Co-Ordination of Overcurrent Relay for Chemical Industrial Plant Using ETAP

International Journal of Futuristic Trends in Engineering and Technology ISSN 2348 - 5264 (Print), ISSN 2348-4071(Online)

Vol. 1 (02) 2014

Akshar Publication © 2014 http://www.ijftet.wix.com/research 36

Co-ordination of Overcurrent Relay for Chemical Industrial Plant using ETAP

Prof. Vipul N. Rajput Prof. Tejas M. Vala

Assistant Professor, Department of Electrical Engineering Assistant Professor, Department of Electrical Engineering Dr. Jivraj Mehta Institute of Technology Dr. Jivraj Mehta Institute of Technology

Gujarat Technological University Gujarat Technological University [email protected] [email protected]

Abstract: Recent past scenario various practices were invented for relay coordination. Typical power system comprises number of important equipments which have to be protected. In order to provide sufficient reliable protection to ensure smooth working of power system numbers of installation of relay and circuit breaker sets are required. Primary protection relay must operate within its pre-determined time period. In case of failure of primary protection relay operation which may be because of any reason, back-up protection has to take care by its operation and hence overcurrent relay coordination is must. Here, overcurrent relay coordination of typical chemical industrial plant is obtained with the use of Electrical Transient Analysis Program (ETAP) software. ETAP outcomes are compared with hand calculated overcurrent relay coordination results. Here star view of relays which is sole quality of ETAP for coordinating them in the proper manner is shown. Keywords: Radial power system, Overcurrent relays, Star view of relay curves, Relay coordination.

I. INTRODUCTION

The demand for electrical power is generally increased at faster rate in economical emerging countries. So the requirement of power system equipment like transformer, transmission lines, distribution lines and also protective device like relays, circuit breakers, fuses is increased. These transmission lines and distribution feeders are required to be protected by comprehensive and quite involved protective schemes so that the power system interruption is reduce to a minimum with regard to time of interruption and the area affected. The protective scheme must operate speed and selective before the power system becomes unstable. The feeders of 11 kV and medium transmission lines of 66 kV are protected by overcurrent and earth fault relays as primary protection. The transmission lines of 132 kV and 220 kV are protected by distance relays as primary protection & overcurrent and earth fault relays as back-up protection. The complicated distance relays like quadrilateral relays are used in lines above 400 kV [1][6]. Using Linear Programming the power system can be decomposed into subsystem and we can get constrained matrix of diagonal structure along with linking variables. Sparse dual revised simplex method of linear programming is helpful to solve subsystem. Whenever the fault is occurred it is sensed by primary and back-up relays both. On occurrence of fault primary protection initiates first to clear the fault as per the scheme of back-up protection.

Simplex method proves one of the superior methods for realistic solution. In case if solution is not optimal, this method neighboring realistic which matches with lower or equal value of function. In iterations we are getting optimal solution. In radial feeder distribution system overcurrent relay coordination is the highly constrained optimization objective. Since the pickup currents of the relays are pre determined from the system requirements, the optimization is said to be linear program problem [2]. Also the coordination of distance relays zone-2 with overcurrent protection is carried out using linear programming method like simplex and duplex. For an interconnected network, by using a directional incident matrix relating transmission lines to bus bars, the network loops are identified. Considering two main relays for any line sections, i.e. one at each end, the loops are specified by the relays number. Then, by using the concept of break point set (BPS), loops are broken at these points resulting a radial network. In fact, these break points are used as the starting point for setting the relays. First relays at the break points are set with minimum operating time and then next set of relays are set as back-up to BPS relays. This procedure continues until all relays are set [4]. The Real Time Digital simulator which is part of closed loop relay test system is also used to coordinate in underground medium voltage radial distribution network [5]. In past decades the design engineers were dependent on conventional computers in designing and analyzing power system. Study of power system plays vital role in 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 the best suitable program of requirements as mentioned above. Further, ETAP does mathematical manipulations with relatively high speed, accepts standards automatically and generates outputs in required formats which can be easily analyzed [7], [8].

II. SYSTEM MODEL

A chemical plant is supplied from a 69 kV system from two different substations. A one-line diagram of the electrical system of the plant is shown in Figure 1. The plant is supplied through two 20 MVA step down transformers from the 69 kV system. These transformers supply power to the plant through the 4.16 kV bus. The plant load consists of several induction


Vol. 1 (02) 2014


motors and lumped load at 4.16 kV, 660 V and 480 V levels. The existing plant load is 12 MW and the operating power factor is 97%. The required capacitor bank size is 6.6 MVAR.

Fig. 1. Chemical Plant Model

Following are the guidelines for overcurrent relay setting for redial distribution system are: A. Plug Setting: Plug setting are to be decide considering

three rules: The relays shall reach at least up to the end of the next

protected zone. This is required to ensure the back-up protection.

