#3 Difference between Power Transformer and Distribution Transformer



In this article, we will know what are the difference between power transformer and distribution transformer. There are many aspect which indicate the difference between them such as :

  1. Utility

Power transformers are used in transmission network of higher voltages for step-up and step down application (400 kV, 200 kV, 110 kV, 66 kV, 33kV) and are generally rated above 200MVA.

Distribution transformers are used for lower voltage distribution networks as a means to end user connectivity. (11kV, 6.6 kV, 3.3 kV, 440V, 230V) and are generally rated less than 200 MVA.

  1. Size / insulation level

Power transformer is used for the transmission purpose at heavy load, high voltage greater than 33 KV & 100% efficiency. It also having a big in size as compare to distribution transformer, it used in generating station and Transmission substation .high insulation level.

The distribution transformer is used for the distribution of electrical energy at low voltage as less than 33KV in industrial purpose and 440v-220v in domestic purpose. It work at low efficiency at 50-70%, small size, easy in installation, having low magnetic losses & it is not always fully loaded.

  1. Iron Losses and Copper Losses

Power Transformers are used in Transmission network so they do not directly connect to the consumers, so load fluctuations are very less. These are loaded fully during 24 hr’s a day, so Cu losses & Fe losses takes place throughout day the specific weight i.e. (iron weight)/(cu weight) is very less.

The average loads are nearer to full loaded or full load and these are designed in such a way that maximum efficiency at full load condition. These are independent of time so in calculating the efficiency only power basis is enough.

Power Transformers are used in Distribution Network so directly connected to the consumer so load fluctuations are very high. these are not loaded fully at all time so iron losses takes place 24hr a day and cu losses takes place based on load cycle. the specific weight is more i.e. (iron weight)/(cu weight).average loads are about only 75% of full load and these are designed in such a way that max efficiency occurs at 75% of full load.

As these are time dependent the all day efficiency is defined in order to calculate the efficiency.

Power transformers are used for transmission as a step up devices so that the I2r loss can be minimized for a given power flow. These transformers are designed to utilize the core to maximum and will operate very much near to the knee point of B-H curve (slightly above the knee point value).This brings down the mass of the core enormously. Naturally these transformers have the matched iron losses and copper losses at peak load (i.e. the maximum efficiency point where both the losses match).

Distribution transformers obviously cannot be designed like this. Hence the all-day-efficiency comes into picture while designing it. It depends on the typical load cycle for which it has to supply. Definitely Core design will be done to take care of peak load and as well as all-day-efficiency. It is a bargain between these two points.

Power transformer generally operated at full load. Hence, it is designed such that copper losses are minimal. However, a distribution transformer is always online and operated at loads less than full load for most of time. Hence, it is designed such that core losses are minimal.

In Power Transformer the flux density is higher than the distribution transformer.

  1. Maximum efficiency

The main difference between power and distribution transformer is distribution transformer is designed for maximum efficiency at 60% to 70% load as normally doesn’t operate at full load all the time. Its load depends on distribution demand. Whereas power transformer is designed for maximum efficiency at 100% load as it always runs at 100% load being near to generating station.

Distribution Transformer is used at the distribution level where voltages tend to be lower .The secondary voltage is almost always the voltage delivered to the end consumer. Because of voltage drop limitations, it is usually not possible to deliver that secondary voltage over great distances.

As a result, most distribution systems tend to involve many ‘clusters’ of loads fed from distribution transformers, and this in turn means that the thermal rating of distribution transformers doesn’t have to be very high to support the loads that they have to serve.

Rudd Transformer

Rudd Transformer

Source   :

–        Electrical engineering portal web. “Difference between Power Transformer and Distribution Transformer”. 17 Mei 2014. http://electrical-engineering-portal.com/difference-between-power-transformer-and-distribution-transformer

–        Picture http://www.meppi.com/Products/Transformers/Power/PublishingImages/rudd%20transformer%20001.jpg

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#2 Electrical Wiring Diagram

Wiring diagram in home

Wiring diagram in home

A wiring diagram is intended to show the actual connection and physical location of all component parts in a circuit. Coils, contacts, motors, and the like are shown in the actual position that would be found on an installation. We will usually need an electrical wiring diagram to carry out electrical work in a home. Wiring diagram can be a blueprint that shows everything in the house or just a single circuit.

