Technical Data
P12y/EN TD/D32
MiCOM P125/P126 & P127
Page 27/28
The RI curve has the following definition:
( )
Is
I
K
=
t
236
.
0
339
.
0
1
−
⋅
K setting is from 0.10 to 10 in steps of 0.05.
The equation is valid for 1.1
≤
I/Is
≤
20.
12.1.2 Reset
Timer
The first stage thresholds for phase and earth overcurrent protection, negative sequence
overcurrent and wattmetric/IeCos are provided with a timer hold facility "t Reset".
It may be set to a definite time value or to an inverse definite minimum time characteristic
(IEEE/ANSI curves only). This may be useful in certain applications, for example when
grading with upstream electromechanical overcurrent relays that have inherent reset time
delays.
The second and third stage thresholds for the wattmetric/IeCos protection and earth fault
overcurrent protection only have a definite time reset.
A possible situation where the reset timer may be used is to reduce fault clearance times
where intermittent faults occur.
An example may occur in a cable with plastic insulation. In this application it is possible that
the fault energy melts the cable insulation, which then reseals after clearance, thereby
eliminating the cause for the fault. This process repeats itself to give a succession of fault
current pulses, each of increasing duration with reducing intervals between the pulses, until
the fault becomes permanent.
When the reset time of the overcurrent relay is set to minimum the P125, P126 and P127
relays will be repeatedly reset and will not be able to trip until the fault becomes permanent.
By using the reset timer hold function the relay will integrate the fault current pulses, thereby
reducing fault clearance time.
The mathematical formula applicable to the five curves is:
(
)
−
×
=
α
S
I
I
K
T
t
1
Where:
t
Reset time
K
Factor (see table)
I
Value of the measured current
Is
Value of the programmed threshold (pick-up value)
α
Factor (see table)
T
Reset time multiplier (RTMS) setting between 0.025 and 1.5.
Type of curve
Standard
K factor
α
factor
Short time inverse
C02
2.261
2
Moderately inverse ANSI/IEEE 4.850 2
Long time inverse
C08
5.950
2
Very inverse
ANSI/IEEE
21.600
2
Extremely Inverse
ANSI/IEEE
29.100
2
Summary of Contents for MiCOM P125
Page 1: ...MiCOM P125 P126 P127 Directional Non directional Relay Technical Guide P12Y EN T E32...
Page 2: ......
Page 4: ...P12y EN T E32 Technical Guide Page 2 2 MiCOM P125 P126 P127 BLANK PAGE...
Page 5: ...Pxxxx EN SS B11 SAFETY SECTION...
Page 6: ......
Page 8: ...Pxxxx EN SS B11 Page 2 10 Safety Section BLANK PAGE...
Page 16: ...Pxxxx EN SS B11 Page 10 10 Safety Section BLANK PAGE...
Page 17: ...Getting Started P12y EN GS D32 MiCOM P125 P126 P127 GETTING STARTED...
Page 18: ......
Page 66: ...P12y EN GS D32 Getting Started Page 48 48 MiCOM P125 P126 P127 BLANK PAGE...
Page 68: ......
Page 79: ...User Guide P12y EN FT D32 MiCOM P125 P126 P127 USER GUIDE...
Page 80: ......
Page 166: ...P12y EN FT D32 User Guide Page 86 86 MiCOM P125 P126 P127 BLANK PAGE...
Page 167: ...Technical Data P12y EN TD D32 MiCOM P125 P126 P127 TECHNICAL DATA AND CHARACTERISTIC CURVES...
Page 168: ......
Page 197: ...Application Guide P12y EN AP D32 MiCOM P125 P126 P127 APPLICATION GUIDE...
Page 198: ......
Page 202: ...P12y EN AP D32 Application Guide Page 4 74 MiCOM P125 P126 P127 BLANK PAGE...
Page 274: ......
Page 298: ...P12y EN CM C22 Commissioning and Maintenance Page 24 24 MiCOM P125 P126 P127 BLANK PAGE...
Page 300: ......
Page 302: ...P12y EN CO C22 Connections and Wiring Diagrams Page 2 10 MiCOM P125 P126 P127 BLANK PAGE...
Page 310: ...P12y EN CO C22 Connections and Wiring Diagrams Page 10 10 MiCOM P125 P126 P127 BLANK PAGE...
Page 312: ......
Page 360: ...P12y EN RS D32 Commissioning Test and Record Sheet Page 48 48 MiCOM P125 P126 P127 BLANK PAGE...
Page 361: ......