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A SUMMER TRAINING REPORT ON OPERATION AND MAINTANANCE OF SUBSTATION UPCL BY SMITA DOBHAL – (07090105048) Submitted to the Department of Electrical Engineering In partial fulfillment of requirements for the award of Degree of Bachelor of Technology In Electrical Engineering Department of Electrical Engineering GOVIND BALLABH PANT ENGINEERING COLLEGE UTTARAKHAND TECHNICAL UNIVERSITY GHURDAURI,PAURI GARHWAL UTTARAKHAND, India. 2007-2011 TABLE OF CONTENTS DECLARATION……………………………………………………………………………. 3 CERTIFICATE……………………………………………………………………………. …4 ACKNOWLEDGEMENTS……………………………………………………………….. 5 CHAPTER 1 (INTRODUCTION)……………………………………………………….. …. 6 1. 1 About the Substation…. ………………………….. ……………………………………6 1. 2 Power Station…………………………………………………………………………. 7 1. 2. 1 Principle of Power Station……………………………………………………. ……7 CHAPTER 2 (TRANSFORMER)…………………………………………………….. ……. 9 2. 1 Transformer…………………………………………………………………………………………………… 9 2. 1. 1 Basic Principle……………………………………………………………….. ……. 9 2. 1. 2 Induction law…………………………………………………………………. ……9 2. 1. 3 Ideal power equation………………………………………………………….. ….. 10 2. 1. Detailed Operation…………………………………………………………………10 2. 2 Types…………………………………………………………………………………. 11 2. 2. 1 Power Transformer………………………………………………………………. 11 2. 2. 2 Instrument Transformer………………………………………………….. ………. 12 2. 2. 3 Pulse Transformer ………………………………………………………………… 13 2. 2. 4 RF Transformer……………………………………………………………………13 2. 2. 5 Audio Transformer……………………………………………………… …………13 CHAPTER 3 (RELAYS)……………………………………………………………………14 3. 1 Relays………………………………………………………………………… ………. 14 3. 1. 1 Basic Design and Operation………… …………………………………… ……. …. 14 3. 2 Types……………………………………………………………………………. ……15 3. . 1 Latching Relay…………………………………………………….. ………………. 15 3. 2. 2 Reed Relay …………………………………………………….. …………………. 16 3. 2. 3 Solid State Relay……………………………………………………… ……………16. 3. 2. 4 Buchholz Relay…………………………………………………………………. …16 3. 2. 5 Overvoltage Protection Relay…………………………………………………. ….. 16 CHAPTER4(CIRCUIT BREAKER)…………………………………………………….. …17 4. 1 Circuit Breaker……………………………………………………………….. ………17 4. 1. 1 Operation………………………………………………………………………… …17 CHAPTER 5 (PROTECTION OF TRANSFORMER) 5. 1 Lightning Arrester…………………………………………………………………….. 18 5. 1. 1 Construction …………………………………………………………………….. 18 5. 1. 2 Maintanace……………………………………………………………………. ……18 5. 1. 3 Testing…………………………………………………………………………. ……18 5. 2 OverCurrent Protection……………………………………………………………… 19 5. 3 Internal Fault Protection………………………………………………………. ……19 5. 4 Overvoltage Protection………………………………………………………. …. …. 20 5. 4. 1 External Elbow Arrester………………………………………………………… …20 5. 4. 2 External Live Front Arrester………………………………………………………. 20 5. 4. 3 Under Oil Arrester…………………………………………………………….. ….. 20 CHAPTER6 (MAINTANANCE)…………………………………………………. ……….. 21 6. 1 Infrared Imaging…………………………………………………………. ……….. …. 21 6. Sampling………………………………………………………………………… ……. 21 6. 3 Maintanance…………………………………………………………………. ………. 21 6. 4 Testing ……………………………………………………………………………. …22 THANKS…………………………………………………………………………… ……. 23 DECLARATION We hereby declare that this submission is our own work and that to the best of my knowledge and belief, it contains no material previously published or written by another person nor material which to a substantial extent has been accepted for the award of any other degree of the university or other institute of higher learning, except where due acknowledgement has been made in the text.

