CHAPTER 4 SUBSTATION CONFIGURATION RELIABILITY ESTIMATION BY SUCCESSFUL PATH METHOD

Transcription

1 60 CHAPTER 4 SUBSTATION CONFIGURATION RELIABILITY ESTIMATION BY SUCCESSFUL PATH METHOD Substations are integral parts of a power system. They are important links between the generating station, transmission systems, distribution systems and the loads at consumer level. The electrical voltage is stepped up and down to higher and lower voltage levels several times on its way from the generation station to the consumer at the substation. An electrical substation is an assembly of electrical components including bus bars, circuit breakers, power transformers, instrument transformers, surge arrestors or lightning arresters, isolators or disconnecting switches, neutral grounding equipments, power line carrier communication equipments, line traps, tuning units, coupling capacitor,protection systems, earthling switches, earth electrodes, shunt reactors, shunt capacitances, series reactors, series capacitors, isolated phase bus systems, metering, control and relay panels and d.c. battery system. The substation s important functions are establishment of economic load distribution, protection of transmission systems, controlling the power exchange, ensuring steady state and transient stability, prevention of loss in synchronism by load shedding, maintaining the system frequency within acceptable limits, data transmission via power line carrier communication for the purpose of network monitoring, control, protection and ensuring reliable supply to the consumers.

2 61 The substations are classified in various ways as follows: Outdoor substation or in door substation based on location E.H.V. substation, H.V. substation, M.V. substation and L.V. substation based on voltage levels Grid substation or Distribution substation based on application Conventional air insulated outdoor substation, or SF6 Gas Insulated Substation (GIS), or hybrid substations having combination of the above two based on design. 4.1 AIR INSULATED SUBSTATION (AIS) AIS has galvanized steel structures for supporting the equipments, insulators, incoming and outgoing transmission lines. Circuit breakers, isolators, transformers, current transformers, potential transformers are installed in the outdoor. Bus bars are supported on the post insulators or strain Insulators. This substation occupies large area. One of the most important innovations in electrical engineering in the 20 th century is the launch of gas insulated switchgear in 1965 since a conventional air insulated substation occupied large area. The dimensions were reduced from air insulated substation due to the introduction of Gas Insulated Substation (GIS) technology. The maintenance intervals are also reduced to once in every ten years. This had improved availability and reliability with lowered operating costs. The SF6 gas enclosure has made the switchgear insensitive to pollution like the corrosive effects of salt, sand and snow.

3 GAS INSULATED SUBSTATION (GIS) The size of substation reduces to 8% to 10% of the Air Insulated Substation since circuit breakers, current Transformers, voltage transformers, bus bars, earth switches, surge arresters and isolators are in the form of metal enclosed SF6 gas modules. These modules are assembled in accordance with the required design. The various live parts are enclosed in the metal enclosures containing SF6 gas at high pressure. GIS sulfur hexafluoride (SF6) gas. Aluminum is used for the enclosure. This assures freedom from corrosion and low weight of the equipment. The low weight ensures minimal floor loading. Gas tight bushings allow subdivision of the bay into a number of separate gas compartments. Each gas compartment is provided with its own gas monitoring equipment, a rupture diaphragm and filter material. The static filter in the gas compartments absorb moisture and decompose it. The rupture diaphragm prevents build up of high pressure in the enclosure. A gas diverter nozzle on the rupture diaphragm ensures that the gas is expelled in a defined direction in the event of bursting, thus ensuring that the operating personnel are not endangered. All the modules are connected to one another by means of flanges. The gas tightness of the flange connections is assured by proven O ring seals. Temperature related changes in the length of the enclosure and installation tolerances are compensated by bellows type expansion joints. Circuit breaker module has a central element of the gas insulated switchgear.the three pole circuit breaker module enclosures comprises of the two main components, interrupter unit and operating mechanism. The spring stored operating mechanism provides the force for opening and closing the circuit breaker. It is installed in compact corrosion free aluminum housing. The entire operating mechanism unit is completely isolated from the SF6 gas

4 63 compartments. Antifriction bearings and maintenance free charging mechanism ensures decades of reliable operation. The functions of a disconnect switch and an earthling switch are combined in a three position switching device. The moving contact either closes the isolating gap or connects the high voltage conductor to the fixed contact of the earthling switch. Integral mutual inter locking of the two functions is achieved as a result of this design An insulated connection to the fixed contact of the earthling switch is provided outside the enclosure for test purposes. In the third neutral position neither the disconnect switch contact nor the earthling switch contact is closed. The three poles of a bay are mutually coupled and all the three poles are operated at the same time by a motor. The gas compartments are constantly observed by means of density monitors with integrated indicators. 4.3 HYBRID SUBSTATION Hybrid substations are the combination of both AIS and GIS Some bays in a substation are gas insulated type and some are air insulated type. The design is based on convenience, local conditions, area availability and the economics of cost implications. An important function performed by a substation is switching. Switching events may be planned or unplanned. A transmission line or other component may need to be de-energized for maintenance or for commissioning of equipment. To maintain reliability of supply, no one ever brings down its whole system for maintenance. In addition, the function of the substation is to isolate the faulted portion of the system in the shortest possible time since fault tends to cause equipment damage and destabilize the whole system.

