Ques 71. If the length of the cable is doubled, its capacitance C will become
Doubled
Half
One-fourth
Remain Unchanged
Answer.1. Doubled
Explanation:
Capacitance exists between two things with different electric charge and a dielectric in between.
The transmission line and the earth below it, have a charge difference and the air between them is dielectric. This constitutes a capacitance.
The longer the cable, the more part of it runs parallel to the earth and hence, more capacitance between them since the length of the cable and the capacitance of the cable are directly proportional to each other.
Ques 72. The advantages of high transmission voltage are
Area of cross-section is reduced
Reduced line losses
Increase efficiency
All of the above
Answer.4. All of the above
Explanation:
Advantages of High Voltage Transmission
The line losses are inversely proportional to the square of the voltage and the power factor (Pl∝ 1/V²P). Therefore line losses are reduced.
For constant current density, the line efficiency is high for the high voltage transmission line.
The volume of copper required is inversely proportional to the square of the voltage and the power factor. Hence the requirement of copper is less for the high voltage transmission line. A ∝ 1/V²
As the line losses are decreased the efficiency of the transmission line is increased.
Ques 73. The voltage regulation of flat voltage profile system is
100 %
50 %
0 %
Any of the above
Answer.3. 0%
Explanation:
The % voltage regulation is given as (Vs-Vr)/Vr*100 where
Vs = Supply voltage
Vr = Receiving end Voltage
For flat voltage profile system all the voltage drop in the line are neglected therefore supply voltage (Vs) is equal to the Receiving end voltage (Vr) i.e Vs = Vr
Hence the voltage regulation for flat voltage profile system is zero.
Ques 74. The maximum power can be achieved in a transmission line by
Reducing system transfer Reactance
Increasing the Voltage level
Both 1 and 2
None of the above
Answer.3. Both 1 and 2
Explanation:
To reduce the power loss in the transmission line the source voltage is stepped up by using the transformer.
By increasing the voltage level the same amount of power can transfer with much smaller current thus reducing transmission line losses (I2R losses).
The system transfer reactance of a transmission line can be reduced by the series capacitance, bundled conductor, or by using parallel transmission line.
Ques 75. Ferranti effect can be reduced by which of the following method?
Shunt Reactor
Series Reactor
Shunt Capacitor
Series Capacitor
Answer.1. Shunt Reactor
Explanation:
A long transmission line can be considered to be composed of a high amount of capacitance and inductor distributed across the entire length of the line. Ferranti Effect occurs when the current drawn by the distributed capacitance of the line is greater than the current associated with the load at the receiving end of the line which occurs during light or no load.
Shunt Reactor compensation at the receiving end help to reduce the effect of capacitance thus reducing the Ferranti effect.
Shunt Reactor absorbs the excess reactive power during no load or light load conditions and thus helps in stabilizing the voltage of the Transmission Line.
Ques 76. A transmission line has a reactance of 4 Pu is operating at Vs = Vr = 2 Pu. The generator is connected at source end which is delivering 0.5 Pu of active power. Find the load angle?
60°
45°
30°
35°
Answer.3.
Explanation:
Power delivered P = (Vs × Vr × sinδ)/X
Vs = sending end voltage = 2
Vr = receiving end voltage = 2
X = reactance = 4
P = 0.5 pu
δ = load angle
0.5 = (2 × 2× sinδ)/4
sin-1(0.5) = δ
δ = 30°
Ques 77. Under excited Synchronous phase modifier works as
Shunt capacitor
Shunt Reactor
Series capacitor
Series Reactor
Answer.2. Shunt Reactor
Explanation:
The synchronous phase modifier is a synchronous motor which is not connected to any load.
When a synchronous motor is under-excited its works as an inductor or shunt Reactor.
The shunt reactors are used across capacitive loads or lightly loaded lines to absorb leading vars to control the voltage across the load to within certain desirable limits.
Ques 78. Over-excited Synchronous phase modifier work as
Shunt capacitor
Shunt Reactor
Series capacitor
Series Reactor
Answer.1. Shunt Capacitor
Explanation:
The synchronous phase modifier is a synchronous motor which is not connected to any load.
When a synchronous motor is over-excited its works as a shunt capacitor.
The shunt capacitors are used across an inductive load to provide leading volt-ampere-reactive vAR to reduce the line current and total kVA loading of the substation.
Ques 79. The specified quantities of load bus are
Q and V
V and δ
P and Q
Q and V
Answer.4. P and Q
Explanation:
All the bus in the power system is generally categorized into three categories
Generation Bus
Load Bus
Slack Bus
The two of the four quantities are mentioned above are specified for each of the buses.
Load bus: This is also called as PQ bus and here the real power |P| and reactive power |Q| are specified.
Ques 80. The specified quantities of Generation bus is
Q and V
V and δ
P and V
Q and V
Answer.3. P and V
Explanation:
Generation Bus is also called as the voltage-controlled bus.
The specified quantities of Generation bus is P and V and here the real power |P| and voltage magnitude |V| are specified.