The plug-setting must not be less than the maximum normal load including permissible continuous overload unless monitor by undervoltage relay, otherwise the relay will not allow the normal load to be delivered.

In estimating the plug-setting, an allowance must be made for the fact that the relay pick-up varies from 1.05 to 1.3 times pug-settings, as per standards.

B. Time Setting: The time-multiplier setting must be chosen to give lowest

possible time for the relay at the end of the radial feeder. In the preceding sections towards the source, the time multiplier should be chosen to give desire selective interval from the down-stream relay at maximum fault conditions.

The time multiplier setting should allow not only for the time of the breaker but also for the overshoot of the relay and allowable time-errors in the time of operation of successive relays.

It is a common practice to use a fixed selective interval of 0.25 second (considering 2cycle breakers) between the successive relays. Time interval between primary and secondary relays to be decided on the base of operation time of primary relay, error in operating time of primary relay, breaker time to quench arc, overshoot time, factor of safety, error in operating time of secondary relay[1].

III. MANUAL CALCULATION OF RELAY SETTING

The load flow analysis gives the current, voltage and power flow of line, bus, transformer, circuit breakers, motors and other equipments. Using the load flow study, we can decide the plug setting of relay. Same as load flow study, the short circuit study is essential to find PSM of relay. Then using this PSM, we can find the TMS of back up relay. Thus, load flow and short circuit study must be required in relay coordination.

Fig. 2. Chemical Plant Model in ETAP

The general equation for IEC (International Electro technical Commission) standard:

푇 = ∝ × TMS)

푇 = Operating time in second

= Applied multiples of set current value

C and α = Constant of Relay

Table 1. Constants for IEC Standard Time Overcurrent Characteristics

IEC Standard

Type of

characteristics

C α

Normal Inverse 0.14 0.02 Very Inverse 13.5 1

Extremely Inverse 80 2

Long Time Inverse 120 1

Short Time Inverse 0.05 0.04

Inverse 9.4 0.7


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In this model, we have used normal inverse relays. The fault current of relays are taken from short circuit analysis in ETAP.

Table 2. Table 2. Relay fault current & CT ratio

Relay Fault

current(kA)

CTs CT ratio

R1 39.53 CT1 4000/1

R2 39.53 CT2 500/1

R3 69.28 CT3 3000/1

R4 69.28 CT4 500/1

R5, R8 74 CT5, CT8 3000/1

R6, R7 74 CT6, CT7 200/1

Relay parameter calculation for relays R1 & R2: Plug setting: The plug setting of R1 has to be decided on the basis of the rated secondary current.

The rated secondary current of transformer T3 ,

= 3 × 10√3 × 480

= 3608.44

Current transformer ratio, CT1 ratio is 3000:1, So, plug setting of R1

= 3608.44

4000 × 100 = 90.21% Here, we take plug setting 100 % of 4000 A. Now, plug setting of R2,

> 1.3

1.05 ×480

4160 × 1 × 4000 > 571.43 퐴 > . × 100 > 114 % 표푓 500 퐴 푆표,푤푒 푡푎푘푒 125 % 표푓 500 퐴 Plug setting Multiplier:

푃푆푀 표푓 푅 =퐹푎푢푙푡 푐푢푟푟푒푛푡

푝푙푢푔 푠푒푡푡푖푛푔 × 퐶푇 푟푎푡푖표

=39530

1 × 4000 = 9.88

푃푆푀 표푓 푅 =39530

1.25 × 500×

4804160

= 7.23

Time Multiplier Setting: Initially TMS of R1 is selected 0.1 second.

푇푂푃 표푓 푅 =0.14

푃푆푀 . − 1 × 0.1

=0.14

9.88 . − 1 × 0.1 = 0.29

Here, the time discrimination margin is taken 0.25 sec. So time of operation of R2 =0.29+0.25=0.54 and we can find TMS of R2.

푇푂푃 표푓 푅 = 0.54 =0.14

7.23 . − 1 × 푇푀푆

푇푀푆 표푓 푅 =0.54 × [7.23 . − 1]

0.14 = 0.1556 ≅ 0.16 Same way, the plug setting, PSM and TMS of Relays R1 to R8 are calculated as shown in Table 3 [1],[9],[10].

Table 3. Table 3. Calculated Parameters of Relay

IV. RELAY COORDINATION USING ETAP

In the ETAP software, the star-view is good feature to show exact coordination of relays. The star-view of ETAP is time-current curve which gives the relay coordination between whole the relays of system. ETAP facilitates selection of relay along with its model and manufacturer for protection of feeder, transmission line, transformer and generator etc. ETAP also gives graphical representation of relay characteristic curves individually for each relay. Coordination can also do by dragging out the relay characteristic curves. By doing so the relay parameters such as TMS and PSM are changed automatically.

