4.4a Single and Three Phase

What is the UK phase voltage?

Answer explanation

The UK phase voltage is now 230V although previously it was 240V so both answers would be allowed in the exam.

What is the frequency of the AC supplied to households in the UK?

What is the line voltage in the UK?

In 3 phase power how far apart is each phase?

• 90 degrees

• 120 degrees

• 180 degrees

• 270 degrees

Which of the following are advantages of 3 phase power as apposed to single phase?

• Cheaper installation as less copper needed for same power transmission

• 2 voltages are available, a line and a phase voltage

• 3 voltages are available, a line, phase and live voltage

• Almost constant power delivery as opposed to pulsating power in single phase can eg reduce vibration in motors

• The voltage is faster in a 3 phase system due to the power transmission

Which of the following are advantages of single phase as opposed to 3 phase power?

• Simple installation

• Single phase devices are simpler and cheaper than 3 phase

• Single phase devices are more powerful that 3 phase

• Almost constant power delivery as opposed to pulsating power can eg reduce vibration in motors

• Pulsating of power means for a more reliable power transmission.

Which of these are the UK convention for delivery of a 3 phase supply?

• Delta formation

• Star formation

• 4 wire

• 3 wire

• 120 degree phase shift

How many voltages are available from a 3 phase Delta configuration?

• 3 phase voltages

• 3 line voltages

• 3 phase and 3 line voltages

• 3 live voltages

How many voltages are available from a 3 phase Star configuration?

• 3 phase voltages

• 3 line voltages

• 3 phase and 3 line voltages

• 3 live voltages

If the neutral line is black in a 3 phase system which colours are the live wires?

• red

• green

• yellow

• blue

• brown

Answer explanation

The new colours for the UK are blue neutral and brown, black and grey for the 3 live. If you want a distinction you should know this.