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Abstract— With the opening of Croatian electricity market the system operators are confronted with new obligations. One of them is the necessity to know customers’ load profiles, which are to be used for consumption planning and calculation of balance settlements. A method has to be implemented that would give a sufficiently accurate picture of hourly consumption of customers without appropriate meters. The paper presents currently used load profiles and the project that will establish Croatian standard load profiles.

Index Terms— Analytic approach, load profile, market

opening, synthetic approach

I. INTRODUCTION OAD profiling has always been of great importance. It has been used for consumption planning, billing and

distribution of balance settlement, as well as for system planning and maintenance [1], [2]. Besides, market opening sets new requests on transmission and distribution system operators, market operator, and suppliers. One of them is the necessity to know customers' load profiles [1]-[7]. Installing appropriate meters for time related (hourly or quarter-hourly) metering of all customers' consumption is a complicated and expensive process. Therefore, some customer categories are supposed never to have hourly metering.

Croatian electricity market is not yet fully opened. As of 1 July 2006 all customers with yearly consumption of 9 GWh or above are considered eligible customers [3]. According to [3] the electricity market will be fully opened starting 1 July 2008 when all the customers will become eligible and be able to change their supplier. With the market opening some new obligations regarding load profiles are set upon the system operators: − Producers, suppliers and traders are obligated to send the market operator their hourly commitments of production, consumption, purchase or sale [4]. In order to form hourly consumption plans for customers without hourly metering of consumption, it is necessary to know their standard load profiles. − The market operator calculates and performs balance settlement based on aforementioned hourly commitments and metered values collected by the system operators. Precise

Manuscript received March 2, 2007. T. Marijanić and D. Karavidović are with the HEP-Distribution System

Operator, Zagreb, Croatia. (e-mail: tanja.marijanic@hep.hr, damir.karavidovic@hep.hr).

prediction of load profiles is crucial for fair balance settlement.

Reference [5] defines the transition period lasting until 31 December 2008 during which all functions of completely opened electricity market are to be established.

The obligation of the distribution system operator is to produce standard load profiles and rules for their application during the transition period [5]. These profiles must be produced for customers without hourly metering of consumption.

A unique load profile will be used for consumption planning until the beginning of the application of standard load profiles [5].

II. LOAD PROFILING A method that gives an approximately accurate picture of

customers' hourly consumption must be chosen for production of standard load profiles. There are two basic methods for definition of standard load profiles [6], [8]: − Analytic approach ("top-down" approach, area or regional model), − Synthetic approach ("bottom-up" approach, customer-group-related model).

According to [5], during the process of market opening (until 31 December 2008) standard load profiles given by the "top-down" approach will be used. Standard load profiles derived from the "bottom-up" approach will be used after that.

A. Analytic approach Analytic, or the "top-down" approach for determining

standard load profiles starts from the total hourly input into the distribution network. Expected distribution network losses are deducted from this profile. All known (metered) consumption is also deducted. This residual profile, also known as the rest curve or the adjusted system load profile (ASLP), is then distributed among all customers without hourly metering [6], [8]. Fig. 1. presents an example of forming an adjusted system load profile based on data for the last known year [9]. This profile is distributed among various suppliers and customers by percentages of their yearly not-hourly metered consumption.

Load Profiling in an Opening Electricity Market Tanja Marijanić, Damir Karavidović

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1) Analytic approach for Croatian power system The process of obtaining Croatian adjusted system load

profile slightly differs from abovementioned. Total load profile, i.e. total hourly input into the Croatian power system for the representative day is shown in Fig. 2 [1]. Adjusted system load profile is obtained by deducting the expected transmission and distribution network losses.

This adjusted system load profile is distributed among suppliers or customers based on their proportion in total yearly consumption. Therefore, all customers without hourly metering of consumption have the same profile, scaled by their yearly consumption [9]. Fig. 3. presents an example of the load profile for the representative day of a customer with yearly consumption of 100.000 kWh.

Hourly metering of consumption of all high voltage and medium voltage customers, as well as low voltage customers having a demand of 30 kW or above will be implemented as soon as possible [11]. This consumption will then also be deducted from the total system load profile that will make the adjusted system load profile more accurate.

2) Benefits and challenges of adjusted system load profile The main advantage of this model is instantly available data

sufficient for definition of load profiles. This makes the process less costly; there is no need for supplemental metering neither complex IT support.

There are some risks associated with this procedure. Load

profiles may not be accurate enough for the individual customer. This may present a problem for the suppliers of specific groups of customers whose load profiles considerably differ from the adjusted system load profile. This leads to higher settlements.

Network owners are not exposed to risks associated with the adjusted system load profile.

B. Synthetic approach With synthetic approach there is no unique load profile for

all customers. Each customer is assigned a standard load profile depending on consumption characteristics. Standard load profiles are common for groups of customers with similar consumption. Load profiles are normalized to specific yearly consumption (usually 100.000 kWh) f6]. The customer’s load profile is then reconstructed using ones expected yearly or monthly consumption [1], [6], [12].

Obtaining standard load profiles demands extensive research. It is necessary to meter consumption of a representative customer sample for at least a year. At this point the research becomes extremely complicated.

