electrical circuit and measurement systems

electrical circuit and measurement

1. UNIT - 1 ELECTRICAL CIRCUITS & MEASURMENTS

2. Syllabus Ohm’s Law – Kirchhoff’s Laws – Mesh and Nodal analysis– Introduction to AC circuits – Power and Power factor - Classification of instruments – Operating principles of moving coil, moving iron instruments and dynamometer type wattmeter - Induction type energy meter.

3. Difference between Electrical and Electronics The main difference between electrical and electronic circuits is that electrical circuits have no decisio n makin g (processing ) capability, whilst electronic circuits do. An electric circuit simply powers machines with electricity . ... Most modern appliances use a combination of electronic and electrical circuitry.

4. The devices which convert the current into other forms of energy or work such type of devices is known as the electrical devices. It uses the metal for conduction. The electrical devices mainly work on the high alternating current. The power consumption of the electrical devices is also very high. The electrical devices are more dangerous and less reliable because it causes the hazardous electrical shock. The size of the electrical devices is very large, and hence it requires more space. Example – The fan is the electrical devices which convert the electrical current in the form of rotational motions. The electric bulb, lamp, tube light, converts the current into light. The heater converts the current into heat, etc.

5. Key Differences Between Electrical and Electronics Devices The following are the key differences between the electrical and electronic devices. The electrical device changes the current into another form of energy like heat, light, etc. whereas the electronic device controls the movement of electrons for performing the operation. The electrical devices use copper and aluminium wires for the flow of electrical current whereas the electronics devices use the semiconductor material. The electrical devices mainly work on the alternating current whereas the electronics device works on the direct current. The electrical devices work on high voltages whereas the electronics devices work on low voltages. The power consumption of the electrical devices is more as compared to the electronics devices.

6. The conductivity of the electrical devices is high whereas it is low for electronics devices. The electrical devices do not manipulate the data whereas the electronic devices manipulate the data. The electrical device directly works on the current due to which it gives the quick response.The electrons are the only moving charge of the electronic device and hence their response time is less. The electrical device is heavy and larger in size and hence requires more space whereas the electronics components are very smaller and placed on the single chip or we can say it requires very less space. The electrical device is more dangerous as compared to the electronic device because in electric devices heavy short circuit occurs because of the fault which is very dangerous for life. The fan, transformer , motor, generators are the examples of the electrical device whereas the transistor, thyristor, microcontroller are the examples of the electronics device.

7. Resistance: Resistance is  a measure of the opposition to current flow in an electrical circuit . Resistance is measured in ohms, symbolized by the Greek letter omega (Ω). Conductors: Materials that offer very little resistance where electrons can move easily. Components of Electrical and Electronics Capacitor: Capacitance  is the ability of a component or circuit to collect and store energy in the form of an electrical charge. Capacitors are used to linearize the change in supply voltage Inductance Inductance is the tendency of an electrical conductor to oppose a change in the electric current flowing through it. The flow of electric current creates a magnetic field around the conductor. The field strength depends on the magnitude of the current, and follows any changes in current. Inductors are used to linearize the change in supply current

8. OHMS LAW

9. Definition Georg Oh m , i n full Georg Simo n Oh m , (bor n Marc h 16, 1789 , Erlange n , Bavari a [Germany]—die d Jul y 6 , 1854 , Munich) , German physicist who discmpovered the law, named after him, He proposed a law by relating voltage, current and resistance parameter in the electrical field I t state s that at a constant temperatur e th e current flo w throug h a conductor is directly proportional to the potential difference (voltage) betwee n th e tw o ends o f th e conductor and inversel y proportiona l to the resistance .

10. Simple Example for ohms law

11. Voltage, Current, Resistance Relation

12. Use of Ohm’s Law By knowing this concept we can give required electrical ratings to the components to utilize the components effectively and efficiently The main applications of Ohm's law are: To determine the voltage, resistance or current of an electric circuit. Ohm's law is used to choose the required current and voltage for any application to run safely.

