All questions of Power Systems for Electrical Engineering (EE) Exam
Unit of heat rate curve is- a)Rs-hr
- b)Rs/MWh
- c)Rs/hr
- d)Million kcal/hr
Correct answer is option 'D'. Can you explain this answer?
Unit of heat rate curve is
a)
Rs-hr
b)
Rs/MWh
c)
Rs/hr
d)
Million kcal/hr
|
Samarth Khanna answered |
Unit of Heat Rate Curve is Million kcal/hr because it represents the rate at which heat is being generated or consumed in a power plant. The heat rate is a measure of the thermal efficiency of a power plant and is usually expressed in units of energy per unit of time.
- Heat Rate Curve:
The heat rate curve is a graphical representation of the relationship between the heat input to a power plant and the power output. It shows how the heat rate varies with the power output of the plant. The heat rate curve is typically plotted with heat rate on the y-axis and power output on the x-axis.
- Importance of Heat Rate:
The heat rate of a power plant is an important parameter as it indicates how efficiently the plant converts fuel into electricity. A lower heat rate means that the plant is more efficient and requires less fuel to generate a given amount of electricity. On the other hand, a higher heat rate indicates that the plant is less efficient and requires more fuel for the same power output.
- Million kcal/hr:
The unit of heat rate in the heat rate curve is Million kcal/hr. This unit represents the amount of heat energy generated or consumed by the power plant in one hour. It is a large unit of energy and is commonly used in the power generation industry.
- Conversion to Other Units:
The heat rate can also be expressed in other units such as BTU/kWh or MMBtu/MWh. These units represent the amount of heat energy required to generate one kilowatt-hour or one megawatt-hour of electricity, respectively. However, the unit of Million kcal/hr is widely used in the industry and is convenient for comparing the performance of different power plants.
- Conclusion:
In conclusion, the unit of heat rate curve is Million kcal/hr. This unit represents the rate at which heat energy is being generated or consumed by a power plant. The heat rate curve is an important tool for assessing the efficiency of a power plant and comparing the performance of different plants.
- Heat Rate Curve:
The heat rate curve is a graphical representation of the relationship between the heat input to a power plant and the power output. It shows how the heat rate varies with the power output of the plant. The heat rate curve is typically plotted with heat rate on the y-axis and power output on the x-axis.
- Importance of Heat Rate:
The heat rate of a power plant is an important parameter as it indicates how efficiently the plant converts fuel into electricity. A lower heat rate means that the plant is more efficient and requires less fuel to generate a given amount of electricity. On the other hand, a higher heat rate indicates that the plant is less efficient and requires more fuel for the same power output.
- Million kcal/hr:
The unit of heat rate in the heat rate curve is Million kcal/hr. This unit represents the amount of heat energy generated or consumed by the power plant in one hour. It is a large unit of energy and is commonly used in the power generation industry.
- Conversion to Other Units:
The heat rate can also be expressed in other units such as BTU/kWh or MMBtu/MWh. These units represent the amount of heat energy required to generate one kilowatt-hour or one megawatt-hour of electricity, respectively. However, the unit of Million kcal/hr is widely used in the industry and is convenient for comparing the performance of different power plants.
- Conclusion:
In conclusion, the unit of heat rate curve is Million kcal/hr. This unit represents the rate at which heat energy is being generated or consumed by a power plant. The heat rate curve is an important tool for assessing the efficiency of a power plant and comparing the performance of different plants.
In which part of the thermal power plant, the steam pressure is less than that of atmosphere?- a)Boiler
- b)Turbine
- c)Superheater
- d)Condenser
Correct answer is option 'D'. Can you explain this answer?
In which part of the thermal power plant, the steam pressure is less than that of atmosphere?
a)
Boiler
b)
Turbine
c)
Superheater
d)
Condenser
|
Zoya Sharma answered |
Condenser in a steam power plant has lowest operating pressure.
Which is the conventional source of energy?- a)Solar
- b)Radio-active substances
- c)Geothermal
- d)Wind
Correct answer is option 'B'. Can you explain this answer?
Which is the conventional source of energy?
a)
Solar
b)
Radio-active substances
c)
Geothermal
d)
Wind
|
Juhi Joshi answered |
Conventional source of energy are: Water, Coal, Gas, radioactive substances. Non-conventional source of energy are: Wind, Solar energy, Geothermal.
Series capacitive compensation on EHV transmission lines is used to- a)reduce the line loading
- b)improve the protection of the line
- c)reduce the voltage profile
- d)improve the stability of the system
Correct answer is option 'D'. Can you explain this answer?
Series capacitive compensation on EHV transmission lines is used to
a)
reduce the line loading
b)
improve the protection of the line
c)
reduce the voltage profile
d)
improve the stability of the system
|
Prasenjit Yadav answered |
With series capacitive compensation, the net transfer reactance of the line will be X = (XL - XC) due to which the power transmitted from sending to the receiving end is increased. Thus, it will improve the steady-state stability of the system.
A single-phase, two wire transmission line, 15 km long, is made up of round conductors, each 0.8 cm radius, separated from each other by 40 cm. The equivalent diameter of a fictitious hollow, thin-walled conductor having the same inductance as the original line is given by- a)1.557 cm '
- b)1.246 cm
- c)1.6 cm
- d)0.623 cm
Correct answer is option 'B'. Can you explain this answer?
A single-phase, two wire transmission line, 15 km long, is made up of round conductors, each 0.8 cm radius, separated from each other by 40 cm. The equivalent diameter of a fictitious hollow, thin-walled conductor having the same inductance as the original line is given by
a)
1.557 cm '
b)
1.246 cm
c)
1.6 cm
d)
0.623 cm
|
Avik Iyer answered |
The fictitious conductor is one whose radius is r' and whose diameter is therefore,
Shunt capacitance in an EHV line is restored to- a)improve the stability
- b)reduce fault level
- c)improve the voltage
- d)none of the above
Correct answer is option 'C'. Can you explain this answer?
Shunt capacitance in an EHV line is restored to
a)
improve the stability
b)
reduce fault level
c)
improve the voltage
d)
none of the above
|
Srestha Gupta answered |
Shunt Capacitance in EHV Line
Shunt capacitance is an important parameter of an EHV transmission line. It is the capacitance between the line conductors and the ground.
