Power. Power is the rate of using energy in joules per second 1 joule per second Is 1 Watt

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1 3 phase

2 Power All we need electricity for is as a source of transport for energy. We can connect to a battery, which is a source of stored energy. Or we can plug into and electric socket at home or in the workplace Depending on the device we use we can obtain the energy we require

3 Power A light bulb will give us light energy An electric heater will give us heat energy An electric motor will give us kinetic energy A loud speaker gives us sound energy

4 Power Power is the rate of using energy in joules per second 1 joule per second Is 1 Watt

5 Power 1,000 Watts is 1 Kilowatt 1, Watts is 1 Megawatt 1, Watts is 1 Gigawatt

6 Power In electricity power is calculated by multiplying volt by amps P = V x I

7 Power Other versions are: P = I 2 R P = V 2 /R (Because V = I x R, from ohm s Law)

8 Power AC systems supply or consume two kind of power: real ( active) power and reactive power. Real power accomplishes useful work while reactive power supports the voltage that must be controlled for system reliability.

9 Real power (true power) is the average of power over cycle and measured by volt-amperes or watts The portion of power with zero average value called reactive power is measured in volt-amperes reactive or VAR.

10 The total power is called the apparent power (symbolized by the capital letter S) and measured by volt-amperes or VA

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13 Power

14 Power factor correction Low power factor is a problem, which can be resolved by adding power factor correction capacitors. the capacitors work as reactive current generators "providing" needed reactive power (KVAr) into the power supply. Power factor correction capacitors reduce the total current drawn from the distribution system and subsequently increase the system's capacity by raising the power factor level.

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18 3 phase In the early days of electric power generation, Tesla not only led the battle concerning whether the nation should be powered with low-voltage direct current or high-voltage alternating current, but he also proved that three-phase power was the most efficient way that electricity could be produced, transmitted, and consumed

19 3 phase The power plant produces three different phases of AC power simultaneously, and the three phases are offset 120 degrees from each other. There are four wires coming out of every power plant the three phases plus a neutral or ground common to all three. If you were to look at the three phases on a graph, they would look like this relative to ground

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21 3 phase

22 3 phase There is nothing magical about threephase power. It is simply three single phases synchronized and offset by 120 degrees

23 3 phase Three phase power transmission has become the standard for power distribution. Three phase power generation and distribution is advantageous over single phase power distribution.

24 3 phase Three phase power distribution requires lesser amounts of copper or aluminium for transferring the same amount of power as compared to single phase power

25 3 phase The size of a three phase motor is smaller than that of a single phase motor of the same rating. Three phase motors are self starting as they can produce a rotating magnetic field. The single phase motor requires a special starting winding as it produces only a pulsating magnetic field.

26 3 phase In single phase motors, the power transferred in motors is a function of the instantaneous current which is constantly varying. Hence, single phase motors are more prone to vibrations. In three phase motors, however, the power transferred is uniform through out the cycle and hence vibrations are greatly reduced.

27 3 phase The ripple factor of rectified DC produced from three phase power is less than the DC produced from single phase supply. Three phase motors have better power factor regulation. Motors above 10HP are usually three phase. Three phase generators are smaller in size than single phase generators as winding phase can be more efficiently used.

28 3 phase

29 Star or Y configuration Line voltage = 3 x Phase voltage L1 Phase voltage L2 Phase current = Line current L line = I phase L3 Neutral (optional)

30 3 phase Line voltage refers to the amount of voltage measured between any two line conductors in a balanced three-phase system. With the above circuit, the line voltage is roughly 208 volts. Phase voltage refers to the voltage measured across any one component (source winding or load impedance) in a balanced three-phase source or load. For the circuit shown above, the phase voltage is 120 volts

31 Delta configuration Line voltage = phase voltage L1 Line current = 3 x phase current L2 I line = 3 x I phase L3

32 3 phase If line values of voltage and current are known, the power (watts) of a pure resistive load can be computed using the formula: Total Power = 3 E line X I Line

