Electrical safety and quality assurance big mark qn with answers PDF

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BM8076-ELECTRICAL SAFETY AND QUALITY ASSURANCEBIG QUESTIONS 16 MARKSUNIT-IELECTRICAL HAZARDSPART-B Explain electrical Hazards and its types. An electrical hazard can be defined as. a dangerous condition where a worker could make electrical contact with energized equipment or a conductor, and from wh...

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Subject Code / Name: BM8076-ELECTRICAL SAFETY AND QUALITY ASSURANCE

BM8076-ELECTRICAL SAFETY AND QUALITY ASSURANCE BIG QUESTIONS 16 MARKS UNIT-I ELECTRICAL HAZARDS PART-B 1. Explain electrical Hazards and its types. An electrical hazard can be defined as. a dangerous condition where a worker could make electrical contact with energized equipment or a conductor, and from which the person may sustain an injury from shock; and/or, there is potential for the worker to receive an arc flash burn, thermal burn, or blast injury. Electrical injuries can be divided into four types:  

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Electrocution, Electric shock, Burns, Falls caused by contact with electric energy.

Burns: Three types; electrical, arc flash, or thermal contact. Electrocution: Electrocution is fatal; it means to kill with electricity. Shock: A response to electric current passing through the body. Arc Flash/Blast: Emits heat and intense light that causes burns. Fire: Occurs with faulty outlets, old wiring, cords, and switches. Explosions: When electricity ignites explosive material in the air. Electrocution is one of the major hazards on construction sites. It can be fatal and can result in serious and permanent burn injuries to the skin, internal tissues and damage to the heart depending on the length and severity of the shock. When electric current flows through tissues or bone, it produces heat that causes electrical burns. Electrical burns cause tissue damage and need immediate medical attention. Electric shocks can result in the injuries like muscle spasms, palpitations, nausea, vomiting, collapse, and unconsciousness. Faulty electrical connections and damaged electrical equipment can lead to an electric shock to workers and to others at or near the workplace.

Contact with Energized Sources: Hazards regarding contact with energized sources are electrical shock and burns. Electrical shock occurs when the body becomes part of the electric circuit (when an individual comes in contact with both wires of an electrical circuit, one wire of an energized circuit and the ground, or a metallic part that has become energized by contact with an electrical conductor).

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Subject Code / Name: BM8076-ELECTRICAL SAFETY AND QUALITY ASSURANCE

Contact with Power Lines: Overhead and buried power lines are hazardous because they carry extremely high voltage. Fatalities are possible as electrocution is the main risk; however, burns and falls from elevations are also hazards that workers are exposed to while working in the vicinity of high voltage power lines. Improper Use of Extension and Flexible Cords: Normal wear and tear on extension and flexible cords can loosen or expose wires, creating a hazardous condition. Hazards are created when cords, cord connectors, receptacles, and cord- and plug connected equipment are improperly used and maintained. If the electrical conductors become exposed, there is a danger of shocks, burns, or fire.

How to Protect Yourself: Inspect all electrical tools and equipment PRIOR to use. GFCIs are required on temporary electricity and wet locations. Never use anything that is damaged. Treat all electrical wires as if they were energized. Maintain a 10 FT clearance from all overheard lines. Allow only Qualified Electricians to perform electrical work. Keep at least 3 feet from all electrical panels. Ensure all tools and wiring are properly grounded. Require the proper PPE for the work being performed. NEVER work on hot electrical equipment, always de-energize. Follow the NEC and other Electrical Safe Work Practices. Train others on basic electrical safety and hazard recognition

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2. Illustrate static electricity, its causes and discuss about its prevention methods. Static electricity is the result of an imbalance between negative and positive charges in an object. These charges can build up on the surface of an object until they find a way to be released or discharged. One way to discharge them is through a circuit. Causes of Static Electricity:     

Contact-induced charge separation Pressure-induced charge separation Heat-induced charge separation Charge-induced charge separation Static discharge

