Electric machine

 Three phase induction  motor

NTRODUCTION

Three-Phase
Synchronous Machines
Synchronous machines are called "synchronous" as their speed is directly related to the line
frequency.

 

          ns = 120 f/p
                                 revlm s p

where ns is the synchronous speed in rpm, 

p the number of magnetic poles designed into each
machine and

 f is the frequency in Hz of the supply voltage. Thus when two or more synchronous
machines are connected to the same supply line, they will all run in synchronism because they
are all operating at the same supply frequency. Of course, if one machine has 2 poles (Turboalternators)
and another has 12 poles, the 12-pole machine will run at precisely �th the speed of
the 2-pole machine.

 CONSTRUCTION

Rotating machines have an outside (stationary) part called the stator. The inner (rotating) part is
called the rotor. The rotor is centred within the stator so that the rotor axis is concentric with
that of the stator. The space between the outside of the rotor and inside of the stator is called the
air gap.
The rotor is mounted on a stiff rod (usually steel) called a shaft. The shaft is supported in
bearings so that the rotor is free to rotate. The shaft extends through one or both of the bearings
to provide a means to connect the machine to the mechanical system. It is to be noted that the
rotor is solidly fastened to the shaft so that the rotor and the shaft rotate at the same speed.
Therefore, the terms 'rotor speed', 'shaft speed' or machine speed all mean the same thing and are
used interchangeably.
The rotor and stator each have three basic parts, the core, the windings and the insulation.
Thus, it is proper to speak of "the rotor core", 'the stator windings' 'the rotor insulation' and so on.
The purpose of the rotor and stator cores is to conduct the magnetic field through the coils of the
windings. The cores are almost always made of iron or steel.
The stator winding is known as armature winding as it carries the load current whereas
the rotor winding is known as field winding as this winding provides exciting current or magnetiscurrent. Since the armature winding carries load current, it has to handle all of the power being

converted or transformed by the device, however, the magnetising power requirement is relatively
small. The steady state power input to a field winding is only about 1/2 to 2 per cent of the rated 
power of the machine. The input power to de field winding is all consumed as I2R loss except
during transient period which lasts for almost a second or two during which energy is being
stored in magnetic field.
The winding conductors are either of copper or aluminium and that could be in the form of
coils of wire or heavy bars depending upon the current carrying capacity required. Also each
winding consists of several coils or bars in series or in series-parallel combination depending upon
the voltage and current requirements of the machine. The ends of certain of the windings are
brought out to terminals to allow easy connection to the electrical system.
In some machines, the windings of either the rotor or the stator may be placed around
projecting magnetic pole pieces, called salient poles (salient means prominent). When a core has
salient poles the coils of the winding are wound around the waists of the pole pieces. These
narrower parts of the salient poles are called the pole cores. The shaped ends of the poles are called
the pole shoes. Their purpose is to provide the correct flux density distribution in the air gap.
Salient poles are used on the stator cores of de machines and on the rotor cores of many synchronous
machines and in both cases they carry de field windings. The mechanical weakness and air
resistance of salient poles prohibit their use on rotors oflarge high speed synchronous generator
designed to he driven hy steam or gas turbines. Turhoalternators as these are usually called
always have cylindrical rotors with the field windings embedded in slots cut into the rotor surface.
A machine having both its rotor and stator windings in slots is known as round rotor machine or
non-salient pole machine.
The insulation system consists of (i) the conductor or wire insulation e.g. superenamelled
wires or conductors ; (ii) the coil insulation usually some kind of tape or several layers of tapes
depending upon operating voltage ; and (iii) the slot lines when the windings consist of coils that
are located in slots, the coils are held in place in the slots by slot wedges. The insulation system
thus prevents short circuits between turns of a given winding coil and insulate the winding from
the iron core which is always grounded for safety's sake. The insulation system must protect the
machine against damage due to overvoltages and overcurrents that may occur during the operation
of the machine. 

Microprocessor and Microcontrollers

INSTRUCTION SET AND EXECUTION IN 8085

Based on the design of the ALU and decoding unit, the microprocessor manufacturer 

provides instruction set for every microprocessor. The instruction set consists of both 

machine code and mnemonics.

