Vocabulary: multiple choice questionnaire.

1. In electric machines, electromotive or back electromotive force is developed by the ...

magnetic circuit

flux variation through a turn

fan blades

network frequency

2. The compensator poles of D.C. machines have the job of considerably reducing the ...

armature reaction effects speed variation machine size armature current

3. For a digital input, a stepping motor produces an output which is

a rotational velocity

an alternating electromotive force

an absolute permeability

a shaft position

4. When the step frequency increases, the motor's static torque

stays constant

increases

decreases

varies in a sinusoidal manner

5. For producing excitation voltage phase and frequency in the windings of double supply asynchronous motors, ... is used.

a tachometric generator

an electronic device

the network voltage

a mechanical device

6. The squirrel cage induction motor has for a rotor...

a winding linked to external resistors

bars, cast or fitted in the stator slots

a solid rotor, that is to say, being only in iron conducting bars, joined at each end by a ring

7. Splash-proof motors are motors where the casing is provided with

orifices necessary for ventilation closed by gratings

orifices plus devices for protecting the machine from water falling into it

vapour or gas-tight joints

mechanical reinforcement against internalexplosions

8. On load transformer voltage setting is carried out by ...

a tap changer

an electronic device

a D.C. generator

a 3-phase induction motor

9. The magnetic circuit of a power transformer consists of...

a solid core and yoke

a bare sheet steel core and yoke

a core and yoke made of silicate magnesium insulated sheet steel

an insulated copper strip core and yoke

10.The insulation of power transformer windings is achieved from ...

a thermosetting product

a silicon-based varnish

successive cotton layers

successive paper layers

11.On-load voltage regulators are devices where the rotor...

is absolutely fixed

turns at the rotating field speed

is set in an adjustable position

advances in steps, always in the same direction

12.A four quadrant solid-state converter is ...

one-way

double-way

reversible

double-way and reversible

13.The fuses used for the protection of thyristors or power transistors should be of the ... type.

quick-acting

normal

motor-following automatic-tripping

14.Saturable reactances, used in series with triacs to control the supply of a star-connected 3-phase motor, have the role of...

creating a neutral point

protecting the triacs against high values of di/dt

replacing fuses

helping the R.C. protective circuit to get over the dv/dt limitation

15.Star-delta starting is applicate to ... motors whose voltage in the delta corresponds to the main voltage.

d.c. (direct current)

single-phase A.C. (alternating current)

6 output-terminal three-phase A.C.

commutator

16.Contactors used for reverse current braking withstand large variations in current. The current varies ...

from the maximum braking reverse current to the rated current

from the rated current to the zero value

from the R.M.S. current to the instantaneous current value

from the homopolar current to the inverse current

17.Shock proof contactors are unaffected by ...

temperature

the magnetic field

the current flowing through them

linear acceleration

18.A protection relay, whether of the thermal or magnetic type, always acts on a device for breaking the circuit it monitors His device is called a ...

insulator

contactor

drum combiner

switch

19.A magnetic protection relay controls starting peaks and high over voltages. It provides ... tripping.

accelerated

delayed

instantaneous

differential

20.When a contactor electromagnet coil is fed from a rectified A.C. supply ... is used.

a rectifier and economy resistor

a triac and an inductance

an R.C. (resistance-capacitance) circuit

a triode valve and a thermistor

21.The arching horns found on breaking poles fitted with blowout coil and arc chute allow the ...

potential gradient to be changed

current to be lead away

contact resistance to be varied

electric arc to be elongated (lengthened)

22.Electronic time delayed relays have a high adjusted time delay accuracy. The latter may be continually set by ...

a stepping motor

a remote-control potentiometer

a velocity transducer

a terminal box

23.To prevent the spontaneous propagation of a flame in an explosive mixture causing an explosion, electrical apparatus are designed with ...

ventilation holes

no joints

racks

a gas-tight enclosure

24.When a D.C. supplied device includes silver parts used under highly humid conditions silver migration may take place onto insulation surfaces. This migration is avoided by excluding… materials.

phenolic materials and free ammonia glass

mica

asbestos

25.In order not to affect a system's characteristics, a power circuit breaker should ...

break the current at its maximum value

ionize the breaking zone

offer a zero arc resistance

be mounted on a rubber block

26.During current decrease, an elongation of the arc in an air circuit-breaker is created by using ...

mechanical forces electromagnetic forces compressed air

an injection of cooled oil

27.Sulphur hexafluoride (SF6) is a colourless, odourless gas at room temperature, and has ... density in comparison with air.

a relatively high

an almost equal

a very low

a very high

28.Closing resistors are used to limit switching surges. They come into play ... the closing of the main contacts.

a few milliseconds after

a few milliseconds before

several seconds before

at the same time as

29.A vacuum cartridge has the advantage of being small, with a good current-breaking life, but also runs the risk of...

high overvoltages

cascade ionization

contact welding

dielectric break-down

30.Solid-state circuit breaking is considered as being the ideal breaking. Unfortunately, semiconductors inherently have ... which makes them incapable of withstanding large overloads.

a low potential gradient

a reduced size

a long current rise time

a very low thermal inertia

31.Resistance heaters use ... type heating.

conduction convection

radiation

induction

32.Induction heating results from hysteresis and eddy current losses. ... is one of the materials which produce hysteresis losses.

copper

graphite

nickel

silver

33.In the case of solid-state converters supplying induction furnaces, the converter frequency is determined by ... within the electronic control circuit.

a single function transistor

a free wheeling diode

an oscillator

a triac

34.Due to magnetic and electrical fields associated with the electrodes of a high frequency dielectric heating generator, it is a legal requirement to surround the equipment with ...

an insulating cover

a radioelectric shield

a special paint

asbestos

35.When, in electrical resistance welding, the electrodes are of wheel form, rotating about their axes on the overlap of the parts to be assembled, the process is called ...

projection welding

seam welding

spot welding

but welding

36.Fusion welding carried out by striking an arc between a non-consumable electrode and the workpiece to be welded requires ...

an inert gas

an active gas

vacuum

air

37.The electrical connections between the generator and the high voltage transformer in a hydroelectric complex are made by ...

insulated cables

cables cooled to a very low temperature