Power Plant
Arrangement
and Construction
The LV
The direct current shall be 125V non-grounded for control.
The electrical
characteristics shall be matched with the transformer to withstand the short
circuit current.
The insulation
level shall be 1,000V according to IEC recommendation.
The degree of
protection shall be IP-21 for IEC-529 for indoor air-conditioned installations
and IP-54 as per IEC-529 for outdoor installation under shade. The degree of
protection for installations in air-ventilated rooms shall be IP41.
All panels and equipment
installed outside shall be under a canopy.
Each switchgear/switchboard
and MCC shall be a coordinated factory assembled unit, completely wired and
ready for connection to power and control cables.
Each switchgear/switchboard and MCC shall have enclosed dead-front construction, arranged in a group consisting of vertical sections, each forming an independent structural unit.
The vertical sections shall be joined together side by side to form a rigid freestanding assembly. Each vertical section shall be fabricated of steel sheet, reinforced to form a rigid freestanding structure. Structural details of each section shall be the same as those of all other sections and shall be so arranged that additional sections may be added to either end.
Vertical and
horizontal sections shall be divided by sheet steel barriers into individual
compartments to localize the fault.
Each vertical section shall be provided with a main three-phase horizontal bus at the top and with a three-phase vertical bus to distribute power to the starter and breaker feeder units in the vertical section.
The main bus and bus taps shall be copper bars. Busbar joints shall have silver-to-silver contact surfaces securely bolted to provide low resistance contact.
Both vertical
and horizontal buses shall be held rigidly with the structure by bus supports
fabricated from materials, which maintain their physical and dielectric
properties indefinitely under all possible service conditions.
Each vertical
section shall be provided with horizontal wire was at the top and bottom, which are
isolated by steel barriers from the horizontal bus. These shall lineup with similar
wire ways in adjacent sections to form wire ways at the top and bottom for the full
length of the control center.
A vertical
wire way of ample cross-sectional area shall be provided in each vertical
sections to permit power and control cable entrance to the individual
units. Vertical wire ways shall be free
of live parts and shall contain cable supports and hinged front doors.
Horizontal
wire ways shall have removable front covers to permit access when installing
cables.
Each vertical
section shall be equipped with blank steel removable plates to permit drilling
of the plates for conduit entrance to the wire ways.
Internal bus
connections, equipment, material, and wiring connections shall be completely
accessible from the front of the assembly so that mounting of the control
center against a wall will be possible.
Each starter or
breaker feeder circuit compartment shall be completely segregated from
neighboring compartments and shall have its own door with hinges arranged so
that the door will open a minimum of 105 degrees. The door shall remain in place when the
circuit equipment is removed.
Unoccupied compartments,
which result from the manner in which the available space within the enclosure
is used, shall be grouped, if possible, in one section and combined into one
common space. This space shall be arranged into compartments of such size or
sizes as may be required for later subdivisions.
The framework
and fittings provided shall be suitable for later installation of circuit
equipment and doors of the sizes required.
The front of the
unoccupied compartment space shall be closed with a blank, bolted-on cover.
Combination
Starter and Feeder Units
Feeder
disconnect units shall consist of circuit breakers as required.
Circuit breakers
shall be molded-case manually operated 3-pole air circuit breakers.
The association
with fuses to increase the short circuit breaking capacity is forbidden.
The short
circuit breaking capacity shall be determined according to PI short circuit
performance category of IEC recommendation No. 60157-1.
Circuit breakers
shall have a toggle-operated mechanism, which shall provide positive trip free
operation on over current and shall provide quick-make and quick-break contact
movement under both manual and automatic operation.
Combination
starter circuit breakers shall be equipped with instantaneous magnetic
adjustable tripping element only.
Feeder unit
circuit breakers shall be equipped with both thermal and instantaneous magnetic
tripping elements.
Feeder circuit
breaker for motors, transformers, or miscellaneous loads shall be manually or
electrically operated.
Circuit breakers
and overload heater elements shall be temperature compensated for the environment in which they will be installed.
Motor starters
shall be a full-voltage combination magnetic type with air circuit breakers.
Magnetic contactors
shall be single-throw, shall disconnect all lead to the motor, shall be provided with magnetic blowouts and arc shields, and shall be capable of interrupting 10 times the full load current corresponding to the maximum horsepower for which they are rated at the service voltage.
The contactors shall have a mechanical life time of 5x106 operations and an electrical lifetime of 2x106 operations under nominal current of the driven load and 5x105 operations under two times the nominal current.
For
AC3 category of use, it shall be according to IEC classification.
Each starter
shall be furnished with two extra auxiliary contacts in addition to the
seal-in-contacts. Extra contacts shall be suitable for either normally open or
normally closed use and shall be wired to terminal blocks.
For each auxiliary
distribution, main feeder boards/compartment/drawer shall be provided with
voltmeter and ammeter along with push buttons (on, off, test) and indicating
lights.
Compartments shall be the dead-front type with the front mounting of the combination motor starters or feeder units
.
Each combination
starter or individual feeder disconnect unit shall be individually baffled and
shall have individual accessories.
Each starter unit shall be capable of being easily withdrawn from the structure without disconnecting power and control leads. It shall not be necessary to unbolt or otherwise work on live parts to withdraw a unit.
Starter units
shall be draw-out type and units of the same size and rating shall be
physically interchangeable. Wiring and
terminal block arrangements on each starter or feeder unit shall be identical
to other units of the same size.
Starter and feeder unit
compartment doors shall be mechanically interlocked with the breaker operating handle so that the disconnect must be in the off position before the door can be opened. With the door open, an interlock shall be provided to prevent accidental closing of the breaker.
Facilities shall
be provided so that authorized personnel may open the door with the breaker
closed, or operate the breaker when the door is open.
Padlocking
facilities shall be provided in the breaker-operating handle to positively lock
the breaker in the off position with the door open or closed. A mechanical position indicator shall be
provided to indicate the ON, Tripped, and positions of the breaker.
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