Show Mobile Navigation

Featured post

How to Make a Digital Lock Using Arduino?

Interesting Articles

Latest Stories

Video: How Stepper Motor Works?



How does a robotic arm in a production plant repeat exactly the same movements over and over again? How can you move an automatic milling machine so precisely? It is available with stepper motor. 
What is special about the stepper motor. It is that it can control the angular position the rotor without closed loop feedback.
Let us see the working of a variable reluctance motor, that is the kind of step by simple step motor. Then we turn to hybrid stepper motor, a type of more accurate and used motor.  

How Star Delta Starter Works?

Star-Delta starting is frequently referred to as “Soft-starting” a motor. But what is soft about his starting method? Why is it used? What are the advantages? What are the disadvantages?

Let’s first analyse what Star Delta starting is! It will be explained by using an example motor.

What is Star Delta starting?

Star Delta starting is when the motor is connected (normally externally from the motor) in STAR during the starting sequence. When the motor has accelerated to close to the normal running speed, the motor is connected in DELTA. Pictures 1 and 2 show the two connections for a series connected, three phase motor.



The change of the external connection of the motor from Star to Delta is normally achieved by what is commonly referred to a soft starter or a Star Delta starter. This starter is simply a number of contactors (switches) that connect the different leads together to form the required connection, i.e. Star or Delta.

These starters are normally set to a specific starting sequence, mostly using a time setting to switch between Star and Delta. There can be extensive protection on these starters, monitoring the starting time, current, Voltage, motor speed etc.

The cost of the soft starter will depend on the number of starts required per hour, run-up time, Voltage, power rating, and protection devices required.

Video - Understanding STAR-DELTA Starter

If a picture is worth a thousand words, then a video is worth a million. Watch the video below for better understanding of Star-Delta Starter.

 Advantages of using Star Delta starting

The most significant advantage is the reduction in starting current. The starting current will to a large extent determine the size of the cables used, the size of the circuit breakers, the size of the fuses, as well as the transformers.

Requiring 67% less starting current can have a tremendous cost saving implication!

The most significant advantage of using Star-Delta starting is the huge reduction in the starting current of the motor, which will result in a significant cost saving on cables, transformers and switch gear.

Insulating Materials for Power Cables


We have already discussed about the construction of underground cables in the previous article. In this article we will discuss about the insulating materials used in underground cables.

Insulation is a non-conductive material, or a material resistant to the flow of electric current. It is often called a dielectric in radio frequency cables. Insulation resists electrical leakage, prevents the wire’s current from coming into contact with other conductors, and preserves the material integrity of the wire by protecting against environmental threats such as water and heat. Both the safety and effectiveness of the wire depend on its insulation.

The satisfactory operation of a cable depends to a great extent upon the characteristics of insulation used. Therefore, the proper choice of insulating material for cables is of considerable importance.

Properties Required for Insulating Materials

In general, the insulating materials used in cables should have the following properties :

  1. High insulation resistance to avoid leakage current.
  2. High dielectric strength to avoid electrical breakdown of the cable.
  3. High mechanical strength to withstand the mechanical handling of cables.
  4. Non-hygroscopic i.e., it should not absorb moisture from air or soil. The moisture tends to decrease the insulation resistance and hastens the breakdown of the cable. In case the insulating material is hygroscopic, it must be enclosed in a waterproof covering like lead sheath.
  5. Non-inflammable.
  6. Low cost so as to make the underground system a viable proposition.
  7. Unaffected by acids and alkalies to avoid any chemical action

No one insulating material possesses all the above mentioned properties. Therefore, the type of insulating material to be used depends upon the purpose for which the cable is required and the quality of insulation to be aimed at. 

The principal insulating materials used in cables are rubber, vulcanised India rubber, impregnated paper, varnished cambric and polyvinyl chloride.

Rubber

Rubber may be obtained from milky sap of tropical trees or it may be produced from oil products. It has relative permittivity varying between 2 and 3, dielectric strength is about 30 kV/mm and resistivity of insulation is 1017 Ω cm. 

