Du{an Prodanovi}, Dragutin Pavlovi}, Nenad Ja}imovi}

Gra|evinski fakultet Beograd

Du{an Prodanovi}, Dragutin Pavlovi}, Nenad Ja}imovi}

Faculty of Civil Engineering, Belgrade, Yugoslavia

1. UVOD

Vodovodni sistemi, kao i mnogi drugi tehni~ki sistemi, prolaze kroz fazu ubrzanog tehni~kog i tehnolo{kog razvoja. Od klasi~nih organizacija ~iji je zadatak bio da bez obzira na cenu i kvalitet usluga isporu~i vodu ka potro{a~ima, transformi{u se u preduze}a visoke tehnologije i informatike, gde je jedan od dominantnih kriterijuma i ostvareni profit (Obradovi}, 1999). U takvim uslovima, stvarni podaci o proizvedenoj i distribuiranoj vodi, kao i ta~ni podaci o kvalitetu vode postaju imperativ, jer se na osnovu wih donose odluke o upravqawu radom sistema kao i ocene ekonomske isplativosti.

Problem gotovo svih vodovodnih sistema na podru~ju biv{e Jugoslavije je potpuno odsustvo kulture merewa. Danas prakti~no ni jedan vodovodni sistem nema kvalitetne podatke o ukupnom bilansu, a da se ne pomiwe ne postojawe podataka o trenutnim stawima distributivne mre`e. Uvo|ewe kvalitetnog monitoringa na takvim sistemima je veoma skup poduhvat, koji uglavnom nema podr{ku ni gradskih finansijera ni unutar vodovoda.

U uslovima potpunog odsustva kvalitetnih informacija o distributivnom sistemu vodovoda, svaka detaqnija hidrauli~ka analiza vodovodnog sistema zahteva obavqawe dijagnosti~ka merewa. Autori ovog rada su imali prilike da u posledwih desetak godina rade na vi{e ovakvih poslova, kako na vodovodnim tako i na drugim slo`enim sistemima (TE Obrenovac A i B, HE \erdap - prevodnica, itd). Na osnovu ste~enog iskustva, u ovom radu autori ukazuju na probleme u dijagnosti~kim merewima, vrste merewa kao i na~ine wihove organizacije. Osnovni ciq ovog rada je, me|utim, da se uka`e na neophodnost vra}awa kulture merewa i rada sa ta~nim podacima, kao osnovnog elementa obezbe|ewa odr`ivosti slo`enih vodovodnih sistema.

2. DIJAGNOSTIKA = MEREWA+ANALIZA

U "`ivotu" jednog vodovodnog sistema, u svakoj od faza realizacije se obavqaju (ili bi trebalo) odre|ena merewa i wihova analiza (Maksimovi}, 1993). Dijagnostika sistema treba da se obavqa u redovnim radnim uslovima, radi dobijawa kvalitetnih dopunskih podataka o radu pojedinih elemenata sistema, i ona se kombinuje sa stalnim merewima koja se koriste za upravqawe radom sistema. Na osnovu dijagnosti~kih merewa obavqaju se hidrauli~ke analize kojima se ili re{ava odre|eni aktuelni problem (udar pri ga{ewu pumpe, na primer) ili se sprovode simulacije rada vodovoda u planiranim fazama pro{irewa sistema.

Na `alost, postoje}a situacija je takva da su dijagnosti~ka merewa prakti~no jedina merewa i da se obavqaju samo kada je to neophodno: u slu~aju velikih nesta{ica vode (Prodanovi} i Maksimovi}, 1995.), ~estih havarija (Prodanovi}, Iveti} i Pavlovi}, 1994) ili kada se o~ekuju strane donacije pa se `uri sa izradom master plana. Po pravilu, vodovodi prestaju da se interesuju za daqe pra}ewe rada sistema ~im se otklone uo~eni problemi.

Dijagnostika vodovodnog sistema se mora sprovesti sa precizno definisanim zahtevima i sa ta~no planiranim krajwim ciqem koji treba ispuniti. U zavisnosti od postavqenog krajweg ciqa, vr{i se izbor mernih metoda i opreme, kao i na~ina obrade dobijenih rezultata. ^esto se, potpuno nerealno, o~ekuje da se na osnovu ispitivawa jednog detaqa na sistemu (na primer, karakteristika pumpi na izvori{tu) dobije odgovor na goru}e pitawe: gde su glavni gubici vode i koliki su?

2.1. Merewa

1. INTRODUCTION

Water Supply Systems, as well as many other technical systems, are passing through an accelerated technical and technological development phase. From the obsolete organizations, whose only task was to deliver a certain quantity of water, regardless to the economical or quality issues, they are transforming to high-tech Companies, where one of the most important criteria is a realized profit (Obradovic, 1999). In such environment, real information about produced and delivered water, as well as accurate data regarding water quality issues are becoming significant, mostly because the system control is based on that information, as well as the evaluation of economical sustainability. The main problem of almost all Water Supply Systems on Ex Yugoslavia area is a total lack of measurement culture. Currently, there is no Water Supply System with reliable data about water balance, neither with data about the actual water supply network state (position, diameter, pipe type, etc.) and hydraulic quantities (pressure, flow, estimated losses). Introduction of the high-tech monitoring systems in such cases can be very expensive adventure, which usually neither has support from municipal authorities, nor from the Water Supply Company.

In conditions of a complete absence of reliable information about a water supply system, the diagnostic measurements are the only solution when the detailed hydraulic analysis of system is needed. In last 10 years, authors were conducted a number of such measurements on water supply systems as well as on other complex systems (TPP Obrenovac A and B, HE Djerdap – a ship lock, etc.) Based on the accumulated experience, authors emphasize problems in diagnostic measurements, types of measurements as well as their organization issues in this paper. Nevertheless, the main objective of this paper is to stress the need of reestablishment of a measurement culture and the work with accurate data, as the basic element of complex Water Supply System sustainability improvement.

2. DIAGNOSTIC = MEASUREMENTS+ANALYSIS

Through the "life" of a Water Supply System, there are (or should be) some kind of measurements and analysis of their results in every realisation phase (Maksimovic, 1993). The system diagnosis should be performed in regular working conditions, to obtain the valuable additional data about the behavior of individual system elements, and it has to be combined with continuous measurements used for the system process management. The hydraulic system analysis are based on the diagnostic measurements, and they are used either for solving the certain actual problem (water hammer at a pump switch-off, for example), or for simulations of the Water Supply System behavior in planned future system extension phases.

