Induction stoves work on the principle of induction.  The stove contains a coil which is excited by a high frequency AC supply.  Above this coil is a plate.  The vessel to be heated is placed on this plate.  The alternating magnetic field set up by the coil induces currents in the vessel surface.  This current generates heat as it circulates in the vessel. 

In theory, this principle should work for all metals.  However, the heating is not efficient in non-magnetic materials such as aluminium, copper, etc.  This is because non-magnetic materials such as aluminium and copper have a lesser skin effect.  It means that the current can circulate for a greater depth in the vessel walls.  This reduces the surface resistance which is important for heat to be generated.  Hence, induction heating is not efficient in non-magnetic materials such as copper and aluminium.

All metal induction stoves are in the process of development which can heat vessels of all  metals.  Non-magnetic metals can also be heated, though, at a lesser efficiency. 

The light which falls on a solar cell first makes contact with the shiny surface of the cell.  This results in the light getting reflected.  Thus, this the energy of the light rays are also lost along with the reflected rays.  Hence, it is essential that all photovoltaic cell have an effective anti-reflective coating which prevents the light from getting reflected. 

A reflective coating ensures that the energy from all the rays incident on the photo voltaic cell is made available for conversion into electricity thereby increasing the efficiency of the cell.

Anti reflective coatings are similar to the coatings used on camera lenses.  They interfere with the process of reflection by creating another light wave which is out of phase with the reflected wave.  This causes the reflected waves to cancel each other out and no energy is lost through reflection. This phenomenon is called destructive interference.

The thickness of the anti-reflective coating is critical.  It should be perfectly selected so that the light from the surface of the anti-reflective coating is out of phase with the light reflected from the surface of the photocell. 

Another method of preventing light from getting reflected off the surface is by texturing the surface of the photocell.  This causes the light to get reflected multiple times by the textured surface and a greater amount of the energy in light is captured by the photo cell.  This is called "light trapping"

The Electrolyte in a lead acid battery is sulphuric acid mixed in water.  During the discharging process, the sulphuric acid dissociates into water and sulphate which is deposited in the electrodes. 

When the battery is charged, the sulphate recombines with the water to form sulphuric acid.  The specific gravity of the electrolyte thus varies from 1.1 to 1.3 depending on the level of charge. Over a period of time, there is a chance of the water in the electrolyte evaporating. 

This may lead to a change in the level of the electrolyte along with a variation in the specific gravity.   This may result in a deterioration in the battery performance.   In such situations, it may be necessary to add water to the electrolyte.

Only distilled and demineralized water should be used, as ordinary water contains minerals such as calcium, magnesium, etc which can cause deposits in the electrodes and affect the battery's life and performance. The vent caps of the batteries need to be removed.  Once, the vent caps are removed, the plates will be visible.  See if the plates are completely covered by the electrolyte.  Add water if the level of the electrolyte is low and the plates are exposed.  Take care that excess water is not added this will result in an "overflow".  The acid can overflow and cause damage.

Safety Precautions
Follow the manufacturer's instructions before topping the electrolyte with water.  Always wear protection goggles for your eyes.  The acidic electrolyte is corrosive.  Take care that you do not accidentally come in contact with it.  The sulphurous gases which may escape the electrolyte are explosive.  Do not smoke near the battery as a spark can trigger an explosion.

Fluke CNX 3000 Wireless Test Tools is a set of measuring instruments which can be used for making remote measurements of electrical parameters.  The set consists of a central multimeter which can communicate with measuring probes wirelessly.  Fluke says that this enables simultaneous measurements of currents and voltages.  The multimeter can collect signals within a radius of 20 metres. 

The data can be read on a computer screen using a wireless PC adapter.  The data is also recordable.  This measuring tool set would be ideal for process industries which require simultaneous measurement of current at different points in the system. 

Video from Fluke

Photo-Voltaic energy is an ideal choice of power for locations which are far from the electric grid. 

In many countries, it is not feasible to lay power lines to certain far-flung areas as there may be a small no of consumers.  Investing huge amounts of money in laying powerlines and maintaining them may not be economically viable.  Providing power by means of diesel generators may be expensive.

