Fundamentals of Electricity & Electrical Equipment

Fundamentals of Electricity & Electrical Equipment : 

Fundamentals of Electricity & Electrical Equipment If You Know It You Can Handle It? E.T.Masih

Introduction : 

Introduction ELECTRICITY The invisible energy which constitutes the flow of electrons in a closed circuit to do work is called electricity It is a form of energy which can be converted to any other form very easily.

Modern Electron Theory : 

Modern Electron Theory Modern Electron theory says that every matter (solid, liquid or gaseous) consists of very small divisible particles called molecules. Molecules are further made of very minute particles called atoms. Atom further consists of the following parts – Nucleus This is the central part of the Atom which contains protons & neutrons. Proton has positive charge (1.692 X 10 –19 coulombs), where as neutron has no charge In the nucleus, the protons & neutrons are held together with tremendous forces of attraction. The protons and neutrons carry equal mass and this total mass constitute total mass of an atom.

Slide 4: 

Modern Electron Theory Extra-nucleus (Space) The outer part of the atom which contains only electrons is called extra-nucleus. An electron has a negative charge (1.692 X 10 –19 coulombs) equal to that of a proton. The mass of an electron is nearly 1/1840 time to that of a proton and thus neglected. Atomic weight = No of protons plus No. of neutrons in the nucleus Electrons are not stationary particles, they move around the nucleus in different paths or orbits. The shape of an orbit is more elliptical than round but in drawing it is shown circular. The number of electrons is same as that of protons in an atom, thus an atom on the whole is NEUTRAL. Atomic Number = No. of protons Or No. of electrons in an atom

Slide 5: 

Modern Electron Theory To understand the electrical behavior of a matter, its simple atomic structure required to be drawn. For drawing simple atomic structure of an atom, the number of electrons in any orbit is determined by the following rules. The number of electrons in any orbit is given by relation 2n2 , where n is the number of orbit counting from nucleus and going outward. Example: First orbit 2 x 12 = 2 electrons Second orbit 2 x 22 = 8 electrons Third orbit 2 x 32 = 18 electrons 2. The last orbit cannot have more than 8 electrons. The last but one orbit cannot have more than 18 electrons

Slide 6: 

Modern Electron Theory Simple atomic structure of Silver (Ag), Copper (Cu), & Aluminium (Al) are shown below Atomic structure of Silver - Atomic weight of silver = 108 Atomic number of silver = 47 No. of electrons = No. of protons = 47 No. of Neutrons = Atomic weight - Atomic number Atomic structure of Copper - Atomic weight of Copper = 64 Atomic number of Copper = 29 No. of electrons = No. of protons = 29

Simple Atomic Structure : 

Simple Atomic Structure Simple atomic structure of Copper (Cu), Silver (Ag), & Aluminium (Al) Copper (Cu) Silver (Ag)

Slide 8: 

Simple Atomic Structure Atomic weight of Aluminium = 27 Atomic number of Aluminium = 13 No. of electrons = No. of Protons = 13 Nature of Electricity Every matter is electrical in nature since it contains charged particle like Protons & Electrons – Ordinarily, a body is neutral as it contains same number of protons and electrons. If some of the electrons are removed from the atom, there occurs deficit of electrons and the body attains a positive charge. If some of the electrons are supplied to the body, there occurs excess of electrons and the body attains a negative charge.

Slide 9: 

Charged Body Ordinarily, every substance or body is electrically neutral, as all the atoms of the body contain equal number of electrons and protons. Deficit of electrons Excess of electrons However when some electrons are detached from the body, there occurs a deficit of electrons from its normal status and body attains positive charge, similarly when electrons are supplied to body it attains negative charge. So deficit or excess of electrons can cause Positive or Negative charge

Slide 10: 

Unit of Charge The negative charge on the electron is very small and it is not convenient to take it as the unit charge, so Coulomb is used as the Unit of charge. The practical unit of charge is Coulomb. 1 Coulomb = Charge on 628 x 1016 (6.28 x 1018) electrons. If a body is said to have a negative charge of one coulomb, it means that the body has an excess of 628 x 1016 electrons, these electrons are supplied to this body from outside. Free Electrons The valance electrons which are very loosely attached to the nucleus of an atom and can be easily detached are called Free Electrons.

