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Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Power System Protection
S.A.Soman
Department of Electrical EngineeringIIT Bombay
Fundamentals of Overcurrent Protection
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
1 Principles of Overcurrent ProtectionLimitations of a FuseAlgorithm for Overcurrent RelayTime Multiplier Setting
2 Classification of Overcurrent RelayLack of Coordination ProblemIEC Standard EquationsIEEE Standard Equations
3 Pick up Current SettingGuidelinesPrimary and Back up RelaysSetting and Coordination
4 Summary
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
1 Principles of Overcurrent ProtectionLimitations of a FuseAlgorithm for Overcurrent RelayTime Multiplier Setting
2 Classification of Overcurrent RelayLack of Coordination ProblemIEC Standard EquationsIEEE Standard Equations
3 Pick up Current SettingGuidelinesPrimary and Back up RelaysSetting and Coordination
4 Summary
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
Limitations of a Fuse
It is difficult to control the time to trip.
This makes primary backup relay coordination difficult.
Once fuse melts, it has to be replaced forreenergization of the equipment.
Thus it is difficult to have remote operation.
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
1 Principles of Overcurrent ProtectionLimitations of a FuseAlgorithm for Overcurrent RelayTime Multiplier Setting
2 Classification of Overcurrent RelayLack of Coordination ProblemIEC Standard EquationsIEEE Standard Equations
3 Pick up Current SettingGuidelinesPrimary and Back up RelaysSetting and Coordination
4 Summary
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
Algorithm for Overcurrent Relay
Set reference or threshold for discriminatingovercurrent Iref .
Measure device current I.
Compute the ratio abs( IIref
) which is known as the PlugSetting Multiplier.
Trip the device, if PSM is above the threshold. Thethreshold is always greater than 1.
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
1 Principles of Overcurrent ProtectionLimitations of a FuseAlgorithm for Overcurrent RelayTime Multiplier Setting
2 Classification of Overcurrent RelayLack of Coordination ProblemIEC Standard EquationsIEEE Standard Equations
3 Pick up Current SettingGuidelinesPrimary and Back up RelaysSetting and Coordination
4 Summary
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
Time Multiplier Setting
Overcurrent relays normally play the dual roles ofprimary and backup protection.
Backup action requires a wait state.
By providing the additional setting feature of TMS, thiscan be achieved.
TMS is defined as the ratio TTm
, where T is the desiredrelay operating time for a given PSM and Tm is thecorresponding operating time at TMS=1.
Relay operating time can be varied by varying the TMSsetting.
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
Classification of Overcurrent Relay
Instantaneous relayIts action is very fast.It has only pick up setting.It does not have any TMS setting.This relay is not suitable for backup protection.
Time delayed definite time relay
It can be adjusted to issue trip decision after a specifieddelay.This delay is independant of PSM value.It has both time setting and pick up setting.It is used for short length feeders.
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
Classification of Overcurrent Relay
Instantaneous relayIts action is very fast.It has only pick up setting.It does not have any TMS setting.This relay is not suitable for backup protection.
Time delayed definite time relayIt can be adjusted to issue trip decision after a specifieddelay.This delay is independant of PSM value.It has both time setting and pick up setting.It is used for short length feeders.
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
Overcurrent Protection Using Definite Time Relay
R1 trips without any intentional time delay.R2 has to coordinate with R1 and its operation isdelayed by CTI.R3 has to back up R2 and it is again time delayed.
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
1 Principles of Overcurrent ProtectionLimitations of a FuseAlgorithm for Overcurrent RelayTime Multiplier Setting
2 Classification of Overcurrent RelayLack of Coordination ProblemIEC Standard EquationsIEEE Standard Equations
3 Pick up Current SettingGuidelinesPrimary and Back up RelaysSetting and Coordination
4 Summary
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
Lack of Coordination Between Fuse and DT relay
DT relay R1 has to backup fuse.
After point X relay actsfaster than fuse.
This lack of coordinationis due to differentcharacteristics of fuseand relay.
This lead to thedevelopment of inversecharacteristics forovercurrent relay.
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
Classification of Overcurrent RelayInverse definite minimum time relay
It is inverse in the initial part and tends to approach adefinite minimum operating time characteristics as thecurrent becomes high.This is the most widely used characteristics.
