12
TB MRD1-T 10.01 E
Trip characteristic
The
MRD1
identifies such factors by using the har-
monic analysis and calculates a second dynamic stabi-
lizing quantity, i.e. stabilzing factor m. Harmonic
analysis makes also detection of an inrush and trans-
former saturation caused by overvoltage possible and
are added to the calculation of the stabilizing factor.
The
MRD1
ascertains stabilizing factor m for the
present situation with the effect of further lifting the
complete characteristic. Calculation of m is defined
and cannot be adjusted.
m and I
S
each stabilize the relay entirely separate from
each other, but never have a complete blocking effect.
Both stabilizing quantities together define the pickup
value in the trip characteristic.
A basic stabilization is performed by the parameter
d[Id]. For all cases m>0 (rush current, single sided ct-
saturation and external faults) the characteristic curve is
raised up for the minimum amount of d(Id). Another
additional raising is performed for raising m (more
servere rush, more severe ct-saturation).
The additionally adjustable parameter Idiff high set
(Idiff >>) is a high current differential element. This set-
ting value is not subjected to stabilization and specifies
the highest permissible differential current. This pa-
rameter defines characteristic sector III.
Tripping procedure
The protection program permanently checks the meas-
urements that the DSP (digital signal processor) deliv-
ers. When the DSP gives a new differential current the
protection task checks whether it lies within the tripping
limits. If this is the case the
MRD1
is internally ener-
gized. Tripping occurs when the calculated difference
current is consecutively three times within the tripping
limits. To prevent the energized state from being reset
too quickly, a hysteresis of 75 % is programmed. This
means that a newly calculated difference current must
be smaller than 75 % of the present characteristic trip
value in order for the energized condition to be reset.
The total tripping time of the Relay is below 35 ms.
0
Stabilisierungstrom
stabilizing current
Is / In
Differenzstrom
differential current
Id / In
I
II
III
AUSLÖSUNG
TRIP
KEINE AUSLÖSUNG
NO TRIP
m
Idiff >>
(Für interne Fehler)
(for internal faults)
d[Id]
Fig. 6: Dynamic stabilized trip characteristic (pick-up value).
Summary of Contents for MRD1-T
Page 1: ...MRD1 T Transformer Differential Protection System ...
Page 26: ...26 TB MRD1 T 10 01 E ...
Page 40: ...40 TB MRD1 T 10 01 E Scheme ...
Page 64: ...64 TB MRD1 T 10 01 E ...