Contact-induced charge separation Electrons can be exchanged between materials on contact; materials with weakly bound electrons tend to lose them while materials with sparsely filled outer shells tend to gain them. This is known as the turboelectric effect and results in one material becoming positively charged and the other negatively charged. The polarity and strength of the charge on a material once they are separated depends on their relative positions in the turboelectric series. The turboelectric effect is the main cause of static electricity as observed in everyday life, and in common highschool science demonstrations involving rubbing different materials together (e.g., fur against an

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Subject Code / Name: BM8076-ELECTRICAL SAFETY AND QUALITY ASSURANCE

acrylic rod). Contact-induced charge separation causes your hair to stand up and causes "static cling".

Pressure-induced charge separation Applied mechanical stress generates a separation of charge in certain types of crystals and ceramics molecules. Heat-induced charge separation Heating generates a separation of charge in the atoms or molecules of certain materials. All pyroelectric materials are also piezoelectric. The atomic or molecular properties of heat and pressure response are closely related. Charge-induced charge separation A charged object brought close to an electrically neutral object causes a separation of charge within the neutral object. Charges of the same polarity are repelled and charges of the opposite polarity are attracted. As the force due to the interaction of electric charges falls off rapidly with increasing distance, the effect of the closer (opposite polarity) charges is greater and the two objects feel a force of attraction. The effect is most pronounced when the neutral object is an electrical conductor as the charges are more free to move around. Careful grounding of part of an object with a charge-induced charge separation can permanently add or remove electrons, leaving the object with a global, permanent charge Static discharge 

The spark associated with static electricity is caused by electrostatic discharge, or simply static discharge, as excess charge is neutralized by a flow of charges from or to the surroundings.

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The feeling of an electric shock is caused by the stimulation of nerves as the neutralizing current flows through the human body. The energy stored as static electricity on an object varies depending on the size of the object and its capacitance, the voltage to which it is charged, and the dielectric constant of the surrounding medium.

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For modelling the effect of static discharge on sensitive electronic devices, a human being is represented as a capacitor of 100 picofarads, charged to a voltage of 4000 to 35000 volts. When touching an object this energy is discharged in less than a microsecond. [7] While the total energy is small, on the order of millijoules, it can still damage sensitive electronic devices. Larger objects will store more energy, which may be directly hazardous to human contact or which may give a spark that can ignite flammable gas or dust.

Prevention Method Removing or preventing a buildup of static charge can be as simple as opening a window or using a humidifier to increase the moisture content of the air, making the atmosphere more conductive. Air ionizers can perform the same task that are particularly sensitive to static discharge may be treated with the application of an antistatic agent, which adds a conducting surface layer that ensures any excess charge is evenly distributed. Fabric softeners and dryer sheets used in washing machines and clothes dryers are an example of an antistatic agent used to prevent and remove static cling. Many semiconductor devices used in electronics are particularly sensitive to static discharge. Conductive antistatic bags are commonly used to protect such components. People ESQA

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Subject Code / Name: BM8076-ELECTRICAL SAFETY AND QUALITY ASSURANCE

who work on circuits that contain these devices often ground themselves with a conductive antistatic strap. In the industrial settings such as paint or flour plants as well as in hospitals, antistatic safety boots are sometimes used to prevent a buildup of static charge due to contact with the floor. These shoes have soles with good conductivity. Anti-static shoes should not be confused with insulating shoes, which provide exactly the opposite benefit – some protection against serious electric shocks from the mains voltage.

