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INEC 2008 EMBRACING THE FUTURE HAMBURG, 1 - 3 April 2008

INEC 2008 EMBRACING THE FUTURE HAMBURG, 1 - 3 April 2008. On electric load characterization and categorization in ship electric installations. I.K. Hatzilau , Prof. Dr.-Ing., Hellenic Naval Academy G . J. Tsekouras , PhD, National Technical University of Athens

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INEC 2008 EMBRACING THE FUTURE HAMBURG, 1 - 3 April 2008

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  1. INEC 2008 EMBRACING THE FUTURE HAMBURG, 1 - 3 April 2008 On electric load characterizationandcategorization in ship electric installations I.K. Hatzilau ,Prof. Dr.-Ing.,Hellenic Naval Academy G.J. Tsekouras ,PhD, National Technical University of Athens J. Prousalidis ,Ass. Prof., National Technical University of Athens I.K. Gyparis ,MSc MESE, Cdr (Eng.),Hellenic Navy

  2. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 1. Scope of the Paper Eachelectric equipmentof a ship electric network (also called “load” or “consumer”) can becharacterizedandcategorized by severalcharacteristic operating parameters. This parameters are required inperforming several useful studies , such as Load Estimation, Load Shedding, Modulation, Power Sources Selection, Power Cable Rating, Short Circuit Analysis, Harmonics etc, as indicatively summarized in the Table : INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 2

  3. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 1. Scope of the Paper Table I : Indicative overview of the use of load characteristic parameters in some methodologies of studies INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 3

  4. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 1. Scope of the Paper The paper offers a discussion * on “Priority Index” * on “Load Demand Profile”, i.e.thechronological energy demand curve of a load and the related issues,“ Representative load demand profilePd,r(t)”, “ characteristic time period percentage indices ”and“ Load factor fs ”. in conjunction to methodologies of studies, in an attempt to highlight some fundamental steps for establishing additional classification criteria, according to which electric loads could be grouped into categories. The values of thesecharacteristic parameters of a consumer vary, depending on the network the equipment is connected, as well as the rest of the operating equipment in the same network and depending on ship type, state and mission. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 4

  5. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 1. Scope of the Paper The paper focuses further on electric load profile classification. * A two-stage methodology is presented, based on artificial intelligence techniques and actual data measured on ships, which estimates both the typical load curves of each consumer and the consumer clusters together with their respective representative load curves, in order to successfully describe the respective behavior. * As a case study, results for a set of consumers and for the generators of Hellenic Navy MEKO type frigates are presented, based on records taken by the control and monitoring system “NAUTOS”. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 5

  6. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis CONTENTS … the paper arrangement is the following : 1. INTRODUCTION and BACKGROUND – - SCOPE OF WORK 2. LOAD PARAMETERS 3. CORRELATION TO METHODOLOGIES OF STUDIES 4. LOAD PROFILE CATEGORIZATION 4.a Pattern Recognition Methodology (Clustering k-mean Method and WCBCR Adequacy Measure) 4.b Case Study for Hellenic Navy MEKO type Frigates 5. CONCLUSIONS 6. Acknowledgements 7. References INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 6

  7. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 2. LOAD PARAMETERS and their CORRELATION to METHODOLOGIES OF STUDIES In this section of the paper we define and comment first the “Priority index” and then the “Load demand profilePd(t)” along with its related issues of : “ Representative load demand profilePd,r(t)”, “ characteristic time period percentage indices ” and “ Load factor fs ”. After that we present the correlation of these parameters (and some others) to several studies. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 7

  8. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 2a. Priority index The “Priority index” shows the relevant criticality of an installed load , on the safe accomplishment of the vessel’s missions and survivability. * This index is not static and unique, but depends on the particular conditions for each ship’s situation (ship’s state and mission), and plays a significant role in certain studieslike : - Load shedding system - Emergency generator rating - Back-up feeder installation (double cabling) - Extra local power supply unit prescription etc INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 8

  9. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 2b.1 Load Demand Profile Pd(t) The onboard demand for each load is not at all constant, but can vary between zero and the equipment nominal power, depending on the "Ship Operating Condition" (SOpC) , often categorized in warships in the following four (4) main states : “SHORE”, “ANCHOR”, “AT SEA” and “GENERAL QUARTER”. The Load demand profile Pd(t) is the chronological energy demand curve of the load. It is a very significant characteristic, which should be involved in many analyses and studies, like : Load Estimation, Power Cable Rating, Short Circuit Analysis, Load Shedding, Harmonics, Modulation. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 9

