1 Luminita Georgeta Popescu

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MONITORIZAREA FUNCIONRIIECHIPAMENTELOR ELECTRICE PRINTERMOGRAFIE

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  • Analele Universitii Constantin Brncui din Trgu Jiu, Seria Inginerie, Nr. 2/2010

    Annals of the Constantin Brncui University of Trgu Jiu, Engineering Series, Issue 2/2010

    7

    MONITORIZAREA FUNCIONRII

    ECHIPAMENTELOR ELECTRICE PRIN

    TERMOGRAFIE

    Prof.univ.dr.ing. Luminia Georgeta POPESCU

    Universitatea Constantin Brncui din Trgu Jiu

    Dr. ing. Cristinel POPESCU

    Universitatea Constantin Brncui din Trgu Jiu

    Ing. Alina DINC

    Universitatea Constantin Brncui din Trgu Jiu

    Rezumat: n timpul funcionrii, cile de curent ale

    aparatelor electrice sunt parcurse de curentul nominal. Acestea, conin rezistenele electrice ale conductoarelor, rezistenele de contact, i deci, prin trecerea curentului electric au loc pierderi de putere electric RI2 care se transform n cldur i determin nclzirea aparatelor electrice. Aadar, nclzirea aparatelor este un regim normal de funcionare, valorile pe care temparatura unui echipament electric le poate atinge n timpul funcionrii fiind prescrise de standarde. n aceast lucrare ne propunem s studiem nclzirea unui contactor electric pentru diferite regimuri de funcionare prin intermediul expertizrii termografice.

    Cuvinte cheie: monitorizare, echipamente

    electrice, termografie 1. Introducere. nclzirea echipamentelor electrice n timpul funcionrii, cile de curent ale aparatelor electrice sunt parcurse de curentul nominal. Aceste ci, conin rezistenele electrice ale conductoarelor, rezistenele de contact, i deci, prin trecerea curentului electric au loc pierderi de putere electric RI2 care se transform n cldur i

    MONITORING THE OPERATION OF

    ELECTRIC EQUIPMENTS THROUGH

    THERMOGRAPHY

    Prof. Ph.D Luminia Georgeta POPESCU

    Constantin Brncui University of Trgu Jiu

    Ph.D Eng. Cristinel POPESCU Constantin Brncui University of

    Trgu Jiu

    Eng. Alina DINC Constantin Brncui University of

    Trgu Jiu

    Abstract: During operation, the paths of current of electric

    devices are crossed by the rated current. They include the wasteful resistances of conductors, contact resistances ad therefore, the passing of the electric current results in losses of power RI2 which transform into heat and cause the heating of electric devices. Therefore, devices heating is a normal operation regime, the values that can be reached by an electric device during operation being prescribed by standards. In this paper we want to study the heating of an electric contactor for various operation regimes through thermographic expertise.

    Key words: monitoring, equipments,

    thermography

    1. Introduction. Electric equipment heating During operation, the paths of current of electric devices are crossed by the rated current. They include the wasteful resistances of conductors, contact resistances ad therefore, the passing of the electric current results in losses of power RI2 which

  • Analele Universitii Constantin Brncui din Trgu Jiu, Seria Inginerie, Nr. 2/2010

    Annals of the Constantin Brncui University of Trgu Jiu, Engineering Series, Issue 2/2010

