Worksheets5357 103 / 2365 302
Total questions: 29
Worksheet time: 15mins
Identify the various voltages used for generation, transmission and distribution.
110V, 220V, 330V
25kV, 33kV, 400kV
230V, 400V, 690V
5V, 12V, 24V
Describe how the power of the sun is used to generate electricity.
Through wind turbines
By burning fossil fuels
Using solar panels
With hydroelectric dams
State how electricity is generated in a fossil fuelled power station.
By nuclear fission
By burning coal, oil, or gas
Through solar panels
Using wind turbines
How many live conductors will be in the CCU for a 230 V installation supplied from the DNO?
One
Two
Three
Four
What is the BS number for the supply protective device in a 230 V installation?
BS 7671
BS 1363
BS 88-3
BS 3036
What will the maximum rating of the supply protective device be in a 230 V installation?
30A
60A
100A
200A
State two different types of transformer as identified by their cooling methods.
Oil-cooled and air-cooled
Water-cooled and gas-cooled
Liquid-cooled and solid-cooled
Steam-cooled and vacuum-cooled
Identify the transformer shown in the diagram.
Step-up transformer
Step-down transformer
Isolation transformer
Autotransformer
A step-down transformer has a windings ratio of 10:1 and is supplied from a 230 V source with 1 A of primary load current. The primary winding has 2000 turns. What is the secondary voltage?
23 V
230 V
2.3 V
46 V
With regards to resistance and reactance, what is an impedance triangle used for?
To calculate power factor
To measure voltage
To determine current flow
To find resistance only
A coil of inductance 0.5H and resistance 40 ohms is connected to a 230V 50Hz supply. What is the reactance of the circuit?
157 ohms
100 ohms
50 ohms
25 ohms
A 250V, single-phase machine draws a current of 10A at a power factor of 0.9. What is the power dissipated by the machine?
2250 W
2500 W
2000 W
2750 W
For a 30kW electric motor with a power factor of 0.9 lagging, what is the apparent power in kVA?
33.33 kVA
27 kVA
30 kVA
35 kVA
List 3 items that may require power factor correction to be applied.
Electric motors, transformers, and fluorescent lamps
Toasters, hair dryers, and electric kettles
LED lights, solar panels, and wind turbines
Smartphones, laptops, and tablets
What is the purpose of a capacitor in a fluorescent light fitting, and what is the effect on power factor if this is removed?
To reduce flickering; power factor decreases
To increase brightness; power factor increases
To stabilize voltage; power factor remains unchanged
To reduce energy consumption; power factor increases
Determine the neutral current, using a phasor diagram, with the following values: L1 = 50A, L2 = 40A, L3 = 30A.
10A
17A
20A
27A
Calculate the phase and line current when three resistors each having a resistance of 20 ohms are connected to a 400V three-phase supply, in Star.
Phase current = 11.5A, Line current = 11.5A
Phase current = 11.5A, Line current = 6.64A
Phase current = 6.64A, Line current = 6.64A
Phase current = 6.64A, Line current = 11.5A
Identify from the diagram the type of motor and a typical application.
DC Series Motor; used in cranes
DC Shunt Motor; used in fans
Induction Motor; used in washing machines
Synchronous Motor; used in clocks
What are the benefits of a DC series motor?
High starting torque
Low starting torque
Constant speed
Low efficiency
Explain how the capacitor start split phase effect is achieved in an induction start single-phase motor.
By using a capacitor in series with the start winding
By using a capacitor in series with the run winding
By using a capacitor in parallel with the start winding
By using a capacitor in parallel with the run winding
What type of motor would be used in a 230V Vacuum Cleaner, and how could the direction of rotation be reversed?
Universal Motor; by reversing the field winding or armature connections
DC Motor; by changing the armature connections
Induction Motor; by changing the rotor connections
Synchronous Motor; by changing the stator connections
A three-phase motor self-starts by using a rotating magnetic field. How many degrees is each magnetic field separated?
90
180
120
60
A 32 A type B RCBO to BS EN 61009 is to be used to protect a circuit. Which mechanism of the device operates under an earth fault of 60 mA?
Thermal mechanism
Magnetic mechanism
Residual current mechanism
Overload mechanism
For the below types of MCB, which type would be required for resistive loads?
Type B
Type C
Type D
Type K
Explain how light is produced in a low pressure mercury vapour lamp.
By heating a filament until it glows.
By exciting mercury atoms to emit ultraviolet light, which then excites a phosphor coating to emit visible light.
By passing electricity through a gas to produce light directly.
By using a chemical reaction to produce light.
Explain the term efficacy.
Power input to power output
Power input to light output
Light input to power output
light input to light output
Give an example of a low efficacy rated lamp.
LED lamp
Incandescent lamp
Fluorescent lamp
Halogen lamp
Give the 3 different principles of providing heat.
Conduction, convection, radiation
Reflection, refraction, absorption
Induction, insulation, illumination
Compression, expansion, vibration
Briefly describe the principle operating procedure of an immersion heater.
It uses a chemical reaction to produce heat.
It uses a coil to generate heat through electrical resistance.
It uses solar energy to heat water.
It uses a fan to circulate warm air.
