Load Characteristics
Load
Distribution systems obviously exist to supply electricity to end
users, so loads and their characteristics are important. Utilities
supply a broad range of loads, from rural areas with load
densities of 10 kVA/mi² to urban areas with 300 MVA/mi².
A utility may feed houses with a 10- to 20-kVA peak load on
the same circuit as an industrial customer peaking at 5 MW.
The electrical load on a feeder is the sum of all individual
customer loads. And the electrical load of a customer is the sum
of the load drawn by the customer’s individual appliances.
The electrical load on a feeder is the sum of all individual
customer loads. And the electrical load of a customer is the sum
of the load drawn by the customer’s individual appliances.
Customer loads have many common characteristics. Load
levels vary through the day, peaking in the afternoon or early
evening. Several definitions are used to quantify load
characteristics at a given location on a circuit:
Load Graph or Load Curve
Load Graph or Load Curve
➔Is a chart illustrating the variation in demand/electrical load
over a specific time.
➔Load curve or chronological curve is the graphical
representation of load (in kW or MW) in proper time
sequence and the time in hours. It shows the variation of load
on the power station. When the load curve is plotted for 24
hours a day, then it is called daily load curve. If the one year
is considered then, it is called annual load curve.
➔The load curve of the power system is not same all the day. It
differs from day to day and season to season. The load curve
is mainly classified into two types, i.e., the summer load curve
and the winter load curve.
➔The load curve of the power system is not same all the day. It
differs from day to day and season to season. The load curve
is mainly classified into two types, i.e., the summer load curve
and the winter load curve.
The following are the information obtained from load curves.
1. Load duration curve determines the load variation during
different hours of the day.
2. It indicates the peak load which determines the maximum
demand on the power station.
3. The area under the load curve gives the total energy
generated in the period under consideration.
4. The area under the curve divided by the total numbers of
hours gives the load.
5. The ratio of the area under the load curve of the total area of
the rectangle in which it is contained gives the load factor.
Utility of Load Curve
Utility of Load Curve
The following are the utility of the load curve.
1.Load curve decides the installed capacity of a power station.
2. It is helpful in choosing the most economical sizes of the
various generating units.
3.The load curve estimates the generating cost.
4.It decides the operating schedules of the power station, i.e.,
the sequence in which the different generating units should
run.
Load Duration Curve
The load duration curve is defined as the curve between the
load and time in which the ordinates representing the load,
plotted in the order of decreasing magnitude, i.e., with the
greatest load at the left, lesser loads towards the rights and the
lowest loads at the time extreme right.
Maximum Demand
➔The maximum demand of an installation or system is the
greatest of all demands which have occurred during the specified
period of time.
➔Is not the greatest instantaneous demand but the greatest
average power demand occurring during any of the relatively
short intervals of 1 min., 15 min. or 30 min. duration within the
period.
➔Maximum demand determinations are mostly used for estimating
the capacity of its generator and other electrical apparatus
required serving a certain specified load.
Demand / Average Demand
➔The demand of an installation or system is the load at the
receiving terminals averaged over a specified interval of time.
➔Its meant is average power requirement during some
specified period of time of considerable duration such as a
day or a month or a year.
Demand / Average Demand
➔The demand of an installation or system is the load at the
receiving terminals averaged over a specified interval of time.
➔Its meant is average power requirement during some
specified period of time of considerable duration such as a
day or a month or a year.
𝑻𝒐𝒕𝒂𝒍 𝑬𝒏𝒆𝒓𝒈𝒚 (𝑲𝒘𝒉𝒓 𝒄𝒐𝒏𝒔𝒖𝒎𝒆𝒅 𝒊𝒏 𝒕𝒉𝒆 𝒑𝒆𝒓𝒊𝒐𝒅)
𝑨𝒗𝒆𝒓𝒂𝒈𝒆 𝑫𝒆𝒎𝒂𝒏𝒅 =
𝑻𝒐𝒕𝒂𝒍 𝒉𝒐𝒖𝒓𝒔 (𝒉𝒐𝒖𝒓𝒔 𝒊𝒏 𝒕𝒉𝒆 𝒑𝒆𝒓𝒊𝒐𝒅)
Demand Factor
➔Defined as the ratio of the actual maximum demand made by
the load to the rating of the connected load.
➔The total connected load of the system is defined as ‘the sum
of the continuous ratings of the load consuming equipment
connected to the system’. Both the maximum demand and the
total connected load should be expressed in the same units
thus making the demand factor dimensionless.
𝑴𝒂𝒙𝒊𝒎𝒖𝒎 𝑫𝒆𝒎𝒂𝒏𝒅 𝒐𝒇 𝒕𝒉𝒆 𝑺𝒚𝒔𝒕𝒆𝒎
𝑫𝒆𝒎𝒂𝒏𝒅 𝑭𝒂𝒄𝒕𝒐𝒓 =
𝑻𝒐𝒕𝒂𝒍 𝑪𝒐𝒏𝒏𝒆𝒄𝒕𝒆𝒅 𝑳𝒐𝒂𝒅
Connected Load
➔Is the total rating (in kilowatts) of all the apparatus installed in
the consumer’s premises.
➔It is the sum of continuous ratings of all the equipment
connected to supply system. A power station supplies load to
thousands of consumers. Each consumer has certain
equipment installed in his premises. The sum of the
continuous ratings of all the equipment in the consumer’s
premises is the “connected load” of the consumer.
Utilization Factor
➔The utilization factor is the ratio of the maximum demand of a
system to the rated capacity of the system.
