Analysis and Monitoring of 500 KV Grid; Innovation in Power, Control, and Optimization, using ETAP Software

In this research work, we have modeled and analyzed an existing 500 KV power station located at Shiekh Muhammadi, Peshawar in ETAP, using the actual real time data taken carefully for simulation in order to improve the voltage profile of the system using different techniques. It was revealed that voltage profiles of most of the buses are far below the nominal values with high losses causing considerable voltage drop at the bus. The optimization was very carefully performed by analyzing each simulation results in light of classical Newton Raphson technique in order to get the best possible optimized value without going through tedious iterations. Reactive power compensation using Static Capacitor Banks was used for voltage profile improvement of the power system. After performing optimization through above techniques, the voltages of all the buses including those with previously critical under voltage conditions, experienced boost in voltage to the nominal value with increased in real power supplied, thus improving the overall efficiency of the system. Keywords—Newton Raphson Technique, Voltage Profile, ETAP-Electrical Transient and Analyzer Program, Static Capacitor Banks, Distributed Generator.


INTRODUCTION
Energy plays vital role in economics development of a country. Though energy may be required in different forms but amongst all, electrical energy has dominance mainly due to ease in its conversion into any form of energy. Besides, it can be easily regulated, has superior flexibility, cleanliness and high transmission efficiency. These characteristics of electrical energy make it essential for the overall advancement and prosperity of the modern world [1].
The aim of this project is to derive a mechanism to analyze a complex power grid using Electrical transient analyzer program (ETAP). Power system analysis is the process of assessing the magnitude of line current and voltages during different types of disturbances. The magnitude of these parameters mainly depends on the internal impedances of generators and intervening circuits. The magnitude of fault current which are usually to the tune of tens of thousands of Amperes, must be precisely calculated in order to estimate the impact of mechanical and thermal stresses on operational equipments. These estimations are also helpful while selecting appropriate protective equipments i.e. circuit breakers, relays and isolators etc. and other allied devices of switchgears.
The process of determining the line voltages and currents in case of fault conditions is a tedious task; requires multifaceted mathematical calculations. These calculations get more and more complex as the number of busses in a grid increases. Thus mathematical calculations are only possible for simpler power system with lesser number of busses. However, dealing with large number of busses requires programming software to perform complex calculations.
It has always been a challenge for electrical engineers to first generate electrical energy and then transport it to the end users without compromising the efficiency, reliability and safety. Modern age electrical power system consist of complex integrated network where electrical energy is collected from generating units mostly located at remote areas and then transported through transmission and distribution system for ultimate utilization by consumers. The power demand of these consumers varies with time so as the load on power station thus the different parameters i.e. voltage and currents of different segments do not remain constant, rather varies from time to time [2].
Power system in its normal operating condition is analyzed and investigated by load flow studies. A typical electric power grid has a large number of buses and that can only be analyzed with computational tools. A variety of computational tools are available for load flow analysis.
In recent past, Pakistan Electric Power Company (PEPCO) has gone through frequent black outs in different part of the country due to power shortages. One of the reasons of these energy crises is the lack of technological capabilities in the field of power system analysis and monitoring as the existing power distribution system is mainly analyzed by FDR-ANA(Feeder Analysis) software [3].
Whereas, ETAP (Electrical Transient Analyzer Program) offers a state of the art Electrical Engineering programming arrangements with the help of which offline monitoring i.e. current flowing in every branch, power factor, active and reactive power flow of a power system, voltage drops, can be effective performed.
International Journal of Engineering Works Vol. 6, Issue 12, PP. 448-452, December 2019 www.ijew.io ETAP can also be handful in performing monitoring and real time simulation for energy management system. ETAP is fully equipped with the software solutions; required in an electrical system i.e. load flow, transient stability, relay coordination, open circuit and short circuit analysis, arc flash, conductor and cable ampacity and many more, by simply creating and editing one line diagram.
The above characteristics of ETAP make it suitable for any electrical power company [4,11,12].