Electrical Potential : 

Electrical Potential When a body is charged, either electrons are supplied to it or they are removed from it. In both the cases work is done. This work done is stored in the body in the form of Potential. Thus the body has the ability to work by exerting a force of attraction or repulsion on the other charged particles ‘Capacity of a charged body to do work is called Electrical Potential’ The measure of electric potential is the work done to charge a body to one coulomb. Electrical Potential = or V = W Q

Slide 12: 

Electrical Potential Unit of Potential: Work done is measured in in Joules & Charge is measured in Coulomb, so the Unit of potential is Jules/Coulomb or Volt If W = 1 joules and Q = 1 coulombs Then V = 1/1 = 1 volt Hence a body is said to have an electric potential of 1 volt if one joule of work is done to charge the body to one coulomb. Potential Difference: The difference in the electric potential of the two charged bodies is called (PD) Potential Difference , the unit of potential difference is Volt.

Electric Current : 

Electric Current In metals or conducting materials, a large number of free electrons are available which move from one atom to the other at random. Flow of electrons Flow of Conventional current When an electrical potential difference is applied across the metallic wire, the loosely attached free electrons start moving towards the positive terminal of the Cell, this flow of electrons constitute the electric current.

Slide 14: 

Electric Current The magnitude of flow of current at any section of the conductor is the rate of flow of electrons (i.e) charge flowing per second. Mathematically stated; Current, I = Q/t Unit of Current: Since the Charge is measured in Coulombs and time in seconds, the unit of current is Coulomb/sec (C/s) or Amperes (A) If Q = 1 coulomb; t = 1 second; then I = 1 Ampere A wire is said to carry a current of One Ampere when Charge flows through it at the rate of one coulomb per second.

Conductor Resistance : 

Conductor Resistance When a potential difference is applied across a conductor, the free electrons start moving in a particular direction. While moving through the material these electron collide with other atom & molecules, this causes opposition to the flow of electrons (current) through it. This opposition is called Resistance. Heat is produced because of the collisions of moving electrons with the other atoms and molecules. Other atoms and molecules Free electrons

Slide 16: 

Conductor Resistance Resistance Unit: Resistance is measured in Ohms or Kilo-ohms & is denoted by symbol Ω or (K Ω). A wire is said to have a resistance of 1 ohm, if one ampere current is passing through it produces heat of 0.24 calories. Laws of Resistance: The resistance (R) of a wire depends upon the various factors - 1. It is directly proportional to its length, l i.e. R l 2. It is inversely proportional to its area of cross section, a i.e. R l/a 3. It depends upon the atomic structure of the material of which wire …is made. 4. It also depends upon the temperature of the wire.

Laws of Resistance : 

Laws of Resistance Analyzing further – R R = ρ Where ρ (Rho a greek letter) is a constant of proportionality called resistivity of the wire material. The value of Rho (ρ) depends upon the nature of wire material (atomic structure of the material). l .a l .a

Magnetism & Electromagnetism : 

Magnetism & Electromagnetism Magnetic Polarity: In a bar magnet the two ends exhibit the maximum magnetic effect and they are called the poles of the magnet, these poles are South Pole & North Pole. The poles of magnet cannot be separated & they have equal strength i.e. m Weber. Laws of Magnetic Force: First Law: Like poles repel each other unlike poles attract. Second Law: The magnitude between two poles is directly proportional to the product of their pole strength & inversely proportional to the square of distance between them.

Laws of Magnetic Force : 

Laws of Magnetic Force Mathematically: F m1m2 d2 Where m1 & m2 is the force between two magnetic poles placed in a medium at a distance of d meters. m1 m2 medium d F = K. m1m2 d2 Where K is a constant. Its value depends upon the surrounding medium and the system of units used.

Magnetic Field : 

Magnetic Field The magnetic lines of force stretch from one pole to the other, collectively the magnetic lines of force are referred to as magnetic flux or magnetic field. Magnetic Induction: The phenomenon by which a soft iron piece is magnetized when placed in the magnetic field is called magnetic induction. Magnetic Flux: The quantity (total number) of magnetic lines of force produced by a magnet is called magnetic flux. It is represented by Ф (Phi), it is measured in weber. 1 wb = 108 lines of force or maxwells

Electro-magnetic Induction : 

Electro-magnetic Induction Introduction Michael Faraday discovered that an e.m.f. is induced in the conductor when flux linking with it changes. This phenomenon was named electro-magnetic induction Faraday’s Laws of Electromagnetic Induction First Law: Whenever a conductor cuts the magnetic field an e.m.f. is induced in the conductor. Motion Field EMF