A practical and environmentally friendly source of power are Solar Cells.  Solar cells convert the sunlight into electricity.

Solar Cells work on the principle of the photo-voltaic effect.  When light falls on certain materials, the atoms absorb the photons and release an electron.  These electrons create an electric potential.  When an external circuit is connected, a current flows.  The direct conversion of sunlight to electricity makes the modules compact without any emissions or residue.  Photovoltaic cells are thus popular for powering small electronic devices  and lighting.

Photovoltaic modules have been used for powering aircraft, cars and even the international space station.

Photovoltaic modules are made of materials such as silicon, cadmium telluride, gallium arsenide, etc.  The basic silicon cell consists of a NP junction. When light is incident on the PN junction, electron-hole pairs are produced.  This creates a voltage across the junction.  When an external load is connected, current flows.

Photovoltaic cells are usually covered by an anti-reflective coating to prevent the incident light from being reflected away.

Current Photovoltaic cells can achieve effiency of around 30%.  Cells with concentrated sunlight focused on them can achieve still higher efficiencies.

It would be interesting to note that a solar cells is just an LED in reverse.  An LED (A light emitting diode) functions by emiting light when a voltage is applied, while the solar cell generates a voltage when light is incident.  A solar cell is specially designed to have a wide PN junction which can collect more light.   

The solar cell technology needs further development before it can be widely used for base power generation.  It is hoped that further research with new materials will improve efficiency and lower the high initial capital costs. 

The df/dt protection is used to identify abnormal changes in system frequency and take remedial actions in order to prevent generator overload and the resulting blackout.  The df/dt operates faster than ordinary under frequency relays as it is able to predict the under frequency much earlier.   

df/dt relays are also known as ROCOF relays (Rate Of Change of Frequency Relays) The df/dt is usually wired to a load shedding system which trips select breakers to isolate loads. 

The df/dt functions by measuring the rate of change of frequency.  When the frequency changes too fast, it is an indicator of a forthcoming under frequency.  The setting of the df/dt relay is in Frequency/Time in seconds. e.g. 0.3Hz/second or 0.4 Hz/.5 seconds.

Some manufacturers provide a more reliable setting involves specifying two frequency set points and the time taken for the frequency to cross the two limits.  For instance, a df/dt relays can be programmed to operate if the system frequency crosses 48.5 Hz and 48 Hz in 0.4 seconds

The Factor of Earthing in a three phase system is defined as the ratio of the phase voltage (phase to earth voltage) on a healthy phase during the fault at the rated frequency to the phase voltage of the healthy phase during normal situation.  

When an earth fault occurs in one of the phases of a three phase system, the voltage vectors are distorted.  The neutral shifts in the direction of the fault phase.  This causes the voltage in the other two healthy phases to rise. 

The factor of earthing determines the rise of voltage in the healthy phases when one of the phases has a earth fault.

The factor of safety is 100% for an isolated neutral (floating neutral) system.  It is 80% for an effectively earthed system while it is 57.7% for a solidly earthed system.

The factor of safety is an important parameter while performing an insulation coordination in a system.  

Thermistors are temperature sensors which have a sensing element usually made of polymers or ceramics.  Thermistors function by changing their resistance when the temperature increases. 

Thermistors find wide application in the industry, in automobiles and in electric appliances.  Their small size makes them ideal for use in electronic circuit boards and digital thermostats.

The principle of the Thermistor was first discovered by Michael Faraday in 1833.  However, the first practical thermistor was constructed by Samuel Ruben in the year 1930.

When the temperature of the Thermistor changes, the resistance of the Thermistor also changes.  The change can be either positive or negative.  Thus, we have PTC Thermistors (Positive Temperature Coefficient) and NTC Thermistors (Negative Temperature Coefficient).

NTC thermistors are used in temperature measurement while PTC thermistors are used in Electric current control. 

Thermistors are generally formed into a disc or bead and sealed in an enclosure made of plastic or gas.

