ABB Relion REG670, Technical Manual

Page: 531 / 1298

The Tailor-Made law allows a user to design an arbitrary delay characteristic. In this
case the interval between M = V/Hz> , and M = Mmax is automatically divided into
five equal subintervals, with six delays. (settings t1 , t2 , t3 , t4 , t5 and t6 ) as shown in
figure 252 . These times should be set so that t1 => t2 => t3 => t4 => t5 => t6.
0
E
maxcont
M
max
- E
maxcont
M
max
tMin
tMax
delay in s
Overexcitation M-E
maxcont
Excitation M
under-
excitation
99001068.vsd
IEC99001068 V1 EN
Figure 252: An example of a Tailor-Made delay characteristic
Delays between two consecutive points, for example t3 and t4, are obtained by linear
interpolation.
Should it happen that tMax be lower than, for example, delays t1, and t2, the actual
delay would be tMax . Above Mmax, the delay can only be tMin .
9.4.7.3 Cooling
Overexcitation protection OEXPVPH is basically a thermal protection; therefore a
cooling process has been introduced. Exponential cooling process is applied.
Parameter Setting tool is an OEXPVPH setting, with a default time constant
tCooling
of 20 minutes. This means that if the voltage and frequency return to their previous
normal values (no more overexcitation), the normal temperature is assumed to be
reached not before approximately 5 times
tCooling minutes. If an overexcitation
condition would return before that, the time to trip will be shorter than it would be
otherwise.
9.4.7.4 Overexcitation protection function measurands
A monitored data value, TMTOTRIP, is available on the local HMI and in PCM600.
This value is an estimation of the remaining time to trip (in seconds), if the
overexcitation remained on the level it had when the estimation was done. This
information can be useful during small or moderate overexcitation situations.
If the overexcitation is so low that the valid delay is tMax , then the estimation of the
remaining time to trip is done against tMax .
The relative excitation M, shown on the local HMI and in PCM600 has a monitored
data value VPERHZ and is calculated from the expression:
1MRK502052-UEN B
Section 9
Voltage protection
525
Technical manual