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Electrical Theory > Random Questions > Flashcards

Random Questions Flashcards

1
Q

Swer?

A

Single wire earth return

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2
Q

Luminous flux? And unit

A

The quantity of light emitted by a source in any direction measured in lumens

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3
Q

Mins elements fixed wire appliances or damp situation IRT reading should be?

A

10,000 ohms

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4
Q

What tester would you determine short circuit capacity rating On protective devices?

A

Earth impedance tester

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5
Q

Why are transformer cores iron laminated?

A

To reduce eddy currents

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6
Q

Define peak inverse voltage as applied to a semiconductor?

A

The max voltage a semi conductor can withstand in reverse bias

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7
Q

Inverse time current characteristics?

A

An increase of current through a protective device beyond its normal rating causes a decrease in operating time

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8
Q

How is the voltage regulation of a power transformer achieved with varying loads?

A

Use of a tap charger

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9
Q

An increase of resistance in the protective earth conductor would effect the operation of the circuit protection device how?

A

It may not operate due to reduced fault current

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10
Q

Three phase half wave rectifier frequency?

A

150 hz full wave is 300 hz

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11
Q

This motor has low starting torque and poor efficiency, commonly found in small appliances such as small fans, coffee grinders. Non reversible

A

Shaded pole motor

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12
Q

A low power motor, series wound that gets its name from its ability to operate from DC OR AC, for reversal it cannot be achieved by swapping supply connections over. What motor is this and How is it reversed?

A

Universal/series motor. Reversed by interchanging either armature or field leads but not both.

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13
Q

In this motor both windings are identical and therefore have the same resistance and number of turns. Found in electric lawnmowers. What is the motor and how is it reversed?

A

Permanently split capacitor motor. Reversal comes from connecting a reversing switch to enable the capacitor to be shifted from one winding to the other.

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14
Q

How to reverse 3 phase motor?

A

Switch two phases

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15
Q

Loss caused by the alternating of flux in the core molecules. Energy is consumed in this process and the energy loss is called?

A

Hysteresis

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16
Q

Transformer used for variable load?

A

Distribution transformers

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17
Q

Luminous intensity? And unit

A

Means the luminous flux per unit solid angle in a specified direction measure in candela (CD)

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18
Q

Voltage and torque relationship at induction motor terminals?

A

Torque is proportional to speed

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19
Q

The current transformer must be shorted out before removal why?

A

Magnetic field saturated, burnt out, shock hazard

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20
Q

Smallest and largest your main earthing conductor can be?

A

4mm and 120 mm

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21
Q

How are zener diode connected?

A

In reverse bias

22
Q

Close excess current protection?

A

Will operate 1.5x rating within 4 hours

23
Q

Ladder ratio?

A

1:4

24
Q

What rcd is voltage dependant?

A

Portable rcd

25
Q

Relationship between avaliable torque at a given speed and voltage at an induction motor terminal?

A

Torque is proportional to voltage squared

26
Q

Define clearance time?

A

Total time for any fuse to operate and clear a fault

27
Q

In what form is the voltage output from a PWM converter?

A

A series of rectangular pulses

28
Q

Hi

A

Dude

29
Q

Why are induction motor rotor bars normally skewed?

A

To give smoother quieter running and more uniform torque

30
Q

Three phase 50hz output ripple frequency of a full wave rectifier

A

300 hz

31
Q

Pull out torque as it applies to an AC induction motor?

A

That’s the max torque it can produce

32
Q

Main purpose of a fault loop impedance test at the main switchboard of a low voltage installation?

A

Confirm that the protective device can safely interrupt the installation pscc

33
Q

Rated current of property RCD?

A

300 ma

34
Q

Personal protection rcd and medical rcd ma?

A

Personal 30 ma medical 10 ma

35
Q

What is burden?

A

The max load in VA which may be applied to the secondary terminals in a voltage or current transformer

36
Q

Course excess current protection?

A

When it may not operate within 4 hours at 1.5x current

37
Q

Define discrimination?

A

To install in such a way that the fault in a circuit will trip the closest protective device first

38
Q

Medical grade RCD ms time at 1x and 5x current

A

40 ms and 40 ms

39
Q

Person protection ms at 1x and 5x current rating

A

300 ms and 40 ms

40
Q

Property protected RCD ms time at 1x and 5x current

A

500 ms and 150 ms

41
Q

What replaced the term fusing factors?

A

Utilisation category

42
Q

What do all course excess protection devices need?

A

Overload protection

43
Q

In regards to fuses what is the 100 a?

A

Max current fuse can carry without deterioration

44
Q

With regards to fuses what is the ACka

A

Max fault current the fuse can safely interrupt

45
Q

With regards to fuses what is GG

A

Fusing factor

46
Q

Testing checklist? With numbers 1-7

A

1) visual check
2) earth continuity
3) IRT
4) polarity
5) correct circuit connection
6)earth impedance
7) operation of RCDs

47
Q

Medical grade MS 1x and 5x PROPER QUESTION

A

40 ma and 40 ms

48
Q

This motors start winding has fewer turns and is of finer wire than the run winding (main winding). Disconnection comes from a centrifugal switch. Used in fans and places where you don’t need high torque. What is the motor and how is it reversed?

A

Standard split phase motor. Reversed by reversing the start or run winding but not both.

49
Q

Cap start motor how is it reversed?

A

Reversing start or run winding but not both. Disconnection comes from centrifugal switch

50
Q

Cap start/ cap run motor and how it is reversed?

A

Used for concrete mixers/ large air con that needs high start and run torque. Disconnection comes from centrifugal switch, reversal comes from fitting an reversal switch

51
Q

Lux for offices?

A

500 or 300-400 probably 500

Electrical Theory (3 decks)

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