Electrical safety and quality assurance PDF

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Conduct site surveys to ensure that nothing is stored under overhead power lines. Also, safety barriers and signs must be installed to warn nearby non-electrical workers of the hazards present in the area. Damaged Tools and Equipment Exposure to damaged electrical tools and equipment can be very dangerous. Do not fix anything unless you are qualified to do so. Thoroughly check for cracks, cuts or abrasions on cables, wires, and cords. In case of any defects, have them repaired or replaced. Lock Out Tag Out (LOTO) procedures should be performed at all times before commencing electrical maintenance and repairs. LOTO procedures are there to protect all workers on a worksite. Inadequate Wiring and Overload Overloaded ed Circuits Using wires with inappropriate size for the current can cause overheating and fires to occur. Use the correct wire suitable for the operation and the electrical load to work on. Use the correct extension cord designed for heavy-duty use. Also, do not overload an outlet and use proper circuit breakers. Perform regular fire risk assessments to identify areas at risk of of bad wiring and circuits. Exposed Electrical Parts Examples of exposed electrical parts include temporary lighting, open power distribution units, and detached insulation parts on electrical cords. These hazards can cause potential shocks and burns. Secure these items with proper guarding mechanisms and always check for any exposed parts to be repaired immediately. Improper Grounding

The most common OSHA electrical violation is the improper grounding of equipment. Proper grounding can eliminate unwanted voltage and reduce the risk of electrocution. Never remove the metallic ground pin as it is responsible for returning unwanted voltage to the ground. Damaged Insulation Defective or inadequate insulation is a hazard. Be aware of damaged insulation and report it immediately. Turn off all power sources before replacing damaged insulation and never attempt to cover them with electrical tape. Wet Conditions Never operate electrical equipment in wet locations. Water greatly increases the risk of electrocution especially if the equipment has damaged insulation. Have a qualified electrician inspect electrical equipment that has gotten wet before energizing it 3.Explain the review of electrical concepts? Electric current: An electric current is a flow of electric charge in a circuit. More specifically, the electric current is the rate of charge flow past a given point in an electric circuit. The charge can be negatively charged electrons or positive charge carriers including protons, positive ions or holes. Conventional current flow flow: The conventional current flow is from positive to the negative terminal and indicates the direction that positive charges would flow.

Electron flow flow: The electron flow is from negative to positive terminal. Electrons are negatively charged and are therefore attracted to the positive terminal as unlike charges attract. Resistance Resistance is the hindrance to the flow of electrons in material. While a potential difference across the conductor encourages the flow of electrons, resistance discourages it. The rate at which charge flows between two terminals is a combination of these two factors. Ohms law Ohm's Law states that the current flowing in a circuit is directly proportional to the applied potential difference and inversely proportional to the resistance in the circuit. v= IR Where, V = voltage expressed in Volts I = current expressed in Amps R = resistance expressed in Ohms Resistivity Resistivity: The resistivity of a substance is the resistance of a cube of that substance having edges of unit length, with the understanding that the current flows normal to opposite faces and is distributed uniformly over them. The electrical resistivity is the electrical resistance per unit length

and per unit of cross-sectional area at a specified temperature. ρ=E/J Where, ρ is the resistivity of the material in ohm metres, Ωm E is the magnitude of the electric field in volts per metre, Vm^-1 J is the magnitude of the current density in amperes per square metre, Am^-2 Capacitanc Capacitance: e: The Farad is defined defined: A capacitor has a capacitance of one Farad when a potential difference of one volt will charge it with one coulomb of electricity (i.e. one Amp for one second). Inductance: Inductance is the ability of an inductor to store energy and it does this in the magnetic field that is created by the flow of electrical current. Inductance is caused by the magnetic field generated by electric currents flowing within an electrical circuit. Typically coils of wire are used as a coil increases the coupling of the magnetic field and increases the effect. The inductance of a circuit is one henry if the rate of change of current in a circuit is one ampere per second and this results in an electromotive force of one volt. There are two ways in which inductance is used: Self-inductance Self-inductance: Self-inductance is the property of a circuit, often a coil, whereby a change in current causes a change in voltage in that circuit due to the

magnetic effect of caused by the current flow. It can be seen that self-inductance applies to a single circuit - in other words it is an inductance, typically within a single coil. This effect is used in single coils or chokes. Mutual-inductanc Mutual-inductance: e: Mutual inductance is an inductive effect where a change in current in one circuit causes a change in voltage across a second circuit as a result of a magnetic field that links both circuits. This effect is used in transformers. Quality factor: The definition of quality factor is often needed to give a more exact understanding of what this quantity actually is for electronic circuits, Q is defined as the ratio of the energy stored in the resonator to the energy supplied to it, per cycle, to keep signal amplitude constant, at a frequency where the stored energy is constant with time. It can also be defined for an inductor as the ratio of its inductive reactance to its resistance at a particular frequency, and it is a measure of its efficiency. 4. What is electrostatics and explain in detail about coulombs law and electrostatic approximation? Electrostatics is a branch of physics that studies electric charges at rest. 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