Slide 22: 

Electro-magnetic Induction Second Law: This law states that “The magnitude of induced e.m.f. in a coil is directly proportional to the rate of change of flux linkages.” Where N = No. of turns of the coil (Φ1 - Φ2) = Change of flux in wb t = Time in seconds for the change In differential form e = N Volt N (Φ1 - Φ2) t Rate of change of linkages = dΦ dt wb-turns/s

Induced EMF : 

Induced EMF INDUCED EMF: When flux linking with a conductor (coil) changes, an e.m.f. is induced in it. This change in flux linkages can be obtained in the following two ways : By moving the conductor and keeping the magnetic field stationary or by moving the magnetic field and keeping the conductor stationary, as in AC, DC generators. (It is called dynamically induced e.m.f.) By changing the flux linking with the coil without moving coil or field. The change of flux produced by the field linking with the coil is obtained by changing the current in the field as in Transformers. (It is called statically induced e.m.f.)

Slide 24: 

Induced EMF Dynamically Induced EMF: Considering a conductor of length l meters placed in the magnetic field of flux density B wb/m2 is moving right angle to the field at a velocity v meters/sec. Let the conductor move a small distance dx meters in time dt sec. v dx v vsinφ Mathematical Expression Consider a conductor of length l meters placed in the magnetic field of flux density B wb/m2 is moving at right angle to the field at velocity v meters/sec. Let conductor move a small distance dx meters in time dt seconds. dx l Area swept

Slide 25: 

Induced EMF Dynamically Induced EMF: Area swept by the conductor, A = l x dx Flux cut by the conductor, Φ = B x A = Bldx According to Faradays Laws of electro-magnetic induction: Induced e.m.f, e = Flux cut time = Φ dt = Bldx dt If the conductor is moved at an angle φ with the direction of magnetic field at a velocity v m/s & a small distance covered by the conductor in that direction is dx in time dt seconds, then the component of distance perpendicular to the magnetic field, which produces e.m.f. is dx sin φ. Area swept by conductor, A = l x dx sin φ Flux cut by the conductor, Φ = B x A = Bldx sin φ = Blv (dx/dt = v) e = Bldx sin φ … dt = B l v sin φ

Statically Induced EMF : 

Statically Induced EMF Self induced emf, e dI1 dt or e = L dI dt When the coil and magnetic field both are stationary but the magnetic field liking with coil changes (Current producing the flux is changing), the emf thus induced in the coil is called statically induced emf. The statically induced emf can be of two types – a) Self induced emf b) Mutually induced emf (L is proportionality constant . & is called inductance) Mutually induced emf, em dI dt or em = M dI1 dt (M is proportionality constant & is called mutual inductance or co-efficient of mutual inductance)

Working Principle of DC Motors : 

Working Principle of DC Motors The operation of DC Motor is based on the principle that when a current carrying conductor is placed in a magnetic field, a mechanical force is experienced by it. The direction of this force is determined by Fleming’s Left Hand rule, its magnitude is given by the following equation – F = B.I.l (Newton) MNE N S F (a) (b) (c) Magnetic field of the magnet. Magnetic field of the coil due to flowing current Resultant magnetic field of both ω

Types of DC Motors : 

Types of DC Motors The DC motors can be classified as follows - 1. Separately exited DC Motors: The motor field is separately exited . by supplying DC current to the motor field. Eb Ra Shunt Motor Eb Ra V V 2. Self exited DC Motors: These motors can be further classified as: Shunt Motor: Where speed between no load to full load has to be maintained almost constant. Machine Tools. Its Voltage equation: Eb = V – Ia Ra – 2vb Very accurate speed motor, These are best suited where speed variation is required from very low to high. (Rolling Mills, Paper M/C)

Slide 29: 

Types of DC Motors Series Motor: Where high torque is required at the time of starting to accelerate heavy loads. Electric Traction, Cranes, Compressors. Eb Ra Eb Ra Compound Motor: Where high torque is required at the time of starting, where the load may be thrown off suddenly, where the load is subjected to heavy fluctuation. Shearing m/c, Mines, Hoists V V

Induction Motors : 

Induction Motors Induction motors are also known as asynchronous machines, which means the machines that never run at synchronous speed. Induction motors can be single phase or three phase. The three phase motors are the most commonly used AC motors in the industry main reasons are - Simple and rugged construction Low cost High efficiency Reasonably good power factor Self starting torque Low maintenance More than 90% of the mechanical power used in industry is provided by three phase induction motors.