  10. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 2b.1 Load demand profile Pd(t) InthisFigure we seeanexample of dailyON/OFF chronological curve of the “REFRIGERATION PLANT”in condition at “SHORE”, of HN MEKO type frigate (a segment is shown, between 6 to 20 hour), based on records taken, every 1 min. 100% 0% 6 h 20 h INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 10

  11. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 2b.1 Load demand profile Pd(t) Day 1 These daily load demand profiles of ship’s consumers generally vary from day to day, evenin the same Ship Operating Condition, but their picture remains - more or less - the same, and characterizes the behaviour of each consumer for each Ship Operating Condition. In the Figure we see the same time-segment of the Load demand profile of the “REFRIGERATION PLANT” in three different days. Day 2 Day 3 INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 11

  12. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 2b.2 Representative load demand profile Pd,r(t) * Using a number of daily load demand profilesfrom the same consumer and in the same Ship Operating Condition, we can calculate the “ Representative load demand profile Pd,r(t) ” for this one consumer in that Ship Operating Condition, by using statistical tools or pattern recognitions methods, as it is proposed in the last section of this presentation. * This load curve gives the probability of this consumer, to be in status “ON” for each time step. For example, if in the time-moment t of the day, the respective mean value is 0.7, it means, that this consumer will be “ON” with 70% probability and it will be “OFF” with the rest 30%. Alternatively, this probability expresses the expected normalized active power with respect to the nominal (peak) load of this consumer. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 12

  13. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 2b.2 Representative load demand profilePd,r(t) In this Figure the normalized representative daily chronological load curve for the “REFRIGERATION PLANT” of HN MEKO type frigate at “SHORE”is presented - (a segment is shown, between 6 to 12 hour) - with the confidence limits of the variations(mean value  standard deviation), which has a probability of occurrence equal to 68.27%, assuming a normal distribution . INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 13

  14. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 2b.3 Characteristic Time Period Percentage Indices In order to characterize the load profile in more details, we can calculate some “characteristic time period percentage indices” as they are explained in the Figure. (a)OFF-time period index toff (%), (b)ON-time period index ton (%) (c)deterministic time period index tdet (%) =toff (%)+ton (%) (d)lower 10% time period index t<10% (%) (e)upper 90% time period index t>90% (%) INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 14

  15. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 2b.3 Characteristic Time Period Percentage Indices The complete definitions, for these “characteristic time period percentage indices”, are given in the paper : (a)off - time period index toff (%) : time percentage for which the typical load is always OFF, meaning that the respective load is zero. (b)on - time period index ton (%) : time percentage for which the typical load is always ON, meaning that the respective load is maximum. (c)deterministic time period index tdet (%) : time percentage for which the typical load is deterministically known (constantly always ON or always OFF), meaning that the respective load is unchanged for specific time intervals of the day. It is also equal to the sum of the off-time period index toff (%) and the on-time period index ton (%). (d)lower 10% time period index t<10% (%) : time percentage for which the typical load is equal or lower than 10% of the maximum demand, meaning that the respective load has 10% or lower possibility to be ON. (e)upper 90% time period index t>90% (%) : time percentage for which the typical load is equal or upper than 90% of the maximum demand, meaning that the respective load has 90% or higher possibility to be ON. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 15

  16. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 2b.4 Load factor fs Indicates the relative average (%) loadof the equipment - on a daily basis ( or any other plausible period T ) -, specifying how much power is absorbed, in an actual ship operating condition, with respect to the nominal power Pnom. It varies between 0% and 100%. , and it can be calculated from the “ Representative load demand profile Pd,r(t) ” Pnom : the nominal power Pi : the operating power level during time interval Δti INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 16

  17. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 2b.4 Load factor fs As shown in Figure the load factor, as a simple index, cannot describe the load profile curve accurately : The consumer of Figure-a fatigues the ship’s generators less than the consumer of Figure-b for the same peak load, load factor (and power factor), because the number of the load demand changes is smaller. If an energy storage system is used, the second consumer will need smaller battery system than the first one. These inferences cannot be drawn without the consumers’ load profiles. b a INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 17

