Download ps1 viva notes

POWER SYSTEM VIVA QUESTION
Q1. What is the Power Station?
A. Power Station is a place where Power is Generated and Transmitted, eg. Thermal power station, Hydel
power station, Nuclear power station etc.
Q2. What is Slack Bus ?
A. Slack Bus is the responsible for the delivering losses in the power system. in this bus the magnitude of
voltage and phase angle are specified. This bus is first to respond to a changing load condition.
Q3. What is critical disruptive voltage?
A. The minimum voltage at which the breakdown of the insulating properties of air occurs and corona
start is called D C V.
Q4. How many types of fault occurs in the 3 P power system ?
A. Faults in the 3 P system can be classified under the following :a. single line to ground (LG) fault
b.line to line (LL) fault
c. Double line to ground (LLG) fault
d. Thee Phase short circuit (LLL) fault
e. three phase to ground (LLLG) fault
Q5. How many methods uses for the load flow solution ?
A Gauss-seidel method using Ybus
Newton- Rap son method (NR)
Power flow through line and slack bus power
Decouple load flow method Fast Decouple load flow method.
Q6. What is skin effect?
A. When the AC passed through the conductor the density of the current is not uniform over the crosssection of the conductor, the density of the current is very high near the surface of the conductor and very
low at middle this effect is called skin effect. This effect is only in the ac.
Q7. What is the Bundle conductor and why is used?
A. A bundle conductor consists of two more parallel sub conductors at a spacing of several diameters. this
is use to reduce the corona and skin effect.
Q8. What is the power system stability?
A. The ability of the system to reach a normal or stable condition after being disturbed is called stability.
Under stable condition system stay in synchronism.
Q9. What is the stability limit and transmission capability?
A.b The stability limit is the max. power that can be transferred in a n/w b/w sources and loads without
loss of synchronism. this is two type- 1 steady-state limit , 2 transient limit.
Q10. What is Infinite Bus.
A. A group of machines located at one place may be treated as a single machine, the capacity of s/s is too
large is so large that its voltage and frequency may be taken constant such system is called infinite bus
system or simply infinite bus.
Q11. What is Transient stability ?
A. The transient stability is ability of the system to maintain synchronous operation and reach a stable
state.
Q12. What is Swing equation ?
A. The equation of motion of
the machine rotor is given
by
is called swing equation.
where
J
is the total moment of inertia of the rotor mass in
kgm2
POWER SYSTEM VIVA QUESTION
is the mechanical torque supplied by the prime mover
Tm
in N-m
Te is the electrical torque output of the alternator in N-m
θ is the angular position of the rotor in rad
SAG AND TENSION
Q13. what for Centenary word stand for ?
A. The curve made by a free hanging line conductor due to its own weight is called Centenary and that
wire is caller centenary wire.
Q14. What is span?
A. The horizontal distance b/w two adjacent supports is called the span.
Q15. What is sag?
A. The vertical distance b/w the conductor at midpoint and the line joining the two adjacent level support
is called Sag.
Q16. What is the relation among sag, span and tension?
A.
Sag =wl*l/8H
where w = per unit weight of conductor
l = span
H = horizontal Tension
Q17. Where are sag template use ?
A. The use of sag Template is essential to allocate the position and hight of the supports correctly on the
profile.
Q18.What is the Electrical Load?
A. The load can be defined as several ways1.Load indicates a device which consume electrical energy.
2. Load indicate the power requirement from a supply circuit.
3. Load indicates the current or power passing through a line or machine.
Types of LoadA. Load may be Resistive, capacitive, inductive or some combination of them.
Q19 What is Demand ?
The Demand of installation of the system is the load that is drawn from the source of supply at the
receiving terminals avg. over a suitable and specified interval of time.
Q20.What is Load Factor?
Energy consumed during a time
Load Factor =
Peak Load * time
Q21.What is Diversity Factor ?
Sum of individual maximum demand
Diversity Factor =
Max. demand of whole system
Q22What is Refrigeration system ?
A. There are three refrigeration system1 Vapour compression Refrigeration system.
2 Vapour absorption Refrigeration system.
3 Thermo electric Refrigeration system
Q23What is air conditioning ?
A. Air conditioning means to make air fit to promote human comfort and efficiency or to ensure proper
POWER SYSTEM VIVA QUESTION
operation of dedicated equipments.
Types of Air conditioning ?
A. 1 Unitary Type
2. Central type
Q24. When a capacitor bank connect in series ?
A. A capacitor bank is connected in serious for improving the voltage profile at load end in the
transmission.
Q25. when a Capacitor bank is use in parallel ?
A. A capacitor bank is connected in serious for improving the Power Factor of load .
Q26. what is the normal domestic power factor ?
A.
0.75 to0.8
Q27. what is the normal Industrial power factor ?
A.
0.9
Q28. what is the Phase Modifier ?
A. Phase Modifier is also use to improve the power factor. this is nothing but synchronous moter without
load and connected with parallel to load.
here are some very important question and answers which are very use full fof that candidates who are
beating the tough electrical interviews .
Q29. What is the Line Regulation ?
A. Voltage regulation of the line is defined by the change in the voltage at the receiving end when full
load at constant power factor is removed, the voltage at the sending end being kept constant.
I Vrnl I - I Vrfl I
Per unit regulation =
I Vrfl I
Q30. What is the Line regulation for short Lines ?
A. For short Line
I Vrfl I = I Vr I
at no Lioad I Vrnl I = I Vs I
I Vs I - I Vr I
So Line regulation =
I Vr I
Q31. What is the unit of the Voltage regulation ?
