Faraday's law of electromagnetism and Lenz's law

 

64 identical spheres of charge q and capacitance C each are combined to form a large sphere. The charge and capacitance of the large sphere is:

 

A battery of e.m.f. E and internal resistance r is connected to an external resistance R what is the condition for maximum power transfer and maximum heat produce is external resistance

Answer: When R=r Power on External Resistance will Maximum 

 

Electrical Earthing

 Earthing is defined as the connection to the general mass of earth by means of an earth electrode. An equipment is said to be earthed when it is electrically connected to an earth electrode.

The purpose of earthing is to avoid the risk of fire hazards which may arise due to the leakage current flowing to earth through some accidental path which is not intended to carry such current, and to eliminate the danger of serious injury from electrical shock to persons who may come in contact with the metal frames or metal enclosure etc., which may have become live due to the insulation failure. To Protect equipment buildings from LIGHTNING

EARTH ELECTRODE: A metal pipe or rod and metal plate or other conductor buried in the earth and electrically in contact with the general mass of used for wiring installation, viz, Pipe Earth, Rod Earth and Plate Earth.

According to I.S.S. the pipe electrode is to be of galvanised iron is not less than 38 mm. in diameter and 2.5 meter long. The minimum size of the road electrode is to be 16mm dia and 2.5m long. 19 m dia and 1.8m long are also commonly used, specially  for pole earthing of OH line. The top of the pipe or road is to be buried to depth of not less than 1.25m under the ground level.

The plate electrode is to be of GI or copper plate. The size of the GI plate is not to be less than 60cm×60cm×6.30mm and the size of the copper plate is not to be less than 60cm×60cm×3.15mm. they are to be buried in the earth with there faces vertical and their tops are to be not less than 1.5m, below the ground level

Indication for Full Charge Cell

 

The indication for full charge cell are follows:

Cell Color:

The color plates on full charge is deep chocolate brown for positive plate and clear slate gray for negative plate and the cell looks quite brisk and alive.

Gassing:

When the cell is fully charged, it freely gives Hydrogen in Cathode and Oxygen in Anode, The process is known as GASSING. Gassing at both plates indicates that the current is no longer doing any useful work and hence should be stopped. Moreover, when the cell is fully charged the electrolyte is assumes a milky appearance.

Voltage:

The voltage ceases to rise when the cell becomes fully charged. The value of the voltage of a fully charged cell is a variable quantity. being affected by the rate of charging, the temperature and specific gravity of the electrolytic etc. The approximate value of emf is 2.1V or so.

Specific Gravity of the Electrolyte:

A third indication of the state of charged of a battery is given by the specific gravity of the electrolyte. We have seen from the chemical equation, that during charging the density of electrolyte decreases due to other production of water. Where it increases during charging due to the absorption of water. The value of density when the cell is fully charged is 1.21 and 1.18 When discharged up to 1.8V. Specific Gravity can be measured with a suitable hydrometer which consists of a float, a chamber for the electrolyte and a squeeze bulb.

to know about Primary and Secondary Battery- click here

to know about Battery Charging – click here

to know about Battery Ratings - click here

Resistance problem Physics Electricity RING

 

what is a Fuse?

 Fuse is an electrical safety device that operates to provide overcurrent Protection of an electrical circuit.

Fuse is a pices of wire of a metarial with very low melting point. When a high current flows through the circuit due to overload or short circuit, the wires gets heated and melt, as a result the circuit is broken and the current stop flowing.

Fuse wire

Fuse wire made of lead and tin alloy (63 % tin and 37% lead) having low melting point, Specific resistance is more than aluminium and  copper, so that as result resistance of short and thin fuse is more than connecting wire (basically copper and aluminium).

Its permits current upto its safe limit to passes through it, but an excessive current melt it so circuit will break.

Melting point of fuse wire is about 400 C where copper is 1080 C and aluminium is 660 C

A cell supplies a current of 1.2 A through two resistor each of 2 Ω connected in parallel.When the resistor are connected in series, it supply a current of 0.4 A. Calculate : the internal resistance and emf

 

Relation between electricity and Magnetism

We know that when an electric current flowing though a conductor a magnetic field is brought into existence in the space surrounding the conductor. it can say that when electrons are in motion they produce magnetic field. 

 

when a magnetic field embracing a conductor moves relative to the conductor it produces a flow electrons in the conductor. This phenomenon whereby an e.m.f and current is induced in any conductor which cut across or cut by a magnetic flux is known as ELECTROMAGNETIC INDUCTION.

