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WorksheetsPower Systems Analysis
Total questions: 40
Worksheet time: 40mins
The load flow solution is always assured in case of:
Newton-Raphson method
Gauss method
Gauss-Seidel method
None of these methods guarantees
The disadvantage of large memory requirement can be overcome by decoupling the coupling between
p-δ and Q-V
p-δ or Q-V
P-V and Q-δ
None of these methods guarantees
Which among the following quantities are specified at the generator bus?
P and Q
P and |V|
Q and |V|
P and δ
Which among the following quantities are specified at the load bus?
P and Q
P and |V|
Q and |V|
P and δ
Why are load flow studies carried out?
To study of stability of the system
For fault calculations
For planning the power system
All of these
The G-S load flow method has following disadvantages
Unreliable convergence
Slow convergence
Choice of slack bus affects convergence
A good initial guess for voltages is essential for convergence
If a PV bus is treated as a load bus then which one of the following limits would violated
Voltage
Active power
Reactive power
Phase angle
GAUSS SEIDEL method can be used for solving the set of
Linear algebraic equations
Non Linear algebraic equations
Arithmatic equations
None of above these methods
Zero sequence current can flow from a line in to transformer bank if the winding's are in
Grounded star/delta
Delta/star
Star/grounded star
Delta/delta
What is the value of zero sequence impedance in line to line faults?
Z0 = 1
Z0 = ∞
Z0 = 3 Zn
Z0 = 0
What percentage of fault occurring in the power system is line to line fault
5 %
30 %
25 %
15 %
What is the expression for fault current in line to line fault?
If = √3 * (Ea / Z1 + Z2)
If = 3 * (Ea / Z1 + Z2)
If = √3 * (Ea / Z1 + Z2 + Z0)
If = 3 * (Ea / Z1 + Z2 + Z05)
What happens to the value of the fault current in case of SLG fault, if fault impedance is introduced?
The fault current increase
The fault current remains same as in case of SLG fault.
The fault current becomes zero
The fault current is reduced
What is the simplified diagram called, after omitting all resistances, static loads, capacitance of the transmission lines and magnetizing circuit of the transformer?
Single line diagram
Resistance diagram
Reactance diagram
Both (a) and (b)
Which of the following type of reactors are popularly used in power systems?
Compensation reactors
Current limiting reactors
Suppression or Peterson reactors
All of these
What are the terminal conditions in case of SLG fault, if the fault occurs in the phase A?
Vb = 0, Ia = 0, Ic = 0
Va = 0, Ib = 0, Ic = 0
Va = 0, Ia = 0, Ic = 0
Vb = 0, Ia = 0, Ib = 0
What are cross country faults?
A fault occurring at any point of the power system
Two or more faults occurring simultaneously on the power system
Line to line fault
All of these
What is the fault current expression in case of LLG faults?
If = 3 Ia1
If = 0
If = 3 Ia0
If = Ia1
The load current in short circuit calculation is neglected because
1. Short circuit current much larger than load currents
2. Short circuit current out of phase with load currents
1 and 2
1 or 2
1 alone
2 alone
The short circuit current of an alternator when short circuited on three phases will be
Zero as time goes to infinity
Maximum when time goes to infinity
Infinity when time goes to infinity
Small as time goes to infinity but not zero
When a line to ground fault occurs,the current in faulted phase is 100 A.The zero sequence current in this case will be
0 A
33.3 A
66.6 A
100 A
a’ is an operator used to symmetrical component analysis
Which rotates the vector, it operates upon, through an angle 90° in the clockwise direction
Which rotates the vector, it operates upon, through an angle 120°, in the counter-clockwise direction
Which rotates the vector, it operates upon, through an angle 120°, in the clockwise direction
Which rotates the vector, it operates upon, through an angle 240°, in the clockwise direction
Various power system faults in increasing order of severity are
LG,LL,LLG,LLLG
LLLG,LLG,LG,LL
LLG,LLLG,LL,LG
LL,LG,LLLG,LLG
When a line-to-line fault occurs, the short circuit current of an alternator depends upon its
Sub transient reactance
Transient reactance
Synchronous reactance
Short circuit reactance
What is the value of transient stability limit?
Higher than steady state stability limit
Lower than steady state stability limit.
Depending upon the severity of load
None of these
By using which component can the transient stability limit of a power system be improved?
Series resistance
Series capacitor
Series inductor
a. Shunt resistance
The inertia constant of 100 MVA , 50 Hz ,4 pole generator is ,10 MJ/MVA .If the mechanical input to the machine is suddenly increased from 50 MW to 75 MW ,the rotor acceleration is
225 electrical degree/sec2
22.5 electrical degree/sec2
125 electrical degree/sec2
12.5 electrical degree/sec2
The stability of the power system is not affected by which among these?
Generator reactance
Line losses
Excitation of generators
All of these
The Critical Clearance time of a fault in the power system is related to
Reactive power limit
Short Circuit limit
Steady state stability limit
Transient stability limit
The equal area criteria of stability is used for
No load on the bus bar
One machine and infinite bus bar
More than one machine and infinite bus bar
None of the above
If the torque angle of the alternator increases indefinitely the system will show
Steady state stability limit
Transient state stability limit
Instability
None of the above
The steady state stability of the power system can be improved by
Increasing the number of parallel lines between the transmission points
Connecting capacitors in series with the line
Reducing the excitation of the machines
Both a and b
The use of high speed breakers can
Increase the transient stability
Decrease the transient stability
Increase the steady state stability
Decrease the steady state stability
Equal area criterion is applicable to:
Single machine connected to infinite bus
Two machines connected to infinite bus
Multi machine system connected to infinite bus
All of these
The quantity H in swing equation is:
Kelvin constant
Motion of synchronous motor
Inertia constant
None of these
Which among these is related to the critical clearing time
of a fault in a power system?
Transient stability limit
Steady state stability limit
Frequency limit
All of these
What are the common assumptions made for the equal area criterion?
The transmission line and machine resistances are neglected
Rotor speed of the machine is constant
Mechanical input remains constant.
All of these
Under what condition is the system stable under equal area
criterion?
The area under the curve Pa – δ curve must increase to ∞.
The area under the curve Pa – δ curve must become equal to 1
The area under the curve Pa – δ curve must reduce to zero
None of these
What is the value of transient stability limit?
Higher than steady state stability limit
Lower than steady state stability limit
Depending upon the severity of load
All of these
At what value of ‘δ’ the maximum power transfer takes place
90 degree
0 degree
45 degree
30 degree
