Review Materials: Three Phase Circuits
Prepared By: Engr. Rhaffy C. Arenas
1. In a balanced 2-phase voltage system, the phase voltages are 100 volts, what
is the line to line voltage?
A. 120 volts C. 141 volts
B. 170 volts D. 60 volts
2. In a balance three phase voltage, Van=110/30. What is Vbn using ACB
sequence?
A. 95.2 โ j165 C. 95.3 + j165
B. -95.2 + j55 D. 0 โ j110
3. A balanced three phase wye connected source has using positive phase
sequence, Vca = 230 Vrms with 90 degrees angle. Determine Vbc.
A. 230 + j0 volts C. 115 โ j199 volts
B. -199 โ j115 volts D. โj220 volts
4. A three phase, balanced delta connected resistive load draws 30 amperes
phase current from balanced three phase supply. An open circuit faults occurs
in one of the lines. Determine the line current.
A. 45 Amp C. 90 Amp
B. 60 Amp D. 100 Amp
5. Three 3.33 ohms resistance are connected in wye across 220 V, 3-phase
supply. What is its equivalent delta connected resistance.
A. 2.22 ohms C. 6.7 ohms
B. 20 ohms D. 10 ohms
6. Three identical resistances connected in wye carry a line current of 30 Amp. If
the same resistances are connected in delta across the same supply, what is
the line current?
A. 10 Amps C. 30 Amps
B. 60 Amps D. 90 Amps
7. The secondary of a transformer bank is wye-grounded, it has a balance
voltage and the balanced load. The voltage to ground is 132V and its line
current is 40A. What is kVA of the load?
A. 9.1 C. 27.4
B. 19.2 D. 15.84
8. The phase b line voltage and the phase a line current of a balanced 3-phase
system are: V = 220 sin (wt + 2100) Volts and I = 10 sin (wt - 300) Amp
respectively. What is the power of the system?
A. 1905 Watts C. 5716 Watts
B. 3300 Watts D. 3810 Watts
