Availability Analysis of A Power Plant by Computer Simulation
Availability Analysis of A Power Plant by Computer Simulation
Availability Analysis of A Power Plant by Computer Simulation
used to analyze the effects of different maintenance policies on optimal distribution of electrical generation, reliability, losses,
availability of these stations. The results show that significant and possible improvements. Alardhi et al. [6] developed a
improvements can be achieved in power plant availabilities if
appropriate maintenance policies are implemented.
preventive maintenance schedule for multi cogeneration
power plants with production constraints by using
Keywords—Power plants, steam turbines, gas turbines, mathematical programming. Kancev and Cepin [7] showed
maintenance, availability, simulation. that testing and maintenance improve the reliability of safety
systems and components in nuclear power plants, which is of
I. INTRODUCTION special importance for standby systems. Marseguerra. and Zio
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Vol:9, No:4, 2015
Table II shows different types of failures, which have obtain overall combined mean time between all maintenance
frequently occurred in Sabiya steam turbines. The related and mean time to perform a maintenance (MT) for both
mean time between failures (MTBF), failure rates (λ) and corrective and preventive actions:
mean time to repair (MTTR) are given in the table based on
historical data. Table II shows the two different types of MTBMc=1/(1/MTBF+1/MTBM) =1/(λ+π) (3)
failures for the gas turbines in Sabiya Station and related
MTBF, mean corrective time (Mct) and failure rates. Table IV MT=(λ*Mct + π*Mpt)/(λ+π) (4)
shows the maintenance parameters, including mean time
MTBMc calculations are done by using combined MTBF,
between preventive maintenance (MTBM), mean preventive
combined failure rates, MTBM, and maintenance rates from
time (MPMT), and related rates for steam turbine and gas
Tables II and III for steam and gas turbines. Furthermore, MT
turbine units. Note that two failures are combined as follows:
calculations are made using the combined Mct values from
TABLE I Tables II and III and Mpt values from Table IV for the steam
POWER STATIONS IN KUWAIT and gas turbines separately. Table V shows the calculated
Number Installed Number Installed combined MTBMc and mean maintenance time (MT) values
Station Name of Steam Capacity of Gas Capacity
Turbines (MW) Turbines (MW)
for each type of turbine. There are three types of availabilities
Shuwaikh 0 6 42 in a system with related formulas as given below:
Shuaiba 6 120 4 108
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International Journal of Energy and Power Engineering
Vol:9, No:4, 2015
stoppage due to preventive maintenance (PM), which require rescheduled from the time the repair is completed. Effectively,
time to perform PM. The corrective time is denoted as MCt, it is assumed that the equipment is renewed and starts as fresh.
while the preventive time is denoted as Mpt. As a result of The second policy is called block based maintenance (BBM)
these two stoppages, there are two general types of policy, in which case, each stoppage is independent of the
maintenance, called maintenance policies. The first policy is others and if a failure occurs and a repair is completed, the
called age-based maintenance (ABM) policy, in which case, following PM is not rescheduled; it is performed at the
whenever the equipment is stopped for either CM or PM, scheduled time even if it is shortly after the failure.
whichever comes first, the next maintenance for CM or PM is
ST C M Firs t C M
0
0 Tru e
R es c hedule PM
PM Before CM W ait U ntil PM Perfor m PM
and C M
0 Fa l s e
ST PM Firs t PM
0
W ait U ntil C M Per for m C M
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0 T ru e
ST CM First CM PM Schedule Wait Until PM Perform PM Reschedule PM Count CMs
0
0 Fa ls e
ST PM First PM
Wait Until CM Perform CM Reschedule CM Count PMs
0
The simulation model is run for each maintenance policy is changed from blocked based policy to age-based policy. For
for each type of system, steam turbines and gas turbines, in example, for the case of steam turbines, the availability is
order to observe the system availability under different increased from 85.88% to 88.60%, while in the case of gas
operational conditions. Fig. 1 shows a snapshot of the turbines, it is increased from 78.72% to 93.1%. This very high
simulation model for the ABP and Fig. 2 shows a snapshot for increase in the gas turbines is because gas turbines fail more
BBP. In the simulation model, failures and maintenance are frequently and each time a failure occurs, the following PM is
generated based on the random times and the necessary repairs eliminated by combining with the failure. The next PM is
are done based on the selected policy. As it can be seen in the rescheduled from the time repair is completed. Effectively, the
model of Fig. 1, in ABP, the next failure or maintenance is majority of the times the PM are combined with the CM since
rescheduled after any failure or maintenance is performed. MTBF is much smaller than MTBM.
However, in the BBP, the next failure or maintenance is
rescheduled after occurrence the respective failure or the TABLE VI
STEAM AND GAS TURBINE AVAILABILITIES UNDER DIFFERENT MAINTENANCE
maintenance operation and the completion of the necessary POLICIES
repair or maintenance action. The difference is in the Types of Ao Ao- ABP Ao Ao- BBP
rescheduling of the next CM or PM. Using the data collected Turbines ABP Confidence Limits BBP Confidence Limits
for each type of turbine unit in the power station, we have Steam 0.886 (0.876, 0.896) 0.8588 (0.839, 0.879)
simulated the steam turbines and gas turbines separately and Gas 0.931 (0.930, 0.932) 0.7872 (0.7772,0.7972)
determined the effect of different policies on system
availabilities. The simulation was run for a period of 10 years, V. CONCLUSIONS
assuming 24 hours of operation per day. Each case was One of the major problems faced in the operation of power
replicated 30 times in order to determine 95% confidence plants is a determination of turbine unit availability under
limits on availability values estimated. Table VI shows the different operational conditions and maintenance policies.
simulation results for each case. This is essential in order to estimate the expected maximum
As it can be seen from the results in Table VI, power station possible electrical utility output from the se stations. In this
availability is significantly increased when maintenance policy paper, we have taken a particular power station, which
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World Academy of Science, Engineering and Technology
International Journal of Energy and Power Engineering
Vol:9, No:4, 2015
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