Assignment *

*. Explain RLC parallel circuit.

Answer)

Consider a RLC circuit in which resistor, inductor and capacitor are connected in parallel to each other. This parallel combination is supplied by voltage supply, VS.

In parallel circuit, the voltage across each element remains the same and the current gets divided in each component depending upon the impedance of each component. That is why parallel RLC circuit is said to have dual relationship with series RLC circuit.

The total current, IS drawn from the supply is equal to the vector sum of the resistive, inductive and capacitive current, not the mathematic sum of the three individual branch currents, as the current flowing in resistor, inductor and capacitor are not in same phase with each other; so they cannot be added arithmetically.

2. Explain phasor representation in polar and rectangular form.

Answer)

Let V is the supply voltage. IS is the total source current. IR is the current flowing through the resistor. IC is the current flowing through the capacitor. IL is the current flowing through the inductor. θ is the phase angle difference between supply voltage and current.

For drawing the phasor diagram of parallel RLC circuit, voltage is taken as reference because voltage across each element remains the same and all the other currents i.e IR, IC, IL are drawn relative to this voltage vector. We know that in case of resistor, voltage and current are in same phase; so draw current vector IR in same phase and direction to voltage. In case of capacitor, current leads the voltage by 90 so, draw IC vector leading voltage vector, V by 90 . For inductor, current vector IL lags voltage by 90 so draw IL lagging voltage vector, V by 90 . Now draw the resultant of IR, IC, IL i.e current IS at a phase angle difference of θ with respect to voltage vector, V.

Simplifying the phasor diagram, we get a simplified phasor diagram on right hand side. On this phasor diagram, we can easily apply Pythagoras's theorem and we get,

3. Write a short note on RC and RL circuit with derivation.

Answer) RL Circuit:

Consider a simple RL circuit in which resistor, R and inductor, L are connected in series with a voltage supply of V volts. Let us think the current flowing in the circuit is I (amp) and current through resistor and inductor is IR and IL respectively. Since both resistance and inductor are connected in series, so the current in both the elements and the circuit remains the same. i.e IR = IL = I. Let VR and Vl be the voltage drop across resistor and inductor. Applying Kirchhoff voltage law ( i.e sum of voltage drop must be equal to apply voltage) to this circuit we get,

Derivation:

Apply Kirchhoff's voltage law in the above series RL circuit,

Rearranging the above equation,

Integrating both sides, we get,

Now integrate right hand side by using substitution method, Substituting the values we get,

We know that integration of,

So we get,

By applying limits we get,

Simplifying again,

Taking antilog on both sides,

We know that e ln x = x, so we get,

Moving the term containing 'i' on one side we get,

The term L/R in the equation is called the Time Constant, (τ) of the RL series circuit, and it is defined as time taken by the current to reach its maximum steady state value and the term V/R represents the final steady state value of current in the circuit.

RC Circuit:

A resistor–capacitor circuit (RC circuit), or RC filter or RC network, is an electric circuit composed of resistors and capacitors driven by a voltage or current source. A first order RC circuit is composed of one resistor and one capacitor and is the simplest type of RC circuit. Charge transport behaviour in various complex systems, including battery anodes and fuel cells can be described using models of many-element RC networks.RC circuits can be used to filter a signal by blocking certain frequencies and passing others. The two most common RC filters are the high-pass filters and low-pass filters; band-pass filters and band-stop filters usually require RLC filters, though crude ones can be made with RC filters.

The procedure for deriving the equation for the discharging capacitor is similar, though you have to use i = -dq/dt because dq/dt is negative for a discharging capacitor, by definition.

4. Explain types of wiring system.

Answer)

Different Types of Electrical Wiring Systems

The types of internal wiring usually used are

Cleat wiring

Wooden casing and capping wiring

CTS or TRS or PVC sheath wiring

Lead sheathed or metal sheathed wiring

Conduit wiring

1. Cleat Wiring

This system of wiring comprise of ordinary VIR or PVC insulated wires (occasionally, sheathed and weather proof cable) braided and compounded held on walls or ceilings by means of porcelain cleats, Plastic or wood. Cleat wiring system is a temporary wiring system therefore it is not suitable for domestic premises. The use of cleat wiring system is over nowadays.