Unfortunately, existing situation is such that diagnostic measurements are the only measurements, and they are performed only when it is necessary: in the case of significant water shortage (Prodanovic and Maksimovic, 1995 ), often pipe breaks (Prodanovic, Iveyic and Pavlovic, 1994) or when a foreign donations are expected, and a master plan completing is urgent. As a rule, when the problem is solved, there is no further interest for the system monitoring.

The diagnostic of a Water Supply System must be accomplished with precisely defined requirements and with precisely planned objectives, which are to be achieved. Depending on the final objective, a suitable choice of measuring methods and equipment is done, as well as the data processing tools. It is expected oftenly (but completely unrealistic) that based on the examination of one system detail (for example, the pump characteristic in the wellhead), to get the answer on the hot question: where are the main water losses and how big they are?

2.1. Measurements

Slika 1. Rekalibracija fiksnog merila protoka snimawem poqa brzina u neustaqenim uslovima

Na primer, na slici 1. je prikazan postupak provere ugra|enog fiksnog merila protoka putem snimawa profila brzina. Kako postupak traje i preko 1 sat, nije realno pretpostaviti da je protok u cevi konstantan, ve} treba kori{}ewem druge sonde (ili ispitivanog merila) pratiti promene protoka i to korigovati u analizi dobijenih brzina. Tako|e, brzina promene jedne iste veli~ine se mo`e razlikovati za red veli~ine (nivo vode u crpnom bazenu u periodu kretawa pumpe i u ustaqenom re`imu rada) u toku samog merewa, pa algoritam rada sistema za prikupqawe podataka treba sa time usaglasiti.

Izbor merne opreme uglavnom zavisi od problema koji se istra`uje. Ako treba snimiti pojedine veli~ine kroz du`i period (vi{e dana, nedeqa), tada je neophodno koristiti savremene ure|aje sa logerima - specijalnim ra~unarima koji mogu da obave merewa, primarnu obradu izmerene veli~ine i weno memorisawe u realnom vremenu. Za merewa u trajawu do jednog dana, mogu}e je i "ru~no" zapisivawe podataka, s time {to je tada wihova pouzdanost ne{to ni`a (na primer, ako treba o~itavati manometar na svaki sat, ve}ina qudi }e uredno ispisivati na papir vremena na ceo sat, 14:00, 15:00, ... mada su u stvari manometar o~itavali u 14:16, 15:03, ~ime unose velike probleme u fazi analize rezultata).

^esto se dijagnosti~ka merewa mogu obaviti i jednostavnim, priru~nim metodama. Na primer, autori su imali prilike da u jednom mawem mestu prate rad vodovoda koji "pati" od hroni~ne nesta{ice vode. Utvr|ivawe protoka na izvori{tu nije bio predmet posla, ali kada se posumqalo u dobijeni podatak, jednostavnim merewem visine prelivnog mlaza na kapta`i kao i protoka vode koja se preliva i odlazi malim potokom (merewem povr{inske brzine pomo}u papiri}a i popre~nog preseka), ustanovqeno je da su gubici u dovodnom cevovodu ve}i od 50%.

Sam izbor merne metode, kao i ure|aja za merewa je lak{i deo posla. Autori rada su se u ve}ini obavqenih dijagnosti~kih merewa, uglavnom najvi{e "borili" sa samim qudima iz vodovoda, koji su ta merewa i naru~ivali i pla}ali. Mada su svi na~elno svesni da su merewa neophodna, kada do|e do toga da na cevi treba postaviti neki prikqu~ak, predihtovati ventil da ne curi ili zameniti neispravan vodomer, entuzijazam naglo splasne, jer taj konkretan radnik nije motivisan na dodatni rad.

2.2. Analiza

Podatke dobijene dijagnosti~kim merewima treba prvo kroz proces predprocesirawa dovesti na standardni sistem veli~ina i mera (ako se pritisak meri senzorima, merna veli~ina je struja ili napon - to treba prevesti prvo u pritisak a zatim u Pijezometarsku kotu). Nakon toga, kre}e se u analizirawe dobijenih veli~ina, u zavisnosti od problema koji se istra`uje. To mogu da budu relativno proste analize, kao na primer odre|ivawe karakteristika pumpe u vodovodu Lakta{i (Prodanovi}, Pavlovi} i Ja}imovi}, 2001) na osnovu merewa nivoa u rezervoaru (posredno odre|en protok), nivoa u crpnom bunaru i pritiska nizvodno od pumpe, ali i kompletne analize primenom odgovaraju}eg matemati~kog modela.

For example, the figure 1. presents the procedure of checking the built-in fixed flow meter by measurement of the velocity profile in the pipe. As the procedure lasts often more than an hour, it is not reasonable to assume that the flow in the pipe is constant during that time. Because of that, the another flow/velocity sensor (or the flow gauge under the test, as shown on figure 1.), has to be used in order to record the flow changes, those data are then used in off-line velocity profile processing to correct the flow field to mean flow. Rate of particular quantity change can also differ for an order of magnitude (water level in a pumping reservoir during a pump start period, and in a stationary work regime) throughout the measurement, so data acquisition algorithm has to match it.

The choice of measurement equipment mostly depends on the explored problem. If there is a need for long time recording of certain quantities (for several days or weeks), it is necessary to use modern, computer based devices (loggers) that are able to measure data, preprocess measured values and store them in real time. For measurements that lasts for up to one day, the "manual" data storing can be done, but it is usually less reliable (for example, if there is a need to observed pressure gauge on every hour, most of us will write the time as the whole hour, eg. 14:00, 15:00, … although the readings were done at 14:15, 15:03; that causes significant problems during the result analysis phase).

Simple, handy methods could often be used in diagnostic measurements. For example, the authors had opportunity to monitor a water supply system in a small municipality with a constant water shortage. Measurements of a flow rate at the wellhead were not a part of planned activities. But when some unexpected measurement results were obtained, it was enough to do a simple measurement of an overflow depth at the water intake structure, as well as a measurement of a water flow that overflows to a small creek (by measuring a superficial velocity with a small piece of a paper and a cross section) to found that the water loss rates in the main pipe were over 50 %.

