
98
agility
TM
Series Soft Start User Manual
MAN-AGY-001. Version 04. 21/09/2018
.
Maximum Motor Cable Length
The length of the cable between the output terminals of the starter and the motor should not
normally be greater than 100 metres.
Power Factor Correction Capacitors
Power factor correction capacitors applied to a single motor MUST always be connected by a
separate contactor placed on the SUPPLY side of the agility
TM
soft-start. Capacitors should be
switched in after top-of-ramp (full line voltage) is reached and switched out of circuit before a stop
is initiated.
It is important that any total system PFC scheme that automatically corrects for a range of
inductive loads is not operated in such a way as to leave it heavily over compensated since this
might introduce oscillations leading to damaging over-voltages.
Lightly Loaded, Small Motors
Lightly loaded, small-sized (less than 2kW), star connected motors can produce high voltages at
the motor terminals when shut down by simply opening the line contactor. As these voltages can
damage the soft-starter, it is safer to control the opening of the line contactor with the soft start
run relay contacts.
Motors Fitted with Integral Brakes
Motors that include an integral, electrically operated brake, internally connected to the motor
input terminals, can only be soft-started when the brake is re-connected to the supply through its
own contactor.
Older Motors
The action of the fully-controlled soft-starter introduces harmonic currents and voltages to the
motor. It is therefore, important to ensure that the motor employs techniques such as rotor
skewing in its construction to suppress the effects of harmonic fluxes and avoid rough starting.
This is rarely a problem with modern motors because nearly all motors designed in the last 20
years employ these techniques.
Wound-rotor or Slip-ring Motors
Slip-ring induction motors ALWAYS need some resistance in the rotor circuit to ensure that
sufficient rotational torque is generated to overcome any alignment torque, which is present at
start-up. The resistance can be safely shorted out in the normal fashion with a contactor
controlled by the programmable relay set as ‘top
-of-
ramp’ contacts.
Enclosures
Thyristors are not perfect conductors, and the passage of current through them causes heat
dissipation in the body of the device, which in turn causes the heatsink temperature to increase.
As a rough guide, the heat generated is 1 watt/amp/phase when energy saving, which equates to
a dissipation of 30 watts from the heatsink for a line current of 10 amps. Therefore, all cabinets or
enclosures that house soft-starters should have adequate ventilation. (Refer to the Mechanical
installation procedures, section for more detailed information.)
Applications (continued)