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AJAY BHATNAGAR, NRLDC
Load Forecasting Techniques &
Scheduling
POSOCO - NRLDC
lOAD FORECASTING IS USED by POwER COMPANIES TO
ANTICIPATE THE AMOUNT OF POwER NEEDED TO SUPPly THE
DEMAND.
JURISDICTION OF LOAD DESPATCH CENTERS
NLDC:Apex body to ensure integrated operation of National Power System
RLDC:Apex body to ensure integrated operation of power system in the concerned region
SLDC:Apex body to ensure integrated operation of power system in a state
POSOCO - NRLDC
PECULIARITIES OF REGIONAL GRIDS
SOUTHERN REGION
WESTERNREGION
EASTERN REGION
NORTHERN REGION NORTH-
EASTERN REGION
REGIONAL GRIDS
Deficit Region
Snow fed – run-of –the –river hydro
Highly weather sensitive load
Adverse weather conditions: Fog & Dust Storm
Very low load
High hydro potential
Evacuation problems
Industrial load and agricultural load
Low load
High coal reserves
Pit head base load plants
High load (40% agricultural load)
Monsoon dependent hydro
CHICKEN-NECK
POSOCO - NRLDC
POSOCO - NRLDC
lOAD FORECASTING
What is Load forecasting
POSOCO - NRLDC
Load forecasting is sort of planning & It issaid that “To work with plan is to work withaccuracy”.
Load forecasting is used by powercompanies to anticipate the amount ofpower needed to supply the demand.
LOAD FORECASTING
• The first crucial step for any planning study
• Forecasting refers to the prediction of the load behaviour for the future
• Words such as, demand and consumption are also used instead of electric load
• Energy (MWh, kWh) and power (MW,kW) are the two basic parameters of a load.
• By load, we mean the power.
• Demand forecast
• To determine capacity of generation, transmission and distribution required
• Energy forecast
• To determine the type of generation facilities required
POSOCO - NRLDC
NATURE OF LOADS
Load characteristics:• Demand factor
• Load factor
• Diversity factor
• Utilization factor
• Power factor
• Higher the values of load factor and diversity factor, lower will be the overall cost per unit generated.
• Higher the diversity factor of the loads, the fixed charges due to capital investment will be reduced.
POSOCO - NRLDC
loadConnected
demandMaxfactorDemand
.
demandMax
demandAvgfactorLoad
.
.
stationpowerofdemandMax
demandsindividualofSumfactorDiversity
.
.max
stationpowerofcapacityRated
stationpowerondemandMaxfactornUtilisatio
.
TYPES OF LOADS
Five broad categories:• Domestic
• Demand factor: 70-100%
• Diversity factor: 1.2-1.3
• Load factor: 10-15%
• Commercial
• Demand factor: 90-100%
• Diversity factor: 1.1-1.2
• Load factor: 25-30%
• Industrial
• Small-scale: 0-20 kW
• Medium-scale: 20-100 kW
• Large-scale: 100 kW and above
• Demand factor: 70-80%
• Load factor: 60-65%
POSOCO - NRLDC
TYPES OF LOADS
• Agricultural
• Demand factor: 90-100%
• Diversity factor: 1-1.5
• Load factor: 15-25%
• Other loads
• Street lights, bulk supplies, traction etc.
Commercial and agricultural loads are characterized by seasonal variations.
Industrial loads are base loads and are little weather dependent.
POSOCO - NRLDC
DEMAND ESTIMATION AS PER
IEGC PROVISIONS
POSOCO - NRLDC
DEMAND ESTIMATION
Demand estimation for operational purposes is to be done on adaily/weekly/monthly basis. The mechanism and facilities at SLDCs shallbe created to facilitate on-line estimation of demand for daily operationaluse for each 15 minutes block.
The monthly estimated demand by the SLDC shall be provided to RLDCand RPC
The SLDC shall take into account the Wind Energy forecasting to meetthe active and reactive power requirement.
In order to facilitate estimation of Total Transfer Capability / AvailableTransfer Capability on three month ahead basis , the SLDC shall furnishestimated demand and availability data to RLDCs.