5 64 The type of high voltage switching scheme may be selected after a careful study of the flexibility and protection needed in the station for the initial installation, and also when the station is developed to its probable maximum capacity. In an ideal substation all circuits and equipments would be duplicated such that following a fault or during maintenance, one connection remains available. Practically this is not feasible since the cost of implementing such a design is very high. Methods have been adopted to achieve a compromise between reliability of supply and cost. There are four categories of substation that give varying reliability of supply: Category 1 or fault conditions. Category 2 No outage is necessary within the substation for either maintenance Short outage is necessary to transfer the load to an alternative circuit for maintenance or fault conditions. Category 3 maintenance. Category 4 Loss of a circuit or section of the substation due to fault or Loss of the entire substation due to fault or maintenance. 4.4 SUBSTATION CONFIGURATION Substation configuration implies different methods employed to connect electrical circuits in the power system to transfer the electrical power in reliable manner. It helps in delivering the electrical power to power system if any part of the system is faulty or under maintenance.

6 65 Substations use different types of bus bar arrangements, which depend upon the application, reliability of the supply and cost of installation. In every substation, bus bar plays a pivotal role to connect different circuits. However,switching is possible in the power system with the help of circuit breakers and isolators Considerations for Selection of Bus Bar Arrangement Different types of bus bar arrangements are employed based on the voltage, reliability of the supply, flexibility in transmitting power and cost. The other aspects considered for designing the bus bars arrangements are: Simplicity in the design Maintenance of different equipment without interruption of the power supply Feasibility in expansion Economical installation and operational cost Different Bus Bar Arrangements Some of the switching schemes used by bus bar arrangements employed in the substations are listed below: Single bus-bar configuration Sectionalized single bus bar configuration Breaker and a half configuration Double bus, double breaker configuration

7 66 The substation configuration is investigated since the recent trend in urban area is to improve the system reliability by adjustment of substation bus bar configuration with hybrid switchgear within the same space constraint. The new technique of Successful Path Method (SPM) is proposed to analyze the reliability of various substation configurations. The results are compared with the Cut Set Method of Daniel Nack (2005). The author has published a paper on A Novel Approach for Reliability Analysis of Power System Configurations, International Journal of College Sciences in India. vol 3, pp 49-72, July DANIEL NACK METHOD Daniel Nack had presented the minimal cut set method based on the criteria of continuity or availability of power supply. It considers each failure state as an exclusive state, so that the probability of occurrence of system failure is the sum of all the failure event probability. The components modeled are transformers, bus bars, breakers and outgoing lines from substation. The incoming lines were assumed to have 100% reliability for developing substation indices. Daniel Nack (2005) had proposed the substation component failure rate value as shown in Table 4.1. These are converted into the corresponding reliability value. The Reliability of the component is given by the relationship as per equation (2.10). R(t) = e t (4.1) where R(t) = Reliability t = Failure rate = Time period

8 67 Table 4.1 Substation component reliability indices Component Total component failure rate per year () Total reliability per year (R),R= e -t Line Transformer Breaker Bus Bar The existing method of Daniel Nack had estimated the indices by cut set method for the four substation configurations including line failures. These are shown in Table 4.2. Table 4.2 Daniel Nack reliability indices Configuration Total component failure rate per year () Total reliability per year (R), R= e -t Single bus bar Sectionalized single bus bar Breaker and a half bus bar Double bus double breaker PROPOSED SUCCESSFUL PATH METHOD (SPM) Boundaries are required to be established before proceeding with the reliability evaluation of the substation configurations. In this dissertation work, the boundary is constructed within the substation for reliability assessment. The components modeled are transformers, bus bars and breakers.