 HISTORY OF MAGNETIC INDUCTION:

After discovery of that electric current produces  magnetic field, scientist are trying to search for the converse phenomenon from about 1821. The problem they put themselves was - how to convert Magnetism to Electricity. It is recorded that Michael Faraday ( A English Physicist and Chemist) was in the habit of walking about with magnets in his pocket so as constantly remind him of the problem to solve.

After Nine year of continuous full phase research and experiment he succeeded in the producing electricity by converting magnetism. In 1831 he formulated basic laws underlying the phenomenon of electromagnetic induction, after that these know by Faraday's Law. Motor, Generator, Transformer, Induction cooker and many other apparatus based on this law.

Resistance Problem Solve technic 1

Trickle Charging

TRICKLE CHARGING

When a battery is kept entirely as an emergency condition, it is essential to be fully charged and ready for service in emergency.

Due to Leakage action and other open circuit losses, the battery deteriorates even when idle or open circuit. So, to keep it fresh, the battery kept in Trickle Charge. 

The rate of Trickle Charge is small and just sufficient to balance open circuit losses.. 

Examples of Trickle Charge:

a standby battery for station bus bar capable of giving 3000 A for 1 hr having normal charging rate 600 A, but continuous trickle charge of 1.5 A or so will keep the cell fully charged and in perfect condition. when any emergency situation occurred battery can be use, after discharged the battery it is recharged at its normal charging rate and then kept it on continuous trickle charge. 

FACT - FLEXIBLE A.C. TRANSMISSION SYSTEM

FACT

(FLEXIBLE A.C. TRANSMISSION SYSTEM)

INTRODUCTION: 

  FACTS  A flexible alternating current transmission system (FACTS) is a system composed of static equipment used for the AC transmission of electrical energy. It is meant to enhance controllability and increase power transfer capability of the network. It is generally a power electronics -based system.

A FACT is defined by the IEEE as "a power electronic based system and other static equipment that provide control of one or more AC transmission system parameters to enhance control-ability and increase power transfer capability.

For a time being let us forget the word FLEXIBLE, we are left with A.C Transmission System. In power system, there are various stages like Generation, Transmission & Distribution. Transmission can be done in both A.C & D.C. We are all aware of the advantages & disadvantages of A.C & D.C transmission system but all over it is seen that D.C transmission system has an upper hand over A.C transmission system due to numerous reasons.

In-spite of this in Northern Oregon, the 1^st FACTS installation was adopted at the C.J. Slatt sub-station. The answer is hidden in the word “FLEXIBLE”. FACTS technology can be used to optimize existing electrical transmission system & provides flexibility to it.

At present, electrical demands are not steady, but fluctuate widely with customer needs. Static transmission lines cannot quickly adapt to these changes which result in voltage losses to customers. Reduced voltages & blowouts can also damage equipment. FACTS technology includes software that responds to changing utility conditions & optimizing system performance.

ABOUT FACTS:

A flexible A.C. transmission system (FACTS) is a combination of hardware and software installed in power transmission substations designed to improve capacity and reliability. AC refers to alternating current the electrical power supplied by electrical utilities to homes and businesses. FACTS technology can be used to optimize existing electrical transmission systems and often prevent or delay construction of new transmission systems.

Electric utilities face continued demands for greater capacity as customers consume greater quantities of electricity. Conservation programs, higher efficiency appliances and lighting, and smarter consumer electronics can slightly reduce electrical use. Environmental concerns for overhead electrical lines, magnetic fields and damage from new construction can delay new equipment construction. A flexible AC transmission system can provide better performance of existing transmission lines, improve power quality and reduce electrical losses.

Installation of FACTS equipment in series, or in-line, with the transmission lines is used to control system voltage. Equipment designed in shunt, or parallel across transmission lines, controls current or electrical flow. FACTS include software, capacitors, voltage regulators and other equipment that manages the electrical system.

Increasing development and population density can make construction of new transmission equipment difficult. FACTS technology is compact and can be installed within the existing footprint of a substation or electric transmission facility. Existing transmission lines carry higher loads without overheating or exceeding their rated power limits. Customers typically see improved electric supply quality and reliability.

FACTS technology helps us to provide uninterrupted flow of power as is not possible in case of D.C. system & thus the installation of rectifiers, inverters; D.C. switchgear & circuit breakers are obsolete & does not cause harmonics injection in the system. It improves the capacity of existing electrical transmission system.

