Short notes
Objective questions (Answers are given below)
- The minimum number of wattmeter (s) required
to measure 3-phase, 3-wire balanced or
unbalanced power is
(a) 1
(b) 2
(c) 3
(d) 4
(GATE 2001) - A wattmeter reads 400 W when its current coil
is connected in the R phase and its pressure
coil is connected between this phase and the
neutral of a symmetrical 3-phase system
supplying a balanced star connected 0.8 p.f.
inductive load. The phase sequence is RYB.
What will be the reading of this wattmeter if
its pressure coil alone is reconnected between
the B and Y phases, all other connections
remaining as before?
(a) 400.0 (b) 519.6
(c) 300.0 (d) 692.8
(GATE 2003) - Total instantaneous power supplied by a 3-
phase ac supply to a balanced R-L load is
(a) zero
(b) constant
(c) pulsating with zero average
(d) pulsating with non-zero average
(GATE 2004) - 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) 33 1/3
(b) 50
(c) 66 2/3
(d) 75 (GATE)