Diversity Vs. Demand

Don’t Be Confused By These Terms

Published: March 2009By James G. Stallcup

There are two terms that seem to confuse designers. These terms are “diversity factor” and “demand factor.” To better understand the application of these terms when calculating the load for a service or a feeder supplying a facility, one must understand their meaning.

Diversity factor is the ratio of the sum of the individual maximum demands of the various subdivisions of a system (or part of a system) to the maximum demand of the whole system (or part of the system) under consideration. Diversity is usually more than one.

Demand factor is the ratio of the sum of the maximum demand of a system (or part of a system) to the total connected load on the system (or part of the system) under consideration. Demand factor is always less than one.

Application of diversity factor

Consider two facilities with the same maximum demand but that occur at different intervals of time. When supplied by the same feeder, the demand on such is less the sum of the two demands. In electrical design, this condition is known as diversity.

Diversity factors have been developed for main feeders supplying a number of feeders, and typically, they are 1.10 to 1.50 for lighting loads and 1.50 to 2.00 for power and lighting loads.

Diversity factor and load factor are closely related. For example, consider that a feeder supplies five users with the following load conditions: On Monday, user one reaches a maximum demand of 100 amps; on Tuesday, two reaches 95 amps; on Wednesday, three reaches 85 amps; on Thursday, four reaches 75 amps; on Friday, five reaches 65 amps. The feeder’s maximum demand is 250 amps.

The diversity factor can be determined as follows:

Diversity factor = Sum of total demands ÷ Maximum demand on feeder = 420 ÷ 250 = 1.68 × 100 = 168%

Given

Calculate the size of a main feeder from substation switchgear that is supplying five feeders with connected loads of 400, 350, 300, 250 and 200 kilovolt-amperes (kVA) with demand factors of 95, 90, 85, 80 and 75 percent respectively. Use a diversity factor of 1.5.

Solution

Calculate demand for each feeder:

400 kVA × 95% = 380 kVA •

350 kVA × 90% = 315 kVA •

300 kVA × 85% = 255 kVA •

250 kVA × 80% = 200 kVA •

200 kVA × 75% = 150 kVA •

The sum of the individual demands is equal to 1,300 kVA •

If the feeder were sized at unity diversity, then 1,300 kVA ÷ 1.00 = 1,300 kVA

However, using the diversity factor of 1.5, the kVA = 1,300 kVA ÷ 1.5 = 866 kVA for the feeder. Transformer supplying the main feeder plus wiring methods and equipment can be sized from this kilovolt-ampere rating.

Applying demand factors

Although feeder conductors should have an ampacity sufficient to carry the load, the ampacity needs not always be equal to the total of all loads on connected branch-circuits.

A study of the National Electrical Code (NEC) will show that a demand factor may be applied to the total load. Remember, the demand factor permits a feeder ampacity to be less than 100 percent of all the branch-circuit loads connected to it.

Keep in mind that demand factor is a percentage by which the total connected load on a service or feeder is multiplied to determine the greatest probable load it may be called on to carry.

When additional loads are connected to existing facilities having services and feeders as originally calculated per 220.87, the maximum kilovolt-ampere calculations in determining the load on existing services and feeders should be used if these conditions are met:

If the maximum data for the demand in kVA, such as demand meter ratings, is available for a minimum of one year •

If 125 percent of the demand ratings • for the period of one year added to the new load does not exceed the rating of the service; where demand factors are used, often the load as calculated will probably be less than the demand meter indications.

The Ex. to 220.87 contains requirements for where the maximum data for one year is not available. In such, the calculated load is permitted to be based on the maximum demand (measure of average power demand over a 15-minute period) continuously recorded over a minimum 30-day period using a recording ammeter connected to the highest loaded ungrounded (phase) of the feeder or service based on the initial loading at the start of the recording.

By referencing Parts III and IV in the NEC, designers can find other useful demand factors that are applicable to specific loads.

STALLCUP is the CEO of Grayboy Inc., which develops and authors publications for the electrical industry and specializes in classroom training on the NEC and OSHA, as well as other standards. Contact him at 817.581.2206.

Diversity Factor in Electrical Wiring Installation In a building, the whole load of Electrical Wiring installation doesn’t use at the same time. In other words, we do not use all the loads at once at home i.e., we do not Switch ON all the fans, light points, Air conditioner, TV, fridge, Water gazer, heater, Electric iron etc at once. Therefore,

keep in mind this (diversity factor) factor while selecting the proper and most suitable size of cable for electrical wiring installation. Diversity factor may e defined as:Diversity Factor = Total Connected Load / Actual Maximum LoadGood to know:

Diversity factor may neglect in case of final sub circuits. Instead of Homes and buildings, Diversity factor in electrical wiring installation may

neglect in offices or those places where all connected loads operate at once.

