Week 2

Question 1

How much is the starting current for motors?
How to reduce it? And to what?

Answer 1

7.5 times In
Using star-delta starter , reduce it to 4 times In

Question 2

The use of power factor correction

Answer 2

To reduce the current supplied without affecting the power output, by adding shunt connected capacitors to reduce the apparent power (kVA) so the input current will be reduced after without changing the voltage

Question 3

Most electrical appliances and equipment are marked to indicate their?

Answer 3

Nominal power rating Pn

Question 4

What is the installed power?

Answer 4

It is the sum of the nominal powers of all the power consuming devices in the installation (not the power to be supplied in practice)

Question 5

Ku
Name:
Definition:
Applied to:
How to calculate:

Answer 5

Maximum utilization factor

The estimation of the realistic values of power rating under normal operating conditions cuz it’s usually less than indicated

Applied to each individual load

Ku= maximum demand / Installed capacity

Question 6

Ku for:
Motors
Incandescent lightning loads
Socket outlets

Answer 6

Motors = 0.75
Incandescent lightning loads = 1
Socket outlets = depends on the type of appliances being supplied from it

Question 7

Ks
Name:
Definition:
Applied to:
How to calculate:

Answer 7

Diversity factor

Estimating the diversity of the operation of all installed loads of an installation cuz they don’t usually operate simultaneously (at the same time)

Applied to each group of loads

Ks= sum of individual maximum demand of loads / maximum demand of the entire system

Question 8

What are the considerations to be taken for deciding the suitable rating of a transformer? (4)

Answer 8

1- the possibility of improving the power factor of the installation

2- anticipated extensions to the installation

3- installation constrains (like temperature مثلاً )

4- standard transformer rating