WorksheetsELAD DEPTALS
Total questions: 14
Worksheet time: 7mins
Positive coupling occurs when currents:
Enter both dots
Leave both dots
Enter/leave opposite
(A) and (B)
Transformer size for a $42\text{ kVA}$ load + $25\%$ spare:
45
75
112.5
30
Referred secondary resistance when k = N_2 / N_1:
R_2 x K
R_2 / K^2
R_2 x K^3
R_@ / K
In approximate equivalent circuit, exciting branch is
Moved lefr
Removed
Series with R2
Shorted
Ideal transformer has:
Zero copper loss
Zero leakage flux
Infinite permeability
All
Copper loss varies with:
I
V
I^2
f
A $230\text{ V}/11.5\text{ V}$ transformer supplies $20\text{ A}$ on the secondary. The primary current (ideal) is:
0.5 A
1 A
2 A
4 A
Magnetizing current is responsible for:
Copper loss
Producing flux
Output power
Regulation
Transformer impedance is obtained from:
OC test
SC test
Load test
Efficiency Test
Transformer efficiency is maximum when:
Copper loss > iron loss
Copper loss < iron loss
Copper loss = iron loss
Output power is maximum
A $10\text{ kVA}$ transformer has an efficiency of $96\%$ at full load. Total losses are approximately:
200 W
300 W
400 W
500 W
A per-unit value of $0.05$ represents:
5 ohms
0.5 ohms
5% of base value
50% of base value
A $208\text{Y}/120\text{ V}$ panelboard has $68\text{ kVA}$ load and requires $30\%$ spare capacity. Find required kVA:
88.4 kVA
96 kVA
72.5 kVA
100 kVA
Referring secondary resistance to the primary. Given that $a = N_1 / N_2:
R_2 / a
R_2 / a^2
R_2 x a^2
R_2 x a