A. There is no unit of voltage regulation so voltage regulation is unit less quantity .
Q32. What is the transmission efficiency ?
A. The line or Transmission efficiency is the ratio of the output of the line to the power input to the line.
neta = power output
Power input
Q33. How many model are use to solve the Median Transmission line ?
A. Pie and T Model .
Transmission line parameters
1.What are the different types of conductors?
a)Solid conductors b)Stranded conductorsc)Composite stranded conductors (upto 200KV)d)Bundle
conductors ( above 400KV )
2.
Why all overhead lines use ACSR (Aluminium Conductor Steel Reinforced)conductors
?ACSR conductors comprises of hard drawn aluminium wires stranded around a core of singleor multiple
strand galvanized steel wire. They provide the necessary conductivity while thesteel provides the
necessary mechanical strength and it has less corona loss.
3.
What is a bundle conductor and mention the advantages of using bundled conductors
?It is a conductor made up of 2 or more sub conductors and is used as one phaseconductors.
Advantages of bundle conductors
:a)Reduced reactance b)Reduced voltage gradientc)Reduced corona lossd)Reduced Interference.
4. What is the necessity of Double circuit lines and List out the advantages of doubleCircuit lines?
POWER SYSTEM VIVA QUESTION
Necessity of Double circuit lines is to enhance the power handling capacity
Advantages of double circuit lines:
a)Half of the load is shared by the other line b)The increase in load current can be easily handled
c)
In case of power failure in one circuit, the power will be supplied by the other
5.
What is skin effect
?The steady current when flowing through the conductor, does not distribute uniformly, rather it has the
tendency to concentrate near the surface of the conductor. This phenomenon iscalled skin effect
6.Why Skin effect is absent in dc system?
The steady current when flowing through a conductor distributes itself uniformly over thewhole cross
section of the conductor .That is why skin effect is absent in DC system.
7
.
On what factors the skin effect depend
? Nature of the material,Diameter of the wire, Frequency and shape of the wire.
8
.
Define proximity effect
?The alternating magnetic flux in a conductor caused by the current flowing in a neighboringconductor
gives rise to a circulating current which cause an apparent increase in the resistanceof the conductor. This
phenomenon is called as proximity effect.
9
.
What is the effect of proximity effect
?
It results in the non uniform distribution of current in the cross section, and the increase of resistance.
10. What is meant by transposition of line conductors and advantages of transposition?
Transposition of conductors is defined as the interchanging the positions of the lineconductors at regular
intervals along the line so that each conductor occupies the original position of every other conductor at
an equal distance.
Advantages of transposition:
a)Elimination of interference by using Transposition of lines b)Average Inductance is same in each
section of the line. i.e G.M.D’s are equal for eachsection.
11. Define Self GMD and Mutual GMD?SelfGMD(GMR) :
The Self-GMD means self geometrical mean distance .It reduces thecomplexity of Inductance
calculationGMR = 0.7788r =1r
Mutual GMD:The mutual GMD is the geometrical mean of the distances from oneConductor to the other.
12
.
What is meant by Inductive Interference?
Usually, common lines are run along the power lines, in such cases, these lines are run on
thesame support and the same route. Under such conditions the power lines are likely tointerfere with the
communication lines. The interference is mainly due to electromagneticand electrostatic fields. This can
be eliminated by using transposition of lines.
POWER SYSTEM VIVA QUESTION
13. Define Symmetrical spacing and Unsymmetrical spacing?
In 3-phase system when the line conductors are equidistant from each other then it is calledSymmetrical
spacing.Ex: When 3-phase line conductors are not equidistant from each other, the conductor spacing
issaid to be Unsymmetrical spacing.Ex:
Q34What is the difference between a battery and a capacitor?
Q35Why A.C needs more insulation than D.C at same voltage level?
Q36What is The Difference between a VOLTAMETER and a VOLTMETER?
Q37What is the objection to have lamps in a house-lighting circuit connected in series?
Q38How To Find/Calculate the Number of Fluorescent Lamps in a Sub Circuit?
Q39How to Determine the Number of Lamps in Final Sub Circuit?
Q40How much Watts Solar Panel We need for our Home Electrical appliances?
Q41Will a D.C Shunt Motor operate on an A.C Supply?
Q42Why the reactance of a system under fault condition is low and faults currents may raise dangerously
high value. ? (With simple example)
Q43Explain the statement that induction motor is fundamentally a Transformer?
Q44What is the difference between Power Transformers and Distribution Transformers?
Q45What is the purpose of ground wires in over-Head Transmission lines?
Q46What is the difference between real ground and virtual ground?
Q47How To Calculate Your Electricity Bill. Easy and simple Explanation.
Q48Under what condition is D.C supply applied safely to the primary of a transformer?
Q49A step up transformer which has 110/220 turns. Can we replace it with 10/20 turns? Turns ratio is
same shall its rating be same? Give appropriate reason?
Q50What are the fundamental differences between E.M.F (Electro motive force) and P.d (Potential
difference)?
Q51Why alternator rated in kVA. Not in kW?
Q52Can we operate a 60HZ Transformer on 50Hz Supply Source and Vice Versa?
POWER SYSTEM VIVA QUESTION
Q53What would happen if a power transformer designed for operation on 50 Hz (frequency) were
connected to a 5 Hz (frequency) source of the same voltage?
Q54What would happen if a power transformer designed for operation on 50 Hz (frequency) were
connected to a 500 Hz (frequency) source of the same voltage?
Q55What will happen if the primary of a transformer is connected to D.C supply?