Power plant relábility

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Reliability and performance indices of power generating units in Poland
Conference Paper · October 2004
DOI: 10.1109/PMAPS.2004.241771 · Source: IEEE Xplore
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Warsaw University of Technology
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2. 8th
International Conference on Probabilistic Methods Applied to Power Systems, Iowa State University, Ames, Iowa,
September 12-16, 2004
Copyright Iowa State University, 2004
Reliability and Performance Indices
of Power Generating Units in Poland
Abstract − The description of collecting and processing system
of unavailability data of generating units of 120÷500 MW,
maintained in Energy Market Agency (ARE SA) is given in the
paper. This system concerns 112 units with total capacity of
about 2/3 of Polish power system’s generation capacity. The
definitions of calculated indices are given as well as comparison
with used by NERC (North American Electric Reliability
Council) in GADS (Generating Availability Data System). Also
the values of reliability and performance indices of Polish
generating units from the last years are given and compared with
American generating units’ data.
Index Terms − Electric power system reliability, generating
unit outage statistics, reliability and performance indices.
I. INTRODUCTION
HE electric power system (EPS), and particularly the
generation subsystem, is the technical system in which
there is no practical possibility to obtain the reliability data
with the use of accelerated laboratory studies. Only the
process of operation of the equipment gives the information
on the events having the influence on reliability of electricity
generation and its supply to the customers. This information
must be then analyzed mathematically to determine the
fundamental reliability indices and their distributions, taking
into consideration some rational circumstances [8].
The investigation of unreliability of electric power devices
has a very rich tradition. The reliability of large generating
units (≥ 120 MW) always had, and still has, a great
importance for work of national electric power system [7-8].
An attempt to implement the system for collecting and
processing data concerning failures (called SENE) in the
power plants was undertaken in late 1970s. But power plants
have consequently rejected this system because of the great
number of data introduced into it. The second reason for
power plants unwilling was then computer hardware.
Establishing in the year 1987 of „Instruction of the
Examination of Disturbances in Electric Power Plants and
Electric Power Networks” [1] has created the base for
elaborating the new computer system, called
“UNRELIABILITY” - different for power networks, and
different for power plants.
The system for examination of failures and outages in
power plants was introduced from 1st
January 1989, on three
J. Paska (D.Sc., Ph.D., MEE) is with Warsaw University of Technology,
Institute of Electric Power Engineering, Warsaw, POLAND (e-mail:
Jozef.Paska@ien.pw.edu.pl).
levels of organizational structure of electric power industry: in
power plants, in power dispatching areas, and in the
Informatics Center of Power Industry, acting on behalf of the
Community of Power Industry and Brown (Lignite) Coal.
This system, for all power plants, operated only one year,
until the time of electric power industry disintegration. Part of
the system, for large generating units, is still operating. For the
“price” of data and financial support for database, power
plants obtain in chosen cycles: cumulative statements, all
other information from the huge set, and each new edition of
system software.
Blackout, which took place in 1965 in north-eastern part of
the United States and in Canada, deprived of electricity of
about 30 million people. In consequence of that the North
American Electric Reliability Council (NERC) was created.
Liberalization and deregulation of power electric sector have
carried menace of electric energy supply. The Californian
lesson of the years 2000/2001 and the last blackouts in the US,
in UK, in Italy, have confirmed great importance of electric
power system reliability.
The North American Electric Reliability Council maintains
the Generating Availability Data System (GADS) on behalf of
all US utilities and participating Canadian NERC members.
Participation in NERC GADS is voluntary, and GADS
participants represent about 90% of the installed capacity in
North America [3]-[4], [6].
Elaborated by NERC instruction provides an outline of
procedures and format for submitting information for the
GADS needs. Those are targeted to enable consistent
reporting of the generating unit design information, outage
and derating descriptions, and selected overall unit
performance information. All reporting requirements and
definitions are based on ANSI/IEEE Standard 762
"Definitions for Reporting Electrical Generating Unit
Reliability, Availability and Productivity".
Data acquisition using present GADS reporting format
began in 1982, replacing procedures used since the early
1960s. The GADS reporting format provides means for
describing the type and cause of outage and derating events on
both the generating unit as a whole and the component(s) that
failed. This may be further amplified by a written description
of the type and mode of failure, cause of immediate failure
and any contributing factors and corrective actions taken.
Performance reporting includes information on generating unit
ratings, energy generated, unit loading characteristics and a
description of fuels consumed. All participants receive annual
Józef Paska
T

3. GADS publications and reporting instructions. The annual
publications are also available to non-NERC utilities.
