over current relays
TRANSCRIPT
![Page 1: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/1.jpg)
Classification of Protective Relays
• Based on Technology
• Based on Function
![Page 2: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/2.jpg)
Over current Relay
• Definite time over current relay• Instantaneous over current relay• Inverse time over current relay• Inverse definite minimum time (IDMT) over
current relay• Very inverse –time over current relay• Extremely inverse time over current relay
![Page 3: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/3.jpg)
Overcurrent Protection Definite (Independent) Time Relays
TOP
TIME
IS Applied Current(Relay Current Setting)
![Page 4: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/4.jpg)
Overcurrent Protection IDMT
TIME
Applied Current(Relay Current Setting)
IS
• Inverse Definite Minimum Time characteristic
![Page 5: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/5.jpg)
Inverse Time current characteristics
![Page 6: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/6.jpg)
• By suitable design of magnetic circuit• Saturation above a certain value of actuating current• Below saturation inverse characteristic• Above saturation straight line characteristic• Saturation at pick up value – Definite time
characteristic• Saturation at later stage – IDMT characteristic• Saturation at still later – very inverse• Saturation at a very late stage – extremely inverse
Realization of Time current characteristics using EM relays
![Page 7: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/7.jpg)
Relay Current Setting
• Over current relay – Provided with tappings
•Phase to phase fault protection – 50%-200% -steps of 25%
•If rating of the relay is 5 A
then 2.5A, 3.75A, 5A, 6.25A,…………, 10A
•Earth fault protection - 20%-80% - steps of 10%
•Normal current rating of earth fault relay 1 A
• Time-current characteristic -current in ampere on X-axis
• Different curves for the same relay for different settings
![Page 8: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/8.jpg)
Time Current characteristics for 5 A current setting
![Page 9: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/9.jpg)
0 10 20 30 40 50 60 70 80 90 100 1100
2
4
6
8
10
12
Time Current characteristics for 5 A current setting
![Page 10: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/10.jpg)
0 10 20 30 40 50 60 70 80 90 100 1100
2
4
6
8
10
12
Time Current characteristics for 10 A current setting
![Page 11: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/11.jpg)
0 10 20 30 40 50 60 70 80 90 100 1100
2
4
6
8
10
12
Time Current characteristics for two different settings of relay (5 A & 10 A)
![Page 12: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/12.jpg)
0 10 20 30 40 50 60 70 80 90 100 1100
2
4
6
8
10
12
Plug Setting Multiplier (PSM)
![Page 13: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/13.jpg)
Ex 1: 5 A relay set at 200 %Relay current setting = 200% of 5 A = 10 ASecondary current = 10 A ( current through relay)PSM = 10/10 = 1 Ex 2: If relay set at 50 % ; Relay current setting = 50% of 5 A = 2.5 ASecondary current = 10 A ( current through relay)PSM = 10/2.5 = 4 AEx 3: If fault current is 6000 A and CT ratio = 400/5Then secondary current = 6000/80 = 75 A;
Plug Setting Multiplier (PSM)
![Page 14: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/14.jpg)
Plug Setting Multiplier (PSM) for 5 A setting
![Page 15: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/15.jpg)
Plug Setting Multiplier (PSM) for 5 A & 10 A
![Page 16: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/16.jpg)
• Different operating times possible for the same relay
• By adjusting the angular distance by which the moving part of the
relay travels for closing the relay contacts
• Can be set up to 10 steps from 0.1,0.2,…..,0.9,1
Ex 4: For, TMS =1, if operating time = 4 s
then with TMS = 0.5 it will be 4x0.5= 2 s
with TMS = 0.2 it will be 4x0.2= 0.8 s
Note :All these op. times are for the same value of current
Time Multiplier Setting(TMS)
![Page 17: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/17.jpg)
Time Current characteristics for different time settings of relay
![Page 18: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/18.jpg)
![Page 19: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/19.jpg)
![Page 20: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/20.jpg)
• To protect an equipment or section of the line• One or more relays of same or different types
Classification of Protective Schemes
![Page 21: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/21.jpg)
• To protect an equipment or section of the line• One or more relays of same or different types
Classification of Protective Schemes
![Page 22: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/22.jpg)
• Widely used for protection of distribution lines• Radial feeder sectionalized – 2 or 3 relays used• Relays must be selective with each other
Over Current Protective Schemes
![Page 23: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/23.jpg)
Over current Protective Schemes
For proper selectivity• Time Graded System• Current Graded System• A combination of time and Current Grading
![Page 24: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/24.jpg)
Time Graded system• Definite time overcurrent relays
• Preset time –independent of fault current• Definite time relays are cheaper than IDMT Relays
• Starts a timing unit to trip the circuit breaker• Operating time is in increasing order• Difference in time settings of adjacent relays
To cover operating time of circuit Breaker To cover errors in relay usually 0.5 sec More accurate relays and fast CB can reduce the difference in the time
![Page 25: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/25.jpg)
Time graded overcurrent protection
Faults near the power source Involves a large current Most destructive Should be cleared quickly
Time graded system takes longest timeSuitable when impedance between substations is low
![Page 26: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/26.jpg)
Current graded system
Pick-up current in increasing order
High speed instantaneous over current relays
Operating time same for all relays
![Page 27: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/27.jpg)
Combination of Current and Time Grading
![Page 28: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/28.jpg)
![Page 29: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/29.jpg)
![Page 30: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/30.jpg)
![Page 31: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/31.jpg)
![Page 32: Over current Relays](https://reader035.vdocuments.us/reader035/viewer/2022081513/5871c2491a28ab55058b6d49/html5/thumbnails/32.jpg)