Importance of Shunt Capacitance
- Shunt capacitance helps in maintaining the voltage level of the transmission line.
- It also helps in reducing the corona losses.
- Shunt capacitance is responsible for the charging current of the transmission line.
- It affects the overall transmission line impedance.
Restoring Shunt Capacitance to Improve Voltage
The shunt capacitance in an EHV line is restored to improve the voltage level of the transmission line. When the shunt capacitance is low, the voltage level of the transmission line decreases. This can lead to power losses and also affect the stability of the system.
By restoring the shunt capacitance, the voltage level can be improved. This is particularly important in long transmission lines where the voltage drop is significant. The shunt capacitance helps in maintaining the voltage level within acceptable limits.
Conclusion
Shunt capacitance is an important parameter of an EHV transmission line. It helps in maintaining the voltage level and reducing corona losses. Restoring shunt capacitance can improve the voltage level of the transmission line and ensure stable operation.
Shunt capacitance is an important parameter of an EHV transmission line. It is the capacitance between the line conductors and the ground.
Importance of Shunt Capacitance
- Shunt capacitance helps in maintaining the voltage level of the transmission line.
- It also helps in reducing the corona losses.
- Shunt capacitance is responsible for the charging current of the transmission line.
- It affects the overall transmission line impedance.
Restoring Shunt Capacitance to Improve Voltage
The shunt capacitance in an EHV line is restored to improve the voltage level of the transmission line. When the shunt capacitance is low, the voltage level of the transmission line decreases. This can lead to power losses and also affect the stability of the system.
By restoring the shunt capacitance, the voltage level can be improved. This is particularly important in long transmission lines where the voltage drop is significant. The shunt capacitance helps in maintaining the voltage level within acceptable limits.
Conclusion
Shunt capacitance is an important parameter of an EHV transmission line. It helps in maintaining the voltage level and reducing corona losses. Restoring shunt capacitance can improve the voltage level of the transmission line and ensure stable operation.
Within the boiler, the steam has highest temperature in- a)superheater
- b)water tubes
- c)water walls
- d)water drum
Correct answer is option 'A'. Can you explain this answer?
Within the boiler, the steam has highest temperature in
a)
superheater
b)
water tubes
c)
water walls
d)
water drum
|
|
Avik Iyer answered |
Superheated steam has the highest temperature which comes out from super heater.
Consider the following statements:
1. AAC (All Aluminium conductors) are universaly employed for feeders as well as distributors.
2. The conductor size for a feeder is mainly governed by the permissible voltage drop in the line.
Which of the above statement(s) is/are true?- a)1 only
- b)1 and 2
- c)none
- d)2 only
Correct answer is option 'C'. Can you explain this answer?
Consider the following statements:
1. AAC (All Aluminium conductors) are universaly employed for feeders as well as distributors.
2. The conductor size for a feeder is mainly governed by the permissible voltage drop in the line.
Which of the above statement(s) is/are true?
1. AAC (All Aluminium conductors) are universaly employed for feeders as well as distributors.
2. The conductor size for a feeder is mainly governed by the permissible voltage drop in the line.
Which of the above statement(s) is/are true?
a)
1 only
b)
1 and 2
c)
none
d)
2 only
|
Isha Singh answered |
ACSR conductors are universally employed for distribution systems (feeders as well as distributors), AAC can be used for distribution purpose provided the spans are small.
Hence, statement-1 is false.
The conductor size for a feeder is mainly governed by current carrying capacity and overall economy. Hence, 2 is also a false statement.
Hence, statement-1 is false.
The conductor size for a feeder is mainly governed by current carrying capacity and overall economy. Hence, 2 is also a false statement.
The insulation resistance of a cable of 10 km length is 1 MΩ. The resistance for a length of 40 km is
- a)1 MΩ
- b)4 MΩ
- c)0.25 MΩ
- d)Can’t be determined
Correct answer is option 'C'. Can you explain this answer?
The insulation resistance of a cable of 10 km length is 1 MΩ. The resistance for a length of 40 km is
a)
1 MΩ
b)
4 MΩ
c)
0.25 MΩ
d)
Can’t be determined
|
|
Tanishq Majumdar answered |
l1 = 10 km, R1 = 1 MΩ, l2 = 40 km
1/R2 = 40/10
R2 = 1/4 = 0.25 MΩ
The resistance and reactance of a short line are equal. At zero regulation the load will be- a)upf
- b)zpf
- c)0.707 lag
- d)0.707 lead
Correct answer is option 'D'. Can you explain this answer?
The resistance and reactance of a short line are equal. At zero regulation the load will be
a)
upf
b)
zpf
c)
0.707 lag
d)
0.707 lead
|
Harsh Kulkarni answered |
Zero regulation of a transmission line occurs at a leading power factor when φ = θ.
Since R = X
Since R = X
HVDC transmission is preferred to EHV AC because- a)HVDC terminal equipment are inexpensive
- b)VAR compensation is not required in HVDC system
- c)system reliability can be improved
- d)harmonic problem is avoided
Correct answer is option 'C'. Can you explain this answer?
HVDC transmission is preferred to EHV AC because
a)
HVDC terminal equipment are inexpensive
b)
VAR compensation is not required in HVDC system
c)
system reliability can be improved
d)
harmonic problem is avoided
|
Hrishikesh Yadav answered |
HVDC transmission is more reliable than EHV AC because it uses ground or sea return and therefore, in case of fault on a line it can still be used to supply power with the help of healthy lines.
The sequence networks for a three-phase faults are connected in- a)series
- b)parallel
- c)series opposition
- d)none of the above
Correct answer is option 'D'. Can you explain this answer?
The sequence networks for a three-phase faults are connected in
a)
series
b)
parallel
c)
series opposition
d)
none of the above
|
Gayatri Menon answered |
A three-phase fault is a symmetrical fault where only positive sequence network (current exists).
If the initial acceleration power of a 100 MVA, 50 Hz synchronous generator having H= 5 MJ/MVA is Xpu, the initial acceleration in elec-deg/s2 and the inertia constant in M J-s/ele-deg respectively will be - a)31.4X, 18
- b)1800X, 0.056
- c)X/1800, 0.056
- d)X/31.4, 18
Correct answer is option 'B'. Can you explain this answer?
