Development of a Macro-level Approach to Estimate Technical Losses in Malaysia Distribution Network

Transcription

1 Development of a Macro-level Approach to Estimate Technical es in Malaysia Distribution Network Asnawi. Mohd Busrah, Mau Teng. Au, and Ching Hooi. Tan Abstract This paper describes the macro-level approach in estimating technical losses of Malaysia distribution system and its components which consist of medium voltage (MV) and low voltage (LV) feeders, MV power and distribution s. Based on this approach, web based software to estimate technical losses of distribution system is developed incorporating analytical equations developed in this study. The developed software which applies the macro-level approach is proved to be efficient and capable of providing an accurate indication of the overall technical loss level of a distribution system and also its components. I Keywords technical losses, peak power loss, load loss I. INTRODUCTION N 1, the total distribution losses estimated by Malaysia power utility, Tenaga Nasional Berhad (TNB) is.9 %. There is a high value proposition for reducing losses since a 1% reduction can generate estimated savings of between RM5 to RM3 million annually to TNB. Before any concrete mitigation effort is taken to reduce technical or non technical losses in distribution system, there is a need to first establish the accurate technical loss level of the distribution system. This study is proposed to further strengthen the estimated figures on technical losses based on the analytical model. An enhanced software or tool for technical loss estimation in distribution system is developed to improve the current tool in Excel Spread Sheet format. Theoretical calculations of technical losses in distribution system are generally well established. In almost all approaches used in the calculation of technical losses of large distribution system, the main challenge has been the availability of extensive data required. In [1], energy loss in power system elements were determined based on typical load curves using statistical mathematics which organize the entire data into statistical moments needed to calculate energy losses. This technique is faster than direct techniques using simulations. In [], a top down/bottom up approach is used when a complete set of modeling data is not available. In the top down approach, explanatory variables, such as kilowatt-hour per customer and number of customers per feeder length of feeder are used to determine loss ratio. The loss ratio is then used to compare closeness of the distribution system to other distribution system whose characteristics are known with certainty. Asnawi. Mohd Busrah, Mau Teng. Au, and Ching Hooi. Tan are with TNB Research, Malaysia. This approach is similar to bench marking technical losses of a distribution system with an established distribution system. In bottom up approach, a complete and detail system planning is modeled using specialized software extensive data to determine technical losses. The main advantage of the top down/bottom up approach is that it can handle varying degrees of data availability. In [3], energy and demand losses were calculated using percent loading on the different components of the distribution systems. In this system wide energy flowing through a distribution system component is divided by the system wide energy handling capacity of the component for the period of time the losses are calculated. In [4], technical losses in distribution system losses are calculated using loss adjustment factors and loss factor. This approach requires extensive data. Most of the techniques mentioned above engage a lot of mathematical manipulations and rely on extensive data input and accuracy of the system models to compute technical losses, particularly for large utility distribution network. The results obtained from these techniques are proven to be good but they need high computational time and voluminous load data. II. TECHNICAL LOSSES ESTIMATION IN DISTRIBUTION SYSTEM In previous studies, simplified methods and methodology to calculate technical losses for TNB distribution system and its components are established by considering feeders and customer load characteristics [6]. Typically, load losses of feeders are calculated under peak demand condition using load flow simulation software. The associated energy losses, E are then calculated using Factor, F and Peak Power, PP as shown in following equation. E = (PP ) (F) 3 4 hrs (1) F in (1) is calculated from its load factor,lf using the following equation: F = α LF + β LF () where α and β are the loss coefficients which need to satisfy the conditions,. α. 15 and β = ( 1 α). A. Technical in Underground Cables and Over Head Lines Power loss in underground cables and overhead lines are primarily due to load losses. As the power loss varies with the square of current, the amount of current flowing in the cable