A choice of a measurement method, as well as measurement equipment, is an easier part of the job. The authors of the paper, in most of the conducted diagnostic measurements, had the biggest organizational problems with the people from the local Water Supply company. Although everybody is generally aware of the measurement necessity, when the sensor connection has to be installed, the leaking valve repaired or malfunctioning flow meter replaced, the enthusiasm rapidly vanishes because of the worker's lack of motivation for additional engagement.

2.2. The Analysis

Diagnostic measurement data should be first translated to the standard system of measurement units through a preprocessing phase (if a pressure is measured by sensors, a measured quantity is electricity or voltage – it should be translated first to pressure, and then to Piezometric level). After that, the measured data processing can be done, mostly off-line, depending on the explored problem. It could be relatively simple analysis, assessment of pump characteristics in the water supply system in Laktasi (Prodanovic, Pavlovic and Jacimovic, 2001), for example, based on water levels measured in the upstream reservoir (indirectly determinate flow rate), water levels in the well and pressures downstream the pump, but also a complex network analysis based on the appropriate mathematical model.

Slika 2 . Oscilacije protoka na vodovodnom distribucionom sistemu Tabanovi} - [abac

prilago|avawa kazana sa spre~avawe udara.

Rezultati analiza dijagnosti~kih merewa su ~esto ulazni parametar za kompleksnije modele celih vodovodnih sistema. Za wihovu korektnu primenu, neophodno je raspolagati i sa preprocesiranim veli~inama kao i na~inom wihove obrade. U svojoj praksi, me|utim, autori rada su se ~esto sretali sa projektima dijagnosti~kih merewa u kojima su dati samo gotovi rezultati bez ikakvog uvida u polazne podatke kao i u na~in kako su obra|ivani.

2.3. Analiza ta~nosti rezultata

Sistem kontrole kvaliteta, na svakom nivou i u svakoj oblasti, je op{te prihva}eni svetski trend. U oblasti dijagnostike, neophodno je na svakom koraku ispo{tovati to pravilo: u fazi merewa, svi kori{}eni ure|aji moraju biti korektno i redovno kalibrisani, a u fazi analize moraju se koristiti vaqani i provereni podaci. Da bi se neizvesnost smawila, neophodno je merewa tako planirati da postoje redundantni podaci. Na primer, dovoqno je meriti dotok vode u rezervoar i nivo vode u rezervoaru da bi se znao izlazni protok. Ali, istovremenim merewem i izlaznog protoka, mo`e se proveriti dobijeni podatak o povr{ini rezervoara - a taj podatak je veoma va`an za matemati~ki model vodovoda.

Analizom gre{aka se dobija opseg vrednosti u kojoj se odre|ena veli~ina mo`e nalaziti. Ako se `eli odrediti hrapavost cevi na osnovu merewa pritiska na dve me|usobno udaqene lokacije, pri ~emu sve merene veli~ine nose odre|enu gre{ku (merewa pritiska manometrima, odre|ivawe geodetskoh kota manometara, merewe protoka, procena unutra{weg pre~nika - koja nosi ~esto najve}u te`inu), mo`e se dobiti opseg mogu}ih vrednosti za hrapavost . Ako se na to doda jo{ i problem neustaqenosti protoka kao i mogu}nost postojawa nekog lokalnog poreme}aja koji nije identifikovan, sledi da je ovakav prora~un koeficijenta hrapavosti neupotrebqiv.

2.4. Primena dobijenih rezultata

Sastavni deo dijagnosti~kog paketa (merewa - analiza - analiza gre{aka) je i primena dobijenih rezultata. Naime, nije retka situacija da se nakon izvr{enih analiza uka`e na odgovaraju}i problem, ali da vodovod ne krene u wegovo re{avawe. Na primer, u toku merewa karakteristika pumpi, ustanovqeno je da je ugra|ena pumpa vi{e nego duplo ja~a. Predlo`ena je ugradwa tiristorske regulacije snage, uz obra~un da se ulo`ena investicija ispla}uje ve} posle 6 meseci samo kroz smaweni ra~un za struju. U toj ra~unici je, me|utim, zanemaren jedan va`an podatak, a to je da doti~ni vodovod i onako ve} godinama ne pla}a struju!

3. VRSTE DIJAGNOSTIKE SISTEMA

3.1. Standardno merewe protoka i pritisaka

Za potrebe kalibracije modela, obi~no se vr{e kontinualna vi{ednevna merewa protoka i pritiska na izabranim delovima sistema. Na slici 3 je dat rezultat kontinualnog merewa na vodovodu Lakta{i, i to nivoi u rezervoaru i protok i pritisak na mestu kod hotela "Milka". U toku merewa je do{lo do havarije na cevovodu u Jakupovcima, tako da je zatvaran izlaz iz rezervoara i prsten koji snabdeva taj deo vodom. Kori{}ewem ovog i drugih rezultata merewa, treba obaviti kalibraciju matemati~kog modela vodovoda Lakta{i. Test verifikacije modela bi bio simulacija uslova koji su se odigrali na terenu 05.07.2001. (slika 3).

The results of analysis are often used as an input parameter for more complex models of a whole Water Supply Systems. In order to use correctly those values, it is necessary to save all preprocessed quantities, as well as method of their analysis. However, the authors of this paper were often in position to see the results of some diagnostic measurement projects, where only final results were presented, without any insight information about raw data same as about numerical method used.

2.3. Accuracy assessment

The commonly accepted worldwide trend is the introduction of quality control system, on every level and in every field. In the field of diagnostics the rule is applied on each step: in the phase of measurement the equipment has to be regularly calibrated, and in the phase of analysis, only reliable data can be used. In order to minimize the uncertainty, the measurements should be planned in that way to have some redundant data. For example, it is enough to measure the inflow of the water into a reservoir and a water level to know an outflow from the reservoir. But, if the outflow is also measured at the same time, there is a way of checking the preliminary record of a reservoir surface area – and that value is very important for the mathematical model of a water supply system.

Error analysis gives the scope of the measured quantity. If one wants to calculate the pipe roughness based on the pressure measurements at two distant locations, assuming that all measured quantities have certain errors (the pressure measurement using manometers, determination of manometer geodetic heights, flow measurements, estimation of interior pipe diameter - that is often significant), the roughness values scope can be . And if there is also a problem with unsteadiness of water flow, as well as a possibility of existence of some unidentified local disturbance, the conclusion is that such calculation of friction coefficient is useless.