Although pure rubber has reasonably high insulating properties, it suffers form some major drawbacks viz., readily absorbs moisture, maximum safe temperature is low (about 38ºC), soft and liable to damage due to rough handling and ages when exposed to light. Therefore, pure rubber cannot be used as an insulating material.

Vulcanised India Rubber (V.I.R.)

It is prepared by mixing pure rubber with mineral matter such as zine oxide, red lead etc., and 3 to 5% of sulphur. The compound so formed is rolled into thin sheets and cut into strips. The rubber compound is then applied to the conductor and is heated to a temperature of about 150ºC. The whole process is called vulcanisation and the product obtained is known as vulcanised India rubber.

Vulcanised India rubber has greater mechanical strength, durability and wear resistant property than pure rubber. 

Its main drawback is that sulphur reacts very quickly with copper and for this reason, cables using VIR insulation have tinned copper conductor. The VIR insulation is generally used for low and moderate voltage cables.

Impregnated Paper

It consists of chemically pulped paper made from wood chippings and impregnated with some compound such as paraffinic or napthenic material. 

This type of insulation has almost superseded the rubber insulation. It is because it has the advantages of low cost, low capacitance, high dielectric strength and high insulation resistance. 

The only disadvantage is that paper is hygroscopic and even if it is impregnated with suitable compound, it absorbs moisture and thus lowers the insulation resistance of the cable. For this reason, paper insulated cables are always provided with some protective covering and are never left unsealed. If it is required to be left unused on the site during laying, its ends are temporarily covered with wax or tar. 

Since the paper insulated cables have the tendency to absorb moisture, they are used where the cable route has a few joints. [ Special precautions have to be taken to preclude moisture at joints. If the number of joints is more, the installation cost increases rapidly and prohibits the use of paper insulated cables.]

For instance, they can be profitably used for distribution at low voltages in congested areas where the joints are generally provided only at the terminal apparatus. 

However, for smaller installations, where the lengths are small and joints are required at a number of places, VIR cables will be cheaper and durable than paper insulated cables.

Varnished Cambric

It is a cotton cloth impregnated and coated with varnish. This type of insulation is also known as empire tape. 

The cambric is lapped on to the conductor in the form of a tape and its surfaces are coated with petroleum jelly compound to allow for the sliding of one turn over another as the cable is bent. 

As the varnished cambric is hygroscopic, therefore, such cables are always provided with metallic sheath. Its dielectric strength is about 4 kV/mm and permittivity is 2.5 to 3.8.

Polyvinyl chloride (PVC)

This insulating material is a synthetic compound. It is obtained from the polymerisation of acetylene and is in the form of white powder. 

For obtaining this material as a cable insulation, it is compounded with certain materials known as plasticizers which are liquids with high boiling point. The plasticizer forms a gell and renders the material plastic over the desired range of temperature.

Polyvinyl chloride has high insulation resistance, good dielectric strength and mechanical toughness over a wide range of temperatures. 

It is inert to oxygen and almost inert to many alkalies and acids. Therefore, this type of insulation is preferred over VIR in extreme enviormental conditions  such as in cement factory or chemical factory. 

As the mechanical properties (i.e., elasticity etc.) of PVC are not so good as those of rubber, therefore, PVC insulated cables are generally used for low and medium domestic lights and power installations.

It is cheap, durable and widely available. However, the chlorine in PVC (a halogen) causes the production of thick, toxic, black smoke when burnt and can be a health hazard in areas where low smoke and toxicity are required (e.g. confined areas such as tunnels). Normal operating temperatures are typically between 75ºC and 105ºC (depending on PVC type). Temperature limit is 160ºC (<300mm2) and 140ºC (>300mm2).

PolyEthylene (PE)

PVC and polyethylene are thermoplastic materials which means that they go soft when heated and harden when cooled. Most common thermoplastic material is PVC. Another one is polyethylene.

PE is part of a class of polymers called polyolefins. Polyethylene has lower dielectric losses than PVC and is sensitive to moisture under voltage stress (i.e. for high voltages only).

This compound is used most in coaxial and low capacitance cables because of its exemplary electric qualities. Many times it is used in these applications because it is affordable and can be foamed to reduce the dielectric constant to 1.50, making it an attractive option for cables requiring high-speed transmission. 

