Allen-Bradley Rockwell Automation 857 User Manual page 70

3-20
Protection Functions
857-UM001A-EN-P – July 2009
Equation 3.2
I
T =
START
T
START
I
MEAS
T = Operation time
I = Start current of the motor. Default 6.00xI
START
I = Measured current during start
MEAS
T = Maximum allowed start time for the motor
START
TIME
T
START
IstartMin I
START
Figure 3.12 – Operation time delay of the stall protection stage Ist>
If the measured current is less than the specified start current I
the operation time will be longer than the specified start time T
and vice versa.
Im1
>
Im2
MAX
t
Im3 s
Block
Motor nom. Delay
start current
Figure 3.13 – Block diagram of the stall protection stage Ist>
, where
CURRENT
&
t
r
t
³1
Inverse delay
Definite / inverse
time
MOT
START
START
Istlohko
Start
&
Register
event
Trip
&
Register
event
Enable events