2.10 Frequent start protection N> (66)
2 Protection functions
Technical description
60
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VM50.EN004
Parameters of the stall protection stage I
st
> (48):
Parameter Value/unit Description
ImotSt xImot
Nominal motor starting
current
Ist> %Imot
Motor start detection current.
Must be less than initial motor
starting current.
DT
Operation charact./ definite
time
Type
Inv
Operation charact./ inverse
time
tDT>
s
Operation time [s]
Setting
values
tInv> s
Time multiplier at inverse
time
SCntr
Start counter (Start) reading
TCntr
Trip counter (Trip) reading
Flt
xImot
Max. value of fault.
Recorded
values
EDly %
Elapsed time as compared to
the set operate time, 100% =
tripping
2.10.
Frequent start protection N> (66)
The simplest way to start an asynchronous motor is just to
switch the stator windings to the supply voltages. However
every such start will heat up the motor considerably because
the initial currents are significantly above the rated current.
If the motor manufacturer has defined the maximum number of
starts within on hour or/and the minimum time between two
consecutive starts this stage is easy to apply to prevent too
frequent starts.
When current has been less than 10% of I
mot
and then exceeds
I
st
>, the situation is recognized as a start.
When the current is less than 10 % of I
mot,
the motor is
regarded as stopped.
The stage will give a start signal when the second last start has
been done. The trip signal is normally activated and released
when there are no starts left. Figure 2.10-1 shows an
application.
