class4 questions elect

8/22/2019 Class4 Questions Elect

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Question

Sketch and describe an arrangement for automatic connection of emergency

batteries upon loss of main power.

Include in your answer:

Means of obtaining d.c. charging supply from a.c. mains;

A method of maintaining charge on lead acid batteries;

The arrangement to check that batteries operate at loss of main power

The length of time for which emergency batteries of passenger and cargo ships

must provide power.

Question.

Sketch and describe a Reverse Power Protection, explain why there there is a tme

delay incorporated

QUESTION

Explain the difference between the following motor enclosure

Drip proof

Totally enclosed

Deck water tight

Flame proof

Question

Describe the devices used to protect 3phase A.C. induction motor against the

following faults

Short circuit, overload, single phase fault

Motor protection

Single-phasing

Protection Discrimination


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Question

a) Sketch the circuit diagram of an instrument used for measuring electrical

insulation resistance.

b) Describe the circuit diagram sketched, explaining how it operates when

measuring electrical insulation resistance.

Question

(a) With reference to the insulation testing of marine electrical plant:

State the reason for insulation testing;

State the precautions to be observed when testing intrinsically safe

equipment Type Ex. I'

Describe the overhaul of a a.c.\ d.c. motor which has been subject to excessively

damp condition or flooding with seawater.

SOME TIMES IT IS ALSO ASKED TO DESCRIBE overhaul of a.c. motor

Question

a) With reference to single phasing applied to a.c motors

i) Explain the meaning of single phasing

ii) Describe it's effect

iii) State the most common cause of single phasing

b) Sketch a simple diagram of a direct on line starter, showing in detail, the

overload and single phase Protection trip.

Question

a) Make a diagrammatic sketch of a self excited alternator and explain it's

operation

b) State how two alternators may be paralleled safely

Question

Describe the basic principle of self excited generators

Question


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Sketch a lamp bright, lamp dark system configuration for synchronizing lamps

Question

Describe the effects of voltage change and frequency on an induction motor.

Question

Describe W.T.A. Of Sketch the operation of a synchroscope

State the information obtained from it

Suggest a substitute in the event of sychroscope and stand by light failure

Synchroscope

QUESTION:

The incomer is always synchronized when slightly faster than the running

machine.

What would happen if the incomer was slower than the running machine when the

incomer breaker is closed?

Question

List the routine maintenance required on Generator

Question

a) Sketch a direct on line starter for a three phase AC motor.

b) Explain the limitations of a direct on line starter with respect to length of

starting time and repeated successive starts.

Question

a) Sketch the following electrical connections

i) A star connection

ii) A delta connection

b) Explain how the star and delta connections are combined to produce a star /

delta starter for an electrical motor.

Question

a) Describe the principal of operation of each of the following detecting elements


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i) Resistance thermometer

ii) Thermo - couples

iii) Thermisters

b) State one application for each of the detecting elements referred to above

Question

W.R.T. Preferential tripping

State why this facility is required

W.T.A. of sketches describe a typical arrangement to provide instantaneous

tripping

Question

a) Sketch in detail a High Rupture Capacity ( H.R.C ) cartridge fuse which

incorporates an indicator showing fuse operation.

b) Explain how the following special features of an H.R.C cartridge fuse are

achieved; i) non-deterioration

ii) High rupturing capacity, iii) high speed of operation on short circuit, iv)

consistent operation, v) no danger of arcing to metal case of fuse box.

Question

a)Explain the principle of the impressed current system of cathodic protection.

b)Sketch a cathodic protection system of the impressed current type.

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