The document provides information about load forecasting, earthing, megger testing, and earth leakage circuit breakers (ELCBs). It discusses several methods for short, medium, and long-term load forecasting including regression analysis and considering factors like weather, time of day, and customer class. It also describes the principles of earthing systems and equipment, how megger devices test insulation resistance, and the purpose and components of ELCBs in providing electrical safety.

1. DATTA MEGHE INSTITUTE OF ENGINEERING
TECHNOLOGY AND
RESEARCH,WARDHA
1
SURYAKANT MOREY
MR. SURYAKANT B. MOREY
DEPARTMENT OF ELECTRICAL ENGINEERING
PREPARED BY
Presentation on
LOAD
FORECASTING,EARTHING,
MEGGER & ELCB

2. CONTENTS –
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1. Load forecasting, Regression Analysis, Numerical Based on Linear and Exponential
trends
2. Electrical Installation for domestic, commercial and industrial consumers
3. Calculation of connected load,
4. selection of transformer, switchgears, cables and wires
5. Single line diagram, Special provisions for high rise buildings ( IER - 50 - A )
6. Earthing requirements, megger, and earth test use of earth leakage circuit breakers
7. Special reference to be given to IER - 2 (I,n,o,p,v,aa,aaa,aq,aqq,ar,av)

3. LOAD FORECASTING
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Introduction –
Accurate models for electric power load forecasting are essential to the
operation and planning of a utility company. Load forecasting helps an electric utility to
make important decisions including decisions on purchasing and generating electric power,
load switching, and infrastructure development. Load forecasts are extremely important
for energy suppliers, ISOs, financial institutions, and other participants in electric energy
generation, transmission, distribution, and markets.
Load forecasts can be divided into three categories: short-term forecasts which
are usually from one hour to one week, medium forecasts which are usually from a week
to a year, and long-term forecasts which are longer than a year.

4. FACTORS CONNECTED WITH A GENERATING STATION:
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• Connected Load:
The sum of the continuous rating of all the equipments connected to supply system.
eg: If a consumer has connections of five 100 Watts lamps and a power point of 500
Watts, then the connected load of the consumer is (5 * 100) + 500 = 1000 Watts.
The sum of the connected load of all the consumers is the connected load to the
power station.
• Maximum Demand:
It is the greatest demand of the load on the power station during a given period.
The load on the power station varies from time to time. The maximum demand of all
the demands that have occurred during a given period is maximum demand. The station
should be capable of meeting the maximum demand.
• Demand Factor:
It is the ratio of the maximum demand on the power station to its connected load.
Demand Factor = Maximum Demand / Connected Load
The value of demand factor is usually less than 1. It is expected because maximum
demand on the power station is generally less than the connected load. If the maximum
demand on the power station is 80 MW and the connected load is 100 MW, then the
demand factor is 80 / 100 = 0.8. The knowledge of demand factor is vital in determining
the capacity of plant equipments.

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•Load Forecasting:
Forecast of demand and energy are required to estimate the additional installed
capacity required to facilitate the plant maintenance programmed and to
estimate the firm capacity.
Load forecasting can be divided into three categories –
• Long term forecasting
• Medium term forecasting
• Short term forecasting
Following methods are generally used for forecast of future demand of electrical
energy.
i) Load survey method
ii) Method of extrapolation
iii) Mathematical Modeling
iv) Mathematical method considering economic parameters

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Important Factors for Forecasts
For short-term load forecasting several factors should be considered, such as
time factors, weather data, and possible customers’ classes. The medium- and long-term
forecasts take into account the historical load and weather data, the number of customers
in different categories, the appliances in the area and their characteristics including age,
the economic
and demographic data and their forecasts, the appliance sales data, and other factors.
The time factors include the time of the year, the day of the week, and the hour
of the day. There are important differences in load between weekdays and weekends. The
load on different weekdays also can behave differently. For example, Mondays and Fridays
being adjacent to weekends, may have structurally different loads than Tuesday through
Thursday. This is particularly true during the summer time. Holidays are more difficult to
forecast than non-holidays because of their relative infrequent occurrence.
Weather conditions influence the load. In fact, forecasted weather parameters
are the most important factors in short-term load forecasts. Various weather variables
could be considered for load forecasting. Temperature and humidity are the most
commonly used load predictors. An electric load prediction survey published in [17]
indicated that of the 22 research reports considered, 13 made use of temperature only, 3
made use of temperature and humidity, 3 utilized additional weather parameters, and 3
used only load parameters.