Slide 31: 

Induction Motors Construction: Three phase induction motor consists of two main parts namely Stator & Rotor. Stator: It is the stationary part of the motor. It has three main parts; a) Outer frame, b) Stator core, c) Stator winding Outer Frame: It is the outer body of the Motor. It supports the stator core. Stator Core: Stator core is to carry the alternating magnetic field, It is made of high grade silicon steel stampings. Stator Winding: Stator core carries a three-phase winding. Greater is the number of poles lower is the speed. Ns or 1 P Ns 120 f . P =

Slide 32: 

Induction Motors Rotor: It is the rotating part of the motor. There are two types of rotors, which are employed in 3 phase motors – i) Squirrel cage rotor ii) Phase wound rotor Squirrel Cage: Motors employing this type of rotor are known as Squirrel Cage motors Most of the motors are of this type because of simple & rugged construction Phase Wound Rotor: Phase wound rotor is also called slip ring rotor and the motors employing this type of rotor are called as phase wound or slip ring induction motors.

Slide 33: 

Induction Motors The rotor slots are usually not parallel to the shaft but are skewed. Skewing of rotor has the following advantages – It reduces humming thus ensuring quite running of motor. It results in a smoother torque curves for different positions . of motor. It reduces the magnetic locking of the stator & rotor. It increases the rotor resistance due to the increased . length of the rotor bar conductor In phase wound slip ring rotor consists of a laminated cylindrical core having semi-closed slots at the outer periphery & carries a 3 phase insulated winding.

Synchronous Machines : 

Synchronous Machines The machine which converts mechanical power into AC electrical power is called synchronous generator or alternator. However the same machine can be operated as motor and is called Synchronous Motor. A synchronous machine is an AC machine whose satisfactory operation depends upon the following relationship: Ns = 120f . P Or f = PNs 120 Where Ns is the synchronous speed in rpm; f is the supply frequency & P is the number of Poles. A synchronous machine always maintains this relationship. If a synchronous motor fails to maintain this average speed (Ns) the m/c will not develop sufficient torque to maintain its rotation & will stop. The motor is said to be pulled out of step.

Slide 35: 

Synchronous Machines In case, A synchronous machine is operating as a generator, it has to run at a fixed speed called synchronous speed to generate power at a particular frequency since all the appliances or machines are designed to operate at this frequency. In our country this frequency is 50 Hz. A synchronous machine is an electro-mechanical transducer which converts mechanical energy into electrical energy or vice-versa.

Slide 36: 

Basic Principles The fundamental Laws: The fundamental phenomena which make these conversions possible are - ω ω F F M M T T a) The law electromagnetic induction: EMF is produced in a conductor when . ever it cuts across the magnetic field, . . Faraday’s first law of electromagnetic b) The Law of Interaction: This relates to the Force or Torque, . Whenever a current carrying . conductor is placed in the magnetic . field, by the interaction of the magnetic field produced by the current carrying conductor . and the main field, force is exerted which produces Torque.

Slide 37: 

Relation Between Frequency, Speed & Number of Poles S S N N Cycle ω ROTOR Suppose a machine is having P number of Poles on the rotor revolving at a speed of Ns r.p.m. When a conductor passes through a pair of poles one cycle of e.m.f. is induced in it. No. of cycles made per Rev. = No. of Rev. made per second = P .2 Ns .60 No. of cycles per second = No.of cycles/Rev x No. of Rev/s f = P .2 Ns .60 x PNs .120 =

Transformers : 

Transformers Introduction: One of the main reasons of adopting AC system instead of DC system for generation, transmission & distribution of electric power is that alternating voltage can be increased or decreased conveniently by means of Transformer. In fact, for economical reasons, electrical power is required to be transmitted at high voltages whereas it has to be utilized at low voltage from safety point of view This is only possible by use of Transformers.

Slide 39: 

What Is A Transformer A transformer is a static device which transfers AC electrical power from one circuit to the other at the same frequency but at different voltages. When the voltage is raised on the out side (V2 > V1), the transformer is called step-up transformer, whereas, if the voltage is lowered on the outside (V1 > V2), the transformer is is called step-down transformer Input V1 V2 Output I1 I2 V2 > V1 (Step Up) . V2 < V1 (Step Down)

Working Principle of Transformer : 

Working Principle of Transformer The basic principle of transformer is electromagnetic induction. A simple form of transformer is shown in the figure, it essentially consists of two separate windings placed over L O A D ф V1 E1 the laminated silicon steel core. The windings to which AC supply is connected is called primary winding & the winding to which load is connected is called secondary winding. When AC supply voltage V1 causes alternating flux (ф) in the PW an emf in the SW is induced due to flux linkage.