Polyethylene can also be cross-linked to produce high resistance to cracking, cut-through, soldering, and solvents. Polyethylene can be used in temperatures ranging from -65°C to 80°C. 

All densities of Polyethylene are stiff, hard, and inflexible. The material is also flammable. Additives can be used to make it flame retardant, but this will sacrifice the dielectric constant and increase power loss.

Thermosetting

Thermosetting compounds are polymer resins that are irreversibly cured (e.g. by heat in the vulcanization process) to form a plastic or rubber:

XLPE (Cross-Linked Polyethylene)

XLPE has different polyethylene chains linked together (“cross-linking”) which helps prevent the polymer from melting or separating at elevated temperatures. Therefore XLPE is useful for higher temperature applications. 

XLPE has higher dielectric losses than PE, but has better ageing characteristics and resistance to water treeing. Normal operating temperatures are typically between 90ºC and 110ºC. Temperature limit is 250ºC.

EPR (Ethylene Propylene Rubber)

EPR is a copolymer of ethylene and propylene, and commonly called an “elastomer”. 

EPR is more flexible than PE and XLPE, but has higher dielectric losses than both. Normal operating temperatures are typically between 90C and 110C. Temperature limit is 250C.

Relay Timing Characteristics | Instantaneous, Inverse Time and Definite Time Lag Relays



An important characteristic of a relay is its time of operation. By ‘the time of operation’ is meant length of the time from the instant when the actuating element is energised to the instant when the relay contacts are closed. 

Sometimes it is desirable and necessary to control the operating time of a relay. For this purpose, mechanical accessories are used with relays.

Instantaneous Relay

An instantaneous relay is one in which no intentional time delay is provided. 

In this case, the relay contacts are closed immediately after current in the relay coil exceeds
the minimum calibrated value. 

Figure shows an instantaneous solenoid type of relay. Although there will be a short time interval between the instant of pickup and the closing of relay contacts, no intentional time delay has been added. 

The instantaneous relays have operating time less than 0·1 second. The instantaneous relay is effective only where the impedance between the relay and source is small compared to the protected section impedance.

The operating time of instantaneous relay is sometimes expressed in cycles based on the power system frequency.
e.g. one-cycle would be 1/50 second in a 50-cycle system.

Inverse Time Relay

An inverse-time relay is one in which the operating time is approximately inversely proportional to the magnitude of the actuating quantity. 

Figure shows the time-current characteristics of an inverse current relay. At values of current less than pickup, the relay never operates. At higher values, the time of operation of the relay decreases steadily with the increase of current. 

The inverse-time delay can be achieved by associating mechanical accessories with relays.


  • In an induction relay, the inverse-time delay can be achieved by positioning a permanent magnet (known as a drag magnet) in such a way that relay disc cuts the flux between the poles of the magnet. When the disc moves, currents set up in it produce a drag on the disc which slows its motion.

  • In other types of relays, the inverse time delay can be introduced by oil dashpot or a timelimit fuse. Figure shows an inverse time solenoid relay using oil dashpot. The piston in the oil dashpot  attached to the moving plunger slows its upward motion. At a current value just equal to the pickup, the plunger moves slowly and time delay is at a maximum. At higher values of relay current, the delay time is shortened due to greater pull on the plunger.

The inverse-time characteristic can also be obtained by connecting a time-limit fuse in parallel with the trip coil terminals as shown in figure below. 

The shunt path formed by time-limit fuse is of negligible impedance as compared with the relatively high impedance of the trip coil. Therefore, so long as the fuse remains intact, it will divert practically the whole secondary current of CT from the trip coil. 

When the secondary current exceeds the current carrying capacity of the fuse, the fuse will blow and the whole current will pass through the trip coil, thus opening the circuit breaker. The timelag between the incidence of excess current and the tripping of the breaker is governed by the characteristics of the fuse. Careful selection of the fuse can give the desired inverse-time characteristics, although necessity for replacement after operation is a disadvantage.

Definite Time Lag Relay

In this type of relay, there is a definite time elapse between the instant of pickup and the closing of relay contacts. This particular time setting is independent of the amount of current through the relay coil ; being the same for all values of current in excess of the pickup value. 