Thermistors are highly accurate and have a quick response.  However, they have a limited range of measurement.  Another downside is that they do not have a linear response. 

Thermistors have high stability and are not affected by ageing.  This means that they need not be calibrated for long periods of time.    They are cheaper, rugged and are easy to produce. 

Pressure is an important physical quantity to be measured in industrial systems.  

Transducers are one of the popular means of measuring Pressure.   Pressure Transducers work by converting the pressure signal into an analog electric signal usually a 4...20 mA signal. 

Pressure Transducers can be designed using many principles.  The most widely used of these are the capacitive and the Piezo-resistive transducer. 

Capacitive Pressure Transducers
The capacitive transducer consists of a diaphragm which works as one of the plates of a capacitor.  A fixed conductive surface acts as the other plate.  The permittivity of the space in between these plates varies as the diaphragm moves in response to the measured pressure. 

This change in capacitance is measured as the process pressure.  

The capacitive transducer is used to measure very low pressure values.  Very Accurate measurements are possible using the capacitive pressure Transducers. 

Piezo Resistive Pressure Transducers
Piezo Resistive Transducers work on the principle of the piezoresistive effect.  The piezo resistive effect refers to the change in the resistivity of a material in response to force or pressure.  The piezo resistive sensor is used widely in biomedical applications as well as in the automobile industry. 

Piezo Resistive Pressure Transducers
These sensors are low in cost and have high sensitivity.  They can be manufactured for a wide range of pressure measurement.

Piezo Resistive Pressure transducers consist of a diaphragm which is made of silicon.  The diaphragm bends due to the pressure of the system to be measured. 

Mounted on the diaphragm are four piezo-resistors which are usually arranged in the form of a Wheatstone bridge.  When the diaphragm bends due to the pressure, the piezoresistors are subject to either tensile or compressive stress.  This results in a change in resistance values which is measured through the Wheatstone bridge formation and is scaled as a pressure measurement

Inductive Proximity sensors find wide application in the field of industrial instrumentation.  These sensors are extremely popular as they are reliable, robust and have a simple construction.  Inductive Proximity sensors are used to measure speed, detect motion and sense the position of objects.

The inductive proximity sensor consists of an oscillator, a coil and a detector.  The oscillator develops a high frequency signal which is fed to the coil. 

The high frequency signal develops a corresponding high frequency magnetic field at
the tip of the sensor.  When a metallic object comes in front of the sensor, eddy currents are induced in the object.  This acts as a load on the oscillator and the amplitude of the high frequency output drops.  This drop in the voltage is detected by the detector unit which causes the switching on or off of a transistor.  This results in a change of voltage level which is interpreted as a digital signal 0 or 1.

The inductive proximity principle can also be applied to speed sensors.  In speed measurement, the inductive proximity sensor is placed near the rim of a rotating object. The rotating object has a number of teeth along its rim.  When a tooth passes near the inductive proximity sensor, a pulse is produced. 

This sequence of pulses can be converted into an analog signal can be measured as the speed of the device.

Sympathetic Tripping refers to the phenomenon in Electrical Systems when a protective device in a healthy section of the system operates for a fault in another section of the system.  Sympathetic tripping results in unnecessary loss of power for healthy equipment. 

There are many causes for sympathetic tripping.  The most common reason is undervoltage which occurs across the system when there is a heavy current due to a short-circuit or an earth fault. 

Another reason for sympathetic tripping can be the flow of capacitive currents in the healthy feeders when one of the feeders gets grounded. 

In Transformers and Generators the Differential relay sometimes operates for an overcurrent which is outside its zone.  This is due to the dc component of the earth fault current.

Preventing Sympathetic Tripping   

Sympathetic Tripping can be prevented by designing smaller feeders with the total loads equally balanced across the different feeders

Reducing the fault level can result in lesser currents in the event of faults.  The fault level can be reduced by the use of current limiting reactors which increase the impedance.

Extreme Inverse settings in IDMT relays can also help the relays discriminate between sympathetic overcurrents and genuine faults. 

Increasing fault clearing times in the faulty feeders reduces the duration of the undervoltage across the system. 