2 will have the highest impact on the energy loss in cables and overhead lines. Fig. 1 shows the power loss of 11 kv, 4 mm XLPE Aluminum cable varies with different capacity factor. Power [kw] L=1 km L= km L= 3 km Capacity Factor L=1 km L= km L= 3 km Fig. 1 Power Variations with Capacity Factor of XLPE 11 kv, 4 mm Al cables Following Table I shows a sample calculation of technical losses in the single 11 kv cable using the relevant parameters. TABLE I TECHNICAL LOSSES OF A 11 KV UNDERGROUND FEEDER Cable & Load Parameters Feeder length (L) [km] Cable Capacity [MVA] 6 11kV, Al XLPE 3C 4 mmp. Capacity factor at feeder peak demand (CF).5 Peak demand is 3 MVA,.9 pf lagging Factor (LOF).384 Refer Equation () Peak Power (PPL) [kw] 5.3 Refer Figure 1 Energy es through cable over a 3 days 6,9.9 Refer Equation (1) Energy Supplied through cable over a 3 days Technical es of Cable [%] 5.3 1,166,4 Equation; (No of Fdrs)x(CF x Cable Capacity x pf x LF) x 4 x 3 E ( P + (CF) (P )(F))(4 3) Tx = no load full load TABLE II REDUCTION IN TECHNICAL LOSSES OF UNDERGROUND CABLES WITH AN ADDITIONAL FEEDER (LOAD SPLITTING) Cable & Load Parameters Average Feeder length (L) feeders of km each [km] Cable Capacity [MVA] 6 11kV, Al XLPE 3C 4 mmp. Capacity factor at feeder peak demand (CF) (4).5 feeders of km each, assuming coincident factor =1. Factor (LOF).384 Refer Equation () Peak Power (PPL) [kw] 5. Refer Figure 1 Energy es through cables over 3 days period 9,141. Refer Equation (1) Energy Supplied through cable over 3 days period Technical es of Cable [%].5 1,166,4 Evaluate using; (No of Fdrs)x(CF x Cable Capacity x pf x LF) x 4 x 3 In (4), the loss factor is not applied to the no-load loss as these losses are not dependent on loading. Fig. shows the variation in load and no-load loss for 11/.4 kv s of capacity ranging from 1 kva to 1 kva. Power (kw) y =.6x + 1. y =.1x +.39 No Load Load Linear (Load ) Following Table II shows a sample calculation which results in a reduction in technical losses by supplying the same load through two cables Transformer Capacity (kva) B. Technical in Power and Distribution Transformers Power losses in s are contributed by load losses and core losses [6-8] as in following equation: PTx = P no-load + (CF) (P full-load where, CF is the capacity factor of a. Capacity factor is ratio of s peak demand and its rated capacity. It follows that to estimate energy loss of s, ) (3) Fig. Power with Respect to Transformer Capacity Table III shows a sample calculation of technical losses for a single 5 kva, 11/.4 kv using the relevant parameters. 3

3 TABLE III TECHNICAL LOSSES OF A 11/.4 KV, 5 KVA TRANSFORMER Transformer & Load Parameters Transformer Capacity [kva] 5 11/.4 kv distribution Capacity Factor (CF).5 Peak demand is 5kVA,.9 pf lagging Factor (LOF).384 Refer Equation () No Load [kw] 1. Refer Figure Load [kw] 4. Refer Figure Peak Power (PPL) [kw]. Refer Equation (3) Energy es through over a 3 days Refer Equation (4) Energy Supplied through over a 3 days Technical es of Transformer [%] 9,. Evaluate using; (No of Tx)x(CF x Average Tx Capacity x pf x LF) x 4 x 3 1. medium voltage (MV) feeders, Power Transformers, Distribution Transformers and low voltage (LV) network, as well as the whole distribution network is developed in this study. In the TNB system, power and energy supplied to the distribution network is registered by the respective energy meters installed at the 13/5kV main intake substation. MV and LV feeders are normally not installed with energy meters. Hence, the general principle behind the approach taken in estimating technical losses of a distribution network is by taking the amount of power and energy which are recorded at each substation and dividing them in the distribution network that draws power from that particular substation. Fig. 3 visualizes the energy flow from main intake substation to LV networks in TNB. When more s are used to supply the same load, theoretically there will be an increase in technical losses. This is envisaged in a sample calculation in Table IV. TABLE IV INCREASED IN TECHNICAL LOSSES OF TRANSFORMERS WITH (N-1) REDUNDANCY Transformer & Load Parameters Average Transformer Capacity [kva] 5 x 5 kva, 11/.4 kv distribution Capacity Factor (CF).5 Peak demand is 15kVA,.9 pf lagging for each Factor (LOF).384 Refer Equation () No Load [kw] 1. Refer Figure Load [kw] 4. Refer Figure Peak Power (PPL) [kw].5 Refer Equation (3) Energy es through units of s over 3 days 1,58.4 Refer Equation (4) x Energy Supplied