If the initial acceleration power of a 100 MVA, 50 Hz synchronous generator having H= 5 MJ/MVA is Xpu, the initial acceleration in elec-deg/s2 and the inertia constant in M J-s/ele-deg respectively will be
a)
31.4X, 18
b)
1800X, 0.056
c)
X/1800, 0.056
d)
X/31.4, 18
|
|
Maulik Choudhury answered |
From swing equation,
Also, inertia constant,
Also, inertia constant,
The incremental transmission loss of a plant can’t be a- a)negative quantity
- b)positive quantity
- c)a zero value
- d)non-zero value
Correct answer is option 'C'. Can you explain this answer?
The incremental transmission loss of a plant can’t be a
a)
negative quantity
b)
positive quantity
c)
a zero value
d)
non-zero value
|
Kajal Mukherjee answered |
The incremental transmission loss of a plant can be positive, a non-zero value but, can’t be zero.
A 500-MVA synchronous machine has H1 = 4.6 MJ/MVA, and a 1500 MVA machine has H2 = 3.0 MJ/MVA. The two machines operate in parallel in a power station. The equivalent H constant for the two, relative to a 100 MVA base will be- a)22 MJ/MVA
- b)45 MJ/MVA
- c)52 MJ/MVA
- d)68 MJ/MVA
Correct answer is option 'D'. Can you explain this answer?
A 500-MVA synchronous machine has H1 = 4.6 MJ/MVA, and a 1500 MVA machine has H2 = 3.0 MJ/MVA. The two machines operate in parallel in a power station. The equivalent H constant for the two, relative to a 100 MVA base will be
a)
22 MJ/MVA
b)
45 MJ/MVA
c)
52 MJ/MVA
d)
68 MJ/MVA
|
Anoushka Choudhury answered |
We know that,
Pilot relaying schemes are used for protection of- a)bus bars
- b)transformers
- c)transmission lines
- d)instrument transfomers
Correct answer is option 'C'. Can you explain this answer?
Pilot relaying schemes are used for protection of
a)
bus bars
b)
transformers
c)
transmission lines
d)
instrument transfomers
|
|
Anshika Khanna answered |
Pilot relaying schemes provide high speed protection for transmission lines.
Consider the following phenomenon occuring in a power system:
1. Corona loss
2. Charging current
3. Ferranti effect
4. Dielectric loss
5. Skin effect
Which of the above are associated with transmission lines?- a)1,3 and 5
- b)2, 3, 4 and 5
- c)3, 2 and 4
- d)1,2, 3 and 5
Correct answer is option 'D'. Can you explain this answer?
Consider the following phenomenon occuring in a power system:
1. Corona loss
2. Charging current
3. Ferranti effect
4. Dielectric loss
5. Skin effect
Which of the above are associated with transmission lines?
1. Corona loss
2. Charging current
3. Ferranti effect
4. Dielectric loss
5. Skin effect
Which of the above are associated with transmission lines?
a)
1,3 and 5
b)
2, 3, 4 and 5
c)
3, 2 and 4
d)
1,2, 3 and 5
|
Gargi Basak answered |
Dielectric loss occurs in underground cables not in a transmission line.
Three synchronous generators, each of which is rated to 100 MVA, 11 KV, have an impedance per unit of 0.15. If all three generators are replaced by a single equivalent generator, what will be the effective per unit impedance of each generator?- a)0.45
- b)0.15
- c)0.025
- d)0.05
Correct answer is option 'D'. Can you explain this answer?
Three synchronous generators, each of which is rated to 100 MVA, 11 KV, have an impedance per unit of 0.15. If all three generators are replaced by a single equivalent generator, what will be the effective per unit impedance of each generator?
a)
0.45
b)
0.15
c)
0.025
d)
0.05
|
|
Mahesh Singh answered |
Calculation:
Given data:
- Number of generators: 3
- Rating of each generator: 100 MVA
- Voltage rating: 11 kV
- Impedance per unit: 0.15
To find:
- Effective per unit impedance of each generator when replaced by a single equivalent generator
Step 1: Calculation of equivalent impedance
The total impedance of the three generators connected in parallel can be calculated as follows:
Zeq = Zg / N
Where,
Zeq = Equivalent impedance
Zg = Impedance of a single generator
N = Number of generators
Given that Zg = 0.15, and N = 3, we can substitute these values into the equation:
Zeq = 0.15 / 3
Zeq = 0.05
Therefore, the equivalent impedance of the three generators connected in parallel is 0.05 per unit.
Step 2: Calculation of effective per unit impedance
To find the effective per unit impedance of each generator, we need to divide the equivalent impedance by the number of generators:
Effective per unit impedance = Zeq / N
Given that Zeq = 0.05 and N = 3, we can substitute these values into the equation:
Effective per unit impedance = 0.05 / 3
Effective per unit impedance = 0.0167
Therefore, the effective per unit impedance of each generator when replaced by a single equivalent generator is 0.0167.
Step 3: Comparing the options
a) 0.45 - This is not the correct answer.
b) 0.15 - This is not the correct answer.
c) 0.025 - This is not the correct answer.
d) 0.05 - This is the correct answer.
Therefore, option D, 0.05, is the correct answer.
Conclusion:
When three synchronous generators with an impedance per unit of 0.15 are replaced by a single equivalent generator, the effective per unit impedance of each generator becomes 0.05.
Given data:
- Number of generators: 3
- Rating of each generator: 100 MVA
- Voltage rating: 11 kV
- Impedance per unit: 0.15
To find:
- Effective per unit impedance of each generator when replaced by a single equivalent generator
Step 1: Calculation of equivalent impedance
The total impedance of the three generators connected in parallel can be calculated as follows:
Zeq = Zg / N
Where,
Zeq = Equivalent impedance
Zg = Impedance of a single generator
N = Number of generators
Given that Zg = 0.15, and N = 3, we can substitute these values into the equation:
Zeq = 0.15 / 3
Zeq = 0.05
Therefore, the equivalent impedance of the three generators connected in parallel is 0.05 per unit.
Step 2: Calculation of effective per unit impedance
To find the effective per unit impedance of each generator, we need to divide the equivalent impedance by the number of generators:
Effective per unit impedance = Zeq / N
Given that Zeq = 0.05 and N = 3, we can substitute these values into the equation:
Effective per unit impedance = 0.05 / 3
Effective per unit impedance = 0.0167
Therefore, the effective per unit impedance of each generator when replaced by a single equivalent generator is 0.0167.
