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Demand Factor-Diversity Factor-Utilization Factor-LoadFactor

(1) Demand factorDemand Factor = Maximum demand of a system / Total connected load on the system

Demand factor is always less than one.

Example: if a residence having 6000W equipment connected has a maximum demand of300W,Than demand factor = 6000W / 3300W = 55%.

The lower the demand factor, the less system capacity required to serve the connectedload.

Feeder-circuit conductors should have an ampere sufficient to carry the load; the ampere ofthe feeder-circuit need not always be equal to the total of all loads on all branch-circuitsconnected to it.Remember that the demand factor permits a feeder-circuit ampere to be less than 100% of thesum of all branch-circuit loads connected to the feeder.

Example: One Machine Shop hasFluorescent fixtures=1 No, 5kw each, Receptacle outlets =1 No, 1500w each.Lathe=1No, 10 Hp, Air Compressor=1 No, 20 Hp, Fire Pump=1 No, 15 Hp.

After questioning the customer about the various loads, the information is further deciphered asfollows:

1. The shop lights are on only during the hours of 8 a.m. to 5 p.m.

2. The receptacle outlets are in the office only, and will have computers and other smallloads plugged into them.

3. The lathe is fully loaded for 5 minutes periods. The rest of the time is setup time. Thisprocedure repeats every 15 minutes.

4. The air compressor supplies air to air tools and cycles off and on about half the time.

5. The fire pump only runs for 30 minutes when tested which is once a month after hours.

Calculation:

Lighting Demand Factor = Demand Interval Factor x Diversity Factor.

= (15 minute run time/ 15 minutes) x 1.0 = 1.0

Lighting Demand Load = 5 kW x 1.0 = 5 kW

Receptacle Outlet Demand Factor = Demand Interval Factor x Diversity Factor

= (15 minute run time / 15 minutes) x 0.1 = 0.1
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Receptacle Outlet Demand Load = 15 x 1500 watts x 0.1 = 2.25 kW

Lathe Demand Factor = Demand Interval Factor x Diversity Factor.

= (5 minute run time / 15 minutes) x 1.0 =0 .33

Lathe Demand Load = 10 hp x .746 x .33 = 2.46 kW

Air Compressor Demand Factor = Demand Interval Factor x Diversity Factor.

= (7.5 minute run time / 15 minutes) x 1.0 = 0.5

Air Compressor Demand Load = 20 hp x .746 x .5 = 7.46 kW

Fire Pump Demand Factor = Demand Interval Factor x Diversity Factor.

= (15 minute run time/ 15 minutes) x 0.0 = 0.0

Fire Pump Demand Load = 15 hp x .746 x 0.0 = 0.0 kW

Summary of Demand Loads :

Equipment kW D.F. Demand KW

Lighting 5 1 5

Receptacle Outlets 22.5 .1 2.25

Lathe 7.5 .33 2.46

Air Compressor 15 0.5 7.46

Fire Pump 11.25 0.0 0.0

TOTAL 61.25 Kw 17.17 Kw

(2) Diversity factor / simultaneity factor (Ks)

Diversity Factor = Sum of Individual Max. Demand. / Max. Demand on Power Station.

Diversity Factor = Installed load. / Running load.

Diversity factor is usually more than one.(Since the sum of individual max. demands>Max. Demand)

The load is time dependent as well as being dependent upon equipment characteristics. Thediversity factor recognizes that the whole load does not equal the sum of its parts due to this timeInterdependence (i.e. diverseness).


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When the maximum demand of a supply is being assessed it is not sufficient to simply addtogether the ratings of all electrical equipment that could be connected to that supply. If this isdone, a figure somewhat higher than the true maximum demand will be produced. This isbecause it is unlikely that all the electrical equipment on a supply will be used simultaneously.

The concept of being able to De-rate a potential maximum load to an actual maximum demandis known as the application of a diversity factor.

70% diversity means that the device in question operates at its nominal or maximum load level

70% of the time that it is connected and turned on.

If total installed full load ampere is twice your running load ampere then the diversity factor istwo.

If total installed full load ampere is four times your load a ampere then the diversity factor isfour.

If everything (all electrical equipment) was running at full load at the same time the diversityfactor is equal to One

Greater the diversity factor, lesser is the cost of generation of power.

