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The overwhelming majority of smallturbine overspeed trip devices
are mechan-ical; they incorporate a spring-activated trip
bolt that moves out and contacts a trip lever whenever apreset
overspeed is reached. A number of factors make itnecessary to
check, and possibly recalibrate, these built-in devices yearly.
Needless to say, process plants are notalways performing this
preventive maintenance activity in
a timely and procedurally correct fashion. Unscheduleddowntime
events and serious injury, even deaths, haveresulted from such
oversights.
Well-engineered and highly reliable electronic over-speed
prevention (OSP) systems are now available fornew and retrofit
applications. These systems offer endusers the security and
dependability of a two-out-of-three voting system, with the
flexibility and ease of do-it-yourself installation
andconfiguration.
One relatively recent OSPsystem incorporates a two-out-of-three
voting feature
that monitors turbine speedand will initiate a trip com-mand to
prevent overspeedevents (Fig. 1). Designed andmanufactured by Des
Moines,Iowa-based Compressor Con-trols Corporation
(www.ccc-global.com), the systemincludes three identical
speedmodules that individuallymeasure a frequency inputsignal from
a passive or activemagnetic pickup sensor. A supervisory module
continually
monitors the three speed modules for proper operation,which
helps to eliminate unnecessary downtime and increasesystem
availability.
Multilevel password ensures security.The OSP systemprovides
users with a multilevel password function foradded security. Each
level provides access to higher sys-tem functions, including Peak
Speed Reset, OverspeedTest Mode, Configuration Mode and Set New
Passwords.
The three speed modules provide a greater level ofdependability.
Open-pickup detection on passive sen-sors is provided as well as
dynamic sensor failure detec-tion via the supervisory module, which
knows when a
speed module should be receiving a valid frequency input.
Active sensor power is provided as an output as well. Eachspeed
module can display its speed and current setpoint.Additionally,
each speed module includes four dedicatedLEDs for indicating
overspeed test, trip, MPU failure andfault conditions.
Self-diagnostics: supervisory module. CCCs overspeedprotection
system also features complete continuous self-
diagnostics. The supervisory module monitors properoperation of
the speed modules and power supplies. A 4-line by 20-character
alphanumeric display is integrated intothe operator interface. A
test mode provides testing ofeach speed module, including
verification of the votingrelays operation. This module also
includes a dedicatedLED for indicating an alarm condition.
Speed module configuration is performed from thesupervisor user
interface.The OSP system is config-ured through the
supervisormodule during setup. A sin-gle supervisor module
fail-
ure will not affect normaloperation of the OSP sys-tem. The
supervisor operatesas a background device, col-lecting information
andmonitoring speed moduleoperation.
The supervisor moduleprovides additional featuresnot available
from most othertwo-out-of-three voting OSPsystems. For example,
the
supervisor module handles such high-overhead tasks as
Modbus communication. This allows the speed modulesto
concentrate on their primary task of monitoring thefrequency input
signal. With CCCs Guardian OSP sys-tem, an operator with proper
access privilege can enablethe overspeed test mode and test each
speed module. Alloverspeed tests are verified and time-stamped in
the his-tory log. Alarms and peak-speed recordings are also
timestamped. An overspeed test can not be activated if analarm,
trip or fault condition is present, thereby elimi-nating accidental
trips. During an overspeed test, thesupervisor module turns on an
LED indicator on the frontpanel of the affected speed module to
indicate that a mod-ule is being tested.
The relay board contains socketed output relays and
Consider overspeed protection retrofits
Heinz P. Bloch, Reliability/Equipment Editor
Fig. 1. This OSP system features a tw o-out- of-three votin g
feature thatmonitors turbine speed.
Reprinted from: magazine, Jan. 2002 issue, p. 17. Used w ith
permission.
HPINRELIABILITY
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For more information about our new Guardian Overspeed Prevention
(OSP) system andother state-of-the-art products from the world
leader in turbomachinery control, pleasecontact a CCC office near
you. We are uniquely qualified to solve turbomachinery con-trol
problems. We will help you to achieve maximum performance of your
turbomachin-ery, regardless of your equipment or process.
includes Overspeed Trip Output #1: DPDT relay; OverspeedTrip
Output #2: DPDT relay and alarm: DPDT relay.
Online replacement (hot swapping) of failed supervisor,
powersupply and speed modules is a standard feature. The relay
boardincludes the power supply diode-voting circuitry and contains
con-nectors for the different boards in the system to obtain DC
power.
Flexibility.Two power supply modules provide redundant powerto
the relay board, speed modules and supervisor. These two mod-ules
provide all the system power, and each can be powered by18 to 32
VDC and/or 85 to 265 VAC. Outputs of the two powersupply modules
provide system power through circuitry locatedon the relay board.
With the OSP system, users no longer haveto order separate systems
for specific power requirements orrequired trip logic.
Deenergize-to-trip or energize-to-trip logicis jumper
selectable.
By meeting a broad range of installation requirements, thisOSP
system can be installed with any turbomachinery train for
virtually any application. Whats more, installation and
config-uration can be completed by your in-house personnel.
API/ISO compliant.The Guardian OSP system is API 670 andISO
compliant, making integration with an existing system eas-ier. Even
though some competitive systems are available with sim-plex,
redundant and triplex speed switches, not all of them com-
ply with the latest API and ISO requirements. Many OSP
systemslack self-diagnostic testing and data communication
capability.These are standard features with this OSP system.
Togetherwith the many other advanced features, the resulting
packageopens up safety, reliability and maintenance enhancement
pos-sibilities that merit serious consideration.
Reliability . . .
The author is Hydrocarbon Processings Reliability/Equipment
Editor. Headvises process and power plants worldwide on reliability
improvement andmaintenance cost reduction and can be reached at
[email protected].
COMPRESSOR CONTROLS CORPORATIONInternational Headquarters4725
121st Street
Des Moines, Iowa 50323-2316, U.S.A.Phone: (515) 270-0857FAX:
(515) 270-1331
An ISO 9001 CERTIFIED COMPANYCCC E-mail:
[email protected] Site: www.cccglobal.com
CCC Worldwide:Houston, TexasRio de Janeiro, Brazil
London, U.K.Amsterdam, The NetherlandsFrankfurt, GermanyMilan,
ItalyMoscow, RussiaSingapore, Republic of SingaporeNew Delhi
IndiaDammam, Saudi ArabiaDubai, United Arab EmiratesBeijing,
China
LK/1M/2-02 Article copyright 2002 by Gulf Publishing Company.
All rights reserved. Printed in USA.
Publication #MS 106
