Chapter 2. Planning Criteria. Turaj Amraee. Fall 2012 K.N.Toosi University of Technology

Transcription

1 Chapter 2 Planning Criteria By Turaj Amraee Fall 2012 K.N.Toosi University of Technology

2 Outline 1- Introduction 2- System Adequacy and Security 3- Planning Purposes 4- Planning Standards 5- Reliability Assessment

3 Introduction Reliability and Planning Planning could be interpreted as an optimization task The planning decision are made as the result of a reasonable tradeoff between Technical and Economical constraints. How to quantify the reliability Reliability begins with Planning

4 System Adequacy and Security Reliability of the interconnected bulk electric systems is defined using the following two terms: Adequacy - The ability of the electric systems to supply the aggregate electrical demand and energy requirements of their customers at all times, taking into account scheduled and reasonably expected unscheduled outages of system elements. Security - The ability of the electric systems to withstand sudden disturbances such as electric short circuits or unanticipated loss of system elements.

5 Planning Purposes Power systems must be planned, designed, and constructed to operate reliably within thermal, voltage, and stability limits while achieving their major purposes. These purposes are to: Deliver Electric Power to Areas of Customer Demand Provide Flexibility for Changing System Conditions Reduce Installed Generating Capacity Allow Economic Exchange of Electric Power Among Systems

6 Planning Standards North American Electric Reliability Corporation Standards International Electrotechnical Commission NERC WECC IEC WESTERN ELECTRICITY COORDINATING COUNCIL Facility Connection Requirements Voltage Support and Reactive Power Transfer Capability System Modeling Data Requirements System Protection and Control System Restoration

7 Planning Standards NERC Example Cat. A Cat. B Cat. C Cat. D Normal N-1 N-2 and higher Cascading S1. The interconnected transmission systems shall be planned, designed, and constructed such that with all transmission facilities in service and with normal (precontingency) operating procedures in effect, the network can deliver generator unit output to meet projected customer demands and projected firm (non-recallable reserved) transmission services, at all demand levels over the range of forecast system demands, under the conditions defined in Category A of Table I (attached).

8 NERC Planning Criteria

9 NERC Planning Criteria

10 Reliability An introduction Power equipment such as generator, transformers, Trans. Lines, etc., are generally considered to be system components. In their service life time, they can be in many states: Running Fault Repair Planned maintenance Temporary maintenance

11 Reliability failure characteristics Characteristics of component failure Continuous working time T of a component is a random variable. F(t) : failure function of a component, F( t) P( T t) t 0 R( t) P( T t) t 0 R(t) : the probability that a component still operates after a designated time t, and is called the reliability function of a component or Reliability F( t) R( t) 1 dr( t) dt df( t) dt f ( t) f ( t ) is the failure probability density function

12 Reliability failure characteristics Failure rate function The conditional probability that a component is working before the time instant t and develops a fault in the unit time Del(t) after the time instant t, 1 ( t) lim t0 P( t T t t T t) t f ( t) ( t) R( t) 1 R( t) dr( t) dt

13 Reliability failure characteristics Mean time between failures (MTBF) The mean of the random variable T is called a component's mean time between failures (MTBF), which is another index to evaluate a component's reliability. MTBF 1

14 Reliability repair characteristics Characteristics of component repair The repair rate can be defined in a form similar to that for the failure rate: 1 ( t) lim t0 P( t TD t t TD t) t Mean time to repair (MTTR) The mean of a component's repair time TD or the mean time to repair can be written as MTTR 1

15 Reliability Availability Availability The probability PA(t) that a component is in service state is called the availability A P UP ( ) A MTBF MTBF MTTR FOR : U Dn 1 A P ( ) U MTTR MTBF MTTR

16 Reliability Evaluation Process Reliability Calculation Define the boundary of the system and list all the components included Provide reliability data such as failure rate, repair rate, repair time, scheduled maintenance time, etc., for every component. Establish reliability models for every component. Define the mode of system failure, or define the criterion for normal and faulty systems. 5. Establish a mathematical model for the system reliability assumptions. 6. Select an algorithm to calculate the system reliability

17 Reliability Evaluation Process Generation: Transmission is ignored Composite: Generation+Transmission Distribution: Gen+Trans. Are ignored Here HLI is considered Gen Load Generation: Two or three states model Transmission Line, Transformer: Two or three states model Load: Load Duration Curve

