6 Customer Requirements For a Generator Regarding Power Demand

Power Demand //

To select an on-site engine/generator sets (gensets), you’ll need to determine the power demand requirements which must be met under operating conditions, of course.

Let’s talk about six recognized customer genset requirements regarding power demand //

6 Customer Requirements For a Generator Regarding Power Demand
6 Customer Requirements For a Generator Regarding Power Demand (on photo: Three new Caterpillar 2.38MVA 3 Phase Generators and associated equipment; credit:
  1. On Site Power Requirement
  2. Load Management
  3. Loads Profiles
  4. Estimating Load Data
  5. Categorizing Loads and
  6. VA/FT2 Load Estimating

1. On Site Power Requirement

Before selecting an engine model and rating, a load analysis needs to be performed. This section will consider the factors which affect generator sizing including load management needs, voltage and frequency dip limitations, motor starting considerations, start-up needs and all required standards.

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2. Load Management

Load management is the deliberate control of loads on a genset and/or utility to have the lowest possible electrical costs.

Assessing the customer’s load profiles is a key component to establishing their load management profile and ultimately the size of genset needed to operate within that profile.

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3. Loads Profiles

The duration and nature of a load must be established to select and operate a genset system at maximum efficiency. To analyze a load, a family of load profile charts is necessary. Chronological and duration load profiles best serve this purpose.

NOTE // Unless the load is known to be steady, this average cannot be used to establish the engine and generator requirements because the average will always be lower than the maximum kW power demand.

The purpose of the monthly average number is to be able to graph a complete year and determine any seasonal variations. A daily chronological load curve, illustrated in Figure 1, shows load power demand throughout the day. A chronological curve establishes the peak daily power demand and an energy usage profile which can aid in the selection of an appropriately sized engine.

This load curve is also useful in programming units for economical operation.

Daily chronological load curve
Figure 1 – Daily chronological load curve

Daily typical peaks for various industries can be graphed based on typical loads as shown in Figure 2 below.

Daily typical peaks for various industries
Figure 2 – Daily typical peaks for various industries

Duration curves, as shown in Figure 3, rearrange chronological curves and summarize daily load.

Duration curves
Figure 3 – Duration curves

Such curves are developed for a week, month, season or year. The daily chart represents the average kilowatt load for each day, while the twelve-month chart, shown in Figure 4 below, represents the average kilowatt load for each month.

Average kilowatt load for each month
Figure 4 – Average kilowatt load for each month

For existing loads that are served by a utility, power bills or power consumption records will provide the needed data for a twelve-month period.

The average kW load can be determined by the following equation:

Average kW load for month

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4. Estimating Load Data

Obviously, historical load data does not exist for a plant or facility not yet constructed. Table 1 estimates the average load of various facilities.

While these numbers will have variations depending on site conditions, they are reliable and helpful in making preliminary feasibility studies for installation.

Estimation of average load of various facilities
Table 1 – Estimation of average load of various facilities

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5. Categorizing Loads

When developing a load estimate, it is helpful to categorize lighting and power loads. These loads are distinctly different.

Lighting loads are relatively constant. They are most often expressed as load density in voltamperes (VA) per square foot (VA/FT2). In a commercial building, lighting loads typically range from 1.0 VA/FT2 in a storage area to 15.0 VA/FT2 or more in an office area.

Power loads involve loads other than lighting. Examples are motors, furnaces and rectifiers. Unlike lighting loads, power loads vary based on a variety of factors; these including start and stop times, percentage of output and the associated power factor.

In addition to categorizing the loads, lighting and power loads are also estimated separately. The loads are later combined to determine the approximate total load.

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6. VA/FT2 Load Estimating

For estimating purposes, power loads and lighting loads can be measured in VA/FT2 . However, a detailed analysis requires individual measurement of power loads to ensure accuracy. A simple table, based on VA/FT2, is used to obtain a rough estimate of a load as expressed in total kVA generated. Table 2 below shows such a table.

Load Example //

Calculate the load for a 10,000 square foot office with electric air conditioning.

Solution //

The left-hand column of Table 2 below indicates the maximum lighting load in an office building is 4.0 VA/FT2. Therefore, the lighting load equates to:

4.0 VA/FT2 x 10,000 (square feet) = 40,000 VA

Rough estimation of load expressed in total kVA generated
Table 2 – Rough estimation of load expressed in total kVA generated

Reading the table from left to right:

2.0 VA/FT2 is required for miscellaneous power loads:
2.0 VA/FT2 x 10,000 (square feet) = 20,000 VA

7.0 A/FT2 is required for electrical air conditioning loads:
7.0 VA/FT2 x 10,000 (square feet) = 70,000 VA

Add the individual loads to determine the combined load:
40,000 + 20,000 + 70,000 = 130,000 VA

When using the table, it is important to remember that the table does not account for power losses caused by the resistance found in wires and cables. A power loss of up to 6% would be factored into the VA total when estimating a facility with extensive wiring.

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Reference // Electric power applications, engine and generator sizing – Caterpillar

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About Author //


Edvard Csanyi

Edvard - Electrical engineer, programmer and founder of EEP. Highly specialized for design of LV/MV switchgears and LV high power busbar trunking (<6300A) in power substations, commercial buildings and industry fascilities. Professional in AutoCAD programming. Present on


  1. Fidel Fornolles
    Feb 09, 2017

    It is good a great help enough to those newly practetioner

  2. al amin
    Nov 19, 2015

    Very good

  3. Jawad
    Sep 14, 2015

    i want know more a bout the substation

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