power system reliability presentation

1. SEMINAR TOPIC ON
“POWER SYSTEM RELIABILITY”
SHRI RAMSWAROOP MEMORIAL UNIVERSITY
Presented By: Presented To:
Md Afzal Asst. Prof. Yaswant Kumar
Singh
Roll No. 201610103010003 (EED)

2. TABLE OF CONTENT
S.No. Topic
1. Introduction
2. Power system reliability definition
3. Transmission planning
4. Perspective on reliability
5. Measuring reliability
6. Optimum reliability
7. Outage
8. Bath tube curve
9. Power supply quality survey
10. Power quality monitoring
11. Risk management
12. Continuous markov process
13. conclusion

3. WHAT IS POWER SYSTEM RELIABILITY
An electric power system serves the basic function of supplying
customers, both large and small, with electrical energy as
economically and as reliably as possible. The reliability associated
with a power system is a measure of its ability to provide an adequate
supply of electrical energy for the period of time intended under the
operating conditions encountered.

4. POWER SYSTEM RELIABILITY
 Adequacy
A measure of the ability of the power system to supply the aggregate electric power and
energy requirements of the customers within components ratings and voltage limits, taking
into account planned and unplanned outages of system components. Adequacy measures the
capability of the power system to supply the load in all the steady states in which the power
system may exist considering standards conditions.
Reliability
Adequacy Security

5. POWER SYSTEM RELIABILITY
 Security
o A measure of power system ability to withstand sudden disturbances such as electric
short circuits or unanticipated losses of system components or load conditions together
with operating constraints.
o Another aspect of security is system integrity, which is the ability to maintain
interconnected operation.
 Generation Adequacy In Energy Only Markets
o Economic theory tell us that in a long-term equilibrium of energy only markets, the
optimal capacity stock is such that scarcity payments to the marginal generators when
demand exceed supply will exactly cover the capacity cost of these generators and will
provide the correct incentives for demand side mitigation of the shortage (i.e. the
security rand will induce sufficient demand response so that available supply can meet
the remaining load)

6. FIGURE- OPTIMAL CAPACITY AND ENERGY PRICES IN
LONG TERM EQUILIBRIUM

7. TRANSMISSION PLANNING
 Once we have the load forecast and generation location, it is easy to identify ‘where to
build lines and how many’.
 In India the transmission planning is done as per the Manual on Transmission Planning
Criteria prepared by CEA in June 1994.
Transmission planning criteria:
The system shall be evolved based on detailed power system studies which shall include:
The following options may be considered for strengthening of the transmission network.
o Addition of new Transmission lines to avoid overloading of existing system. (whenever
three or more circuits of the same voltage class are envisaged between two sub stations,
the next transmission voltage should also be considered.)
o Application of Series Capacitors in existing transmission line to increase power transfer
capability.
o Upgradation of the existing AC transmission lines
o Reconductoring of the existing AC transmission line with higher size conductors or with
AAAC.
Power Flow
studies
Short circuit
Studies
Stability Studies(including:
transient stability, voltage
stability, and steady state stability
studies)

8. PERSPECTIVE ON RELIABILITY
 The appropriate definitions of reliability may vary with respect to the perspective taken
of the system.
 The figure below summarizes the varying concerns of different constituents, including
the perspectives of the separate parts of the electric power system that are individually
responsible for generation, transmission, and distribution.
The customer perspective:
o The customer perspective is fundamental.
o The customer, or user, experiences outages. The occurrence of an outage indicates that
service reliability is not perfect.
The utility perspective:
o The utility perspective may differ from the customer or user perspective.
o The definition of reliability for the utility should be related to that of the end user, the
customer. (That is, the utility's definition of reliability should be related to service
reliability.)

