POWER February 2013 - 30

INSTRUMENTATION & CONTROL
Table 2. A sample of the categories and scores for plant operability assessment. Source: Provecta Process Automation
Feature
Considerations
Plant complexity
Plant condition
Protection system
integrity
Alarm system
Fuel
Operator panel
arrangement
Type of mills, SFP/EFP, on-load bypass system, more complex has
lower value
Extent of forced outages, condition of actuators, instruments and drives
causing manual intervention, monitoring, outages, etc.
Sequence automation Extent of mid- and high-level sequence automation
Self-protection extent, integrity level, testing regime, failure history,
protection redundancy
Modulating automation Whether mostly AGC mode, design avoids tripping to manual, high instrument
redundancy, high level of modulating control
Panel-based controls with some HMI operations
HMI segregated
HMI designed for low attendance
0.6 to 1.0
0.6 to 1.0
0.4 to 1.0
0.6 to 1.0
EEMUA or better frequency, consistent grading and action philosophies 0.4 to 1.0
0.4 to 1.0
Coal, gas, multiple fuels; whether common coal issues (such as wet
coal), changing CV
0.3 to 1.0
0.6
0.8
1.0
Value
range Weight
1
2
3
4
4
3
3
3
Station
A
0.95
0.6
0.5
0.7
0.55
0.55
1.0
0.65
B
0.7
0.8
0.7
0.7
0.85
0.7
0.6
1.0
C
0.7
0.85
1.0
1.0
0.85
1.0
0.65
1.0
D
0.7
0.7
0.7
0.7
0.6
0.6
0.6
0.6
Total
6.6
7.6
9.0
6.4
Notes: AGC = automatic generation control; CV = calorific value; EEUMA = Engineering Equipment Materials and Users Association, Publication 191, " Alarm Systems: A Guide to
Design, Management and Procurement " (2nd ed., 2007), www.eemua.co.uk; HMI = human-machine interface; SFP/EFP = steam-driven feedwater pumps/electric feedwater pumps.
4. Identifying candidate plants. Operability index versus operation regime is mapped
for a variety of power stations. Note that points within one category are separated horizontally
only for clarity. Source: Provecta Process Automation
10
9
8
7
6
5
4
system for unattended mode. The plant
has achieved:
■ Very high ramp rates.
■ Single-pushbutton hot and warm starts to
full load.
C
G
K
J M
L
D
Shaded regions are considered inappropriate
for the respective operation category
E
B
H
A
F
■ Fully automatic operation from 30% to
110% overload in automatic generation
control (including automatic mill scheduling
and feed heater removal for overload
operation).
■ Advanced modulating control design.
■ Unit islanding.
■ High levels of instrument redundancy and
protection.
■ Hot start times around 2.5 hours from first
fire to full load.
Much of the Australian power industry has
1
2
4. One operator per two units; operator can
leave the control room.
5. One operator per two or more units (or
two units plus station); operator can leave
the control room.
Any utility considering operational
changes can plot its current position to
assess the requirements for a successful
transition. This may require additional
expenditure on plant actuation, alarm
30
Case Study: Station F
Station F is a midsize, supercritical, oncethrough
plant. It utilizes roving operator/
maintainers with a pocket paging alarm
www.powermag.com
3
Operation category
management, or even improved routines
for plant maintenance. For example, Station
M in Figure 4 is currently undergoing
an automation upgrade, which opens the
possibility for moving from category 1 to
category 3.
4
5
embraced high levels of automation and protection,
which have enabled new coal-fired generating
plants to start up with minimal operator
actions-even to the point of enabling singlepushbutton
starting and functioning in an " unattended "
mode. These changes have not been at
the expense of plant reliability or performance.
Indeed, when properly engineered, the higher integrity
levels of control and instrumentation systems
that are needed to achieve these outcomes
often improve plant operational performance. ■
-Don Parker (don.parker@provecta.com
.au) is principal engineer for Provecta Process
Automation. This article was derived
from a technical paper presented at the
2012 ISA POWID Symposium.
POWER | February 2013
Index

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POWER February 2013

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