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
1 Principles of Overcurrent ProtectionLimitations of a FuseAlgorithm for Overcurrent RelayTime Multiplier Setting
2 Classification of Overcurrent RelayLack of Coordination ProblemIEC Standard EquationsIEEE Standard Equations
3 Pick up Current SettingGuidelinesPrimary and Back up RelaysSetting and Coordination
4 Summary
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
IEC Standard Equations for Inverse Characteristics
Standard Inverse Characteristics
t = TMS × 0.14(I/Is)0.02 − 1
Very Inverse Characteristics
t = TMS × 13.5(I/Is)− 1
Extremely Inverse Characteristics
t = TMS × 80(I/Is)2 − 1
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
1 Principles of Overcurrent ProtectionLimitations of a FuseAlgorithm for Overcurrent RelayTime Multiplier Setting
2 Classification of Overcurrent RelayLack of Coordination ProblemIEC Standard EquationsIEEE Standard Equations
3 Pick up Current SettingGuidelinesPrimary and Back up RelaysSetting and Coordination
4 Summary
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
IEEE Stanard Equations for Inverse Characteristics
Moderately inverse: t = TD7
{(0.0515
(I/Is)0.02−1
)+ 0.114
}Very inverse: t = TD
7
{(19.61
(I/Is)2−1
)+ 0.491
}Extremely Inverse: t = TD
7
{(28.2
(I/Is)2−1
)+ 0.1217
}US CO8 Inverse: t = TD
7
{(5.95
(I/Is)2−1
)+ 0.18
}US CO2 Inverse: t = TD
7
{(0.02394
(I/Is)0.02−1
)+ 0.01694
}
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
IEEE Standard Curves
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
1 Principles of Overcurrent ProtectionLimitations of a FuseAlgorithm for Overcurrent RelayTime Multiplier Setting
2 Classification of Overcurrent RelayLack of Coordination ProblemIEC Standard EquationsIEEE Standard Equations
3 Pick up Current SettingGuidelinesPrimary and Back up RelaysSetting and Coordination
4 Summary
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
Faults are classified into two:
Phase fault which do not involve ground.Earth fault which involve ground.
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Guidelines for Setting Pickup Current for Phase FaultRelays
Pickup current should be above the maximum loadcurrent.
Pickup current should be below minimum fault current.
Pickup current should also be below the minimum faultcurrent of the feeder that it has to back up.
The back up relay also should provide time for primaryrelay to operate. This time interval is known ascoordination time interval.
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
1 Principles of Overcurrent ProtectionLimitations of a FuseAlgorithm for Overcurrent RelayTime Multiplier Setting
2 Classification of Overcurrent RelayLack of Coordination ProblemIEC Standard EquationsIEEE Standard Equations
3 Pick up Current SettingGuidelinesPrimary and Back up RelaysSetting and Coordination
4 Summary
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Algorithm for Identifying Primary and Backup Relays
Identify leaf nodes androot nodes.
Find the parents of theactive child nodes.
The correspondingrelays should back upthe leaf node relays.
Update active childnodes to correspondingparent node.
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
1 Principles of Overcurrent ProtectionLimitations of a FuseAlgorithm for Overcurrent RelayTime Multiplier Setting
2 Classification of Overcurrent RelayLack of Coordination ProblemIEC Standard EquationsIEEE Standard Equations
3 Pick up Current SettingGuidelinesPrimary and Back up RelaysSetting and Coordination
4 Summary
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
Algorithm for Setting and Coordination of OvercurrentRelays in a Radial System
Initialize the coordination tree.
Are there any leaf nodes except the root? If yes, go tostep 3, else go to step 7.
Identify the leaf node in coordination tree.
If the PSM of these relays are not set so far, set theirPSM.
Identify the parents of leaf nodes in step 3. Computetheir PSM and TMS for backup protection andcoordination.
Delete the leaf nodes. Update the coordination tree andgo back to step 2.
Coordination activity is complete.
Power SystemProtection
S.A.Soman
Principles ofOvercurrentProtectionLimitations of a Fuse
Algorithm forOvercurrent Relay
Time MultiplierSetting
Classificationof OvercurrentRelayLack of CoordinationProblem
IEC StandardEquations
IEEE StandardEquations
Pick upCurrentSettingGuidelines
Primary and Back upRelays
Setting andCoordination
Summary
Fundamentals of Overcurrent Protection
Summary
Limitations of fuse protection.
Fundamental principle of overcurrent relay.
Plug setting multiplier and time multiplier setting.
Classification of overcurrent relay.
Primary relay and back up relay.
Setting and coordination of overcurrent relays.
Recommended