Distribution Loss Factors for Cost To Serve study Lolo Buys Eskom Electricity Pricing

Contents Outcome Topic 1: Cost of supply study Topic 2: Energy losses overview Topic 3: Modelling Energy losses in HV and MV systems: HV Losses simulation MV Losses simulation End note Each learner must say what is it that they understand about the topic and what are their expectations.

Outcomes of the Training After this session the learner will be able to: Understand cost of supply studies Define technical losses and loss factors. Understand the factors that affect technical losses Understand how the technical losses fit into the cost of supply. Understand how technical losses can be modelled Understand the use of tools to model technical losses

Topic 1:Cost of Supply Study Objective: To provide an overview of cost of supply study

Cost of supply study A cost of supply study is a study in which the total company cost of service (revenue requirement) is spread or allocated to customer classes. Customer Class or Class of Service – A set of customers with similar characteristics who have been grouped for the purpose of setting an applicable rate for electric service Common classifications include residential, commercial, primary service and industrial

Cost of Supply tariff book

Cost of Supply Study Steps Functionalization: costs broken down into production, transmission, distribution Classification: costs classified by customer, energy, demand Allocation: costs allocated to different customer classes – residential, commercial, industrial

Functionalization and Classification Distribution Poles, towers, fixtures Line transformers Meters Station Equipment Production Production Plant Fuel costs Purchased Power Transmission Backbone & Inter-tie Facilities Generation Step-up Facilities Subtransmission Plant Line transformers Poles, towers, fixtures Demand & Customer Station Equipment Demand Meters Customer Purchased Power Production Plant Demand & Energy Fuel costs Energy Demand & Energy Transmission costs are charged to utilities, some of which are based on demand, some on energy. 

Cost Allocation Residential Industrial Commercial Classified Distribution Costs Classified Production Costs Charged Transmission Costs Allocate Residential Industrial Commercial

Topic Summary Cost of supply study Customer classification Various steps of Cost of supply study

Topic 2: Energy losses overview Objective: To provide an overview of energy losses in distribution networks The role of energy losses in cost of supply studies

Definition of Energy Losses Energy losses associated with a distribution system can be classified as follows : Technical Losses - losses associated with the electrical system Series losses which are proportional to the square of the current and to the resistance of the circuit elements and Shunt losses due the excitation losses in transformers and rotating machines, as well as leakage currents in cables Non-technical losses - losses associated with unidentified and uncollected revenue. This covers matters such as illegal connections, meter tampering, metering errors, errors in estimating unmetered supplies, errors in invoicing and revenue collection.

Technical losses Energy losses are incurred as results of transfer of power over the network from the sources to loads. The level of losses are primarily influenced by demand, conductor’s types, the extent of transformation and distance of loads to source amongst other things.

Energy losses on lines Energy losses are a function of the conductor material, the distance, temperature, and loading Output Energy is less than input Energy.

Energy losses on Transformer No load losses are considered fixed losses Load losses vary with the load Other losses are negligibly small

Calculation of Loss factors The loss factors are essentially a function of energy losses as seen in equation 1 and 2. Ploss = energy losses, The losses are proportional to square of the current being supplied through the network Psupplied = energy supplied I is current and R+jX is the line impedance

Distribution network model for cost to serve G 400kV/275kV/220kV 132kV 88kV 33kV 11kV 400V In cost to serve studies, the loss factors are disaggregated as follows: HV: 33kV < Vn ≤ 132kV MV: 1kV < Vn ≤ 33kV LV: Vn ≤ 1kV Urban and rural for MV and LV The generic network diagram below is used to represent various load connections at different voltage levels and to aid in the pooling and calculation of the Distribution Loss Factors (DLFs).

Topic Summary Energy losses Technical losses The relationship between technical losses and loss factors The generic network equivalent model

Topic 3: Modelling Energy losses in HV and MV systems Objectives: To provide an overview of the methodology used in modeling energy losses in distribution networks The use of various tools in simulation of energy losses and the interpretation of the results

Summary of Loss Factor modelling process Simulate technical losses Determine losses per assets group Calculate loss factor for each assets group Adjust loss factors in line with the WD/Energy allocation Power flow analysis on OU networks Use daily load curves Forced load curve for solar and wind generators Lines and transformers are grouped according to assets classes used in the CTS Losses determines for each of the assets class Calculate the loss factors from the technical losses Adjust/scale the loss factor to the energy and demand allocation 2018/10/09