Instrument and Measurement Transformer

In dc circuit when large current are to be measured its normally use low range ammeter with suitable (low resistance) shunt connected in parallel. when large voltage are to be measured use low range voltmeter with high resistance  connected in series. But this method is not convenient for practical use for AC voltage and current instruments.

For this purpose specially constructed with high accuracy Instrument Transformer or Measurement Transformer are used.  Their purpose is to reduce line current or voltage to a value small to be easily measured with meters of moderate capacity.

Instrument Transformer are two in types:

1. CURRENT TRANSFORMER (CT)-    For measuring large alternating current (AC)
2. POTENTIAL TRANSFORMER OR VOLTAGE TRANSFORMER (PT/VT) -   For measuring large Voltage (AC)

CIRCUIT DIAGRAM OF CT-PT:

ADVANTAGE OF INSTRUMENT TRANSFORMER:

(1)  The cost of the instrument or meter together with transformer is less than the instrument alone if it installed for high voltage.

(2)  The instrument is installed from the line voltage, hence it can be grounded.

(3)  If necessary several instrument can be operated from a single transformer for that power consumption is to be low and cheap in cost.

(4) For extension on A.C circuit, instrument transformer are more desirable than shunt for current and multiplier for voltage measurements.

they are as follows:

(a) Range extension is limited by the current carrying capacity of the shunt. that is upto few hundred amperes at all.

(b) If current is high voltage, instrument insulation is a big problem but in case instrument transformer its solved out.

(c) Use of multipliers above 1000 become a impractical.

(d) Time constant of the shunt closely match the time constant of the instrument. hence, a different shunt is need for each instrument, but in this case  If necessary several instrument can be operated from a single transformer for that power consumption is to be low and cheap in cost.

SHOULD KNOW BEFORE USE INSTRUMENT TRANSFORMER:

In using Measurement or Instrument Transformer  for Current and Voltage measurement, firstly we have to know the ration of primary and secondary voltage or current (Transformer Ratio). this ratio gives us multiplying factor for primary values from the instrument reading on the secondary side.

For energy power measurement  we also have to know PHASE ANGLE between primary and secondary current or voltage. its necessary for correction to the meter reading.

Brush-Less DC Motor

INTRODUCTION:  BRUSH-LESS D.C. MOTOR

• Classical DC motors are no doubt good and simple but inefficient in some ways.
• Although dc motors possess good control characteristics and ruggedness, their performance and applications are inhibited due to sparking and commutation problems.
• The Permanent Magnet Brushless DC (PMBLDC) motor .

MOTOR…

>> Converts electrical energy to mechanical energy.

ORIGIN...

>>  Nicola Tesla introduces electric motor in December 1889.

 >> He identifies the principle of rotating magnetic field.

MAIN PARTS OF BRUSHED MOTOR:

Effect of Electric Current on Human Body

At first Bruner (1967) states that "The threshold of perception  of electric shock is about 1 mA." At this level a tingling sensation is felt by the subject when there is a contact with an electrified object through skin. If the magnitude of electric increase the sensation of tingling gives way to contraction of muscles. The muscular contraction increase as current is increase. Finally a value current is reached at a point that the subject cannot release his grip on the current carrying conductor.
The maximum current at which the subject is still capable of releasing a conductor by using muscles directly simulated by the current is called LET GO CURRENT.
The value of this current is significant as an individual can withstand  without serious after effects, repeated exposures to his LET GO CURRENT for at least the time required for him to release the conductor.  Currents slightly in excess of LET GO CURRENT would not permit the individual to release his grip from the current carrying conductor.
Based on the experiment conducted on male and female it is generally accepted that the safe LET GO CURRENT approximately 9 mA for male and 6 mA for female.
At current level higher than the LET GO CURRENT the subject loses ability to control his own muscle actions and he/she unable to release grip on current carrying conductor. These currents are very painful. This type of accident called HOLD ON TYPE accident. current rage for this type accident is about 20-100 mA. These type of accident may cause physical injury due to powerful contraction of the skeletal muscles. the heart and respiration function usually continue because of uniform spread of current through out the whole body.
If current contract intact skin and passes through trunk ( about 100 mA or above) there is a likelihood of pulling the heart into ventricular fibrillation. In this accident the rhythmic action of heart ceases, pumping actions may stops and the pulse disappear.  the brain begins to die as it is robbed of its supply of oxygenated blood.
At a very high Currents is about 6 A or above, there is a danger of temporary respiratory paralysis and also of serious burns.
The tolerable current for human body man to man may vary. this reports is just got from many experiments.

HVDC Transmission WHY?

