IMPORTANT QUESTION FOR POWER SYSTEM (GATE 2019)
Power generation concepts, ac and dc transmission concepts, Models and performance of transmission lines and cables, Series and shunt compensation, Electric field distribution and insulators, Distribution systems, Per‐unit quantities, Bus admittance matrix, Gauss- Seidel and Newton-Raphson load flow methods, Voltage and Frequency control, Power factor correction, Symmetrical components, Symmetrical and unsymmetrical fault analysis, Principles of over‐current, differential and distance protection; Circuit breakers, System stability concepts, Equal area criterion.
q1) Three phase transformers which can not be connected in parallel are
(a) YY with ∆∆
(b) Y∆ with ∆Y
(c) YY with Y∆
(d) (b) and (c).
Q2) A distance relay is said to be inherently directional if its characteristic on R-X diagram
(a) is a straight line off-set from the origin
(b) is a circle that passes through the origin
(c) is a circle that encloses the origin
(d) always a separate directional relay is required
Q3) The voltage and current in a circuit are given by
v = 10 sin (ωt – π/6)
i = 10 sin (ωt + π/6)
The power consumed is given as
(a) 100 watts
(b) 50 watts
(c) 86.6 watts
(d) 25 watts \
Q4) The per unit impedance of a circuit element is 0.15. If the base kV and base MVA are halved, then the new value of the per unit impedance of the circuit element will be
Q5) When two transformers of different KVA ratings are connected in parallel they share the load in proportion to their respective KVA rating only when their
(a) KVA ratings are identical
(b) Efficiencies are equal
(c) pu impedances are equal
(d) equivalent impedances are equal.
Q6) An alternator having induced emf. of 1.6 p.u. is connected to an infinite bus of 1.0 p.u. If the busbar has reactance of 0.6 p.u. and alternator has reactance of 0.2 p.u., the maximum power that can be transferred is given by
(a) 8 p.u.
(b) 2 p.u.
(c) 2.67 p.u.
(d) 5.0 p.u.
Q8) The p.u. impedance value of an alternator corresponding to base values 13.2 kV and 30 MVA is 0.2 p.u. The p.u. value for the base values 13.8 kV and 50 MVA will be:
(a) 0.306 p.u.
(b) 0.33 p.u.
(c) 0.318 p.u.
(d) 0.328 p.u.
Q11 A Bucholz relay is used for
(a) protection of a transformer against all internal faults
(b) protection of a transformer against all external faults
(c) protection of a transformer against both internal and external faults
(d) protection of induction motors.