7. FORECASTING
METHODS
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Statistical approaches usually require a mathematical model that represents load as
function of different factors such as time, weather, and customer class. The two important
categories of such mathematical models are: additive models and multiplicative models.
They differ in whether the forecast load is the sum (additive) of a number of components
or the product (multiplicative) of a number of factors. For example, Chen et al. [4]
presented an additive model that takes the form of predicting load as the function of four
components:
L = Ln + Lw + Ls + Lr,
where L is the total load, Ln represents the “normal” part of the load, which is a set of
standardized load shapes for each “type” of day that has been identified as occurring
throughout the year, Lw represents the weather sensitive part of the load, Ls is a special
event component that create a substantial deviation from the usual load pattern, and Lr is
a completely random term, the noise.

8. MEDIUM- AND LONG-TERM LOAD FORECASTING
METHODS
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End-use models. The end-use approach directly estimates energy consumption by using
extensive information on end use and end users, such as appliances, the customer use,
their age, sizes of houses, and so on. Statistical information about customers along with
dynamics of change is the basis for the forecast. End-use models focus on the various uses
of electricity in the residential, commercial, and industrial sector. These models are based
on the principle that electricity demand is derived from customer’s demand for light,
cooling, heating, refrigeration, etc. Thus end-use models explain energy demand as a
function of the number of appliances in the market [15]. Ideally this approach is very
accurate. However, it is sensitive to the amount and quality of end-use data. For example,
in this method the distribution of equipment age is important for particular types of
appliances. End-use forecast requires less historical data but more information about
customers and their equipment.

9. SHORT-TERM LOAD FORECASTING
METHODS
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A large variety of statistical and artificial intelligence techniques have been developed for
short-term load forecasting.
Similar-day approach. This approach is based on searching historical data for days within
one, two, or three years with similar characteristics to the forecast day. Similar
characteristics include weather, day of the week, and the date. The load of a similar day is
considered as a forecast. Instead of a single similar day load, the forecast can be a linear
combination or regression procedure that can include several similar days. The trend
coefficients can be used for similar days in the previous years.
Regression methods. Regression is the one of most widely used statistical techniques. For
electric load forecasting regression methods are usually used to model the relationship of
load consumption and other factors such as weather, day type, and customer class. Engle et
al. [9] presented several regression models for the next day peak forecasting. Their models
incorporate deterministic influences such as holidays, stochastic influences such as average
loads, and exogenous influences such as weather.

10. EARTHING
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General principles
Earthing can classified in two ways:
1. System earthing;
2. Equipment earthing.
System earthing is essential to the proper operation of the system, whereas equipment
earthing concerns the safety of personnel and plant. A key function of equipment earthing
is to provide a controlled method to prevent the build up of static electricity, thus
reducing the risk of electrical discharge in potentially hazardous environments. Generally,
a resistance to earth of less than 106 W will ensure safe dissipation of static electricity in
all situations.

11. MEGGER
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The megger is a portable instrument used to measure insulation resistance. The
megger consists of a hand-driven DC generator and a direct reading ohm meter. A simplified
circuit diagram of the instrument is shown in Figure 17.
The moving element of the ohm meter consists of two coils, A and B, which are rigidly
mounted to a pivoted central shaft and are free to rotate over a C-shaped core (C on Figure
17). These coils are connected by means of flexible leads. The moving element may point in
any meter position when the generator is not in operation.
As current provided by the hand-driven generator flows through Coil B, the coil will tend to
set itself at right angles to the field of the permanent magnet. With the test terminals
open, giving an infinite resistance, no current flows in Coil A. Thereby, Coil B will govern the
motion of the rotating element, causing it to move to the extreme counter-clockwise
position, which is marked as infinite resistance.