Step 3: Comparing the options
a) 0.45 - This is not the correct answer.
b) 0.15 - This is not the correct answer.
c) 0.025 - This is not the correct answer.
d) 0.05 - This is the correct answer.
Therefore, option D, 0.05, is the correct answer.
Conclusion:
When three synchronous generators with an impedance per unit of 0.15 are replaced by a single equivalent generator, the effective per unit impedance of each generator becomes 0.05.
The series impedance matrix of a short three-phase transmission line in phase coordinates is 
. If the positive sequence impedance is (1 + j 10) Ω, and the zero sequence is (4 + j 31) Ω, then the imaginary part of Zm (in Ω) is _______ (up to 2 decimal places).
Correct answer is '7'. Can you explain this answer?
The series impedance matrix of a short three-phase transmission line in phase coordinates is . If the positive sequence impedance is (1 + j 10) Ω, and the zero sequence is (4 + j 31) Ω, then the imaginary part of Zm (in Ω) is _______ (up to 2 decimal places).
. If the positive sequence impedance is (1 + j 10) Ω, and the zero sequence is (4 + j 31) Ω, then the imaginary part of Zm (in Ω) is _______ (up to 2 decimal places).
|
Pooja Patel answered |
Given that, positive sequence impedance (Z1) = (1 + j10) Ω
Zero sequence impedance (Z0) = (4 + j31) Ω
We know that, Z1 = Zs – Zm
and Z0 = Zs + 2Zm
Z1 = 1 + j10 = Zs – Zm → (1)
and Z0 = 4 + j31 = Zs + 2Zm → (2)
from equations (1) and (2)
⇒ Zm = 1 + j7
Imaginary part of Zm = 7 Ω.
For a 35 km transmission line having a lumped impedance of the line as 20 ohms, is required to be shown in the ABCD form, it is given as- a)
- b)
- c)
- d)
Correct answer is option 'A'. Can you explain this answer?
For a 35 km transmission line having a lumped impedance of the line as 20 ohms, is required to be shown in the ABCD form, it is given as
a)
b)
c)
d)
|
|
Pooja Patel answered |
From the given length, it is a short TL. Hence,
Then ABCD paramteres of this circuit is
Then ABCD paramteres of this circuit is
When generating units are loaded to equal incremental costs, it results in- a)minimum fuel costs
- b)fuel costs are at a maximum
- c)fuel costs are not affected
- d)maximum loading of generating units
Correct answer is option 'A'. Can you explain this answer?
When generating units are loaded to equal incremental costs, it results in
a)
minimum fuel costs
b)
fuel costs are at a maximum
c)
fuel costs are not affected
d)
maximum loading of generating units
|
|
Parth Ghoshal answered |
To minimize the total fuel cost, the generating units must operate at equal incremental cost of production.
The transmission line equations are given by the below set of equations based on the line diagram as given. Identify the missing term marked as ’?’.
Vs = A*Vr + B*Ir
Is = C*Vr + ?*Ir
- a)1+YZ
- b)Z
- c)Y
- d)1
Correct answer is option 'D'. Can you explain this answer?
The transmission line equations are given by the below set of equations based on the line diagram as given. Identify the missing term marked as ’?’.
Vs = A*Vr + B*Ir
Is = C*Vr + ?*Ir
Vs = A*Vr + B*Ir
Is = C*Vr + ?*Ir
a)
1+YZ
b)
Z
c)
Y
d)
1
|
|
Pooja Patel answered |
Using KVL to the line diagram,
Vs = (1+YZ)*Vr + Z*Ir
Is = Y*Vr + Ir.
Vs = (1+YZ)*Vr + Z*Ir
Is = Y*Vr + Ir.
A station operates with a load factor and plant capacity factor of 0.75, with a maximum demand of 100 MW. The reserve capacity is- a)100 MW
- b)75 MW
- c)0 MW
- d)133.33 MW
Correct answer is option 'C'. Can you explain this answer?
A station operates with a load factor and plant capacity factor of 0.75, with a maximum demand of 100 MW. The reserve capacity is
a)
100 MW
b)
75 MW
c)
0 MW
d)
133.33 MW
|
Sanchita Choudhary answered |
Load Factor and Plant Capacity Factor
Load factor is the ratio of average load to the maximum demand, and plant capacity factor is the ratio of actual output to the maximum capacity.
Load factor = (Average load) / (Maximum demand)
Plant capacity factor = (Actual output) / (Maximum capacity)
Given load factor and plant capacity factor are 0.75, the maximum demand is 100 MW.
Reserve Capacity
Reserve capacity is the amount of extra capacity available to meet sudden increases in demand or unexpected outages. It is calculated by subtracting the maximum demand from the maximum capacity.
Reserve capacity = Maximum capacity - Maximum demand
Since the load factor and plant capacity factor are both 0.75, it means that the actual output is 75 MW, which is 75% of the maximum capacity. Therefore, the maximum capacity is:
Maximum capacity = Actual output / Plant capacity factor
Maximum capacity = 75 MW / 0.75
Maximum capacity = 100 MW
Thus, the reserve capacity is:
Reserve capacity = Maximum capacity - Maximum demand
Reserve capacity = 100 MW - 100 MW
Reserve capacity = 0 MW
Therefore, the correct answer is option C, which is 0 MW.
Load factor is the ratio of average load to the maximum demand, and plant capacity factor is the ratio of actual output to the maximum capacity.
Load factor = (Average load) / (Maximum demand)
Plant capacity factor = (Actual output) / (Maximum capacity)
Given load factor and plant capacity factor are 0.75, the maximum demand is 100 MW.
Reserve Capacity
Reserve capacity is the amount of extra capacity available to meet sudden increases in demand or unexpected outages. It is calculated by subtracting the maximum demand from the maximum capacity.
Reserve capacity = Maximum capacity - Maximum demand
Since the load factor and plant capacity factor are both 0.75, it means that the actual output is 75 MW, which is 75% of the maximum capacity. Therefore, the maximum capacity is:
Maximum capacity = Actual output / Plant capacity factor
Maximum capacity = 75 MW / 0.75
Maximum capacity = 100 MW
Thus, the reserve capacity is:
Reserve capacity = Maximum capacity - Maximum demand
Reserve capacity = 100 MW - 100 MW
Reserve capacity = 0 MW
Therefore, the correct answer is option C, which is 0 MW.