Diversity factor in a distribution network is the ratio of the sum of the peak demands of theindividual customers to the peak demand of the network.

This will be determined by the type of service, i.e., residential, commercial, industrial andcombinations of such.

Example-I: A distribution feeder serves 5 houses, each of which has a peak demand of 5 KWThe feeder peak turns out to be 20 kw. The diversity is then 20/25 or 0.8. This results from thetiming differences between the individual heating/cooling, appliance usages in the individualcustomers.

As supply availability decreases, the diversity factor will tend to increase toward 1.00. This can

be demonstrated when restoring service after outages (called cold starts) as the system initialsurge can be much greater than the historical peak loads.

Example-II: A sub-station has three outgoing feeders:

1. feeder 1 has maximum demand 10 MW at 10:00 am,

2. feeder 2 has maximum demand 12 MW at 7:00 pm and

3. feeder 3 has maximum demand 15 MW at 9:00 pm,

4. While the maximum demand of all three feeders is 33 MW at 8:00 pm.

Here, the sum of the maximum demand of the individual sub-systems (feeders) is 10 + 12 + 15= 37 MW, while the system maximum demand is 33 MW. The diversity factor is 37/33 = 1.12. Thediversity factor is usually greater than 1; its value also can be 1 which indicates the maximumdemand of the individual sub-system occurs simultaneously.

Diversity is the relationship between the rated full loads of the equipment downstream of aconnection point, and the rated load of the connection point. To illustrate:

1. The building at these co-ordinates is fitted with a 100A main supply fuse.

2. The distribution board has 2no. 6A breakers, 1no. 20A breaker and 5no. 32A breakers, a total,


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potentially, of 192A.

Not all these rated loads are turned on at once. If they were, then the 100A supply fuse wouldrupture, as it cannot pass 192A. So the diversity factor of the distribution board can be said to be192A/100A, or1.92, or 52%.

Many designers prefer to use unity as the diversity factor in calculations for planningconservatism because of plant load growth uncertainties. Local experience can justify using adiversity factor larger than unity, and smaller service entrance conductors and transformer

requirements chosen accordingly.

The diversity factor for all other installations will be different, and would be based upon a localevaluation of the loads to be applied at different moments in time. Assuming it to be 1.0 may, onsome occasions, result in a supply feeder and equipment rating that is rather larger than the localinstallation warrants, and an over-investment in cable and equipment to handle the rated loadcurrent. It is better to evaluate the pattern of usage of the loads and calculate an acceptablediversity factor for each particular case.

In the case of the example given above, achieving a diversity of 1.0 or 100% would require wellover twice the cross-sectional area of copper cable to be installed in a deep trench underneath afield, the rebuild of a feeder cabinet to larger dimensions, more substantial overhead supplycables for a distance exceeding 2km northwards and a different tariff, where one pays rathermore for a kWh than at present. The investment required to achieve 1.0 simply isnt justifiable inthis particular case.

Diversity factor is mostly used for distribution feeder size and transformer as well as todetermine the maximum peak load and diversity factor is always based on knowing the process.You have to understand what will be on or off at a given time for different buildings and this willsize the feeder. Note for typical buildings diversity factor is always one. You have to estimate orhave a data records to create 24 hours load graph and you can determine the maximum demandload for node then you can easily determine the feeder and transformer size.

The diversity factor of a feeder would be the sum of the maximum demands of the individualconsumers divided by the maximum demand of the feeder. In the same manner, it is possible tocompute the diversity factor on a substation, a transmission line or a whole utility system.

The residential load has the highest diversity factor. Industrial loads have low diversity factorsusually of 1.4, street light practically unity and other loads vary between these limits.