13. We saw in the Resistors tutorial that a single equivalent resistance, ( R T ) can be found when two or more resistors are connected together in either series, parallel or combinations of both, and that these circuits obey Ohm’s Law. However, sometimes in complex circuits such as bridge or T networks, we can not simply use Ohm’s Law alone to find the voltages or currents circulating within the circuit. For these types of calculations we need certain rules which allow us to obtain the circuit equations and for this we can use Kirchhoffs Circuit Law . These two rules are commonly known as: Kirchhoffs Circuit Laws with one of Kirchhoffs laws dealing with the current flowing around a closed circuit, Kirchhoffs Current Law, (KCL) while the other law deals with the voltage sources present in a closed circuit, Kirchhoffs Voltage Law, (KVL) .

14. KCL Kirchhoffs Current Law or KCL, states that the “ total current or charge entering a junction or node is exactly equal to the charge leaving the junction or node Or In other words the algebraic sum of ALL the currents entering and leaving a node must be equal to zero,

15. KVL Kirchhoffs Voltage Law or KVL, states that “ in any closed loop network, the total voltage around the loop is equal to the sum of all the voltage drops within the same loop ” which is also equal to zero. In other words the algebraic sum of all voltages within the loop must be equal to zero. This idea by Kirchhoff is known as the Conservation of Energy . Or In any closed loop of an electric network sum of the voltage drop is equal to sum of voltage

16. Introduction to AC circuits An electrical circuit is a complete conductive path through which electrons flow from the source to the load and back to the source. The direction and magnitude of the electrons flow however depend on the kind of source. In Electrical Engineering, there are basically two types of voltage or current (Electrical Energy) source which defines the kind of circuit and they are; Alternating Current (or voltage) and Direct Current. For the next couple of posts, we will be focusing on the Alternating current, and move through topics ranging from what is Alternating current to AC wave forms and so on.

17. AC Circuits AC circuits as the name (Alternating Current) implies are simply circuits powered by an Alternating Source, either voltage or current. An  Alternating Current or Voltage , is one in which the value of either the voltage or the current varies about a particular mean value and reverses direction periodically.

18. Basic AC Source (Single Coil AC Generator) The principle around AC generation is simple. If a magnetic field or magnet is rotated along a stationary set of coils (wires) or the rotation of a coil around a stationary magnetic field, an Alternating current is generated using an AC generator(Alternator). The simplest form of AC generator consists of a loop of wire that is mechanically rotated about an axis while positioned between the north and south poles of a magnet. As the armature coil rotates within the magnetic field created by the north and south pole magnets, the magnetic flux through the coil changes, and charges are thus forced through the wire, giving rise to an effective voltage or induced voltage. The magnetic flux through the loop is as a result of the angle of the loop relative to the direction of the magnetic field. Consider the images below;

19. Wave form produced at different position of armature

20. Power Electric power  is the rate, per unit time, at which  electrical energy  is transferred by an  electric circuit . The  SI  unit of  power  is the  watt , one  joule  per  second . Electric power is usually produced by  electric generators , but can also be supplied by sources such as  electric batteries . It is usually supplied to businesses and homes (as domestic  mains electricity ) by the  electric power industry  through an  electric power grid . Electric power can be delivered over long distances by  transmission lines  and used for applications such as  motion ,  light  or  heat  with high  efficiency

21. Power Factor Power factor can be calculated for AC signals only Power factor (PF) is the ratio of working power, measured in kilowatts (kW), to apparent power, measured in kilovolt amperes (kVA).  Working Power or True power or Active power or Real power: The  power which is actually consumed or utilised in an AC Circuit  is called true power Formula : VICosѲ where, Ѳ – Phase difference between Voltage and Current Apparent Power: The total power flowing in the circuit is known as the “apparent power” Formula : VI Formula: Power factor = Power factor = Power factor = Practical best power factor is between 0.8 and 0.9 If the power factor goes below this that instruments performs poor behaviour, either the instrument need to serviced or replaced to avoid more than the rated power consumption which makes the user economically in difficult situation  

22. Classification of Measuring Instruments

23. The instrument used for measuring the physical and electrical quantities is known as the measuring instrument.  The term measurement means the comparison between the two quantities of the same unit. The magnitude of one of the quantity is unknown, and it is compared with the predefined value. The result of the comparison obtained regarding numerical value.