Slide 41: 

Losses In Transformers The losses which occur in transformers are given below – Core or Iron loss: The alternating flux is set up in the core, therefore, hysteresis and Eddy current losses occur in the magnetic core. . Ph = Kh Vf Bm Hysteresis loss: When the magnetic material is subjected to reversal of flux, power is required for the continuous reversal of molecular magnets. This power is dissipated in the form of heat & is known as Hysteresis Loss. This loss can be minimized by using silicon steel material for the construction of core. 1.6

Slide 42: 

Losses In Transformers (b) Eddy Current Loss: Since the flux in a transformer core is . alternating , it links with the magnetic material of the core . and induces emf in the core which causes to circulate . Eddy currents. This power is dissipated in the form heat & . is known as Eddy Current Loss. Pe = Ke V f 2 t2 Bm This loss can be minimized by making the core with very thin laminations. The flux set up in the core of the transformer remains constant from no load to full load, therefore iron loss is independent of the load & is known as constant loss. (c) Copper loss: Copper loss occur in both the windings due . to their ohmic resistance 2

Electrical Motor Troubleshooting : 

Electrical Motor Troubleshooting Troubleshooting In The Field Unless prior experience dictates otherwise, always start at the beginning. Ask questions of the Operator of the faulty equipment: Was equipment running when problem occurred? Does the Operator know what caused the problem, and if so, what, in . their opinion, caused the problem? Is the equipment out of sequence? Check to ensure there is power . Turn on circuit breaker, ensure motor disconnect switch is on, and operate start button/switch

Slide 44: 

Troubleshooting In The Field Use voltmeter to check the following at incoming and load side of circuit breaker(s) and/or fuses, ensure that voltages are normal on all legs and read voltage to ground from each leg: Main power, usually 440 V AC between phases and 272 to . Ground. Control Power, 208/240 between phases and 220 to ground . and 220 V AC to neutral on a grounded system Low voltage control power, usually 24 to 30 V AC and/or . V DC between phases and possibly to ground, usually . negative is connected to ground.

Slide 45: 

Troubleshooting In The Field Check controlling sensors in area of problem, then make complete check of all sensors, limit switches and other switches to ensure they are in correct position, have power, are programmed, set, and are functioning correctly. If and when a problem is found, whether electrical or mechanical, the problem should be corrected and the faultfinding begun anew, a seemingly unrelated fault or defect could be the cause of the problem. When there is more than one fault, the troubleshooting is exponentially more difficult, do not assume that all problems are solved after completing one, always test the circuit and operation prior to returning the equipment to service.

Slide 46: 

Troubleshooting In The Field If available, check wiring diagrams and PLC programs to isolate problem. Variable Frequency Drive (VFD) can be reset by turning power off, wait till screen is blank and restore power; on some VFD's, press Stop/Reset - then press Start. Check that wiring is complete and that wires and connections are tight with no copper strands crossing from one terminal to another or to ground. Ensure that the neutral reading is good and that the neutral is complete and not open.

Motor Testing In Shop : 

Motor Testing In Shop Prior to connecting a motor: Move motor to electric shop motor test and repair station. Connect motor leads for 460 volt operation and wrap . connections with black electrical tape. Check motor windings with an ohmmeter, each reading . between phases should be within one or two ohms of each . other; A to B, B to C, A to C. Use megohmmeter to check insulation resistance to ground . of motor windings on 500 volt scale; minimum reading is . 1000 ohms of resistance per volt of incoming power that . motor will be connected to.

Slide 48: 

Motor Testing In Shop Connect motor to power test leads and safety ground after . checking that test lead power is shut off; secure motor to . table to prevent motor from jumping when started; turn . disconnect on; press start button; check "T" leads for . motor amperage; check for abnormal sounds and heat in . bearings or windings; clean motor shaft; shut down and . disconnect

Motor Testing In Field : 

Motor Testing In Field When a motor overload or circuit breaker trips and/or blows fuses, certain procedures and tests should be carried out: Lockout and tag out main circuit breaker; Test insulation resistance of motor wires and windings by . using megohmmeter between T1, T2, & T3 leads and . ground, then; Test "T" leads to motor with ohmmeter for continuity and . ohmage of windings between A to B, B to C, A to C; each . resistance should be within 1 or 2 ohms of each other; if the . ohms readings are significantly different, or, if there is no . continuity; go to the motor disconnect box, turn it off, . perform the continuity and resistance test on the "T" leads, . again; if the readings are good, the problem is in the wires . from the motor controller to the disconnect switch.

