Rehabilitation and Techno design of Distribution transformer and 11kV feeder of a radial distribution system

. In any transmission and distribution system-the performance of that system mainly depends on voltage regulation and efficiency. Hence for the better operation of the system, it is required to maintain constant voltage regulation with good power factor and low power loss throughout the feeder. This can be achieved by using various methods. Out of those, placement of a capacitor bank at the densely loaded areas is the best-proven method compared to any other method. This research work considered the feeder-5 of the Al-Uwainath primary substation which was suffering from low voltage–poor regulation-problems. Here in this research modeled and analyzed 3 different techniques for rehabilitation to this low voltage, poor regulation, and power factor problem and recommended the most efficient method out of the three methods. As a part of this project simulated the same conditions of the site after collecting the data of the feeder from the site by using ETAP software and checked the performance by calculating its voltage regulation, power losses, and power factor in all three 3 different methods and recommended the most efficient method of feeder-5 rehabilitation by comparing the results of three methods with the exciting system.


Introduction
In recent times, there has been a notable shift in the attributes of electrical load, resulting in a widespread prevalence of low power factor in diverse electrical apparatus such as mercury lamps, transformers, motors, and switchgear.This suggests that power supply authorities are required to deliver a far greater quantity of electric current than what is theoretically required.The existing high amount of electrical current in our system requires a decrease, and efforts should be made to improve the system's energy management skills while minimizing associated costs.Nevertheless, it is crucial to acknowledge that the distribution sector is presently experiencing a swift expansion, with utility providers primarily prioritizing the effective fulfillment of consumers' increasing needs.The rapid expansion has resulted in the emergence of the distribution system as the least efficient element within the power system [1].The transmission and distribution system plays a crucial role in facilitating the linkage between electricity-generating sources and end consumers.The evaluation of distribution systems and the assessment of service quality are contingent upon the absence of interruptions and the preservation of voltage levels at the customer's location that adhere to appropriate thresholds for this specific service.Therefore, it is a widely adopted practice in the electric utility industry to comply with the specified voltage levels and allowable ranges of deviation as stipulated by the Oman Electricity Standards, with the aim of ensuring the optimal performance of equipment.This is done to guarantee the effective operation of the power system.The prevailing voltage norms adhered by the majority of electric utilities in Oman, in order to cater to the needs of both residential and business consumers, are as follows: The electrical system under consideration is a single-phase, two-wire configuration operating at a voltage of 240 volts and 10.8 kV to 11.2 kV LT distribution system [2].
Initiatives aimed at reducing losses in distribution systems have been implemented in response to the escalating expenses associated with electricity delivery, the scarcity of fuel and its rising costs for power generation, as well as worries over global warming.Incentives and penalties have been implemented within the utilities sector as a means of promoting these approaches.In the present day, there has been a notable initiative in Oman to provide incentives to power distribution firms with the aim of mitigating both technical and non-technical losses in distribution.This initiative entails the implementation of a consistent yearly decrease rate over a span of six years.A thorough comprehension of the losses incurred inside the power system is necessary.The power losses that occur in distribution networks can be categorized into two distinct classifications: technical losses and non-technical losses [3].The notion of technical losses applies to the properties of materials and their capacity to hinder the passage of electrical current, leading to the dissipation of energy in the form of thermal energy.The most apparent examples are related to the loss of power in distribution lines and transformers due to their intrinsic electrical resistance.In addition, the simulation and calculation of technical losses can be easily performed [4].The losses incurred in transformers can be classified into two distinct components, namely the no-load losses and the load losses.No-load losses occur as a result of the energy expended in sustaining the fluctuating magnetic flux within the core of the transformer, irrespective of the magnitude of the load imposed on the transformer.Resistance losses within the conducting material of the windings are identified as the main factor contributing to load loss.The extent of this loss is influenced by the level of loading.[5] Hence, it is imperative to enhance the efficiency of the distribution system in order to attain advantages and guarantee sufficient power quality for consumers, thereby establishing a conducive setting for minimizing losses.