Modern Differential relays have an inbuilt dc filter which prevent sympathetic tripping due to dc components during earth faults.

Useful Videos on Power Transformer Testing by OMICRON

Lighting within the home currently accounts for about 8% of energy bills in the UK. Incandescent and tungsten bulbs have been a standard feature of electrical use since the 19th century, but are gradually being phased out in favour of more energy saving options that save consumers money and benefit the environment. A number of different options are available from online electrical wholesalers or high street retailers, from energy saving bulbs to compact fluorescents, LEDs and dimmers that can help to cut costs and generate more efficient energy. Moreover, these bulbs can be combined with a number of simple energy saving practices that can be followed within the home.

Types of Bulbs and their Benefits

Early incandescent and halogen bulbs relied on a tungsten filament, and remain the norm for most homes. Halogen bulbs are more efficient than incandescent forms, but still lag behind energy saving bulbs in terms of efficiency. The UK Government have promoted schemes to gradually phase out the use of older bulbs, while encouraging a switchover to energy saving lighting options. Energy saving bulbs and lights remains fairly expensive compared to older bulbs, but have the benefit of lasting longer, and reduce electricity bills.

A basic energy saving bulb is 5 times brighter than a standard bulb, and uses 80% less power. If used responsibly, some energy saving bulbs can have a 10 year life span. This length is based on using certain bulbs for three hours a day in parts of the home, and can be an ideal solution for rooms that are not used very often. Energy saving bulbs can result in 75-80% energy savings, and use 4 times less of the wattage of standard bulbs.

Other energy saving bulb options include compact fluorescents. These bulbs use an alternative gas charging method to standard bulbs, and use 20 to 25% less electricity. Again, higher costs for initial purchases can be offset by their long lasting potential and greater energy efficiency.

Another option is to invest in LEDs, or light emitting diodes. These represent strips of about 36 to 48 lights, which when installed can generate 50,000 hours of capacity. Representing 50 times as much capacity as a standard incandescent light, small LED arrays also act as a stylish alternative to hanging fittings, bulbs and lamps within rooms, and are particularly recommended for kitchens.

These lights emit less carbon dioxide than standard incandescent lights, and can consequently help conserve energy and the environment. When looking for energy saving bulbs always check for an Energy Saving Trust Recommended label, or an Energy Related A tag. Energy saving bulbs can also be recycled, and form part of the EU’s Waste Electrical and Electronic Equipment Initiative.

Other Tips

As well as investing in energy saving bulbs, you can also follow some simple steps when using lights in the home. The most basic solution remains turning lights off when they are not being used. Moreover, try to use lights for particular roles, with bulbs being turned off when watching a brightly lit television or computer. If reading, a single lamp is more efficient than keeping a whole room’s lights on. Dimmer switches are also useful in this regard for regulating the amount of light in a room, and can result in 4-9% of electricity savings.

About the author
Serena is a copywriter for a leading supplier of energy saving discount electrical supplies at Discount Electrical. In her spare time she writes various other blogs online on numerous other subjects such as automotive, health and the theatre.

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Schweitzer Engineering Laboratories
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Selinc Engineering Laboratories
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Schaffer GmBH
Isolation Transformers for PCBs up to 60VA  for screw fixture.

Victron Energy
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Knel Control
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Manufactures single phase isolation transformers up to 2 kVA and three phase isolation transformers up to 9 kVA

General Electric
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Capacitor Trip modules are used in breaker circuits to provide a source of back up power for trip operations in the event of the failure of the breaker control supply.  The capacitor Trip device is usually used in switchgear systems which use an AC control supply. 

If the control supply of a breaker panel fails during operation, the operator will not be able to operate the breakers from a remote location.  This would also compromise the protection scheme as the breaker will not trip even if a command is sent by a protection relay. 

The capacitor trip module consists of a capacitor which stores charge.  This charge is enough to trip the breaker for a certain number of times, say 5 times.  This ensures that the breaker can trip even if the control supply fails during operation.  Capacitor Trip modules are available for both AC and DC control systems. 