  18. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 2b.5 Categorization of Consumers InthisFigure we seeexamples of dailyON/OFF chronological curves of seven different consumersat condition “AT SEA”, based on records taken, every 1 min, from HN MEKO type frigates. (A) Leak Oil Pump, (B) Fuel Booster Pump, (C) Fuel Purifier, (D) H.P. Compressor, (E) GT Enclosure Fan, (F) CCP Control Oil Pump, (G) Lub Oil Pump for Main Gear. A B C D E F G INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 18

  19. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 2b.5 Categorization of Consumers Hence,we can “classified”(“categorized”) each one consumer or a set of different consumers in every "Ship Operating Condition" by “grouping” (“clustering”) them into “classes” or “categories”, according to their “ Representative load demand profile Pd,r(t) ”. For example a first approach categorization of consumers could be simply “a visual one” , e.g. : INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 19

  20. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 2b.5 Categorization of Consumers Examples, of a first approach categorization of consumers : Category 1 :Pulsed-load, or quasi-Pulsed-load profile, i.e. quasi-periodic operation with “ON/OFF” period of some minutes (e.g. Leak Oil Pump (Α)) Category 2 :Quasi-periodic-profilewith “ON/OFF” period of some hours (e.g. Fuel Purifier (C)) Category 3 : The most time the load is “OFF” and operates only for a relative short time ( 1-2 hours ) (e.g. Fuel Booster Pump (B), H.P. Compressor (D), GT Enclosure Fan (E)) ,   etc … INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 20

  21. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 2b.5 Categorization of Consumers A more adequate categorization can be realized, by using statistical tools or pattern recognitions methods, as it is proposed in the last section of this presentation. With those methods a respective “ Representative Load Demand ProfilePd,r(t) ” for each consumer or for a set of different consumers can be estimated. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 21

  22. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3. CORRELATION of CHARACTERISTIC LOAD PARAMETERS to some METHODOLOGIES of STUDIES * In the following we will show briefly, how some Load Characteristic Parameters, like Load Demand Profile, Load Factor, Priority Index etc are involved to methodologies of studies, e.g concerning : * 3a. Load Estimation * 3b. Power Source selection * 3c. Power Cable Rating * 3d. Short Circuit Studies * 3e. Load Shedding * 3f. Harmonics * 3g. Modulation – Pulsed Loads INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 22

  23. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis CORRELATION METHODOLOGIES of STUDIES 3a. Load Estimation The purpose of electric “Load Estimation”, is to define the total average daily required load”TPdl of the electrical network. It is based on the use of daily“load factor”fs,j for every electrical consumer ( the jth one) and for each "Ship Operating Condition" (SOpC), as already defined. Taking into consideration the Power Efficiencyη,jof each consumer, then the estimation of TPdl for that (SOpC) is : TPdl = 1Σm ( N,j Pdl,j ) where Pdl,j = (Pnom,j/η,j) fs,j is the “average daily required load”Pdl,j from the jth consumer with Pnom,j nominal power. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 23

  24. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis CORRELATION METHODOLOGIES of STUDIES 3b. Power Sources The selection of power sources is of primary importance, as several parameters of the consumers have to be taken into account. * Depending on the criticality i.e on the Priority Index of the loads considered, back-up alternative sources e.g. UPS’s, SMES’s etc are investigated. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 24

  25. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis CORRELATION METHODOLOGIES of STUDIES 3c. Power Cable Rating In certain cases standards allow cabling to be of lower dimensions than those calculated on the basis of equipment nominal power. -This cables’ undersizing is based on the partial loading conditions of the equipment and moreover on theirload factors fs’sandLoad Demand Profiles. * For example, according to standards, the power cable size can be reduced, when the equipment works only for a short interval (of e.g. 1 hour) followed by a long cease of operation. - e.g.this is the case of CATEGORY 3 of load profiles, as categorized previously in this paper (e.g. Fuel Booster Pump, H.P. Compressor etc). 0 h 24 h INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 25

