JOHNSON CONTROLS
59
SECTION 3 - SYSTEM COMPONENTS DESCRIPTION
FORM 160.67-O2
ISSUE DATE: 10/9/2020
3
TURBINE GOVERNOR AND OVERSPEED
CONTROLS
Protection from turbine overspeed is an important con-
sideration and the following are four methods of pro-
tection against overspeed:
• Protection against overspeed is built into the au-
tomatic speed control for the chiller system. The
turbine operating speed for capacity control is
controlled by a governor valve that is integrated
with the chiller controls. The governor valve is
designed to control ow throughout the entire op-
erating range of the turbine. If the speed sensed
by the automatic controls exceeds the maximum
speed of 4500 RPM it will automatically begin
closing the governor valve. If the speed should
continue to increase the controls will continue to
send a signal to close the governor valve.
• If the automatic speed controls should fail to slow
the turbine by closing the governor valve in an
overspeed condition, the software overspeed logic
will de-energize the turbine trip solenoid at a pro-
grammable setpoint that is usually set 50 RPM be-
low the mechanical trip activation speed.
• A mechanical spring loaded overspeed device
will trip at 110% of maximum design speed. This
mechanical overspeed trip mechanism will im-
mediately close the overspeed trip buttery valve.
The mechanical overspeed device is connected by
mechanical linkage to a normally open 3 way trip
valve in the instrument air supply to the actuator
on the overspeed trip buttery valve. The valve, a
normally closed valve, will close when the supply
air pressure is relieved.
• There is an overspeed trip that can be used by
the operator in an emergency. This manual trip is
activated by an emergency trip knob at the base of
the turbine, that is connected to the same linkage
as the mechanical overspeed trip. See Figure 13
on page 60.
HEAT EXCHANGERS
Evaporator and refrigerant condenser shells are fabri-
cated from rolled carbon steel plates with fusion weld-
ed seams.
Heat exchanger tubes are internally enhanced type.
The evaporator is a shell and tube, flooded type heat
exchanger. A distributor trough provides uniform dis-
tribution of refrigerant over the entire shell length.
Stainless steel mesh eliminators or suction baffles are
located above the tube bundle to prevent liquid refrig-
erant carryover into the compressor. A 2" liquid level
sight glass is located on the side of the shell to aid in
determining proper refrigerant charge. The evaporator
shell contains dual refrigerant relief valves.
The refrigerant condenser is a shell and tube type, with
a discharge gas baffle to prevent direct high velocity
impingement on the tubes. A separate subcooler is lo-
cated in the condenser to enhance performance. Dual
refrigerant relief valves are located on condenser shells
with optional isolation refrigerant isolation valves.
The removable compact water boxes are fabricated of
steel. The design working pressure is 150 PSIG (1034
kPa) and the boxes are tested at 225 PSIG (1551 kPa).
Integral steel water baffles provide the required pass
arrangements. Stub-out water nozzle connections with
Victaulic grooves are welded to the water boxes.
These nozzle connections are suitable for Victaulic
couplings, welding or flanges, and are capped for ship-
ment. Plugged 3/4" drain and vent connections are pro-
vided in each water box.
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