2. Casing and Capping wiring

Casing and Capping wiring system was famous wiring system in the past but, it is considered obsolete this days because of Conduit and sheathed wiring system. The cables used in this kind of wiring were either VIR or PVC or any other approved insulated cables.

The cables were carried through the wooden casing enclosures. The casing is made up of a strip of wood with parallel grooves cut length wise so as to accommodate VIR cables. The grooves were made to separate opposite polarity. the capping (also made of wood) used to cover the wires and cables installed and fitted in the casing.

3. Batten Wiring (CTS or TRS)

Single core or double core or three core TRS cables with a circular oval shape cables are used in this kind of wiring. Mostly, single core cables are preferred. TRS cables are chemical proof, water proof, steam proof, but are slightly affected by lubricating oil. The TRS cables are run on well seasoned and straight teak wood batten with at least a thickness of 10mm.

The cables are held on the wooden batten by means of tinned brass link clips (buckle clip) already fixed on the batten with brass pins and spaced at an interval of 10cm for horizontal runs and 15cm for vertical runs.

4. Lead Sheathed Wiring

The type of wiring employs conductors that are insulated with VIR and covered with an outer sheath of lead aluminum alloy containing about 95% of lead. The metal sheath given protection to cables from mechanical damage, moisture and atmospheric corrosion.

The whole lead covering is made electrically continuous and is connected to earth at the point of entry to protect against electrolytic action due to leaking current and to provide safety in case the sheath becomes alive. The cables are run on wooden batten and fixed by means of link clips just as in TRS wiring.

5. Conduit Wiring

There are two additional types of conduit wiring according to pipe installation

1.Surface Conduit Wiring

2.Concealed Conduit Wiring

5.1 Surface Conduit Wiring

If conduits installed on roof or wall, It is known as surface conduit wiring. in this wiring method, they make holes on the surface of wall on equal distances and conduit is installed then with the help of rawal plugs.

5.2 Concealed Conduit wiring

If the conduits is hidden inside the wall slots with the help of plastering, it is called concealed conduit wiring. In other words, the electrical wiring system inside wall, roof or floor with the help of plastic or metallic piping is called concealed conduit wiring. obliviously, It is the most popular, beautiful, stronger and common electrical wiring system nowadays.

In conduit wiring, steel tubes known as conduits are installed on the surface of walls by means of pipe hooks (surface conduit wiring) or buried in walls under plaster and VIR or PVC cables are afterwards drawn by means of a GI wire of size if about 18SWG.

In Conduit wiring system, The conduits should be electrically continuous and connected to earth at some suitable points in case of steel conduit. Conduit wiring is a professional way of wiring a building. Mostly PVC conduits are used in domestic wiring.

The conduit protects the cables from being damaged by rodents (when rodents bites the cables it will cause short circuit) that is why circuit breakers are in place though but hey! Prevention is better than cure. Lead conduits are used in factories or when the building is prone to fire accident. Trunking is more of like surface conduit wiring. It’s gaining popularity too.

It is done by screwing a PVC trunking pipe to a wall then passing the cables through the pipe. The cables in conduit should not be too tight. Space factor have to be put into consideration.

Types of Conduit

Following conduits are used in the conduit wiring systems (both concealed and surface conduit wiring) which are shown in the above image.

Metallic Conduit

Non-metallic conduit

Metallic Conduit:

Metallic conduits are made of steel which are very strong but costly as well.

There are two types of metallic conduits.

Class A Conduit: Low gauge conduit (Thin layer steel sheet conduit)

Class B Conduit: High gauge conduit (Thick sheet of steel conduit)

Non-metallic Conduit:

A solid PVC conduit is used as non-metallic conduit now a days, which is flexible and easy to bend.

5. Explain earthing and its various types.

Answer)

Electrical Earthing

Definition:The method of connecting noncurrent carrying parts of the electrical equipment or the neutral point of the supply system to the earth through the wire having negligible resistance is called electrical earthing. Earthing protects the electrical equipment from lightning strokes and earth fault conditions. It provides the easiest path to the fault or leakage current to flow through it.