    8

    determin nclzirea aparatelor electrice. Aadar, nclzirea aparatelor este un regim normal de funcionare, valorile pe care temparatura unui echipament electric le poate atinge n timpul funcionrii fiind prescrise de standarde. Deoarece echipamentele electrice sunt formate dintr-un numr mare de elemente, solicitate termic direct, calculul temperaturilor pe ansamblul echipamentului este complicat. Ca urmare, temperatura echipamentului se stabilete, n general, experimental, iar prin calcul se determin numai temperaturile elementelor componente. Limitele de temperatur sunt date n standarde att pentru curentul nominal, ct i pentru curentul de scurtcircuit, care apare, n general, dup funcionarea aparatelor n regim nominal de durat. Temperaturile admisibile pentru conductoare i aparate sunt temperaturile maxime pentru care se garanteaz funcionarea sigur i de lung durat a acestora, fr modificarea proprietilor lor electrice i mecanice. nclzirea excesiv este periculoas pentru legturile de contact ntruct proprietile lor mecanice se modific. De asemenea, aceasta provoac oxidarea intens a contactelor, ceea ce duce la mrirea rezistenelor lor de trecere rezultnd deci o cretere i mai mare a temperaturii, conducnd aadar la distrugerea lor. Cercetrile au artat c o oxidare foarte intens are loc dac temperatura trece de 70...75 oC i de aceea normele prevd o temperatur limit pentru contacte de 75 oC.

    2. Regimul termic al unei ci de curent. Ecuaia nclzirii. Ecuaia rcirii Multe din cazurile practice de regimuri termice pot fi reduse la regimul conductorului drept cu seciunea constant. Pentru aceasta, se pleac de la ecuaia:

    2 2p

    2l J

    t c c A cx

    = + (1)

    transform into heat and cause the heating of electric devices. Therefore, devices heating is a normal operation regime, the values that can be reached by an electric device during operation being prescribed by standards. Because electric equipments consist of a large number of thermally stressed elements, temperatures calculation on the entire equipment is complicated. Consequently, the temperature is generally established experimentally, and the calculation determines only the temperatures of the components. The temperature limits are given by standards both for the rated current and for the short-circuit current which generally appears after the operation of the devices in conventional duration regime. The allowed temperatures for conductors and devices are the maximal temperatures for which safe and long-term operation is guaranteed, without altering their electric and mechanic characteristics. Excessive heating is dangerous for contact connections because their mechanic characteristics are altered. They also cause intense oxidation of contacts which results in the increase of their passing resistances and to a higher increase of the temperature which causes their destruction. Researches have indicated that an intense oxidation occurs if the temperature exceeds 70...75 oC and this is why regulations provid a limit temperature for contacts of 75 oC.

    2. The thermal condition of a path of current. Heating equation. Cooling equation Many of the practical cases of thermal conditions can be reduced to the regime of the right conductor with constant section. For this, we start from the equation:

    2 2p

    2l J

    t c c A cx

    = + (1) If we consider a constant section conductor and a big length, we can neglect the variation of the temperature along the

  • Analele Universitii Constantin Brncui din Trgu Jiu, Seria Inginerie, Nr. 2/2010

    Annals of the Constantin Brncui University of Trgu Jiu, Engineering Series, Issue 2/2010

    9

    Dac se consider un conductor de seciune constant i lungime foarte mare, se poate neglija variaia temperaturii n lungul axei (dup axa ox), adic:

    0x = ,

    relaia (1) devenind:

    2

    pld Jdt c A c

    = + (2)

    2

    pld J 0dt c A c

    + = (3) Pentru rezolvarea acestei ecuaii, se observ c n regim staionar se ajunge la

    max = , iar 0x = (cu alte cuvinte pentru

    t , temperatura nu se modific n timp). Avnd n vedere toate acestea, rezult:

    2

    maxp

    J Al

    = = (4) mprind relaia (4) la

    plc A

    obinem:

    2

    p p

    c A d J A 0l dt l

    + = (5)

    maxp

    c A dl dt

    + =

    pmax

    ld dtc A = (6)

    n relaia (6) se noteaz: p

    c Al

    = - constanta de timp termic, rezultnd:

    max

    d dt =

    t0 0 max

    dt d =

    t

    max 1 e

    = (6)

    axis (after ox axis), that is:

    0x = ,

    relation (1) becoming:

    2

    pld Jdt c A c

    = + (2)