Grounding Transformers are used in Ungrounded systems to provide a earth point.  Grounding Transformers are classified into two types

1) Zig Zag Transformers and

2) The Star-Delta Grounding Transformer with secondary unloaded.

We had looked at the Zig-zag Transformer in an earlier Post (Click here). 

Let us now look at the Star-Delta Grounding Transformer

The Star-delta grounding Transformer has a primary which is star connected and a delta secondary.  The phases of the star primary are connected to the busbar while the neutral is grounded.  The secondary of the transformer which is delta connected is usually left unloaded, though it can also be used to supply power.  The delta serves to provide a return flux path for unbalanced loads.  

During an earth fault, the zero sequence currents can flow through the grounded neutral of the transformer.  If the current is to be limited, a resistor can be added in series to the neutral of the transformer primary. 

Braking Resistors are used in Variable Frequency Drives to dissipate the energy released by the motor into the power system.  The Braking Resistors perform the duty of absorbing the power from the rotor when the VFD reduces the speed to zero and preventing rotor heating.  They also prevent the rotor from exceeding the synchronous speed set by the Variable frequency drive.

A variable Frequency drive consists of three main components - the rectfier which converts the AC supply into DC, the DC busbars and the inverter which converts the DC supply into a variable AC supply.  The VFD varies the speed of the motor by varying the frequency of the AC supply applied at the motor terminals. 

When the motor is required to be stopped suddenly, the Variable frequency drive reduces the supply frequency to 0 HZ.  In this condition, the rotor is rotating at speed higher than the synchronous speed.  This causes the motor to behave like a generator and send power in the reverse direction, into the DC bus bars.  During this time, the voltage across the DC busbars can rise to very highlevels.  The braking resistors absorb power in this situation and prevent the voltage from rising beyond limit and damaging the Drive.     

The value of the resistances determines the rate of fall of the motor speed (braking). 

Special provision is made for cooling the resistors which can generate a huge amount of heat when in operation. 

Resistance Temperature Detectors or RTDs are sensors which measure the temperature by altering their resistance. >The Resistance temperature detector consists of an element made of a metal such as platinum  located in a metallic casing.

When the temperature increases, the resistance of the sensor increases (positive temperature coefficient of resistance) This increase in the resistance is measured through a wheatstone bridge. The relationship between temperature and the resistance is linear.  Thus, the temperature can be deduced from the measured resistance.

Platinum and Nickel are two metals used to construct the sensing elements.  

Some common types of RTDs are the Pt-100 and Pt-1000. 

The Pt stands for Platinum while the number 100 stands for the ohmic value at 0 degrees Celsius.

The resistance increases linearly with temperature.

For example, the Pt100 has an ohmic value of 100 ohms at 0 °C and a value of 161 ohms at 160°C  

Advantages of RTDs
Long Term Stability
Ability to withstand shock and vibration

Disadvantages of RTDs 
Errors due to lead resistance,
Slow response
Internal Self heating

2 Wire, 3 wire and 4 wire RTDs

One of the disadvantages of the RTD is the error caused by the lead resistance.  That is, the indicating device which measures the sensor resistance to calculate resistance also measures the resistance of the leads connecting the sensor to the device.  This is unavoidable, though the error can be minimized by running a wire in parallel to one or both the leads. (Refer diagram)

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Global manufacturers of Transformers

Crompton Greaves

Provides transformers from 25 kVA to 600 MVA

Ruhstrat GmbH

Manufacturers of transformers from 50 VA upto 8 MVA with voltage rating upto 36 kV

Jelonek Transformers

Suppliers of three phase transformers upto 20 MVA and single phase transformers upto

ABB Transformers

Provides  a full range of transformer products and solutions for ANSI, IEC and other local standards.

Transformers and Rectifiers India

Manufactures transformers for diverse applications upto 1000MVA and 1200 kV

Oil Filtration  and Regeneration Services

Provides Transformer Oil Regeneration 

The 4 - 20 mA signal is an extremely popular signal specification in instruments.  The 4 to 20 mA signal provides "live zero" function.  i.e. in the event of a wire break, the signal drops to zero mA.  This can be used to detect wire break or sensor failure.  This is a crucial advantage of the 4 to 20 mA format.

