1. Starters are used with D.C. motors because (a) these motors have high starting torque (b) these motors are not self-starting (c) back e.m.f. of these motors is zero initially (d) to restrict armature current as there is no back e.m.f. while starting 2. For starting a D.C. motor a starter is required because (a) […]
1. Which of the following statement about SF6 gas is incorrect? (a) it is a non-toxic gas (b) it is non-inflammable (c) it has density 5 times that of air at 20oC (d) it has dark yellow color. 2. SF6 gas is transported in (a) gas cylinders (b) liquid form in cylinders (c) solid form
1. The contact resistance is least affected by (a) the mechanical force applied (b) the shape of the contact faces (c) the amount of surface contamination (d) the ambient temperature. 2. As the force on contact is increased, the contact resistance will (a) increase linearly (b) increase exponentially (c) remain unchanged (d) decrease. 3. Minimum
1. Low voltage circuit breakers have rated voltage of less than (a) 220 V (b) 400 V (c) 1000 V (d) 10,000 V 2. The fault clearing time of a circuit breaker is usually (a) few minutes (b) few seconds (c) one second (d) few cycles of supply voltage 3. When a HVAC circuit breaker
1. The insulating material for cable should have (a) low cost (b) high dielectric strength (c) high mechanical strength (d) all of the above. 2. Which of the following Protects a cable against mechanical injury ? (a) Bedding (b) Sheath (c) Armouring (d) None of the above 3. Empire tape is (a) varnished cambric (b)
1. Overheating of generator’s winding (a) reduces life of the machine (b) does not have any significant effect (c) reduces generated voltage (d) reduces power factor 2. The maximum current that can be supplied by an alternator depends on (a) exciter current (b) strength of the magnetic field (c) number of poles (d) speed of
1. In air-crafts, alternators have operating frequency of (a) 800 Hz (b) 400 HZ (c) 60 Hz (d) 50 HZ 2. Alternators, now-a-days, are designed to have poor regulation because (a) it reduces the construction cost (b) it limits the value of short-circuit current (c) we employ automatic voltage regulators (d) none of the above
1. Salient pole type alternators are generally used on (a) low voltage alternators (b) hydrogen cooled prime-movers (c) high speed prime-movers (d) low and medium speed prime-movers 2. Turbo-alternators are generally used to run at (a) 500 R.P.M. (b) R.P.M. (c) 5000 R.P.M. (d) 16000 R.P.M. 3. The rotor preferred for alternators applied to hydraulic
1. The circle diagram for an induction motor cannot be used to determine (a) efficiency (b) power factor (c) frequency (d) output 2. Blocked rotor test on induction motor is used to find out (a) leakage reactance (b) power factor on short circuit (c) short-circuit current under rated voltage (d) all of the above. 3.
1. The frame of an induction motor is made of carbon (a) closed grained cast iron (b) aluminium (c) stainless steel 2. Slip rings for induction motors are made of (a) phosphor bronze (b) aluminium (c) carbon (d) cobalt steel 3 . If ‘s’ is the slip and ‘f’ is the supply frequency, the frequency