𝑴𝒂𝒙𝒊𝒎𝒖𝒎 𝑫𝒆𝒎𝒂𝒏𝒅 𝒐𝒇 𝒕𝒉𝒆 𝑺𝒚𝒔𝒕𝒆𝒎
𝑼𝒕𝒊𝒍𝒊𝒛𝒂𝒕𝒊𝒐𝒏 𝑭𝒂𝒄𝒕𝒐𝒓 =
𝑹𝒂𝒕𝒆𝒅 𝑪𝒂𝒑𝒂𝒄𝒊𝒕𝒚
Load Factor
➔The ratio of the average power to the maximum demand.
➔Necessary to specify time intervals in to which maximum
demand is based and the period which the power is averaged.
𝑨𝒗𝒆𝒓𝒂𝒈𝒆 𝑳𝒐𝒂𝒅
𝑳𝒐𝒂𝒅 𝑭𝒂𝒄𝒕𝒐𝒓 =
𝑴𝒂𝒙𝒊𝒎𝒖𝒎 𝑫𝒆𝒎𝒂𝒏𝒅
Diversity Factor
➔Maximum demands of various consumer occur at different
times during the day and not simultaneously. Ex: residential
lighting load is maximum in the evening, whereas
manufacturing establishment require maximum power during
daytime.
➔The diversity factor is the ratio of the sum of the individual
maximum demands of the various subdivisions of a system to
the maximum demand of the whole system.
σ(𝑰𝒏𝒅𝒊𝒗𝒊𝒅𝒖𝒂𝒍 𝑴𝒂𝒙𝒊𝒎𝒖𝒎 𝑫𝒆𝒎𝒂𝒏𝒅)
𝑫𝒊𝒗𝒆𝒓𝒔𝒊𝒕𝒚 𝑭𝒂𝒄𝒕𝒐𝒓 =
𝑴𝒂𝒙𝒊𝒎𝒖𝒎 𝑫𝒆𝒎𝒂𝒏𝒅 𝒐𝒇 𝒕𝒉𝒆 𝑺𝒚𝒔𝒕𝒆𝒎
Load Diversity
➔Load diversity is the difference between the sum of the
peaks of two or more individual loads and the peak of the
combined load.
𝑳𝑫 = 𝑰𝒏𝒅𝒊𝒗𝒊𝒅𝒖𝒂𝒍 𝑴𝒂𝒙𝒊𝒎𝒖𝒎 𝑫𝒆𝒎𝒂𝒏𝒅 − 𝑴𝒂𝒙𝒊𝒎𝒖𝒎 𝑫𝒆𝒎𝒂𝒏𝒅 𝒐𝒇 𝒕𝒉𝒆 𝒔𝒚𝒔𝒕𝒆𝒎
Demand Interval
➔The time interval for demand usually 15 or 30 min. This is
obtained from daily demand curves or load duration curves.
Demand Interval
➔The time interval for demand usually 15 or 30 min. This is
obtained from daily demand curves or load duration curves.
Coincident Factor
➔Some engineers prefer to have a factor which describes the
characteristics of loads that have a value equal to or less than
unity. The reciprocal of the diversity factor is known as the
coincident factor.
𝟏 𝟏
𝑪𝑭 = 𝑪𝑭 = 𝟎. 𝟓(𝟏 + )
𝑫𝑭 𝟐𝒏+𝟑
Coincident Maximum Demand
➔Any demand occurs simultaneously with any other demand and
also the sum of any set of coincident demands.
Contribution Factor
➔This is factor that is usually referred in distribution systems
regarding the importance of weighted effects of a particular load.
Loss Factor
➔Ratio of average power loss in the system to power loss during
peak load period & referred to the variable power loss.
Types of Loads
A device which taps electrical energy from the electric power
system is called a load on the system. The load may be
resistive (e.g., electric lamp), inductive (e.g., induction motor),
capacitive or some combination of them. The various types of
loads on the power system are:
i. Domestic load and Residential load
• The most important part in the D.S. because they are variable
and erratic.
• PF is less and may vary 0.5 - 0.7
• In residential D.F. is between 1.1 – 1.15
• L.F. for domestic loads will be usually 0.5 – 0.6
ii. Commercial load
iii. Industrial load
• Greater important in D.S. with D.F. 0.7 – 0.8 and L.F. 0.6 –
0.7
• For heavy industry D.F. may be 0.9 & L.F. 0.7 – 0.8
• Cottage and small scale industry 3 – 20kW
• Medium Industry (Ricemill, oil mill, workshop) 25 -100kW
• Large Industry Connected to the Distribution Feeders 100 –
500kW
iv.Municipal load
iv.Irrigation load
iv.Traction load
Example 1. A Residential consumer has 10 lamps of 40W each
connected at each premises.
His demands is as follows:
From 12 midnight to 5 a.m. 40W
From 5 a.m. to 6 p.m. No load
From 6 p.m.to 7 p.m. 320W
From 7 p.m.to 9 p.m. 360W
From 9 p.m.to 12 midnight 160W
Find the average load, the maximum load, the load factor and the
electric energy consumption during the day.
Example 2. A 10 MW substation delivers 10 MW for 2 hours, 5
MW for 6 hours and is shutdown for the rest of each day. It is
also shutdown for maintenance for 45 days each year. Calculate
the load factor and annual load factor.
Example 3. A substation having the following loads:
Type of load MD(kw) Diversity of Group D.F.
Domestic 1,500 1.2 0.8
Industrial 10,000 1.25 1
Commercial 2,000 1.1 0.9
The overall system Diversity Factor is 1.35
Determine a.) MD, b.) CL of each type,