It may be worthwhile to mention here that practically all inverse-time relays are also provided with definite minimum time feature in order that the relay may never become instantaneous in its action for very long overloads.

Substation Earthing System Design

We have already given an introduction to substation earthing system in an article published earlier. Today we are going to discuss about the design of substation earthing system.

Before 1960s the design criterion of substation earthing system was "low earth resistance.” (Earth Resistance< 0.5 ohms for High Voltage installations). 
During 1960s, the new criteria for the design and evaluation of Substation Earthing System were evolved particularly for EHV AC and HVDC Substations. The new criteria are :
  1. Low Step Potential 
  2. Low Touch Potential 
  3. Low Earth Resistance.
The conventional “Low earth resistance criterion” and Low Current Earth Resistance Measurement continues to be in practice for Substations and Power Station upto and including 220 kV.


The parts of the Earthing System include the entire solid metallic conductor system between various earthed points and the underground earth-mat. The earthed points are held near-earth potential by low resistance conductor connections with earth-mat.

Substation Earthing System Design

Underground Horizontal Earth Mesh (Mat/Grid)

The mesh is formed by placing mild steel bars placed in X and Y directions in mesh formation in the soil at a depth of about 0.5 m below the surface of substation floor in the entire substation area except the foundations. 

The crossings of the horizontal bars in X and Y directions are welded.

The earthing rods are also placed the border of the fence, surrounding building foundations, surrounding the transformer foundations, inside fenced areas etc. 

The mesh ensures uniform and zero potential distribution on horizontal surface of the floor of the substation hence low “step potential" in the event of flow of earth fault current.


Earthing Electrodes (Spikes)

Several identical earth electrode are driven vertically into the soil and are welded to the earthing rods of the underground Mesh. Larger number of earth electrodes gives lower earth resistance.

  • The number of Earth-Electrodes (Spikes) Ns for soil resistivity 500 ohm meter and earth fault current Is is :
Ns = Is / 250 Amperes
i.e., approximately 250 Amp per spike, for soil resistivity of 500 ohm-meter.


  • The number of Earth-Electrodes (Spikes) Ns for soil resistivity 5000 ohm meter is 
Ns = Is / 500 Amperes
i.e., approximately 500 Amp per spike, for soil resistivity of < 5000 ohm-meter.
Is = Short Circuit level of the substation, A
    Example:
    33 kV sub stations     : 25000 to 31000 A
    400 kV Substations   : 40000 A


    Earthing Risers

    These are generally mild steel rods bent in vertical and horizontal shapes and welded to the earthing mesh at one end and brought directly upto equipment / structure foundation.

    Earthing Connection

    Galvanized Steel Strips or Electrolytic Copper Flats or Strips/Stranded Wires (Cables) /Flexibles. 
    These are used for final connection  (bolted/welded/clamped) between the Earthing Riser and the points to be earthed. 

    For Transformer Neutral/High Current Discharge paths copper strips/stranded wires are preferred. 
    Galvanised Iron Strips/stranded wires are more common for all other earthing connections. The earthing strips are finally welded or bolted or clamped to the Earthed Point.

    Different Types of Capacitors and their Uses

    Basically a capacitor is formed from two conducting plates separated by a thin insulating layer. They are manufactured in many forms, styles, and from many materials. Capacitors are widely used in electrical and electronic circuits.

    In electronic circuits, small value capacitors are used
    • to couple signals between stages of amplifiers.
    • as components of electric filters and tuned circuits.
    • as parts of power supply systems to smooth rectified current.

    In electrical circuits, larger value capacitors are used
    • for energy storage in such applications as strobe lights.
    • as parts of some types of electric motors.
    • for power factor correction in AC power distribution systems

    Standard capacitors have a fixed value of capacitance, but adjustable capacitors are frequently used in tuned circuits.

    Types of Capacitors

    Capacitors are divided in to two common groups:
    1. Fixed Capacitor with fixed capacitance values
    2. Variable Capacitors with variable (trimmer) or adjustable (tunable) capacitance values.

