Substation plays an important role among generation, transmission and distribution system. Electrical power that flows through several substations may be at different voltage levels from generation to consumers end in a network. A substations primary function is to transform voltage levels from high to low and vice versa keeping constant power flow. It works like a hub in the power system among the electrical gene- ration plants, transmission lines and distribution system. Distribution system consists of several components, that work together to transfer and distribute power to the end users. End users consume electrical energy in the form of current through electrical loads. These electrical loads, which can be categorized as resistive, capacitive and inductive loads, are generally referred to linear and non-linear loads. Linear loads only consume electrical energy whereas non- linear loads also generate energy and create power factor problem by returning the energy to the source in a network (Witherden et al., 2010). 

A proper design approach is vital for ensuring reli- ability and quality of power supply, keeping the vol- tage and frequency fixed while satisfying the demand. These conditions can be achieved by load flow studies performed utilizing dedicated computer aided programs (Pai, 2014). Various factors like maintain- ability, simplicity of operation, safety, economy, international code, recommended practices and stan- dards must be taken into consideration in the design phase (Kezunovic et al., 2010). Location of the pro- posed substation, single line diagram, full details of electrical equipment to be installed, layouts of equip- ment and provision for metering units, arrangement for voltage regulation, and power factor improvement (PFI) plant should also be considered.

Load Flow Analysis

Load flow study is the best approach to find out the voltage, current, power at any point under normal or fault conditions in a system. The available tools for load flow analysis are Newton-based load flow solu- tion, conventional Newton method, Newton-Raphson method, Fast Decoupled method, Gauss- Seidel met- hod, etc (Stott, 1974; Stott & Alsac, 1974). Load flow analysis provides information about power gener- ation, delivery, losses occurred in the network, branch current, voltage on buses, active, reactive and apparent power, etc (Katira and Porate, 2009). Load flow analysis reports are also required for operating the existing system satisfactorily and for the future expansion of the network (Ademola & kareem, 2014). 

Power Flow Analysis using ETAP Software

ETAP is an analyzer program containing document- tation elements and task-oriented program modules, which uses the Newton-Raphson method for ana- lyzing the load flow. ETAP is faster than real-time and gives accurate, precise, and reliable outcomes (Baby & Sreekumar, 2017). The analysis provides steady-state characteristic data of active power, reac- tive power, voltage magnitude, voltage phase angles, system losses, and power consumption (Hasan et al., 2020; Shahriari et al., 2012). 

ETAP monitors the system network ac- curately and generates a detailed and organized representation of the output result (Ijeoma & Olisa, 2019). The obt- ained results from the analysis help to check the system voltage profile, phase angles, trans- former loadings, system losses, and contribution of our optimization technique (PFI plant) in system im- provement. 

Objectives

The main objective of this paper is designing and simulating 2500KVA 11/.04 kV substation and ana- lyzing the output data using Load Flow Result Ana- lyzer, overcoming the voltage regulation problem, and improving the power factor for an optimal, safe, and reliable power system.

Load flow simulations give us result on one-line diagram and generate tabulation reports of calculated bus voltage, its magnitude, angle, currents, and power flow through the electrical network etc. We analyzed the output data for different values of equipment by using ETAP Load Flow Result Analyzer, which presents data in a compact and summarized way (Chandan et al., 2017).

Simulation before Application of PFI Plant

Fig 3 & 4 shows the sub-stations one-line diagram before applying the PFI plant. By performing analysis using ETAP simulation, the result shows that the percentage (%) voltage regulation (drop) across the 2500 kVA transformer is 4.37, input power to the bus  no. 03 is  (1956+ j1323) kVA, and the total power factor is 82.83%, which accounts for the high power losses, and voltage drop.

Simulation after Application of PFI Plant

Fig 5 shows the load flow analysis after the injection of the capacitor bank into the network. The PFI plant consists of a total capacity of 1200 kVAR capacitors, which are in delta connection. After applying the capacitor bank, the systems voltage profile and power factor improved drastically, and total losses of 

the system reduced significantly. The power level to the network improved from (1956+ j1323) kVA to (1978 + j171.3) KVA.

The low power factor (82.83%) caused the bus to flag critical, which improved extrinsically to 99.63%.  The bus voltage (%) was improved from 95.63 to 98. 62. Therefore it is obvious that the systems power factor and losses have improved dramatically. We also observed that the operating bus voltage (Bus 03) has increased significantly. The real power load supply was improved. 

Table 1: Parameters with/without PFI Plant.

From Table 1 and Chart 1 & 2, we can observe that the indication of voltage regulation changes from critical situation to marginal condition but still lies in the under-voltage range. In addition, the losses on transformer have decreased.

Chart: 03

From Chart 3, we can conclude that current drawn by different loads have decreased after the insertion of the PFI plant, which allows using lower capacity circuit breakers and minimizes the insulation cost of high capacity cables and other equipment.

From the reports, it can be concluded that the voltage drops are within the permissible limit, and the systems overall power factor has improved. The transformers specified capacity is perfect, and there is adequate provision to meet the future load demand.

In this paper, we designed a 3-phase 2500 KVA 11/0.415 KV distribution substation, with the details of equipment parameters and simulated on ETAP software. The substation is simulated with and with- out the PFI plant, and the obtained results are ana- lyzed and compared. The results suggest that im- plementation of the properly sized transformer, rightly sized and placement of PFI plant, properly rated circuit breakers and cables, etc. improve the power factor, reduce the reactive power consumption, and improve the active power. 

I would like to express our gratitude and thanks to our colleagues for their support and advice in completing this paper successfully.