Fundamental Harmonic Extraction and Application with Relay Protection Algorithm

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1 Fundamental Harmonic Extraction and Application with Relay Protection Algorithm Manthan Kamleshkumar Talati Student of Final Year M.E.(Power System) Sardar Vallabhbhai Institute of Technology (SVIT) Prof. Sanjay N. Patel Asst. Prof. Electrical Engg. Dept. SVIT,Vasad,Gujarat,India ABSTRACT Power system starts with generation, transmission and ends with distribution. In that, protection scheme must be installed very effectively at each level of system. Any protective device must have been supplied correct input reading. due to that requirement harmonics must be separated and reduced up to possible level for safe and better operation of power system. This paper includes how to extract fundamental harmonic from input meter reading. when any current reading is coming from current transformer secondary, that we can convert it in to number of sample, and then from Discrete Fourier Transform(DFT) method we are calculating fundamental as well as other harmonics peak value. And we also calculate RMS value of current. So that we can use fundamental RMS current value in next steps like any relay protection algorithm. INTRODUCTION Protective relays greatly impact power systems. Protective relays are used to detect any abnormalities in a power system and isolate the faulty part of the system in the shortest time. Protective relays are designed to maintain high degree of service continuity and limit equipment damage in the power systems. Severe disruption to the normal routine of modern society such as power outages is likely to increase the emphasis on reliability and security of electrical energy to consumers. So settings of protection devices must be check time to time. METHODOLOGY This paper represents that any waveform which is coming from current transformer, that is not pure sinusoidal wave. So we have to extract fundamental waveshape of current value. And from that we can calculate RMS value for further relay protection part.for fundamental extraction done by using Discrete Fourier Transform (DFT). From this method we can get peak value of all harmonics separately. And from fundamental peak value, we can expand the sine wave and at the end of this method we can get RMS value of fundamental wave. From this RMS value, overcurrent relay protection algorithm can be start. From IEC standards, we can calculate time of operation of particular characteristics of relay. And we can see the scenario of the system in case of abnormal condition. Same method we can apply for all other characteristics of relay. This all steps we are going for MS-EXCEL HARMONICS The objective of the electric utility is to deliver sinusoidal voltage at fairly constant magnitude throughout their system. This objective is complicated by the fact that there are loads on the system that produce harmonic currents. These currents result in distorted voltages and currents that can adversely impact the system performance in different ways. To fully appreciate the impact of this phenomena, there are two important concepts to bear in mind with regard to power system harmonics. The first is the nature of harmonic-current producing loads (non-linear loads) and the 108

2 second is the way in which harmonic currents flow and how the resulting harmonic voltages develop. Linear loads A linear element in a power system is a component in which the current is proportional to the voltage. In general, this means that the current wave shape will be the same as the voltage (See Figure 1). Typical examples of linear loads include motors, heaters and incandescent lamps. Non linear load the current wave shape on a non-linear load is not the same as the voltage. Typical examples of nonlinear loads include rectifiers (power supplies, UPS units, discharge lighting), adjustable speed motor drives, ferromagnetic devices, DC motor drives and arcing equipment Fig.1 - Voltage and current waveforms for linear load and nonlinear load. CLASSIFICATION OF OVER-CURRENT RELAYS Overcurrent relays are classified on the basis of their operation time, in the following three categories: 1) Instantaneous Overcurrent Relay: These relays instantaneously send a trip command to the breaker as soon as the fault is detected (input current greater than the preset value). They do not have any intentional time delay. They are usually implemented close to the source where the fault current level is very high and a small delay in operation of relay can cause heavy damage to the equipment. So an instantaneous relay is used there to detect and respond to a fault in few cycles. 2) Definite Time Overcurrent Relay: This type of overcurrent relay is used for backup protection (e.g. back up protection for transmission line where primary protection is distance relay). If the distance relay does not detect a line fault and does not trip the breaker, then after a specific time delay, the overcurrent relay will send a trip command to the breaker. In this case, the overcurrent relay is time delayed by a specific time which is just greater than the normal operating time of the distance relay plus the breaker operation time. 3) Inverse Definite Minimum Time (IDMT) Overcurrent Relay: This relay has an inverse time characteristic. This means that the relay operating time is inversely proportional to the fault current. If the fault current is higher, the operating time will be lesser [6]. It can be graded for a very large range of operating times and fault currents [7]. The characteristics 109

of an IDMT overcurrent relay depend on the type of standard selected for the relay operation. These standards can be ANSI, IEEE, lac or user defined.