An instruction is a binary pattern designed inside a microprocessor to perform a specific 

function. The entire group of instructions that a microprocessor supports is called 

instruction set. Microprocessor instructions can be classified based on the parameters such 

functionality, length and operand addressing.

Classification based on functionality:

I. Data transfer operations:   This group of   instructions copies data from source to destination. The content of the source  is  not altered.

II. Arithmetic operations: Instructions       of    this group perform operations         like    addition,                                             subtraction,increment &                           decrement.    One    of the data used       in arithmetic     operation is 

     stored in accumulator and the                result   is  also stored in                              accumulator.

III. Logical operations: Logical operation include AND, OR, EXOR, NOT. The  operations like AND, OR and EXOR use   two operands, one is stored in 

  accumulator and other can be any         register or memory location. The result       is stored in accumulator. NOT  operation    requires single operand,  which is stored in           accumulator.

  IV. Branching operations: Instructions in   this group can be used to transfer        program sequence from one memory         location to another either conditionally      or unconditionally.

V. Machine control operations: Instruction       in this group control execution of other  instructions and control operations   like   interrupt, halt etc.

       Classification based on length:

I. One-byte instructions: Instruction          having   one byte in machine code           Examples are depicted in table

Opcode ~Operand ~Machinecode/He                                              x code                      MOV      ~    A, B            ~   78

     ADD             ~      M           ~        8 6

2.Two-byte instructions: Instruction having two byte in machine code. Examples are 

depicted in Table 

3. Three-byte instructions: Instruction having three byte in machine code. Examples are depicted in Table 

Addressing Modes in Instructions:

   The process of specifying the data to     be operated on by the instruction is       called addressing.The various                 formats for specifying operands are       called addressing modes. The 8085         has the following five types of                 addressing:

I. Immediate addressing

II. Memory direct addressing

III. Register direct addressing

IV. Indirect addressing

V. Implicit addressing

1.Immediate Addressing:

In this mode, the operand given in the instruction - a byte or word – transfers to the destination register or memory location.

Ex: MVI A, 9AH

 The operand is a part of the                      instruction.

 The operand is stored in the register      mentioned in the instruction.

 2.   Memory Direct Addressing:

    Memory direct addressing moves a        byte or word between a memory            location and register. 

    The memory location address is              given in the instruction.

Ex: LDA 850FH

       This instruction is used to load the         content of memory address 850FH         in the accumulator.

3.Register Direct Addressing:

Register direct addressing transfer a copy of a byte or word from source register to destination register.

Ex: MOV B, C

        It copies the content of register C            to register B.

4.Indirect Addressing:

       Indirect addressing transfers a             byte or word between a register             and     a memory location.

Ex: MOV A, M

     Here the data is in the memory              location pointed to by the contents of HL pair. The data is 

       moved to the accumulator.

5.Implicit Addressing.

In this addressing mode the data itself specifies the data to be operated upon. 

Ex: CMA

      The instruction complements the            content of the accumulator. No                specific data or operand is 

      mentioned in the instruction

Microprocessor and Microcontroller

 INTRODUCTION TO MICROPROCESSOR AND MICROCOMPUTER ARCHITECTURE

    A microprocessor is a programmable            electronics chip that has computing and       decision   making capabilities similar to      centra   processing unit of a    computer     Any microprocessor   based systems             having limited number of    resources           are   called microcomputers.   Nowadays,     microprocessor can be seen in almost           all types of electronics devices like                   mobile phones,    printers, washing              machines etc.   Microprocessors are also     used in    advanced applications like             radars, satellites and flights. Due to the        rapid advancements in electronic                   industry and large scale integration of           devices results in a significant cost                 reduction and increase application of            microprocessors and their derivatives.

 Bit: A bit is a single binary digit.

 Word: A word refers to the basic data         size or bit size that can be processed by        the arithmetic and logic unit of the                processor. A 16-bit binary number is              called a word in a 16-bit processor.