9 Modeling There are number of methods described in the standard literature to evaluate the availability of the power system. This work considers the availability and unavailability as a two state up or down model to represent all components in the simplest way for the reliability assessment. The level of performance criteria evaluated is based on the total failure rate per year of each component. This is converted into reliability or availability of substation components.the repair time and its duration are ignored. Sudden opening of circuit breaker online, without any command is known as passive failure. If the circuit breaker fails to open after the command from the protective relay, then it is known as stuck condition of breaker. If many circuit breaker failures occur simultaneously, then it is known an overlapping failure. In modern substations, the possibilities of multiple failure events are rare due to the transition from AIS to superior performing GIS. Hence, this dissertation work considers total failure rate per year occurring in isolation separately for each component in the substation. The proposed method of SPM for receiving continuous power supply is expressed using Boolean logic.all the developed reliability values for the various substation configurations are estimated from component values listed in the Table 4.1. The basic difference between FTA and SPM is the direction of the analysis. A FTA starts with the undesired event and traces backward to the causes. The fault tree ends with initiating basic events and failures that are identified as the primary causes. Success path is associated with the degree of its usefulness. A SPM starts with an initiating cause and traces forward the resulting consequences. This forward stepping is repeated for different selected initiating causes. The end consequences can vary depending on the

10 69 initiating cause. Thus the principle of SPM modeling is to identify in each step the immediate cause of success, which is to be analyzed. Most failure probabilities are small (less than 0.1), which uses approximations when combining failure probabilities. Success probabilities are usually close to 1.0, these approximations cannot be used and the solution of success models are more accurate than the solution of failure models. The single bus bar substation, sectionalized bus bar substation, breaker and a half bus bar sub station and double bus bar double breaker substations are analyzed for reliability estimation with the following assumptions: Boundaries are defined within the perimeter of the substations. Reliability is defined as the ability of a component to perform a required function under given environmental and operational conditions for a specified period of time. The term component is used to denote any subsystem that can be considered as an entity. A required function will be necessary to provide a specified service. The reliability of the components is assessed based on the required function under consideration. Set theory is used for event A and event B indicating the successful paths in the same substation system domain(s) whose universal set (U) is shown in Figures 4.1 and 4.2.

11 70 S A B U Figure 4.1 A OR B (A B) S A B U Figure 4.2 A B (A B) A union of set A and set B consists of all components which belong to either A or B as shown in Figure 4.1. The algebraic operation with probabilities A B for two A and B events, which are independent high probability events are given by

12 71 (A B) = P (A) + P(B) P(A). P (B) (4.3) This means that the occurrence of set A has no influence on the successful occurrence or non successful occurrence of set B and vice versa. In other words, if two successful paths have components which are operating in parallel and are isolated from one another, then the success of one event does not affect the success of the other event. Thus, the success paths of the components of all events are independent. The intersection of set A set and set B consists of only elements, which belong to both sets A and B. This is denoted by A B as shown in Figure The algebraic operation with probabilities A B for two A and B events, which are independent high probability events are given by P (A B) = P(A) P(B). This is known as the multiplication rule for probabilities. The development of a quantitative success model is based on the need to get the best possible estimate for the top success event probability. The success modeling for successful path method includes the procedure and nomenclature by which events and gates are named for the specific success of the top event. The process of SPM gives the information about nature of the basic event and the number of such events in the combined set of the occurrence of the top event showing the quantitative importance of each basic event contributing to the top event.

13 72 Each set is evaluated by probability of its occurrence and it s inter relationships. The quantitative results are interpreted to provide the potential impact upon the success of the top event. The immediate cause concept of the successful immediate steps is determined from the necessary and sufficient occurrence of the next sequence of its events. The final successful event is achieved proceeding up the success tree continuously transferring the success mechanism to success mode till the success tree is completed. The success mechanisms are evaluated using two basic types of gates, the OR gate and the gate. The reliable supply is available at the High Voltage transmission line feeders L 1 or L 2 in the substations as shown in Figures The bus bars, breakers, transformers and lines are considered as components in the sub-station as shown in Figures They are expressed as HV bus no.1, HV bus no.2, LV bus, breakers B 1, B 2, B 3, B 4, B 5, B 6, B 7, B 8, B 9, B 10, B 11, B 12, B 13, B 14, B 15, B 16, B 17, B 18, B 19, transformers T 1 and T 2. The substation component reliability values are substituted from Table 4.1 Each component is checked for meeting its two criteria. The first criterion checks its healthy status. If a component is healthy then it can be used. In other words, it will allow the current to flow. The second criterion checks whether the current flow is available to the component. If these two criteria are full filled then the component forms an gate, whose current output is available.