  Being a Current signal, it is also less susceptible to external interference.

The 4 to 20 mA format works by varying the resistance to a constant source voltage.  The sensor consists of a transistor which regulates the current passing through it in accordance with the measured value.  Sensors which use this format can be categorized into active and passive transducers.  Active transducers are devices which can provide the system voltage as well as regulate the current.  Passive devices require an external voltage and only regulate the current.

Another advantage of this 4 to 20 mA format is that it can be easily converted into a voltage signal by means of a resistor. (1 - 5 volts for a 250 ohm resistor).

List of Electrical Software

Popular design software used across the industry for a wide range of design applications  in areas such as power management, substation automation, load shedding, etc..  Demo Version Available.

Popular Software for Electrical Design.  Offers Trial Version.

Electrical Design Software with a free demo version. Suitable for Electrical Panel Design, Plant Instrumentation, Wiring Diagram, Plant Raceway Design, Cable Routing,

CAD software with free Trial version.

Electrical Software for designing electronic Circuits, Automotive Wiring, Circuit Schematics and designing digital circuits.

Electrical Estimating Software
Software for Estimating Electrical projects. Contains online demo.

Software for Arc Flash Analysis and short circuit Calculations, Relay setting coordination and Equipment Sizing.  Offers Trial Version.

Schneider Electric CAD
Software for designing electrical installations in industrial and tertiary buildings.  Trial version available.

MTOE is the acronym for Million tonnes of Oil Equivalent.  It is a unit to quantify the amount of energy which is released by the burning of a million tonnes of crude oil.  

Different fuels have different MTOE values.  The OECD defines one tonne of energy equivalent for crude oil to be 11,630 kWh.  That is, 11630 units can be produced from one tonne of crude oil. 

MTOE is important as it helps one understand how many units of electricity can be from an given fuel.  This depends on the calorific value of the fuel and the efficiency of the generating process. 

Hydroelectricity can also be quantified in terms of MTOE (million tonnes of Energy Equivalent).  When we say that Brazil has 89.6 tonnes of oil equivalent in hydroelectricity.  It means that the power generated by the total hydroelectric resources and infrastructure is equal to the power which could be generated by 89.6 tonnes of oil.

MTOE is a unit which helps compare the potential and contribution of different sources of power such as hydroelectricty, wind electricity, etc. 

When a dc coil connected to a contactor or a solenoid is energized, it draws a high current. This high current is necessary to generate enough magnetism to pull the plunger or the contactor. This is known as the pull in current. 

After the the contactor has been pulled in, less current will be sufficient to hold the coil. This is called the holding current. 

Hence, to limit the current after the contactor has operated, a series resistance is connected. This is known as the economy resistor. The economy resistor enables the design of contactors which can draw heavy initial current and less holding current (resulting in lower power consumption during normal operation). 

In the case of AC coils this is not required as the current is limited after the initial inrush due to the back-emf.

The chief losses in a transformer are the losses that occur in the core.  These are the the eddy current loss and the hysteresis losses.  About 1 to 4 percent of the power which passes through a transformer is lost due to these losses.

The losses in the distribution transformers constitute nearly 20% of the total losses in the distribution system. Since transformers are online continually, the no load losses of the transformers is constant throughout the day regardless of the load. 

The Amorphous Metal Transformer is fast emerging as an efficient alternative to the conventional transformer.  The Amorphous Metal transformer has a core which is made of ferromagnetic materials such as Iron or Cobalt in a glass former such as phosphorous, silicon or boron.

Metglas, as this substance is known, has high susceptibility, low coercivity and high resistance.  The low coercivity reduces the hysteresis losses while the high resistance greatly reduces the eddy current losses.

By using Amorphous Metal Transformers, it is estimated that many millions of units of electricity can be saved.  Amorphous Metal Transformers are widely used in developing economies such as India and China in an effort to bring down the distribution losses.  

