Electrical Machines IWEEK 1: OVERVIEW, DC CIRCUIT REVISION

Course Contents1 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

Power PlantStep up

transformer

Step down

transformer

Large

industrial

customer

Step down

transformer

Step down

transformer

Step down

transformer

Commercial /

industrial

customer

11 kV/ 400 V

11 kV feeder

11 kV feeder

11 kV rural feeder

11 kV feeder

Primary distribution

substationSecondary distribution

substation

66 kV su transmission line

13.8 kV 220 kV rural feeder

Station switch yardSub transmission

sub station

400 v

Radial distributor

Ring distributor

220/66 kV

Other 66 kV sub

transmission lines

66 kV

66 kV sub

transmission line

66/11 kV

13.8/220 kV

11 kV/ 400 V

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

Generation : 24- 30 kV محطات التوليد

Transmission : محطات الرفع لأغراض النقل علي أكثر من مستوي

220 kV: (سيناء-حدود مصر-وجه بحري-القاهرة الكبري-غرب الدلتا–شرق الدلتا )معظم الجمهوريه

500 kV: كم950خط رابط بين أسوان و القاهرة طوله تقريبا

الشبكة الموحدة 220 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:

بهذه القيمة لان المسافة بعيدة بين الصعيد ووجه بحري و بالتالي المقاومة الكلية للكابلات ممكن تؤدي لانخفاض إختيارهاكيلو فولت تم 500شبكة ال

تقريبا 500أو ال 440إلي 220التيار للنصف تقريبا و بالتالي الجهد سيزداد للضعف من

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

Egyptian Grid Useful Statisticsإجمالي الطاقة الكهربية المنتجة % البيان

7.94 الطاقة المائية

0.79 طاقة الرياح

0.07 الطاقة الشمسية

91.02 كهرباء مولدة من المحطات الحرارية المربوطة بالشبكة

0.14 كهرباء مولدة من المحطات الغير مربوطة بالشبكة

0.04 كهرباء مشتراة من فائض الشركات الصناعية

168069 (س.و.مليون ك)إجمالي

2014-2013تقرير وزارة الكهرباء عم

What do we see???

Generation:

ELECTRICAL:

Generators & Turbines

Transformers

Switches

Busses

Circuit Breakers

Capacitor banks

Measuring devices

320 MW generator Steam turbine

Power Transformer Circuit breaker Capacitor banks

Current 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:

Pole mounted Pad mounted transformer

ELECTRICAL:

Distribution transformer

Protection

Loads

Motors LV switch gears

Cables

Electrical loads

Illumination

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 connection of componentsmeans: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 ormore components in series is the samethrough 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

“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”

“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.