منتدي ممدوح عزت موسي MAMDOUH EZAT MOUSA FORUM

هلا وسهلا بك عزيزي الزائر لمنتدي النخبه..منتدي ممدوح عزت موسي
أن لم تكن مسجلا ارجو سرعة التسجيل حتي نستمتع بوجودك معنا عضوا متميزا
نورت المنتدي وزدته بهاءا ونورا
منتدي ممدوح عزت موسي MAMDOUH EZAT MOUSA FORUM

محبي االقصه العربيه والثقافه والفنون الزواج والأسره وشئون المرأه المال والاقتصاد والعلوم الطبيه والعلوم الهندسيه بمختلف تخصصاتها والدين والدنيا

المنتدي يرحب بالأعضاء جميعا وفي انتظار رأي الجميع فيما يتم نشره بالمنتدي ومقترحات الأعضاء في تطوير المنتدي بما يتوافق مع الأحتياجات العلميه والأدبيه والفنيه

المواضيع الأخيرة

التبادل الاعلاني

ديسمبر 2016

الأحدالإثنينالثلاثاءالأربعاءالخميسالجمعةالسبت
    123
45678910
11121314151617
18192021222324
25262728293031

اليومية اليومية


    Star-delta switching of three-phase motors

    شاطر

    ممدوح عزت موسي
    مدير عام المنتدي
    المشرف العام
    مشرف منتدي القصه
    مشرف منتدي العلوم الهندسيه
    مدير عام المنتدي  المشرف العاممشرف منتدي القصهمشرف منتدي العلوم الهندسيه

    عدد المساهمات : 350
    التميز : 9
    تاريخ التسجيل : 13/05/2010

    Star-delta switching of three-phase motors

    مُساهمة من طرف ممدوح عزت موسي في السبت ديسمبر 18, 2010 10:52 am


    What is a star delta starter and how does it work?

    Read more:
    [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط]


    The starting current of any heavy electric motor can be more than 4 times the normal load current it draws when it has gained speed and has reached its normal running output power and temperature.

    So, if it were started simply when connected in DELTA, the starting current would be huge and - just to be able to start the motor, not to run it normally - would require:



    • large circuit breakers, big enough to allow the start-up surge current to pass without immediately shutting it off. (But the breakers would then be much too big to be able to protect the motor from over-current faults whilst it is running normally.)

    • very thick 3-phase power service cables. (But the cable would then be much bigger than is necessary whilst the motor is running normally.)

    • very large coils and contacts on the relays or contactors used to control the motor. (But they would then be much bigger than is necessary whilst the motor is running normally.)



    One solution to this problem is to start the motor in STAR and then, when the motor has gained sufficient speed, change its connections to DELTA to allow the motor to run at its full speed and torque from then on. It's a bit like using the gears of an automobile.

    Update: Electronic motor-control systems, which offer soft-starts in DELTA configuration, are now replacing the use of manual or semi-automatic star-delta starters.

    Technical explanation

    When the windings of a 3-phase motor are connected in STAR:



    • the voltage applied to each winding is reduced to only (1 /.'/'3) [1 divided by root three] of the voltage applied to the winding when it is connected directly across two incoming power service line phases in DELTA.


    • the current per winding is reduced to only (1 /.'/'3) [1 divided by root three] of the normal running current taken when it is connected in DELTA.



    • so, because of the Power Law V [in volts] x I [in amps] = P [in watts],

      the total output power when the motor is connected in STAR is:

      PS = [VL x (1/.'/'3)] x [ID x (1/.'/'3 )] = PD x (1/3) [one third of the power in DELTA]

      where:
      VL is the line-to-line voltage of the incoming 3-phase power service
      ID is the line current drawn in DELTA
      PS is the total power the motor can produce when running in STAR
      PD is the total power it can produce when running in DELTA.



    • a further disadvantage when the motor is connected in STAR is that the total output torque is only 1/3 of the total torque it can produce when running in DELTA.


    Read more: [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط]



    Star-delta switching of three-phase motors

    Star-delta starters with overload relay [t-head1-first]




    Arrangement in the motor line


    [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذه الصورة]
    In a standard circuit configuration, the star-delta starter with overload relay, including a thermally delayed overcurrent relay are situated in the cables leading to the motor terminals U1, V1, W1 or V2, W2, U2. The overload relay can also be operated in a star circuit as it is usually connected in series with the motor winding and the relay current flowing through it = rated motor current × 0.58.
    For the complete circuit diagram → section Automatic star-delta starters SDAINL.


    Arrangement in the mains supply line


    [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذه الصورة]
    Instead of the arrangement in the motor line, the overload relay can be placed in the mains supply line. The section shown here indicates how the circuit differs from that on → section Automatic star-delta starters SDAINL. For drives where the F2 relay trips out when the motor is starting in the star circuit, the F2 relay rated for the rated motor current can be switched in the mains line. The tripping delay is thus increased by approximately four to six times. In the star circuit the current also flows through the relay but here the relay does not offer full protection since its limit current is increased to 1.73 times the phase current. It does, however, offer protection against non-starting.


    Configuration in the delta circuit


    [ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذه الصورة]
    Instead of the arrangement in the motor line or mains supply line, the overload relay can be placed in the delta circuit. The section shown here indicates the modified circuit diagram from → section Automatic star-delta starters SDAINL. When heavy, long-starting procedures are involved (e.g. for centrifuges) the F2 relay, rated for relay current = rated motor current × 0.58, can also be connected in the connecting lines between delta contactor Q15 and star contactor Q13. In the star circuit no current then flows through relay F2. This circuit is used wherever exceptionally heavy and long starting procedures are involved and when saturable core current transformer-operated relays react too quickly.



    _________________

    "لا اله الا الله العليم الحليم،لا اله الا الله رب العرش العظيم،لا اله الا الله رب السموات والأرض ورب العرش الكريم."



     


      الوقت/التاريخ الآن هو الخميس ديسمبر 08, 2016 12:51 am