In many countries, the standard is the basis for that country's regulatory commission ruling on setting forth voltage requirements and limits for various classes of electric service.To maintain distribution circuit voltages within acceptable parameters, it is necessary to implement measures that enable voltage control.This entails raising the circuit voltage when it falls below the desired level and lowering it when it exceeds the desired level.Another potential option involves minimizing the length of cables used in the low-voltage distribution grid.Consequently, the impedance of the line connecting the consumer nodes and the substation is reduced, resulting in a decrease in the voltage drop or rise.Nevertheless, this approach entails a greater quantity of substations, necessitating further investments in equipment, property, the installation of medium voltage cables, and the implementation of more intricate protective mechanisms.[6] There exist a multitude of methods to enhance the overall voltage regulation of the distribution system.The choice of a technique or approach is contingent upon the specific system requirement.However, the provision of automatic voltage regulation is consistently ensured by: (i)Bus regulation at the substation.(ii) Individual feeder regulation in the substation, and (iii) supplementary regulation along the main by regulators mounted on poles.Distribution substations are typically outfitted with on-load-tap changing (OLTC) transformers, which are capable of operating autonomously when under load.Alternatively, these substations may be provided with separate voltage regulators that are responsible for ensuring bus regulation.Voltageregulating devices are engineered to automatically sustain a predetermined voltage level, which would otherwise fluctuate in response to changes in the load.As the electrical demand escalates, the regulating mechanism amplifies the voltage at the substation in order to counterbalance the augmented voltage decline in the distribution feeder.Supplementary regulation is provided through the installation of step voltage regulators or shunt capacitors at suitable points along the feeder in situations when consumers are situated at considerable distances from the substation or when there is a significant voltage drop along the primary circuit.Numerous utility companies have observed that the most cost-effective method of maintaining voltage levels within the prescribed limits is achieved by employing a combination of step voltage regulators and shunt capacitors.Sufficient quantities of capacitors are strategically positioned on the feeders and substation bus to achieve the desired economic power factor.A significant number of these facilities are equipped with advanced control systems that are specifically designed to facilitate automated switching operations.Feeder voltage regulators are widely employed for the purpose of individually regulating the voltage of each feeder, with the aim of ensuring a consistent and acceptable voltage level at the point of utilization.This improvement in voltage regulation of 11 kV feeder as well as the reduction in the feeder loss due to continuous increase in demand can also be obtained by reconductoring (changing OHL into UG cables) and by shifting the load to the neighboring feeder or transformers.Within this organization, a significant quantity of substations and feeders were discovered to be in a state of non-compliance with the Distribution System Security Standard (DSSS).As a result, a total of 33 projects have been proposed with the aim of ensuring that 29 substations and 28 feeders, which currently do not meet the prescribed standards, are brought into compliance and aligned with the Distributed System Safety Standards (DSSS).After thorough deliberation, it is advisable to address the issue of an 11kV feeder voltage level and losses as the primary subject of our research.This investigation focuses on the examination of the feeder-5 of 33/11kV substation situated in close proximity to Al-UWAYNAT after receiving the consultancy help request from the MJEC.This research assessed the design parameters and current loading on distribution transformers and low-voltage (LV) lines in the Majan Electricity Distribution Company (MJEC) service area.Current MJEC design practices are evaluated.Peak and minimum load data are captured.The sample network is modeled using ETAP or other load flow software.The objectives of this study are: 1. Capture the load for distribution transformers and LV lines.2. Evaluate the load in terms of voltage drop/quality, A/C motor starting capability, and system losses.
3. Analyze existing MJEC design practices in terms of design standards.4. Recommend new design practices to maximize the quality of electricity delivered to the consumer by employing the above three methods of rehabilitation