    2

    pld J 0dt c A c

    + = (3) In order to solve this equation, we notice that in stationary regime we reach

    max = , and 0x = (in other words for

    t , the temperature does not alter in time). Taking this into consideration:

    2

    maxp

    J Al

    = = (4)

    Dividing relation (4) to pl

    c A

    we get:

    2

    p p

    c A d J A 0l dt l

    + = (5)

    maxp

    c A dl dt

    + =

    p

    max

    ld dtc A = (6)

    In relation (6) we note: p

    c Al

    = - thermal time constant, resulting:

    max

    d dt =

    t0 0 max

    dt d =

    t

    max 1 e

    = (6)

    Relation (6) is called heating equation. Observation. If conductor heating

  • Analele Universitii Constantin Brncui din Trgu Jiu, Seria Inginerie, Nr. 2/2010

    Annals of the Constantin Brncui University of Trgu Jiu, Engineering Series, Issue 2/2010

    10

    Relaia (6) poart numele de ecuaia nclzirii. Observaie. Dac nclzirea conductorului nu ncepe de la temperatura mediului ambiant, integrala trebuie calculat astfel:

    0

    , unde 0 este temperatura iniial

    a conductorului corespunztoare momentului n care ncepe nclzirea. Pentru a stabili ecuaia rcirii, se ntrerupe curentul care circul prin conductor (I= 0 => J = 0), astfel c din relaia (2) se obine:

    pld

    dt c A = = (7)

    sau

    d dt =

    max max

    tt0

    0

    d dt tln = =

    t

    max e = (8)

    Relaia (8) reprezint ecuaia rcirii pentru un conductor de seciune constant

    does not start from the environmental temperature, the integral has to be

    calculated as follows:0

    , where 0 is the

    initial temperature of the conductor which corresponds to the time when heating begins. In order to determine the cooling equation, the current which passes through the conductor is interrupted (I= 0 => J = 0), therefore relation (2) results in:

    pld

    dt c A = = (7)

    or

    d dt =

    max max

    tt0

    0

    d dt tln = =

    t

    max e = (8)

    Relation (8) is the cooling equation for a constant section conductor.

    Fig. 2. Diagramele corespunztoare nclzirii, respectiv rcirii unui conductor de seciune constant /

    Heating, respectively cooling related diagrams of a constant section conductor 3. Studiu de caz. Studiul comportrii unui contactor electromagnetic la nclzire

    n continuare vom studia evoluia temperaturii prin cile de curent ale unui contactor trifazat tip RG 125, cu datele nominale: Un=500 V, In=125 A, Pn=30 kW, Ub=220 V (fig. 3). Monitorizarea nclzirii s-a realizat cu o camer de termoviziune Flir Systems, tip T 200, din gama MediumPro.

    3. Case study. Behaviour study for an electromagnetic contactor during heating We will study next the evolution of the temperature through the paths of current for a RG 125 three-phase contactor, with the rated data: Un=500 V, In=125 A, Pn=30 kW, Ub=220 V (fig. 3). Heating monitoring was made with a Flir Systems thermo-vision camera, type T 200, range MediumPro.

    nclzire

    [oC] max

    rcire t[s]

  • Analele Universitii Constantin Brncui din Trgu Jiu, Seria Inginerie, Nr. 2/2010

    Annals of the Constantin Brncui University of Trgu Jiu, Engineering Series, Issue 2/2010

    11

    Fig. 2. Contactor trifazat supus analizei / Analyzed three-phase contactor

    Pentru nceput, prin intermediul trusei de curent TC 1200, am introdus n cile de curent ale contactorului un curent de 125 A (curentul nominal al contactorului). Aadar, pornind din stare rece (se consider stare rece temperatura mediului ambiant), contactorul a fost alimentat timp de 72 s la un curent de 125 A.

    n fig. 3 se prezint termograma celor trei faze ale contactorului la momentul t = 0 iar n fig. 4 se prezint termograma celor trei faze ale contactorului la momentul t = 72 s.