So, in North America, the utilities participate in the NERC,
which collects, processes and publishes statistics on
generating units reliability. GADS [3]-[4] contains over 25
years of data on performance of generating units and related
equipment. This information is available through special
reports, for example, the Generating Availability Report.
II. INDICES CALCULATED IN “UNRELIABILITY”
SYSTEM (POLISH GADS) AND GADS
In the Energy Market Agency (formerly Center for Power
Informatics) the reliability and availability assessment of large
Polish generating units (with rated capacity ≥ 120 MW), in
thermal electric power plants, and large co-generation units (in
CHP Siekierki and CHP Krakow-Leg), for the particular period
of time has been done [2], [5]. For each generating unit and
group of units of the same rated capacity, the suitable reliability
and performance parameters are calculated.
In the first stage numbers and durations of specified states are
calculated:
〈Tp, Tr, Tkp, Ts, Tb, Ta, Tk, Lr, Lkp, Ls, Lb, La, Lw〉
where: Tp – service duration of generating unit or group of
units in analyzed period, Tr – reserve duration of
generating unit or group of units in analyzed period,
Tkp – scheduled outage (for major repair) duration,
Ts - scheduled outage (for medium repair) duration,
Tb - scheduled outage (for current repair) duration,
Ta – forced outage duration of generating unit or group
of units, Tk - time of period (calendar time), for that
calculations are performed, Lr – number of reserve
shutdowns, Lkp - number of major repair shutdowns, Ls
- number of medium repair shutdowns, Lb - number of
current repair shutdowns, La - number of forced
outages, Lw - number of all outages.
Basing on above mentioned quantities the following indices
are calculated [2], [9]-[10]:
• availability factor, AF = 100
×
+
k
r
p
T
T
T
;
• forced outage factor, FOF = 100
×
k
a
T
T
;
• forced outage rate, FOR = 100
×
+ a
p
a
T
T
T
;
• generation capacity factor, GCF = 100
×
z
k
n
P
T
A
,
where: An - net electricity generated,
Pz - installed capacity;
• achievable capacity factor, GOF = 100
×
os
p
n
P
T
A
,
where Pos - achievable capacity;
• scheduled (planned) outage factor,
• SOF = 100
×
+
+
k
b
s
kp
T
T
T
T
;
• service factor, SF = 100
×
k
p
T
T
;
average run time, ART =
w
p
L
T
.
In GADS 12 “direct” indices for generating units and 7
“weighted” indices, for group of units only, are calculated.
They are: ART (Average Run Time), SR (Starting Reliability),
NCF (Net Capacity Factor), NOF (Net Output Factor), SF
(Service Factor), AF (Availability Factor), EAF (Equivalent
Availability Factor), FOR (Forced Outage Rate), EFOR
(Equivalent Forced Outage Rate), SOF (Scheduled Outage
Factor), FOF (Forced Outage Factor), EFORd (Equivalent
Forced Outage Rate demand), WSF (Weighted Service
Factor), WAF (Weighted Availability Factor), WEAF
(Weighted Equivalent Availability Factor), WFOR (Weighted
Forced Outage Factor), WEFOR (Weighted Equivalent
Forced Outage Rate), WSOF (Weighted Scheduled Outage
Factor), WFOF (Weighted Forced Outage Factor). As a
"weight" the NMC - Net Maximum Capacity is used, and from
the Polish perspective a special attention should be focused on
the SR, EAF, EFOR indices, not calculated in
“UNRELIABILITY” system, but in which capacity deratings
(planned, seasonal, forced) are taken into account (EAF,
EFOR).
The approach and quantities existing in GADS are
illustrated in Fig. 1.
MW
PH
AH
SH RSH FOH MOH POH
I
D E
B
A C F G H
Fig. 1. Illustration of quantities used for generating unit reliability indices
calculation in GADS: SH – service hours; RSH – reserve shutdown hours;
FOH – forced outage hours; MOH – maintenance outage hours;
POH – planned (scheduled) outage hours; AH – availability hours;
PH – period hours; I – stable capacity deratings (technological system
defects); D – service of generating unit with derated capacity because of
external conditions; B - service of generating unit with derated capacity
because of power dispatching; A – generating unit service, real generation of
electricity; E – reserve capacity derating for the same reasons as in D;
C - reserve capacity; F – forced outage; G – maintenance outage;
H – scheduled outage.

4. Basing on durations of different generating unit states,
capacity levels, and values of generated energy, the important
reliability and performance indices of the unit could be
calculated. Some of them are calculated using hours of
analyzed period and could be described by Fig. 1, which
presents capacity as a function of time. The total height of the
graph is Net Maximum Capacity – NMC, and its total length
is period of time – period hours (PH). So, the total area, Y =
NMC⋅PH, is the total electrical energy, which could be
generated in analyzed period if generating unit was still in
service with maximum capacity.
