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Tutorial Sheet 1

The document contains a tutorial sheet with various questions related to electrical engineering concepts, particularly focusing on transformers and alternators. Each question requires calculations to determine per unit values, reactance, and impedance based on given specifications and ratings. The problems involve both single-phase and three-phase systems, including different voltage levels and load conditions.

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22bee009
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44 views3 pages

Tutorial Sheet 1

The document contains a tutorial sheet with various questions related to electrical engineering concepts, particularly focusing on transformers and alternators. Each question requires calculations to determine per unit values, reactance, and impedance based on given specifications and ratings. The problems involve both single-phase and three-phase systems, including different voltage levels and load conditions.

Uploaded by

22bee009
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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Tutorial Sheet 1

Q: No. 1 A 5 kVA, 400/200 V, 50Hz, 1-phase transformer has primary and secondary leakage

reactances each of 2.5 . Determine the total reactance in per unit.

Q: No. 2 A three phase alternator with a rating of 10 MVA, 33 kV has its armature resistance

of 15 /phase and synchronous reactance of 80 /phase, Determine p.u. impedance of the

alternator.

Q: No. 3 A single phase transformer of 11 kV/400 V, 50 Hz, 150 kVA has primary resistance

and reactances are 2 and 10 , the secondary resistance and reactances are 0.01 and

0.05 respectively. Determine the per unit values of transformer.

Q: No. 4 A single phase transformer is rated 110/440 V, 2.5 kVA. Leakage reactance as

measured from the low-tension side is 0.06 . Determine leakage reactance in p.u.
Q: No. 5 A single phase two-winding transformer is rated 25 kVA, 1100/440 volts, 50 Hz.
The equivalent leakage impedance of the transformer referred to the low voltage side is

0.06<780 . Using transformer rating as base value, determine the per-unit leakage

impedance referred to low voltage winding and referred to high voltage winding.

Q: No. 6 Three parts of a single-phase electric system are designated A, B and C and are
connected to each other through transformers, as shown in the Fig 1.1. The transformers are
rated as follows.

​ A-B​ ​ 10,000 kVA, 138/13.8 kV, leakage reactance 10%

​ B-C​ ​ 10,000 kVA, 138/69 kV, leakage reactance 8%

If the base in circuit B is chosen as 10,000 kVA, 145 kV, find the per-unit impedance of the

300- resistive load in circuit C referred to circuits C, B and A.


Fig 1.1: Circuit for Q: No. 6

Q: No 7 The three transformers rated 25 MVA, 38.1/3.81 kV are connected Y-∆ as shown in

Fig 1.2 with a balanced load of three 0.6 , Y-connected resistors. Choose a base of 75

MVA, 66kV for the high tension side of the transformer and specify the base for the low
tension side. Determine the per-unit resistance of the load on the base for the low-tension
side. Then determine the load resistance RL referred to the high-tension side and the per-unit
value of this resistance on the chosen base.

Fig 1.2: Circuit for Q: No. 7

Q: No. 8 A three phase transformer is rated 400 MVA, 220Y/22∆ kV. The short-circuit

impedance measured on the low voltage side of the transformer is 0.121 and because of

the low resistance this value may be considered equal to the leakage reactance. Determine the
per-unit reactance of the transformer and the value to be used to represent this transformer in
a system whose base on the high-tension side of the transformer is 100 MVA, 230 kV.

Q: No. 9 Solve Q: No. 8 using the change of base of per unit quantities formula.

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