Utilizing Load and Loss Factors in Determination of the Technical Power Losses in Distribution System’s Feeders: Case Study

This study uses load factor and loss factor to determine the power losses of the electrical feeders. An approach is presented to calculate the power losses in the distribution system. The feeder’s technical data and daily operation recorded data are used to calculate and analyze power losses. This paper presents more realistic method for calculating the power losses based on load and loss factors instead of the traditional methods of calculating the power losses that uses the RMS value of the load current which not consider the load varying with respect to the time. Eight 11kV feeders are taken as a case study for our work to calculate load factor, loss factor and power losses. Four of them (F40, F42, F43 and F45) are overhead lines while the others (F185, F186, F187 and F188) are underground cables. The greater differences between their losses were obtained, due to various types of route length, type, and dimension of conductors. The study takes different configuration feeders for computation with determination in power losses.

Minimizing energy losses strategy has been used by (Hamed Emara Kassem, et al., 2013) for the electrical distribution network based on Genetic Algorithm. Their results showed that the multi criterion algorithm has succeeded to reduce technical losses for all sample networks to reach the acceptable limit. Finally, (Sarang Pande, and Prof. Dr. J.G. Ghodekar, 2012) presented a method for energy loss calculation that demonstrates the capability of Load factor and load loss factor to calculate the power losses of the network, where the results obtained can be used for tariff process.

METHODOLOGY
Iraq-slemani Azmer and kampy zanko substations 11kV feeders are taken as a case study for this work to calculate load factor, loss factor and power losses. Azmer substation, shown in figure .1, 11kV feeders (F40, F42, F43 and F45) are overhead lines, while kampy zanko substation shown in Fig.2 11kV feeders (F185, F186, F187 and F188) are underground cables. The study takes different configuration feeders for computation with determination in power losses. About more than 30 years passed over Azmer substation 11kV feeder's installation. While kampy zanko substation 11kV feeders are much newer compare to Azmer substation 11kV feeders that about less than 10 years. For the mentioned reasons this paper took these feeders as a sample of the study among the existing feeders of Slemani city distribution network. The data of daily loads are taken from data center of Slemani Communication and Control Directorate, and the route length of 11 kV feeders, type and dimension of conductors are taken from Slemani General Directorate of Electricity.  The obtained data (Minimum loading, Maximum loading and Average loading) are calculated from the daily load data. The load Factor, Loss Factor and Power Losses are calculated according the equations of later sections, and MS Excel package is used as tool for calculating of the obtained data and charts.

EQUATIONS OF LINE LOSSES
The main reason for losses in transmission and distribution lines is the resistance of conductors against the flow of current. The creation of heat in conductor as a result of the flow of current increases more temperature in it. This increase in the conductor's temperature further increases the resistance of the conductor and this will therefore rise the losses. This indicates that ohmic power loss is the main component of losses in transmission and distribution lines. The value of the ohmic power loss, is given as (1) The resistance (R, in Ω) of the line is given as: Where IL: Indicates current along the conductor. R: Indicates resistance of the conductor. ρ: Is the resistivity of the conductor, l: Denotes the length of the conductor and A: Denotes the cross-sectional area of conductor. Feeder losses were computed using maximum return on loading of feeders considering the place of loss factor Mufutau, W.O., et al., 2015. The value of the current at all times is less than the maximum current. Due to this, the computation of feeder losses employs the loss factor approach.
Upon considering loss factor, eqn. (1) becomes: (2) and the route length of 11 kV feeders, type and dimension of feeder conductors that taken from Slemani General Directorate of Electricity, the result is as shown in Table (1).  Table (2) - Table (9). The Load Factor, Loss Factor and Technical loss in the system were computed using power factor of 0.8 and Eq.
(2) -Eq.(5).  The results are as presented in Table (10) - Table (17). The yearly average maximum loading and the average power losses on the feeders are presented in Table (18) and Table ( 19). For the sake of clearness, simplicity of observation and comparison of power losses, the obtained results that presented in Table (10) - Table (19) were also shown on the Fig.3 -Fig.12 respectively.  Fig.3, which represents the power losses of three years for Azmar substation that, supply residential and tourism areas which are very active on summer times so it is clearly seen that the power losses for the feeder F40 is much more than the other feeders of the the corresponding summer months. On other hand, the same case can be seen in Fig.7, where the feeder 185 is feeding University of Sulaymaniyah and it its maximum power losses on June among 90 the other months because June the most active month in the university which is the month of the final examinations and all halls are occupied, so the load is at its maximum values. In Figs.8, and Fig.10 it is also seen that the power losses is dramatically reduced in 2016 and 2017 compared with 2015 due to the fact that the a new power factor compensators has been installed across the feeders 186, and 188 Referring to Table (10) to Table 19, the obtained results have been analyzed. We have observed that the losses on Azmer feeders are much greater than Kampy Zanko feeders. Where, Kampy Zanko feeders are newer and they were installed underground thus the corona losses would be omitted. Also, Kampy Zanko feeders' line cables are made of copper, which result in lower resistivity than Azmar aluminum conductor made lines. Moreover, Kampy Zanko feeders feed approximately a constant load (University campus), while Azmar feeder feeds different residential loads.

CONCLUSION
The calculation and determination of technical power losses of some different 11 kV feeders of two power substation of Slemani Distribution System has been performed in this paper using load factor and loss factor approach. The results show that some feeders have highest average power losses due to their long route, overhead construction and the nature of the connected load. According to the fact that amount of power is lost in power system, the losses can be minimize by using the several techniques like Power Capacitor installation, Transformer Relocation, and Load Balancing. For the current case study, minimize the power losses of feeders can be achieved by decreasing the route length of feeders and distinguish the feeders based on the nature of load (commercial, residential, industrial, or other).