Signature :- Name :- Roll No:- Date:- cERTIFICATE This is to certify that Project Report entitled “ SPEED CONTROL OF DC SERIES MOTOR BY SCR AND PHASE ANGLE CONTROL” which is submitted by “ AJEET KUMAR PANDEY, JITENDRA SINGH, SHRINIWAS YADAV, SUMIT KUMAR” in partial fulfillment of the requirement for the award of B. Tech degree in department of “ELECTRICAL AND ELECTRONICS ENGINEERING” of U. P. Technical University, is a record of the candidate own work carried out by them under my supervision The matter embodied in this thesis is original and has not submitted for the award of any degree.

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Date : Supervisor acknowledgement It gives us a great sense of pleasure to present the report of the B. Tech training report undertaken during B. Tech third year. We are grateful to the S. D. O. Mr. Ankit Jain, for his time to time very much needed valuble guidance. His sincerity, thoroughness and perseverance have been a constant source of inspiration for us. It is only cognizant efforts that our endeavors have seen light of the day.

We wish to express our profound thanks to all those who helped in making this report a reality. Much need moral support and encouragement is provided on numerous occasions by our whole friends, UPCL members and seniors We would also like to take the opportunity to acknowledge the contribution of all faculty members of the department for their kind assistance and cooperation during development of our project. SMITA DOBHAL – (07090105048) 1. 1 – Substation Secondary unit substation are essentially a repeat of configurationof the station auxiliary transformer and the medium voltage transformer but at a lower voltage.

Breakers one of the plant switchgear will feed a transformer (in the one-line diagram the feed breakers is the 2A-3 Breaker on the 2A 4160 votage bus) that will reduce the voltage to 480 volts. This transformer is an integral part of aline up 480 volt Switchgear. Sometimes Unit Substation are designed with a transformer at each end of the Switchgear. These are referred to as “Double Ended” secondary unit substation. The configuration shown in the one line above is single ended substation tie breaker which provide essentially the same reliability as a double ended substation.

Secondary Unit Substation are used to feed the large component in a power plant by further distributing power to load centers,motor control centers,and battery charger. In addition, medium range motor 200 to 300 horse power are fed by individual 480 V SUS circuit breaker. SUBSTATION 1. 2 – Power Station A power station (also referred to as a generating station, power plant, or powerhouse) is an industrial facility for the generation of electric power. Power plant is also used to refer to the engine in ships, aircraft and other large vehicles.

Some prefer to use the term energy center because it more accurately describes what the plants do, which is the conversion of other forms of energy, like chemical energy, gravitational potential energy or heat energy into electrical energy. At the center of nearly all power stations is a generator, a rotating machine that converts mechanical energy into electrical energy by creating relative motion between a magnetic field and a conductor. The energy source harnessed to turn the generator varies widely. It depends chiefly on which fuels are easily available and on the types of technology that the power company has access to. Chibro Power Station) (Khodri Power Station) 1. 2. 1 – Operation of Power Station The power station operator has several duties in the electrical generating facility. Operators are responsible for the safety of the work crews that frequently do repairs on the mechanical and electrical equipment. They maintain the equipment with periodic inspections and log temperatures, pressures and other important information at regular intervals. Operators are responsible for starting and stopping the generators depending on need.

They are able to synchronize and adjust the voltage output of the added generation with the running electrical system without upsetting the system. They must know the electrical and mechanical systems in order to troubleshoot problems in the facility and add to the reliability of the facility. Operators must be able to respond to an emergency and know the procedures in place to deal with it. 2. 1 – Transformer A transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer’s coils.

