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Common Control
Problems
Problem (General) - Lack of OEM support for
older Electronic Circuits. [top]
MD&A's Control Systems Division fully supports all GE analog control
systems in the areas of calibration services, circuit board replacement
and repair, and upgrade. Life extension for the analog systems is
a primary focus for the division.
Problem - Load Demand vs. Output relationship
non-linear causing problems with coordinated control and dispatch
control. [top]
Digital position control circuit boards have a response curve for
each valve stored in an EPROM. The curves can be reprogrammed based
on actual operating data, to improve output linearity. Valve line-up
during preventive maintenance calibration is shortened considerably
and valve curves can also be changed while the unit is running.
Problem - Linear power supplies are, in time,
subject to drift due to component degradation. [top]
Power supply replacements and power system modifications are available
for all GE analog control systems. Linear supplies are replaced
with switching supplies which eliminate the need for periodic maintenance.
On MST and LSTG MKI these power supplies are rack mounted and hot-swappable.
On LSTG MKII the power supplies are direct plug-in replacements
for the existing supplies.
Problem - Older Analog circuits do not interface
well with modern DCS controls. [top]
Our Digital HMI is a plug-in replacement for the units "button
and light" control panel. This allows the turbine control system
to interface to the DCS or other coordinated systems over Ethernet
or Modbus data highways. DHMI improves the overall operability of
the controls and replaces many of the electro-mechanical set point
circuits as well.
Problem - HPU pumps are obsolete and prone
to cavitation and pressure swings. [top]
Many "control system" problems are actually hydraulic problems.
The HPU pump modification replaces the antiquated horizontally mounted
pumps with vertically mounted Bosch-Rexroth manufactured pumps.
This mounting places the pump suction well below the fluid level
eliminating cavitation on start-up. The modern pump design eliminates
skid vibration, prolonging instrumentation life and reduces pressure
swings during valve tests and operational transients to less than
25 psi. The advantage over floor mounting the pump is that the fluid
containment feature of the skid is kept in tact and no additional
floor space is necessary. This modification also replaces troublesome
space heaters with pad heaters specifically designed for the HPU
application.
Problem - No one knows how to calibrate or
test our excitation system controls! [top]
(Automatic Voltage Regulator / AVR) Call MD&A's Control Systems
Division!
Problem (General) - Turbine and generator preventive
maintenance calibration is lacking due to short staffed instrumentation
departments. [top]
MD&A's iMaps and Outage Calibration Services can turn around sliding
preventive maintenance programs and restore the reliability of the
turbine hardware without expending in-house man hours. Calibration,
repair and modification of instrumentation and hydraulic components
can be included with other MD&A contact outage services.
Problem - "Our spares have been dramatically
reduced by new inventory policies" [top]
MD&A's Control Systems Division stocks spares for quick turnaround.
Our upgrade circuits can replace maintenance-prone circuits with
more reliable, modern alternatives.
Problem - "No one knows how to work on our
MHC controls any more." [top]
WE DO! Not only can we maintain, repair and calibrate the existing
systems, in many cases we also offer "hybrid" solutions for the
upgrade of set point motor drives to improve coordinated control.
For more information on MD&A Control Systems' products and
services, please call (970) 224-2223 Ext. 140 or email: amcneill@mdaturbines.com
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