2.4. Application of obtained results

An important part of the diagnostic package (measurements – analysis – error analysis) is also the application of obtained results. It often happens that suggestions regarding some problems in system are made, but there is no action from the Water Supply company to apply it. For example, during the pump characteristics measurement, it was notified that the installed pump is more than twice stronger than it should be. Installing the frequency-thyristor power regulator was proposed, with estimation that the investment will repay within 6 months only through a lowered electricity bill. Nevertheless, that calculation didn't take into consideration one important fact: the Water Supply company doesn’t pay for years the electricity at all!

3. TYPES OF A SYSTEM DIAGNOSIS

3.1. Standard flow and pressure measurements

Mathematical models are used for better in depth understanding of Water Supply System functioning (Gotoh, Jacobs, Hosoda and Gerstberg, 1993). Creation of the model implies digitalization of all water supply system elements data (pipes, reservoirs, valves, pumps, consumers etc.), their characteristics and interrelations. After finishing the model creation, its calibration is necessary to achieve the reliable simulation of the existing system. A calibration procedure is done by fine adjustment of certain system element parameters (consumption disposition, water losses, etc.) so that simulation results and diagnostic measurement results fit well.

A model calibration usually requires continuous, a few day long measurements of flow and pressure at selected system locations. The figure 3 presents the results of a continuous measurement on the water supply system Laktasi – water levels in the reservoir, flow and pressure at the location near the "Milka" hotel. Pipe break occurred at the location in Jakupovci during the measurements, so the outlet from the reservoir was closed, same as the distribution pipe ring that supplies that area. Using this, and other measurement results, numerical model calibration of water supply system Laktasi can be performed. The model will pass the verification if it can reliably simulate conditions that occurred at the site on the date 05.07.2001. (Figure 3).

Slika 3 - Merewa iz Lakta{a za 5.7.2001 - Protok i pritisak za vreme kvara na cevi

Figure 3. Measurements from Laktasi, for 5.7.2001 - Flow and pressure during pipe brake

Slika 4. Sirov (ne obra|en) podatak o brzini u cevi

Figure 4. Raw (unprocessed) velocity data in pipe

Sam izbor broja lokacija na kojima }e se meriti kao i potrebno vreme merewa je direktna povezano sa raspolo`ivim resursima (vreme i novac). Pravilo je da na vodovodnim sistemima na kojima ne postoje prethodna merewa i na kojima nema dovoqno pouzdanih informacije o o~ekivanim vrednostima merenih veli~ina, potrebno je uraditi dve serije kontinualnih merewa: prvom serijom se dobijaju op{ti podaci o sistemu, na osnovu tih podataka se grubo kalibri{e matemati~ki model i na modelu se proveravaju mogu}a uska grla. U drugoj seriji merewa se vr{i novi izbor mernih lokacija, koncentri{u}i se na ve} uo~ene probleme. Na slici 4. je dat primer merewa protoka na sistemu gde nisu postojale prethodne informacije o mogu}im radnim re`imima. Merene su brzine u cevi elektromagnetnom sondom, koja u principu mo`e da meri brzine do 10 m/s ali je u toku procesirawa signala maksimalna brzina limitirana na 3 m/s. Me|utim, ispostavilo se kasnije, da je cev u kojoj su merene brzine direktna veza izme|u dve visinske zone (!) pa su i brzine u cevi znatno izvan o~ekivnih.

Kontinualnim merewima (naj~e{}e) protoka i pritisaka, u toku kalibracije modela, ~esto se ustanovi postojawe nekih ve}ih lokalnih problema (veliki pad pritiska du` neke deonice kao rezultat nekog pritvorenog ventila, ve}i gubici vode na nekim pravcima) ili znatnijeg odstupawa karakteristika od o~ekivanih (pre~nik cevi nije kao u projektu, znatan pad karakteristike pumpe itd.). Na osnovu tih zapa`awa, neophodno je planirati i obaviti dijagnostiku takvih detaqa.

3.2. Dijagnostika detaqa sistema

Duga~ak je spisak mogu}ih dijagnosti~kih merewa za potrebe odre|ivawa karakteristika pojedinih detaqa vodovodnih sistema. Neka od mogu}ih merewa su: odre|ivawe karakteristike pumpi, kalibracija ugra|enih merila protoka u nestandardnim uslovima, analiza rada filterskih poqa u redovnim uslovima i pri preoptere}ewu, fluktuacije pritisaka pri ispadu pumpi (hidrauli~ki udar), odre|ivawe polo`aja pritvorenog zatvara~a koji je negde zatrpan na osnovu prostirawa poreme}aja, itd.

Selection of the number of measurement locations, same as the measurement duration is in direct relation with available resources (time and money). The rule is: on water supply systems where there is no previous measurement results and enough reliable information about expected values of measured quantities, two series of continuous measurements are needed. The first one will give the general information about the system. Rough calibration of the numerical model should be performed based on that information. Using model and site visiting, the possible critical parts of Water Supply System are detected. In the second series of measurements, some new measurement locations should be selected, focusing on already noticed problems. The figure 4 presents an example of flow measurement, where there was no previous information about the measured quantities. Velocities were measured with the electromagnetic probe, which is generally able to measure velocities up to 10 mps, but during the signal conditioning procedure they were limited on 3 mps. However, it came out later that two level zones were directly connected (!) through that pipe, so velocities were significantly beyond expected.

Based on continuous measurements (most often) of flow and pressure rates, the existence of some significant local problems can be observed during a model calibration (significant grade of pressure along a pipe as a result of certain half-opened valve, significant leakages along pipelines) or significant variation of characteristics from expected (a pipe diameter is not as designed, a significant degradation of a pump characteristics etc.). With such notices, planning and performing diagnosis of those details is necessary.