Some of the other advantages of Amorphous Metal Transformers are the lower operating temperature, higher overloading capability, slower ageing of the winding insulation and better performance when subjected to harmonics. 

Surface charge and surface discharge in batteries refers to the superficial charging and discharging which occurs only on the surface of the electrodes.  A lead acid battery consists of lead oxide anode and a lead cathode.  When discharging, the lead oxide in the anode and the lead in the cathode get converted to lead sulphate.  When charging, the reverse happens.  

Surface charge refers to a condition when the chemical changes mentioned above occur only in the surface of the electrode.  For instance, if only the lead sulphate in the surface of the anode of a discharged battery gets converted into lead oxide, the battery will indicate a full charge when the open circuit voltage is  measured.  However, the charge in the battery will last only for a short time. 

Surface discharge is a condition when the open circuit voltage of the battery wrongly indicates a discharged condition, when the battery is still holding charge.  This too relates to chemical changes which occur superficially on the surface of the electrode. 

The surface charge can be removed by applying a slight load on the battery.  In vehicles, switching on the headlights for a while can help remove the surface charge.

Sulfation in lead acid batteries refers to a condition when the battery is not able to hold any charge.  It occurs when the plates of a battery get hardened with a layer of lead sulphate. 

Sulfation occurs when the battery is kept unused for long periods of time in the discharged state.  This makes the lead sulfate in the plates to get hardened.  These hardened plates prevent the battery from charging.

The lead acid battery consists of an anode made of lead oxide and a cathode made of lead.  These two electrodes are placed in an electrolyte of sulphuric acid.  When the battery is discharged, the sulphuric acid reacts with the electrodes which are transformed into lead sulphate.  As a result, the sulphuric acid in the electrolyte becomes dilute and almost becomes water.  The specific gravity of the electrolyte thus drops.

When the battery is recharged, the lead sulphate in the cathode and anode is converted into lead and lead oxide respectively.  The sulphate in the electrodes react with water to again form sulphuric acid. 

When the battery is kept unused for long periods of time in the discharged condition.  The lead sulphate which is in the electrodes solidifies into a layer which has high electrical resistance. 

When the battery is recharged using an external supply, this hardened layer of lead sulphate prevents charging.  The electrolyte too, does not become sulphuric acid.  Thus the battery is not able to absorb charge. 

Another reason for sulfation is incomplete charge and discharge, When the battery is not charged capacity and  not discharged completely, a small amount of the sulphate always remains in the electrodes.  This forms a hardened layer and diminishes battery capacity. 
Identifying Sulfation in batteries

If your battery is connected to the charger for a long time and still does not have charge.  Test the specific gravity with a hydrometer.  If the specific gravity is low, the battery probably has the problem of sulfation.

Repairing Sulfated batteries

Sulfated batteries can be repaired by applying a high charging voltage and low charging current from the battery charger. 

When batteries are to be kept unused for long periods, they can be connected to a battery minder, an electronic device which continually monitors the voltage level of the battery and prevents sulfation from occuring by firing electronic pulses into the battery to break any sulphate layer which may have formed. 

Single Phase Pole Mounted Transformers are usually used in rural areas where three phase power may not be required.  These Transformers reduce the voltage from the line voltage 11kV to a single phase voltage usually 230V.

The secondary of the Pole mounted Distribution is usually connected between the two phases of a MV line.  The secondary voltage is a single phase voltage which is fed to the house.  These transformers can be easily installed and do not require extensive mounting Structures.
Pole mounted Transformers come in sizes up to 500 kVA.

These transformers have a fuse to protect against faults inside the transformer.  They are also equipped with an interrupting device.  These Transformers are tested to withstand the impulse of lightning. In the US, The secondary of these transformers has a centre tapping and therefore has three terminals.

The voltage between the end terminal and the centre tapping will provide 120V while the voltage between two end terminals will be 220 volts. These Single Phase Pole Mounted transformers can also be used to provide three phase LV supply.

