Topic 8 - Maintenance Of Electrical Services

Question 1

What are electrical protective device and how do they operate?

Answer 1

Protective devices are equipment applied to electric power systems to detect abnormal and intolerable conditions and to initiate appropriate corrective actions. Example, an over current protection operates when there is excess current passing through it

Question 2

3 types of situations when excess current occurs

Answer 2

1. Overload
2. Earth fault current
3. Short circuit current

Question 3

Describe overloading

Answer 3

A current exceeds the design of the protective device
e.g. multi adaptors used in sockets, unauthorized extending of existing circuit, incorrect selection of circuit breakers

Question 4

Describe earth fault current

Answer 4

Occurs when live conductor comes into contact with metalwork
e.g. insulation failure, bad workmanship allowing conductor to come in contact with earth

Question 5

Describe short circuit current

Answer 5

Occurs when live conductor comes into contact with neutral conductor
e.g. insulation failure due to age, mechanical damage, bad workmanship during installation

Question 6

What does static plant contain?

Answer 6

1. Transformers
2. Capacitors
3. Rectifiers

Question 7

How to maintain static plant?

Answer 7

Ensure naturally or mechanically cooled transformers are cleaned and free of obstruction. Check temperature of cooling oil.