Coulomb's law states that: 'The magnitude of the electrostatic force of attraction or repulsion between two point charges is directly proportional to the product of the magnitudes of charges and inversely proportional to the square of the distance between them. The force is along the straight line joining them. If the two charges have the same sign, the electrostatic force between them is repulsive; if they have different signs, the force between them is attractive. Electrostatic potential: As the electric field is irrotational, it is possible to express the electric field as the gradient of a scalar function, called the electrostatic potential (also known as the voltage). An electric field E, points from regions of high electric potential to regions of low electric potential Electrostatic generator: The presence of surface charge imbalance means that the objects will exhibit attractive or repulsive forces. This surface charge imbalance, which yields static electricity, can be generated by touching two differing surfaces together and then separating them due to the phenomena of contact electrification and the tribo electric effect.

Rubbing two nonconductive objects generates a great amount of static electricity. This is not just the result of friction; two nonconductive surfaces can become charged by just being placed one on top of the other. Since most surfaces have a rough texture, it takes longer to achieve charging through contact than through rubbing. Rubbing objects together increases amount of adhesive contact between the two surfaces. Usually insulators, e.g., substances that do not conduct electricity, are good at both generating, and holding, a surface charge. Electrostatic induction: If a positively charged object is brought near an uncharged metal object, the mobile negatively-charged electrons in the metal will be attracted by the external charge, and move to the side of the metal facing it, creating a negative charge on the surface. When the electrons move out of an area they leave a positive charge due to the metal atoms' nuclei, so the side of the metal object facing away from the charge acquires a positive charge. These induced charges disappear when the external charge is removed. Induction is also responsible for the attraction of light objects, such as balloons. The surface charges induced in conductive objects exactly cancel external electric fields inside the conductor, so there is no electric field inside a metal object. This is the basis for the electric field shielding action of a Faraday cage. Since the electric field is the gradient of the voltage, electrostatic induction is also responsible for making the electric potential (voltage) constant throughout a conductive object. 5. What is current surges and explain in detai detail? l? Inrush current, input surge current, or switch-on surge is the

maximal instantaneous input current drawn by an electrical device when first turned on.

Alternating-current electric motors and

transformers may draw several times their normal full-load current when first energized, for a few cycles of the input waveform. Power converters also often have inrush currents much higher than their steady-state currents, due to the charging current of the input capacitance. The selection of over-current-protection devices such as fuses and circuit breakers is made more complicated when high inrush currents must be tolerated. The over-current protection must react quickly to overload or short-circuit faults but must not interrupt the circuit when the (usually harmless) inrush current flows. Transformer: When a transformer is first energized, a transient current up to 10 to 15 times larger than the rated transformer current can flow for several cycles. Toroidal transformers transformers, using less copper for the same power handling, can have up to 60 times inrush to running current. Worst-case inrush happens when the primary winding is connected at an instant around the zero crossing of the primary voltage (which for a pure inductance would be the current maximum in the AC cycle) and if the polarity of the voltage half-cycle has the same polarity as the remanence in the iron core has (the magnetic remanence was left high from a preceding half cycle). Inrush current can be divided in three categories categories:

Energization inrush current result of re-energization of transformer. The residual flux in this case can be zero or depending on energization timing. Recovery inrush current flow when transformer voltage is restored after having been reduced by system disturbance. Sympathetic inrush current flow when multiple transformer connected in same line and one of them energized. Motor: When an electric motor, AC or DC, is first energized, the rotor is not moving, and a current equivalent to the stalled current will flow, reducing as the motor picks up speed and develops a back EMF to oppose the supply. AC induction motors behave as transformers with a shorted secondary until the rotor begins to move, while brushed motors present essentially the winding resistance. Protection: Resistor in series with the line can be used to limit the current charging input capacitors. However, this approach is not very efficient, especially in high-power devices, since the resistor will have a voltage drop and dissipate some power. Inrush current can also be reduced by inrush current limiters. Negative-temperature-coefficient (NTC) thermistors are commonly used in switching power supplies, motor drives and audio equipment to prevent damage caused by inrush current. A thermistor is a thermally-sensitive resistor with a resistance that changes significantly and predictably as a result of temperature changes. The resistance of an NTC thermistor decreases as its temperature

increases. 6. Brief Explain about clearance is used as a basic insulation, protective separation and functional insulation? The normal operating conditions of the equipment, but also possible failure conditions, expected failure, and environmental influences such as temperature, altitude, pollution, and humidity. Safety standards have clear statements and regulations on manufactured equipment and parts to provide safe and high-quality products to endusers. To achieve electric shock protection, electronic equipments must have an effective insulation method, which can be divided into clearance and creepage distance and solid insulation materials. Basic clearanc clearance: e: Clearance: In the "line of sight" distance or the shortest air path between two conductors. The shortest distance that can achieve insulated through the air. insulation methods include meeting the requirements of distance and solid insulating materials also. If the gel materials used as insulation, the characteristic needs to be evaluated such as flammability, RTI, thermal conductivity, pressure resistance, and so on. Protective separation: Classes of equipment with respect to protection from electric shock. There is no dangerous voltage, and this energy does not cause pain or injury. The equipment has protection against electric shock, in addition