  26. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis CORRELATION METHODOLOGIES of STUDIES 3d. Short Circuit Studies Short Circuit calculationsfor shipboard installations are performed according to IEC 61363,which stipulates for three-phase symmetrical short circuit calculations, performed during the first half fundamental period considering the contribution of the loads and large power motors in particular. This load contribution is in the order of 15% -20% of the total short circuit current and has to be estimated based on the loading conditions just before the short circuit takes place. The most tangible manner, to identify these pre-fault loading conditions, is via the Load Factors, fs’s, which reflect the partial loading power demand of all operating equipment. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 26

  27. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis CORRELATION METHODOLOGIES of STUDIES 3e. Load Shedding Naval ships usually have load-shedding systems, that automatically disconnect pre-selected loads from the ship’s distribution system, whenever an overload condition develops, in order to ensure the survivability of the electrical power system and ship. -We can have a “static”classical and usually dual load-shedding scheme, in which the loads are characterized as mainandsecondary, ( or vital and non-vital ). INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 27

  28. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3e. Load Shedding *But we can have a more flexible and usable shedding scheme, based on “dynamic load prioritization” byapplying different priority indexes to the same load according to each of ship’s states and missions. Towards this “dynamic multi-staged shedding scheme”is feasible to select between loads with equal priority-index, by the use of the “Representative load demand profile”Pd,r(t) and especially by the use of the “mean predicted normalized power demand” Pd,r,m,(Dt,t), on the time t in which a ship-power-shortage is supposed to occur and for a selected next time-window of duration Dt . INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 28

  29. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3e. Load Shedding Such a “dynamic multi-staged shedding scheme” is based -as a first step - on a as indicatively is shown here. Ships’ state/mission-dependent load Priority Table INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 29

  30. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3e. Load Shedding Ships’ state/mission-dependent load Priority Table In this Table the following ‘operational’categorization is used : Floating, Navigating and Fighting [the “Fighting” state has 3 sub-states : Anti Aircraft Warfare (AAW), Anti Surface Warfare (ASurW) and Anti Submarine Warfare (ASubW ) ]. Electric loads are characterized by aPriority Index of the typeim for the ‘m’ ship’s state or mission, which is set to 1 for the most vital loads(for that state) and to 6 for the least vital. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 30

  31. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3e. Load Shedding For a Example . . . when ship’s state is set to ‘floating’ (that is, ship cannot fight and can hardly navigate) loads that can directly contribute to that goal – as the fireand thebilge pumps – become the most vital and their priority index is set to1. Fire and bilge pumps have an intermediate priority for the other ship’ states, in a sense that are not immediately vital, but can become so anytime the ship is in a fighting state. On the other hand, loads like the sonarand themissile launcher get low priorities for the ‘floating’ state and their priority index is set to6. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 31

  32. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3e. Load Shedding - Since, assigning different priority indexes to all installed loads for each one of the possible ship’s states and missions is not expected to be technically achievable, the second step towards a dynamic multi-stage shedding scheme is a feasible method for selecting between loads with equal priority-index. -During extreme power-shortage cases, it is proposed to examine the possibilityof shedding those loads that, as indicated by their “Representative load demand profile”Pd,r(t), are less likely to absorb power during the immediately next time-window of the crisis periods. In other words,in that particular time-window the reduced probability of a load to demand power, will dictate its usefulness. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 32

  33. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3e. Load Shedding Lets take the “Representative load demand profile” of the “Refrigeration Plant” of HN MEKO type frigates, only as an indicative example to illustrate the concept, because it is of course not at all a vital load in a short-time crisis situation Pd,r,m(Dt,t) = = (1/Dt)t∫ t+Dt Pd,r(Dt,τ).dτ From this profile we calculate the “mean predicted normalized power demand” Pd,r,m,(Dt,t), on the timet - in which a ship-power-shortage is supposed to occur - and for a selected next time-window of duration Dt . INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 33

  34. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3e. Load Shedding Mean predicted normalized power demand This Figure shows - for two selected next time-windowofdifferent duration Dt [ 5 min and 60 min respectively ] - the resulting dependence of the “mean predicted normalized power demand” Pd,r,m,(Dt,t), on the time t, in which a ship-power-shortage is supposed to occur [the “power shortage outbreak” time]. The calculations for the specific example have been done for 24 discrete points tn ( tn= 0, 1, 2,…, 24 h ). - In contrast to the 60 minutes one the diagram for the 5 min ‘next time-window’ shows a larger variation and deviation, as it was intuitively expected. Dt = 5 min Dt = 60 min INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 34