3.2. System details diagnosis

Slika 5. Odre|ivawe raspodele protoka po filterima u nestandardnim mernim uslovima

Figure 5. Flow distribution measurement in unsuitable conditions

Slika 6. Dijagram starewa pumpe Slika 7. Kriva buster pumpe koja radi u kavitaciji

Figure 6. Pump aging diagram Figure 7. Buster pump working in cavitations regime

Na slikama 5, 6 i 7. su dati neki od primera dijagnosti~kih merewa. Na starom filterskom postrojewu "[trand" u Novom Sadu (slika 5) dolazilo je do oscilacija u radu automatske opreme za upravqawe, te je trebalo ustanoviti u kojim re`imima postrojewe radi. Kao osnovni podatak sa kojim vodovod uop{te nije raspolagao je kakva je raspodela vode na levu i desnu polovinu postrojewa. Kako su uslovi na terenu bili daleko od idealnih za merewe protoka, izvr{eno je detaqno snimawe poqa brzina i wihovom integracijom je dobijen protok (Prodanovi} i Iveti}, 2000). Na izabranoj lokaciji u profilu cevi odre|ena je veza izme|u trenutne brzine i protoka, te su se sva daqa merewa protoka svela na merewe jedne brzine (indeks brzine).

Kao drugi interesantan primer, na slikama 6 i 7. su dati rezultati snimawa karakteristika pumpi. Na ve}ini vodovodnih sistema na kojima su autori radili merewa, odre|ivani su protoci i ra|en bilans vodovoda na osnovu broja sati rada pumpi, uz pretpostavku da su karakteristike pumpi istovetne fabri~kim. Tek kada se izvr{i merewe stvarnih karakteristika pumpi mo`e se ustanoviti kolike se gre{ke ~ine takvom ra~unicom. Na slici 6. je prikazan pad karakteristika pumpe kroz vreme (radi se o muqnim pumpama, Prodanovi}, Iveti} i Pavlovi}, 1996) a na slici 7. karakteristika pumpe koja radi u kavitacionom re`imu, pa su ostvareni protoci znatno ni`i od o~ekivanih (Prodanovi}, Pavlovi} i Ja}imovi}, 2001).

Izbor mernih metoda i merne opreme zavisi od problema koji se istra`uje kao i uslova koji vladaju na terenu. Mo`e se uzeti kao pravilo da je potrebno posti}i ta~nost merewa za red veli~ine ve}u nego kod kontinualnih merewa, te i taj faktor treba imati u vidu. Na primer, prilikom kalibracije postoje}ih fiksnih merila protoka (koji su klase ta~nosti 0.5 ili 1%), nije mogu}e koristiti ultrazvu~ne merne ure|aje, koji su veoma elegantni za kori{}ewe, ali ~ija je ta~nost reda veli~ine 5%.

3.3. Dijagnostika gubitaka

Utvr|ivawe koliki su stvarni gubici vode na nekom vodovodnom sistemu je izuzetno te`ak zadatak. Po{to skoro ni jedan vodovodni sistem kod nas nema pouzdana merewa proizvodwe i raspodele vode po sektorima, podaci o izgubqenoj vodi su vi{e politi~ka kategorija a mawe rezultat analiti~kih metoda. Vodovodi se uglavnom bave lokalnim sanirawem sistema u slu~ajevima kada je do{lo do potpunog loma cevi ili ukoliko voda u ve}oj meri izbije na povr{inu terena. Neki vodovodi su opremqeni ure|ajima za detekciju gubitaka koji im u tim slu~ajevima dosta poma`u.

Figures 5, 6 and 7 present some diagnostic measurement examples. At the old filter plant "Strand" in Novi Sad (Figure 5) some instability in control equipment performance was detected, and the task was to determine a working conditions of the plant. The fundamental information about the water distribution between the left and the right half of the plant the Water Supply company didn’t possess at all. As conditions for flow rate measurement were bad, detailed recording of velocities profile in unsteady conditions was performed. The flow field was integrated to give the flow rate (Prodanovic and Ivetic, 2000). At the established profile location, a relation between an instant flow rate an velocity was determined, so afterwards the flow rate measurement was reduced to a single velocity measurement (velocity index).

As other interesting example, figures 6 and 7 present results of a pump characteristic recording. At most of Water Supply Systems, where the authors took measurements, a flow rate and a water balance in the system was estimated based on number of hours that pumps were running, with assumption that characteristics are the same as in the pump catalogue. Only true pump characteristic measurement can show how big error is done with that kind of water balance calculation. Figure 6. presents the deteriorate of pump characteristics during the time (or pump aging) for sludge pump (Prodanovic, Ivetic and Pavlovic, 1996), and the figure 7 presents characteristics of pump running in a cavitations regime, producing significantly lowered flow rates than expected (Prodanovic, Pavlovic and Jacimovic, 2001).

A choice of measurement methods and measurement equipment is directly related to a problem that is to be explored, as well as to conditions at the site. It could be taken as a rule that it is necessary to obtain accuracy of measurements in the order of the scale higher than for continuous measurements, so that factor has to be considered. For example, during a calibration process of existing flow meters (which are in accuracy category of 0.5 or 1%), it is not possible to use echo flow meter equipment, which is very handy, but with accuracy of 5 % or even worse.

3.3 Diagnosis of leakage losses

Slika 8. Protok na sekcijskom vodomeru u periodu od dva meseca

po~eo da raste uz opadawe odnosa izme|u dnevnog maksimuma i minimuma. Ovakav kontinualni zapis jasno ukazuje na postepen razvoj pukotine na cevi. Nakon sanirawa kvara, sredinom januara, dnevni dijagram protoka se vratio u prvobitne granice. Na osnovu ovakvih podataka, mogu}e je obra~unati stvarnu koli~inu izgubqene vode, proceniti potrebna ulagawa za sanirawe kvara, pa ~ak napraviti i analizu kada krenuti u sanirawe kvara.

Slika 9. Protok bez dnevne neravnomernosti ukazuje na velike gubitke

Figure 9. Flow without daily irregularities shows that losses are substantial

Na slici 9. je prikazan ne{to druga~iji rezultat - protok u periodu od dva dana snimqen na pre~niku cevi 300 mm na ulazu u primorsko naseqe, u zimskom periodu, bez turista i bez privrede koja radi. Koliki su gubici na toj cevi kada nema dnevnih neravnomernosti protoka? 90% ili 95%? Kako proceniti koliki je normalan protok kroz cev kada je prikazani rezultat jedinog ikad napravqenog merewa na sistemu. I da li su gubici vode kada se namerno otvori neki od ventila i voda pu{ta u more samo da bi se obarawem pijezometraske kote postiglo da susedno mesto ne dobije vodu? Naravno, prikazani primer je ekstreman slu~aj (ali ne redak), ~e{}e se dobija dnevni dijagram protoka sa odnosom maksimuma i minimuma od 2:1 do 3:1, {to ukazuje na postojawe gubitaka u nizvodnim delovima mre`e, ali ne omogu}ava wihovu precizniju procenu.