There are 3 different types of electrical wiring diagrams, namely :

  • wiring diagram is a diagram that will represent the wiring within the house in a series of horizontal and vertical lines. The different outlets, switches, and components of the system are represented by symbols which are as close as possible to their real physical location. This is the most useful kind of electrical wiring diagram.
  • schematic diagram is a diagram that shows the flow of the circuit rather than the wiring, so it actually serves a different function. It doesn’t try to be an accurate representation of the wiring within a system.
  • pictorial diagram is a diagram that even less useful to anyone doing work on a circuit since it makes no pretense of being an accurate representation of the layout of a circuit.

There are several advantage of electrical wiring diagram, namely :

  1. Wiring as a Map

The importance of an electrical wiring diagram is that it gives you a map from which to work on with regards to the wiring in your house. Just as you need a map to find the way to a destination in a car, you need a map to understand the complex system of wiring.

Like any map, this diagram has its own symbols and you need to be able to read these in order to make sense of an electrical wiring diagram. Wiring can be quite simple to repair once you understand how the circuit works. To do this, however, you will usually need an electrical wiring diagram.

  1. Ease of Use

With an electrical wiring diagram, it becomes easy to work on the electrical systems in your house with confidence. You will know where everything is and can trace the system back effectively when carrying out repairs or adding new components to a system. By understanding the circuit, you can readily isolate where the problem is and just work on that particular section without having to trace problems further.

  1. Understanding Components

Knowing what makes up the electrical system in your home means you can readily buy the components you need for a repair without having to worry about whether you’ve bought the correct item. This cuts down on time and frustration for you which is a great payoff.

  1. Ideal for New Constructions

If you’re building an addition to your house or a complete new home, you’ll need a full electrical wiring diagram for the work to be carried out. This isn’t simply to guide the installation, but also to pass the building code and receive a permit for the construction. Keep all electrical wiring diagrams since they can be useful later for repairing of amending the circuits with new outlets or other components. If you need to employ a professional electrician, an electrical wiring diagram will make the job easier to complete and ultimately cost you less money.

Source :

–        Do it yourself web. “Five Benefits Of Making An Electrical Wiring Diagram”. 12 Mei 2014. http://www.doityourself.com/stry/five-benefits-of-making-an-electrical-wiring-diagram#b.

–        Petruzella, Frank D. Industrial Electronics. 1996. McGraw-Hill International Editions. pg. 20.

–        Picture : http://instalasilistrik-jn.com/wp-content/uploads/2012/10/instalasi-listrik-rumah.jpg

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#1 Grounding



Electricity is the flow of electrons. The flow of electric current is something like the flow of water from the mountains to the ocean. Water always tries to find a way to the ocean whereas electricity always tries to find a way to the ground. The route electricity takes is called its path to ground. If you are part of an electrical path to ground, electricity may pass through you. It could seriously burn or kill you. If you touch a live electrical wire while standing on the ground, or something that is in touch with the ground, you may become part of a path to ground.

Grounding is the process of removing the excess charge on an object by means of the transfer of electrons between it and another object of substantial size. When a charged object is grounded, the excess charge is balanced by the transfer of electrons between the charged object and a ground. A ground is simply an object that serves as a seemingly infinite reservoir of electrons; the ground is capable of transferring electrons to or receiving electrons from a charged object in order to neutralize that object.

