KSB S 100D - Operation with Soft Starters

Voltage [%]
Time [s]
Run-up
Operation
Run-down
4s
4s
120
100
80
60
40
20
0
Submersible Borehole Pumps60 Hz
5
Operation of KSB Submersible Borehole Pumps with Soft Starters
Soft starters electronically reduce the incoming line voltage
and, hence, the initial starting torque and starting current of
electric motors. During run--up they gently ramp up the applied
voltage to the motor.
In the case of submersible motors, the extremely slim design
and consequential small moments of inertia result in special
characteristics, which differ strongly from normal asynchro-
nous motors.
Effects on submersible borehole pumps
-- Starting current ⇒ approx. 40% to 65% of I
A
required for
d.o.l. starting.
-- Run-up time t
H
increased to approx. 1s to 3s compared
with approx. 0.2s to 0.5s for direct-starting.
-- Starting torque M
A
roughly
1
/
4
of the direct-starting torque.
-- No current or torque peaks (I
A
,M
A
), as in star-delta
switching arrangement.
-- Hydraulic pressure surges (waterhammer) upon starting
and stopping of the pump can be reduced, but not fully
eliminated. Therefore, soft starters are not suitable for
solving water hammer problems.
This would require the use of hydraulic control equipment
or a frequency inverter. To prevent effects due to power
failure, additional measures are required.
Note
Conspicuous noise or vibrations during run-up could well be an
indication of incorrect settings on the soft starter. This might be
due to exceeded ramp--up periods, incorrect operating mode
(setting), activated special functions, etc.
Soft starter settings
Parameter / Function Setting Comments
Minimum starting voltage 40% of the motor’s rated voltage
Ramp time / acceleration
(run-up) time
< 4s Ramp time is not identical with the motor’s
actual running-up time
Current limitation I
A
/I
N
preset to approx. 3.5 Should only be altered with allowance for
t
H
< 4s
Deceleration (run-down) time /
stop ramp
Deceleration time t
A
< 4s Better without a ramp.
Special functions, e.g.:
-- special “pump function”
-- kick-start / boost function
-- speed adjustment
-- Current controller
-- cos ϕ / economy function
-- delayed starting
OFF Do not use, as they tend to be troublesome,
particularly in submersible borehole applica-
tions.
During operation the soft starter must be bridged (bypass). This helps to avoid losses at the machine and motor to secure proper
permanent operation.