Diversity Factor in distribution Network

Elements of System Diversity Factors

Residential Commercial GeneralPower

LargeIndustrial

Between individual users 2.00 1.46 1.45

Between transformers 1.30 1.30 1.35 1.05


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Between feeders 1.15 1.15 1.15 1.05

Between substations 1.10 1.10 1.10 1.10

From users to transformers 2.00 1.46 1.44

From users to feeder 2.60 1.90 1.95 1.15

From users to substation 3.00 2.18 2.24 1.32

From users to generatingstation

3.29 2.40 2.46 1.45

Diversity Factor for distribution switchboards

Number of circuits Diversity Factor (ks)

Assemblies entirely tested 2 and 3 0.9

4 and 5 0.8

6 to 9 0.7

10 and more 0.6

Assemblies partially tested in every case choose 1

Diversity Factor for according to circuit function (IEC 60439)

Circuits Function Diversity Factor (ks)

Lighting 0.9

Heating and air conditioning 0.8

Socket-outlets 0.7


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Lifts and catering hoist

For the most powerful motor 1

For the second most powerful motor 0.75

For all motors 0.8

Diversity Factor for an apartment block

Apartment Diversity Factor (ks)

2 To 4 1

5To 19 0.78

10To 14 0.63

15To 19 0.53

20To 24 0.49

25To 29 0.46

30 To 34 0.44

35 To 39 0.42

40To 40 0.41

50 To Above 0.40

Example: 5 storey apartment building with 25 consumers, each having 6 kVA of installed load.The total installed load for the building is: 36 + 24 + 30 + 36 + 24 = 150 kVAThe apparent-power supply required for the building is: 150 x 0.46 = 69 kVA

It is a matter of common experience that the simultaneous operation of all installed loads of agiven installation never occurs in practice, i.e. there is always some degree of diversity and this


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fact is taken into account for estimating purposes by the use of a simultaneity factor / DiversityFactor (ks).

The Diversity factor ks is applied to each group of loads (e.g. being supplied from a distributionor sub-distribution board). The determination of these factors is the responsibility of the designersince it requires a detailed knowledge of the installation and the conditions in which the individuacircuits are to be exploited. For this reason, it is not possible to give precise values for generalapplication.

Designing Size of Electrical Switchgear by use of Demand Factor and Diversity Factor:

Diversity factors are used by utilities for distribution transformer sizing and load predictions.

Demand factors are more conservative and are used by NEC for service and feeder sizing.

Demand factors and diversity factors are used in design.

For example, the sum of the connected loads supplied by a feeder is multiplied by the demandfactor to determine the load for which the feeder must be sized. This load is termed the maximumdemand of the feeder. The sum of the maximum demand loads for a number of sub feedersdivided by the diversity factor for the sub feeders will give the maximum demand load to besupplied by the feeder from which the sub feeders are derived.

Example-1: Suppose We have four individual feeder-circuits with connected loads of 250kVA, 200 kVA, 150 kVA and 400 kVA and demand factors of 90%, 80%, 75% and 85%respectively.Use a diversity factor of 1.5.

Calculating demand for feeder-circuits

250 kVA x 90% = 225 kVA

200 kVA x 80% = 160 kVA

150 kVA x 75% = 112.5 kVA400 kVA x 85% = 340 kVA

837.5 kVA

The sum of the individual demands is equal to 837.5 kVA.

If the main feeder-circuit were sized at unity diversity: kVA = 837.5 kVA 1.00 = 837.5kVA.

The main feeder-circuit would have to be supplied by an 850 kVA transformer.

However, using the diversity factor of 1.5, the kVA = 837.5 kVA 1.5 = 558 kVA for themain feeder.

For diversity factor of 1.5, a 600 kVA transformer could be used.

Example-2: A conveyor belt made up of six sections, each driven by a 2 kW motor. Asmaterial is transported along this belt, it is first carried by section 1, and then each sectionin succession until the final section is reached. In this simple example only one section ofconveyor is carrying material at any point in time. Therefore five motors are only handlingno-load mechanical losses (say .1 kW) keeping the belts moving whilst one motor ishandling the load (say 1 kW). The demand presented by each motor when it is carrying itsload is 1 kW, the sum of the demand loads is 6 kW but the maximum load presented by the


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system at any time is only 1.5 kW.

Diversity factor =Sum of Individual Max. Demand / Max. Demand = 6 Kw / 1.5 Kw =4.

Demand Factor = Maximum demand / Total connected load = 1.5 Kw / 12 Kw = 0.125.

(3) Load factor

Load Factor = Average load. /Maximum load during a given period.

It can be calculated for a single day, for a month or for a year.

Its value is always less than one. Because maximum demand is always more than avg.demand.

It is used for determining the overall cost per unit generated. Higher the load factor,lesser will be the cost per unit.

Load Factor = Load that a piece of equipment actually draws / Load it could draw (full load).