III. VALUES OF RELIABILITY INDICES OF POLISH
GENERATING UNITS IN LAST YEARS
Table I lists the collective statement of reliability
parameters of the Polish generating units in the years 2000-
2002.
TABLE I
RELIABILITY AND PERFORMANCE PARAMETERS
OF GENERATING UNITS IN THE YEARS 2000-2002
Indices
AF FOF FOR GCF GOF SOF SF ART
Group of units
% h
Brown (lignite) coal - condenser units (35 units)
82.4 2.1 2.9 64.4 91.8 15.5 71.0 281.0
120 MW (7 units) 90.0 1.3 1.8 63.3 90.6 8.7 69.8 240.4
200 MW (16 units) 76.1 3.1 4.4 55.0 89.7 20.8 67.2 276.6
360 MW (12 units) 86.3 1.3 1.7 71.6 93.3 12.4 76.7 315.2
Heating oil - condenser units
200 MW (2 units) 3.1 0.0 0.0 0.0 0.0 96.9 0.0 0.0
Hard coal - condenser units (67 units)
87.3 1.1 1.8 46.2 76.6 11.6 59.3 219.4
120 MW (16 units) 82.4 1.5 2.5 47.2 79.7 16.1 59.7 279.3
200 MW (45 units) 90.3 1.0 1.6 46.3 74.7 8.7 59.5 204.2
360 MW (4 units) 90.3 0.3 0.4 46.3 74.7 9.5 70.2 217.8
500 MW (2 units) 73.8 1.4 4.3 22.9 73.3 24.8 30.9 80.9
Hard coal – co-generation units (8 units - about 120 MW each)
80.5 2.0 3.0 49.1 78.4 17.5 64.2 337.0
TOGETHER CONDENSING AND CHP UNITS (112)
84.3 1.4 2.2 51.9 82.7 14.3 61.9 238.1
120 MW (32 units) 84.1 1.5 2.3 50.9 82.5 14.4 62.0 268.2
200 MW (63 units) 84.9 1.5 2.4 47.1 78.5 13.6 59.5 220.7
360 MW (16 units) 87.3 1.0 1.4 68.7 90.9 11.6 75.1 285.4
500 MW (2 units) 73.8 1.4 4.3 22.9 73.3 24.8 30.9 80.9
It follows from Table I that the lowest forced outage rate
(FOR) in analyzed period had the generating units of 360
MW, while the highest - units of the capacity 200 MW
working on brown coal and two units of 500 MW (hard coal
fired). The highest availability (AF) reach the modern units of
360 MW, while the lowest - 200 MW units working on brown
coal and 500 MW units, from the beginning causing large
operational difficulties.
The generating unit is a complex set of cooperating
components. The assumption in the reliability analysis of
single smallest components of the unit would direct to so
complex structures that their solution would be extremely
laborious and sometimes not possible due to the lack of
credible information on damages of those small components.
Therefore it is necessary to perform the suitable
decomposition of the unit. This decomposition is also
specified by the instruction [1], and according to it in
“UNRELIABILITY” system the generating unit consists of
eight main devices (or their groups):
• generator,
• boiler,
• boiler auxiliaries,
• turbine,
• turbine auxiliaries,
• heating devices,
• electric power substation devices,
• control devices.
Their participation in overall number of forced outages of
Polish generating units in the year 2002 is shown in Fig. 2.
0
50
100
150
200
250
300
350
Generator
Boiler
Boiler
auxiliaries
Turbine
Turbine
auxiliaries
Heating
devices
Substation
devices
Control
devices
Fig. 2. Participation of specified main generating unit’s devices in overall
number of forced outages in the year 2002.
There is also the possibility to analyze what or who was
responsible for failures leading to generating units outages. In
“UNRELIABILITY” system the following “failure causes”
are differentiated: non proper exploitation, bad quality of
devices or works, disaster effects, material deteriorating, non
personnel persons, different persons, fuel, disturbances
without failures.
Their participation in overall number of forced outages of
Polish generating units in the year 2002 is shown in Fig. 3.
Non personnel
persons
2%
Disturbances
without failures
12%
Different persons
37%
Bad quality
of devices
12%
Material
deteriorating
30%
Non proper
exploitation
5% Disaster effects
1%
Fuel
1%

5. Fig. 3. Participation of specified “failure causes” in overall number of
generating units’ forced outages in the year 2002.