    Out of these the most important group is fixed capacitors. Many capacitors got their names from the dielectric. But this is not true for all capacitors because some old electrolytic capacitors are named by its cathode construction. So the most used names are simply historical.

    Fixed capacitors include polarized and non-polarized. Ceramic and Film capacitors are examples of  non-polarized capacitors. Electrolytic and Super Capacitors are included in the group of polarized capacitors.

    The classification of fixed capacitors are shown in the figure below. Some of the important capacitors are listed here.

    • Ceramic capacitors
    • Film and paper capacitors 
    • Aluminum, tantalum and niobium electrolytic capacitors
    • Polymer capacitors
    • Supercapacitor
    • Silver mica, glass, silicon, air-gap and vacuum capacitors



    In addition to the above shown capacitor types, which derived their name from historical development, there are many individual capacitors that have been named based on their application. 

    They include:
    Power capacitors, motor capacitors, DC-link capacitors, suppression capacitors, audio crossover capacitors, lighting ballast capacitors, snubber capacitors, coupling, decoupling or bypassing capacitors.

    Often, more than one capacitor family is employed for these applications, e.g. interference suppression can use ceramic capacitors or film capacitors.

    Overview of Different Types of Capacitors

    As we explained above, there are many different types of capacitor that can be used. Some of the major types are outlined below:

    Ceramic capacitor:   

    The ceramic capacitor is a type of capacitor that is used in many applications from audio to RF. 

    Values range from a few picofarads to around 0.1 microfarads. Ceramic capacitor types are by far the most commonly used type of capacitor being cheap and reliable and their loss factor is particularly low although this is dependent on the exact dielectric in use. 

    In view of their constructional properties, these capacitors are widely used both in leaded and surface mount formats.

    Electrolytic capacitor:   

    Electrolytic capacitors are a type of capacitor that is polarised. 

    They are able to offer high capacitance values - typically above 1μF, and are most widely used for low frequency applications - power supplies, decoupling and audio coupling applications as they have a frequency limit if around 100 kHz. 

    Tantalum capacitor:  

    Like electrolytic capacitors, tantalum capacitors are also polarised and offer a very high
    capacitance level for their volume. 

    However this type of capacitor is very intolerant of being reverse biased, often exploding when placed under stress. This type of capacitor must also not be subject to high ripple currents or voltages above their working voltage. 

    They are available in both leaded and surface mount formats. 

    Silver Mica Capacitor:   

    Silver mica capacitors are not as widely used these days, but they still offer very high levels of stability, low loss and accuracy where space is not an issue. 

    They are primarily used for RF applications and and they are limited to maximum values of 1000 pF or so. 

    Polystyrene Film Capacitor:   

    Polystyrene capacitors are a relatively cheap form of capacitor but offer a close tolerance capacitor where needed. 

    They are tubular in shape resulting from the fact that the plate / dielectric sandwich is rolled together, but this adds inductance limiting their frequency response to a few hundred kHz. 

    They are generally only available as leaded electronics components.

    Polyester Film Capacitor:   

    Polyester film capacitors are used where cost is a consideration as they do not offer a high tolerance. 

    Many polyester film capacitors have a tolerance of 5% or 10%, which is adequate for many applications. 
    They are generally only available as leaded electronics components. 

    Metallised Polyester Film Capacitor:   

    This type of capacitor is a essentially a form of polyester film capacitor where the polyester films themselves are metallised.

    The advantage of using this process is that because their electrodes are thin, the overall capacitor can be contained within a relatively small package. 

    The metallised polyester film capacitors are generally only available as leaded electronics components.

    Polycarbonate capacitor:   

    The polycarbonate capacitors has been used in applications where reliability and performance are critical. 

    The polycarbonate film is very stable and enables high tolerance capacitors to be made which will hold their capacitance value over time. In addition they have a low dissipation factor, and they remain stable over a wide temperature range, many being specified from -55°C to +125°C. 

    However the manufacture of polycarbonate dielectric has ceased and their production is now very limited. 

    Polypropylene Capacitor:   

    The polypropylene capacitor is sometimes used when a higher tolerance type of capacitor is necessary than polyester capacitors offer. 