Trenutno uglavnom vlada mi{qewe da je dovoqno da vodovod ugovori sa nekom firmom par dana dijagnosti~kih merewa i da }e samim tim da se smawe gubici. Istina je ne{to druga~ija: ovakva merewa su najkompleksnija, zahtevaju stalno anga`ovawe vodovoda i wihov rad kako na monitoringu tako i na upornom odr`avawu svih potencijalnih mesta za gubitke (ventili koji ne dr`e, ovazdu{ewa, povratne klapne, itd.).

3.4. Dijagnostika u havarijskom re`imu

The figure 9 presents a somewhat different result – a flow rate during two days period is recorded in pipe with 300 mm diameter at the entrance of a small coastal settlement, during a winter period, without tourists and commercial working. What are water losses on that pipe when there is almost perfect daily uniformity of flow rate? 90 % or 95 %? How to estimate what is normal flow rate through a pipe, if this was the only, ever made measurement in the system? And can we call it "the water losses" when some of the valves are purposely left opened and water runs into the sea, just to reduce the piezometer level so that the next village doesn't get the water? Naturally, illustrated example is an extreme case (but not unusual). More often the result of diagnostic measurement is the daily flow rate diagram with maximum/minimum rate of 2:1 up to 3:1 that indicates the existence of water losses at downstream part of a water supply network, but doesn't allows their better estimation.

Currently, there is principally opinion that it is enough to engage someone to make a few diagnostics measurements in order to reduce water losses. The truth is somewhat different: that kind of measurements are extremely complex, they require permanently Water Supply Company engagement and effort on monitoring, as well as on a persistence maintenance of all potential locations for water losses (bad valves, air relief valves, by-pass valves, etc.).

3.4. Diagnosis in accidental regime

Slika 10. Pucawe cevovoda usled pogre{ne manipulacije zatvara~ima

Figure 10. Pipe brake due to misuse of section valve

Na sistemima koji nemaju kontinualno merewe, ovakva vrsta dijagnostike je mogu}a samo ako se u periodu nameskih kontinualnim merewa ili simulira kvar, ili se kvar slu~ajno dogodi (kao u slu~aju merewa na vodovodnom sistemu Lakta{i, prikazano na slici 3.).

Na slici 10. je prikazana jo{ jedna snimqena havarija cevovoda (Prodanovi}, Iveti} i Pavlovi}, 1994) u mestu Mala Vrbica, kod Kladova. Na delu cevovoda koji je i{ao dolinom dolazilo je do ~estih havarija. Obavqena je jedna serija merewa od 10-tak dana, kao i niz brzih merewa hidrauli~kog udara, ali svi pokazateqi su bili u granicama normale. Onda je "simulirano" odno{ewe opreme ali je ostavqen data loger za pritiske koji je nastavio da prati pritisak kod bunarske pumpe. Nakon par dana se dogodila havarija, prskawe cevovoda (vidi se kao nagli pad pritiska na slici 10.). Analizom dijagrama sa slike, me|utim, uo~ava se da je pre havarije, do{lo do pove}awa pritiska u sistemu. Nakon razgovora sa qudima na terenu otkriven je i razlog: lokalni majstor kada popravqa bojlere po selu, u slu~aju kada nema ili ne radi ventil na ku}nom prikqu~ku, zatvara ventile na distribucionom cevovodu (na slici Z1 i Z2). Kada zavr{i popravku, povremeno zaboravi da otvori Z2, te pumpa radi bez rezervoara, koji joj ograni~ava pritiske.

4. ORGANIZACIJA DIJAGNOSTIKE

Dijagnosti~ka merewa bi trebala da budu sastavni deo aktivnosti svakog vodovoda. Organizaciono treba predvideti grupu qudi ~iji }e posao biti:

• da vodi ra~una o ugra|enoj mernoj opremi
• vr{i redovnu kalibraciju
• vodi dnevnik svih radova i o~itavawa (ru~nog ili automatskog)
• obavqa primarnu obradu rezultata
• proverava validnost (da li je neki ure|aj po~eo da pokazuje znatno ve}e/mawe vrednosti)
• trajno arhivira rezultate sa komentarima
• formira redovne izve{taje u formi nedeqnih/mese~nih/sezonskih dijagrama, formira izve{taje o vanrednim situacijama, itd.

Oprema za dijagnostiku bi trebala da bude savremena elektronska merna oprema sa mogu}no{}u vi{ednevnog ili vi{enedeqnog kontinualnog zapisa pritisaka i protoka ili samo pritisaka, kao i nivoa u rezervoarima. Me|utim, i obi~ni manometri i vodomeri ako se redovno kalibri{u i ru~no o~itavaju, mogu da se iskoriste. Na slici 11. su dati rezultati redovnog o~itavawa jednog od dva vodomera na izlazu iz rezervoara Lakta{i, koje je sprovodio vodovod od trenutka wegove ugradwe. Dobijeni podaci su od su{tinskog zna~aja u analizama rada sistema, planovima za naredni period, analizi sezonskih uticaja itd.

On the systems without continuous measurements, this kind of diagnosis is possible only if during the specific continuous measurements either accident is simulated, or it randomly happens (as happened in the case of measurements in the water supply system Laktasi, showed on the figure 3).

The figure 10 presents another recorded pipe break (Prodanovic, Ivetic and Pavlovic, 1994) in Mala Vrbica, nearby Kladovo. On the pipeline segment that has been positioned along the valley, failures were occurred rather often. One 10 days measurement series, as well as series of fast measurements of water hammer, showed that all parameters were normal. After that, a "simulation" of equipment removal was done, but with one data logger left to record the pressure at the well pump. A few days later, pipe was broken (presented as a rapidly pressure drop on the figure 10). The recorded diagram on the figure 10 presents a pressure increase, starting from 12/09 till the pipe failure on 16/09. After contacting local people at the site, the reason was found: some local serviceman was keen on closing the valves on pipeline (Z1 and Z2 on the figure) when doing some home repairs. When a repair is over, sometimes he forgets to open valve Z2, and afterwards a pump is running without the reservoir that limits the pump pressures.