    For starting, with the help of TC 1200 current box, we introduced a 125 A current into the contactor paths of current (rated current of the contactor). Therefore, starting from cold state (cold state is the environmental temperature), the contactor was supplied to a current of 125 A for 72 s.

    Fig. 3 presents the thermogram of the three phases of the contactor at time t = 0 and fig. 4 presents the thermogram of the three phases of the contactor at time t = 72 s.

    SR T

    22.3

    47.1 C

    25

    30

    35

    40

    45

    Fig. 3. Termograma celor trei faze de curent ale contactorului la momentul t = 0 / Thermogram of the

    three current phases of the contactor at time t = 0

    n conformitate cu notaiile de pe figur, de la nceput se identific pe faza R o

    According to the notations of the figure, since the beginning we identify on

    Date 5/11/2010 Filename IR_1848.jpg Max Temperature 48.9 C Min Temperature 22.5 C Image Time 4:37:11 PM R Max. Temperature 48.9 C S Max. Temperature 41.4 C T Max. Temperature 45.8 C

  • Analele Universitii Constantin Brncui din Trgu Jiu, Seria Inginerie, Nr. 2/2010

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    zon cu nclzire mai mare (zona colorat cu alb) i, de asemenea, pe faza T sunt puncte n care temperatura crete mult, pe termogram identificndu-se zone difuze colorate n alb fapt ce semnific existena unui defect (n condiii normale de funcionare i fr defecte - ex. presiune insuficient pe contacte -, culoarea ar trebui s fie aceeai pe toate cele trei faze, adic temperatura ar trebui s fie aproximativ aceeai deoarece materialul din care sunt alctuite este acelai, curentul prin cele trei faze este acelai, fazele fiind nseriate).

    phase R a higher heating area (white area) and also on phase T there are points in which the temperature increases a lot, on the thermogram appeared diffuse areas coloured in white, which means the existence of a fault (in normal conditions of operation without any faults - e.g., insufficient pressure on contacts -, the colour should be the same on all the three phases, meaning the temperature should be approximately the same because the material they are made of is the same, the current through the three phases is the same).

    R TS

    21.9

    127.8 C

    40

    60

    80

    100

    120

    Fig. 4. Termogramele celor trei ci de curent ale contactorului la momentul t =72s / The thermograms

    of the three paths of currents of the contactor at time t =72s

    Pe termograma din fig. 4 se observ creterea excesiv a temperaturii n punctele de conexiune de pe faza R (128,3 0C), respectiv T (123,6 0C), n timp ce pe faza S, temperatura este de 84,3 0C.

    Plecnd din aceast stare, se majoreaz curentul la 1,2x125 A, acesta parcurgnd cile de curent timp de 39 s, obinndu-se rezultatele din fig. 5.

    On the thermogram from fig. 4 we notice an excessive growth of temperature in the connection points from phase R (128,3 0C), respectively T (123,6 0C), while on phase S, the temperature is of 84,3 0C.

    Starting from this state, the current increases to 1,2x125 A, passing through the paths of current for 39 s, and achieving the results from fig. 5.

    Date 5/11/2010 Filename IR_1853.jpg Max Temperature 128.3 C Min Temperature 22.0 C Image Time 4:38:23 PM R Max. Temperature 128.3 C S Max. Temperature 84.3 C T Max. Temperature 123.6 C

  • Analele Universitii Constantin Brncui din Trgu Jiu, Seria Inginerie, Nr. 2/2010

    Annals of the Constantin Brncui University of Trgu Jiu, Engineering Series, Issue 2/2010

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    R S T

    20.8

    222.9 C

    50

    100

    150

    200

    Fig. 5. Evoluia temperaturii prin cile de curent pentru un curent de 1,2xIn / Temperature evolution

    through the paths of current for a current of 1,2xIn

    n continuare, se ntrerupe c...