Rockwell Automation 865 Differential Protection Relay - Manual (Page 66)

3-22 Protection Functions
865-UM001A-EN-P – July 2009
Recorded Values of the Latest Eight Faults
Detailed information is available on the eight latest earth faults: Time
stamp, fault current, elapsed delay and setting group.
Table 3.13 – Parameters of the Undirectional Earth Fault Stages
(8 latest faults) I
0 >>, I 0 >>>, I 0 >>>> (50N/51N)
Parameter Value Unit Description
yyyy-mm-dd Time stamp of the recording, date
hh:mm:ss.ms Time stamp, time of day
Flt pu Maximum earth fault current
EDly % Elapsed time of the operating time setting.
100% = trip
SetGrp 1
2 Active setting group during the fault
The thermal overload function protects the transformer against
excessive temperatures.
Thermal model
The temperature is calculated using rms values of phase currents and
a thermal model according IEC 60255-8. The rms value is calculated
using harmonic components up to the 15
th .
Trip time: 2 2
2 2
ln
a I
I I
t P
−
−
⋅ =τ
Alarm:
alarm I k k a
e
⋅ ⋅ Θ ⋅ =
mod
(Alarm 60% = 0.6)
Trip: e
I k k a
mod
⋅ Θ ⋅ =
Release time: 2 2
2
ln
I a
I
C t P
−
⋅ ⋅ =
τ
τ
Trip release:
n
I k a Ч Ч = 95 . 0
Start release:
alarm I k a
n
Ч Ч Ч = 95 . 0
(Alarm 60% = 0.6)
T = Operation time
τ = Thermal time constant tau (Setting value)
ln = Natural logarithm function
I = Measured rms phase current (the max. value
of three phase currents)
Thermal Overload
Protection T> (49)