9. FIGURE- PERSPECTIVE ON RELIABILITY

10. MEASURING RELIABILITY
The reliability indices used to measure distribution system reliability, how to calculate the
indices, and discusses some of the factors that influence the indices.
 Distribution Indices:
o Momentary Interruption -
A single operation of an interrupting device that results in a voltage zero.
o Momentary Interruption Event -
An interruption of duration limited to the period required to restore service by an
interrupting device. This must be completed within five minutes.
o Sustained Interruption –
Any interruption not classified as a momentary event.

11. COMMON DISTRIBUTION INDICES
 System Average Interruption Duration Index (SAIDI),
 Customer Average Interruption Duration Index (CAIDI),
 System Average Interruption Frequency Index (SAIFI),
 Momentary Average Interruption Frequency Index (MAIFI),
 Customer Average Interruption Frequency Index (CAIFI),
 Customers Interrupted per Interruption Index (CIII), and the
 Average Service Availability Index (ASAI).
Use of reliability indices
A. System Average Interruption Duration Index (SAIDI)
To calculate SAIDI, each interruption during the time period is multiplied by the duration of
the interruption to find the customer-minutes of interruption.
SAIDI = S(ri * Ni ) / NT
Where,
SAIDI = System Average Interruption Duration Index, minutes.
S = Summation function.
ri = Restoration time, minutes.
Ni = Total number of customers interrupted.
NT = Total number of customers served.

12. CONTINUED- USE OF RELIABILITY INDICES
B. Customer Average Interruption Duration Index (CAIDI)
Once an outage occurs the average time to restore service is found from the
Customer Average Interruption Duration Index (CAIDI). CAIDI is calculated similar to
SAIDI except that the denominator is the number of customers interrupted versus the total
number of utility customers.
CAIDI = S(ri * Ni ) / S( Ni )
C. System Average Interruption Frequency Index (SAIFI)
The System Average Interruption Frequency Index (SAIFI) is the average number of times
that a system customer experiences an outage during the year (or time period under study).
The SAIFI is found by divided the total number of customers interrupted by the total number
of customers served.
SAIFI = S(Ni ) / NT
D. Customer Average Interruption Frequency Index (CAIFI)
Similar to SAIFI is CAIFI, which is the Customer Average Interruption Frequency Index.
The CAIFI measures the average number of interruptions per customer interrupted per year.
CAIFI = S( No ) / S( Ni )

13. CONTINUED- USE OF RELIABILITY INDICES
E. Momentary Average Interruption Frequency Index (MAIFI)
The MAIFI is the Momentary Average Interruption Frequency Index and measures the average
number of momentary interruptions that a customer experiences during a given time period.
MAIFI is rarely used in reporting distribution indices because of the difficulty in knowing when a
momentary interruption has occurred.
MAIFI = S( IDi * Ni ) / NT
F. Average Service Availability Index (ASAI)
The Average Service Availability Index (ASAI) is the ratio of the total number of customer hours
that service was available during a given time period to the total customer hours demanded.
ASAI = [1 – (S(ri * Ni ) / (NT * T))] * 100
G. Customer Interrupted per Interruption Index (CIII)
The Customer Interrupted per Interruption Index (CIII) gives the average number
of customers interrupted during an outage. It is the reciprocal of the CAIFI and is,
CIII = S( Ni ) / S( No )

14. OPTIMUM RELIABILITY
 Higher reliability can be achieved by the installation of better equipment or by providing
more redundancy. Capital and the operating costs are associated with both solutions, and
the capitalized value of these investments is the price the utility has to pay for an
intended higher level of reliability.
 For residential consumers, the losses arising from serving interruptions are rather
intangible, they are mostly associated with comfort and convenience.
 When C and D are known, total cost associated with various levels of system reliability
is given by the sum of two curves, and optimal reliability cost at point ‘O’ evaluated.
Figure: relation
between
reliability and
cost.

15. OUTAGE
 An outage (also called a power cut, a power blackout, power failure or a blackout) is
a short-term or a long-term loss of the electric power to a particular area.
 There are many causes of power failures in an electricity network. Examples of these
causes include faults at power stations, damage to electric transmission lines, substations
or other parts of the distribution system, a short circuit, or the overloading of electricity
mains.