3 of an IDMT overcurrent relay depend on the type of standard selected for the relay operation. These standards can be ANSI, IEEE, lac or user defined. The relay calculates the operation time by using the characteristic curves and their corresponding parameters [8]. Any of the above mentioned standards can be used to implement a characteristic curve for an overcurrent relay. The overcurrent relay will then calculate the operation time corresponding to that particular characteristic curve. In accordance with IEC or BS142, the characteristics of IDMT relays are represented with the following equation (1). Where, t - relay operation time C - constant for relay characteristics TMS- time multiplier setting I - current detected by relay, I > IS I S - current setpoint α - constant representing inverse time type, α > 0.. (1) 110 Table 1: characteristics constants as per standards. METHODOLOGY FOR HARMONIC SEPERATION Now we consider that if reading of current transformer have already present 3 rd harmonic then we have composite waveform of fundamental and 3 rd harmonic waveform. Now methodology for harmonic separation is that, we can calculate peak values of both harmonic separately from 20 samples which are made from composite waveform of fundamental and 3 rd harmonic. There are mainly two methods for harmonic analysis and separation. (1)Discrete Fourier Transform (DFT) And (2)Fast Fourier Transform (FFT). Here we take equations of Discrete Fourier Transform (DFT), that is given below, N realpart { x( i).cos( i. h.( )}. (2) N i 0 N N imag part { x( i).sin( i. h.( )} (3) N i 0 N Where, Re= Real Part.

4 Im= Imaginary Part. x(i)= Sample Value. h= Harmonic Number. N= Total Samples Per Cycle. These equations are for discrete values and also for digital form. In analog form, we simply use Fourier Transform for analysis. But in our case we have to take discrete fourier transform. MAIN METHOD First of all how to separate fundamental harmonic from incoming composite wave. For that normal example we take, If for any composite wave, the equation of Discrete Fourier Transform (DFT) we have to check. Then we are taking simple waveshape of fundamental + 3 rd harmonic wave. And check that all other harmonics are present or not? For that composite wave, first of all we can draw fundamental wave with use of equation of sine wave i.e I=I m Sin wt. in which w is 2*pi*f, pi=3.14, f=system frequency = 50 Hz. We assume 20 samples/cycle. So at every 1 milisecond sample value can be calculate. In our case, Im= 1A., f=50 Hz., t= 0 to 19 miliseconds. Now that value convert in to digital value. For that, we consider 12 bit ADC. So range of ADC is from 000H to FFFH. Now at each increment of binary values how much increse in value of current,that is called count value. Multiplication factor is miliampere. That is calculated from 1000 ma/4095 That is ma. Where 4095 is range of ADC which is calculated from 2^n.(for 12 bit ADC, take n=12) Any controller can t read negative value,so that here we shift the sine wave with Im value.digital shifted sine wave is shown in fig.2 below. Fig 2: fundamental sine wave for 20 samples.(digital) Same method use for 3 rd harmonic waveform. only change is change in frequency. In fundamental wave frequency is 50 Hz. For 3 rd harmonic waveform frequency is 150 Hz. 111

5 I=Im Sin 3wt.. (4) Fig 3: 3 rd harmonic wave for 20 samples.(digital) ADDITION OF BOTH WAVE Now we assume that reading from current transformer is addition of fundamental and 3 rd harmonic wave shown in Fig. 4. And composite wave is shown in Table 2. Table 2: fundamental + 3 rd harmonic wave. Fig 4: fundamental + 3 rd harmonic sine wave METHODOLOGY FOR HARMONIC SEPERATION Now we consider that if reading of current transformer have already present 3 rd harmonic then we have composite waveform of fundamental and 3 rd harmonic waveform. 112

Now methodology for harmonic separation is that, we can calculate peak values of both harmonic separately from 20 samples which are made from composite waveform of fundamental and 3 rd harmonic.

6 Now methodology for harmonic separation is that, we can calculate peak values of both harmonic separately from 20 samples which are made from composite waveform of fundamental and 3 rd harmonic. These equations are for discrete values and also for digital form. In analog form, we simply use Fourier Transform for analysis. But in our case we have to take discrete fourier transform. When real and imaginary part calculated, then we get peak value of fundamental and 3 rd harmonic separately. Real and imaginary part also calculate from fundamental to 7 th harmonic. But in our case we know that only fundamental and 3 rd harmonic is present. So for just verification purpose, we can take only fundamental and 3 rd harmonics. But in actual system reading also varying and we don t know which harmonics are present actually. In actual power systems, harmonics up to 7 th order is considered in most cases. Because above that number harmonic value is almost negligible. So that in our case we also take harmonic order up to 7 th harmonic. We have to put only general equation and range of n is from 0 to 7. So that it automatically calculate all harmonic values. DATA ANALYSIS RESULT As per last methodology, for checking this method, firstly we take only composite wave of fundamental and third harmonic. And we check that other harmonics are present or not. From given equations, calculated table in MS-EXCEL is shown bolow. Table 3:fundamental calculation from DFT 113