A varying current in the first or primary winding creates a varying magnetic flux in the transformer’s core, and thus a varying magnetic field through the secondary winding. This varying magnetic field induces a varying electromotive force (EMF) or “voltage” in the secondary winding. This effect is called mutual induction. Tranformer Faraday’s experiment between with of induction coils wire If a load is connected to the secondary, an electric current will flow in the secondary winding and electrical energy will be transferred from the primary circuit through the transformer to the load.

In an ideal transformer, the induced voltage in the secondary winding (VS) is in proportion to the primary voltage (VP), and is given by the ratio of the number of turns in the secondary (NS) to the number of turns in the primary (NP) as follows: Transformers range in size from a thumbnail-sized coupling transformer hidden inside a stage microphone to huge units weighing hundreds of tons used to interconnect portions of power grids. All operate with the same basic principles, although the range of designs is wide.

Transformers are essential for high voltage power transmission, which makes long distance transmission economically practical. 2. 1. 1 – Basic principles The transformer is based on two principles: firstly, that an electric current can produce a magnetic field (electromagnetism) and secondly that a changing magnetic field within a coil of wire induces a voltage across the ends of the coil (electromagnetic induction). Changing the current in the primary coil changes the magnetic flux that is developed. The changing magnetic flux induces a voltage in the secondary coil.

An ideal transformer An ideal transformer is shown in the adjacent figure. Current passing through the primary coil creates a magnetic field. The primary and secondary coils are wrapped around a core of very high magnetic permeability, such as iron, so that most of the magnetic flux passes through both the primary and secondary coils. 2. 1. 2 – Induction law-: The voltage induced across the secondary coil may be calculated from Faraday’s law of induction, which states that: where VS is the instantaneous voltage, NS is the number of turns in the secondary coil and ? quals the magnetic flux through one turn of the coil. If the turns of the coil are oriented perpendicular to the magnetic field lines, the flux is the product of the magnetic flux density B and the area A through which it cuts. The area is constant, being equal to the cross-sectional area of the transformer core, whereas the magnetic field varies with time according to the excitation of the primary. Since the same magnetic flux passes through both the primary and secondary coils in an ideal transformer, the instantaneous voltage across the primary winding equals 2. 1. 3 – Ideal power equation-:

If the secondary coil is attached to a load that allows current to flow, electrical power is transmitted from the primary circuit to the secondary circuit. Ideally, the transformer is perfectly efficient; all the incoming energy is transformed from the primary circuit to the magnetic field and into the secondary circuit. If this condition is met, the incoming electric power must equal the outgoing power. The ideal transformer as a circuit element If the voltage is increased, then the current is decreased by the same factor. The impedance in one circuit is transformed by the square of the turns ratio. 26] For example, if an impedance ZS is attached across the terminals of the secondary coil, it appears to the primary circuit to have an impedance of . This relationship is reciprocal, so that the impedance ZP of the primary circuit appears to the secondary to be . 2. 1. 4 – Detailed operation-: Models of an ideal transformer typically assume a core of negligible reluctance with two windings of zero resistance. [28] When a voltage is applied to the primary winding, a small current flows, driving flux around the magnetic circuit of the core. 28] The current required to create the flux is termed the magnetizing current; since the ideal core has been assumed to have near-zero reluctance, the magnetizing current is negligible, although still required to create the magnetic field. The changing magnetic field induces an electromotive force (EMF) across each winding. Since the ideal windings have no impedance, they have no associated voltage drop, and so the voltages VP and VS measured at the terminals of the transformer, are equal to the corresponding EMFs.

The primary EMF, acting as it does in opposition to the primary voltage, is sometimes termed the “back EMF”. [30] This is due to Lenz’s law which states that the induction of EMF would always be such that it will oppose development of any such change in magnetic field 2. 2 – Transformer Types-: 1) Power Transformer a) Auto Transformer 2) Instrument Transformer a) Voltage transformer b) Current Transformer 3) Pulse transformer 4) RF Transformer a) Air core Transformer b) Ferrite core Transformer 5) Audio Transformer a) Loudspeaker Transformer 2. 2. – Power Transformer-(Auto Transformer) An autotransformer has a single winding with two end terminals, and one or more terminals at intermediate tap points. The primary voltage is applied across two of the terminals, and the secondary voltage taken from two terminals, almost always having one terminal in common with the primary voltage. The primary and secondary circuits therefore have a number of windings turns in common. [43] Since the volts-per-turn is the same in both windings, each develops a voltage in proportion to its number of turns.