through units of s over a 3 days Technical es of Transformer [%] III. 9,. Evaluate using, (No of Tx)x(CF x Average Tx Capacity x pf x LF) x 4 x MACRO LEVEL APPROACH IN ESTIMATING TECHNICAL LOSSES OF DISTRIBUTION SYSTEM Typically, hundreds of kilometers of feeders and s are connected to each main intake substation. Due to the vast numbers of feeders, sub-substations, diversity of customers and load patterns, it is not feasible to either to measure or to calculate the losses of each feeder or. Hence, a macro level approach to determine technical losses of each network components which are Fig. 3 Energy Flow from TNB Main Intake Substation to LV Networks A. Estimation of Technical es of Medium Voltage Network Peak demand recorded at the main intake substation is essentially the sum of power demand of all MV feeders taken at the time when peak demand occurs at the power s (e.g., 5/33 kv, 13/11 kv, etc) of the substation. In general, peak demand of the MV feeders is likely to occur at different time, depending on the customers load profile. Hence, in order to determine the peak demand of m numbers of individual MV feeders, MDMVFdr from the recorder peak demand at the substation MD PMU, a coincident factor (CIF) is applied based on the following, 4

4 MD MVFdr MD PMU = m CIF Table V shows a sample calculation of technical losses for eight numbers of 11 kv feeders using this approached. TABLE V TECHNICAL LOSS CALCULATIONS FOR EIGHT (8) 11 KV FEEDERS Input 11 kv Network & Load Parameters Peak demand recorded at PMU [MW] 1.8 Energy recorded at PMU [MWh] 5,59.6 Load Factor at PMU.6 Power Factor recorded at PMU.9 Total Number of MV Feeders Connected to PMU 11 kv Bus (m) 8 Coincident Factor (CIF).8 Total Feeder Length (L) [km] 1 Cable Capacity [MVA] 6 11kV, Al XLPE 3C 4 mmp. Power Factor at Feeder (pf).9 Technical Calculations of 11 kv Feeders Peak demand per Feeder (MD) [MW]. Refer Equation (5) Energy per Feeder [MWh] 691. Average Length per Feeder [km] 15 L/m Load Factor of Feeder (LF).48 Capacity Factor at Feeder Peak Demand.3 MD/pf (CF) CF = 6 Factor (LOF).55 Refer Equation () Peak Power (PPL) per Feeder [kw] 11.4 Refer Figure 1 at CF =.3, L= 15 km Energy es through 8x11 kv feeders over 3 days Energy Supplied through cables over 3 days period [MWh] 148,936. Technical es of 11 kv Feeders [%].69 (5) Refer Equation (1) x no of feeders 5,59.6 Evaluate using; (No of Fdrs)x(CF x Cable Capacity x pf x LF) x 4 x 3 B. Estimation of Technical es of Transformers Theoretical calculations of technical losses for s have been discussed earlier by utilizing (), (3) and (4). Continuing from the example as in Table 5, the net power and energy feeding the distribution s is the power and energy supplied to the eight numbers of 11 kv feeders from the substation minus the technical losses that occur in the 11 kv feeders. A sample calculation to illustrate the approach is shown in Table VI. TABLE VI TECHNICAL LOSS CALCULATIONS FOR THE SIXTY-EIGHT (68) 11//4 KV TRANSFORMERS Input Transformer & Load Parameters Total peak demand of s x 8 MW [MW] Energy supplied [MWh] 5,38.6 Total number of s 68 Total capacity of s [kva] 54, Coincident Factor (CIF). Power factor (pf).9 Technical Calculation of Transformers Capacity per [kva] 9 Peak Demand per [kva] 355 Capacity Factor (CF).445 Load Factor (LF).344 Factor (LOF).14 Refer Equation () No Load [kw].83 Refer Figure Load [kw] 3.13 Refer Figure Peak Power (PPL) [kw] 1.44 Refer Equation (3) Energy through 68 units of s over 3 days period Energy Supplied through 68 units of s over a 3 days period [MWh] 44,54. 5,38.6 Technical es of Transformer [%].88 Refer Equation (4) Evaluate using; (No of Tx)x(CF x Average Tx Capacity x pf x LF) x 4 x 3 C. Estimation of of Technical es of Low Voltage (LV) Network Peak power loss equations for LV feeders are obtained based on a typical feeder consists of 5 meters 185 mm aerial bundled conductor (ABC) and 5 meters 95 mm ABC connected to evenly distributed loads. For LV underground cable systems, peak power loss equations are obtained based on meters of 4 mm Al cable with loads connected at mid-point and end of feeders. IV. DEVELOPMENT OF TECHNICAL LOSSES ESTIMATION SOFTWARE Based on all equations, formulas and methodology described earlier, web based software that runs on Microsoft Asp.net technology is developed to estimate technical losses in distribution system and its components. Fig. 4 shows the main page of the software. The program is structured to compute technical losses of distribution systems and its components based on energy and peak power demand recorded by energy meters at individual main in take substation. Users are required to input and update network and load parameters, total energy and maximum demand of bulk customer sales, as well as distributed generation (DG) to compute technical losses of the distribution systems at respective districts and state. With this web based software, energy data from the main intake substation can be imported from TNB metering web. 5