Table 4: 2 nd and 3 rd harmonic calculation from DFT. Upper table shows the peak value of fundamental harmonic. same method apply for 2 nd harmonic and 3 rd harmonics. Table for that given above.

7 Table 4: 2 nd and 3 rd harmonic calculation from DFT. Upper table shows the peak value of fundamental harmonic. same method apply for 2 nd harmonic and 3 rd harmonics. Table for that given above. In which we can wee that only fundamental and 3 rd harmonic are present in input wave. 2 nd harmonic value is zero. Now to calculate RMS value,maximum value is already calculated using Discrete Fourier Transform(DFT).Now that peak value is put in the same equation for sine wave generation. And we get RMS value from equation which is given below..(5) Fig 5: fundamental wave(final) 114

8 Table 5: RMS value calculation From this calculated RMS value, we can do next procedure like any relay protection algorithm. because any relay device operation must require root mean square(rms) value for its operation. Now for overcurrent relay characteristics, equations already given above.in which ratio of measured current value and set value is calculated and from that value we can calculate time of operation of relay in abnormal condition. When fault occur in the system, relay must be operate as per its settings.we can see the scenario of relay operation in any condition of the system. CONCLUSION With this study it has been observed that, how real time system interface with our system. We study main method (Discrete Fourier Transform) for harmonic extraction. How to test the relay operation that can also be checked by this method. REFERENCES [1] MUDHAFAR A. AL-NEMA, SINAN M. BASHI, AND ABDULHADI A. UBAID; Microprocessor-Based Overcurrent Relays ; IEEE TRANSACTIONS ON INDUSTRIAL ELECTRONICS, VOL. IE-33, NO. 1, FEBRUARY [2] A.Y. Abdelaziz, H.E.A. Talaat, A.I. Nosseir, Ammar A. Hajjar ; An adaptive protection scheme for optimal coordination of overcurrent relays ;ELSEVIER, Electric Power Systems Research 61 (2002) 1 9. [3] Yin Lee Goh, Agileswari K. Ramasamy, Farrukh Hafiz Nagi, Aidil Azwin Zainul Abidin; Evaluation of DSP based Numerical Relay for Overcurrent Protection ; INTERNATIONAL JOURNAL OF SYSTEMS APPLICATIONS, ENGINEERING & DEVELOPMENT Issue 3, Volume 5, [4] Saeed Lotfifard, Jawad Faiz, Mladen Kezunovic; Over-current relay implementation assuring fast and secure operation in transient conditions ;ELSEVIER; Electric Power Systems Research 91 (2012)

9 [5] Md.Aminur Rahman, Kazi Main Uddin Ahmed, Md. Rayhanus Sakib; MODELING OF A NOVEL FUZZY BASED OVERCURRENT RELAY USING SIMULINK ; International Journal of Scientific & Technology Research Volume 1, Issue 4, May [6] Muhammad Shoaib Almas, Rujiroj Leelaruji, and Luigi Vanfretti; Over-Current Relay Model Implementation for Real Time Simulation & Hardware-In-the-Loop (HIL) Validation ; /12/$ IEEE. [7]Thomas Bajánek; DEVELOPMENT OF OVERCURRENT PROTECTION RELAY MODEL USING IEC SAMPLED VALUES. [8] B.A.Oza,Date,Mehta And Nayar; Power System Protection And Switchgear ;Tmh Publication [9]Bhavesh Bhalja,R.P.Maheshwari,Nilesh.G.Chotani; Protection And Switchgear Oxford University Press [10]Francisco C. De La Rosa (2006). Harmonics and power system. CRC Press. [11] J. Arrillaga, N.R. Watson, Power System Harmonics, Second Edition, John Wiley & Sons, Ltd ISBN:

Testing of Circuit Breaker and over Current Relay Implementation by Using MATLAB / SIMULINK

Testing of Circuit Breaker and over Current Relay Implementation by Using MATLAB / SIMULINK Dinesh Kumar Singh dsdineshsingh012@gmail.com Abstract Circuit breaker and relays are being utilized for secure,