to basic insulation, there is supplementary insulation or provide reinforced insulation. This type of equipment does not provide protective grounding, but itself can provide protection from electric shock. Class I equipment In addition to basic insulation, it also includes additional protective measures. If the basic insulation fails, the external wires connect to the protective earthing conductor to conduct dangerous currents to the earth. Class II equipment The equipment has protection against electric shock, in addition to basic insulation, there is supplementary insulation or provide reinforced insulation. This type of equipment does not provide protective grounding, but itself can provide protection from electric shock. Class III equipment There is no dangerous voltage, and this energy does not cause pain or injury. Insulation type Insulation type can be defined as standards for five different purposes: 1.Basic insulation Single-layer insulation can provide users with basic protection against electric shock. 2.Double insulation Double insulation includes both basic insulation and supplementary insulation. 3. Functional insula insulation tion

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. 4. Reinforced insulation A single-layer insulation system can reach the level of protection against electric shock equivalent to double insulation. 5. Supplementary insulation The second layer of insulation independent of the basic insulation can protect the user from dangerous voltage when the basic insulation fails. Functional insula insulation: tion: The path under consideration includes parallel or converging-sided grooves with any depth and width less than X mm. The clearance and creepage are directly measured across the groove. The path under consideration includes parallel or converging-sided grooves with any depth and width equal to or greater than X mm. The clearance is the distance of the "line of sight", and the creepage distance path follows the contour of the groove. The path under consideration includes V-shaped grooves with an internal angle less than 80° and a width greater than X mm. The clearance is the "line of sight" distance, and the creepage distance path follows the contour of the groove but "short-circuits" the bottom of the groove by X mm link. The path under consideration includes rib-shaped protrusions, the clearance distance is the shortest air path over the top of the protrusions, and the creepage distance along the surface follows the

rib-shaped protrusions. The path under consideration includes an uncemented joint width of the groove on one side less than X mm, and the other equal to or greater than X mm. The clearance distance on the left is the distance of the "line of sight", and the creepage distance path follows the contour of the groove. The clearance distance and creepage on the right is the distance of the "line of sight".

7. Explain about Human interface with electricity? The electrical properties of biological tissues and cell suspensions determine the pathways of current flow through the body and, thus, are very important in the analysis of injuries by electric current and a wide range of biomedical applications such as functional electrical stimulation and the diagnosis and treatment of various physiological conditions with weak electric currents, radio-frequency hyperthermia, electrocardiography, and body composition. Electric shock occurs upon contact of a (human) body part with any source of electricity that causes a sufficient current through the skin, muscles, or hair. Typically, the expression is used to describe an injurious exposure to electricity. A sustained electric shock from AC at 120 V, 60 Hz is an especially dangerous source of ventricular fibrillation because it usually exceeds the let-go threshold, while not delivering enough initial energy to propel the person away from the source. However, the potential seriousness of the shock depends on paths through the body that the currents take. Death caused by an

electric shock is called electrocution. Three primary factors affect the severity of the shock a person receives when he or she is a part of an electrical circuit:  Amount of current flowing through the body (measured in amperes)  Path of the current through the body  Length of time the body is in the circuit  Other factors that may affect the severity of the shock are:  The voltage of the current  The presence of moisture in the environment  The phase of the heart cycle when the shock occurs  The general health of the person prior to the shock  How quickly the person is treated.  Shock-related injuries include burns, internal injuries, and injuries due to involuntary muscle contractions.

BURNS The most common shock-related injury is a burn. Burns suffered in electrical incidents may be one or more of the following three types: Electrical burns cause tissue damage, and are the result of heat generated by the flow of electric current through the body. Electrical burns are one of the most serious injuries you can receive and should be given immediate attention. INTERNAL INJURIES

Excessive electricity flowing through the human body can cause serious damage to internal organs. Resulting medical problems include haemorrhage (or internal bleeding), tissue destruction, and nerve or muscle damage. These internal injuries may not be immediately apparent to the victim or observers; however, left untreated, they can result in death. CAUTION  Don't touch the person with your bare hands if he or she is still in contact with the electrical current.  Don't get near high-voltage wires until the power is turned off. Stay at least 20 feet away — farther if wires are jumping and sparking. Don't move a person with an electrical injury unless the person is in immediate danger.

8. Explain the causes & effects of electrical fire & explosion? Most electrical fires are caused by faulty electrical outlets and old. Running cords under rugs is another cause of electrical fires. Electrical fire cause: l; Faul...