In an autotransformer part of the current flows directly from the input to the output, and only part is transferred inductively, allowing a smaller, lighter, cheaper core to be used as well as requiring only a single winding[44]. However, a transformer with separate windings isolates the primary from the secondary, which is safer when using mains voltages. An adjustable autotransformer is made by exposing part of the winding coils and making the secondary connection through a sliding brush, giving a variable turns ratio. [45] Such a device is often referred to as a variac. An autotransformer with a sliding brush contact 2. . 2 – Instrument Transformer a) Capacitor voltage transformer A capacitor voltage transformer (CVT), or capacitance coupled voltage transformer (CCVT) is a transformer used in power systems to step down extra high voltage signals and provide a low voltage signal, for measurement or to operate a protective relay. In its most basic form the device consists of three parts: two capacitors across which the transmission line signal is split, an inductive element to tune the device to the line frequency, and a transformer to isolate and further step down the voltage for the instrumentation or protective relay.

The device has at least four terminals: a terminal for connection to the high voltage signal, a ground terminal, and two secondary terminals which connect to the instrumentation or protective relay. A capacitor voltage transformer (CVT) b) Current Transformer Current transformers are often constructed by passing a single primary turn (either an insulated cable or an uninsulated bus bar) through a well-insulated toroidal core wrapped with many turns of wire. The CT is typically described by its current ratio from primary to secondary.

For example, a 4000:5 CT would provide an output current of 5 amperes when the primary was passing 4000 amperes. The secondary winding can be single ratio or have several tap points to provide a range of ratios. Care must be taken that the secondary winding is not disconnected from its load while current flows in the primary, as this will produce a dangerously high voltage across the open secondary and may permanently affect the accuracy of the transformer. Current transformers 2. 2. 3 – Pulse Transformer

A pulse transformer is a transformer that is optimized for transmitting rectangular electrical pulses (that is, pulses with fast rise and fall times and a relatively constant amplitude). Small versions called signal types are used in digital logic and telecommunications circuits, often for matching logic drivers to transmission lines. Medium-sized power versions are used in power-control circuits such as camera flash controllers. Larger power versions are used in the electrical power distribution industry to interface low-voltage control circuitry to the high-voltage gates of power semiconductors.

Special high voltage pulse transformers are also used to generate high power pulses for radar, particle accelerators, or other high energy pulsed power applications. To minimize distortion of the pulse shape, a pulse transformer needs to have low values of leakage inductance and distributed capacitance, and a high open-circuit inductance. 2. 2. 4 – RF Transformer a) Air-core transformers These are used for high frequency work. The lack of a core means very low inductance. Such transformers may be nothing more than a few turns of wire soldered onto a printed circuit board. b) Ferrite-core transformers

Widely used in intermediate frequency (IF) stages in super heterodyne radio receivers. Are mostly tuned transformers, containing a threaded ferrite slug that is screwed in or out to adjust IF tuning. The transformers are usually canned for stability and to reduce interference. 2. 2. 5 – Audio Transformer-(Loudspeaker Transformer) In the same way that transformers are used to create high voltage power transmission circuits that minimize transmission losses, loudspeaker transformers can be used to allow many individual loudspeakers to be powered from a single audio circuit operated at higher-than normal loudspeaker voltages.

This application is common in industrial public address applications. Such circuits are commonly referred to as constant voltage speaker systems, although the audio waveform is a changing voltage. Such systems are also known by other terms such as 25-, 70- and 100-volt speaker systems, referring to the nominal voltage of the loudspeaker line. 3. 1 – Relays A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism, but other operating principles are also used.