Example: Motor of 20 hp drives a constant 15 hp load whenever it is on.

The motor load factor is then 15/20 = 75%.

Load factor is term that does not appear on your utility bill, but does affect electricity costs.Load factor indicates how efficiently the customer is using peak demand.

Load Factor= ( energy (kWh per month) ) / ( peak demand (kW) x hours/month )

A high load factor means power usage is relatively constant. Low load factor shows thatoccasionally a high demand is set. To service that peak, capacity is sitting idle for long periods,thereby imposing higher costs on the system. Electrical rates are designed so that customerswith high load factor are charged less overall per kWh.

For Example

Customer A High Load Factor

82% load factor = (3000 kWh per month x 100%) / 5 kW x 730 hours/month.

Customer B Low Load Factor

41% load factor = (3000 kWh per month x 100%) / 10kW x 730 hours/month.

To encourage the efficient use of installed capacity, electricity rates are structured so the priceper kWh above a certain load factor is lower. The actual structure of the price blocks varies by

rate.

(4) Utilization factor (Ku)

In normal operating conditions the power consumption of a load is sometimes less than thatindicated as its nominal power rating, a fairly common occurrence that justifies the application ofan utilization factor (ku) in the estimation of realistic values.

Utilization Factor = The time that a equipment is in use./ The total time that it could bein use.


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Example: The motor may only be used for eight hours a day, 50 weeks a year. The hours ofoperation would then be 2000 hours, and the motor Utilization factor for a base of 8760 hoursper year would be 2000/8760 = 22.83%. With a base of 2000 hours per year, the motorUtilization factor would be 100%. The bottom line is that the use factor is applied to get thecorrect number of hours that the motor is in use.

This factor must be applied to each individual load, with particular attention to electric motors,which are very rarely operated at full load. In an industrial installation this factor may be estimatedon an average at 0.75 for motors.

For incandescent-lighting loads, the factor always equals 1.

For socket-outlet circuits, the factors depend entirely on the type of appliances being suppliedfrom the sockets concerned.

Maximum demand

Maximum demand (often referred to as MD) is the largest current normally carried by circuits,switches and protective devices. It does not include the levels of current flowing under overload orshort circuit conditions.

Assessment of maximum demand is sometimes straightforward. For example, the maximumdemand of a 240 V single-phase 8 kW shower heater can be calculated by dividing the power (8kW) by the voltage (240 V) to give a current of 33.3 A. This calculation assumes a power factor ofunity, which is a reasonable assumption for such a purely resistive load.

There are times, however, when assessment of maximum demand is less obvious. Forexample, if a ring circuit feeds fifteen 13 A sockets, the maximum demand clearly should not be15 x 13 = 195 A, if only because the circuit protection will not be rated at more than 32 A. Some13 A sockets may feed table lamps with 60 W lamps fitted, whilst others may feed 3 kW washingmachines; others again may not be loaded at all.

Lighting circuits pose a special problem when determining MD. Each lamp-holder must beassumed to carry the current required by the connected load, subject to a minimum loading of100 W per lamp holder (a demand of 0.42 A per lamp holder at 240 V). Discharge lamps areparticularly difficult to assess, and current cannot be calculated simply by dividing lamp power bysupply voltage. The reasons for this are:

1. Control gear losses result in additional current,

2. the power factor is usually less than unity so current is greater, and

3. Chokes and other control gear usually distort the waveform of the current so that it contains

harmonics which are additional to the fundamental supply current.

So long as the power factor of a discharge lighting circuit is not less than 0.85, the currentdemand for the circuit can be calculated from:

current (A) = (lamp power (W) x 1.8) / supply voltage (V)

For example, the steady state current demand of a 240 V circuit supplying ten 65 W fluorescentlamps would be: I = 10X65X1.8A / 240 = 4.88A

Switches for circuits feeding discharge lamps must be rated at twice the current they arerequired to carry, unless they have been specially constructed to withstand the severe arcingresulting from the switching of such inductive and capacitive loads.