A dc line carries- a)same power as an ac line
- b)less power than an equivalent ac line
- c)more power than the ac line
- d)both (a) and (c)
Correct answer is option 'C'. Can you explain this answer?
A dc line carries
a)
same power as an ac line
b)
less power than an equivalent ac line
c)
more power than the ac line
d)
both (a) and (c)
|
Pranjal Datta answered |
Due to requirement of less number of conductors, a dc line carries more power than a ac line, (losses of the line reduces in HVDC).
The line current in a three phase unbalanced load are Ia = 4 + j6, Ib = 2 - j2, Ic = -3 + j2, then zero sequence component of current will be- a)3 + j6
- b)9 + j10
- c)1 + j2
- d)3 - j6
Correct answer is option 'C'. Can you explain this answer?
The line current in a three phase unbalanced load are Ia = 4 + j6, Ib = 2 - j2, Ic = -3 + j2, then zero sequence component of current will be
a)
3 + j6
b)
9 + j10
c)
1 + j2
d)
3 - j6
|
|
Pooja Patel answered |
Concept:
The relation between the line currents in terms of the symmetrical components of currents is given below.
The relation between the line currents in terms of the symmetrical components of currents is given below.
Ia0 = Zero Sequence Component of Current
Ia1 = Positive Sequence Component of Current
Ia2 = Negative Sequence Component of Current
a = 1∠120°, which represents the rotation of 120° in the clockwise direction.
a2 = 1∠-120° or 1∠240° in anticlockwise direction or clockwise direction, respectively.
1 + a + a2 = 0
Calculation:
Given that
Ia = 4 + j6, Ib = 2 - j2, Ic = -3 + j2
Zero sequence component of current,
∴ I0 = 1 + j2 A
There is a problem of high transient over voltages while interrupting- a)capacitive currents
- b)inductive currents
- c)heavy short circuit current
- d)(a) or (c)
Correct answer is option 'A'. Can you explain this answer?
There is a problem of high transient over voltages while interrupting
a)
capacitive currents
b)
inductive currents
c)
heavy short circuit current
d)
(a) or (c)
|
Palak Verma answered |
High transient over voltages occurs in power system due to formation of capacitance across the breaker poles. These are also called switching over voltages.
The base impedance and base voltage for a given power system are 10Ω and 400 V respectively. The base kVA and the base current will be respectively- a)16000 kVA and 40 A
- b)4 kVA and 16 A
- c)16 kVA and 40 A
- d)4 kVA and 400 A
Correct answer is option 'C'. Can you explain this answer?
The base impedance and base voltage for a given power system are 10Ω and 400 V respectively. The base kVA and the base current will be respectively
a)
16000 kVA and 40 A
b)
4 kVA and 16 A
c)
16 kVA and 40 A
d)
4 kVA and 400 A
|
|
Maulik Choudhury answered |
For a given power system, its zero and maximum regulation will occur at the impedance angle of- a)45
- b)90
- c)0
- d)60
Correct answer is option 'A'. Can you explain this answer?
For a given power system, its zero and maximum regulation will occur at the impedance angle of
a)
45
b)
90
c)
0
d)
60
|
|
Pooja Patel answered |
At θ = 45°, ZVR and maximum VR coincide.
A balanced 3-phase load is supplied from a 3-phase supply. The contact in line c of the triple pole switch contactor fails to connect when switched on. If the line currents in lines a and b record 25A each, then the positive sequence component of the current is
- a)14.4 ∠30° A
- b)25.0 ∠-30° A
- c)14.4 ∠-30° A
- d)25 ∠80° A
Correct answer is option 'C'. Can you explain this answer?
A balanced 3-phase load is supplied from a 3-phase supply. The contact in line c of the triple pole switch contactor fails to connect when switched on. If the line currents in lines a and b record 25A each, then the positive sequence component of the current is
a)
14.4 ∠30° A
b)
25.0 ∠-30° A
c)
14.4 ∠-30° A
d)
25 ∠80° A
|
|
Pooja Patel answered |
The contact in line C of the triple pole switch contactor fails to connect when switched on.
⇒ Ic = 0 A
And Ia + Ib = 0
⇒ Ia = -Ib
⇒ Ia = 25 ∠0°, Ib = 25 ∠-180°
Positive sequence current,
Positive sequence current,
= 1/3(25 ∠ 0∘ + 1∠120 × 25∠ −180)
= 14.4 ∠ -30°
In a dc transmision- a)it is necessary for the sending and receiving end to be operated in synchronism.
- b)the effects of inductive and capacitive reactances are greater than in ac transmission line of the same rating.
- c)there are no effects due to inductive and capacitive reactances.
- d)power transfer capability is limited by stability considerations.
Correct answer is option 'C'. Can you explain this answer?
In a dc transmision
a)
it is necessary for the sending and receiving end to be operated in synchronism.
b)
the effects of inductive and capacitive reactances are greater than in ac transmission line of the same rating.
c)
there are no effects due to inductive and capacitive reactances.
d)
power transfer capability is limited by stability considerations.
|
|
Gayatri Menon answered |
As operating frequency, f = 0 therefore, there is no effect of XL and XC.
For a synchronous phase modifier the load angle is- a)00
- b)250
- c)300
- d)None of these
Correct answer is option 'A'. Can you explain this answer?
For a synchronous phase modifier the load angle is
a)
00
b)
250
c)
300
d)
None of these
|
Arya Mukherjee answered |
Synchronous phase modifier is an overexcited synchronous motor operating on no-load under wide variation of excitation. For no-load operation, δ = 0.
The receiving end active power for a short transmission line is (where the angles have their usual meanings)- a)
- b)
- c)
- d)
Correct answer is option 'A'. Can you explain this answer?
The receiving end active power for a short transmission line is (where the angles have their usual meanings)
a)
b)
c)
d)
|
|
Pooja Patel answered |
Receiving end active power for a short transmission line is
A generator is supplying a load. An incremental change in load of 4 MW requires generation to be increased by 6 MW. The cost at plant bus is ₹ 30/MWhr. The incremental cost at the receiving end is- a)₹ 30/MWhr
- b)₹ 5/MWhr
- c)₹ 33.4/MWhr
- d)₹ 6.0/MWhr
Correct answer is option 'B'. Can you explain this answer?
