JOHNSON CONTROLS
27
SECTION 2 - PRE-STARTUP AND SYSTEM OPERATING PROCEDURES
FORM 160.67-O2
ISSUE DATE: 10/9/2020
2
A period of slow roll at idle speed is required before the
turbine can be run continuously. After SLOW ROLL,
the turbine speed can be increased to normal operat-
ing speed. Slow roll is shown in the above diagram as
a solid line. The dotted line shows where the turbine
speed is ramped up to minimum governor speed after
the chilled liquid flow has been established.
The amount of time required to slow roll at idle speed
varies, depending on the inlet steam temperature and
the number of stages in the turbine. The following for-
mula is used by the OptiView™ Control Center to de-
termine the minimum slow roll time required:
SRT = 20 + Ti-350 / 50 + Ns
where SRT = Slow Roll Time in minutes
Ti = Inlet Temperature in °F
Ns = Number of Turbine Stages
Example: Consider a KD71750125 turbine with an in-
let temperature of 353°F.
So we know that Ti = 353, Ns = 7
SRT = 20 + 353-350 / 50 + 7
Therefore, this turbine should slow roll for a minimum
of 27 minutes.
Because steam turbines operate at rela-
tively high temperatures which cause
relatively high thermal expansion of many
turbine components, a period of slow
rolling startup of the turbine is necessary
to avoid problems with thermal stresses
and expansion. This slow roll startup is
accomplished manually from the control
panel on systems furnished with “Manual
Startup”, and is accomplished automati-
cally on systems furnished with “Auto-
matic Startup”.
If the steam turbine has remained warm
for some time after a shutdown because of
a leaking throttle valve, or if it displays ab-
normal vibration during slow roll startup
or at design speed, it is possible the shaft
has taken a bow because of heat distor-
tion. The shaft on the turbine design is
returned to its normal shape by rotating
slowly at 750-1200 RPM for 15-30 min-
utes with the auxiliary oil pump in opera-
tion. If the KG turbine displays the same
indications it must be slow rolled for 15-30
minutes at 1200 RPM to assure a high
enough speed to provide lubrication by
the oil ring lubrication system. The control
panel display includes a countdown timer
showing the time remaining in the slow
roll warm-up. Vibration on either turbine
design may indicate other problems. Refer
to SECTION 5 – TROUBLESHOOTING.
OVERVIEW
Standard YST chillers manufactured prior to Decem-
ber 2006 require the operator to manually open and
close various steam inlet valves and drain valves at the
appropriate times during the startup and shutdown of
the chiller. The initiation of the slow roll warm-up and
ramp to rated speed also requires operator intervention.
If the chiller is supplied with the “Automatic Start” op-
tion, the chiller is supplied with solenoid valves and
automatic control valves to allow a single operator
action (or a remote signal) to start and shutdown the
chiller. In the following steps the standard Manual
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