There are many types of grounding, it depends on its media. In this article we only learn about grounding to an object. Grounding could be done by an object, for example an electroscope. There are two types of grounding which is charged by object, namely :

  1. Grounding a Negatively Charged Object

We will consider the grounding of a negatively charged electroscope. Any negatively charged object has an excess of electrons. If it is to have its charge removed, then it will have to lose its excess electrons. Once the excess electrons are removed from the object, there will be equal numbers of protons and electrons within the object and it will have a balance of charge. To remove the excess of electrons from a negatively charged electroscope, the electroscope will have to be connected by a conducting pathway to another object that is capable of receiving those electrons. The other object is the ground. In typical electrostatic experiments and demonstrations, this is simply done by touching the electroscope with one’s hand. Upon contact, the excess electrons leave the electroscope and enter the person who touches it. These excess electrons subsequently spread about the surface of the person.

This process of grounding works because excess electrons find each other repulsive. As is always the case, repulsive affects between like-charged electrons forces them to look for a means of spatially separating themselves from each other. This spatial separation is achieved by moving to a larger object that allows a greater surface area over which to spread. Because of the relative size of a person compared to a typical electroscope, the excess electrons (nearly all of them) are capable of reducing the repulsive forces by moving into the person (i.e., the ground). Grounding is simply another example of charge sharing between two objects. The extent to which an object is willing to share excess charge is proportional to its size. So an effective ground is simply an object with significant enough size to share the overwhelming majority of excess charge.

  1. Grounding a Positively Charged Object

We will consider the grounding of a positively charged electroscope. A positively charged electroscope must gain electrons in order to acquire an equal number of protons and electrons. By gaining electrons from the ground, the electroscope will have a balance of charge and therefore be neutral. Thus, the grounding of a positively charged electroscope involves the transfer of electrons from the ground into the electroscope. This process works because excess positive charge on the electroscope attracts electrons from the ground (in this case, a person). While this may disrupt any balance of charge present on the person, the significantly larger size of the person allows for the excess charge to distance itself further from each other. As in the case of grounding a negatively charged electroscope, the grounding of a positively charged electroscope involves charge sharing. The excess positive charge is shared between the electroscope and the ground.

In conclusion grounding is simply another example of charge sharing between two objects. The extent to which an object is willing to share excess charge is proportional to its size. So an effective ground is simply an object with significant enough size to share the overwhelming majority of excess charge.

Source :

–        Physucsclassroom web. “Grounding – the Removal of a Charge”. 12 Mei 2014. http://www.physicsclassroom.com/class/estatics/Lesson-2/Grounding-the-Removal-of-a-Charge.

–        Petruzella, Frank D. Industrial Electronics. 1996. McGraw-Hill International Editions. pg. 4

–        Picture : iaei web. 12 Mei 2014. http://www.iaei.org/resource/resmgr/images_magazine_2004/04cjohnstonfigure4_330922769.jpg.

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On Delay Timer

Check it out Video about On delay timer. Sorry if it is not good enough 😀


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In this opportunity I will share you about one of electronic test instruments. From picture above I will share information about galvanometer. And subtopic will be explained are what is galvanometer, type of galvanometer, working principle of galvanometer, and application of galvanometer. Lets check it out.

1. What is Galvanometer ?

     Galvanometer is an electromechanical instrument which is used for the detection of electric currents through electric circuits. Being a sensitive instrument, Galvanometer can not be used for the measurement of heavy currents. However we can measure very small currents by using galvanometer but the primary purpose of galvanometer is the detection of electric current not the measurement of current.
Galvanometers were the first instruments used to determine the presence, direction, and strength of an electric current in a conductor. All galvanometers are based upon the discovery by Hans C. Oersted that a magnetic needle is deflected by the presence of an electric current in a nearby conductor. When an electric current is passing through the conductor, the magnetic needle tends to turn at right angles to the conductor so that its direction is parallel to the lines of induction around the conductor and its north pole points to the direction in which these lines of induction flow. In general, the extent to which the needle turns is dependent upon the strength of the current.
Galvanometer is the historical name given to a moving coil electric current detector. When a current is passed through a coil in a magnetic field, the coil experiences a torque proportional to the current. If the coil’s movement is opposed by a coil spring, then the amount of deflection of a needle attached to the coil may be proportional to the current passing through the coil. Such “meter movements” were at the heart of the moving coil meters such as voltmeters and ammeters until they were largely replaced with solid state meters.
The accuracy of moving coil meters is dependent upon having a uniform and constant magnetic field. The illustration shows one configuration of permanent magnet which was widely used in such meters.

