National Conference on Recent Trends in Engineering & Technology
Coordination of Overcurrent Relays for Industrial Radial System 1
Vipul N Rajput, 2Rashesh P. Mehta, 3Bhuvanesh A. Oza P.G Student, Electrical Engg. Dept., BVM Engg. College, V.V Nagar, Gujarat 2,3 Associate Professor, Electrical Engg. Dept., BVM Engg. College, V.V Nagar, Gujarat 1
[email protected] ,
[email protected] 1
Abstract: - A power system network consists of number of circuit breakers and relays which are required to protect costly equipments. The relays in the power system have to be coordinated so as to avoid mal-operation and hence to avoid unnecessary outage of healthy part of the system. In this paper, the overcurrent relay coordination of 230 kV radial industrial power plant is presented using Electrical Transient Analysis Program (ETAP). It also presents load flow and short circuit analysis of radial industrial power plant using ETAP. This paper shows the star view of relays which is unique feature of ETAP for coordinating them correctly. Based up on recorded data of 230 kV industrial power plant obtained from IEEE recommended practice for calculating short circuit currents in industrial and commercial power system. Results obtained are verified by manual calculation. Key words- Radial power system, Overcurrent relays, ETAP software, Star view of relay curves, Relay coordination.
I.
INTRODUCTION
The demand for electrical power generally is increased at a faster rate in economically emerging countries. So the networks of electricity companies become very complicated. The exercise of load flow analysis, fault calculations and listing the primary and back-up pairs will be very tedious. In one of the linear programming method, the power system is decomposed into subsystem to give constrained matrix of diagonal structure with linking variables. The subsystem is solved using sparse dual revised simplex algorithm of linear programming [1],[10]. Benders algorithm for linear programming is also used to coordinate the solution for each subsystem and the master system [2]. The linear programming method is also used to coordination of distance relay zone-2 with overcurrent protection [4]. The Real Time Digital simulator which is part of closed loop relay test system is also used to coordinate in underground MV radial distribution network [5]. But nowadays, several iterations would be required to calculate TMS of relays so that minimum discrimination margin as required is found between a relay and all its back-up relays in large electrical system. This is possible only through computer programming. The main or primary protective schemes are used in the first line of defense. There must be second line of defense provide by back-up schemes, which will clear fault if primary relays fail to operate for some reasons [3]. Since the purpose of power system protection is to detect faults or abnormal condition, relays must be able to evaluate a wide variety of parameters to establish that corrective action is required. The field of relaying is almost 100 years old [6],[7].
13-14 May 2011
For many years electrical engineers have relied on the power (but not necessarily the convenience) of mainframe computers to analyze and design power systems. System studies are an integral part of power system engineering and design. A structured computer program that uses technically correct models, employs a user-friendly interface, uses a common data base, and traps user errors is a powerful tool which greatly enhances the engineer's efficiency and productivity. ETAP is an engineering design and analysis program which satisfies these criteria. In addition, ETAP performs numerical calculations with tremendous speed, automatically applies industry accepted standards, and provides easy to follow output reports. The Electrical Transient Analyzer Program, commonly known as ETAP, began as a mainframe program and was rewritten for the PC as an interactive power system analysis and design tool. ETAP, while capable of handling 1000 buses, contains a load schedule program which tracks up to 10,000,000 load items, and reports the voltage and short-circuit current at the terminals of each load item. This capability makes ETAP suitable for large industrial facilities, as well as utility systems [8],[9]. In this paper, we have presented industrial radial power plant model in section II. The load flow and short-circuits analysis and output report is presented in section III. In the section IV the manual calculation of relay coordination and relay coordination using ETAP software are shown. Finally conclusion is shown in section IV. II. SYSTEM MODEL A. Industrial radial power plant model An industrial power plant is shown in figure 1. The 230 kV source has a three-phase circuit current rating of 28,000 A. The step down transformer (T1) is 100 MVA, 230/24 kV, 0.10 p.u. reactance, delta/wye grounded with an X/R ratio of 20. A 500 MVA standby generator connected to the 24 kV bus. The reactance of the generator is 0.2 p.u. with X/R ratio of 20. Transformer (T2) is 25 MVA, 24/4.16 kV, delta/wye, 0.11 p.u. reactance with X/R ratio of 30. There are two 2,000 hp, 0.92 power factor, Xd" = 0.2 , Xd' = 0.26 p.u. with X/R ratio of 20. The low voltage system contains a transformer (T3), 4.16 kV/600 V, 0.08 p.u. reactance and X/R = 30. There is a low voltage motor at the 600 V bus with a rating of 400 hp, Xd" = 0.3 p.u., and X/R = 30 [11].
B.V.M. Engineering College, V.V.Nagar,Gujarat,India