24. The measuring instrument categorized into three types: Electrical Instrument Electronic Instrument Mechanical Instrument

25. The mechanical instrument uses for measuring the physical quantities . This instrument is suitable for measuring the static and stable condition because the instrument is unable to give the response to the dynamic condition.  The electronic instrument has quick response time . The instrument provides the quick response as compared to the electrical and mechanical instrument.

26. Electrical Instruments: The electrical instrument is used for measuring electrical quantities likes current, voltage, power, etc. The  ammeter ,  voltmeter , wattmeter are the examples of the electrical measuring instrument. The ammeter measures the current in amps; voltmeter measures voltage and Wattmeter are used for measuring the power. The classification of the electric instruments depends on the methods of representing the output reading.

27. Absolute Instrument The absolute instrument gives the value of measures quantities regarding the physical constant. The physical constant means the angle of deflection, degree and meter constant. The mathematical calculation requires for knowing the value of a physical constant. The tangent galvanometer is the examples of the absolute instruments. In tangent galvanometer, the magnitude of current passes through the coil determines by the tangent of the angle of deflection of their coil, the horizontal component of the earth magnetic field, radius and the number of turns of wire used. The most common applications of this type of instrument are found in laboratories.

28. Secondary Instrument In the secondary instrument, the deflection shows the magnitude of the measurable quantities .   The calibration of the instruments with the standard instrument is essential for the measurement. The output of this type of device is directly obtained, and no mathematical calculation requires for knowing their value. Digital Instrument The digital instrument gives the output in the numeric form .  The instrument is more accurate as compared to the analogue instrument because no human error occurs in the reading. Analog instrument The instrument whose output varies continuously is known as the analogue instrument. The analogue instrument has the pointer which shows the magnitude of the measurable quantities. The analogue device classifies into two types.

29. Analog instruments classification Null Type Instrument In this instrument, the zero or null deflection indicates the magnitude of the measured quantity. The instrument has high accuracy and sensitivity. In null deflection instrument, the one known and one unknown quantity use. When the value of the known and the unknown measuring quantities are equal, the pointer shows the zero or null deflection. The null deflection instrument is used in the potentiometer and in galvanometer for obtaining the null point.

30. The deflection type instrument is further sub-classified into three types. Indicating Instrument  – The instrument which indicates the magnitude of the measured quantity is known as the indicating instrument .  The indicating instrument has the dial which moves on the graduated dial. The voltmeter, ammeter,  power factor meter  are the examples of the indicating instrument. Integrating Instrument  – The instrument which measures the total energy supplied at a particular interval of time is known as the integrating instrument. The total energy measured by the instrument is the product of the time and the measures electrical quantities. The  energy meter , watt-hour meter and the energy meter are the examples of  integrating instrument. Recording Instrument  – The instrument records the circuit condition at a particular interval of time is known as the recording instrument .  The moving system of the recording instrument carries a pen which lightly touches on the paper sheet. The movement of the coil is traced on the paper sheet. The curve drawn on the paper shows the variation in the measurement of the electrical quantities.

31. Moving Iron Instruments Moving iron Instrument  or  Moving iron meter  is used to measure the  current and voltage  of AC and DC. They are non-directional. The working principle depends upon the movement of iron attracted by the  magnetic field  towards it and for repulsive type repulsion between them. The magnetic field is produced by the current in the coil. This instrument can be used as an ammeter, voltmeter, and wattmeter. The coil has less number of turns if the instrument is ammeter and more turns if the instrument is a voltmeter. The moving iron type supports both AC and DC. To use this instrument as ammeter, connect the circuit in series and the coil must have fewer turns of thick wire which shows less resistance. To use it as a voltmeter, connect the circuit in parallel and the coil has a high impedance and a large number of turns.