5 E. User friendly and simplified process, This web-based software promotes simplified flow/process compared to conventional excel method. It reduces number of inputs as system will do most of the calculation. This will eliminate and minimize human errors. Fig. 4 Web Based Software to Compute Technical in Distribution Network Technical losses of individual components and the distribution systems are calculated using previously discussed analytical equations build into the program. The program is able to generate reports of individual system components and distribution system according to the respective main in take substations, districts, states, and for the whole of TNB distribution system. This will allow regular monitoring of technical losses at component and system levels for all the districts and states, and initiation of mitigation plan. The web based software developed in this project has a number of new, advanced features as described below: A. Centralized reporting feature This feature promotes ease of reporting. It allows the higher level of authorized user to view the report, i.e. State user could view District report; Regional user could view State and District report: Head Quarters users can view all reports. B. Central database repository This feature reduces data redundancy whereby user would be able to keep track of the latest data entry. C. Maintains data integrity This important element maintains formula consistency. Users are not allowed to change the formula and it is centralized for the whole peninsular Malaysia. The new software also has capability to eliminate duplicates report. Only the latest data is stored. User could always update their data and system will recalculate and reflect the latest changes in the reporting module. D. Automation of energy data Energy data at substation is imported from TNB Metering web database. This feature automates the energy data entry, while eliminating human errors and mistakes. V. CONCLUSION The web based software developed in this study has proven to be useful and efficient after going through a few rounds of User Acceptance Tests (UAT). In general, the software is well received by users at all levels, from District to Head Office of TNB Distribution. A series of sensitivity tests have been carried out by varying different network and load parameters to validate that the program generates results of technical losses which are in agreement with theoretical principles and system characteristics. By performing case study using real data and network, the technical losses of distribution systems estimated using the web based software are within typical range of between 3.% and 1.% which is consistent with technical losses of distribution system of other electric utilities. ACKNOWLEDGEMENT The authors gratefully acknowledges the financial support of TNB Research for this project, and System Planning and Development Unit of Asset Management Department TNB Distribution for their constructive ideas and feedback in carrying out the development of the software. And also, staff of TNBD Bangi, TNBD Rawang and Protection Department of TNBD Selangor for their assist and support in field measurement exercise. REFERENCES [1] A. L. Shenkman, Energy loss computation by using statistical techniques, IEEE Transactions on Power Delivery, Vol. 5, No 1, January 199. [] C A. Dortolina and R. Nadira, The loss that is unknown is no loss at all: a top down/bottom up approach for estimating distribution losses, IEEE Transactions on Power Systems, Vol., No., May 5. [3] D. L. Flatten, Distribution system losses calculated by percent loading, IEEE Transactions on Power Systems, Vol. 3, No. 3, August [4] J. J. Grainger and T. J. Kendrew, Evaluation of technical losses on electric distribution system, CIRED [5] Electricity Distribution es, A Consultation Document, January 3. [6] M. Yusoff, Analysis and development of improved methodologies for technical losses estimation in tnb distribution system (TNB 698/), TNBR Final Report 9 [] M. T. Au, M. Mohamad, A. Busrah and M. Yusoff, A simplified methods in estimating technical losses in Malaysia distribution network, WSEAS Conference 1, Penang, Malaysia. [8] M. T. Au, T.M. Anthony, N. Kamaruddin, R. Verayiah, S. A. Syed Mustaffa and M. Yusoff, A simplified approach in estimating technical losses in distribution network based on load profile and feeder characteristics, PECON 8, Johor Baharu, Malaysia 6