14 73 Considering the worst case, one of the bus bar is functioning satisfactorily out of the available two bus bar units as shown in Figures Considering the worst case, one of the transformer is functioning satisfactorily out of the available two transformer units as shown in Figures Single Bus Bar Substation L 1 L 2 B 1 B 2 HV Bus B 3 B 4 T 1 T 2 LV Bus Figure 4.3 Single bus bar configuration

15 74 A single bus bar substation configuration consists of transformers T 1 and T 2. These transformers are connected in parallel between the low voltage bus bar (LV bus) and high voltage bus bar (HV bus) through breakers B 3 and B 4. The high voltage transmission lines L1 and L2 are connected to the high voltage bus bar (HV bus) through breakers B 1 and B2. The single bus bar substation is shown in Figure 4.3. This is the simplest bus bar scheme available, which consists of single bus bar connected to the transformers and load feeders. All the feeders are connected by circuit breakers and set of isolators. This arrangement helps to remove the connecting equipments for maintenance by opening the circuit breaker and isolator contacts. Single bus bar configuration is lower in installation cost. It requires less maintenance. It is simple in construction. However, single bus bar configuration is not very reliable since incase of fault on bus bar the feeders L 1 and L 2 connected to bus bar loose supply. The single bus bar substation reliability is estimated for various modes of operations as follows: Mode 1 Successful operation of the single bus bar substation. The logic for single bus bar configuration during the operation of transformer T 1, when T 2 transformer is not available is shown in Figure 4.4.

16 75 Current Output Current flow to LV bus LV bus allows current to flow Current flow to transformer (T 1 ) Transformer (T 1 ) allows current to flow Current flow to breaker (B 3 ) Breaker (B 3 ) allows current to flow Current flow to HV bus HV bus allows current to flow OR Current flow to HV bus Current flow to HV bus Current flow to Breaker (B1) Current flow to Line (L 1 ) A Current flow to Breaker(B 2 ) B 1 allows current to flow B 1 allows current to flow Current flow to line L 2 Line L 1 allows Current to flow Breaker (B2) allows Current to flow Line (L 2) allows Current to flow Figure 4.4 Logic for single bus bar configuration during T 1 operation

17 76 A reliability value is estimated in mode 1 by substituting the substation component reliability indices from Table 4.1 The estimated value of reliability in mode 1 = [L 1 B 1 L 2 B 2 ) HV Bus B 3 T 1 LV Bus = [L1* B1 L 2 *B 2 ] *HV Bus* B 3.*T 1 *LV Bus = [L 1 * B 1 + L 2 *B 2 L 1 * B 1 *L 2 * B 2 ] *HV Bus* B 3 *T 1 *LV Bus = Mode 2 Successful operation of the single bus bar substation The logic for single bus bar configuration during the operation of transformer T 2, when transformer T 1 is not available is shown in Figure 4.5. A reliability value is estimated in mode 2 by substituting the substation component reliability indices from Table 4.1 The estimated value of reliability in mode 2 = [L 1 B 1 L 2 B 2 ) HV Bus B 3 T 2 LV Bus = [L 1 *B 1 L 2 *B 2 ] *HV Bus* B 3 * T 2 *LV Bus = [L 1 *B 1 + L 2 *B 2 L 1 *B 1 *L 2. *B 2 ] *HV Bus*B 3 *T 1 *LV Bus =

18 77 Current Output Current flow to LV bus LV bus allows current to flow Current flow to transformer (T 2 ) Transformer (T 2 ) allows current to flow Current flow to breaker (B 3 ) Breaker (B 3 ) allows current to flow Current flow to HV bus HV bus allows current to flow OR Current flow to HV bus Current flow to HV bus Current flow to Breaker (B1) A Current flow to Breaker(B 2 ) B 1 allows current to flow Breaker (B2) allows Current to flow Current flow to Line (L 1 ) Current flow to line L 2 Line L 1 allows Current to flow Line (L 2) allows Current to flow Figure 4.5 Logic for single bus bar configuration during T 2 operation

19 78 Mode 3 Operation of single bus bar configuration in Mode 1 Mode 2. Model 3 is a logic of operation in mode 1 OR mode 2. The reliability value in mode 3 = = configuration. A reliability value of is obtained for single bus bar Sectionalized Single Bus Bar Substation Figure 4.6. Sectionalized single bus bar substation configuration is shown in L 1 L 2 B 1 B 2 HV Bus B 5 HV Bus B 3 B 4 T 1 T 2 LV Bus LV Bus Figure.4.6 Sectionalized single bus bar configuration

20 79 In a sectionalized single bus bar configuration, the bus bar is split into sections by means of a bus coupler (B 5 ). A sectionalized single bus bar configuration is flexible in operation. It is higher in reliability than single bus bar configuration. Isolation of bus sections for maintenance is possible in this scheme. However, it has a higher cost than a single bus bar configuration as additional circuit breaker and isolator is required. A logic for sectionalized single bus bar configuration during the operation of transformer T 1 is shown in Figure 4.4. Mode 1 Successful operation of the sectionalized single bus bar substation. The logic for single bus bar configuration during the operation of transformer T 1, when bus coupler B 5 is on and transformer T 2 is not available is shown in Figure 4.4. A reliability value is estimated in model 1 by substituting the substation component reliability indices from Table 4.1 The estimated value of reliability in mode 1 = [(L 1 B 1 L 2 B 2) HV Bus B 3 T 1 LV Bus = [L1*B1 L2 *B 2 ] *HV Bus* B 3 * T 1 *LV Bus. = [L 1 *B 1 + L 2 *B 2 L 1 *B 1 *L 2 *B 2 ] * HV Bus * B 3 *T 1 *LV Bus. = Mode 2 in Mode 2. Successful operation of the sectionalized single bus bar substation