12. Fig. Simple Megger Circuit Diagram
COIL A IS WOUND IN A MANNER TO PRODUCE A CLOCKWISE TORQUE ON
THE MOVING ELEMENT. WITH THE TERMINALS MARKED "LINE" AND
"EARTH" SHORTED, GIVING A ZERO RESISTANCE, THE CURRENT FLOW
THROUGH THE COIL A IS SUFFICIENT TO PRODUCE ENOUGH TORQUE TO
OVERCOME THE TORQUE OF COIL B. THE POINTER THEN MOVES TO THE
EXTREME CLOCKWISE POSITION, WHICH IS MARKED AS ZERO RESISTANCE.
RESISTANCE (RL) WILL PROTECT COIL A FROM EXCESSIVE CURRENT FLOW IN
THIS CONDITION.
WHEN AN UNKNOWN RESISTANCE IS CONNECTED ACROSS THE TEST
TERMINALS, LINE AND EARTH, THE OPPOSING TORQUES OF COILS A AND B
BALANCE EACH OTHER SO THAT THE INSTRUMENT POINTER COMES TO
REST AT SOME POINT ON THE SCALE. THE SCALE IS CALIBRATED SUCH THAT
THE POINTER DIRECTLY INDICATES THE VALUE OF RESISTANCE BEING
MEASURED.
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13. EARTH LEAKAGE CIRCUIT
BREAKER
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An Earth Leakage Circuit Breaker (ELCB) is a safety device used in electrical installations with high earth
impedance to prevent shock.
Purpose
Many electrical installations have a relatively high earth impedance. This may be due to the use of a
local earth rod (TT systems), or to dry local ground conditions.
These installations are dangerous and a safety risk if a live to earth fault current flows. Because earth
impedance is high:
not enough current exists to trip a fuse or circuit breaker, so the condition persists un cleared
indefinitely
the high impedance earth cannot keep the voltage of all exposed metal to a safe voltage, all such
metalwork may rise to close to live conductor voltage.
These dangers can be drastically reduced by the use of an ELCB or Residual-current device (RCD).
The ELCB makes such installations much safer by cutting the power if these dangerous conditions occur.
This approach to electrical safety is called EEBAD. In Britain EEBAD domestic installations became
standard in the 1950s.
In non-technical terms if a person touches something, typically a metal part on faulty electrical
equipment, which is at a significant voltage relative to the earth, electrical current will flow through
him/her to the earth. The current that flows is too small to trip an electrical fuse which could
disconnect the electricity supply, but can be enough to kill. An ELCB detects even a small current to
earth (Earth Leakage) and disconnects the equipment (Circuit Breaker).

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Advantages -
ELCBs have one advantage over RCDs: they are less sensitive to fault conditions,
and therefore have fewer nuisance trips. (This does not mean they always do, as practical
performance depends on installation details and the discrimination enhancing filtering in
the ELCB.) Therefore by electrically separating cable armor from cable CPC, an ELCB can be
arranged to protect against cable damage only, and not trip on faults in down line
installations.
Disadvantages -
ELCBs have some disadvantages:
1. They do not detect faults that don't pass current through the CPC to the earth rod.
2. They do not allow a single building system to be easily split into multiple sections with
independent fault protection, because earthing systems are usually bonded to pipe
work.
3. They may be tripped by external voltages from something connected to the earthing
system such as metal pipes, a TN-S earth or a TN-C-S combined neutral and earth.
4. As with RCDs, electrically leaky appliances such as some water heaters, washing
machines and cookers may cause the ELCB to trip.
5. ELCBs introduce additional resistance and an additional point of failure into the
earthing system.

15. Fig. Earth Leakage Circuit Breaker
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