Page 66 - July-August 2012
Basic HTML Version
Evolution
of Controls
for
Nuclear-
Safety
Engine-
Generators
By Steve Greuel, PE, Fairbanks Morse
Engine.
Steve Greuel
Steve Greuel, PE, is manager of
electrical engineering for Fairbanks
Morse Engine, Beloit, Wisconsin.
Fairbanks Morse provides custom-
engineered diesel engines for
commercial, military, and nuclear
applications.
Objective
Because of changes in the technical
and regulatory landscape, nuclear plant
owners and engineers are faced with the
need—and opportunity—to rethink how
they handle controls for their emergency
generators.
Introduction
Key electromechanical components
used in emergency diesel generators
(EDGs) are fast disappearing from the
market. The computer-based digital
controls that are taking their place
introduce a whole new set of benefits
and issues that need to be addressed. The
upshot is that engineers must change the
way controls for EDGs for nuclear plants
are designed.
With this change come two major
challenges: (1) ensuring the security of
such digital control systems, especially
as requirements for safety qualification
become more demanding, and (2)
making optimal use of the wealth of
monitoring data that is now routinely
available in processor-controlled engine
systems. Fairbanks Morse Engine has
been designing control systems for
nuclear, commercial, and military diesel
generators for 40 years and is now
working closely with clients to define the
new landscape of digital controls. This
article reviews some of the ways in which
we’ve been thinking about nuclear EDG
control systems.
Analog,
Electromechanical
Control
By way of background, though,
let’s take a look at the traditional design,
which has served the industry extremely
well. For nearly four decades, nuclear
EDG systems have relied on analog,
electromechanical controls. In the start
circuit, with air pressure and station
battery power systems aligned, closure
of a switch contact allows that power
to work through to air-start solenoid
valves. In the engine, an electrohydraulic
governor actuator controls mechanical-
injection fuel pumps. With few variations,
this design has remained the mainstay of
nuclear EDGs until quite recently. These
systems are wonderful workhorses,
performing to roughly the same
requirements with the same components
as they did 40 years ago.
The traditional controls have two
major attributes, each of which has its
tradeoffs. First of all, such systems are
simple; consequently, they’re reliable.
Both diagnosis of a problem and repair
can be done quickly. However, this
simplicity means the system has only
a limited capability for monitoring its
condition. These days, even a very basic
commercial system has more monitoring
capacity than a traditional-design nuclear
EDG.
Second, traditional systems can be
calibrated and adjusted in the field by
several means, typically by screwdriver
adjustments. Among those who keep this
equipment operating, such adjustments
are a respected art, but in the face of time
and personnel turnover, it becomes very
hard to track changes; as a result, the state
of the system cannot be known precisely
nor returned precisely to its default
settings.
Fairbanks Morse still designs
traditional systems for clients that
prefer them, but the design options are
becoming quite limited because many
of the once-abundant electromechanical
components are no longer manufactured.
Finding parts that meet the requirements
for safety qualification has become a
time-consuming task.
A new concern about traditional
systems is that, according to reports of
which Fairbanks Morse is aware (one
published and one pending), aging legacy
EDG controls have been identified as a
known cause of several documented EDG
failures.
Embedded-Processor
Controls
While some clients are seeking the
time-tested certainty of electromechanics,
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Nuclear Plant Journal, July-August 2012