 Bus: A bus is a group of wires/lines that          carry similar information.

 System Bus: The system bus is a group of wires/lines used for communication 

between the microprocessor and peripherals.

 Memory Word: The number of bits that can be stored in a register or memory element is called a memory word.

 Address Bus: It carries the address,              which is a unique binary pattern used           to   identify a memory location or an             I/O     port. For example, an eight bit              address bus      has eight lines and thus         it can address 28= 256 different                    locations. The locations in hexadecimal         format can be written as 00H – FFH.

 Data Bus: The data bus is used to                    transfer data between memory and                 processor or between I/O device and              processor. For example, an 8-bit                   processor will generally have an 8-bit           data bus and a 16-bit processor will                have 16-bit data bus.

 Control Bus: The control bus carry                control signals, which consists of signals       for selection of memory or I/O device           from the given address, direction of            data transfer and synchronization of             data transfer in case of slow devices.

Power Electronic

 Thyristors – Silicon Controlled Rectifiers (SCR’s)

A silicon controlled rectifier or semiconductor-controlled rectifier is a four-layer solidstate current-

controlling device. The name "silicon controlled rectifier" is General Electric's trade name for a type of thyristor

SCRs are mainly used in electronic devices that require control of high voltage and power. This makes 

them applicable in medium and high AC power operations such as motor control function.

An SCR conducts when a gate pulse is applied to it, just like a diode. It has four layers of 

semiconductors that form two structures namely; NPNP or PNPN. In addition, it has three junctions 

labeled as J1, J2 and J3 and three terminals(anode, cathode and a gate). An SCR is diagramatically 

represented as shown below.

The anode connects to the P-type, cathode to the N-type and the gate to the P-type as shown below.

In an SCR, the intrinsic semiconductor is silicon to which the required dopants are infused. However, 

doping a PNPN junction is dependent on the SCR application

Modes of Operation in SCR

 OFF state (forward blocking mode) −                 Here the anode is assigned a positive          voltage, the gate is 

       Nnassigned a zero voltage                              (disconnected) and the cathode is              assigned   a negative voltage. As a 

  result, Junctions J1 and J3 are in forward      bias while J2 is in reverse bias. J2                  reaches its 

     breakdown avalanche value and starts       to conduct. Below this value, the         resistance of J1 is 

    significantly high and is thus said to be        in the off state.

 ON state (conducting mode) − An SCR is        brought to this state either by increasing       the potential 

       difference between the anode and                   cathode above the avalanche voltage          or by applying a positive 

     signal at the gate. Immediately the SCR          starts to conduct, gate voltage is no                longer needed to 

maintain the ON state and is, therefore, switched off by −

      Decreasing the current flow through            it     to the lowest value called holding         current

       Using a transistor placed across the            junction.

 Reverse blocking − This compensates the        drop in forward voltage. This is due to           the fact that a 

      low doped region in P1 is needed. It is          important to note that the voltage                 ratings of forward and 

     reverse blocking are equal.

Power Electronics

  Introduction to power electronics:

            Power Electronics is a field which combines Power (electric power), Electronics and Control systems. 
Power engineering deals with the static and rotating power equipment for the generation, transmission 
and distribution of electric power. Electronics deals with the study of solid state semiconductor power 
devices and circuits for Power conversion to meet the desired control objectives (to control the output 
voltage and output power). Power electronics may be defined as the subject of applications of solid state 
power semiconductor devices (Thyristors) for the control and conversion of electric power. Power 
electronics deals with the study and design of Thyristorised power controllers for variety of application 
like Heat control, Light/Illumination control and Motor control - AC/DC motor drives used in industries, 
High voltage power supplies, Vehicle propulsion systems, High voltage direct current (HVDC) 
transmission. 
Power Electronics refers to the process of controlling the flow of current and voltage and converting it to 
a form that is suitable for user loads. The most desirable power electronic system is one whose efficiency    and reliability is 100%.
                   