16. BATH TUBE CURVE

17. CONTINUED- BATH TUBE CURVE
It describes a particular form of the hazard function which comprises three parts:
 The first part is a decreasing failure rate, known as early failures.
 The second part is a constant failure rate, known as random failures.
 The third part is an increasing failure rate, known as wear-out failures.
 The bathtub curve is generated by mapping the rate of early "infant mortality" failures
when first introduced, the rate of random failures with constant failure rate during its
"useful life", and finally the rate of "wear out" failures as the product exceeds its design
lifetime.
 In less technical terms, in the early life of a product adhering to the bathtub curve, the
failure rate is high but rapidly decreasing as defective products are identified and
discarded, and early sources of potential failure such as handling and installation error
are surmounted.

18. POWER SUPPLY QUALITY SURVEY
 A systematic power quality survey of the distribution system is of fundamental value
before releasing the power connection for sensitive loads.
 It is common for consumers to use a power electronic system for power supply in the
case of sensitive equipment.
 A power electronic system consists of a power source, filter, a power converters, a load
and a control circuit. The block diagram is shown in figure.
Figure:
Clean
power
process

19. POWER QUALITY MONITORING
Power quality monitoring keeps a check on the following PQ parameters (disturbances)
o Sags/Surges
o Swells
o Dips
o Flicker
o Transient over-voltages
o Harmonics
o Frequency profiles
o Voltage and current unbalance
Figure:
Typical
voltage sag
under fault
condition.

20. RISK MANAGEMENT
 Risk management is an important tool for the power system reliability. Typically the risk
that occur are financial (regulation, varying interest rates and energy price),
environmental, and/or age related mechanism.
 This approach aims to mitigate adverse financial or operational consequences of
uncertain outcomes through economic or operational hedging.
 Risk sharing agreements and syndications is another form of economic risk mitigation.
 Financial hedging is a form of economic risk mitigation in which a risk bearer reduces
its exposure by creating a portfolio of ventures whose outcomes happen to be correlated
so as to reduce total variability.
In particular, it is useful to classify types of risks based on the following categories:
Voluntary Vs.
Involuntary
Private Vs.
Public
Diversification
options(risk
sharing,
portfolio
approaches)
Tradability
(Insurance,
hedging)
Interdependency
(ability to
provide
differential
protection)

21. CONTINUOUS MARKOV PROCESS
o The state space method can be used for reliability evaluation. System is represented by
its states and the possible transition between states.
o A set of random variables with the variables ordered in a given sequence is called
stochastic process.
o The values assumed by the variable form the state space. In power system studies the
state is discrete but the probability index is continuous.
o This special class of stochastic processes is known as Markov process. A Markov
process with discrete index is known as Markov chain.
Figure shows the state space diagram of a single repairable component whose failure and
repair rates are characterized by exponential distributions.
Figure: State
Space
diagram

22. CONCLUSION
o One of the most important elements in power system planning is to find out how much
generation is needed to satisfy given load requirements.
o A second equally important element in the planning process is the development of a
suitable transmission network to provide the energy generated to the customer load
points.
o The two studies gives some clear directions for an improved approach for controlling
and optimizing reliability with respect to costumer needs and values.
o In the costumer needs study we characterized the most fundamental customer needs in
terms of key attributes of electric service, such as number of outages per year and
distribution per outage.
o The two reports suggest that a better reliability planning method would begin with
costumer needs and use those needs to define the important aspects of system
performance.

23. REFERENCES
 Power system analysis – Hadi Saadat
 Power system analysis – Kothari Nagrath
 Modeling and analysis of generation system based on markov process with case study.
Volume 1 | Issue 11 | April 2015 ISSN (online): 2349-6010
 Reliability of Electric Utility Distribution Systems: EPRI White Paper, EPRI, Palo Alto,
CA:2000. 1000424.
 Reliability evaluation of power system, second edition- Roy Billinton.

24. Thank you