21 80 The logic for single bus bar configuration during the operation of transformer T 2, when bus coupler is on and transformer T 1 is not available is shown in Figure 4.5. A reliability value is estimated in mode 2 by substituting the substation component reliability indices from Table 4.1 The estimated value of reliability in mode 2 = [L 1 B 1 L 2 B 2 ) HV Bus B 3 T 2 LV Bus = [L 1 *B 1 L 2 * B 2 ] HV Bus* B 3 *T 2.* LV Bus. = [L 1 *B 1 + L 2 *B 2 L 1 *B 1 *L 2. *B 2 ] *HV Bus *B 3 *T 2 *LV Bus. = Mode 3 Operation of sectionalized single Bus Bar configuration in Mode 1 Mode 2 Mode 3 is a logic of operation in Mode 1 OR Mode 2. The reliability value in mode 3 = Mode 1 Mode 2 = =

22 81 Mode 4 The successful operation of sectionalized single bus bar configuration logic during B5 off in mode 4 is shown in Figure 4.7. Current output Current flow to LV Bus LV Busallows currentto flow OR Current flow to transformer (T 1 ) Current flow to (T 2) Transformer (T 1) Transformer allowscurrent to flow ) (T 2 ) Transformer allows current to flow Current flow to Breaker (B3) (B 3 )Breaker allows current flow Current flow to breaker (B 4) Breaker (B 4 ) allows current flow AN Current flow to HV Bus HV Bus allows Current to flow Current flow to HV Bus HV Busallows current to flow Current flow to Breaker (B 1) (B 1)Breaker allows current toi flow Current flow to Breaker (B 2) (B 2 ) Breaker allows currrent to flow Current flow in line (L 1) (L 1) Line allows current to flow Current flow in line (L 2 ) L 2 Line allows Current to flow Figure 4.7 Logic for Sectionalized Single bus bar configuration during B 5 off

23 82 A reliability value is estimated in Mode 4 by substituting substation component reliability indices from Table 4.1 The estimated value of reliability in mode 4 = [(L 1 B 1 HV BUS B 3 T 1 ) (L 2 B 2 HV BUS B 4 T 2 )] LV BUS. = [(L 1 *B 1 *B 3 *HV BUS *T 1 ) (L 2 *B 2 *B 4 *HV BUS*T 2 ) ]*LV BUS = Mode 5 Model 5 is a logic of operation in Mode 3 OR Mode 4. The reliability value in mode 5 = Mode 3 Mode 4 = = The reliability value of is obtained for sectionalized single bus bar configuration Breaker and a Half Bus Bar Substation Figure 4.8. The Breaker and a half bus bar configuration are shown in

24 83 L 1 L 2 HV Bus no 1 B 6 B 7 B 8 B 9 B 10 B 11 HV Bus no 2 T 1 T 2 LV Bus Figure 4.8 Breaker and half bus bar configuration Figure 4.8 shows two main buses, which are normally energized. There are three circuit breakers and two feeder circuits between the buses. This arrangement allows for breaker maintenance without interruption of service. A fault on either bus may cause no feeder interruption. This configuration has high reliability, operational flexibility, capability of isolating any circuit breaker either of the main bus for maintenance without service interruption. However it has higher cost and protection and control schemes are more complex Mode 1 Successful operation logic for breaker and a half bus bar configuration during transformer T 1 and HV bus bar no 1 in operation, when HV bus No 2 and transformer T 2 are not available is shown in Figure 4.9

25 84 Current Output Current flow to LV Bus LV Bus allows current to flow Current flow to (T 1) Transformer (T 1)Transformer allows to current flow Current flow to (B 8) Breaker (B 8) Breaker allows current to flow OR Current flow to (B8) Current flow to Breaker (B 8) Current flow to Breaker (B 6) (B 6) Breaker allows current to flow Current flow to HV Bus no 1 HV Bus no 1 allows current to flow Current flow to Breaker (B7) (B 7) Breaker allows current to flow Current flow to Line (L 1) (L 1) Line allows current to flow Current flow to Line (L 2) (L 2) Line allows current to flow Figure.4.9 Logic for breaker and half bus bar configuration during T 1 and HV bus bar no1 in operation A reliability value is estimated in mode 1 by substituting the substation component reliability indices from Table 4.1 The estimated value of reliability in mode 1 = [L 1 L 2 B 7 HV BUS no 1 B 6 ] B 8 T 1 LV bus = [L 1 L 2 *B 7 *HV Bus no 1 *B 6 ] *B 8 *T 1 *LV BUS =