18 Reliability Generation Model 1- State Probability Model: Example- Dual State Generation Model The system loses capacity c with a certain probability when the generating unit to stop due to random failures. Therefore, the capacity or the is considered to be a random variable in power system. The unit model is the probability table of a generator unit's capacity state. Probability model The dual-state model assumes that a unit only has two states: operation and failure (repair). Individual state probability P( 1 FOR xi ) FOR x i x i c 0 cumulative state probability 0 xi 0 P( xi ) FOR 0 xi 1 xi c c

19 Reliability Generation Model Example- Dual State Generation Model 2- State Frequency Model: Suppose p(i) = P( = xi) is the individual probability of ith state (capacity), fi is the ith state frequency and fij is the transition frequency from state i to state j. f f i Individual state frequency j p p i i j i i j p ( 1 FOR) ij i ij p (FOR) ji j ji cumulative state frequency F ( x) F( x) f ( ) ik x i

20 Reliability Example Example- Dual State Generation Model Capacity Outage Probability Table

21 Reliability Example Example- Dual State 2-Units Generation Model For multi-generator unit model COPT is constructed using recursive algorithm the table is revised as units are added one after another until the last one and the capacity model for the whole generating system is formed.

22 Reliability Load Model Primary load data Normally primary load data include: 1. The maximum monthly load or weekly load in a year. As a percentage of the maximum load in a year(52 weeks) 2. The maximum load in each day in a week. As a percentage of the maximum load in a week(7 days) It is assumed that it is valid for all the seasons 3. The load in 24 hours in a typical day in each season. As a percentage of the maximum load in every hour(24 hours) For each season a typical different load curve is assumed From 1 and 2 Maximum load for the 365 day in a year From 1,2 and 3 Maximum load for the 8760 hrs in a year

23 Reliability Load Model Load outage capacity table Tha aim is to replace the load curve with a load outage capacity P ( L ) i j t ij T t ij T The pause time of Li inside T The examination period: 365 days or 8760 hrs The load level Li is the negative of operation capacity

24 Reliability Load Model

25 Generating System Reliability Evaluation The system margin state probability and frequency table is formed by convolution of the parallel calculation formula applied to the generator outage table and the load capacity table Generating unit's cumulative P and F: a i a i a N i F P,..., 0,1 ) ( ), ( b i b i b N i F P,..., 0,1 ) ( ), ( Load cumulative P and F: Margin state cumulative probability )] ( ) ( )[ ( ) ( 1 0 j b j b i k N j a k c P P P P b )]} ( ) ( )[ ( )] ( ) ( )[ ( { ) ( j b j b i k a j b j b i k N j a k c F F P P P F F b Margin state cumulative frequency

26 Reliability Indices The power generation system reliability indices are usually a measure of power supply reduction to customers (load point) as a result of faults developed in the power generating unit 1. Loss of load probability (LOLP), LOLP is defined as the probability of the effective system capacity not meeting the load demand, which can be written as LOLP P( R) : system outage capacity R=C-L: system reserve capacity C: system effective capacity L: Maximum load

27 Reliability Indices 2. Loss of Load Expectation (LOLE) The expected number of days or number of hours in the period investigated when the maximum load exceeds the system effective capacity: LOLE LOLP * T hrs/year or day/year Based on load model: T is 8760 hours or 365 days

28 Reliability Indices 3.Expected energy not served (EENS) EENS is the expectation of the energy loss caused to customers by insufficient power supply: EENS M k 0 M k p k *8760 MWh / year Mk=Cj-Li: system margin capacity

29 Reliability Indices 4. Frequency and duration (F& D) If the cost to customers is affected by the frequency of power interruption over a certain period instance to customers e.g. chemical industry or metallurgical then the indices of power interruption duration is needed. The cumulative system interruption frequency and duration F F( R) times / year D P( F( R) R) hours

30 Reliability Indices 5. System-minutes (SM) The SM index is the ratio of energy loss due to power interruption as a result of insufficient system generation over the annual maximum load SM EENS L p min utes Lp the annual maximum load

31 Exercise 1. Write a computer program to obtain the results of Examples 2.2 and 2.3 of the reference # 1.

32 End