  35. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3e. Load Shedding Mean predicted normalized power demand Dt = 5 min Malfunction outbreak time t (h) Next, if for example, the shedding dilemma occurs exactly at 03:00, the probability of thisload to demand power, in the next 5 min , is close to 0.8 and consequently this load won’t be shed in respect with an other equally vital load, the corresponding diagram of which gives e.g. a 0.4, at that particular time of the day. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 35

  36. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3e. Load Shedding Alternatively, instead of using only the “mean predicted normalized power demand”Pd,r,m,(Dt,t), the product Pd,r,m,(Dt,t) x Pop - denoting the “predicted power demand” -, could be used for selecting the shedding of a load among equally vital ones. This product, beyond the probability of a load to demand power in a ‘next time window’, also includes the level of that demand and so it could be used for an optimum shedding selection. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 36

  37. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3e. Load Shedding Although, basing critical decisions on probabilistic reasoning of the “Representative load demand profile” could be, in several cases, the best left in one’s hand, extensive measuring, huge data bases and accurate time referencing are pre-required, in order to avoid erroneous choices. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 37

  38. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3f. Harmonics Harmonic distortion is actually faced by most standards as Voltage Quality, ( the limits set by standards are : between 1.5% and 3% for any high-order voltage harmonic and between 5% and 8% for the THDV ). However, considering that current distortion is also reflected to the voltage one, via the voltage drop on circuit impedances, much attention must be paid to current quality, defined by the entity of loads installed onboard or at least the major ones. Current distortion limits are clearly set only by - USA MIL-STD-1399(NAVY)-Section 300A, - IEEE-519 - and by the (no more valid) Edition 8 of STANAG 1008 . INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 38

  39. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis log(In/I1,fL) logarithmic-scale Small Loads < (1kVA/60Hz or 0.2kVA/400Hz and 2A/115V/400Hz) log(100) Big Loads > (1kVA/60Hz or 0.2kVA/400Hz and 2A/115V/400Hz) log(3) log(n) log(33) log(100) 3f. Harmonics # In USA MIL-STD-1399(and in the no more valid Ed. 8 of STANAG 1008)the limits ofIndividual Harmonics(In ) of each separate loaddepend on load rated powerPr , by distinguishing between “small” and “big” loads. for small loads, where Pr < 1kVA ………..…… In/I1≤ 100/n % for n≤ 33 : …… In/I1≤ 3% for n > 33 : …… In/I1≤ 100/n% for bigloads, where Pr > 1kVA These limitations refer to full load fundamental currentI1,fL (which in general is not the value at the measuring instant) and are shown besides WMTC 2006 (World Maritime Technology Conference – INEC stream), LONDON, March 2006 39

  40. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3f. Harmonics It has been reported in numerous technical papers, that these current harmonic distortion limits, are rather strict, as, according to field measurements, they are often violated by several equipment onboard. However, the voltage harmonic distortion, is often kept well below the limits set by almost all standards. Edition 9 of STANAG 1008 (valid since 2004), on the other hand sets no tangible numerical limits, but only defines courses of actions to be taken depending on the sum, ΣPdist,k , of the rated power of harmonic pollutant devicesPdist,k with respect to the ratio of the rated power of the maximum pollutant deviceMax,k( Pdist,k) to the system short circuit capacity, Ssc. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 40

  41. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis ΣkPdist, k Ssc 2 % Analysis required No action 1 % No action No action Max( Pdist, k) Ssc 0.1% 0.5% 3f. Harmonics These courses of action of Edition 9 of STANAG 1008are shown in the following figure. In the yellow area NO measures are required, whereas in the green area an “Analysis is required”: The applicability problemsof these courses of actions, refer : 1) to Simulationson the entire system,computer programs and modelling and 2) to whathappens in case of system upgrading??? INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 41

  42. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3f. Harmonics *Although, IEEE-519does not directly implies to shipboard installations, but rather to industrial units, it can apply to ships, too, considering that a ship is actually a compact power plant of industrial nature. * The limit values of IEEE-519depend on the voltage level of the electric system studied and on the ratio ofshort circuit current over maximum load current, the latterbeing the “average of maximum loads achieved on a 12-monthly basis”I1,avfL, (at the Point of Common Coupling, PCC) INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 42

