shall be adjustable. Provide an electro-pneumatic transducer to
accept the 4 to 20 mA signal from the controller specified in VAMS
Section 15901N CONTROLS AND INSTRUMENTATIONS BOILER PLANTS.
d.
Emergency Overspeed Governor: Completely independent of the speed
governor and shall operate a separate trip valve.
e.
Insulation: Turbine shall insulated and lagged as specified in
Section 15080 THERMAL INSULATION FOR MECHANICAL SYSTEMS.
2.9.5
Variable Speed Motor Controller
Remotely installed cabinet housed units with solid state rectification and
inverter equipment to vary frequency of electrical power to the drive
motors.
2.9.5.1
Housing
House the controller in a [wall] [floor] mounted, NEMA [_____] enclosure
finished with manufacturers standard painted finish. Provide control panel
complete with fused disconnect switches, magnetic [across the line] [part
winding] starters with thermal overload protection, transformer,
hand-off-automatic selector switches, hand potentiometer for manual speed
control, fuses and running lights.
a.
Manual Switch: Locate the manual switch within the control panel
so that in the event failure of any of the components the motor
can be put across the line at full voltage to maintain air or pump
pressure. Provide a mechanical door interlock that allows the
panel to open only when the fused disconnect is in the off
position.
2.9.5.2
Variable Frequency Controllers
Variable frequency controllers shall use solid-state semiconductor power
conversion equipment. Provide controllers as integrated and assembled
products. Controllers shall be furnished by the same manufacturer.
2.9.5.3
Ratings
Each controller shall be rated for a supply of [_____] volts, three phase,
60 Hz. The output shall be [_____] volts, three phase with frequency
variable between zero and 60 Hz. Controllers shall be rated to operate the
motors continuously at their rated kilowatt horsepower and frequency.
Speed regulation shall be within (+/-) three percent of set point without
tachometer feedback. Electrical supply system shall have an available
short circuit rating of [_____] amperes symmetrical.
2.9.5.4
Minimum Speed
Each controller shall be capable of driving the motor continuously at a
lower speed no greater than 20 percent of full rated motor speed with
stable operation and without overheating the motor under rated ambient
conditions. Provide estimate of minimum speed at which motor can be
operated continuously without overheating or problems of instability due to
overhauling of the load.
SECTION 15511N
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