Methodology
The primary aim of this project is to establish a methodology and set of guidelines for distribution engineers.The purpose is to demonstrate that by mitigating energy losses within the distribution system as well as maintaining the good predetermined voltage regulation it is possible to preserve the system's available capacity without necessitating the installation of more capacity.A computer program with a generalized approach is utilized to assess and analyze HT/LT systems, providing recommendations for capacitor banks at various locations, suggesting different conductor sizes for different segments of the system and shifting of load from heavily loaded feeder or transformer to neighboring feeder or transformer.This leads to an enhancement in the system's stability and energy-handling capabilities while minimizing costs.The distribution system of Al-Uwainat feeder-5 experiences significant strain because of the continuously growing demand for power.Consequently, there has been a consequential shift in the characteristics of the distribution system, resulting in a negative impact on the dependability of power supply and the level of service provided to consumers.The current circumstances necessitate the prompt development of a strategic plan for rehabilitating the overloaded and overextended system in order to effectively accommodate the increasing demands on its capacity.The process for enhancing the system's capacity can be delineated as follows: 1. Acquisition of data pertaining to the specified power distribution system.2. The examination of the power distribution system considers several factors such as loads, voltage levels, conductor sizes, and current levels.3. The power distribution network in Al-Uwainat can be designed by employing computer simulation using ETAP software.This approach allows for the calculation of various system parameters, including power factor (both before and after the addition of kilovolt-ampere reactive power), voltage drops, and power losses.By analyzing these parameters, improvements in the system can be identified and evaluated.4. The determination of the precise rating and amount of capacitors necessary for enhancing the power factor, as well as the calculation of the length of the conductor that has to be replaced with a conductor of the appropriate size, can be accomplished using the aforementioned software.5. Enhancing Energy Efficiency via System Enhancements.The chosen feeder for this study is Feeder-5 which is suffering with low voltage and poor regulation problems due to its heavy load consequently facing the problem of continuous tripping of transformers that operates at a voltage level of 11 kV and originates from the Al-Uwainat substation.The feeder undergoes Rehabilitation Techniques, specifically bifurcation, re-conductoring, and capacitor bank installation.The ETAP Computer Software is utilized for the purpose of computing energy losses, and voltage drop.Figure 1 illustrates the flowchart outlining the sequential procedure employed to simulate the outcomes using ETAP software.The selection of a distribution network for rehabilitation is based on specific planning criteria, including factors such as voltage drop, power loss, and equipment loads.A planning proposal is created for each selected network in order to obtain the intended benefits of Energy Loss Reduction (ELR).The proposed approach involves area planning without the introduction of a new feeder, specifically focusing on redistributing the electrical load from heavily burdened feeders to neighboring feeders with lighter loads in close proximity.The implementation of HT shunt capacitors, whether fixed or switching, for electrical power systems.Reconductoring refers to the process of replacing an old conductor or wires with ones that have a higher capacity.The bifurcation of a feeder involves the addition of a new feeder in order to redistribute some of the loads from the existing feeder.The incorporation of new feeders in area planning.In certain instances, it may be necessary to engage in area planning at the grid station level in order to alleviate the burden on overcrowded grid stations.This is achieved through the redistribution of the electrical demand from heavily burdened grid stations to adjacent grid stations that are underutilised or recently established.The process of area planning may or may not encompass the incorporation of new feeders..The techniques used in the restoration of the LT Distribution System are as follows.
The present study focuses on the area planning of a low tension (LT) distribution system, specifically addressing the incorporation of additional feeders.In this scenario, the process involves the selection of severely loaded feeders, followed by the redistribution of their load to nearby lighter-loaded feeders or the introduction of new feeders.This redistribution aims to achieve load balancing among the feeders.In some situations, the implementation of feeder area planning is employed as a means to redistribute the load from one grid station to another grid station, in response to the excessive burden placed on the grid stations.This is achieved by the establishment of connections between the grids.This will not only alleviate the strain on the grid station equipment, but also accommodate the projected increase in load demand.The inclusion of new feeders is a variable factor in the process of area planning.
The installation of low tension (LT) shunt capacitors leads to a decrease in primary losses in high tension (HT) lines and an enhancement in voltage drop conditions.There is a slight reduction in losses observed in distribution transformers, low tension (LT) lines, and service cables [9][10][11].
The process of reconductoring a low tension (LT) line is typically undertaken in situations when the conductor's percentage loading exceeds the economically viable threshold or when there is a need to replace a damaged or improperly sized conductor with cables or conductors of different sizes.In such cases, it is more cost-effective to utilise conductors with larger cross-sectional areas.The replacement of current line conductors with larger-sized conductors or cables will lead to a proportional decrease in technical losses, based on the ratio between the resistance of the new conductors and the existing ones.It is fundamental to do a comparative analysis between the expenses associated with Reconductoring and the potential benefits derived from reduced losses, increased income, and alleviated distribution system capacity.The assessment of reconductoring should also consider the enhancement of power factor, voltage regulation, and the rise in demand throughout the conductor's lifespan.The data necessary for analysis has been compiled in the specified sequence within the ETAP software.This paper provides a summary of the total generation, loading, and demand in a given context.It can be noticed from the above summary table that, for the existing system the total demand is 3.229MW, 2.160 Mvar, and 3.885 MVA which represent the real reactive and apparent power for the feeder 5 of Al-Uwainatt Primary Sub-Station with a power factor of 83.11% lagging.Those results are the combination of Motor load and Static load.The motor load results is 2.558 MW, 1.586 Mvar, and 3.010 MVA with a power factor of 85 lagging.The static load results are 0.605 MW, 0.375 Mvar, and 0.712 MVA with a power factor of 85% lagging.From the previous results apparently, the power factor is decreasing by 1.93 with respect to the standards of IEC and MJEC, it should be remained at 85%.As rehabilitation to this under power factor, in the next three cases tried to improve the power factor and compared it with the existing system to choose the best one.

