Created by Mohan K M, Ganesh C, Yerriswamy Technology used: Microsoft power point, Excel, Multisim, Proteus, AutoCAD, Solid edge, Arduino. As a final year project in PESIT Bangalore

1. By: Mohan K M, Ganesh C, Yerriswamy A
Microcontroller Based Mho Relay
Under the guidance of
Mrs. Jyothi T N

2. INTRODUCTION
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3. 6/23/2014Dept. EEE PESIT

4. POWER SYSTEM PROTECTION
• Main idea of protection is to remove faults as quickly as possible mean while
maintains the system stability.
• Under abnormal operating conditions protection is necessary for
 Safety of electrical equipments.
 Safety of human personnel.
• Sequence of events in relation with a fault
1. Fault occurrence
2. Sensing of fault
3. Isolation of faulted section
Unit Generator-Tx
zone
Bus zone
Line zone
Bus zone
Transformer
zone
Transformer
zone
Bus zone
Genera
tor
~
XFMR Bus Line Bus XFMR Bus Mot
or
Motor
zone
6/23/2014Dept. EEE PESIT

5. • Primary protection
• Backup protection
Classification of relays based on application
1. Under voltage, under current & under power relays
2. Over voltage, over current & over power relays
3. Directional or reverse current relay
4. Differential relay
5. Distance relay
TYPES OF PROTECTION
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6. • Distance relay
1. Impedance relay
2. Mho relay
3. Reactance relay
Mho relay is a distance relay with inherent directional element.
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7. • It has 3 zones of protections
1. Zone 1: 80-85% of protected line
2. Zone 2(minimum): 120% of protected line
Zone 2(maximum): < protected line + 50% of shortest second line
3. Zone 3F: 1.2(protected line + longest second line)
Zone 3R: 20% of protected line
MHO RELAY
6/23/2014Dept. EEE PESIT

8. Zone 1
Zone 2
Zone 3
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Zseen<Z1set
Iseen>I1
Z1<Zseen<Z2set
I1>Iseen>I2
Z2set<Zseen<Z3set
I2>Iseen>I3
Relay

9. • Zone 1: Instantaneous
• Zone 2: 0.5 sec
• Zone 3: 1 sec
TRIPPING TIME
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10. BLOCK DIAGRAM
VOLTAGE
INPUT
CURRENT
INPUT
ZERO CROSSING
DETECTOR
MICROCONTROLLER
KEYPAD
CONTACT
LCD
ANALOG TO
DIGITAL
CONVERTER
VOLTAGE
INPUT
CURRENT
INPUT
6/23/2014Dept. EEE PESIT

11. • Current sensor is used to get corresponding voltage output and wave
respectively.
• The output wave is sampled using ADC.
• From the repetitive measurement calibration of digital samples into
corresponding current magnitude is achieved.
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12. • High voltage is converted into low voltage by step down transformer.
• Analog voltage converted into Digital by ADC.
• Voltage magnitude is found by sampled digital value.
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13. Multisim 13 MATLAB 2013Proteus 8
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14. CURRENT AND VOLTAGE MEASUREMENT
CIRCUIT
Current Measurement circuit Voltage Measurement circuit
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15. OUTPUT OF MEASUREMENT CIRCUIT
Current Measurement circuit output Voltage Measurement circuit output
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16. Curve fitting to make current measurement Accurate
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17. Current Measurement
Current in
Microcontroller
Current by
Ammeter
-0.441 0
-0.361 0.25
-0.291 0.43
0.071 0.82
0.4471 1.22
0.877 1.62
1.3871 2.1
1.96 2.57
2.5471 3.13
3.3471 3.86
3.7871 4.23
4.3671 4.82
4.9471 5.3
6.0371 6.25
6.9071 7.05
8.6471 8.75
10.461 10.45
12.421 12.47
13.651 13.87
14.671 15.05
After Curve
Fitting
0.0717
0.2235
0.3454
0.8523
1.2446
1.6257
2.0633
2.5758
3.1222
3.8677
4.2670
4.7799
5.2845
6.2455
7.0451
8.6553
10.0992
11.1802
11.2752
10.6593
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18. DESIGNING OF MAIN POWER CIRCUIT
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19. DESIGNING TOOLS
Auto CAD 2010 SOLID EDGE 18
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20. MODEL DESIGNED IN SOLID EDGE
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21. 6/23/2014Dept. EEE PESIT

22. ADVANTAGES OF MICROCONTROLLER
BASED RELAY
1. Flexibility
2. High reliability
3. Fast operation
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23. CONCLUSION
• From the observed performance of several tested cases, it can be seen
that the model works satisfactorily and gives excellent results. Many tests
have been conducted successfully.
• These relays are compact, reliable and flexible over conventional relays.
The relay algorithm computation speed is increased and accuracy is not
compromised. The relay also provides improved performance and user
friendly human interface.
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24. REFERENCE
• [1] “Power system engineering’’ by R.K Rajput page no 912 to 946.
• [2] “Text book on power system engineering” by A.chakrabarthi, M L Soni, P V Gupta, U S Bhatnagar,
revised edition, Dhanpat Rai publishers
• [3] “Power system protection and switchgear” by Bhuvanesh A Oza, Nirmal kumar C Nair,Rashesh P
Mehta,Vijay H Makwana
• [4] IEEE Tutorial Course, “Microprocessor Relays and Protection Systems”. The Institute of Electrical and
Electronics Engineers,INC., 1987
• [5] IEEE Tutorial Course, “Computer Relaying”, The Institute of Electrical and Electronics Engineers, INC.,
1979.
• [6] V. Gurevich, Electric Relays Principles and Applications, Taylor & Francis Group, LLC, 2006.
• [7] K. M. Silva, W. L. A. Neves and B. A. Souza, "EMTP Applied to Evaluate Three- Terminal Line Distance
Protection Schemes," International Conference in Power System Transients (IPST'07) in Lyon, France, pp. 1-6,
June 4-7, 2007.
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25. 6/23/2014Dept. EEE PESIT
Ganesh C
Yerriswamy A
Mohan K M