II. PROBLEM STATEMENT
The power system selected for this study is 500 KV grid station located at Shiekh Muhammadi, Peshawar. It is being feed from Terbella through 500 KV transmission line. It consists of 9 Nos. of power transformers, 11 feeders, 22 circuit breakers, 26 current transformers, 12 potential transformers and total 16 Nos. of buses. The total load connected to all the 11 kV feeders is 21.614 MVA. If a power system comprises of N Nos. of buses and R Nos. of Generators, than the total Nos. of unknown variables during power system analysis are 2 (N − 1) − (R − 1) which requires 2(N − 1) − (R − 1) Nos. of equations to be calculated [5].
Keeping in view the foregoing, the unknown variables in case of power system under study are 30 Nos. which requires 30 Nos. of equations to be solved simultaneously, in order to calculate all the elements for analysis.

III. NEWTON RAPHSON METHOD
Newton Raphson method is one of the famous tools that can be used to solve these non linear equations. However, Newton Raphson method involved series of iterations starting with a suitable guess of unknown variables i.e. voltage magnitude, angle, active and reactive power etc. and then the process is again repeated by taking the most recent values found. The process of iteration continues until the values converge on a stopping limit [6].
After reviewing the literature, it has been revealed that carefully guessing the initial value and then properly analyzing the results can ease the process of iteration. It has been noted that a multiplying factor can also be used to speed up the process.
The above technique of analyzing the results and suggesting the new input value has been used in this research for optimization.

IV. METHODS OF VOLTAGE PROFILE IMPROVEMENT
Load flow study provides different elements of power system but the most important of all is the voltage profile i.e. the voltage value of each bus. If the voltage profile of the system varies greatly, it will results in undue reactive power, causing real power losses to increase and in most of the cases there is an excessive voltage drop leading to the under-voltage condition [6].
Literature review indicates that different methods have been devised to improve the voltage profile of the system each having its own benefit and constrains. The method adopted in this research work is static capacitor.

V. STATIC CAPACITOR PLACEMENT
The power system under study is in readial scheme. In such scheme, all the load are connected to single feeding unit mainly due to simplicity and low cost [7,9,10,13]. But the major drawback in this type of scheme is the fluctuation in system voltage that cause huge disturbance in voltage profile. As most of the load in distribution system are inductive in nature, thus causing deficiency of reactive power available to the load locally. Resultantly, the flow of current increases in distribution lines which reduces the voltage.
Capacitor on other hand is a reactive device with theoretically no power loss. Placing capacitor in the system balances the reactive power requirement causing reduction in reactive power supplied by the system which in turn reduces the current and ultimately improve the voltage profile of the system. It is important to place the capacitor at right location and to identify the optimum size of the capacitor.

VI. PROBLEM METHADOLOGY
The power system under case study is 500kV Sheikh Muhammadi Grid station, which is located at Indus Highway near Badhaber, Peshawar. It consists of 9 Nos. of power transformers, 11 feeders, 22 circuit breakers, 26 current transformers, 12 potential transformers and 500kV incoming Transmission line from Tarbella power station. The total load connected to all the 11 kV feeders is 21.614 MVA. ETAP has been used for simulation purpose in this research work. The SLD using actual real time data of 500kV Shiekh Muhammadi grid station constructed in ETAP for our research work is shown in figure 1.

VII. SIMULATION RESULTS
The simulation results reveal that some of the load buses are in under voltage condition as depicted in Table 1. The under voltage condition is defined as "a condition in which an electrical equipment is receiving less than the required voltages". The under voltage condition occurs when the voltage level goes 90% of the nominal voltage.

A. Load Flow Report
The power flows in different buses are given in Table 2.

B. Voltage Profile
Voltage profile is the graph showing the buses and its voltage levels. As discussed earlier in Table:1, the BUS 1, BUS 2, BUS 3 are not in under voltage condition therefore the graph of voltage profile consists of only BUS 4 to BUS 16 as shown in Figure 2.

C. Optimal Capacitor Placement
The main process involved in achieving the desired voltage level at all the buses without compromising the power delivered, is the determination of optimum size of the capacitor and location [8,14,15,16]. Using the ETAP optimal capacitor placement (OCP) tool, the optimal size and place of the capacitor bank is selected as shown in Table 3.  Table 4 clearly illustrates that the under voltage conditions of all the buses have been improved after placement of capacitors and so does the voltage profile as shown in Figure 3.

E. Comparison of Active Power Delivered
The comparison of active power delivered by the system before and after placement of capacitor banks is shown in Table  5. It is evident from the results that placing of capacitor banks on more than one buses simultaneously is not only helpful in improving the voltage profile of the system but the overall active power delivered by the system will also be increased, thus improving the overall efficiency of the power system.