4. DIAGNOSIS ORGANIZATION

Diagnostic measurements should be the integral part of every water supply system activities. A special team should be established with following obligations:

Diagnosis equipment should be modern electronic measurement equipment with a possibility for several days or weeks of continuous recording of pressure and flow rate, as well as water levels in reservoirs. However, ordinary manometers and flowmeters could be useful also, if regularly calibrated and manually recorded. The figure 11 presents results of a regular readings from one of two flowmeters at the reservoir Laktasi outlet that was performed by Water Supply Company from the moment of its installing. Obtained information is of substantially importance for system performance analysis, further planning, season effect analysis, etc.

Slika 11. Primer upotrebqivih podataka za simulacione modele: sezonska promena protoka na osnovu vi{emese~nih ~itawa vodomera

Situacija u ve}ini na{ih vodovoda je takva da ne postoji organizovan pristup dijagnostici. Po potrebi se posao prepu{ta spoqnim firmama i to samo ukoliko mora. Osnovni pokazateqi sistema su ~esto nepoznati, pa ~ak i sam polo`aj i pre~nici cevi i zatvara~a. Bilo kakav zahtev za otkopavawem cevi i izgradwom {ahta na nekoj pravoj deonici, radi pouzdanijeg merewa protoka, smatra se za nepotreban luksuz (idelno bi bilo ukoliko bi mogla merewa da se obave u kancelariji).

U takvim uslovima, veoma je te{ko obaviti kvalitetna dijagnosti~ka merewa. Na nepoznatom sistemu, neophodno je prvo detaqno sagledati distribucionu mre`u. Detaqi prevezivawa pojedinih ~vorova, (nebitni za redovno funckionisawe sve dok ima dovoqno vode) su od kqu~nog zna~aja u fazi obrade izmerenih rezultata. Ukoliko postoji matemati~ki model sistema, potrebno je na modelu prvo proveriti planiranu strategiju dijagnosti~kih merewa (otvarawe/zatvarawe pojedinih komora rezervoara, rad u razli~itim re`imima pumpawa, iskqu~ivawe pojedinih deonica sistema itd.) kako bi se maksimizirao kvalitet izmerenih podataka uz minimizirawe posledica na redovno snabdevawe potro{a~a. Na modelu, tako|e, treba odabrati potrebna merna mesta kako bi se sa {to mawe merewa dobilo {to vi{e informacija o sistemu.

U situaciji kada ne postoje ni prethodna merewa ni matemati~ki model sistema, po pravilu treba predvideti dijagnosti~ka merewa u dve kampawe. Sa prvim merewima se dobijaju osnovni podaci o sistemu, na osnovu wih se analizom uo~avaju problemi i defini{u nova merna mesta pomo}u kojih se uo~eni problemi mogu boqe izu~iti. U drugoj kampawi merewa fokus se stavqa na pojedine detaqe sistema a zatim na kontinualno funkcionisawe sistema u nekom izabranom periodu (minimalno je za 24 sata, a preporu~qivo je meriti kontinualno bar 7 dana).

5. DA LI JE DIJAGNOSTIKA SKUPA?

Kao odgovor na pitawe: Da li su skupa dijagnosti~ka merewa, daju se dva najsve`ija primera iz prakse autora ovog rada.

Po~etkom ove godine, obavqena su dijagnosti~ka merewa na jednom primorskom vodovodnom sistemu (neki rezultati su ve} dati u ovom radu na slikama 4 i 9). Na sistemu nisu raspolagali sa mernom opremom, kao ni sa prethodnim merewima. Merewa su sprovedena za potrebe kalibracije matemati~kog modela, pri ~emu nije bila ugovorena detaqnija dijagnostika i procena gubitaka vode. Na osnovu dobijenih rezultata, me|utim, moglo se grubo proceniti da su gubici oko 400 L/s, {to sa cenom vode koja se pla}a na ulazu u sistem od 0.5 KM/m3 iznosi dnevno 17000 KM gubitaka (prose~na cena jednog kompaktnog logera za protok je 12000-15000 KM a za pritisak 2000-3000 KM).

Iz izlo`ena dva primera, mo`e se zakqu~iti da se dijagnosti~ka merewa sigurno isplate na du`i period. Me|utim, nasle|en problem kod svih na{ih vodovoda je teku}a nelikvidnost i navika da se {tedwa u bilo kojem obliku, pogotovu ona koja zahteva wihovo direktno investirawe, ne isplati (treba biti dovoqno bogat da bi {tedeo).

6. ZAKQU^AK

Svrha ovog rada nije ube|ivawe ~itaoca, i rasprava, da li je dijagnostika vodovodnih distributivnih sistema potrebna ili nije. Dijagnostika je neophodna ukoliko se `eli doma}insko poslovawe, poslovawe sistemom koje }e mu obezbediti punu odr`ivost. Ideja autora je vi{e bila da uz pomo} obja{wewa {ta sve obuhvata dijagnostika, ilustrovanih brojnim primerima iz prakse, napravi edukativni rad. Direktori i vlasnici vodovoda treba {to pre da sagledaju va`nost sistematskog i pedantnog pra}ewa rada svog sistema. U organizaciji rada treba predvideti va`no mesto formirawu slu`be koja }e biti zadu`ena za kontinualna merewa i wihovu obradu. U po~etku }e se verovatno jedan deo poslova poveravati spoqnim firmama, ali je neophodno da vodovod aktivno "krade znawe" i postepeno preuzima ve}i deo aktivnosti. ^esto se ~ini gre{ka da se nabavka skupocene merne opreme stavqa ispred obrazovawa radnika: i obi~ni manometri i vodomeri mogu da obave veliki deo posla ako je ekipa za dijagnostiku kvalitetno obu~ena i motivisana za rad.

7. LITERATURA

Gotoh, K., J. K. Jacobs, S. Hosoda and R. L. Gerstberg (1993). Instrumentation and Computer Integration of Water Utility Operations. American Water Works Association Research Foundation and Japan Water Works Association. Denver, USA and Tokyo, Japan

Maksimovi}, ^. (1993). Merewa u hidrotehnici. Gra|evinski fakultet Beograd.

Obradovi}, D. (1999). Savremeni vodovodi. Informatika i operativno upravqawe. Udru`ewe za tehnologiju vode i sanitarno in`ewerstvo.

