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Electrical Machines I WEEK 1: OVERVIEW, DC CIRCUIT REVISION Course Contents 1 Review on electric circuits (DC circuits) 2 Magnetic circuits 3 DC Machines (1): DC machines: construction-applications-theory of operation. 4 DC Machines (2): DC machines: equivalent circuit-excitation-voltage control. 5 DC Machines (3): DC motors: performance and speed control. 6 Review on electric circuits (AC circuits) 7 Transformers (1): construction-applications. 8 Transformers (2): theory- equivalent circuits-tests. 9 Transformers (3): voltage regulation- efficiency. 10 Three Phase Induction Motors (1): construction-applications. 11 Three Phase Induction Motors (2): rotating magnetic field-theory of operation-equivalent circuit. 12 3-phase induction motor (3): characteristics-performance-starting. 13 Synchronous Machine (1): construction- applications-equivalent circuit. 14 Synchronous Machine (2): synchronous alternator: theory of operation-characteristics-synchronization. 15 Synchronous Machine (3): synchronous motor. Power System Components 1- Generation System: source of power, ideally with a specified voltage and frequency Generators: • • • • • Thermal (water steam by burning Coal, Oil, NG) Nuclear (water steam by Uranium or Plutonium fission) Geothermal Hydroelectric Wind • solar 2- Transmission Network: transmits power; ideally as a perfect conductor Primary Transmission system Secondary Transmission system 3- Distribution Network: consumes power Distribution Lines Loads Additional components include protection and control Electrical Power System Layout Station switch yard 13.8 kV Power Plant Step up transformer 220 kV rural feeder Step down transformer 66 kV su transmission line 11 kV rural feeder Step down transformer Large industrial customer Secondary distribution substation 11 kV feeder Step down transformer 11 kV feeder 66/11 kV Commercial / industrial customer 66 kV sub transmission line 220/66 kV 13.8/220 kV Primary distribution substation Other 66 kV sub transmission lines Sub transmission sub station 11 kV/ 400 V 11 kV feeder 66 kV 400 v Radial distributor Step down transformer 11 kV/ 400 V Ring distributor Generating Station: The place where electric power produced by parallel connected three phase alternators/generators is called Generating Station. The Ordinary generating voltage may be 11kV, 11.5 kV 12kV or 13kV. But economically, it is good to step up the produced voltage to 132kV, 220kV or 500kV or greater by Step up transformer (power Transformer). Primary Transmission: The electric supply (in 132kV, 220 kV, 500kV or greater) is transmit to load center by overhead transmission system. Secondary transmission: Area far from city which have connected with receiving station by line is called Secondary transmission. At receiving station, the level of voltage reduced by step-down transformers up to 132kV, 66 or 33 kV, and Electric power is transmit by three phase three wire overhead system to different sub stations. Primary Distribution: At a sub station, the level of secondary transmission voltage (132kV, 66 or 33 kV) reduced to 11kV by step down transforms. Generally, electric supply is given to those heavy consumer whose demand is 11 kV. For heavier consumer (at large scale) their demand is about 132 kV or 33 kV, they take electric supply from secondary transmission or primary distribution and then step down the level of voltage by step-down transformers in their own sub station for utilization ( i.e. for electric traction etc). Secondary Distribution: Electric power is given by to distribution sub station. This sub station is located near by consumers areas where the level of voltage reduced by step down transformers 440V by Step down transformers. These transformers called Distribution transformers, three phase four wire system). So there is 400 Volts (Three Phase Supply System) between any two phases and 230 Volts (Single Phase Supply) between a neutral and phase (live) wires. Residential load (i.e. Fans, Lights, and TV etc) may be connected between any one phase and neutral wires, while three phase load may be connected directly to the three phase lines. Egyptian Network الشبكة الموحدة220 kV Any electrical network usually feeds a certain zone or location. In case any power failure in the network, all services will be interrupted and leads to disconnection of loads. The unified grid solves such problems since it connects a number or a group of networks together. In case of any power failure in one network occurs, the rest of the network feeds the loads and prevents their cut out. There Egyptian grid consists of the following: Generation : 24- 30 kV محطات التوليد Transmission : محطات الرفع ألغراض النقل علي أكثر من مستوي 220 kV: ) سيناء- حدود مصر- وجه بحري- القاهرة الكبري-معظم الجمهوريه (شرق الدلتا – غرب الدلتا 500 kV: كم950 خط رابط بين أسوان و القاهرة طوله تقريبا Egypt is connected to Jordan with a marine underground cable at 400 kV and is connected to Lybia with an overhead line that is at 220 kV كيلو فولت تم إختيارها بهذه القيمة الن المسافة بعيدة بين الصعيد ووجه بحري و بالتالي المقاومة الكلية للكابالت ممكن تؤدي النخفاض500 شبكة ال تقريبا500 أو ال440 إلي220 التيار للنصف تقريبا و بالتالي الجهد سيزداد للضعف من Egyptian Grid Useful Statistics %إجمالي الطاقة الكهربية المنتجة البيان الطاقة المائية 7.94 طاقة الرياح 0.79 الطاقة الشمسية 0.07 كهرباء مولدة من المحطات الحرارية المربوطة بالشبكة 91.02 كهرباء مولدة من المحطات الغير مربوطة بالشبكة 0.14 كهرباء مشتراة من فائض الشركات الصناعية 0.04 إجمالي (مليون ك.و.س) 168069 تقرير وزارة الكهرباء عم 2014-2013 What do we see??? Generation: ELECTRICAL: Generators & Turbines Transformers 320 MW generator Steam turbine Current Transformer Circuit breaker Capacitor banks Switches Busses Circuit Breakers Capacitor banks Measuring devices Power Transformer Potential Transformer Bus bars switches What do we see??? Transmission: Transmission lines typically carry voltages of 110 kV, 230 kV, or even higher. The wires are not insulated, so they are kept high off the ground and well separated from each other, to prevent arcing (sparks) and injury or people or animals. Why use such high voltages? Using very high voltages on the transmission lines reduces the amount of energy wasted heating up the wires. And why is that so? Transformers cannot add energy, so if the voltage is increased, the current (in amps) must decrease. The charges flowing through the wires constantly collide with the atoms, losing energy and heating the wire. We call this resistance. Recall that the power (energy per time) lost to that heating is given by the equation P=I2R. If the current is reduced, the power used in heating the wire is reduced. Transmission lines Substation What do we see??? Distribution: ELECTRICAL: Distribution transformer Protection Cables Loads Electrical loads Illumination Pole mounted Pad mounted transformer Motors LV switch gears Circuits Rules: “At any junction in a circuit, the total current leaving the junction is equal to the total current entering the junction. This rule is also known as Kirchhoff’s current law.” Series means: connection of components The current entering a component is the same as the current leaving the component Components do not use up current The current passing through two or more components in series is the same through each component “For two or more components in series, the total potential difference across all the components is equal to the sum of the potential differences across each component” Total current into the junction = 0.5 A Total current out of the junction = 1.5 A Therefore wire 3 must have 1.0 A INTO the junction “The potential difference across components in parallel is the same.” The total current through the two resistors, I is equal to the sum of the individual currents: I = I1 + I2 For any complete loop in a circuit, the sum of the emfs round the loop is equal to the sum of the potential drops round the loop.