Example:In a flat, the max demand of load current is follow (about 85 Amp)                                                        Click image to enlarge

But with the help of using diversity factor, we found total load current about 52 A. So in this case, use 52 A (+ 20% for future load = 62.4A) instead of 90A for calculation and selection of proper size of cable for wiring.

What is load load factor and diversity factor? What is the significance and what should be its value? What is load shedding ? (For Power transmission & Distribution)

Best Answer

sabyashachi b answered 7 years ago

Load factor (electrical) is the average power divided by the peak power over a period of time.n the electricity industry, load factor is a measure of the output of a power plant compared to the maximum output it could produce.

The two commonest definitions are:

* the ratio of average load to capacity * the ratio of average load to peak load in a period.

Assuming the first definition, a higher load factor is better:

* A power plant may be less efficient at low load factors. * A high load factor means fixed costs are spread over more kWh of output. * A high load factor means greater total output.

Therefore a higher load factor usually means more output and a lower cost per unit, which means an electricity generator can sell more electricity at a higher spark spread.

Diversity factor: The ratio of sum of the individual non-coincident maximum demands of various subdivisions of the system to the maximum demand of the complete system. The diversity factor is always less than or equal to 1. The (unofficial) term diversity, as distinguished from diversity factor refers to the percent of time available that a machine, piece of equipment, or facility has its maximum or nominal load or demand (i.e., a 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).

Diversity factor is commonly used for a number of mathematics related topics. One such instance is when completing a coordination study for a system. This diversity factor is used to estimate the load of a particular node in the system.

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

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Moti answered 7 years ago

Load factor is defined as the ratio of Average load to maximum demand during a given period.It can be calculated for a single day,for a month or for an year.Its value is always less than one.B'coz maximum demand is always more than avg.demand.It is used for determining the overall cost per unit generated.Higer the load factor,lesser will be the cost per unit. Diversity factor-Ratio of sum of individual maximum demands to the maximum demand on Power station. Its value is always greater than one.(since the sum of individual max. demands >Max.Demand)Greater the diversity factor,lesser is the cost of generation of power. Load shedding means shedding/off of load during high load conditions.That is mainly during peak hours.At this time almost all consumers are using electrical power.So to reduce the usage of power,load shedding is done compulsary.

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g.c. s answered 7 years ago

Load Factor Actual output of a plant over a period of time ----------------------------------------... Output which should have been as per the full capacity of the plant over the same period of time

This is always equal to or less than 1 Diversity Factor sum of the individual maximum demand of the various divisions / subdivisions / areas of the system or plant ----------------------------------------... maximum demand of the complete system

  Diversity factor

The maximum demands of individual loads do not take place 

at the same moment The sum of individual peaks is not used 

as a measure of the maximumloaddemand The maximum 

installed power is usually less than the sum of individual 

maximum demands The diversity factor is greater than or 

equal unity The ratio of sum of individual maximum demands 

of all customers to the maximum demand for a specific 

station is known as the diversity factor

Capacity factorThe capacity factor takes into account the excess of the

installed power of station more than the actual required 

demand The excess of power is known as the reserve power, 

which takes into account the expected future expansion and 

unexpected sudden load increase The capacity factor is 

defined as the ratio of the average load supplied by a station 

to the rated

(installed) capacity of this station The capacity factor is less 

than or equal unityMultiplying the average demand and the 

rated capacity by time, the capacity factor can be defined as 

the ratio between the actual energy produced and that would be produced if the plant were operated at its full capacity

capacity factor = Annual energy(kWh)/rated capacity*no. of operating hours

stimation of actual maximum kVA demandGeneral rules of electrical installation design

Electrical installation design methodology Electrical installation rules, standards

o Definition of voltage ranges o Electrical regulations and standards o Quality and safety of an electrical installation o Environmental directives

Installed power loads - Characteristics o Induction motors o Resistive-type heating appliances and incandescent lamps (conventional or halogen) o Fluorescent lamps o Discharge lamps o LED lamps & fixtures

Power loading of an installation o Installed power (kW) o Installed apparent power (kVA) o Estimation of actual maximum kVA demand o Example of application of factors ku and ks o Choice of transformer rating o Choice of power-supply sources

Connection to the MV utility distribution network

Connection to the LV utility distribution network

MV and LV architecture selection guide

LV Distribution

Protection against electric shocks

Sizing and protection of conductors

LV switchgear: functions and selection

Overvoltage protection

Energy Efficiency in electrical distribution

Power Factor Correction

Power harmonics management

Characteristics of particular sources and loads

PhotoVoltaic (PV) installation

Residential and other special locations

ElectroMagnetic Compatibility (EMC)

Contents

1 - Factor of maximum utilization (ku) 2 - Diversity factor - Coincidence factor (ks) 3 - Diversity factor for an apartment block 4 - Rated Diversity Factor for distribution switchboards 5 - Diversity factor according to circuit function

All individual loads are not necessarily operating at full rated nominal power nor necessarily at the same time. Factors ku and ks allow the determination of the maximum power and apparent-power demands actually required to dimension the installation.