Discussion of Shifting Some of the Load to another Feeder
It can be noticed from the above summary table that, after shifting the load to a new feeder the total demand is 2.885 MW, 1.931 Mvar, and 3.472 MVA which represent the real, reactive and apparent power for the feeder 5 of Al-Uwainatt Primary Sub-Station with a power factor of 83.1% lagging.These results are the combination of Motor load and Static load.The motor load results are 2.288 MW, 1.586 Mvar, and 3.010 MVA with a power factor of 85% lagging.The static load results are 0.544 MW, 0.377 Mvar, and 0.640 MVA with a power factor of 85% lagging.

Discussion of Adding a Capacitor Bank in the Feeder
It can be noticed from the above summary table that, by adding a capacitor bank in the feeder the total demand is 3.230 MW, 0.314 Mvar, and 3.246 MVA which represent the real, reactive, and apparent power for the feeder 5 of Al-Uwainatt Primary Sub-Station with a power factor of 99.53% lagging.These results are a combination of Motor load and Static load.The motor load results are 2.558 MW, 1.586 Mvar, and 3.010 MVA with a power factor of 85% lagging.The static load results are 0.623 MW, -1.436 Mvar, and 1.566 MVA with a power factor of 39.82% lagging.

Discussion of Changing Over-Head Lines to Under-Ground Cables
It can be noticed from the above summary table that, by changing the OHL into UGC the total demand is 3.222 MW, 2.031 Mvar, and 3.809 MVA which represent the real, reactive, and apparent power for the feeder 5 of Al-Uwainatt Primary Sub-Station with a power factor of 84.59% lagging.These results are the combination of Motor load and Static load.The motor load results are 2.558 MW, 1.586 Mvar, and 3.010 MVA with a power factor of 85% lagging.The static load result is 0.616 MW, 0.382 Mvar, and 0.725 MVA with a power factor of 85% lagging.

Conclusions
The distribution system serves as the ultimate and pivotal component in the supply of electricity system, although regrettably, it is also the most weak.Consequently, it is imperative to identify and enhance the deficient electrical infrastructure within the distribution network in order to optimize its performance.This study examines three strategies, including shunt capacitor placement, reconducturing utilizing appropriate underground (UG) cables, and load shifting from strongly loaded feeders to neighboring lightly loaded feeders, in order to enhance the efficiency of the system.The various strategies were individually utilized, and the outcomes were evaluated through the utilization of ETAP simulation software.Among the three ways considered, it has been determined that the capacitor placement approach proves to be highly effective in improving the power factor from an initial value of 0.83 to a significantly enhanced value of 0.9953.Additionally, this method has successfully resulted in a reduction of losses to a magnitude of 0.544 MW.
The results obtained can be utilized to make the following implementations.In order to enhance the power factor of the system, it is advisable to install shunt capacitors at suitable locations within the network.In order to achieve a reduction in the length of low tension transmission lines, it is vital to consider the relocation of the current distribution substations.The timely disposal of outdated conductors and distribution lines is necessary, as only conductors and lines of suitable sizes should be utilized.The presence of extensive distribution lines results in elevated levels of technical losses, which necessitates their avoidance.It is crucial to make concerted efforts in order to prevent the occurrence of feeders becoming overloaded.This can be achieved by consistently maintaining balanced loads on the feeders.

Table 1 .
Displays the summary report