  43. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3f. Harmonics Considering that many devices onboard are often over-dimensioned in order to meet future needs, working, thus, often in partial load conditions, this average maximum value of the fundamental current I1,avfL must be, somehow, identified. After the proposition of some of the authors’in a previous paper, at an initial approximation of applying IEEE-519, considering that for each load the corresponding PCC is the system power outlet where it is connected, the average maximum load can be estimated by the operation load factorsfs . In case of diversified fs values for several operation profiles, the worst cases leading to maximum operating currents ever encountered should be considered. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 43

  44. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3g. Modulation - Pulsed loads *“Modulation” is defined as the “ voltage and frequency periodic or quasi-periodic variations, such as might be caused by regularly or randomly repeated loading with frequency less than nominal ”. * Electric loads causing VoltageandFrequency Modulation are loads which require high power(from kWs to GWs) for a very short time interval (from msec to seconds) and are known as “Pulsed Loads”( like : controlled heaters, sonars, radars, Electromagnetic Aircraft Launch Systems and Electromagnetic Guns). * VoltageandFrequency Modulation may affect the operation of several subsystems of the ship such as radarscopes, communication equipment, missile guidance systems, weapons, gear systems etc … INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 44

  45. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3g. Modulation - Pulsed loads * The limits set - for the LV Ship Service Power Supply System - by different standards ( e.g. STANAG 1008, USA MIL-STD- 1399(NAVY)-Section 300A, IEEE Standard 45 ) for frequency modulation is normally 0.5%, while for voltage modulation varies between 1% and 5%. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 45

  46. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3g. Modulation - Pulsed loads According toSTANAG 1008, in order modulation not to exceed the limits of 0.5% for the frequency and 2% for the voltage, two characteristic parametersof the Pulsed Load are used : the Power FactorP.F.and the Apparent PowerSpulse In this way an “acceptable” and an “unacceptable”range in the corresponding pulsed load limit-curve P.F.(S%) is defined according these inequalities acceptable range P.F.*x < 0.25 and P.F. > [ 1 – (0.065/x)2 ] 1/2 unacceptable range Pulsed Load P.F. where xis the Pulsed Load apparent powerrelativeto the full rated apparent power of the Supply at the time of occurrence of the pulse x in percentage = S% INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 46

  47. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3g. Modulation - Pulsed loads * But, as it is shown by some of the authorsin a previous paper, besidesP.F.andSpulse additional Pulsed-Load parameters affect the entire phenomenon of modulation, like : - thepulse repetition frequency (periodicity), - theduration of each pulse (duty cycle), - theprofile of each pulse etc. All these parameters can be found by analysing the “Load demand profile Pd(t)” main parameter. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 47

  48. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3g. Modulation - Pulsed loads Here we show the influence ofPulsed Load “Period” T on the P.F.(S%) limit-curve of STANAG The variation of the Pulsed Load Period between 0.02 and 1.6 sec has a significant effect on the limit-curve. The higher the pulsed load period is, the bigger the unacceptable operating area. STANAG limit 0.3sec 0.15sec 0.05sec INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 48

  49. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 3g. Modulation - Pulsed loads Here we show the influence ofPulsed Load “Duty Cycle” on the P.F.(S%) limit-curve of STANAG The variation of the Pulsed Load Duty Cycle between 15 and 90% of the 0.3sec period affects considerably the limit-curve. The higher the Duty Cycle is, the bigger the unacceptable operating area. STANAG limit 70% 30% 15% INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 49

  50. On electric load characterization and categorization in ship electric installations I.K. Hatzilau, G.J. Tsekouras, J. Prousalidis, I.K. Gyparis 4. LOAD PROFILE CATEGORIZATION with Pattern Recognition Methods The scope of this section is 1) to show the MathematicalMethodologyof the evaluation of the “Representative load demand profile”Pd,r(t) of one consumer in a typical “time interval”, using a set of the “chronological load curves” of this consumer. * The mathematical modelling is the same for clustering of N different consumers using the respective representative load curves, in order to categorize the consumers in groups with similar load behaviour. and 2) to present aCase Study concerning consumers of Hellenic Navy MEKO type Frigates. INEC 2008 , Embracing the Future - International Conference , HAMBURG, 1 - 3 April 2008 50

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