Factor of maximum utilization (ku)

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

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 estimated on 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 supplied from the sockets concerned.

For Electric Vehicle the utilization factor will be systematically estimated to 1, as it takes a long time to load completely the batteries (several hours) and a dedicated circuit feeding the charging station or wall box will be required by standards.

Diversity factor - Coincidence factor (ks)

The determination of ks factors is the responsibility of the designer, since it requires a detailed knowledge of the installation and the conditions in which the individual circuits are to be exploited. For this reason, it is not possible to give precise values for general application.

It is a matter of common experience that the simultaneous operation of all installed loads of a given installation never occurs in practice, i.e. there is always some degree of diversity and this fact is taken into account for estimating purposes by the use of a factor (ks).

This factor is defined in IEC60050 - International Electrotechnical Vocabulary,as follows:

Coincidence factor: the ratio, expressed as a numerical value or as a percentage, of the simultaneous maximum demand of a group of electrical appliances or consumers within a specified period, to the sum of their individual maximum demands within the same period. As per this definition, the value is always 1 and can be expressed as a percentage

Diversity factor: the reciprocal of the coincidence factor. It means it will always be 1.

Note: In practice, the most commonly used term is the diversity factor, but it is used in replacement of the coincidence factor, thus will be always <= 1. The term "simultaneity factor" is another alternative that is sometimes used.

The factor ks is applied to each group of loads (e.g. being supplied from a distribution or sub-distribution board).

The following tables are coming from local standards or guides, not from international standards. They should only be used as examples of determination of such factors.

Diversity factor for an apartment block

Some typical values for this case are given in Figure A10, and are applicable to domestic consumers without electrical heating, and supplied at 230/400 V (3-phase 4-wires). In the case of

consumers using electrical heat-storage units for space heating, a factor of 0.8 is recommended, regardless of the number of consumers.

Number of downstream consumers Diversity factor (ks)

2 to 4 1

5 to 9 0.78

10 to 14 0.63

15 to 19 0.53

20 to 24 0.49

25 to 29 0.46

30 to 34 0.44

35 to 39 0.42

40 to 49 0.41

50 and more 0.38

Fig. A10: Example of diversity factors for an apartment block as defined in French standard NFC14-100, and applicable for apartments without electrical heating

Example (see Fig. A11):

5 storeys 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 kVAFrom Figure A10, it is possible to determine the magnitude of currents in different sections of the common main feeder supplying all floors. For vertical rising mains fed at ground level, the cross-sectional area of the conductors can evidently be progressively reduced from the lower floors towards the upper floors.These changes of conductor size are conventionally spaced by at least 3-floor intervals.In the example, the current entering the rising main at ground level is:

the current entering the third floor is:

Fig. A11: Application of the diversity factor (ks) to an apartment block of 5 storeys

Rated Diversity Factor for distribution switchboards

The standards IEC61439-1 and 2 define in a similar way the Rated Diversity Factor for distribution switchboards (in this case, always 1) IEC61439-2 also states that, in the absence of

an agreement between the assembly manufacturer (panel builder) and user concerning the actual load currents (diversity factors), the assumed loading of the outgoing circuits of the assembly or group of outgoing circuits may be based on the values in Fig. A12.

If the circuits are mainly for lighting loads, it is prudent to adopt ks values close to unity.

Type of load Assumed loading factor

Distribution - 2 and 3 circuits 0.9

Distribution - 4 and 5 circuits 0.8

Distribution - 6 to 9 circuits 0.7

Distribution - 10 or more circuits 0.6

Electric actuator 0.2

Motors 100 kW 0.8

Motors > 100 kW 1.0

Fig. A12: Rated diversity factor for distribution boards (cf IEC61439-2 table 101)

Diversity factor according to circuit function

ks factors which may be used for circuits supplying commonly-occurring loads, are shown in Figure A13. It is provided in French practical guide UTE C 15-105.

Circuit function Diversity factor (ks)

Lighting 1

Heating and air conditioning 1

Socket-outlets 0.1 to 0.2 (1)

Lifts and catering hoist (2) For the most powerful motor For the second most powerful motor For all motors

10.750.60

(1) In certain cases, notably in industrial installations, this factor can be higher.(2) The current to take into consideration is equal to the nominal current of the motor, increased by a third of its starting current.

Fig. A13: Diversity factor according to circuit function (see UTE C 15-105 table AC)