A generator is supplying a load. An incremental change in load of 4 MW requires generation to be increased by 6 MW. The cost at plant bus is ₹ 30/MWhr. The incremental cost at the receiving end is
a)
₹ 30/MWhr
b)
₹ 5/MWhr
c)
₹ 33.4/MWhr
d)
₹ 6.0/MWhr
|
Raj Desai answered |
The charging currents due to shunt admittance can be neglected for ______ transmission line?- a)short
- b)long
- c)medium
- d)all of the mentioned
Correct answer is option 'A'. Can you explain this answer?
The charging currents due to shunt admittance can be neglected for ______ transmission line?
a)
short
b)
long
c)
medium
d)
all of the mentioned
|
|
Ashwin Mukherjee answered |
Short Transmission Line:
When the length of the transmission line is relatively short, the charging currents due to shunt admittance can be neglected.
Explanation:
The charging currents in a transmission line are caused by the shunt admittance of the line. The shunt admittance consists of the capacitance of the line. When a voltage is applied to a transmission line, the capacitance of the line allows a small amount of charging current to flow.
Short Transmission Line:
In a short transmission line, the length of the line is relatively short compared to the wavelength of the operating frequency. This means that the time taken for the voltage wave to travel from one end of the line to the other is small compared to the time period of the voltage wave.
Effect of Line Length:
The charging current in a transmission line is directly proportional to the length of the line. In a short transmission line, the length is small, which means that the charging current is also small. Since the charging current is small, it can be neglected in practical calculations and analysis.
Importance of Neglecting Charging Currents:
Neglecting the charging currents simplifies the analysis of the transmission line. It allows for easier calculations of power flow, voltage regulation, and other important parameters. By neglecting the charging currents, the transmission line can be treated as a purely resistive network, which simplifies the analysis and reduces computational complexity.
Conclusion:
In conclusion, the charging currents due to shunt admittance can be neglected for short transmission lines. This is because the length of the line is small compared to the wavelength, resulting in small charging currents. Neglecting the charging currents simplifies the analysis and allows for easier calculations of important parameters.
When the length of the transmission line is relatively short, the charging currents due to shunt admittance can be neglected.
Explanation:
The charging currents in a transmission line are caused by the shunt admittance of the line. The shunt admittance consists of the capacitance of the line. When a voltage is applied to a transmission line, the capacitance of the line allows a small amount of charging current to flow.
Short Transmission Line:
In a short transmission line, the length of the line is relatively short compared to the wavelength of the operating frequency. This means that the time taken for the voltage wave to travel from one end of the line to the other is small compared to the time period of the voltage wave.
Effect of Line Length:
The charging current in a transmission line is directly proportional to the length of the line. In a short transmission line, the length is small, which means that the charging current is also small. Since the charging current is small, it can be neglected in practical calculations and analysis.
Importance of Neglecting Charging Currents:
Neglecting the charging currents simplifies the analysis of the transmission line. It allows for easier calculations of power flow, voltage regulation, and other important parameters. By neglecting the charging currents, the transmission line can be treated as a purely resistive network, which simplifies the analysis and reduces computational complexity.
Conclusion:
In conclusion, the charging currents due to shunt admittance can be neglected for short transmission lines. This is because the length of the line is small compared to the wavelength, resulting in small charging currents. Neglecting the charging currents simplifies the analysis and allows for easier calculations of important parameters.
For an arcing fault where the arc resistance is significant an impedance or admittance relay will- a)over reach
- b)under reach
- c)the reach of relay is unaffected
- d)the reach will depend on the arcing resistance and may under reach or over reach.
Correct answer is option 'B'. Can you explain this answer?
For an arcing fault where the arc resistance is significant an impedance or admittance relay will
a)
over reach
b)
under reach
c)
the reach of relay is unaffected
d)
the reach will depend on the arcing resistance and may under reach or over reach.
|
|
Jatin Mukherjee answered |
The reach of a reactance relay is unaffected due to the arc resistance while an impedance and admittance relay under reaches.
The percent bias for a generator protection lies between- a)15 to 20%
- b)10 to 15%
- c)5 to 10%
- d)None of these
Correct answer is option 'A'. Can you explain this answer?
The percent bias for a generator protection lies between
a)
15 to 20%
b)
10 to 15%
c)
5 to 10%
d)
None of these
|
|
Niharika Basu answered |
Explanation:
Generator protection is an essential aspect of power system operation to ensure the safety and reliability of the power system. One of the critical parameters in generator protection is the percent bias.
The percent bias is a measure of the difference between the actual and expected values of the measured quantity. In generator protection, the measured quantity is the current or voltage, and the expected value is the threshold or setting value of the protection relay.
The percent bias is calculated as follows:
Percent bias = [(Measured value - Expected value) / Expected value] x 100
Ideally, the percent bias should be zero, indicating that the measured value is equal to the expected value. However, due to various factors such as instrument errors, temperature variations, and external interferences, some degree of bias is inevitable.
The acceptable range of percent bias for generator protection is typically between 15 to 20%. This range ensures that the protection relay operates reliably and does not trip unnecessarily due to small variations in the measured value.
If the percent bias is too low, the protection relay may not operate when it should, leading to a potential failure of the generator or other equipment. On the other hand, if the percent bias is too high, the protection relay may trip unnecessarily, leading to a disruption of power supply and unnecessary maintenance.
Therefore, it is essential to ensure that the percent bias of generator protection is within the acceptable range of 15 to 20%. Regular testing and calibration of the protection system can help to maintain the accuracy and reliability of the protection system.
Conclusion:
In conclusion, the acceptable range of percent bias for generator protection is between 15 to 20%. This range ensures that the protection relay operates reliably and does not trip unnecessarily due to small variations in the measured value. Regular testing and calibration of the protection system can help to maintain the accuracy and reliability of the protection system.
Generator protection is an essential aspect of power system operation to ensure the safety and reliability of the power system. One of the critical parameters in generator protection is the percent bias.
The percent bias is a measure of the difference between the actual and expected values of the measured quantity. In generator protection, the measured quantity is the current or voltage, and the expected value is the threshold or setting value of the protection relay.