3. Write short notes on (i) Electromagnetism and (ii) Electrostatics (i)

Electromagnetism Magnetism is a class of physical phenomena that are mediated by magnetic fields. Electric currents and the magnetic moments of elementary particles give rise to a magnetic field, which acts on other currents and magnetic moments. Magnetism is one aspect of the combined phenomenon of electromagnetism. The most familiar effects occur in ferromagnetic materials, which are strongly attracted by magnetic fields and can be magnetized to become permanent magnets, producing magnetic fields themselves. Demagnetizing a magnet is also possible. Only a few substances are ferromagnetic; the most common ones are iron, cobalt and nickel and their alloys. The prefix ferro- refers to iron, because permanent magnetism was first observed in lodestone, a form of natural iron ore called magnetite, Fe3O4. Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of physical interaction that occurs between electrically charged particles. The electromagnetic force is carried by electromagnetic fields composed of electric fields and magnetic fields, and it is responsible for electromagnetic radiation such as light. It is one of the four fundamental interactions (commonly called forces) in nature, together with the strong interaction, the weak interaction, and gravitation.

There are four main effects resulting from these interactions, all of which have been clearly demonstrated by experiments: 1. Electric charges attract or repel one another with a force inversely proportional to the square of the distance between them: unlike charges attract, like ones repel. 2. Magnetic poles (or states of polarization at individual points) attract or repel one another in a manner similar to positive and negative charges and always exist as pairs: every north pole is yoked to a south pole. 3. An electric current inside a wire creates a corresponding circumferential magnetic field outside the wire. Its direction (clockwise or counter-clockwise) depends on the direction of the current in the wire.

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Subject Code / Name: BM8076-ELECTRICAL SAFETY AND QUALITY ASSURANCE

4. A current is induced in a loop of wire when it is moved toward or away from a magnetic field, or a magnet is moved towards or away from it; the direction of current depends on that of the movement.

Fundamental forces The electromagnetic force is one of the four known fundamental forces. The other fundamental forces are: The strong nuclear force, which binds quarks to form nucleons, and binds nucleons to form nuclei. The weak nuclear force, which binds to all known particles in the Standard Model, and causes certain forms of radioactive decay. (In particle physics though, the electroweak interaction is the unified description of two of the four known fundamental interactions of nature: electromagnetism and the weak interaction) the gravitational force.

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ii) Electrostatics Electrostatics is a branch of physics that studies electric charges at rest. Electrostatic phenomena arise from the forces that electric charges exert on each other. Such forces are described by Coulomb's law. Even though electrostatically induced forces seem to be rather weak, some electrostatic forces such as the one between an electron and a proton, that together make up a hydrogen atom, is about 36 orders of magnitude stronger than the gravitational force acting between them. There are many examples of electrostatic phenomena, from those as simple as the attraction of the plastic wrap to one's hand after it is removed from a package to the apparently spontaneous explosion of grain silos, the damage of electronic components during manufacturing, and photocopier & laser printer operation. Electrostatics involves the buildup of charge on the surface of objects due to contact with other surfaces. Although charge exchange happens whenever any two surfaces contact and separate, the effects of charge exchange are usually only noticed when at least one of the surfaces has a high resistance to electrical flow. This is because the charges that transfer are trapped there for a time long enough for their effects to be observed. These charges then remain on the object until they either bleed off to ground or are quickly neutralized by a discharge: e.g., the familiar phenomenon of a static "shock" is caused by the neutralization of charge built up in the body from contact with insulated surfaces. Electric field The electric field, in units of newtons per coulomb or volts per meter, is a vector field that can be defined everywhere, except at the location of point charges (where it diverges to infinity). It is defined as the electrostatic force in newtons on a hypothetical small test charge at the point due to Coulomb's Law, divided by the magnitude of the charge in coulombs

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Subject Code / Name: BM8076-ELECTRICAL SAFETY AND QUALITY ASSURANCE

The electrostatic field (lines with arrows) of a nearby positive charge (+) causes the mobile charges in conductive objects to separate due to electrostatic induction. Negative charges (blue) are attracted and move to the surface of the object facing the external charge. Positive charges (red) are repelled and move to the surface facing away. These induced surface charges are exactly the right size and shape so their opposing electric field cancels the electric field of the external charge throughout the interior of the metal. Therefore, the electrostatic field everywhere inside a conductive object is zero, and the electrostatic potential is constant.