In initial stages DC used to be employed for Generation, Transmission and distribution of electric power. First DC 110 Volt Central Electric Station was installed by Edison in New York in the year 1882. After Introduction of Transformer and single phase, Three Phase AC system the situation changed, in favor of AC.

WHY HVDC:  ADVANTAGES OF HVDC

For many reason such as facility of transformation of voltage from one to another, better performance AC power become popular and starts to use widely in all cases transmission, generation, distribution.

But the supporter of DC did not forget the advantage of DC transmission and extensive research has been carried out in this field. As a result it has staged a sort of come back to the field of electric power transmission at a high and extra high DC voltages.

HISTORY:

Mechanism of Lightning

HISTORY:

Benjamin Franklin performed a famous experiment of FLYING KITE in thunder cloud in the year 1745. Before his discovery the lightning used to be considered to be "ACT OF GOD". He also proved that the lightning stroke is because of the discharge of electricity. He also invented protection of lightning. Lightning rods for fixation on tall buildings and grounding for their protection from lightning stroke. Thus Benjamin Franklin is a great scientist in this field.

WHAT IS LIGHTNING? 

Lighting is a huge spark which is due to electrical discharge taking place between the clouds within the same cloud or between the cloud and earth or ground. Large number of discharge occur between or within clouds than earth. And enough of them terminate on to the earth and result in serious hazards. This discharge occurs between electrically charged regions of a cloud (called intra-cloud lightning or IC), between two clouds (CC lightning), or between a cloud and the ground (CG lightning).

Dielectric Strength and Breakdown Voltage

Dielectric strength and Breakdown Voltage is very important for design high voltage Transformer, Motor, Generator. and also important for high voltage transmission line and FACTS (Flexible AC Transmission).

Breakdown Voltage:

An Insulator or Dielectric Material there are no free electrons to electric conduction, as in normal condition there are no current can be flowing through it. However when the voltage applied between them increase and increase, such an insulator exceeds a certain value,  it break down and allow a heavy electric current to flow through it, the value of this current much larger than the usual leakage current may be as equal to short circuit current. for solid insulator its get cracked also. this certain value of the voltage is Breakdown Voltage.

Breakdown Voltage of an insulator is the minimum voltage required to break it down.

Primary and Secondary Battery

Electric battery consists of a number of electro-chemical cells, which  may connected in either parallel or series. electrical battery is a source of DC voltage,

DEFINATION OF CELL: 

a cell is a basic unit of a battery. it is defined as power generating device, which can converts storage chemical energy into electrical energy.

PRIMARY BATTERY: NON RECHAREABLE

If the stored chemical energy is constitutionally or inherently present in the chemical substances, its called primary cell or non-rechargeable cell. if the battery made up with these kinds of cells the battery is call PRIMARY BATTERY.

EX- zinc chloride cell, alkaline-manganese cell, metal air cell and Leclanche cell.

Limitation of HVDC

Although DC transmission has so many advantages over AC, but it will never fully overtake AC transmission. The problems and Limitations of DC transmission are given below:

MAINTENANCE OF LINE INSULATORS: HVDC

Maintenance of insulators in HVDC line is more than AC line.

VOLTAGE TRANSFORMATION: HVDC

Voltage transformation is not so easy in case of Dc. Hence is has to be accomplished on the AC side of the system. DC system cannot be employed for Sub Transmission and Distribution.

VERY COSTLY TERMINAL EQUIPMENT AND INSTRUMENT: HVDC

• The converter required at both end of the line are much more expensive than the conventional AC equipment.
• The converters have very little overload capacity and absorb considerable reactive power . The reactive power can be as high as 25% of true power.
• The converter produce lot of harmonics both on DC and AC side which may cause interference with the audio frequency communication lines. Filtering and Smoothing equipment are provide at the converter stations in order to remove ripples from the DC output. It is also possible to provide filter on AC side to absorb the harmonic currents. Thus there is considerable increase of cost of the converter substation.
• No reactive power can be transmitted by HVDC transmission system and therefore, equipment such as static or synchronous capacitors are installed at the receiving end to generate reactive power ( MVAR ) according to the demand of the load and converting apparatus.
• HVDC converters need complex cooling system.

CIRCUIT BREAKER SYSTEM: HVDC

Circuit Breaker system comprises several components including the main circuit breaker capacitors, reactors etc, and the total cost is likely to be several times of an AC circuit breaker for equivalent rating.

Circuit breaking in multi terminal Dc system is difficult and costly.

WHY HVDC TRANSMISSION LINE