Relays find applications where it is necessary to control a circuit by a low-power signal, or where several circuits must be controlled by one signal. The first relays were used in long distance telegraph circuits, repeating the signal coming in from one circuit and re-transmitting it to another. Relays found extensive use in telephone exchanges and early computers to perform logical operations. A type of relay that can handle the high power required to directly drive an electric motor is called a contactor. Solid-state relays control power circuits with no moving parts, instead using a semiconductor device to perform switching.

Relays with calibrated operating characteristics and sometimes multiple operating coils are used to protect electrical circuits from overload or faults; in modern electric power systems these functions are performed by digital instruments still called “protection relays”. 3. 1. 1 – Basic Design And Operation A simple electromagnetic relay consists of a coil of wire surrounding a soft iron core, an iron yoke, which provides a low reluctance path for magnetic flux, a movable iron armature, and a set, or sets, of contacts; two in the relay pictured.

The armature is hinged to the yoke and mechanically linked to a moving contact or contacts. It is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. In this condition, one of the two sets of contacts in the relay pictured is closed, and the other set is open. Other relays may have more or fewer sets of contacts depending on their function. The relay in the picture also has a wire connecting the armature to the yoke.

This ensures continuity of the circuit between the moving contacts on the armature, and the circuit track on the printed circuit board(PCB) via the yoke, which is soldered to the PCB. Small relay as used in electronics When an electric current is passed through the coil, the resulting magnetic field attracts the armature, and the consequent movement of the movable contact or contacts either makes or breaks a connection with a fixed contact. If the set of contacts was closed when the relay was de-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open.

When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position. Usually this force is provided by a spring, but gravity is also used commonly in industrial motor starters. Most relays are manufactured to operate quickly. In a low voltage application, this is to reduce noise. In a high voltage or high current application, this is to reduce arcing. 3. 2 – Relay types 1) Latching Relay 2) Reed Relay 3) Solid State Relay 4) Buchholz Relay 5) Overvoltage Protection Relay . 2. 1 – Latching Relay A latching relay has two relaxed states (bistable). These are also called “impulse”, “keep”, or “stay” relays. When the current is switched off, the relay remains in its last state. This is achieved with a solenoid operating a ratchet and cam mechanism, or by having two opposing coils with an over-center spring or permanent magnet to hold the armature and contacts in position while the coil is relaxed, or with a remanent core. In the ratchet and cam example, the first pulse to the coil turns the relay on and the second pulse turns it off.

In the two coil example, a pulse to one coil turns the relay on and a pulse to the opposite coil turns the relay off. This type of relay has the advantage that it consumes power only for an instant, while it is being switched, and it retains its last setting across a power outage. A remanent core latching relay requires a current pulse of opposite polarity to make it change state. Latching Relay 3. 2. 2 – Reed Relay A reed relay has a set of contacts inside a vacuum or inert gas filled glass tube, which protects the contacts against atmospheric corrosion.

The contacts are closed by a magnetic field generated when current passes through a coil around the glass tube. Reed relays are capable of faster switching speeds than larger types of relays, but have low switch current and voltage ratings. Reed Relay 3. 2. 3 – Solid State Relay A solid state relay (SSR) is a solid state electronic component that provides a similar function to an electromechanical relay but does not have any moving components, increasing long-term reliability. With early SSR’s, the tradeoff came from the fact that every transistor has a small voltage drop across it.

This voltage drop limited the amount of current a given SSR could handle. As transistors improved, higher current SSR’s, able to handle 100 to 1,200 Amperes, have become commercially available. Compared to electromagnetic relays, they may be falsely triggered by transients. Solid State Relay 3. 2. 4 – Buchholz Relay A Buchholz relay is a safety device sensing the accumulation of gas in large oil-filled transformers, which will alarm on slow accumulation of gas or shut down the transformer if gas is produced rapidly in the transformer oil. . 1 – Circuit Breaker A circuit breaker is an automatically-operated electrical switch designed to protect an electrical circuit from damage caused by overload orshort circuit. Its basic function is to detect a fault condition and, by interrupting continuity, to immediately discontinue electrical flow. Unlike afuse, which operates once and then has to be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation.