The variations of chosen reliability indices of condensation
units and power (capacity) margin in the Polish electric power
system in the years 1978-2002 are shown in Fig. 4.
0
5
10
15
20
25
30
35
40
45
1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002
Year
[%]
M FOF FOR SOF
Fig. 4. Changes of power margin and chosen reliability indices of
condensation generating units in the years 1978-2002.
Power margin from Fig. 4 has been defined as:
100
)
(
12
1
12
1
×
∑
−
=
=
=
∑
i
i
i
i
P
Z
P
M
so
s
so
,
where: Pso – average monthly achievable capacity of power
industry in evening peak, Zs – average monthly
power demand in evening peak (to be covered by
power industry).
Until 1981 average annual power margin was less than
30%. It means that in winter in critical days it dropped even
below 10%. There were overloads of condensing units in the
peak of power demand. In the hours besides the peak demand
some of the units were taken to the reserve or current repairs.
Such a mode of work had disadvantageous influence on the
technical state of equipment. Additionally the situation was
worse because of lack of so called peak power in the domestic
power system. Permanent lack of power in the system caused
the problem that there was no time for properly done
scheduled maintenance works. In that situation the FOR index
was at that time close to 10%, and an average time of an unite
work, from standstill to standstill (ART), was about 171
hours.
The improvement of the situation was seen when pumped-
storage power plant in Zarnowiec started its operation (1982
and 1983). The plant supplied power system with 680 MW of
peak power. Gradual starts of new units in Polaniec and
Belchatow power plants helped the situation, too. Power
margin in the eighties overrun 30%, at the beginning of
nineties it at first approached 40%, and then it exceeded that
value. The failure index dropped at that time to about 2.5%
(greater value of the failure index in 1999 is the result of
catastrophic failure of the fifth unit in Turow power plant),
and an average time of operation rose to about 250 hours. The
improvement of those indices came together with
simultaneous drop of the unit capacity factor of the installed
power (GCF) to about 54% - it means by more than 10% in
relation with the state from the end of seventies. In that period
the time of reserve standstills rose and the time of standstills
for scheduled maintenance was rising in the eighties until the
year 1992, after which it started to drop.
IV. COMPARISON WITH AMERICAN
GENERATING UNITS DATA
In Table II and in Fig. 5 and Fig. 6 the indices from the
GADS system are given. They have their equivalents in the
"UNRELIABILITY" system.
TABLE II
INDICES OF AMERICAN COAL GENERATING UNITS
IN THE YEARS 1998-2002
AF FOF FOR NCF NOF SOF SF ART
Unit size,
MW % h
100-199
(261)*
87.82 3.84 4.46 63.26 76.79 8.34 82.38 441.3
200-299
(117)
87.44 4.03 4.53 69.27 81.49 8.53 85.00 545.3
300-399
(89)
85.63 4.69 5.31 66.97 79.93 9.68 83.79 427.5
400-599
(164)
85.61 4.69 5.24 71.47 84.27 9.71 84.81 485.8
* - in brackets the number of units is given
0
10
20
30
40
50
60
70
80
90
AF NCF NOF
Value,
%
US 100-199 MW PL 120 MW US 200-299 MW PL 200 MW
US 300-399 MW PL 360 MW US 400-599 MW PL 500 MW
Fig. 5. Comparison of AF, NCF and NOF SOF indices of domestic (Polish)
and American generating units.
Comparing the data from Tables I and II it can be stated that
the domestic power units (except 500 MW units) have:
availability AF close to American;
lower than American values of forced outage rate FOR and
FOF index, which may be the result of the fact, that in the
Polish power plants standstills caused by failures are
sometimes re-qualified as the standstills for reserve or
planned maintenance;

6. greater index of scheduled maintenance factor SOF,
which proves the significance of proper technical
diagnostic and optimal maintenance policy and
modernization for the minimal time of the standstill of the
generating unit;
almost twice shorter average time of the work ART.
0
5
10
15
20
25
FOF FOR SOF
Value,
%
US 100-199 MW PL 120 MW US 200-299 MW PL 200 MW
US 300-399 MW PL 360 MW US 400-599 MW PL 500 MW
Fig. 6. Comparison of FOF, FOR and SOF indices of domestic and American
power units.
V. SUMMARY AND CONCLUSIONS
In the current situation of the power sector in Poland,
besides the official public statistics (GUS – Main Statistic
Office) practically do not exist voluntary, central systems of
acquisition and transformation of the technical and economic
data. The exception of this is, kept in the Agency of Energy
Market, acquisition and transformation data system about
failures of the power units 120-500 MW. The system controls
112 power units with the capacity composing 2/3 of the total
installed power, which may be produced in the domestic
power system.
