2
A 3-phase 50 Hz generator supplies power of 3 MW at 17.32 kV to a balanced 3-phase inductive load through an overhead line. The per phase line resistance and reactance are 0.25 $$\Omega $$ and 3.925 $$\Omega $$ respectively. If the voltage at the generator terminal is 17.87 kV, the power factor of the load is ________.
4
A load is supplied by a $$230$$ $$V,$$ $$50$$ $$Hz$$ source. The active power $$P$$ and the reactive power $$Q$$ consumed by the load are such that $$1$$ $$kW$$ $$ \le P \le 2\,kW\,\,$$ and $$\,1\,\,kVAR \le 2\,\,kVAR.\,\,$$ A capacitor connected across the load for power factor correction generates $$1$$ $$kVAR$$ reactive power. The worst case power factor after power factor correction is
5
A three-phase cable is supplying $$800$$ kW and $$600$$ kVAr to an inductive load. It is intended to supply an additional resistive load of $$100$$ kW through the same cable without increasing the heat dissipation in the cable, by providing a three-phase bank of capacitors connected in star across the load. Given the line voltage is $$3.3$$ kV, $$50$$ Hz, the capacitance per phase of the bank expressed in microfarads, is ________.
6
A single-phase transmission line has two conductors each of 10 mm radius. These are fixed at a center-to-center distance of 1 m in a horizontal plane. This is now converted to a three-phase transmission line by introducing a third conductor of the same radius. This conductor is fixed at an equal distance D from the two single-phase conductors. The three-phase line is fully transposed. The positive sequence inductance per phase of the three phase system is to be 5% more than that of the inductance per conductor of the single phase system. The distance D, in meters, is ________.
8
The horizontally placed conductors of a single phase line operating at $$50$$ $$Hz$$ are having outside diameter of $$1.6$$ cm, and the spacing between centers of the conductors is $$6$$ m. The permittivity of free space is $$8.854 \times {10^{ - 12}}\,\,F/m.$$ The capacitance to ground per kilometer of each line is
9
The complex power consumed by a constant-voltage load is given by $$\left( {{P_1} + {J_{q1}}} \right).\,\,$$ Where, $$\,1\,\,kW \le \,\,{P_1} \le \,\,\,1.5\,\,kW\,\,\,$$ and $$\,\,0.5\,KVAR \le \,\,\,{Q_1} \le 1kVAR.\,\,\,$$ A compensating shunt capacitor is chosen such that $$\,\left| Q \right| \le 0.25\,\,KVAR,\,\,$$ where $$Q$$ is the net reactive power consumed by the capacitor-load combination. The reactive power (in kVAR) supplied by the capacitor is ____________.
10
For a $$400$$ $$km$$ long transmission line, the series impedance is $$(0.0 + j0.5)$$ $$\Omega /km$$ and the shunt admittance is $$(0.0 + j5.0)$$ $$\mu \,mho/km.$$ The magnitude of the series impedance (in $$\Omega $$) of the equivalent $$\pi $$ circuit of the transmission line is __________.
14
A lossy capacitor $${C_x}$$, rated for operation at $$5$$ $$kV,$$ $$50$$ $$Hz$$ is represented by an equivalent circuit with an ideal capacitor $${C_p}$$ in parallel with a resistor $${R_p}$$. The value $${C_p}$$ is found to be $$0.102$$ $$\mu F$$ and the value of $${R_p}$$ $$=$$ $$1.25$$ $$M\Omega .$$ Then the power loss and $$tan\delta $$ of the lossy capacitor operating at the rated voltage, respectively, are
15
A $$50$$ $$Hz$$ synchronous generator is initially connected to a long lossless transmission line which is open circuited at the receiving end. With the field voltage held constant, the generator is disconnected from the transmission line. Which of the following may be said about the steady state terminal voltage and field current of the generator?
19
A lossless transmission line having Surge Impedance Loading $$(SIL)$$ of $$2280$$ $$MW.$$ A Series capacitive compensation of $$30$$% is emplaced. Then $$SIL$$ of the compensated transmission line will be
20
The total reactance and total susceptance of a lossless overhead $$EHV$$ line, operating at $$50$$ $$Hz,$$ are given by $$0.045$$ pu and $$1.2$$ pu respectively. If the velocity of wave propagation is $$3\,\, \times \,\,{10^5}$$ km/s, then the approximate length of line is
21
$$230$$ $$V$$ (phase) $$50$$ Hz, three-phase, $$4$$-wire, system has a sequence $$ABC$$. A unity power-factor load of $$4$$ kW is connected between phase A and neutral $$N$$. It is desired to achieve zero neutral current through the use of a pure inductor and pure capacitor in the other two phases. The Value of inductor and capacitor is......
