GE Industrial Solutions ASTAT-XT RVSS PANEL - Manual (Page 18)

DEH40622 - Page 10 AN BL-0350, Rev.01, 08/20/2010
ASTAT-XT RVSS PANEL
sensing element, which calculates the true rms value of the current every
cycle, resulting in a tripping action, which is very fast. For this reason the
NEC allows the trip level to be set at 700% of the motor FLA to allow for
the high locked rotor current which the motor draws during across-the-line
starts (see NEC section 430-52 and Table 430-152 of the NEC). Because
instantaneous trip circuit breakers are so fast acting, the NEC actually
allows trip level settings up to 1300% of motor FLA if it can be shown to
be required by engineering evaluation. When a motor is started across
the AC line it can draw a very large peak current for the first half-cycle
which can cause nuisance tripping in instantaneous trip breakers set at
700%. GE Motors & Industrial Systems has conducted analyses, which
show that certain models can require this 1300% trip level to avoid
nuisance tripping on across-the-line starts. Generally the trip level will
need to be higher for premium efficiency motors than for standard
efficiency ones.
The rating plugs for the circuit breakers in the Solid State RVSS panels
have been chosen to allow trip level settings up to 13 times the current
ratings of the panel. If the trip level is set at 13 times the motor FLA
and the circuit breaker still trips it is probably due to the fact that your
motor has very high efficiency and therefore exhibits the highest inrush
currents. Refer to section 6 of this document on trouble shooting
assistance
Motor Overload Trip Level The overload relay in your Solid State RVSS panel is the C-2000
TM
Class 20
or Class 30 fixed heater type from GE which is panel mounted. Class 30
overload relays are utilized for panels rated 100Hp and above at 230 VAC
plus 150Hp and above at 460 VAC and 575 VAC. The overload relay
carries all motor current whether it is running from the Soft Starter or
across the AC line (BYPASS mode). Whereas the panel circuit breaker or
input fuses is intended to provide short circuit protection for the panel
components, field wiring and the motor, the overload relay’s function is to
provide continuous long term overload protection against loads which
draw current in excess of the motor’s rating.
According to GE ED&C publication DET-034B entitled C-2000
TM Contactors &
Starters Technical Information , the trip level dial on the contactors should
be set as follows.
• Motors with Service Factor of 1.15 or Greater - adjust OL relay dial to
the motor nameplate FLA.
• Motors with Service Factor Less than 1.15 - adjust OL relay dial
according to the formula FLA times Service Factor times 0.90.
Example: 30 A motor with 1.00 service factor
Set OL dial at 30 x 0.90 = 27.0 A
If the overload relay dial is set correctly but trips in normal running
situations, then your motor is probably undersized for your load. Possible
corrective actions are:
CAUTION: For all ASTAT-XT Bypass AND Non Bypass panels the
overload relay dial should never be set higher than the panel rated current
even if allowed by the above formula because the overload relay protects
panel components such as the contactors in addition to the motor.
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