Choice of the representative customer sample is the first challenge. The solution starts with preliminary definition of customer categories. Elementary categories are households and commercial customers. Load profiles of households differ with regard to their standard, socio-economic activities, means of space and water heating, and their geographic location in the system. Commercial customers’ load profiles vary with the type of commercial activity and location.

Customers’ yearly consumption must be taken into account. Yearly consumption varies from just a few thousand kilowatts to a few hundred thousands kilowatts or more. Thus, regarding their yearly consumption, customers should also be divided into consumption classes.

Obviously, there is a risk of introducing too many customer categories and subcategories, which would make the research and later application complex and expensive. Therefore, the number of categories needs to be limited to a reasonable figure.

The next step is sizing the customer sample. Larger

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Fig. 2. Adjusted system load profile of Croatian power system for therepresentative day

Fig. 1. Adjusted system load profile and other components of electricity use

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customer sample increases the profile accuracy. It also increases the cost of the research.

In the end, the research can still fail, as chosen customers might not be representative of their customer group.

1) Risks associated with category-based load profiles With this model it is possible to achieve higher accuracy.

The customer composition is taken into account for each supplier, enabling more precise distribution of balance settlement.

Complexity and expensiveness are flaws of this model. It is necessary to conduct a long lasting research and metering on a big number of sites (customers). The cost of the research increases with the necessity of procurement of appropriate meters and implementation of remote or local meter reading system and complex IT support.

Increasing the number of customer categories, i.e. standard load profiles increases the accuracy level. This also increases the cost of research.

After investing great resources, there is a risk of inaccurate load profiling caused by choosing inadequate customer sample for the research.

III. PROJECT TO PRODUCE CROATIAN STANDARD LOAD PROFILES

The process of determining standard load profiles in Croatian distribution system operator began immediately after new laws and regulations have been passed [3]-[5].

Having in mind above mentioned risks and their possible consequences, special attention is given to the choice of representative customer sample. In order to choose the right customer it is necessary to understand which factors determine customers’ load profiles.

A. Determining factors The main categories of low voltage customers without

hourly metering are households, commercial customers and public lighting [1], [7], [12]. − Household load profiles are certainly determined by: − Geographic location in the system, − Alternative energy sources, − Rural or urban features, − Specific household appliances.

Commercial customers’ load profiles are mainly influenced by their type of commercial activity. With this customer category the location is less important however it should not be disregarded.

Public lighting is the simplest customer category. The sole influential factors are installed capacity and duration of operation. Load profile is practically rectangular.

Along with the customers' characteristics, load profiles are determined by the type of day (weekdays, weekends) or season of the year [1], [2]. For example, the shape of the load profile of a customer group for working days will differ from the one for weekends. On the other hand, this may not be the case with another customer group.

Customers' consumption also changes with temperature. This too has to be taken into account and temperature has to be measured along with the consumption. Average temperatures can later be used to modify the standard load profiles.

B. Selection of customer sample and specific customers for the research According to [13] the composition of low voltage

customers connected to the Croatian distribution network is: − 1.962.554 household customers, − 19.103 customers of the public lighting category, − 164.551 commercial customers having a demand below 30 kW, and − 10.983 commercial customers having the demand of 30 kW and above.

Therefore, the standard load profiles must be applicable for 2.146.208 customers, as commercial customers having a demand of 30 kW and above are soon to have hourly metering [11].

It is necessary to find the optimum sample size, as detailed research leads to sizable costs. With the number of customers in need of standard load profiles being 2.146.208, the number of 1.600 customers is chosen for the research, to whom meters for hourly metering of consumption will be installed.

The next step is the selection of specific customers. It is not enough to install the chosen number of meters, so in order to determine the most influential customer categories and subcategories, more data must be taken into account, such as: − Total number of customers per category, − Total consumption of all customers per category, − Number of customers per consumption class, − Consumption of all customers per consumption class.

Prior to meter installation on specific sites, a survey must be conducted with the customers. The goal of the survey is to collect information about customers' energy consumption. Understanding the nature of customers' energy consumption ensures that any particularities are taken into account. Being aware of the components of customers' energy consumption helps avoiding inadequate customer sample choice for the research.

Once the necessary equipment is installed, the research sample will remain in place after the end of the project as to verify the obtained load profiles.

C. Application of standard load profiles As mentioned before, in fully opened electricity markets

standard load profiles are used by market participants to form hourly commitments of production, consumption, purchase or sale of energy. The standard profiles together with metered values collected by the system operators are also used to calculate balance settlements.

Once defined, standard load profiles will be unchanged for at least a year. They can only be scaled according to actual temperature.

A set of rules for application of standard profiles must be

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set up. Those rules should regulate assignment of profiles to existing customers as well as to new customers.

IV. CONCLUSION By abovementioned laws and regulations, we are obliged to

use analytic approach until full market opening, and after that load profiles derived from synthetic process. Forming load profiles by synthetic process is a great challenge set before the distribution system operator. The success of the synthetic process will be known only after a year of application of the load profiles has passed.

Our project will be successful only if the new load profiles will match customers' consumption better than the adjusted system load profile does. This will be demonstrated by fair distribution of balance settlements.

In the end, the only real goal is to get the market going.

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