     Power electronic applications 

  1.  Commercial applications  Heating                 Systems Ventilating, Air Conditioners,           Central Refrigeration, 

      Lighting, Computers and Office                     equipments, Uninterruptible Power              Supplies (UPS), Elevators, and 

        Emergency Lamps 

2.Domestic applications .Cooking                        Equipments, Lighting, Heating, Air                Conditioners, Refrigerators & 

    Freezers, Personal Computers,                       Entertainment Equipments, UPS

  3. Industrial applications .Pumps,                        compressors, blowers and fans                      Machine  tools, arc furnaces,                           induction 

        furnaces, lighting control circuits,                   industrial lasers, induction heating,               welding equipments 

  4. Aerospace applications .Space shuttle           power supply systems, satellite power          systems, aircraft power 

          systems. 

     5. Telecommunications Battery                          chargers,         power supplies (DC and          UPS), mobile         cell phone battery 

       chargers 

6. Transportation  .Traction control of               electric vehicles, battery chargers for           electric vehicles, electric 

      locomotives, street cars, trolley buses,          automobile electronics including                    engine controls 

7.Utility systems . High voltage DC                      transmission (HVDC), static VAR                    compensation (SVC), Alternative 

      energy sources (wind, photovoltaic),           fuel cells, energy storage systems,                induced draft fans and boiler feed 

     water pumps 

    Types of power electronic                                converters 

1. Rectifiers (AC to DC converters): These converters convert constant ac voltage to variable dc 

output voltage.

2. Choppers (DC to DC converters): Dc chopper converts fixed dc voltage to a controllable dc 

output voltage.

3. Inverters (DC to AC converters): An inverter converts fixed dc voltage to a variable ac output 

voltage.

4. AC voltage controllers: These converters converts fixed ac voltage to a variable ac output voltage 

at same frequency.

5. Cycloconverters: These circuits convert input power at one frequency to output power at a 

different frequency through one stage conversion.              

Electrical engineering

Mcq Electrical  engineering 

1. The insulating material suitable for   low temperature applications is

     (a) cork. 

     (b) diatomaceous earth.

      (c) asbestos paper

      (d) 75 percent magnesia,

2. The quantity of heat absorbed from          the heater by convection dopends              upon

   (A) the temperature of heating element        above the surroundings

   (b) the surface area of the heater.

   (c) the position of the heater

   (d) all of the above

3.The material of the heating element          should be

    (a) such that it may withstand the                     required temperature without getting            oxidised.

    (b) of low resistivity. 

    (c) of low melting point

    (d) of high temperature coefficient, 

4. The material to be used for heating           element should be of high resistivity         so as to

(a) increase the life of the heating element.   (b) reduce the length of the heating                     element.

 (c) reduce the effect of oxidation

 (d) produce large amount of heat.

5. The material to be used for heating              element should be of low                               temperature  coefficient so as to

  (a) void initial rush of current.

 (b) avoid change in kW rating with                    temperature

 (c) reduce the effect of oxidation

 (d) both (a) and (b) above.

6.Which of the following heating                   element will have the least                       temperature  range ?

 (a) Eureka

 (b) Silicon carbon

(c) Nichrome. (d: Kanthal. 

Utilization of Electrical energy

ELECTRICAL ENGINEERING 

Some important mcq 

( UEE, illumination) 

1.Luminous flux is

   (a) the rate of energy radiation in the                form  of light waves. 

   (b) the part of light energy. radiated by              Sun  that is received on

   (c)measured in lux

2. Glare is caused due to

(a) excessive luminance

(b) excessive lighting contrast in the field of vision 

(c) either (a) or (b)

3. Unit of illumination is

(a) lumen

 (c) lux.

(b) lambert 

(d) steradians.

4. The illumination at a surface due to a      source of light placed at a distance d'       from the surface varies as 

   (a) 1/d²

   (b) l/d. 

   (c) d

   (d) d³

5.The illumination at various points             on    a horizontal surface illu-                        minated by     the same source                     varies as

 (a)   cos(θ)

 (b) cos(θ²)

 (c) cos(θ³)

 d) 1/cos(θ)

 6. Carbon arc lamps are commonly                  used  in

(a) cinema projectors.

