Q2. Consider a 40MVA, 132/11kV transformer with a reactance of 15% on its rating, (a) shown in Figure Q2. It is equipped with an on-load tap-changer that is used to maintain constant voltage at the 11kV busbar by compensating for variations in the voltage of the 132kV network, and for the voltage drop across the transformer. The variation of the network voltage at 132KV transformer busbar for heavy loading conditions is shown in the table below. Active power losses in the transformer are ignored, and it is assumed that the value of the reactance of the transformer is not influenced by the change in the turn ratio. Calculate t, the tap ratio, and the actual voltage at bus 2 in this case. (Note: For instance, a nominal ratio of the transformer is 132/11, when tapped to give 144/11 ratio, therefore t is 144/132=1.09). Load Power factor Voltage at 132kV Desired voltage at busbar (Bus 1) 11kV busbar (Bus 2) 5MVA 0.9 185kV 11kV Bus 2 Bus 1 X=15% t:1 Figure Q2

Q2. Consider a 40MVA, 132/11kV transformer with a reactance of 15% on its rating, (a) shown in Figure Q2. It is equipped with an on-load tap-changer that is used to maintain constant voltage at the 11kV busbar by compensating for variations in the voltage of the 132kV network, and for the voltage drop across the transformer. The variation of the network voltage at 132KV transformer busbar for heavy loading conditions is shown in the table below. Active power losses in the transformer are ignored, and it is assumed that the value of the reactance of the transformer is not influenced by the change in the turn ratio. Calculate t, the tap ratio, and the actual voltage at bus 2 in this case. (Note: For instance, a nominal ratio of the transformer is 132/11, when tapped to give 144/11 ratio, therefore t is 144/132=1.09). Load Power factor Voltage at 132kV Desired voltage at busbar (Bus 1) 11kV busbar (Bus 2) 5MVA 0.9 185kV 11kV Bus 2 Bus 1 X=15% t:1 Figure Q2

Power System Analysis and Design (MindTap Course List)

6th Edition

ISBN:9781305632134

Author:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Publisher:J. Duncan Glover, Thomas Overbye, Mulukutla S. Sarma

Chapter3: Power Transformers

Section: Chapter Questions

Problem 3.26P: A bank of three single-phase transformers, each rated 30MVA,38.1/3.81kV, are connected in Y- with a...

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Question

Q2.
(a) Consider a 40MVA, 132/11kV transformer with a reactance of 15% on its rating,
shown in Figure Q2. It is equipped with an on-load tap-changer that is used to
maintain constant voltage at the 11kV busbar by compensating for variations in
the voltage of the 132kV network, and for the voltage drop across the
transformer. The variation of the network voltage at 132kV transformer busbar
for heavy loading conditions is shown in the table below. Active power losses
in the transformer are ignored, and it is assumed that the value of the reactance
of the transformer is not influenced by the change in the turn ratio. Calculate
t, the tap ratio, and the actual voltage at bus 2 in this case.
(Note: For instance, a nominal ratio of the transformer is 132/11, when tapped
to give 144/11 ratio, therefore t is 144/132=1.09).
Load
Power factor
Voltage at 132kV
Desired voltage at
busbar (Bus 1)
11kV busbar (Bus 2)
5MVA
0.9
185kV
11kV
Bus 2
Bus 1
X-15%
t:1
Figure Q2

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Full calculation with any assumption needed. All sub questions please as it is all related.
Consider a 40MVA, 132/11kV transformer with a reactance of 15% on its rating, shown in Figure Q2. It is equipped with an on-load tap-changer that is used to maintain constant voltage at the 11kV busbar by compensating for variations in the voltage of the 132kV network, and for the voltage drop across the transformer. The variation of the network voltage at 132kV transformer busbar for heavy loading conditions is shown in the table below. Active power losses in the transformer are ignored, and it is assumed that the value of the reactance of the transformer is not influenced by the change in the turn ratio. Calculate t, the tap ratio, and the actual voltage at bus 2 in this case. (Note: For instance, a nominal ratio of the transformer is 132/11, when tapped to give 144/11 ratio, therefore t is 144/132=1.09). Load Power factor Voltage at 132kV Desired voltage at busbar (Bus 1) 11KV busbar (Bus 2) 5MVA 0.9 185kV 11kV Bus 2 Bus 1 X=15% t:1 Figure Q2
P2-Draw the equivalent circuit of a single-phase transformer and explain how the core losses are almost invariant to the load (current). How do they depend on the terminal voltages of the transformer? Also, using the equivalent circuit explain how the copper losses depend on the load current.
A method for determining the equivalent network of a nonideal transformer consists of two tests: the open-circuit test and the short-circuit test. The open-circuit test, shown in figure (a), is usually done by applying rated voltage to the primary side of the transformer while leaving the secondary side open. The current into the primary side is measured, as is the power dissipated. The short-circuit test, shown in figure (b), is performed by increasing the primary voltage until rated current is going into the transformer while the secondary side is short-circuited. The current into the transformer, the applied voltage, and the power dissipated are measured. The equivalent circuit of a transformer is shown in figure (c), where rw and Lw represent the winding resistance and inductance, respectively, and rc and Lc represent the losses in the core of the transformer and the inductance of the core. The ideal transformer is also included in the model. With the open-circuit test, we may…