33 Direction of rotation in 3 phase generator

34 30 o X V The line voltage, the resultant (green arrow) of the phase voltages can be found using the sine rule XV/sin 120 o = 120V/sin 30 o = 208 V 120V 120 o 120V 30 o

35 30 o Phase voltage is line voltage 3 i.e a line voltage of 433 volts has a phase voltage of 250 Volts X V 120V 120 o 120V 30 o

36 Transformers Transformers step up or step down AC voltage depending on the ratio of primary and secondary windings V s /V p = N s /N p

37 Transformers

38 Other transformer/ inductor equations The AC current in the primary coil induces and changing magnetic in the core. The magneto motive force of the coil F if found by the equation F = NI (amp- turns) where N is the number of turns of wire in the coil and I is the current in the wire. the magnetic field strength H is the mmf per unit length ( L) of the coil. H = F L (amp-turns)/m Flux density (B) is closely related to field strength and is flux area unit Tesla (T)

39 Shell transformers

40 Core and shell type transformers Magnetic flux Magnetic flux In the shell type transformer the magnetic flux in the side limbs is half the flux in the centre limb

41 toroidal

42 C core

43 efficiency Normally when we do transformer calculations we assume 100% efficiency. In reality this is not the case Energy can be lost as heat in the coils and the core

44 efficiency This can be calculated as % regulation (V in V out ) x 100/V in % Efficiency = (power out power in ) x 100 ((V x I) out ) ((V x I ) in ) x 100

45 efficiency A power transformer operates from the 240V 50Hz ac mains; it supplies a purely resistive heating load at 110 V. The secondary current is 30 A and the primary current is 15A. When the load is disconnected, the secondary voltage rises to 120 V. Calculate: a) Power supplied from the ac mains b) % regulation c) Transformer efficiency d) Transformer losses e) State TWO reasons for the losses in d)

46 efficiency Answers a) Power supplied from the ac mains 240 x 15 = 3600W b) % regulation ( ) x = 8.3% c) Transformer efficiency (110 x 30) x = 91.6% d) Transformer losses 3600W 3300 W =300W e) State TWO reasons for the losses in d) losses in the winding and losses in the core Core losses are minimised by using a laminated core

47 Other solenoid applications. Relay switch to enable a small circuit to switch on a large circuit

48 Other solenoid applications. When the relay is switched on the core of the solenoid is magnetised by a DC current supply. This attracts the lever closing the switch and activating the large circuit. When the relay is switched off the current in the relay coil stops flowing. This sudden change in current could induce a back emf in the circuit This can be prevented by putting a diode in the circuit

49 Square waves

50 Square waves

51 Square wave Duty cycle the percentage of time that the signal spends in an active state as a fraction of the total time under consideration 0 20% duty cycle 20% duty cycle 50% duty cycle 90% duty cycle

52 rms (Root Mean squared) Rms for a sign wave = peak 2 rms for a square wave = peak

53 Time constant Time taken for 63% of charge to take place

54 The time constant of a series RL circuit equal to the value of inductance divided by the resistance: T = L / R The time constant of a series RL circuit equal to the value of inductance divided by the resistance: T = L / R The time constant of a series RC circuit equal to the value of capacitance multiplied by the resistance T = CR

55 Wave period Time period for one wave is 1 frequency 50 Hz = 0.02 seconds

56 The Differentiator: The differentiator circuit performs the mathematical operation of differentiation. That is the output waveform is the derivative of the input waveform. V R C out F 1 dv dt in

57 The Integrator: A circuit in which the output voltage waveform is the integration of the input is called integrator

58 Differentiation & integration of sine waves The sine / cosine functions differentiate using standard sets of rules: d/dt(sin t) = cos t The differentiation of a sine wave is a cosine wave The integration of a sine wave is a cosine wave

59 Differentiation sine to cosine wave

60 Integration sine to cosine wave