    As the name implies, this capacitor uses a polypropylene film for the dielectric. One of the advantages of the capacitor is that there is very little change of capacitance with time and voltage applied. 

    This type of capacitor is also used for low frequencies, with 100 kHz or so being the upper limit. They are generally only available as leaded electronics components. 

    Glass capacitors:   

    As the name implies, this capacitor type uses glass as the dielectric. 

    Although expensive, these capacitors offer very high levels or performance in terms of extremely low loss, high RF current capability, no piezo-electric noise and other features making them ideal for many performance RF applications. 

    Supercap:   

    Also known as a supercapacitor or ultracapacitor, as the name implies these capacitors have very large values of capacitance, of up to several thousand Farads. 

    They find uses for providing a memory hold-up supply and also within automotive applications. 



    Arduino based Automatic Light Controller

    Automatic light controller offers energy saving and convenience in the areas with a photo sensor (LDR). LDR senses the ambient light conditions in the surrounding area and switches ON-OFF the lighting load. The darkness level in the surrounding is settable.

    It is in-built with an additional PIR Sensor which TURNS ON Light in the presence of human and switches OFF after 10 seconds if no human detected for energy saving operation.

    Thus it provides artificial light only when it is needed. This reduces the large amount of energy wastage and helps in making the most energy efficient lighting.

    Components Needed

    The following components are required for making an automatic light bulb controller.

    1.  Arduino Uno
    2. PIR Sensor.
    3. LDR Sensor.
    4. 1k & 10k Resistors
    5. 12V Relay
    6. BC548 Transistor
    7. Switches.

    Circuit Diagram

    Circuit is constructed with PIR sensor, LDR and Arduino. Light Load is connected to Relay. Manual on off is possible with given switches.

    Program Code

    Day night Switch with Occupancy Sensor (Automatic Light Controller)
    const int RELAY =12;   //Lock Relay or motor
    //Key connections with arduino
    const int on_key =3;
    const int off_key =2;
    int counter =0, manual =0;
    //Sensor Connections
    const int LDR = A5 ;
    const int PIR =4;
    //=================================================================
    // SETUP
    //=================================================================
    void setup (){
    pinMode ( RELAY , OUTPUT );
    pinMode ( on_key , INPUT );
    pinMode ( off_key , INPUT );
    pinMode ( PIR , INPUT );
    //Pull up for setpoint keys
    digitalWrite ( on_key , HIGH );
    digitalWrite ( off_key , HIGH );
    digitalWrite ( PIR , HIGH );
    digitalWrite ( RELAY , LOW );        //Turn off Relay
    }   //
    =================================================================
    // LOOP
    //=================================================================
    void loop (){
    //Turn on Lights if Motion is detected and Light intensity is low
    if( digitalRead ( PIR )== HIGH )
    {
    counter =1000; //Set 10 Seconds time out counter
    if( counter >15) //Motion detected for 1.5 Seconds
    {
    if( analogRead ( LDR )>512) //Light intensity is low
    {
    digitalWrite ( RELAY , HIGH ); //Turn on Lights
    }
    }
    } counter --;
    if( counter ==0)
    {
    if( manual ==0) //Check that it is not manually turned on
    {
    digitalWrite ( RELAY , LOW );
    }
    }
    //Get user input for setpointsif( digitalRead ( on_key )== LOW )
    {
    digitalWrite ( RELAY , HIGH ); //Turn on Lights
    manual =1; //Manually it is turned on
    }     if(digitalRead ( off_key )== LOW )
    {
    digitalWrite ( RELAY , LOW ); //Turn off Lights
    manual =0;
    } delay (10); //Update at every 10mSeconds
    }//
    =================================================================

    Why Voltage Control is Important?


    In a modern power system, electrical energy  from the generating station is delivered to the ultimate consumers through a network of transmission and distribution. 

    For satisfactory operation of motors, lamps and other loads, it is desirable that consumers are supplied with substantially constant voltage. 

    Too wide variations of voltage may cause erratic operation or even malfunctioning of consumer's appliances. 