Circuit breakers are made in varying sizes, from small devices that protect an individual household appliance up to large switchgeardesigned to protect high voltage circuits feeding an entire city. Circuit Breaker 4. 1. 1 – Operation The circuit breaker must detect a fault condition; in low-voltage circuit breakers this is usually done within the breaker enclosure. Circuit breakers for large currents or high voltages are usually arranged with pilot devices to sense a fault current and to operate the trip opening mechanism.

The trip solenoid that releases the latch is usually energized by a separate battery, although some high-voltage circuit breakers are self-contained with current transformers, protection relays, and an internal control power source. Once a fault is detected, contacts within the circuit breaker must open to interrupt the circuit; some mechanically-stored energy (using something such as springs or compressed air) contained within the breaker is used to separate the contacts, although some of the energy required may be obtained from the fault current itself.

Small circuit breakers may be manually operated; larger units have solenoids to trip the mechanism, and electric motors to restore energy to the springs. The circuit breaker contacts must carry the load current without excessive heating, and must also withstand the heat of the arc produced when interrupting the circuit. Contacts are made of copper or copper alloys, silver alloys, and other materials. Service life of the contacts is limited by the erosion due to interrupting the arc 5 – Protection Of Transformer 5. 1 – Lightning (Surge) Arrester

Most transformer installations are subject to surge voltages Originating from lightning switching operation or circuit faults 5. 1. 1 – Construction They use a porcelain exterior shell to provide insulation And mechanical strength, and they use a dielectric filler material (oil, epoxy, or other materials) to increase the dielectric strength see in fig. Lightning arresters, however, are called on to insulate normal operating voltages, and to conduct high level surges to ground.

In its simplest form, a lightning arrester is nothing more than a controlled gap across which normal operating voltages cannot jump. When the voltages exceeds a predetermined level, it will be directed to ground, away from the various components (including the transformer) of the circuit. 5. 1. 2 – Maintanance. Lightning arresters use petticoats to increase the creepage distances across the outer sm. face to ground. Lightning arresters should be kept clean to prevent surface contaminants from forming a flashover path. Lightning arresters have a metallic connection on tlw top and bottom.

The connectors should be kept free of corrosion. 5. 1. 3 – Testing. Lightning arresters are sometimes constructed by stacking a series of the capacitive/dielectric elements to achieve the desired voltage rating. Power factor testing is usually conducted across each of the individual elements, and, much like the power factor test on the transformer’s windings, a ratio is computed between the real and apparent current values to determine the power factor. A standard insulation resistance- dielectric absorption test can also be performed on the lightning arrester between the line connection and ground. . 2 – Over Current Protection 5. 2. 1 – Dry-Well Canister Fuses- These are general purpose current-limiting fuses , accessible from high-voltage compartment, airinsulated whose canister extends into the tank beneath the oil. External replaceable, there are straight and slant type designs (the last ones more appropriate for pad-mountedtransformer shorter dimensions). Canister type fuses (SIEMENS) The fuseholders are hot stick operable and two types canbe distinguished: Dry –Well canister fuses 5. 3 – Internal Fault Protection 5. 3. 1 – Isolation Link-

This element (shown in Figure 7) is used in series withBay-O-Net fuses and Magnex® interrupter, in situations where there is no current-limiting fuse connected in series, to guarantee extra protection in case of an internaltransformer failure and also in refusing and switching operations. Isolation Link(COOPER) It is designed to melt under the high currents produceddue to an internal failure in the pad-mounted transformer,avoiding dangerous re-energizings of failed transformers. This element has no interrupting rating but meltingcharacteristics. Isolation Link (COPPER) 5. – Overvoltage Protection Usually, in pad-mounted transformers, MOV type surge arresters are used for overvoltage protection. It ispossible to distinguish three different types: 5. 4. 1 – External Elbow arresters . They are dead front surge arresters, which are connected to dead front bushings. It is generally used with a Rotatable Feed-Thru Insert to allow its use in the same bushing of the elbow connector. When space problems are important or in certain. Elbow surge arresters (COOPER) applications,other type of elbow surge arresters, called parking stand arresters, can be used.