Slide 50: 

Motor Testing In Field Check the three wires by disconnecting all three wires from . switch and twist together; go to controller and check for . ground with megger, check for continuity between A to C, B . to C, A to C; one or more wires will be open or grounded; Correct solution is to pull all new wires in from controller to . motor disconnect switch, whatever caused the problem . may have damaged the other wires, also; replace all wires. If problem is on motor side of disconnect switch, open . motor connection box and disconnect motor; Check motor for resistance to ground with megohmmeter, if . reading is below 500,000 ohms, motor is grounded and . must be replaced;

Slide 51: 

Motor Testing In Field Test motor windings for ohms between phases with . ohmmeter A to B, B to C, A to C, readings should be within . 1 or 2 ohms of each other; if readings indicate open or a . significant ohmage difference, replace motor; If motor test readings are good, test the motor leads . between the disconnect switch and the motor connection . box for continuity and ground resistance, if readings are . not good, replace wires; If all readings are OK, reconnect motor, remove lockout, . and restore to service; the problem could have been . mechanical in nature; an overload on motor caused by the . chain, belt, bad bearings, faulty gearbox, or power glitch.

Motor Controller : 

Motor Controller Check motor Full Load Amps (FLA) at motor and check setting on . controller overload (OL) device; most newer OL devices are adjustable . between certain ranges, some older OL devices use heaters for a given . Amperage. If circuit disconnecting means in controller is a circuit breaker, it should . be sized correctly. If the disconnecting means is a Motor Circuit Protector (MCP), the MCP . must be correctly sized for the motor it is protecting and the MCP has a . trip setting unit which has to be correctly set based on the Full Load . Amperage of the motor; using a small screwdriver, push in on the screw . head of the device and move to a multiple of thirteen of the FLA; . example: a motor FLA of 10 amps would require that the MCP trip . device be set to an instantaneous trip point of 130 amps. Fuses protecting the motor should be the dual element or current . limiting type and based on the motor FLA.

Programmable Logic Controllers : 

Programmable Logic Controllers Check to ensure main power is on (220 VAC) Check 24V power available. Identify problem area. Check sensor operation in problem area. Check sensor Inputs to PLC. Check on PLC that a change in sensor state causes the . corresponding Input LED on the PLC to go on or off. Identify Output controlled by Input on PLC ladder diagram. Ensure that Output LED is cycling on/off with Input. Check that Output voltage is correct and cycling on/off with . Input.

Slide 54: 

Programmable Logic Controllers Locate Output device and ensure that voltage is reaching . device and cycling with Input Ensure that Output device is working correctly (solenoid . coil, relay coil, contactor coil, etc.) An Input or Output module can be defective in one area or . circuit and work correctly in all other circuits If each field circuit is not fuse protected, the modular . internal circuit becomes a fuse and can be destroyed by a . field short circuit or any other overcurrent condition Check modular circuit; if bad, module must be replaced . after correcting field fault Shut down PLC prior to changing any module -main power . and 24V power

Slide 55: 

Programmable Logic Controllers Locate fault in field circuit by disconnecting wires at . module and field device, check between wires for short . circuit and to ground for short circuit; replace wire if short . circuit found Check device for ground, short circuit, mechanical and . electrical operation, even when problem found in wires, . always also check device for another fault, problem in wires . can cause problem in device or vice versa; if device is . . found defective, replace device and then check total circuit . before placing in operation and after restoring circuit, . check again to ensure circuit and module are operating . correctly Check power supply module; if no output, shut down power . and replace supply module

Slide 56: 

Programmable Logic Controllers Back plane can go bad, some of the modules with power . and others with no power, replace backplane Sometimes, the PLC can be reset using the Reset , keyswitch; ensure that turning the PLC off won't interrupt . other running sub-set programs, turn keyswitch to far right, . after 15 seconds, turn to far left wait, then return to middle . position; this operation should reset program and enable a . restart The PLC program can have a latch relay with no reset . under certain conditions, the keyswitch reset may have no . affect on the latch, try turning the power to the PLC off and . back on, this operation may reset the latch and allow the . program to be restarted