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(5) Coincidence factor

The coincidence factor =Max. demand of a system / sum of the individual maximumdemands

The coincidence factor is the reciprocal of the diversity factor

Demand Factor & Load Factor according to Type of Industries

Type of Industry DemandFactor

LoadFactor

UtilizationFactor (DF x LF)

Arc Furnace 0.55 0.80 0.44

Induction Furnace 0.90 0.80 0.72

Steel Rolling mills 0.80 0.25 0.20

Mechanical/ Electrical

a) Single Shift 0.45 0.25 0.11

b) Double Shift 0.45 0.50 0.22

Cycle Industry 0.40 0.40 0.16

Wire products 0.35 0.40 0.14

Auto Parts 0.40 0.50 0.20

Forgings 0.50 0.35 0.17

Cold Storage

a) Working Season 0.60 0.65 0.39

b) Non-Working Season 0.25 0.15 0.04


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Rice Shellers


b) Non-WorkingSeason

0.05 0.30 0.01

Ice Candy Units



Ice Factories



Cotton Ginning



Spinning Mills 0.60 0.80 0.48

Textile Industry 0.50 0.80 0.40

Dyeing and Printing 0.40 0.50 0.20

Ghee Mills 0.50 0.50 0.25

Oil Mills 0.70 0.50 0.35

Solvent Extraction Mills 0.45 0.50 0.22

Plastic 0.60 0.25 0.11


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Soap 0.50 0.25 0.12

Rubber (Foot Wear) 0.45 0.35 0.16

Distilleries 0.35 0.50 0.17

Chemical Industry 0.40 0.50 0.20

Gas Plant Industry 0.70 0.50 0.35

Pain and Colour Factory 0.50 0.40 0.20

Sugar 0.30 0.45 0.13

Paper 0.50 0.80 0.40

Flour Mills(Single Shift) 0.80 0.25 0.20

Atta Chakies 0.50 0.25 0.12

Milk Plants 0.40 0.80 0.32

Printing Presses 0.35 0.30 0.10

Repair Workshops 0.40 0.25 0.10

Bottling Plants 0.40 0.35 0.14

Radio Stations 0.55 .0.45 0.25

Telephone exchange 0.50 0.90 0.45

Public Water Works 0.75 0.40 0.30

Medical Colleges 0.60 0.25 0.15


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Hospitals 0.25 0.90 0.22

Nursing Homes 0.50 0.50 0.25

Colleges and Schools 0.50 0.20 0.10

Hotels and Restaurants 0.75 0.40 0.30

Marriage Palaces 1.00 0.25 0.25

Demand Factor & Load Factor according to Type ofBuildings:

Individual Facilities DemandFactor

LoadFactor

Communications buildings 60-65 70-75

Telephone exchange building 55-70 20-25

Air passenger terminal building 65-80 28-32

Aircraft fire and rescue station 25-35 13-17

Aircraft line operations building 65-80 24-28

Academic instruction building 40-60 22-26

Applied instruction building 35-65 24-28

Chemistry and ToxicologyLaboratory

70-80 22-28

Materials Laboratory 30-35 27-32

Physics Laboratory 70-80 22-28


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Electrical and electronics systemslaboratory

20-30 3-7

Cold storage warehouse 70-75 20-25

General warehouse 75-80 23-28

Controlled humidity warehouse 60-65 33-38

Hazardous/flammable storehouse 75-80 20-25

Disposal, salvage, scrap building 35-40 25-20

Hospital 38-42 45-50

Laboratory 32-37 20-25

Dental Clinic 35-40 18-23

Medical Clinic 45-50 20-23

Administrative Office 50-65 20-35

Single-family residential housing 60-70 10-15

Detached garages 40-50 2-4

Apartments 35-40 38-42

Fire station 25-35 13-17

Police station 48-53 20-25

Bakery 30-35 45-60

Laundry/dry cleaning plant 30-35 20-25

K-6 schools 75-80 10-15


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7-12 schools 65-70 12-17

Churches 65-70 5-25

Post Office 75-80 20-25

Retail store 65-70 25-32

Bank 75-80 20-25

Supermarket 55-60 25-30

Restaurant 45-75 15-25

Auto repair shop 40-60 15-20

Hobby shop, art/crafts 30-40 25-30

Bowling alley 70-75 10-15

Gymnasium 70-75 20-45

Skating rink 70-75 10-15

Indoor swimming pool 55-60 25-50

Theater 45-55 8-13

Library 75-80 30-35

Golf clubhouse 75-80 15-20

Museum 75-80 30-35

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