26 85 Mode 2 Successful operation of logic for Breaker and a half bus bar configuration during transformer T 2 and HV Bus bar no 1 in operation, when HV bus bar no 2 and transformer T 1 are not available is shown in Figure Current Output Current flow to LV Bus LV Bus allows current to flow Current flow to Transformer (T 2) (T 2) Transformer allows current to flow Current flow to Breaker (B 9) (B 9) Breaker allows current to flow OR Current to Breaker (B 9) (Current to flow to Breaker (B 7) (B 7) Breaker allows current to flow Current flow to Breaker (B 9) (Current to flow to HV Bus no 1 HV Bus no 1allows current to flow (Current to flow to Breaker (B6) (B 6) Breaker allows current to flow Current flow to Line (L 2) (L 2) allows current to flow (Current to flow to Line (L 1) (L 1) Line allows current to flow Figure 4.10 Logic for breaker and half bus bar configuration during T 2 and HV bus bar no1 in operation

27 86 A reliability value is estimated in mode 2 by substituting the substation component reliability indices from Table 4.1. The estimated value of reliability in mode 2 = [L 2 L 1 B 6 HV BUS no 1 B 7 ] B 9 T 2 LV bus = [L 2 L 1 *B 6 *HV Bus no 1* B 7 ] *B 9 *T 2 *LV BUS = Mode 3 Operation of Breaker and half configuration in Mode 1 Mode 2 Mode 3 is a logic of operation in mode 1 OR mode 2. The reliability value in mode 3 = Mode 1 Mode 2 = = Mode 4 Successful operation of logic for Breaker and a half bus bar configuration during transformer T 1 and HV Bus bar no 2 in operation, when HV bus bar no.1 and transformer T 2 are not available is shown in Figure 4.11.

28 87 Current Output Current flow to LV Bus LV bus allows current to flow Current flow to Transformer (T 1) (T 1) transformer allows current to flow OR Current flow to Transformer to transformer (T 1) Current flow to Transformer (T 1 ) Current flow to Breaker (B 10) (B 10) Breaker allows current to flow Current flow to HV Bus no2 HV bus no 2 allows current flow Current flow to Breaker (B 11) (B 11) Breaker allows current to flow Current flow to Breaker (B 8) (B 8) Breaker allows current flow Current flow to Breaker (B 9) (B 11)Breaker allows current to flow Current flow to Line (L 1) (L 1) Line allows current to flow Current flow to Line L 2 (L 2) Line allows current to flow Figure 4.11 Logic for breaker and half bus bar configuration during T 1 and HV bus bar no2 operation A reliability value is estimated in mode 4 by substituting the substation component reliability indices from Table 4.1

29 88 The estimated value of reliability in mode 4 = (L 1 B 8 L 2 B 9 B 11 HV bus no 2 B 10 ) T 1 LV bus = (L 1 *B 8 L 2 *B 9 *B 11 *HV bus no 2 *B 10 ) T 1 *LV bus = Mode 5 Successful operation of logic for Breaker and a half bus bar configuration during transformer T2 and HV Bus bar no 2 in operation, when HV bus bar no 1 and transformer T 1 are not available is shown in Figure Current Output Current flow to LV bus LV bus allows current to flow Current flow to Transformer (T 2) (T 2) Transformer allows current to flow OR Current flow to Transformer (T 2) Current flow to Transformer (T 2) Current flow to Breaker (B 11) Current flow to HV Bus no 2 (B 11) Breaker allows current to flow HV bus no 2 allows current flow Current flow to Breaker (B 10) (B 10) Breaker allows current to flow 9 Current flow to Current flow to Breaker (B 8) Breaker (B 9) (B 9) Breaker allows current to flow (B 8) allows current to flow Current flow to Line (L 2) 2) (L 2) Line allows current to flow Current flow to Line (L 1) (L 1) Line allows current to flow Figure 4.12 Logic for breaker and half bus bar configuration during T 2 and HV bus bar no2 in operation

30 89 A reliability value is estimated in mode 5 by substituting the substation component reliability indices from Table 4.1. The estimated value of reliability in mode 5 = (L 2 B 9 L 1 B 8 B 10 HV Bus no 2 B 11 ) T 2 LV BUS = (L 2 B 9 L 1 *B 8 *B 10 *HV Bus No 2 *B 11 )* T 2 * LV BUS = Mode 6 Operation of Breaker and half configuration in Mode 4 Mode 5 Mode 6 is a logic of operation in mode 4 OR mode 5. The reliability value in mode 6 = Mode 4 Mode 5 = = Mode 7 Operation of Breaker and half configuration in Mode 3 Mode 6 value in mode 7 Mode 7 is a logic of operation in Mode 3 OR Mode 5. The reliability

