Machines - 1st edition - Cambridge University Press - 2018.
Two transformers are connected in parallel. Both have the same number of turns. Transformer "A"
has an impedance of 0.5 + j 3 and transformer "B" has an impedance of 0.6 + j 10
with reference to the secondary. Determine how they share a load of 100 kW with lagging PF = 0.8.
Problem 97-6
Source: Adapted from example 2-57 - page 190 -
SAHDEV, S. K. - Book: Electrical Machines - 1st edition - Cambridge University Press - 2018.
Two single-phase transformers, "A" and "B", of 250 kVA each are connected in parallel.
Their resistances and reactances are 1% and 6% for transformer "A" and 1.2% and 4.8%
for transformer "B". The load to be supplied is 500 kVA with PF = 0.8 lagging. With no load, the EMFs
of the two transformers are equal.
a) Calculate the power that each transformer supplies to the load.
Problem 97-7
Source: Adapted from example 2-60 - page 192 -
SAHDEV, S. K. - Book: Electrical Machines - 1st edition - Cambridge University Press - 2018.
A 500 kVA transformer "A" is connected in parallel with a 150 kVA transformer "B". In this configuration, a 750 kVA load is connected with PF = 0.8 lagging.
Their open-circuit voltages are 405 V and 415 V, respectively. Transformer "A"
has 1% resistance and 5% reactance, and transformer "B" has 1.5% resistance and
4% reactance. Find:
a) The current circulating through the transformer secondaries when they operate without load.
b) The apparent power that each transformer supplies to the load.
