# multiple choice questions regarding electrical systems,,help!!!

Discussion in 'Electronics Homework Help' started by aabbddlah, Nov 8, 2012.

1. ### aabbddlah

1
0
Nov 8, 2012
i v got a quiz and i m unable to find answers for these ,, i will appreciate it if u would assist me gents

q1-Which of the following is NOT an approved transformer configuration by ANSI in regard to voltage phase shift between primary and secondary windings?

a-Delta-Wye with thirty degrees lagging shift at the secondary

b-Wye-Wye with zero phase shift

c-Wye-Delta with thirty degrees lagging shift at the primary

d-Delta-Delta with zero phase shift

q2-What components of the fault current shall be considered during the first half cycle of the short circuit and for what purpose?

a-Transient asymmetrical fault for interrupting rating of the circuit breakers.
b-Sub-transient asymmetrical fault for Close and Latch rating of the circuit breakers.
c-Transient symmetrical fault for Close and Latch rating of the circuit breakers.
d-Sub-transient asymmetrical fault for interrupting rating of the circuit breakers.

q3-Which of the following is NOT true in regard to fault levels in balanced three phase powewr systems?

a-Arcing faults are higher than three phase bolted faults.

b-Ground fault equals approximately the ground resistor current rating fault in resistive grounded systems.

c-Phase to phase fault equals 0.867 of the three phase bolted fault.

d-Ground fault equals approximately three phase bolted fault in solidly grounded systems.

q4-An unbalanced wye with grounded neutral load consists of a 4 + j3 Ohm impedance connected to phase A, a 3 + j3 Ohm impedance connected to phase B, and a 4 + j5 Ohm impedance connected to phase C. The power source is balanced and the sequence is ABC with VAB = 208 at an angle of 0°. Assuming all currents are flowing from the source to the load, calculate the value of I(B) [where I(B) is the phase B current].??

A~ 28.3 A at an angle of 165°
B~ 49.0 A at an angle of -175°
C ~28.3 A at an angle of -145°
D ~28.3 A at an angle of -175°

q5-which of the following statements is incorrect?

a-Normal capacitive currents of the three phases of an ungrounded power system are unequal and hence they do not sum to zero.

b-Phase reversal is a fundamental negative sequence harmonic.

c-Phase to ground fault in an ungrounded balanced system will result in three times the single phase normal capacitive current.

d-Harmonics of triple multiples of the fundamental are zero sequence while harmonics of double multiples of the fundamental are negative sequence.

2. ### CocaCola

3,635
5
Apr 7, 2012
u nd 2 do yr own hmwrk... May I sugest u *t W elimination d options/answers uno r false, thN @ dat point progress 2 researchn d remaining answers 1 @ a tym 'til u narrow it dwn... n wen u myt narrow it dwn 2 2 options n r 404, thN ask 4 direction n we myt B abL 2 provide it...

Last edited: Nov 8, 2012
3. ### Yoa01

214
0
Jun 18, 2012
You, sir, are a genius.

4. ### Harald KappModeratorModerator

11,824
2,756
Nov 17, 2011
Rotfl   