4. Write short notes on (i) Energy Leakage and (ii) Clearance and insulation (i)

Energy Leakage Leakage is the gradual transfer of electrical energy across a boundary normally viewed as insulating, such as the spontaneous discharge of a charged capacitor, magnetic coupling of a transformer with other components, or flow of current across a transistor in the "off" state or a reverse-polarized diode. Leakage current is the current that flows through the protective ground conductor to ground. In the absence of a grounding connection, it is the current that could flow from any conductive part or the surface of non-conductive parts to ground if a conductive path was available (such as a human body).

Leakage-current flows a. through the ground wire – no microshock occurs

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Subject Code / Name: BM8076-ELECTRICAL SAFETY AND QUALITY ASSURANCE

b. through the patient if he touches the chassis and has a grounded catheter etc.

c. through the patient if he is touching ground and has a connected catheter etc.

Electric leakage can be detected by 4 points for home electrical leakage alarms 1. Abnormally high electric bill.

2. The power cut off often. 3. Touch the appliance and feel electric shock. 4. The temperature in the house is abnormally high. Check electrical systems for safe home with Home Service (ii)

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Clearance and insulation Clearance – The shortest path between two conductive parts measured through air; the shortest path between the primary and secondary sides of the transformer that is measured through air. Often times your clearance distance is less than your creepage distance and can be the more critical distance. DSEC/BME/QB/IV YR/ESQA

Subject Code / Name: BM8076-ELECTRICAL SAFETY AND QUALITY ASSURANCE

Safety clearances in extra high voltage substation are very much important to maintain the basic insulation level of the system. If the system is designed without proper clearances there shall be insulation break down and flash over. A substation or a system faces several over voltage condition, due to lightning, due to switching or fault etc  Ensuring clearances and creepage distances meet the minimum requested by the standard avoids problems for nominal voltage and overvoltage such as:  Electrical arc ignition – prevention is critical for arc flash mitigation  Decreasing insulation performance Connection damage

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INSULATION The peak voltage that the insulation under consideration is required to withstand. In simple terms, an electrical strength test used to verify the insulation strength between two conductors. INSULATION TYPE Single-layer insulation can provide users with basic protection against electric shock. Double insulation includes both basic insulation and supplementary insulation. The necessary insulation between the conductive parts in the equipment so that the equipment can operate normally so is not a safety consideration for users. A single-layer insulation system can reach the level of protection against electric shock equivalent to double insulation. The second layer of insulation independent of the basic insulation can protect the user from dangerous voltage when the basic insulation fails. The insulation withstand properties of surge arresters in a substation can be divided into: − Insulation withstand of the surge arrester itself, including the insulation between flanges and grading rings, etc. Insulation withstand between the surge arrester and grounded objects insulation withstand between the surge arrester and other equipment connected to the same phase, e.g. bushings. Insulation withstand between surge arresters in adjacent phases. There are three main insulation types to consider – functional, basic, and double/reinforced. Functional Insulation – Functional insulation is required only for proper functioning of the transformer. It is usually associated with DC/DC applications in which the end user is not exposed to hazardous voltages. Basic Insulation – Basic insulation is not basic. It is typically requested when the end application has a means of providing additional isolation from the hazardous input voltage in case the basic insulation fails. Double/Reinforced Insulation – This is the most common form used in offline applications. The end user is completely isolated from hazardous input voltage by reinforced insulation without the need for additional isolation. Defective insulation hazards Insulation that is defective or inadequate is an electrical hazard. Usually, a plastic or rubber covering insulates wires. Insulation prevents conductors from coming in contact with each other. Insulation also prevents conductors from coming in contact with people.

5. Describe about current surges. ESQA

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Subject Code / Name: BM8076-ELECTRICAL SAFETY AND QUALITY ASSURANCE

Surge currents are the “currents that raise or fall from the normal rated value in the short duration of time”. These are the instantaneous sharp impulse currents. Surge currents occur in the electrical machines during their turn on conditions. ... Surge currents occur due to the sudden change in the loads. Surge currents are the “currents that raise or fall from the nor...