External Elbow arresters 5. 4. 2 – External Live Front arresters . They are used for live front configuration and are made with polymer or porcelain housings. External Live Front arresters . 5. 4. 3 – Under-Oil arresters . They are designed to be mounted inside the transformer tank and operate submerged in oil. These arresters are used to prevent shortened life due to several factors: surface contamination, wildlife damage, vandalism or moisture ingress. When transformer testing is done some kind of disconnector becomes essential.

Under-Oil arrester 6 – Transformer Maintanance A comprehensive maintenance and testing program is instituted for a number of reasons and benefits. The objective of a comprehensive program is not just to get the work done, but to ensure that the work is according to a methodical and priority-oriented paln of action. A comprehensive program ensures that all maintenance needs are fulfilled, and that [email protected] and inspections are performed to verify that the equipment Is not deteriorating at an accelerated rate.

By documenting all activities and performing the work as part of an overall plan, the program also helps to eliminate any redundancies or duplication efforts. There are five basic activities involved In a comprehensive program: 6. 1 – Infrared (IR) Imaging – Infrared Imaging k also an effective inspection tool. Loose connections, unbalawed loads, and faulty wiring will sJl emit relatively higher IeveIs of heat than their surroundings. infrared imaging systems provide a screen display (like a TV) that shows the temperature difference of the items on the screen.

It Is the relative difference in temperature, and not the actual temperature that will indicate any9-l TM 5-686 problems. If the IR scan is performed annually, it should be performed 6 months after the annual maintenance outage, to maximize prtection between the hands-on service intervals. 6. 2 – Sampling- Drawing samples of the transformer’s fluid provides the opportunity to actually remove a portion of the transformer’s insulation and subject it to a battery of standardized tests, under controlled laboratory equipment.

Most transformers can be sampled while energized, so there is no major inconvenience involved. Although samples should be taken more frequently at the outset of a program (every 6 months), once the baseline data and the rate of deterioration have been determined, the frequency can usually be adjusted according to the needs of the transformer (normally once a year). 6. 3 – Maintenance – Most maintenance functions require an outage since they present a hazard to thepersonnel involved.

Maintenance functions involve periodic actions that are performed as a result of the expected wear and tear and deterioration of the trans former. They include wiping down all bushings and external surfaces, topping off fluids, tightening connections, reconditioning deteriorated oil, recharging gas blankets and checking gas bottles, touching-up the paint, ftig minor leaks, and doing any maintenance required for fan systems and tap changer systems. Most of these operations should be performed annually, when the transformer is de-energized for testi 6. – Testing – Testing provides functional verification of the condition of the transformer. All transformer testing requires an outage. The tests that should be performed on a regularly scheduled basis are: Power factor Insulation resistance-Dielectric absorption, Turns ratio and Winding resistance. Testing is an important part of a comprehensive program because it uses electricity to verify the operating condition of the transformer. Most outdoor transformers should be tested annually, although lightly loaded transformers in favorable environments can get by with testing every 3 years. . 5 – Repair – The whole idea of the comprehensive program is to minimize the amount of unplanned downtime necessary for repairs. When the deterioration of the transform& oil is monitored, and arrangements are made to recondition the oil during a planned outage, it can be called a maintenance function. When a txmformer fault occurs, and subsequent testing reveals that the oil is unift for service, the unplanned oil reconditioning becomes a repair function; in this case, there is a much more significant inconvenience factor THANKS

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