The percent bias is calculated as follows:
Percent bias = [(Measured value - Expected value) / Expected value] x 100
Ideally, the percent bias should be zero, indicating that the measured value is equal to the expected value. However, due to various factors such as instrument errors, temperature variations, and external interferences, some degree of bias is inevitable.
The acceptable range of percent bias for generator protection is typically between 15 to 20%. This range ensures that the protection relay operates reliably and does not trip unnecessarily due to small variations in the measured value.
If the percent bias is too low, the protection relay may not operate when it should, leading to a potential failure of the generator or other equipment. On the other hand, if the percent bias is too high, the protection relay may trip unnecessarily, leading to a disruption of power supply and unnecessary maintenance.
Therefore, it is essential to ensure that the percent bias of generator protection is within the acceptable range of 15 to 20%. Regular testing and calibration of the protection system can help to maintain the accuracy and reliability of the protection system.
Conclusion:
In conclusion, the acceptable range of percent bias for generator protection is between 15 to 20%. This range ensures that the protection relay operates reliably and does not trip unnecessarily due to small variations in the measured value. Regular testing and calibration of the protection system can help to maintain the accuracy and reliability of the protection system.
For a fully transposed transmission line- a)positive, negative and zero sequence impedances are equal.
- b)positive and negative sequence impedances are equal.
- c)zero and positive sequence impedances are equal.
- d)negative and zero sequence impedances are equal
Correct answer is option 'B'. Can you explain this answer?
For a fully transposed transmission line
a)
positive, negative and zero sequence impedances are equal.
b)
positive and negative sequence impedances are equal.
c)
zero and positive sequence impedances are equal.
d)
negative and zero sequence impedances are equal
|
|
Pooja Patel answered |
Purpose of Transposition:
- Transmission lines are transposed to prevent interference with neighbouring telephone lines.
- The transposition arrangement of high voltage lines helps to reduce the system power loss.
- We have developed transposition system for Single circuit tower using same tension tower with reduced deviation angle.
- Transposition arrangement of power line helps to reduce the effect of inductive coupling.
- It is proved more economical Solution, in comparison of the conventional transposition system.
Important:
Transposition arrangement
The transposition arrangement of the conductor can simply show in the following the figure. The conductor in Position 1, Position 2 and Position 3 changes in a specific arrangement to reduce the effect of capacitance and the electrostatic unbalanced voltages.
Z1 = Z2 = ZS - Zm
Zo = ZS + 2Zm
Where,
Z1 = positive sequence impedance
Z2 = positive sequence impedance
Zm = mutual impedance
ZS = self impedance
Positive and negative sequence impedances are equal.
Zo = ZS + 2Zm
Where,
Z1 = positive sequence impedance
Z2 = positive sequence impedance
Zm = mutual impedance
ZS = self impedance
Positive and negative sequence impedances are equal.
Providing synchronous condensers at a load bus will control- a)P at bus
- b)Q
- c)p.f.
- d)(b) and (c)
Correct answer is option 'D'. Can you explain this answer?
Providing synchronous condensers at a load bus will control
a)
P at bus
b)
Q
c)
p.f.
d)
(b) and (c)
|
|
Subham Chaudhary answered |
A synchronous condeser regulates Q and thus controls power factor of the system.
In case of HVDC system, there is
- a)both skin effect and corona loss
- b)skin effect but no corona loss
- c)corona loss but no skin effect
- d)neither corona loss nor skin effect
Correct answer is option 'C'. Can you explain this answer?
In case of HVDC system, there is
a)
both skin effect and corona loss
b)
skin effect but no corona loss
c)
corona loss but no skin effect
d)
neither corona loss nor skin effect
|
|
Lakshmi Desai answered |
Corona loss and skin effect are two important phenomena that occur in high voltage direct current (HVDC) systems. The correct answer to the question is option 'C', which states that there is corona loss but no skin effect in a HVDC system. Let's explain this answer in detail:
1. Corona Loss:
- Corona loss is the power loss that occurs due to the ionization of the surrounding air around the conductors in a high voltage system.
- In HVDC systems, the voltage levels are very high, which increases the likelihood of corona discharge.
- When the electric field intensity exceeds a certain threshold, the air molecules around the conductor break down and become ionized, resulting in a corona discharge.
- This corona discharge leads to power loss and can cause interference with communication systems.
- Corona loss is more significant in AC systems compared to DC systems because the polarity reversal in AC systems helps in the recovery of the ionized air molecules.
- However, in HVDC systems, the polarity remains constant, which leads to a continuous corona loss.
2. Skin Effect:
- Skin effect is the tendency of alternating current (AC) to flow near the surface of a conductor, causing the effective cross-sectional area available for current flow to decrease.
- Skin effect occurs due to the self-induced magnetic field generated by the current flowing through the conductor.
- The magnetic field repels the current from the center of the conductor, causing it to concentrate near the surface.
- Skin effect is significant in AC systems, where the current alternates direction periodically.
- In DC systems, the current flows in one direction, and there is no significant skin effect.
Therefore, in the case of HVDC systems:
- There is corona loss because of the high voltage levels and continuous polarity, which leads to corona discharge and power loss.
- There is no skin effect because the DC current flows in one direction, and there is no significant alternating magnetic field that causes the current to concentrate near the surface of the conductor.
Hence, option 'C' is the correct answer, which states that there is corona loss but no skin effect in HVDC systems.
1. Corona Loss:
- Corona loss is the power loss that occurs due to the ionization of the surrounding air around the conductors in a high voltage system.
- In HVDC systems, the voltage levels are very high, which increases the likelihood of corona discharge.
- When the electric field intensity exceeds a certain threshold, the air molecules around the conductor break down and become ionized, resulting in a corona discharge.
- This corona discharge leads to power loss and can cause interference with communication systems.
- Corona loss is more significant in AC systems compared to DC systems because the polarity reversal in AC systems helps in the recovery of the ionized air molecules.
- However, in HVDC systems, the polarity remains constant, which leads to a continuous corona loss.
2. Skin Effect:
- Skin effect is the tendency of alternating current (AC) to flow near the surface of a conductor, causing the effective cross-sectional area available for current flow to decrease.
- Skin effect occurs due to the self-induced magnetic field generated by the current flowing through the conductor.
- The magnetic field repels the current from the center of the conductor, causing it to concentrate near the surface.
- Skin effect is significant in AC systems, where the current alternates direction periodically.