Prodanovi}, D., M. Iveti} i D. Pavlovi} (1994) Ustaqeno i neustaqeno te~ewe na vodovodnom sistemu Mala i Velika Vrbica, merewa i analiza na matemati~kom modelu

Prodanovi}, D. i ^. Maksimovi} (1995) Dijagnostika rada postrojewa za pre~i{}avawe vode grada Smederevska Palanka

Prodanovi}, D., M. Iveti} i D. Pavlovi} (1996) Merewa i primarna analiza karakteristika bager pumpe i transportnog cevovoda TENT Obrenovac A

Prodanovi}, D. i M. Iveti} (2000). Kontinualno merewe raspodele proticaja i analiza rada postrojewa za pre~i{}avawe ~iste vode [trand - Novi Sad

Prodanovi}, D., D. Pavlovi} i N. Ja}imovi} (2001). Izve{taj o merewima na sistemu za vodosnabdevawe op{tine Lakta{i - Republika Srpska.

Simi} M. (1994) Elektronika i merewa u gra|evinarstvu i geodeziji. Gra|evinski fakultet Beograd

even location of pipes, pipe diameters and valve locations. Every requirement for a pipe excavation and a manhole construction on a straight pipeline section, in order to establish a reliable flow rate measurement location, is considered as wasteful luxury (it wood be perfect if measurements could be accomplished in the office).

In such conditions, it is difficult to obtain reliable diagnostic measurements. When presented with an unknown system, it is necessary first to identify a distribution network. Details of node connections (not important for a regular system performance as long as there is enough water) are essential in measurement and data analysis. If a numerical model exists, it is necessary first to check a planned measurement strategy (opening/closing of some reservoir chambers, system performance in various pumping regimes, exclusion of particularly network sections etc.) in order to maximize the measured data reliability with minimal effects on a regular consumption. Using simulation model, measurement locations also should be selected, in order to obtain more system information with a less measurement.

In situation where there are no previous measurements and nor the numerical model, as the rule of thumb, two campaigns of diagnostic measurements should be planned. The first measurement campaign will obtain the fundamental system information as the base for a system problem identification. Then, a selection of a new measurement location and sampling criteria can be done, in order to better enlighten the noticed system problems. The second campaign can be focused on specific system details, same as on continuous system performance monitoring during longer period of time (24 hours at least, but 7 days is recommendable).

5. IS THE DIAGNOSIS EXPENSIVE?

As the answer on that question, there are two novel examples from the authors practice:

In the beginning of this year, diagnostic measurements were performed on a water supply system in a small seaboard town (some of results were already presented on figures 4. and 9.). The system had no measurement equipment and any previous measurement results. Measurements were accomplished in order to obtain data for a numerical simulation model calibration, and no detailed diagnostic measurements of water losses were contracted. However, based on obtained data, a rough estimation showed that water losses were about 400 L/s, and with water price of 0.5 DM/m3 made 17000 DM of losses per day (the price of an compact flow rate and pressure logger is about 12000-15000 DM, and only for pressure 2000-3000 DM).

At the beginning of summer this year, at Water Supply System Laktasi, extensive diagnostic measurements were done. Firstly, the two well pumps and one buster pump for Slatina settlement were analyzed, and then, 24 hours continuous flow rate and pressure measurements in the system was performed using the built in flowmeters, pressure loggers and manometers. Analysis of well pumps characteristics showed a significant difference between the pumps at the first and the second well: the first pump gives 27 L/s. and the second one 40 L/s, where the first pump has almost 10m higher head than the second one (the first pump was from donation program in May 2001.) Obvious incompability between pumps results in reduction of performance of the first pump and an insufficient well utilization. If there were diagnostic measurements on the old pump before it was changed in May 2001, along with analysis of a dynamic water levels in both wells, as well as coupled pump performance, the pump with better system conformation would be chosen, and higher flow rate could be distributed in the network of the Laktasi settlement.

These two examples undoubtly show that diagnostic measurements are a good investment for a longer period. However, a heritable problem in all our Water Supply Systems is the lack of money and a habit that any kind of saving, especially if it requires some direct investments, doesn’t pay off (one must be rich enough to be able to save).

6. CONCLUSION

The paper objective was not to convince or persuade a reader if a water distribution system diagnosis is required or not. Diagnosis is necessary if the economic performance and the performance with full reliability are required. Using explanations what all diagnosis comprises, illustrated with lots of practice examples, the idea of the authors was to write down the educational paper. Managers and Water Supply System owners as soon as possible have to realize the importance of a systematical and a precise system performance monitoring. In the work management a service should be provided that would be responsible for continuous measurements and data analysis. In the beginning, probably one part of the work will have to be contracted with other specialized companies. It will allow the active "knowledge transfer" and fast learning curve. A usual mistake that is made in out Water Supply companies is to buy expensive equipment rather then to educate workers: even ordinary manometers and flowmeters will do a significant part of the work if a diagnosis team is quality educated and motivated for the work.

7. BIBLIOGRAPHY

Gotoh, K., J. K. Jacobs, S. Hosoda and R. L. Gerstberg (1993). Instrumentation and Computer Integration of Water Utility Operations. American Water Works Association Research Foundation and Japan Water Works Association. Denver, USA and Tokyo, Japan

Maksimovic, C. (1993). Measurements in Hydraulic. Faculty of Civil Engineering, Belgrade (in Serbian)

Obradovic, D. (1999). Contemporary Water Works. Informatics and operational management. Yugoslav Association for Water Technology and Sanitation (in Serbian)

Prodanovic, D., M. Ivetic i D. Pavlovic (1994) Steady and unsteady flow in water supply system of Mala and Velika Vrbica, measurements and numerical model analysis (in Serbian)

Prodanovic, D., C. Maksimovic (1995) Diagnostic measurements on water purification station of Smederevska Palanka city (in Serbian)

Prodanovic, D., M. Ivetic i D. Pavlovic (1996) Measurements and analysis of sludge pump and hydraulic transport system characteristics at Thermal Power Plant TENT Obrenovac A (in Serbian)

Prodanovic, D. i M. Ivetic (2000). Continual measurements of flow distribution on filter plant Strand, Novi Sad with system performance evaluation (in Serbian)

Prodanovic, D., D. Pavlovic i N. Jacimovic (2001). The report on diagnostic measurements on Water Supply System Laktasi - Republika Srpska (in Serbian)

Simic M. (1994) Electronics and Measurements in Civil Engineering and Geodesy. Faculty of Civil Engineering, Belgrade (in Serbian)