31 90 = Mode 3 Mode 6 = = 1.0 configuration. A reliability value of 1 is obtained for breaker and a half bus bar Double Bus Bar Double Breaker Substation Figure 4.13 A Double Bus bar double breaker configuration is shown in L 1 L 2 HV Bus no 1 B 12 B 13 B 14 B 15 B 16 B 17 B 18 B 19 HV Bus no 2 T 1 T 2 LV Bus Figure 4.13 Double bus bar double breaker configuration

32 91 Figure 4.13 consists of two main buses, both are normally energized. Between the main buses are two breakers and one circuit. This arrangement allows for any breaker to be removed from service without interruption to its circuit. A fault on either of the main bus may not cause circuit outage. A breaker failure will result in the loss of only one circuit. A double bus bar double breaker configuration has higher reliability and operational flexibility. However it is highest in cost due to the requirement of two breakers per circuit. Current Output Current flow to LV bus LV bus allows current to flow Current flow to transformer (T 1) Transformer (T 1) allows current to flow Current flow to breaker (B 13 ) Breaker (B 13 ) allows current to flow Current flow to HV bus OR HV bus no.1 allows current to flow Current flow to HV bus no1 Current flow to HV bus no1 Current flow to Breaker ( B 12 ) B 12 allows current to flow Breaker ( B 15 ) allows Current to flow Current flow to Line L 1 L Current flow to Line L 2 Line L 1 allows Current to flow Line L 2 allows Current to flow Figure 4.14 Logic for Double bus bar double breaker configuration during T 1 and HV bus no 1 in operation

33 92 Mode 1 Successful operation logic for double bus bar and double breaker configuration during transformer T 1 and HV Bus bar no 1 in operation when HV bus bar 2 and transformer T 2 are not available is shown in figure A reliability value is estimated in mode 1 by substituting the substation component reliability indices from Table 4.1 The estimated value of reliability in Mode 1 = (L 1 B 12 L 2 B 15 ) HV BUS no 1 B 13 T 1 LV Bus = (L 1 *B 12 L 2 *B 15 )*HV BUS No 1* B 13 *T 1 * LV Bus. = Mode 2 Successful operational logic for double bus bar and double breaker configuration during transformer T2 in operation and HV Bus bar no 1 when, HV bus bar no 2 and transformer T 1 are not available is shown in figure A reliability value is estimated in mode 2 by substituting the substation component reliability indices from Table 4.1 The estimated value of reliability in Mode 2 = (L 1 B 12 L 2 B 15 ) HV bus no1 B 14 T 2 LV bus. = (L 1 *B 12 L 2 *B 15 ) *HV bus no 1* B 14 *T 2 *LV bus. =

34 93 Current Output Current flow to LV bus LV bus allows current to flow Current flow to transformer (T 2 ) Transformer (T 2) allows current to flow Current flow to breaker (B 14 ) Breaker (B 14 ) allows current to flow Current flow to HV bus OR HV bus no.1allows current to flow Current flow to HV bus no1 Current flow to HV bus no1 Current flow to Breaker ( B 12 ) B 12 allows current to flow Current to flow to B 15 Breaker ( B 15 ) allows Current to flow Current flow to Line L 1 Current flow to Line L 2 Line L 1 allows Current to flow Line L 2 allows Current to flow Figure 4.15 Logic for Double bus bar double breaker configuration during T 2 and HV bus no 1 in operation

35 94 Mode 3 Operation of Breaker and half configuration in Mode 1 Mode 2 Mode 3 is a logic of operation in mode 1 OR mode 2. The reliability value in mode 3 = Mode 1 Mode 2 = = Mode 4 Successful operation logic for double bus bar and double breaker configuration during transformer T 1 and HV Bus bar no 2 in operation, when bus bar no 1and transformer T 2 are not available is shown in Figure A reliability value is estimated in mode 4 by substituting the substation component reliability indices from Table 4.1 The estimated value of reliability in mode 4 = (L 1 B 16 L 2 B 19 ) HV bus no 2 B 17 T 1 LV bus. = (L 1 *B 16 L 2 * B 19 ) *HV bus no 2* B 17.*T 1 *LV bus. =

36 95 Current Output Current flow to LV bus LV bus allows current to flow Current flow to transformer (T 1 ) Transformer (T 1 ) allows current to flow Current flow to breaker (B17) Breaker (B 17 ) allows current to flow Current flow to HV bus HV bud no.2 allows current to flow OR Current flow to HV bus no 2 Current flow to HV bus no 2 Current flow to Breaker (B 16 ) Current to flow to B 19 B 16 allows current to flow Breaker (B 19 ) allows Current to flow Current flow to Line L 1 Current flow to Line L 2 Line L 1 allows current to flow Line L 2 allows Current to low Figure 4.16 Logic for double bus bar double breaker configuration during T 1 and HV bus no2 in operation Mode 5 Successful operation logic for double bus bar and double breaker configuration during transformer T 2 and HV Bus bar no 2 in operation when HV bus bar no. 1 Figure and transformer T 1 are not available is shown in

