The isolation transformer shall be an SCR drive type specifically designed
for cranes, with a continuous rating which will exceed that required of the
sum of rated full-load full-speed KVA of hoist plus 50 percent of rated
full-load full-speed KVA of trolley and bridge motors plus the rated KVA of
controls. Total KVA is then multiplied by 1.05 (efficiency factor). The
isolation transformer shall be connected to load side of mainline
disconnect of the transformer. Crane dc static control electric power
distributed on the crane shall be supplied through this isolation
transformer.
2.4.10.3
Surge Protection
Surge suppressors shall meet the requirements of UL 1449. Three metal
oxide varistors shall be provided on the line side of each SCR drive
isolation transformer to provide transient over-voltage protection.
2.4.10.4
Circuit breakers shall meet the requirements of UL 489.
2.4.10.5
**************************************************************************
NOTE: Select applicable overload protection based
on control circuit type.
**************************************************************************
[Alternating current circuit overload relays shall be of the ambient
compensated, automatic reset, inverse time type located in all phases
individual motor circuits. Overload relays shall be arranged to
de-energize the associated motor on an overload condition.] [An
automatically reset inverse time-trip running overload relay shall be
provided for each dc motor circuit. An automatically reset instantaneous
trip overload relay shall be provided in each dc motor circuit or for a
pair of series-connected motors. Overload relays shall be arranged to
de-energize the associated motor on an overload condition.] [Alternating
current adjustable frequency-control motor overload-protection shall be
electronic and shall protect by inverse time and current versus output
frequency which will allow less current for a given amount of running time
when frequency (speed) is lower than rated.] [Direct current variable
voltage control motor overload-protection shall be electronic.]
2.4.11
Limit-Switches
**************************************************************************
NOTE: Delete reference to micro-drive control
system if not applicable.
**************************************************************************
Geared limit-switches shall be heavy-duty quick-break double-pole
double-throw type conforming to NEMA ICS 2. The geared limit-switch
interruption of a motion in one direction shall not prevent the opposite
motion. Geared limit-switches shall reset automatically. Limit-switch
housings shall be NEMA Type [1] [4]. Limit-switches shall interrupt power
to the primary and micro-drive control systems.
SECTION 14630A
Page 43
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