1. Which of the following motors always starts on load ? (a) Conveyor motor (b) Floor mill motor (c) Fan motor (d) All of the above 2. ……….. is preferred for automatic drives. (a) Squirrel cage induction motor (b) Synchronous motors (c) Ward-Leonard controlled D.C. motors (d) Any of the above 3. When the load […]
1. Between Field’s test and Hopkinson’s test the main common thing is that both (a) use negligible power (b) are regenerative tests (c) need two similar mechanically coupled motors (d) need two electrically coupled series motors 2. The use of armature divertor in the rheostatic method of speed control for a D.C. shunt motor makes
1. The speed of a motor falls from 1100 r.p.m. at no-load to 1050 r.p.m. at rated load. The speed regulation of the motor is (a) 2.36% (b) 4.76% (c) 6.71% (d) 8.84% 2. The armature voltage control of D.C. motor provides (a) constant torque drive (b) constant voltage drive (c) constant current drive (d)
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