- In DC systems, the current flows in one direction, and there is no significant skin effect.
Therefore, in the case of HVDC systems:
- There is corona loss because of the high voltage levels and continuous polarity, which leads to corona discharge and power loss.
- There is no skin effect because the DC current flows in one direction, and there is no significant alternating magnetic field that causes the current to concentrate near the surface of the conductor.
Hence, option 'C' is the correct answer, which states that there is corona loss but no skin effect in HVDC systems.
A three-phase, 50 Hz, 400 kV, transmission line is 300 km long. The line inductance is 0.97 mH/km per phase and capacitance is 0.0115 μF/km per phase. Assuming a lossless line, the surge impedance of the line will be- a)196.44 Ω
- b)286.62 Ω
- c)250 Ω
- d)290.43 Ω
Correct answer is option 'D'. Can you explain this answer?
A three-phase, 50 Hz, 400 kV, transmission line is 300 km long. The line inductance is 0.97 mH/km per phase and capacitance is 0.0115 μF/km per phase. Assuming a lossless line, the surge impedance of the line will be
a)
196.44 Ω
b)
286.62 Ω
c)
250 Ω
d)
290.43 Ω
|
|
Samarth Khanna answered |
Surge impedance of the line is given by
or,
or,
If the conductor radius increases, inductance of the line,- a)increases
- b)decreases
- c)remains same
- d)may increase or decrease
Correct answer is option 'B'. Can you explain this answer?
If the conductor radius increases, inductance of the line,
a)
increases
b)
decreases
c)
remains same
d)
may increase or decrease
|
|
Dipika Basak answered |
Inductance,
Here, GMR radius of conductor.
Hence, if radius increases, GMR also increases. As a result of which inductance will decrease.
Here, GMR radius of conductor.
Hence, if radius increases, GMR also increases. As a result of which inductance will decrease.
A balanced 3-phase system consists of -- a)Zero sequence currents only
- b)Positive sequence currents only
- c)Negative and zero sequence currents
- d)Zero, negative and positive sequence currents
Correct answer is option 'B'. Can you explain this answer?
A balanced 3-phase system consists of -
a)
Zero sequence currents only
b)
Positive sequence currents only
c)
Negative and zero sequence currents
d)
Zero, negative and positive sequence currents
|
Swati Patel answered |
Answer:
A balanced 3-phase system consists of positive sequence currents only. This means that the three phases of the system have equal magnitudes and are 120 degrees apart from each other in terms of phase angle. The positive sequence currents represent the normal operating conditions of a 3-phase system.
Explanation:
To understand why a balanced 3-phase system consists of positive sequence currents only, let's first understand what positive, negative, and zero sequence currents are.
Positive Sequence Currents:
- In a balanced 3-phase system, the positive sequence currents are the currents that flow in the same sequence and magnitude in all three phases.
- These currents have a phase angle of 120 degrees between each other.
- The positive sequence currents represent the normal operating conditions of a 3-phase system.
Negative Sequence Currents:
- The negative sequence currents are the currents that flow in the opposite sequence as the positive sequence currents.
- These currents have a phase angle of -120 degrees between each other.
- Negative sequence currents can occur due to imbalances in the system, such as unbalanced loads or faults.
Zero Sequence Currents:
- The zero sequence currents are the currents that flow in all three phases in the same direction and at the same magnitude.
- These currents have a phase angle of 0 degrees between each other.
- Zero sequence currents can occur due to imbalances in the system, such as unbalanced loads or faults.
Why a balanced 3-phase system consists of positive sequence currents only:
- A balanced 3-phase system is designed to have equal magnitudes and 120 degrees phase angle separation between the three phases.
- Under normal operating conditions, the loads in a balanced 3-phase system are also balanced, meaning they draw equal currents from each phase.
- When the loads are balanced and the system is operating normally, there are no imbalances that would cause the flow of negative or zero sequence currents.
- Therefore, in a balanced 3-phase system, only positive sequence currents are present.
In conclusion, a balanced 3-phase system consists of positive sequence currents only because under normal operating conditions, the loads are balanced, and there are no imbalances that would cause the flow of negative or zero sequence currents.
A balanced 3-phase system consists of positive sequence currents only. This means that the three phases of the system have equal magnitudes and are 120 degrees apart from each other in terms of phase angle. The positive sequence currents represent the normal operating conditions of a 3-phase system.
Explanation:
To understand why a balanced 3-phase system consists of positive sequence currents only, let's first understand what positive, negative, and zero sequence currents are.
Positive Sequence Currents:
- In a balanced 3-phase system, the positive sequence currents are the currents that flow in the same sequence and magnitude in all three phases.
- These currents have a phase angle of 120 degrees between each other.
- The positive sequence currents represent the normal operating conditions of a 3-phase system.
Negative Sequence Currents:
- The negative sequence currents are the currents that flow in the opposite sequence as the positive sequence currents.
- These currents have a phase angle of -120 degrees between each other.
- Negative sequence currents can occur due to imbalances in the system, such as unbalanced loads or faults.
Zero Sequence Currents:
- The zero sequence currents are the currents that flow in all three phases in the same direction and at the same magnitude.
- These currents have a phase angle of 0 degrees between each other.
- Zero sequence currents can occur due to imbalances in the system, such as unbalanced loads or faults.
Why a balanced 3-phase system consists of positive sequence currents only:
- A balanced 3-phase system is designed to have equal magnitudes and 120 degrees phase angle separation between the three phases.
- Under normal operating conditions, the loads in a balanced 3-phase system are also balanced, meaning they draw equal currents from each phase.
- When the loads are balanced and the system is operating normally, there are no imbalances that would cause the flow of negative or zero sequence currents.
- Therefore, in a balanced 3-phase system, only positive sequence currents are present.
In conclusion, a balanced 3-phase system consists of positive sequence currents only because under normal operating conditions, the loads are balanced, and there are no imbalances that would cause the flow of negative or zero sequence currents.
Chapter doubts & questions for Power Systems - GATE Electrical Engineering (EE) Mock Test Series 2026 2025 is part of Electrical Engineering (EE) exam preparation. The chapters have been prepared according to the Electrical Engineering (EE) exam syllabus. The Chapter doubts & questions, notes, tests & MCQs are made for Electrical Engineering (EE) 2025 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests here.
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