For the circuit shown below Zin is
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Solution
A single phase ac voltage regulator is fed from a 50 Hz supply system. If it supplies a load comprising a resistance of 2Ω connected in series with an inductance of 6.36 mH, then range of firing angle a providing controlled voltage would be
In a 3-phase semi-converter, if firing angle is less than or equal to 60°, then duration of conduction of each thyristor and diode would be respectively
A 110 MVA, 11 kV synchronous generator is connected through a 5-cycle circuit breaker to a transformer. It has direct axis sub-transient reactances X”d= 19%, transient reactance X’d= 26% and synchronous reactance Xd= 130%. It is operating at no load and rated voltage when a three-phase short circuit occurs between the breaker and the transformer. The maximum possible dc component of the short-circuit current in the breaker will be
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Solution
A balanced 3-phase, 3-wire supply feeds balanced star connected resistors. If one of the resistors is disconnected, then the percentage reduction in the load will be
A power system consist of 300 buses out of which 20 buses are generator bus, 25 buses are the ones with reactive power support and 15 buses are the ones with fixed shunt capacitors. All the other buses are load buses.It is proposed to perform a load flow analysis in the system using Newton-Raphs on method. The size of the Newton Raphson Jacobian matrix is
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Solution
Given that no. of busses n= 300
Generator bus = 20
Reactive power support busses =25
Fixed buses with Shunt Capacitor = 15
Slack buses (ns) = 20 + 25 – 15 =30
∴Size of Jacobian Matrix is given as
= 2(n – ns) × 2(n –ns)
= 2(300 – 30) × 2(300 – 30)
= 540 × 540
A bank of three identical single-phase 250 kVA, 11 kV/230 V transformers is used to provide 400 V low tension supply from a 11 kV,3-phase sub-station. The effective kVA rating of the bank will be
For a single phase power system shown in figure,transformer T1 and T2 are identical and their specification are given as following
Transformer ratio = 2 kV /11 kV
The resistance on LV side= 0.04 Ω and HV side = 1.3 Ω
Reactance on LV= 0.125 Ω and HV side =4.5 Ω
The efficiency of the transmission is
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Solution
A sinusoidal source of voltage V and frequently f is connected to a series circuit of variable resistance, R and a fixed reactance, X. The locus of the tip of the current-phasor, I as R is carried from 0 to ∞ is a/an
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Solution
The severity of line to ground and three-phase faults at the terminals of an unloaded synchronous generator is to be same. If terminal voltage is 1.0 pu, Z1= Z2= j0.1pu and Z0= j 0.05 pu for the alternator, then required inductive reactance for neutral grounding is ______
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Solution
0.0166 pu