32. Attraction Type Attraction type  moving iron meter consists of a moving system which has soft iron. The current is passed through a coil placed near it. The moving iron is attracted to the coil which produces a magnetic field when a current flow through the coil. It consists of a fixed coil wounded by a copper wire. Soft iron is free to move on the spindle and a pointer is also attached to the spindle.

33. Attraction type MI instrument

34. How Attraction type Iron Meter Works? When the current flows through the coil, the moving iron attracted to the coil which causes the pointer to move. The pointer will come to zero position where deflecting torque is equal to the controlling torque. When the current in the coil is changed, the direction of the magnetic field also changed and the moving iron will get magnetize in such a way that it is pulled inwards. Hence these types of instruments can be used for both AC and DC currents. Here the air friction damping is provided by the air chamber because the magnets can affect the deflection of the pointer and the readings can be changed. Controlling torque is provided by the spring.

35. The  repulsion type  moving iron instrument consists of soft iron in the form of the vane as the moving element of the meter. It also has a fixed iron vane. A shaft is attached to the moving iron. A cylindrical stationary coil is used to produce the magnetic field when there is a flow of current through it. A pointer is fixed on the shaft which gets deflected shows the reading on a non-uniform scale. The strength of the magnetic field increases or decreases with the magnitude of the current flows through it. The moving iron and fixed iron magnetize with the same polarity due to which the two irons repel each other (when the same type of magnetic materials is placed in a magnetic field they will get magnetized uniformly and they repel each other). Because of their repulsive force, the coil starts moving away from the fixed iron. How Attraction type Iron Meter Works?

36. Cont … The controlling torque is exerted by the spiral spring made of phosphor bronze which is connected to the shaft. An air chamber is provided for air friction damping because the magnets can affect the deflection of the pointer and affect the reading. The deflection torque makes the pointer to move away from the zero position.

37. Deflecting torque: This torque is produced due to the electromagnetic field Td = NBIA Controlling Torque: This torque is produced due to spring set up connected to the pointer Td = Tc NBIA = k c θ θ = NBIA / k c θ = KI Where K = NBA/k c

38. Torque – Weight Ratio Torque is a force that makes an object move and weight is a force applied on the object by gravity. If a pointer in the meter has less weight, it will have a high torque-weight ratio. Even for a small deflection in the meter, the pointer will start moving and it shows measured value.

39. advantages and disadvantages of moving iron instruments . Advantages: This type of instrument is simple and cheap in construction. It is non-directional hence can be used in both AC and DC circuits. Because of the current-carrying part is stationary and has lighter moving parts, the torque weight ratio is high. Due to the high torque weight ratio, the frictional error is very less. Disadvantages: Accuracy is less because of the instrument is non-directional. It cannot be calibrated with a high degree of precision for DC on account of the effect of hysteresis in the iron vanes. High power consumption.

40. Applications This meter is used to measure both AC and DC The moving iron instrument can be used as an ammeter, voltmeter and wattmeter. Whereas the moving coil instrument is used as a voltmeter, ammeter, galvanometer.

41. Moving Iron instrument concept diagram

42. Important torques for proper functioning If the pointer needs to show the stable value means then there should be a balance between controlling torque and deflecting torque Td = Tc In order to ensure proper operation of indicating instruments, the following three torques are required Deflecting Torque Controlling Torque Damping Torque Controlling Torque Spring control Gravity control Damping Torque Air friction damping Fluid friction Damping Eddy current damping

43. Permanent Magnet Moving Coil Instrument (PMMC) What is PMMC? A Permanent Magnet Moving Coil ( PMMC ) meter – also known as a D’Arsonval meter or galvanometer – is an instrument that allows you to measure the current through a coil by observing the coil’s angular deflection in a uniform magnetic field .