Analyses of the statistics of domestic generating units
unreliability show that in the years 1992-2002 the reliability
indices rose systematically in power plants with units of
installed capacity between 120 and 500 MW. The lowest
forced outage rate (FOR) in the period of three years (2000-
2002) had units of 360 MW, but the highest the units of 200
MW on lignite and two units of 500 MW on hard coal. The
highest availability (AF) was received by modern units of 360
MW, whereas the lowest - units of 200 MW on lignite and
500 MW units on hard coal, causing many problems from the
beginning of their exploitation.
Availability of the Polish units AF (with the exception of
500 MW units) is close to American ones, they have lower
than American forced outage rate FOR and FOF index,
higher index of scheduled maintenance SOF, which proves the
meaning of properly done technical diagnostic and optimal
running of maintenance works and modernization for minimal
standstill of a generating unit.
System "UNRELIABILITY" gives much valuable
information, but it has many drawbacks, for example [6], [8]-
[10]:
• The system covers only big generating units in thermal
power plants (units with the rated capacity of 120 MW,
200 MW, 360 MW, and 500 MW), and big cogeneration
units. The units comprising about 1/3 of the installed
capacity of the electric power system do not belong to the
system.
• Failures of the unit elements leading to the lowering of its
capability but not to its standstill are not taken into account
in the system.
• Only “point” indices are calculated, but it seems there is a
need for empirical distributions of the duration of
particular unit exploitation states and its elements,
technological nodes and subsystems [8]. The range of the
“point” indices could also be wider (for example during
the works on the system bid market – calculation of LOLP
for the individual offer price – came out the demand for
the probability of unsuccessful start of a generating unit -
SR) [8].
There is no doubt the further functioning of the
“UNRELIABILITY” system is desired – but the questions
whether there are not any threatens for the system in its actual
state and whether there is a chance for its development are still
open. Is there a possibility of creation of analogical, better
system of reliability data acquisition and processing of
network components?
A good deal of expectancy to expand the functions of
existing “UNRELIABILITY” system, in that: taking into
account equipment not covered by the system until now,
taking into account the drop (derating) of aggregates
capability (forced and planned), caused that there are trials to
establish in Poland the Council for Reliability and Security of
Electric Power System, similarly like it is in the USA. After
acceptance of the Council it will be possible not only to
develop the system of power plants monitoring, but also to
rebuild existing in the past monitoring system of electric
power networks reliability [11].
REFERENCES
[1] "Instruction of the Examination of Disturbances in Electric Power
Plants and Electric Power Networks. Part II" (in Polish), Ministerstwo
Górnictwa i Energetyki, Warszawa, 1987.
[2] "Catalogue of Generating Units Reliability Indices in 2000-2002" (in
Polish), Agencja Rynku Energii SA - Centrum Informatyki Energetyki,
Warszawa, 2003.
[3] "Generating Availability Data System. Data Reporting Instructions",
North American Electric Reliability Council, New Jersey, October
2002.
[4] "Generating Unit Statistical Brochure 1998-2002", North American
Electric Reliability Council, New Jersey, October 2003.
[5] G. Parciński, J. Potocki, J. Mrugalska, A. Jankowska, "Multi-year
Analyses of Reliability Indices of Home Generating Units" (in Polish),
Centrum Informatyki Energetyki, Warszawa, 1995.
[6] J. Paska, M. Stodolski, A. Bordziłowski, J. Łukasiewicz, "Registration
and Analysis of Generating Units Unavailability in Electric Power
System Using Relative Database" (in Polish), Elektroenergetyka -
Technika, Ekonomia, Organizacja, Nr 1, 1996.

7. [7] J. Paska, “Generation system reliability and its assessment”, Archiwum
Energetyki, Nr 1-2, 1999.
[8] J. Paska, “Polish Generating Units Availability Data System”, 6th
International Conference on Probabilistic Methods Applied to Power
Systems – PMAPS’2000, Funchal, Madeira – Portugal, September 25-
28, 2000.
[9] J. Paska, „Generating subsystem reliability in electric power system”
(in Polish), Prace Naukowe PW – Elektryka, Z. 120, 2002.
[10] J. Paska, G. Parciński, „Reliability and Performance Indices of
Domestic Generating Units” (in Polish), Energetyka, Nr 12, 2001.
[11] J. Paska, J. Bargiel, W. Goc, A. Momot, E. Nowakowska-Siwińska, P.
Sowa, “Polish Power System Reliability Performance Assessment”, 7th
International Conference on Probabilistic Methods Applied to Power
Systems – PMAPS 2002, Naples - Italy, September 22-26, 2002.
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