37 96 Current Output Current flow to LV bus LV bus allows current to flow Current flow to transformer (T 2 ) Transformer (T 2 ) allows current to flow Current flow to breaker (B 18 ) Breaker (B 18 ) allows current to flow Current flow to HV bus HV bus no.2 allows current to flow OR Current flow to HV bus no 2 Current flow to HV bus no.2 Current flow to Breaker (B 16 ) Current to flow to B 19 B16 allows current to flow Breaker (B 19 ) allows current to flow Current flow to Line L 1 Current flow to Line L 2 Line L 1 allows current to flow Line L 2 allows Current to flow Figure 4.17 Logic for double bus bar double breaker configuration during T 2 and HV bus no2 in operation

38 97 A reliability value is estimated in mode 5 by substituting the substation component reliability indices from Table 4.1 The estimated value of reliability in mode 5 = (L 1 B 16 L 2 B 19 ) HV BUS no 2 B 18 T 2 LV BUS = (L 1 *B 16 L 2 *B 19 ) *HV BUS no 2 *B 18 *T 2 * LV BUS. = Mode 6 4 Mode 5 Operation of double bus bar double breaker configuration in Mode Mode 6 is a logic of operation in mode 4 OR mode 5. The reliability value in mode 6 = Mode4 Mode 5 = = Mode 7 Operation of Mode 3 Mode 6 double bus bar double breaker configuration in Mode 7 is a logic of operation in mode 3 OR mode 6. The reliability value in mode 7 = Mode 3 Mode 6

39 98 = = A reliability value of = is obtained for double bus bar double breaker configuration. 4.7 RESULT DISCUSSIONS A comparison is done between the proposed and the convention methods to establish the usefulness of the proposed SPM method Comparison of Proposed and Daniel Nack Method for Reliability Assessment of Various Substation Configurations Table 4.3 shows the comparison between the proposed SPM and Daniel Nack method for reliability assessment of various substation configurations. Table 4.3 Proposed and Daniel Nack method for reliability values of various substation configurations Configuration Estimated reliability value as per existing method Estimating reliability value as per proposed method Breaker and a half bus bar Double bus bar double breaker Sectionalized single bus bar Single bus bar The proposed method estimates reliability value of 1 for one and a half bus bar configuration, where as Daniel Nack method estimates a value of The proposed method estimates reliability value of

40 99 for double bus bar double breaker configuration, whereas Daniel Nack method estimates a value of The proposed method estimates reliability value of for sectionalized single bus bar configuration, whereas Daniel Nack method estimates a value of The proposed method estimates reliability value of for single bus bar configuration, where as Daniel Nack method estimates a value of Daniel Nack failure values for various substation configurations were less than 0.01.Lower numerical values obtained for failure will tend to encourage approximations. The failure values are converted to reliability values for comparing with the proposed method. Therefore these minor differences may be due to the effect of approximations. The proposed SPM method has estimated reliability close to one and thus avoided approximations. Hence, the proposed reliability estimates are more accurate. In addition, proposed SPM has less computational time. It is easy to understand as it is based on Boolean logic. 4.8 CONCLUSION The proposed method of SCADA short term forecasting improves load forecasting as given below. It uses 30 samples for estimating the short term load forecasting in advance for the next 30 minutes on one minute interval. This is an improvement over the other standard methods given in literatures, where one sample is taken for one hour. The result shows consistent average variation of actual and estimated load, which are very encouraging.

41 100 MAPE value shows improvement in forecasting the load compared to other method. Thus, the developed projection statistics are useful and powerful diagnostic tool. The estimated frequency is computed at every point in real time with reasonable accuracy. This has resulted in the frequency stability of the system. A special feature of continuously self correcting mechanism built in the proposed algorithm to assess the deviant points gives better accuracy. It used a salient feature of maximum and minimum forecast user points in the algorithm, which can be changed by a forecaster due to the changes in weather. Thus it has improved load forecasting accuracy compared to other conventional methods. The proposed method of SPM usefulness is given below: It uses a simple method of Boolean Logic for reliability assessment of substation configuration. It requires less computational time than the existing method of Daniel Nack. It is easier to understand and simple to implement. It has estimated reliability values accurately. The breaker and a half scheme are generally recommended in the field, for continuity of power supply. The proposed SPM method proves this field utility requirement by estimating its reliability as 1.0.