DEMAND-SIDE MANAGEMENT
Grouping of Loads by SLDC without overlapping between different Groupsas given below
Loads for scheduled power cuts/load shedding
Loads for unscheduled load shedding
Loads to be shed through under frequency relays/df/dt relays
Loads to be shed under any System Protection Scheme identified at theRPC level.
TECHNIQUES OF
lOAD FORECASTING
FACTORS AFFECTING LOAD FORECASTING
• Time factors such as:
• Hours of the day (day/night)
• Day of the week (week day/weekend)
• Time of the year (season)
• Weather conditions (temperature and humidity)
• Class of customers (residential, commercial, industrial, agricultural, public, etc.)
• Special events (TV programmes, public holidays, etc.)
• Population
• Economic indicators (per capita income, Gross National Product (GNP), Gross Domestic Product (GDP), etc.)
• Trends in using new technologies
• Electricity price
POSOCO - NRLDC
FORECASTING METHODOLOGY
• Forecasting: systematic procedure for quantitatively defining future loads.
• Classification depending on the time period:
• Short term
• Intermediate
• Long term
• Forecast will imply an intermediate-range forecast
• Planning for the addition of new generation, transmission and distribution facilities must begin 4-10 years in advance of the actual in-service date.
POSOCO - NRLDC
FORECASTING TECHNIQUES
POSOCO - NRLDC
Three broad categories based on:
• Extrapolation
– Time series method
– Use historical data as the basis of estimating future outcomes.
• Correlation
– Econometric forecasting method
– identify the underlying factors that might influence the variable that is being forecast.
• Combination of both
EXTRAPOLATION
• Based on curve fitting to previous data available.
• With the trend curve obtained from curve fitted load can be forecasted at any future point.
• Simple method and reliable in some cases.
• Deterministic extrapolation:
• Errors in data available and errors in curve fitting are not accounted.
• Probabilistic extrapolation
• Accuracy of the forecast available is tested using statistical measures such as mean and variance.
POSOCO - NRLDC
CORRELATION
• Relates system loads to various demographic and economic factors.
• Knowledge about the interrelationship between nature of load growth and other measurable factors.
• Forecasting demographic and economic factors is a difficult task.
• No forecasting method is effective in all situations.
• Designer must have good judgment and experience to make a forecasting method effective.
POSOCO - NRLDC
IMPACT OF WEATHER IN LOAD FORECASTING
• Weather causes variations in domestic load, public lighting, commercial loads etc.
• Main weather variables that affect the power consumption are:
• Temperature
• Cloud cover
• Visibility
• precipitation
• First two factors affect the heating/cooling loads
• Others affect lighting loads
POSOCO - NRLDC
IMPACT OF WEATHER IN LOAD FORECASTING
• Average temperature is the most significant weather dependent factor that influences load variations.
• Temperature and load are not linearly related.
• Non-linearity is further complicated by the influence of• Humidity
• Extended periods of extreme heat or cold spells
• In load forecast models proper temperature ranges and representative average temperatures which cover all regions of the area served by the electric utility should be selected.
POSOCO - NRLDC
IMPACT OF WEATHER IN LOAD FORECASTING
• Cloud cover is measured in terms of:
• height of cloud cover
• Thickness
• Cloud amount
• Time of occurrence and duration before crossing over a population area.
• Visibility measurements are made in terms of meters/kilometers with fog indication.
• To determine impact of weather variables on load demand, it is essential to analyze data concerning different weather variables through the cross-section of area served by utility and calculate weighted averagesfor incorporation in the modeling.
POSOCO - NRLDC
ENERGY FORECASTING
• To arrive at a total energy forecast, the forecasts for residential, commercial and industrial customers are forecasted separately and then combined.
POSOCO - NRLDC
RESIDENTIAL SALES FORECAST
• Population method
• Residential energy requirements are dependent on:
• Residential customers
• Population per customer
• Per capita energy consumption
• To forecast these factors:
• Simple curve fitting
• Regression analysis
• Multiplying the three factors gives the forecast of residential sales.