44. PMMC Instrument:

45. Principle A PMMC meter places a coil of wire (i.e. a conductor) in between two permanent magnets in order to create stationary magnetic field. According to Faraday’s Laws of electromagnetic induction , a current carrying conductor placed in a magnetic field will experience a force in the direction determined by Fleming’s left hand rule . The magnitude (strength) of this force will be proportional to the amount of current through the wire. A pointer is attached to the end of the wire and it is put along a scale.

46. Advantages:- High sensitivity Accurate and reliable Uniform scale Low power consumption Simple and effective damping mechanism Disadvantages :-  Somewhat costlier as compared to moving-iron instruments. Cannot be used for A.C. measurements. Friction and temperature might introduce errors as in case of other instruments. Some errors are set in due to the ageing of control springs and the permanent magnets.

47. Application Moving Coil Meter is a widely used  measuring instrument  because of its accuracy and sensitivity. These instruments are directional and they can be used for DC measurements. This device can be used as an ammeter, voltmeter, galvanometer, and ohmmeter.

48. Dynamometer type Wattmeter The instrument whose working depends on the reaction between the magnetic field of moving and fixed coils is known as the Electrodynamo -meter Wattmeter. It uses for measuring the power of both the AC and DC circuits. Dynamometer type wattmeter works on very simple principle and this principle can be stated as when any current carrying conductor is placed inside a magnetic field , it experiences a mechanical force and due to this mechanical force deflection of conductor takes place. It has Fixed and Moving coil. The fixed coil also called the Current coil and the moving coil named the Pressure coil. Dynamometer  develops deflected torque (Td) by the interaction  of magnetic fields. Dynamometer instrument can be used as Ammeter, Voltmeter, and Wattmeter.

49. Construction Construction of the Dynamometer wattmeter is similar to the PMMC instrument but the difference is in PMMC permanent magnet is used, but in dynamometer instrument instead of natural magnet electromagnet is replaced as a fixed coil or current coil of two equal halves which is used to measure current flow A moving coil called as pressure is placed in between the two halves of current coil which is used to measure voltage The interaction of this two magnetic fields leads to measure power of the electric circuit that is wattmeter

50. Working The Electrodynamometer Wattmeter has two types of coils; fixed and the moving coil. The fixed coil connects in series with the circuit whose power consumption use to be measured. The supply voltage applies to the moving coil. The resistor controls the current across the moving coil, and it is connected in series with it. The pointer is fixed on the moving coil which is placed between the fixed coils. The current and voltage of the fixed and moving coil generate the two magnetic fields. And the interaction of these two magnetic fields deflects the pointer of the instrument. The deflection of the pointer is directly proportional to the power flows through it.

51. Actual diagram

52. Application Electrodynamometer type instruments are used as  a.c voltmeters and ammeters both  in the range of power frequencies and lower part of the audio frequency range. They are used as watt-meters, varmeters and with some modification as power factor meters and frequency meters.

53. Induction type Energy meter An electrical measuring instrument used to measure the energy consumption of a load is called an Energy Meter. The measurement of electrical energy consumption by the various domestic and industrial loads is very important from the economic point of view. The electrical energy utility by the load is basically power consumed over a period of time. If the time interval is in hours, then the energy measurement is in Watt-hours. Most of the energy meters measures in the unit of Kilowatt-hours (kWh). Generally, energy meters are integrating meters that can record power utilized by the load for a particular interval of time. There are various types of energy meters among induction type energy meter are most popular can be used for ac measurements only.