Three pole mounted transformers are connected in wye or delta to get the desired connection. Besides, small size three phase transformers which can be mounted on poles are also available. Video Showing the Manufacture of Single Phase Transformers

Wireless Switches are used in homes, godowns, offices, etc to remotely control an electric appliance such as a lamp or a fan. Wireless switches work by preventing power from flowing through a receiver into the device.

The switch is mounted to the switchboard of the plug. The appliance to be controlled is connected through the device. When the switch is operated, it emits a radio frequency which activates or deactivates the receiver controlling the supply to the device. Wireless Switches can result in energy savings as it is easy to switch off the lights and fans in the room at the press of a single switch from another room.

Wireless switches can also be used to dim lights or reduce the speed of fans. You can adjust the lighting to suit your moods. You can switch on the lights when opening the front door when you return home in the evening. Wireless switches can be used to save energy. Dimmed lights consume less power. You can control your energy consumption while using optimum lighting.

Wireless switches can also be made part of a lighting program. These lighting programs can be activated when you are on a vacation. Lights can be switched on and off at different times of the day. This gives an impression that your house is occupied and can ward potential burglars and thieves.

Here is a video which describes the wireless switch and its function

Distribution Transformers play a vital role in the system which delivers electricity to the end user.   It is the final part of the transmission system from the power plant to the consumer.  Distribution Transformers step down the MV power, usually 11kv into the domestic LV, 440 V supply.

Distribution Transformers are a critical part of the distribution network.  These transformers are always online throughout the year.  Hence, design of the distribution transformer is made considering the high iron losses.  Besides, the transformer is sized to have high efficiency at 70% of the load as the power output varies through the day as per the load cycle. 

Distribution transformer are protected by fuses in the HV side.  They are also designed to withstand unbalanced loading.  They have ONAN cooling (Oil Natural, Air Natural ). 

Distribution Transformer are usually of the vector Dyn11.  While, designers are not particular about any particular vector group , most systems will standardize on one particular vector group, usually the Dyn11.  Some systems also use the Dyn1.  These vector groups have a difference of 30 degrees between the primary and secondary vectors which is unavoidable in delta to star conversion.

MCBs (Miniature Circuit Breakers) are categorized into B, C and D types.  These three ratings are determined by the level of overload which causes the MCB to trip. 

B type MCBs operate at an overload of 3 to 5 times the rated current.  Type B MCBs are usually used in domestic installations where the inrush currents and surges are low. 

C type MCBs operate at an overload of 5 to 10 times the rated current.  These MCBs are used in commercial and industrial installations where high inrush current are likely due to motor starting or due to large no of fluorescent lighting. 

D type MCBs are used in special applications such as x-ray machines and transformers which can draw heavy inrush current. 

Plante Batteries were invented by the French Scientist Gaston Plante in the year 1859.  The Plante Battery was the first rechargable battery.  It is also the first lead acid battery.

As a  lead acid battery, the Plante Battery uses pure lead plates.  The advantage of the Plante battery is that the capacity remains the same throughout its life.  Its grid design enables it to generate high currents and is thus suitable for applications which require high bursts of currents.  The active material in the positive plate is generated and regenerated throughout its lifetime.  Hence, there is  no loss of capacity. 

Each cell typically has a voltage of 2 volts.  Its ampere hour efficiency is 90%. 

The downside of this battery is its large size and high cost.   

The Trivector meter is a measuring instrument which measures the kW, kVAr, the kVA of a power line.  These instruments can measure both power as well as energy.    Trivector meters are normally used in substations and to measure the power flowing through the feeders.  They are used for billing power drawn by industrial customers.  The Trivector enables the simultaneous measurement of different electrical parameters which enables accurate assessment of the power consumed. 

Trivector is called so as it measures three vectors representing the active, reactive and apparent power of a line.  Trivector meters come in two quadrant and four quadrant models.  The four quadrant model can measure both the incoming (import) and the outgoing power (export) while the two quandrant trivector meter can measure either imported or exported power.

In earlier days, the Electromechanical trivector meters were used.  Today, though, almost all Trivector meters are of the static type.  Modern Trivector meters can measure many parameters apart from the active, reactive and apparent power.

Here are a few videos