Calculation of Loss factors The loss factors are essentially a function of energy losses as seen in equation 1 and 2. Ploss = energy losses, The losses are proportional to square of the current being supplied through the network Psupplied = energy supplied I is current and R+jX is the line impedance

Modelling of Energy losses Two different approaches employed but both use engineering model/simulators. Selection of the approaches is largely influenced by the nature of the network as modelled (case files). A case file for MV networks is made up of a single feeder. A large number of case files is required to draw a representative estimate for losses. Case files for HV Networks have multiple feeders, thus with one case file a representative estimate of losses is possible. The medium and low voltage networks proved to be challenging to model hourly.

HV Losses simulation

HV methodology 𝑓 𝑥 of And 𝑃 𝐿𝑜𝑠𝑠 = 𝐼 2 𝑅 𝑃 𝑖 = 𝑃 𝐿𝑜𝑎𝑑 + 𝑃 𝐿𝑜𝑠𝑠 Generators dispatched to match the load requirement Load profiles Losses estimated Loss factors determined 𝑓 𝑥 of And 𝑃 𝐿𝑜𝑠𝑠 = 𝐼 2 𝑅 𝑃 𝑖 = 𝑃 𝐿𝑜𝑎𝑑 + 𝑃 𝐿𝑜𝑠𝑠 Hourly losses-output Excel/Access and R used for data storage and analysis Network models Digsilent/ReticMaster case files Load flow studies Powerworld simulator used for studies Coded in python The method used to calculate average DLFs is to carry out load flow studies to determine the losses for each hour of day, followed by the statistical analysis of the hourly losses.

Process: Computation of loss factors for 33kV to 132kV (HV) networks The methodology used to calculate average DLFs for high voltage network is to carry out load flow studies to determine the losses for each hour of the day for the different network components. Quasi-dynamic modelling To perform the simulation, load profiles for selected loads and the PowerFactory simulator and steady state case files were used. The results (Losses) are used o determine loss factors The simulation was automated to perform loads flows for every hour. The above process was performed using PowerFactory Digsilent Software and Python scripting language.

Analysis of the Results: HV methodology The results of the HV network for all operating units are depicted for each network. In order to understand the spread of these losses, a histogram was also plotted A weighted average (weighted by load) was calculated to provide alternative estimate of losses where it’s not possible to use statistical results The result, consisting of line losses, transformer losses, line flows and maximum power of the transformer are stored in the excel file for analysis. The analysis was done for six operating units

Analysis of the Results: HV methodology There are significant differences in the losses per assets category. The difference can mainly be attributed to the approaches used in determining the losses factors, as outlined below: The previous methodology: relied on the simulation of losses for types of commonly used conductors/assets in Distribution. The method also assumed various loading of each asset type There was no simulation of a network as modelled by distribution engineers/planners The previous methodology relied on the simulation of network model developed by distribution planning and Load profiles used in Distribution (PowerGLF) Based largely on the Distribution standards

Analysis of the Results: HV methodology

MV Losses simulation

Computation of loss factors for 6.6kV to 22kV MV networks The medium and low voltage networks proved to be challenging to model hourly. As a result a different approach employing simulation of peak snap-shots, load loss factors and load factors to determine energy losses and energy consumed over a period is used. Peak losses and load energy are derived from load flow simulation using ReticMaster case files. Load factors and load loss factors are calculated from the actual metered data. The MV energy losses are expressed as:

Computation of loss factors for 6.6kV to 22kV MV networks The process of determining the MV loss factors involves the steps depicted by the flow diagram

Testing the MV methodology: Results Lower voltage networks tend to have higher losses, since most networks use underground cables and also carry higher currents.

Testing the MV methodology: Results The losses for MV networks of different operating units, and densities range from 2.5% of to 7.6 % on rural density and 3.10% to 7.23% on the urban arrangement as seen on the table. The calculated average is approximately 5.44% for all MV networks used in the model A weighted average (weighted by peak load of each case file) was calculated to provide an estimate of losses The box-and-whisker plot is shown The plot also indicate that there are outliers.

Topic Summary The methodology used in modeling energy losses in distribution networks The use of various tools in simulation of energy losses Interpretation of the results

Course summary Cost of supply study Energy losses in distribution networks The role of energy losses in cost of supply studies The methodology used in modeling energy losses in distribution networks The use of various tools in simulation of energy losses The interpretation of the results

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