2. Type of Galvanometer

a. Tangent Galvanometer


Struers Tangent Galvanometer

     André-Marie Ampère, (1775-1836), is credited with the invention of the galvanometer in 1824. The earliest galvanometers were literally constructed of a compass surrounded by a coil of wire. These meters were called tangent galvanometers because the tangent of the angle of deflection of the needle is proportional to the strength of the current in the coil (at this point in time it was impossible to construct a meter whose needle deflection was directly proportional to the current under measurement).

    Unfortunately, simple galvanometers such as the Struers model shown above were inaccurate and inconsistent in their readings. By placing the compass at the center of a precisely calculated circle, accuracy could be improved substantially (see left). Other improvements were added later including replacing the compass with a specially designed meter movement, adding leveling screws, etc.
These large stationary-coil type galvanometers were used as the standard current measuring instrument into the last quarter of the 19th century.

b. Reflecting Galvanometer

Becker Reflecting Galvanometer c. 1910

Becker Reflecting Galvanometer
c. 1910

One of the limitations of early galvanometers was that the length of the needle had to be kept very short in order to minimize the effects of the earth’s magnetic field and reduce damping errors introduced by the mass of the needle itself. Unfortunately, the shorter the needle, the less distance the tip will travel as it inscribes an arc, and thus the more difficult it will be to read very small changes in current. This problem was solved ingeniously by using a beam of light as the needle; a shaft was placed through the center of the needle and a very small mirror was attached. A beam of light is reflected off of the mirror and onto a scale located about three feet away. The result is that an extremely small deflection of the mirror will cause a much larger movement of the beam on the scale.

c. String Galvanometers

Braun Astatic Galvanometer 1910

Braun Astatic Galvanometer

Sensitivity, (called “sensibility” back then), can be increased by suspending the needle at the end of a long string. At right are a couple of string galvanometers. The Braun model is known as an Astatic type. Astatic galvanometers use a combination of two needles of equal size mounted rigidly together in parallel but with their poles pointing in opposite directions. This combination neutralizes the effect of the earth’s magnetic field and the needle will remain at rest in any position.

d. d’Arsonval Galvanometers

Harris D'Arsonval Galvanometer Early 1900's

Harris D’Arsonval
Early 1900’s

In 1880, Jacques-Arsene d’Arsonval made a dramatic improvement by attaching a small coil to the meter needle and locating both inside the field of a permanent magnet. This d’Arsonval movement and other rapid changes in electrical technology soon made the tangent galvanometer obsolete.

e. Resistance Coils

King Mendham & Co. Wheatstone Bridge Post Office pattern c. 1885

King Mendham & Co.
Wheatstone Bridge
Post Office pattern
c. 1885

Electronic Instruments Ltd. Resistance Coils

Electronic Instruments Ltd.
Resistance Coils

In testing and in duplex telegraphy, the use of an external source of calibrated resistance is sometimes required. For example, the electrical resistance of a coil or length of wire could be determined by comparing it in a galvanometer circuit with a known resistance. Or, in the case of telegraphy, the additional resistance could be used to balance one line against the other.
A Resistance box contains an assortment of coils of known resistance, with the ends of the coils connected together and brought out to brass plates mounted on the top of the box. To configure the box for a specific resistance, brass plugs are inserted into the plates at the appropriate locations. The plugs “short out” one or more of the coils, resulting in the desired resistance at the terminal of the resistance box.
Some boxes, such as the King Mendham bridge above, contain coils wired into a special circuit known as a “bridge”. The bridge makes very accurate resistance measurements possible by balancing an unknown resistance against three other known values.

f. Beautiful Precision Sine Galvanometer

Beautiful Precision Sine Galvanometer

Beautiful Precision Sine Galvanometer

    This incredible piece is over 21″ tall. The coil is 16″ in diameter and can be rotated on two axes around the needle assembly.The force on the compass needle decreases as the coil is tilted since that decreases the component of the field in the plane of the needle. These instruments were used in the 1870’s to measure the large currents produced by power station dynamos.

