Assessing the power loading of a switchboard with help of diversity and utilization factor

1. BASIC CONSIDERATION FOR POWER LOADING OF AN
ELECTRICAL SWITCHBOARD
While assessing the load on a power system simple
arithmetic sum of each individual load is not a correct
approach of evaluation. Two (2) factors namely:
Diversity i.e. non simultaneous operation of load
equipments
and
Utilization i.e. operation of a load equipment beyond
its full load capability
must be considered so that a global value to a
system can be specified. Let us consider the above
said factors in more detail.

2. FACTOR OF UTILIZATION (KU)
Under normal operation it is the percentage
loading individual equipment is subjected to.
For
motors used in industry ku = 0.75 on an
average.
Likewise for light (incandescent type) ku = 1 on
an average.

3. DIVERSITY FACTOR (KS):
 It is the ratio of the sum of the individual non-
coincident maximum loads of various subdivisions
of the system to the maximum demand of the
complete system.
 But, it is obvious that all loads connected to a
system will not peak simultaneously at a given
point of time. IEC-60050 introduces the uses the
concept of reciprocal of the diversity factor and
terms it as coincidence factor. Coincidence factor
(1/ks) also sometimes referred as Simultaneity
factor is thus the ratio of maximum demand on the
complete system over a period of time to individual
non-coincident maximum loads of various
subdivisions of the system.

4. COINCIDENCE FACTOR (1/KS)
 So whereas Diversity factor (ks) is always
greater than 1 the Coincidence factor (1/ks) is
always less than 1.
 IEC 61439 - 2 uses the concept factor (1/ks) for
distribution switchboards. It states that when
there is no agreement between manufacturer
and user regarding the actual load current, the
assumed loading of the outgoing circuits of the
assembly or the group of outgoing circuits shall
follow table 101 which is reproduced here:

5. TABLE-101
Number of Distribution
Circuits
Assumed Coincidence
factor (1/ks)
2 – 3 0.9
4 – 5 0.8
6 - 9 0.7
>10 0.6
Motors <100 KW 0.8
Motors >100 KW 1
Lights 1

6. IN EXAMPLE OF APPLICATION OF
FACTORS KU AND KS, THE TOTAL
INSTALLED APPARENT POWER IS 45
KVA, WHICH CORRESPONDS TO AN
ACTUAL (ESTIMATED) MAXIMUM VALUE
AT THE LV TERMINALS OF THE MAIN
DISTRIBUTION BOARD OF 18.9 KVA
ONLY.

7. Load
Description
Installed
Apparent
Power
(KVA)
Utilization
Factor
Apparent
max
Demand
(KVA)
Diversity
factor of
Sub
Distribution
Boards
Apparent
Power
Demand
(KVA)
Diversity
factor of
Main
distribution
Board
Actual
Max
Demand
(KVA)
Motor-1 5 0.8 4
0.75
0.9
Motor-2 5 0.8 4
Motor-3 5 0.8 4 14.4
Motor-4 5 0.8 4
Motor-5 2 0.8 1.6
Motor-6 2 0.8 1.6 18.9
Sockets 18 1 18 0.2 3.6
Lights 3 1 3 1 3
Total
installed
capacity
(KVA)
45