POSOCO - NRLDC
RESIDENTIAL SALES FORECAST
• Synthetic method
• Detailed look at each customer
• Major factors are:
• Saturation level of major appliances
• Average energy consumption per appliance
• Residential customers
• Forecast these factors using extrapolation.
• Multiplying the three factors gives the forecast of residential sales.
POSOCO - NRLDC
COMMERCIAL SALES FORECAST
• Commercial establishments are service oriented.
• Growth patterns are related closely to growth patterns in residential sales.
• Method 1:
• Extrapolate historical commercial sales which is frequently available.
• Method 2:
• Extrapolate the ratio of commercial to residential sales into the future.
• Multiply this forecast by residential sales forecast.
POSOCO - NRLDC
INDUSTRIAL SALES FORECAST
• Industrial sales are very closely tied to the overall economy.
• Economy is unpredictable over selected periods
• Method 1:
• Multiply forecasted production levels by forecasted energy consumption per unit of production.
• Method 2:
• Multiply forecasted number of industrial workers by forecasted energy consumption per worker.
POSOCO - NRLDC
PEAK LOAD FORECASTING
• Extrapolate historical demand data
• Weather conditions can be included
• Basic approach for weekly peak demand forecast is:
1. Determine seasonal weather load model.
2. Separate historical weather-sensitive and non-weather sensitive components of weekly peak demand using weather load model.
3. Forecast mean and variance of non-weather-sensitive component of demand.
4. Extrapolate weather load model and forecast mean and variance of weather sensitive component.
5. Determine mean, variance and density function of total weekly forecast.
6. Calculate density function of monthly/annual forecast.
POSOCO - NRLDC
WEATHER LOAD MODEL
• Plot a scatter diagram of daily peaks versus an appropriate weather variables.
• Dry-bulb temperature and humidity
• Using curve fitting three line segments can be defined in the example
POSOCO - NRLDC
sw
www
sss
TTTif0
TTifTTk
TTifTTkw
)(
)(
Parameters of the model:• Slopes: ks and kw• Threshold temperatures: Ts and Tw
SEPARATING WEATHER-SENSITIVE AND NON-WEATHER SENSITIVE COMPONENTS
• From the weather load model
• Weather-sensitive (WS) component of weekly peak load demand data is calculated from the weekly peak coincident dry-bulb temperatures.
• Non-weather-sensitive (NWS) component of peak demand is obtained by subtracting the first component from historical data.
• NWS component is used in step-3, of basic approach for weekly peak demand forecast , to forecast the mean and variance of the NWS component of future weekly peak demands.
POSOCO - NRLDC
TOTAL FORECAST
POSOCO - NRLDC
LOAD FORECASTING CATEGORIES
Load Forecasting Categories
Short-term load forecasting
One hour ~ One week
Control and schedule power system in everydayoperations
Medium-term and Long-term load forecasting
One week ~ longer than one year
Determine capacity of generation, transmission,distribution systems, type of facilities required intransmission expansion planning, development ofpower system infrastructure, etc.
POSOCO - NRLDC
LOAD FORECASTING METHODS
Parametric methods
Regression method
Time series
Similar day Approach
Autoregressive Moving Average (ARMA)
Spectral expansion technique (Fourier Series)
State equations
Artificial intelligence methods
Artificial neural networks
Fuzzy logic
Expert systems
POSOCO - NRLDC
INFLUENCE – WEATHER, TIME & TYPE
Electric load has an obvious correlation to weather. The mostimportant variables responsible in load changes are:
Dry and wet bulb temperature Dew point Humidity Wind Speed / Wind Direction Sky Cover Sunshine
In the forecasting model, we should also consider time factorssuch as:
The day of the week
The hour of the day
Holidays
Electric utilities usually serve different types of customers such asresidential, commercial, and industrial. The following graphsshow the load behavior in the above classes by showing theamount of peak load per customer, and the total energy.
