VAMP 257 - Page 110

VAMP 257 Feeder and motor manager
Technical description
VAMP Ltd
68
VAMP 24h support phone : +358 (0)20 753 3264
VM257.EN002
Definite operation time characteristics
Figure 2.3.22-1 shows an example where the df/dt pick-up
value is 0.5 Hz/s and the delay settings are t=0.60 s and
t
Min
=0.60 s. Equal times t == t
Min
will give a definite time delay
characteristics. Although the frequency slope fluctuates the
stage will not release but continues to calculate the average
slope since the initial pick-up. At the defined operation time, t
= 0.6 s, the average slope is 0.75 Hz/s. This exceeds the setting,
and the stage will trip.
At slope settings less than 0.7 Hz/s the fastest possible
operation time is limited according the Figure 2.3.22-2
Figure 2.3.22-2 At very sensitive slope settings the fastest possible
operation time is limited according the figure.
Inverse operation time characteristics
By setting the second delay parameter t
Min
smaller than the
operational delay t, an inverse type of operation time
characteristics is achieved (Figure 2.3.22-3). Figure 2.3.22-4
shows an example, where the frequency behaviour is the same
as in the first figure, but the t
Min
setting is 0.15 s instead of
being equal with t. The operation time depends of the
measured average slope according the following equation.
Equation 2.3.22-1
s
ts
t
SETSET
TRIP
⋅
=
where
t
TRIP
= Resulting operation time (seconds).
s
SET
= df/dt i.e. slope setting (hertz/seconds).
t
SET
= Operation time setting t (seconds).
s = Measured average frequency slope (hertz/seconds).