23
The $$A, B, C, D$$ constant of a $$220$$ $$kV$$ line are:
$$A = D = 0.94\,\angle \,10,\,\,\,B = 130\,\angle \,730,\,\,\,C = 0.001\,\angle \,900.\,\,$$ If the sending end voltage of the line for a given load delivered at nominal voltage is $$240$$ $$kV$$, the % voltage regulation of the line is
24
At an industrial sub-station with a $$4$$ $$MW$$ load, a capacitor of $$2$$ MVAR is installed to maintain the load power factor at $$0.97$$ lagging. If the capacitor goes out of service, the load power factor becomes
25
A $$110$$ $$kV,$$ single core coaxial, XLPE insulated power cable delivering power at $$50$$ $$Hz,$$ has a capacitance of $$125$$ $$nF/km.$$ If the dielectric loss tangent of XLPE is $$\,2\,\, \times \,\,{10^{ - 4}},$$ the dielectric power loss in this cable in $$W/km$$ is
26
A lightning stroke discharges impulse current of $$10$$ kA (peak) on a $$400$$ kV transmission line having surge impedance of $$250\,\Omega $$. The magnitude of transient over-voltage traveling waves in either direction assuming equal distribution form the point of lightning strike will be
27
A $$800$$ $$kV$$ transmission line is having per phase line inductance of $$1.1$$ $$mH/km$$ and per phase line capacitance of $$11.68$$ $$nF/km.$$ Ignoring the length of the line, its ideal power transfer capability in $$MW$$ is
28
The generalized circuit constants of a $$3$$-phase, $$220$$ $$kV$$ rated voltage, medium length transmission line are $$A = D = 0.936 + j\,0.016 = 0.936\angle {0.98^ \circ }$$
$$B = 33.5 + j138 = 142.0\angle {76.4^ \circ }\,\Omega $$
$$\,C = \left( { - 5.18 + j914} \right) \times \,{10^{ - 6}}\,\Omega $$
If the load at the receiving end is $$50$$ MW at $$220$$ $$kV$$ with a power factor of 0.9 lagging, then magnitude of line to line sending end voltage should be
29
The ABCD parameters of a $$3$$-phase overhead transmission line are $$\,A = D = 0.9\angle {0^ \circ }.\,\,B = 200\,\angle {90^ \circ }\,\,\Omega \,\,\,$$ and $$\,\,C = 0.95\, \times \,\,{10^{ - 3}}\angle {90^ \circ }\,\,S.\,\,\,\,$$ At no-load condition, a shunt inductive reactor is connected at the receiving end of the line to limit the receiving end voltage to be equal to the sending-end voltage. The ohmic value of the reactor is
31
A surge of 20 kV magnitude travels along a lossless cable towards its junction with two identical lossless overhead transmission lines. The inductance and the capacitance of the cable are 0.4 mH and 0.5 $$\mu F$$ per km. The inductance and
capacitance of the overhead transmission lines are 1.5 mH and 0.015 $$\mu F$$ per km. The magnitude of the voltage at the junction due to surge is
32
A balanced delta connected load of $$\left( {8 + j6} \right)\Omega $$ per phase is connected to a $$400$$ $$V$$, $$50$$ $$Hz$$, $$3-$$phase supply lines. If the input power factor is to be improved to $$0.9$$ by connecting a bank of star connected capacitors the required KVAR of the bank is
33
The conductors of a $$10$$ km long, single phase, two wire line are separated by a distance of $$1.5$$ m. The diameter of each conductor is $$1$$ cm. If the conductors are of copper, the inductance of the circuit is
35
The corona loss on a particular system at 50 Hz is 1 kW/km per phase. The corona loss at 60 Hz would be
36
A transmission line has equal voltages at the two ends, maintained constant by two sources. A third source is to be provided to maintain constant voltage (equal to end voltages) at either the midpoint of the line or at $$75$$% of the distance from
the sending end. Then the maximum power transfer capabilities of the line in the original case and the other two cases respectively will be in the following ratios.
37
A 3-phase, 11 kV, 50 Hz, 200 kW load has a power factor of 0.8 lag. A delta connected 3-phase capacitor is used to improve the power factor to unity. The capacitance power phase of the capacitor in micro-farads is
39
$$A$$ $$220$$ kV, $$20$$ km long, $$3$$-phase transmission line has the following $$A, B, C, D$$ constants. $$A=D=0.96$$$$\angle {3^0},$$ $$\,B = 55\angle {65^0}\,\,\Omega /$$ phase, $$\,C = 0.5 \times {10^{ - 4}}\angle {90^0}\,\,$$ $$S/$$phase. Its correct charging current per phase is
40
For a single phase overhead line having solid copper conductors of diameter $$1$$ cm, spaced $$60$$ cm between centers, the inductance in $$mH/km$$ is
41
A shunt reactor of $$100$$ MVAR is operated at $$98$$% of its rated voltage and $$96$$% of its rated frequency. The reactive power absorbed by the reactor is;
42
A cable has the following characteristics. $$L = 0.201\,\,\mu H/m\,\,$$ and $$\,C = 196.2\,pF/m.\,$$ The velocity of wave propagation through the cable is
43
For equilateral spacing of conductors of an untransposed $$3$$-phase line, we have
44
The rated load of an underground cable is always _______its natural load.
45
Consider a three-phase, $$50$$ $$Hz$$, $$11$$ $$kV$$ distribution system. Each of the conductors is suspended by an insulator string having two identical porcelain insulators. The self capacitance of the insulator is $$5$$ times shunt capacitance. The voltage drop across botton most disc is:
46
The charging current of a $$400$$ kV transmission line is more than that of a $$220$$ kV line of the same length.