POSOCO - NRLDC
SCHEDUlING AS PER
IEGC PROVISIONS
POSOCO - NRLDC
SCHEDULING RESPONSIBILITY
RLDC has Scheduling Responsibility for
a) Central Generating Stations (excluding stations where full Share isallocated to host state),
b) Ultra-Mega power projects
c) If a generating station is connected only to the ISTS, (except forCentral Generating Stations where full Share is allocated to one State)
d) If a generating station is connected to both ISTS and the Statenetwork and if the state has 50% Share of power or less ( of thegenerating capacity put into commercial operation)
POSOCO - NRLDC
SCHEDULING RESPONSIBILITY
SLDC has Scheduling Responsibility for
a) Generating station which is connected only to the State transmission network
b) Central Generating Station whose full Share is allocated to host state.
c) If a generating station is connected both to ISTS and the State network and if the state has more than 50% Share of power (of the generating capacity put into commercial operation)
d) Generating station supplying power to any state other than host state
POSOCO - NRLDC
SCHEDULING RESPONSIBILITYNLDC shall be responsible for
scheduling and despatch of electricity over inter-regional links inaccordance with the grid code specified by Central Commission incoordination with Regional Load Despatch Centers.
NLDC shall be responsible for coordination with Regional LoadDespatch Centers for the energy accounting of inter-regional exchangeof power.
NLDC shall also be responsible for coordination for trans-nationalexchange of power.
NLDC shall develop a procedure for scheduling of collective transactionthrough Power Exchanges, scheduling of inter-regional power exchangesincluding HVDC setting responsibility and power exchanges of thecountry with other countries.
POSOCO - NRLDC
SCHEDULING PROCEDURE
POSOCO - NRLDC
TIME LINE OF SCHEDULE
By 09.00 hrs. ISGSs shall advise NRLDC the Station-wise MW and MWhcapabilities
By 10.00 Hrs. NRLDC shall advise the States / Beneficiaries the Station wise MW& MWh entitlements.
By 1500 hrs. SLDCs/ Beneficiaries shall communicate the Station-wiserequisitions and details of bilateral exchanges to NRLDC.
By 1800 hrs. NRLDC shall convey the ex-power plant despatch schedule to eachISGS and net drawal schedule to each State / Beneficiary. Thedetails of unrequisitioned surpluses shall also be intimated.
By 2200 hrs.* ISGSs / States / Beneficiaries shall inform the modifications, if any,for incorporating in the final schedule
By 2300 hrs. NRLDC shall issue the final despatch and drawal schedule.
* Since issuing the final despatch and drawal schedule is a critical activity andconsiderable time is involved in its preparation and carrying out requisitemoderation, if any, it has been agreed to complete this activity by 2100 hrs.
POSOCO - NRLDC
COMPOSITE TIMELINE
AvailabilityDeclaration
Entitlements
SLDC
Requisition &Bilateral Agreements
Injection Schedule Drawal Schedule
Revision in DC Revision in Requisition
FinalInjection Schedule
FinalDrawal Schedule
09:00
10:00
15:00
18:00
22:00
23:00
RLDC
ISGS
Time
Revisions duringCurrent day
Revisions duringCurrent day
0 to 24 hours
CollectiveTransactions (PX)
POSOCO - NRLDC
SPECIAL REQUIREMENT OF SOLAR / WIND
5.2
(u) Special requirements for Solar/ wind generators
System operator (SLDC/ RLDC) shall make all efforts to evacuate theavailable solar and wind power and treat as a must-run station. However,System operator may instruct the solar /wind generator to back downgeneration on consideration of grid security or safety of any equipment orpersonnel is endangered and Solar/ wind generator shall comply with thesame. For this, Data Acquisition System facility shall be provided fortransfer of information to concerned SLDC and RLDC
(i) SLDC/RLDC may direct a wind farm to curtail its VAr drawl/injection incase the security of grid or safety of any equipment or personnel isendangered.
(ii) During the wind generator start-up, the wind generator shall ensure thatthe reactive power drawl (inrush currents incase of induction generators)shall not affect the grid performance.
POSOCO - NRLDC
DEVIATIONS FROM SCHEDULE - UI
POSOCO - NRLDC
POSOCO - NRLDC