54. Depending upon the supply available there are two types of induction type energy meters. Single Phase Induction Type Energy Meter Three Phase Induction Type Energy Meter

55. Construction of Single Phase Induction Type Energy Meter

56. Operation: The energy meter is connected in the given circuit to measure the electrical energy. The current coil carries the load current. It produces the in-phase with the line current The pressure coil carries current proportional to the supply voltage. The magnetic field due to pressure coil lags approximately 90 degree behind the supply voltage The magnetic field due to the current coil develops eddy currents in the aluminium disc which react with magnetic field due to the pressure coil. Thus a torque is developed in the disc then it rotates. The braking magnet produces the breaking torque on the disc. The spindle is geared to the recording mechanism. So that the electrical energy consumed in the circuit is directly given in kWh (kilo watt hour)

57. Parts of Energy meter The meter consists of four major parts namely, Driving system Moving system Braking system Registering system

58. Driving system The driving system consists of two ac electromagnets namely, shunt magnet and series magnet which is magnetized proportional to supply voltage and load current respectively. Hence, the winding of the shunt magnet center limb is called a pressure coil and the winding of the series magnet is called a current coil. The shunt magnet provides a low reluctance path through the small air gaps for the circulating fluxes (φ c1  and φ c2 ). So only a small amount of flux φ p  flows through the central limb to the disc which is one of the operating flux. The second operating flux  φ s  is produced by series magnet. The flux φ p  should be exactly in quadrature (i.e., 90° out of phase) with the supply voltage, but due to the resistance of the pressure coil and iron losses in magnetic circuit φ p  will never be in quadrature with voltage which misleads the operation. So, in order to bring φ p  exactly in quadrature with supply voltage, copper-shading bands or rings are provided on the central limb of the shunt magnet whose resistance is adjustable.

59. Moving System : This system consists of a lightweight aluminum disc that is mounted on a shaft and positioned in the air gap between the two magnets. The bottom of the shaft is pivoted into a jewel bearing and the top of the spindle provided with a simple sleeve pin-type bearing. The shaft also carries a pinion (gear) which connects the shaft to the registering mechanism.

60. Braking System : This system is required to control the speed of rotation of the disc and also to bring the disc to an idle state when the load is disconnected, which is done by a permanent magnet called a braking magnet. This magnet is so placed in order to bring the disc in between the poles of the magnet. Whenever the disc rotates, it cuts the field of the braking magnet and an emf is induced in it which makes eddy currents flow. This current set up a field in the disc, which opposes the main field and thereby reduces its magnitude. Hence, the braking torque (which opposes the rotation of the disc) is produced.

61. Registering System Registering system (a mechanism) is also known as the counting system (a mechanism). This system is engaged with the pinion, which is a gear mounted over the shaft of the disc. The mechanism consists of a train of gears. Since the number of rotations of the disc is proportional to the power consumption, the gear-turn ratio is selected so as to rotate the indicators on the panel to indicate the total energy consumed. The gear-turn ratio between the adjacent indicators will be 10:1 so that the energy consumed is integrated up to thousands of kWh.

62. working When the load is not connected, no flux is produced in the series magnet and only a shunt field is present. This alternating flux φ p  links with the disc and induces an emf E p  in the disc, due to this emf an eddy current I p  flows in the disc, which produces an alternating field φ p ' in the disc. But, no torque will be produced in the disc due to these two fluxes, because both the fluxes are 180° out of phase. When the load current I L  flows through the current coil, the series magnet is magnetized and an alternating flux flows through it, and this flux links with the disc, which also produces an emf E se  resulting in the flow of eddy current I se . I se  sets up a field  φ se ' in the disc which interacts with the field due to I p  and hence torque is produced in the disc due to this interaction of both the fields. The torque produced is proportional to the difference of the torques due to I p  and I se .

63. Energy Calculation True Energy = No of revolution/ Energy meter constant Actual Energy = Power*time/3600*1000 %error = (True Energy- Acutal Energy)/ True Energy*100

64. Advantage and Disadvantages: Advantages of Induction Type Energy Meter : They can be used over a long period of time with very little maintenance. It is an inexpensive energy meter and almost used universally for ac measurements. High torque to weight ratio. Can be used for the measurement of energy over a wide range of loads. Disadvantages of Induction Type Energy Meter : If there are no proper adjustments in the meter, large errors are introduced in readings. The principle of induction can be only in ac, hence these meters are limited to ac measurements only.