ELECTRICAL ENGINEERING STUDY PACK Q&A
HIGH, MEDIUM AND LOW VOLTAGES
Explain: The power grid?
National network of transmission lines
Explain: Power station?
Place where electricity is manufactured
Why must the voltage levels on switchgear not be exceeded?
If they are, the equipment will arc – the air gap between the
contacts will be breached by a lighting spark
Why are power stations usually situated far from the
consumers?
In the case of coal power stations, they usually built near
coalmines. (This is to avoid the expense of transporting the
coal)
What are the (a) advantages (b) disadvantages in transmitting
power at high voltages?
Advantages: A saving in:
Conductor material, which is considerably large
The number of pylons used as the lighter conductor material
allows them to be placed further apart
The labour required to erect the lighter conductors
, Disadvantages:
It is more dangerous (Voltage try to escape to earth)
Transformers are required for stepping the voltage up and
down
Increase in voltage require an increase in the amount and
quality as well as the construction and shape of the insulation
What are the disadvantages of a single-phase systems as
apposed to a three phase, four wire a.c. system?
It has only one voltage
The amount of power delivered to the consumer is limited
Single-phase motors are more expensive, large and less
efficient
Why are the star point of a distribution transformer earthed?
The neutral or starpoint of a transformer is earthed and earth
leakage protection can therefore be obtained easily
What is the purpose of low and high voltage insulators?
Their function is to support the conductors on the overhead
cables and to separate the conductors from each other (Pin
type, suspension type and strain type)
Explain automatic synchronizer
The synchronizer checks the conditions and, if correct initiates
the switch closer at the correct instant
HIGH, MEDIUM AND LOW VOLTAGES
Explain: The power grid?
National network of transmission lines
Explain: Power station?
Place where electricity is manufactured
Why must the voltage levels on switchgear not be exceeded?
If they are, the equipment will arc – the air gap between the
contacts will be breached by a lighting spark
Why are power stations usually situated far from the
consumers?
In the case of coal power stations, they usually built near
coalmines. (This is to avoid the expense of transporting the
coal)
What are the (a) advantages (b) disadvantages in transmitting
power at high voltages?
Advantages: A saving in:
Conductor material, which is considerably large
The number of pylons used as the lighter conductor material
allows them to be placed further apart
The labour required to erect the lighter conductors
, Disadvantages:
It is more dangerous (Voltage try to escape to earth)
Transformers are required for stepping the voltage up and
down
Increase in voltage require an increase in the amount and
quality as well as the construction and shape of the insulation
What are the disadvantages of a single-phase systems as
apposed to a three phase, four wire a.c. system?
It has only one voltage
The amount of power delivered to the consumer is limited
Single-phase motors are more expensive, large and less
efficient
Why are the star point of a distribution transformer earthed?
The neutral or starpoint of a transformer is earthed and earth
leakage protection can therefore be obtained easily
What is the purpose of low and high voltage insulators?
Their function is to support the conductors on the overhead
cables and to separate the conductors from each other (Pin
type, suspension type and strain type)
Explain automatic synchronizer
The synchronizer checks the conditions and, if correct initiates
the switch closer at the correct instant
