Tutorial #01
EKT 451/4: Applied Electrical Engineering
TUTORIAL #1
Transformers
EKT 451/4
APPLIED ELECTRICAL
ENGINEERING
Tutorial #01
1.
EKT 451/4: Applied Electrical Engineering
A transformer has the following parameters;
N1= 1000, N2 = 10, I1=200A, V1 = 100kV
a) Determine I2 and V2
b) Which type of transformer is this?
2. A 250 kVA, 11 000V/400V, 50Hz single-phase transformer has 80 turns on the
secondary. Assume the transformer is ideal. Calculate:
a) The values of the primary and secondary currents
b) The number of primary turns
c) The maximum value of flux, Фm.
(22.73A, 625A, 2200 turns, 22.5 mWb)
3. A 60-Hz transformer having a 480-turn primary winding takes 80W power and
1.4A current ant input voltage 240V. if the primary winding resistance is 0.25Ω,
determine
a) the core loss
b) no-load power factor
c) the maximum core flux (neglect the primary resistance and reactance
drop)
4. A 10 kVA 2400/240V 60Hz transformer was tested with the following results:
Power input during short circuit test is 340W, power input during open circuit test
is 168 W. Determine the efficiency of the transformer at full load. Given the load
power factor is 0.8.
(94%)
5. A 1: 10 step-up transformer is placed at the generator end of the transmission line
and a 10:1 step-down transformer is placed at the load end of the line as shown in
Figure 1.2. Determine the load voltage and the transmission line losses.
Figure 1 2
(479.5, 00 V; 16.5 W)
Tutorial #01
EKT 451/4: Applied Electrical Engineering
6. Consider a single phase 2400/240V transformer. The primary is connected to a
2200 V source and the secondary is connected to a load impedance of 2 ∠36.9°.
a)
b)
c)
d)
e)
Find the secondary output current and voltage
Find the primary input current
Find the load impedance as seen from the primary side
Find the output and output apparent powers.
Find the output power factor
(110, -36.90 A; 220,00V; 11, -36.90 A; 200, 36.90 Ω; 24.2, -36.90 kVA; 2420, -36.90 VA; 0.8 lagging)
7. Test are performed on a single phase, 10 kVA, 2200/220V, 60 Hz transformer and
the following results are obtained
Open-circuit test
(HV side open)
Voc = 220 V
Ioc = 2.5 A
Poc = 100 W
Short circuit test
(LV side shorted)
Vsc = 150 V
Isc = 4.55 A
Psc = 215 W
a)
Sketch the approximate circuit model of the transformer referred to:
i) Primary voltage level
ii) Secondary voltage level
b)
Find the impedances of the approximate equivalent circuit referred to the
primary side and secondary side.
c)
Sketch the circuit model for both cases.