This document contains questions and answers related to electrical engineering topics. It discusses suburban and long distance railway voltages, total resistance of circuits, differences between isolators and circuit breakers, effects of decreasing field current in DC motors, uses of delta-star transformers for lighting loads, advantages of speed control using thyristors, and advantages of star-delta connected transformers.

1. QUESTIONS OF THE DAY :- ELECTRICAL ENGG BY ASHUTOSH
Q.1 Suburban railways use
(A) 1500 V DC
(B) 440 V three phase AC
(C) 660 V three phase AC
(D) 3.3 kV three phase AC.
Ans: - (A) 1500 V DC
Q.2 Long distance railways use
(A) 200 V DC
(B) 25 kV Single phase AC
(C) 25 kV Two phase AC
(D) 25 kV Three phase AC.
Ans :-(B) 25 kV Single phase AC
1,500 V DC is used in the Netherlands,
Japan, Republic Of Indonesia, Hong
Kong (parts), Republic of Ireland,
Australia (parts), India (around
the Mumbai area alone has been
converted to 25 kV AC like the rest of
India ), France (also using 25 kV 50 Hz
AC), New Zealand and the United States
(Chicago )

2. Q. Find the total resistance for three resistors .
sol :-
QUESTION OF THE DAY :- ELECTRICAL ENGG BY ASHUTOSH

3. ELECTRICALENGGBY ASHUTOSH
CONCEPTOF THEDAY:-ELECTRICALENGGBY ASHUTOSH
Q. What is the difference between isolators and
electrical circuit breakers? What is bus-bar?
Ans :-Isolators are mainly for switching purpose under
normal conditions but they cannot operate in fault
conditions .Actually they used for isolating the CBs for
maintenance. Whereas CB gets activated under fault
conditions according to the fault detected.Bus bar is
nothing but a junction where the power is getting
distributed for independent loads.

9. CONCEPTOF THEDAY:- ELECTRICAL ENGGBY ASHUTOSH
Q . If field current is decreased in shunt dc motor, the speed
of the motor
a. remains same.
b. increases.
c. decreases.
d. none of the above.
ANS & CONCEPT :- b. increases
Since we know that in a dc motor speed is inversely proportional to
flux - N α
𝟏
Φ
if field current decreases , flux decreases and then
speed increases .

10. CONCEPTOF THEDAY:- ELECTRICAL ENGGBY ASHUTOSH
Q. Why Delta Star Transformers are used for Lighting Loads ?
Ans:-For lighting loads, neutral conductor is must and hence the
secondary must be star winding. and this lighting load is always
unbalanced in all three phases. To minimize the current
unbalance in the primary we use delta winding in the primary. So
delta / star transformer is used for lighting loads.
Main advantages of delta star connection
1. as neutral is available on secondary side,it
can be used as 3 phase,4 wire supply system.
2. no harmonic distortion due to third
harmonics .
3. Delta connection provides a path for the
third order harmonic current and hence no
distortion because of it.

11. CONCEPTOF THEDAY:- ELECTRICAL ENGGBY ASHUTOSH
Advantages of speedcontrol using thyristor :-
1. Fast Switching Characterstics than MOSFET, BJT, IGBT
2. Low cost
3. Higher Accuracy
4. Low power consumption. The drive is voltage controlled one rather then rheostat
control.So power loss will be reduced which will improve the efficiancy
5. Easy Operation
6. Smoother control can be possible unlike step variation in the speed in the
general rheostat control
7. Wide range of control is possible with the provision of firing angle control
8. Size of controller will be small and the heat dissipation provisions are also not
much larger as in case of rheostat controllers.
9. With the advancement of electronic devices its manufacturing cost is very much
reduced so will be cheaper than the rheostatic.

12. CONCEPTOF THEDAY:- ELECTRICAL ENGGBY ASHUTOSH
Q. What are the various advantages of Star-Delta
connected transformer ?
Ans:-Advantages of Star Delta Connection
1. The primary side is star connected. Hence fewer
numbers of turns are required. This makes the connection
economical for large high voltage step down power
transformers.
2. The neutral available on the primary can be earthed to
avoid distortion.
3. The neutral point allows both types of loads (single
phase or three phases) to be met.
4. Large unbalanced loads can be handled satisfactory.
5. The Y-D connection has no problem with third harmonic
components due to circulating currents inD. It is also more
stable to unbalanced loads since the D partially
redistributes any imbalance that occurs.
6. The delta connected winding carries third harmonic