Types of Electrical Earthing

The electrical equipment mainly consists of two non-current carrying parts. These parts are neutral of the system or frame of the electrical equipment. On the basis of the earthing of these two noncurrent carrying parts of the electrical system earthing can be classified into two types.

Neutral Earthing

Equipment Earthing.

Neutral Earthing

Neutral earthing is defined as the earthing of the system neutral to ensure system security and protection. Neutral earthing is called the system earthing. In neutral earthing, the neutral point of the star-connected 3-phase windings of power transformers, generators, motors, the earthing transformer is connected to the low resistance.

Equipment Earthing

Equipment earthing deals with the earthing of noncurrent carrying parts (frame or metallic body) of the electrical equipment to ensure the safety of personnel and protecting against lightning. It also helps in earth fault protection.

Importance of Earthing

The earthing is essential because of the following reasons

Earthing provides the safety of the personnel from the electric shock. It insures that the non-currents carrying parts, such as equipment frames are always safe at ground potential even though the insulation fails.

Earthing is essential for the safety of the equipment and personnel against lightning and voltage surges, providing the discharge path for surge arrestors, gaps, and other similar devices.

It provides the ground connections for the ground neutral system.

It provides a means of positively discharging and de-energizing feeders or equipment before proceeding with maintenance on them.

Earthing can be done by electrically connecting the respective parts in the installation to some system of electrical conductors or electrodes placed near the soil or below the ground level. The earthing mat or electrode under the ground level have flat iron riser through which all the non-current-carrying metallic parts of the equipment are connected.

The contacting assembly is called earthing. The metallic conductors connecting the parts of the installation with the earthing are called electrical connection. The earthing and the earthing connection together called the earthing system.

6. Write a Short note on Sodium Vapour Lamp.

Answer)

A sodium-vapor lamp is a gas-discharge lamp that uses sodium in an excited state to produce light at a characteristic wavelength near 589 nm.There are two varieties of such lamps: low pressure and high pressure. Low-pressure sodium lamps are highly efficient electrical light sources, but their yellow light restricts applications to outdoor lighting such as street lamps. High-pressure sodium lamps produce a broader spectrum of light than the low-pressure lamps, but they still have poorer color rendering than other types of lamps. Low-pressure sodium lamps only give monochromatic yellow light and so inhibit color vision at night.

Low-pressure sodium

Low-pressure sodium (LPS) lamps have a borosilicate glass gas discharge tube (arc tube) containing solid sodium, a small amount of neon, and argon gas in a Penning mixture to start the gas discharge. The discharge tube may be linear (SLI lamp)[4] or U-shaped. When the lamp is first started, it emits a dim red/pink light to warm the sodium metal; within a few minutes as the sodium metal vaporizes, the emission becomes the common bright yellow. These lamps produce a virtually monochromatic light averaging a 589.3 nm wavelength (actually two dominant spectral lines very close together at 589.0 and 589.6 nm). The colors of objects illuminated by only this narrow bandwidth are difficult to distinguish.LPS lamps have an outer glass vacuum envelope around the inner discharge tube for thermal insulation, which improves their efficiency. Earlier LPS lamps had a detachable dewar jacket (SO lamps).[5] Lamps with a permanent vacuum envelope (SOI lamps) were developed to improve thermal insulation.[6] Further improvement was attained by coating the glass envelope with an infrared reflecting layer of indium tin oxide, resulting in SOX lamps

High-pressure sodium

High-pressure sodium lamps (sometimes called HPS lights) have been widely used in industrial lighting, especially in large manufacturing facilities, and are commonly used as plant grow lights. They have also been widely used for outdoor area lighting, such as on roadways, parking lots and security areas. Understanding the change in human color vision sensitivity from photopic to mesopic and scotopic is essential for proper planning when designing lighting for roadways.High-pressure sodium lamps are quite efficient about 100 lm/W when measured for photopic lighting conditions. The higher power lamps (600 W) have an efficiency of 150 lm/W.As the high-pressure sodium arc is extremely chemically reactive, the arc tube is typically made of translucent aluminum oxide. This construction led General Electric to use the tradename "Lucalox" for their line of high-pressure sodium lamps.Xenon at a low pressure is used as a "starter gas" in the HPS lamp. It has the lowest thermal conductivity and lowest ionization potential of all the non-radioactive noble gases.

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