Fig. 3. Star-View of All Relays of Chemical Plant

Relay R1 R2 R3 R4 R5, R8

R6, R7

P.S. (%) 100 125 100 125 100 125

P.S.M 9.88 7.23 23.09 17.5 24.66 17.84

Time Operation of Relays (Sec)

0.29 0.54 0.22 0.47 0.75 1

T.M.S (Sec) 0.1 0.16 0.1 0.19 0.35 0.42


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Hence, the relay coordination from relay R1 to relay R8 is done by using ETAP software. The graphical representation of relays coordination is shown in figure 3. Using this figure one can do whole coordination of primaries and back-up relays. The figure 3 shows the relays function as it is primary or back up according to bus fault. The downstream relay (refer figure 3) provides primary protection and next relay in the upstream direction gives secondary protection. Similarly, all the relays provide primary and secondary protection based on faulted bus.

Table 4. Table 4. Current and operational time of model

Relay R1 Relay R2 Current(Amp) Time(Sec) Current(Amp) Time(Sec)

39538 0.265 39228 0.506

9514 0.6 11375 1.11

5702 1.08 5876 2.97

3300 7.34 4333 12.5

Relay R3 Relay R4

Current(Amp) Time(Sec) Current(Amp) Time(Sec)

69807 0.242 68519 0.427

1021 0.875 2747 0.978

653.3 2.01 1096 3.47

507.7 7.34 687.5 6.3

Relay R5, R8 Relay R6, R7

Current(Amp) Time(Sec) Current(Amp) Time(Sec)

74000 0.771 72437 1

19131 1.26 12362 2.66

4974 4.68 5885 8.85

Now the results obtained from star-view is shown in Table 4. The fault current and time operation for the fault current of entire relays are given in table. The results obtained by manual calculation and from ETAP software are almost same.

V. CONCLUSIONS

Overcurrent relay plays vital role in distribution system protection system. In same regards they should be properly coordinated to provide primary and secondary protection properly. In addition to that malfunction should be avoided so

that there is no unnecessary outage of healthy part of power system. In radial feeder distribution system overcurrent relay coordination is the highly constrained optimization objective. Manual calculation for relay coordination is provided here. But when the size of the system increases, complication also increases and hence manual calculation becomes tedious and it may cause erroneous results. ETAP software proves very good tool for coordination without malfunctioning. Here practical industrial power system case in taken under the analysis. ETAP software solves coordination problem of overcurrent relays for radial distribution system.

VI. ACKNOWLEDGEMENT

The authors would like to thank B.V.M. Engg. College for allowing the project work and procure the licensed package of ETAP software and kind support during project work.

REFERENCES [1] Bhuvanesh Oza, Nirmalkumar Nair, Rashesh Mehta, Vijay

Makwana, “Power System Protection & Switchgear” Tata McGraw Hill Education Private limited, New Delhi, 2010.pp 1-50, 175-270

[2] Prashant P.Bedekar, Sudhir R. Bhide, and Vijay S. Kale, “Coordination of Overcurrent Relays in Distribution System using Linear Programming Technique” IEE International conference on “Control, Automation, Communicated & Energy Conservation” June 2009.

[3] Rashesh P. Mehta “Optimal Relay Coordination” , Journal of Engineering and Technology, Sardar Patel University, 2006, vol.19, Pg 81-86.

[4] S. Jamali, M. Pourtandorost “New approach to coordination of distance relay zone - 2 with over current protection using linear programing methods” IEEE Trans. Disrib on Power delivery.

[5] Van Der Meer, M. Popov, “ Directional relay co-ordination in ungrounded MV radial distribution networks using a RTDS” International Conference on Power Systems Transient in Kyoto, Japan, June 2009.

[6] Stanley Horowitz and Arun G .Phadke Power System Relaying, Third Edition., 2008 Research Studies Press Limited. ISBN: 978-0-470-05712-4, pp 1-21, 23-48, 75-99.

[7] Keith Brown, Herminio Abcede, Farrokh Shokooh, “Interactive simulation of power system & ETAP application and Techniques” IEEE operation Technology, Irvine, California.

[8] Keith Brown, Herminio Abcede, Farrokh Shokooh, “Interactive simulation of power system & ETAP application and Techniques” IEEE operation Technology, Irvine, California.

[9] S.A. Soman, “Power System Protection”, [10] http://www.cdeep.iitb.ac.in/nptel/Electrical%20Engineering/Power

%20System%20Protection/digital_protection/lec15.pdf [11] Siemens PTD EA · Applications for SIPROTEC Protection

Relays, 2005, [12] http://siemens.siprotec.de/download_neu/applications/SIPROTEC/

english/Appl_03_Coordination_of_Overcurrent_Relais_with_Fuses_en.pdf

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Co-Ordination of Overcurrent Relay for Chemical Industrial Plant Using ETAP