VMX
2
Series Digital Solid State Soft Starter User Manual
13 |
P a g e
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3.1.3.c
Overload Protection During Bypass
When an integral Bypass Contactor is used to shunt power around
the SCRs in the
VMX2 Series
(as in the VMX
…-BP version),
overload protection is maintained as long as the
VMX2 Series
is
directly controlling the contactor. No additional Overload Relay is
necessary for normal operation.
▪
When the Bypass Contactor on a
VMX2
…-BP Series
has been
selected to be used for Across-the-Line restart (reference section
1.2.3), supplemental overload protection is necessary. For this
application, refer to the External Overload Relay Applications
supplement and wiring diagram in Appendix 4.
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3.1.3.d
Dynamic Reset Capacity
The
VMX2 Series
includes the ability to dynamically track the
Thermal Capacity needed for a successful restart after an overload
trip. It averages the Thermal Capacity consumed in the previous
three successful starts, and calculates a Thermal Capacity to Start
(viewed in Function
F059
). After tripping on Overload, the Thermal
Register must have regained the amount recorded in
F059
before a
Reset will be allowed. If the display reads
[ Inh]
when attempting to
reset an overload trip, it is indicating that the starter is
Inh
ibited from
being reset.
Refer to details of Function
F071
for information on emergency
override of lockouts such as this.
3.2
NEMA Class Trip Curves
NEMA Class trip curves are based on a common tripping point of 600%
of motor Full Load Amps (FLA). Curves vary by the amount of time
before the unit trips. As an example, a Class 20 curve will trip in 20
seconds at 600% of FLA. The factory default setting of Class 10 will trip
in 10 seconds at 600% of FLA.
3.2.1 Dual Overload Trip Curves
The
VMX2 Series
Soft Starter provides two separate Overload Trip
Protection Curves, one for starting and one for running conditions. The
starter’s At-Speed detection circuit determines when the motor has
reached full speed. When the At-Speed condition is reached, the
overload trip curve will shift from the Start to the Run level, as
programmed in Functions
F003
and
F004
. See Section 5.6.1 for
programming details.
3.2.2 Starting Overload Trip Curve
During the start mode, Overload Trip Curves are selectable from NEMA
Class 5 through Class 30 only. The default setting of Class 10 allows
protection for the overload capacity of the soft starter as well as the
motor. Use a higher Trip Class only if nuisance tripping occurs with the
default setting.