3. Working Principle of Galvanometer

     Galvanometer works on the principle of conversion of electrical energy into mechanical energy. When a current flows in a magnetic field it experiences a magnetic torque. If it is free to rotate under a controlling torque, it rotates through an angle proportional to the current flowing through it.

a. Essential Parts Of Galvanometer

There are five essential parts of a Galvanometer :

1. A U-shaped permanent magnet with concave poles.
2. Flat rectangular coil of thin enameled insulated wire ‘C’.
3. A soft iron cylinder ‘B’.
4. A pointer or needle.
5. A scale.

b. Construction

    The flat rectangular coil of thin enameled insulated wire of suitable number of turns wound on a light nonmetallic or aluminum frame is suspended between the cylindrically concave poles of magnet by a thin phosphor bronze strip. One end of the wire of the coil is soldered to strip. The other end of the strip fixed to the frame of the galvanometer and connected to an external terminal. It serves as one leas current lead through which the current enters or leaves the coil. The other end of the wire of the coil is soldered to a loose and soft spiral of wire connected to another external terminal. The soft spiral of a wire serves as the other current lead. A soft-iron cylinder, coaxial with the pole pieces, is placed within the frame of the coil and is fixed to the body of the galvanometer. In the space between it and the pole pieces, where the coil moves freely, the soft iron cylinder makes the magnetic field stronger and radial such that into whatever position the coil rotates, the magnetic field is always parallel to its plane.

c. Working

    When a current passes through the galvanometer coil, it experiences a magnetic deflecting torque, which tends to rotate it from its rest position. As the coil rotates it produces a twist in the suspension strip. The twist in the strip produces an electric restoring torque. The coil rotates until the elastic restoring torque due to the strip does not equal and cancels the deflecting magnetic torque, then it attains equilibrium and stops rotating any furthers.

4. Application of Galvanometer

Wheatstone Bridge Circuit

Wheatstone Bridge Circuit

Galvanometer usually uses in Wheatstone bridge circuit. The purpose of Wheatstone bridge circuit is to measure resistance. Whitestone bridge consists of four resistance and galvanometer. It requires fixed, known resistance values for R1 and R2 and a variable resistor for R3. Variable resistor R3 is attached to a calibrated dial that shows its adjusted resistance value. Resistor Rx represents the resistance value to be measured. To determine Rx. The variable resistance R3 is adjusted until the galvanometer indicates zero current. Consequently, the galvanometer is usually termed a null detector. The zero galvanometer reading indicates that the bridge is balanced. When the galvanometer indicates null condition, the voltage on each side of galvanometer is equal. If R1 and R2 are the same value, then calibrated dial reading of R3 indicates the resistance value of Rx. If the values of R1 and R2 are different, the unknown resistance value for balanced bridge can be calculated with this equation :

Rx = R2 . R3 / R1

Source :

Hyperphysics web, accessed April 13, 2014.  http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/galvan.html

Circuit specialists web, accessed April 13, 2014.  http://www.circuitspecialists.com/content/88526/csm-1102a-0.jpg

Spark museum web, accessed April 13, 2014.  http://www.sparkmuseum.com/GALV.HTM

City Collegiate web, accessed April 13, 2014.  http://www.citycollegiate.com/galvanometer_XIIb.htm

Petruzella, Frank D. Industrial Electronic pg. 126-127. 1996. McGraw-Hill International Editions.

Picture : wordpress web, accessed April 13,2014.  http://sandirahmadika.files.wordpress.com/2011/05/capture1.jpg

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First Post

Finnaly I made a blog. Hope, can share good and helpful things in here and can enjoy to be a newbie blogger.

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