Slide 57: 

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Slide 58: 

Programmable Logic Controllers The PLC is usually part of a control circuit supplied with 220VAC through a 460V/220V transformer as part of a system with motors, controllers, safety circuits, and other controls; occasionally, cycling the main 480V power off/on will be necessary to try to reset all the safety and control circuits Possession and use of an up-to-date ladder diagram, elementary wiring diagram, manufacturer's manuals & diagrams, troubleshooting skills, operator's knowledge, and time are all required to solve issues involved in maintaining a modern manufacturing production line

Extend Motor Life with Improved Bearing Care : 

Extend Motor Life with Improved Bearing Care Bearing failures are the root cause for the great majority of electric motor downtime, repair and replacement costs. Bearing and motor manufacturers are aware of the situation. Motor repair shops can attribute much of their business to bearing failures. And motor users see bearing failure as the fundamental cause of virtually every electric motor repair expense. Studies conducted by the Electrical Apparatus Service Association also demonstrate that bearing failures are by far the most common cause of motor failures.

Factors Affecting Bearing Life : 

Factors Affecting Bearing Life Electric motors actually present a relatively easy duty for shaft bearings. The motor rotor is lightweight, yet because of its large shaft diameter, the bearings are large. For example, the bearings supporting the 140 lb. Rotor for a typical 40 hp. 1800 rpm industrial motor are so large that they have an L-10 minimum design fatigue life of 3000 years, or 10 percent of the bearings are statistically expected to fail from fatigue after 3000 years of operation. Plant operating experience, however, strongly contradicts such optimistic estimates of motor bearing life.

Slide 61: 

Factors Affecting Bearing Life In actual industrial environments, bearing failure is rarely caused by fatigue; it is caused by less-than-ideal lubrication. Because of contaminated lubrication, bearings fail well before they serve their theoretical fatigue life. There are many reasons for less than-ideal bearing lubrication. Lubricants can leak out; chemical attacks or thermal conditions can decompose or break down lubricants; lubricants can become contaminated with non-lubricants such as water, dust, or rust from the bearings themselves. These lubrication problems can be eliminated.

Slide 62: 

Factors Affecting Bearing Life Motor bearings can last virtually forever by simply providing an ideal contamination-free, well-lubricated bearing environment. Conventional wisdom teaches that such an ideal motor bearing environment can be provided by using a dry-running lip seal or using sealed (lubricated-for-life) bearings. Indeed, for many light-duty applications, such bearing protection techniques are often sufficient to allow bearings to last as long as the equipment itself. However, these bearing protection methods have not significantly reduced the rate of bearing failure in severe-duty industrial motors.

Slide 63: 

Factors Affecting Bearing Life Bearings in industrial applications continue to fail because of inadequate lubrication caused by lubricant loss, contamination, and decomposition and break-down. Lip seals invariably wear out well before the bearing fails, and sealed bearings inherently foreshorten the life of a bearing to the service life of the contained grease (usually only about 3,000 to 5,000 hours for most industrial services). Maintenance professionals may find the following suggestions on how to forestall motor hearing failure obvious, but some new techniques and technologies are available.

Lubricate Bearing at Correct Intervals : 

Lubricate Bearing at Correct Intervals Despite years of warnings from bearing manufacturers, over lubrication continues to plague many motor bearings. Too much grease can cause overheating of the bearings. The lubrication instructions supplied by the motor manufacturer will specify the quantity and frequency of lubrication. Generally, two-pole motors should be greased twice a year, four-pole and slower motors only once a year.

Use the Best Available Grease : 

Use the Best Available Grease The most commonly used bearing grease is polyurea-based, a low-cost, low-performance, highly compatible lubricant. However, it does not handle water well, a serious drawback for many industrial applications. It reacts readily with water and loses its ability to lubricate bearings. Industrial motor bearings should be lubricated with a synthetic-based aluminum complex grease. A high-quality grease pays for its additional cost in reduced motor downtime and repair costs.

Synthetic Aluminum complex EP grease : 

Synthetic Aluminum complex EP grease It is Complex Aluminum Grease Operating Temperature 20 to 1600 C Operations under high Pressure & Temperature Water resistant Corrosion resistant High Thermal Load Capacity ArChine Arcplex AKP 160 Complex Aluminum Grease