 (b) domestic lighting

 (c) factory lighting

 (d) street lighting

7. For two filaments of same material         operating at the same tem perature,         the diameter and current through             filament are related by

       (a) diameter directly proportional to            current. 

   (b) diameter proportional to (current²)

   (c) diameter proportional to (current)⅔

   (d) none of these.

8.The melting point of tungsten is

(a) 3,400°C.

 (b) 2,800°C.

 (C) 2,600°C.

(d) 2,400C. 

9. The vacuum inside an incandescent              lamp is of the order of 

  (a) 10‐2 mm Hg.

 (b) 10‐⁴mmHg. 

  (c) 10‐⁷mm Hg.

(d) 10 ‐⁸mmHg.

1o. The rate of evaporation of Upon                  tungsten filament in a lamp                          depends  Upon  

  (a) exhaust tube diameter. 

  (b) glass shell diameter. 

   (e) vapour pressure inside. 

  (d) none of the above

11. Heat from the lamp filament is                 transmitted to the surrounding                   mainly through

 (a) circulation 

  (b) conduction

  (c) convection. 

   (d) radiation 

12. Which of the following material is            most commonly used for the                      filaments  in incandscent lamps ?

      (a) Tungsten 

      (b) Tantalum

     (c) Osmium 

     (d) Silver

13. A zero watt lamp consumes power of 

(a) zero watt.

 (b) 5-10 W.

(c) about 15 W. 

(d) about 25 W.

 14. The safe operating temperature of a        tungsten filament

(a) 1,000°C 

(b) 3,000°C. 

(c) 2,000°C: 

(d) 3,500°C

15. The output of a tungsten filament                 depends on 

     (a) size of the shell. 

      (b) size of the lamp

     (c) temperature of filament 

     (d) all of the above 

16. What percentage of the input energy         is radiated by filament lamps 

       (5) 60-70 per cent 

        (b) 40-50 per cent

       (c) 25 - 30 per cent.

        (d) 10-15 per cent.

 18. An electric bulb, when broken,                   produces bang It is on account of 

   (a) vacuum inside the bulb.

   (b) pressure inside is equal to that                      outside

   (c) pressure of air in the bulb 

     (d) none of the above. 

19. In an incandescent lamp, bird cage            filament is usually used in Vacuum            bulb so as to

    (a) increase the life span of the filament 

    (b) give uniform radiations

    (c) reduce the oxidation phenomenon 

    (d) reduce the convection loSSes.

20. Filament lamp at starting will take                 current

   (a) equal to its full running current 

   (b) more than its full running current

   (c) less than its full running current.

     (d) none of these 

21. Most affected parameter of a                      filament   lamp due to variation in            operating     voltage is 

    (a) life.

    (b) light output. 

    (c)luminous  efficiency 

   (d) wattage.

22. Which gas is sometimes used in                   filament lamps

(a) Nitrogen.

 (b) Argon

 (c) Curbon dioxide.

 (d) Krypton

23. Which of the following vapour/gas             will give yellow colour in a filamen             lamp ? 

     (a) Helium. 

    (b) Mercury. 

    (c) Magnesium. 

    (d) Sodium.

24. Magnesium vapour in a filament                  lamp    gives 

(a) green colour light.

 (by pink colour light 

(c) blue colour light. 

(d) white colour light.

25. The gas used in a gas-filled filament             lamp is

(a) helium

 (b) oxygen 

(c) nitrogen. 

(d) ozone. 

26. In filament lamps, coiled coil                         filaments are used in

(a) coloured lamps 

(b) gas-filled lamps:

(c) low wastage lamps. 

(d) higher wattage lamps. 

27. In electric discharge lamps, light is               produced by

 (a) magnetic effect of current.

 (b) heating effect of current. 

 (c) cathode ray emission

 (d) ionisation in a gas or vapour

 28. In electric discharge lamps for                     stabilization of are

(a) a choke is connected in series with the          supply

 (b) a variable resistance is connected in            series with the circuit 

(c) a condenser is connected across the            supply