VAMP 265 - 2.8. Thermal Overload Protection T> (49)

2.8 Thermal overload protection T>
(49)
2 Protection functions
Technical description
68
VAMP 24h support phone +358 (0)20 753 3264
VM265.EN011
Recorded values of the undirectional earth fault stages (8
latest faults) I
0
>, 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 fault
2.8. Thermal overload protection T> (49)
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
values is calculated using harmonic components up to the 15
th
.
Trip time:
22
2
2
ln
aI
II
t
P


 
Alarm:
alarmIkka
e

 mod
(Alarm 60% = 0.6)
Trip:
e
Ikka
mod


Release time:
22
2
ln
Ia
I
Ct
P




Trip release:
e
Ika
mod
95.0 

Start release:
alarmIka
e

 mod
95.0
(Alarm 60% = 0.6)
T
=
Operation time

=
Thermal time constant tau (Setting value)
ln
=
Natural logarithm function
I
=
Measured rms phase current (the max. value of
three phase currents)
I
p
=
Preload current,
nP
IkI 


(If temperature
rise is 120%
2.1 
). This parameter is the
memory of the algorithm and corresponds to the
actual temperature rise.
k
=
Overload factor (Maximum continuous current), i.e.
service factor. (Setting value)