    To safeguard the interest of the consumers, the government in each country has enacted a law in this regard. The statutory limit of voltage variation is 6% of declared voltage at consumer's terminals.

    Causes of Voltage Variation

    The principal cause of voltage variation at consumer's premises is the change in load on the supply system. 

    When the load on the system increases, the voltage at the consumer's terminals falls due to the increased voltage drop in 

    (i) alternator synchronous impedance 
    (ii) transmission line 
    (iii) transformer impedance 
    (iv) feeders and
    (v) distributors. 

    The reverse would happen should the load on the system decrease. These voltage variations are undesirable and must be kept within the prescribed limits (i.e. i 6% of the declared voltage). 

    This is achieved by installing voltage regulating equipment at suitable places in the power system.

    Importance of Voltage Control

    When the load on the supply system changes, the voltage at the consumer's terminals also changes.

    The variations of voltage at the consumer’s terminals are undesirable and must be kept within prescribed limits for the following reasons:

    • In case of lighting load, the lamp characteristics are very sensitive to changes of voltage. For instance, if the supply voltage to an incandescent lamp decreases by 6% of rated value, then illuminating power may decrease by 20%. On the other hand, if the supply voltage is 6% above the rated value, the life of the lamp may be reduced by 50% due to rapid deterioration of the filament.

    • In case of power load consisting of induction motors, the voltage variations may cause erratic operation. If the supply voltage is above the normal, the motor may operate with a saturated magnetic circuit, with consequent large magnetizing current, heating and low power factor. On the other hand, if the voltage is too lo\v, it will reduce the starting torque of the motor considerably.

    • Too wide variations of voltage cause excessive heating of distribution transformers. This may reduce their ratings to a considerable extent.

    It is clear from the above discussion that voltage variations in a power system must be kept to minimum level in order to deliver good service to the consumers. 

    With the trend towards larger and larger interconnected system, it has become necessary to employ appropriate methods of voltage control.

    Difference b/w Microprocessor and Microcontroller

    The term microprocessor and microcontroller have always been confused with each other. Both of them have been designed for real time application. They share many common features and at the same time they have significant differences. 

    Both the IC’s i.e., the microprocessor and microcontroller cannot be distinguished by looking at them.  They are available in different version starting from 6 pin to as high as 80 to 100 pins or even higher depending on the features.

    Microprocessor is an IC which has only the CPU inside them i.e. only the processing powers such as Intel’s Pentium 1,2,3,4, core 2 duo, i3, i5 etc. These microprocessors don’t have RAM, ROM, and other peripheral on the chip. A system designer has to add them externally to make them functional. Application of microprocessor includes Desktop PC’s, Laptops, notepads etc.

    The microcontroller incorporates all the features that are found in microprocessor. The important thing is that microcontroller has built in ROM, RAM, Input Output ports, Serial Port, timers, interrupts and clock circuit. A microcontroller is an entire computer manufactured on a single chip. 
    For example, microcontrollers are used as engine controllers in automobiles and as exposure and focus controllers in cameras.

    Microprocessor V/S Microcontroller

    • It is very clear from figure above that in microprocessor we have to interface additional circuitry for providing the function of memory and ports. 
      • For example we have to interface external RAM for data storage, ROM for program storage, programmable peripheral interface (PPI) 8255 for the Input Output ports, 8253 for timers, USART for serial port. 

    • While in the microcontroller RAM, ROM, I/O ports, timers and serial communication ports are in built. Because of this it is called as “system on chip”. 
      • So in microcontroller there is no necessity of additional circuitry which is interfaced in the microprocessor because memory and input output ports are inbuilt in the microcontroller. 

      • Microcontroller gives the satisfactory performance for small applications. But for large applications the memory requirement is limited because only 64 KB memory is available for program storage.  
        • So for large applications we prefer microprocessor than microcontroller due to its high processing speed.

        Criteria for Selection of a Microcontroller in Embedded System

        Criteria for selection of microcontroller in any embedded system is as following:

        • Meeting the computing needs of task at hand efficiently and cost effectively
          • Speed of operation
          • Packing
          • Power consumption
          • Amount of RAM and ROM on chip
          • No. of I/O pins and timers on chip
          • Cost

        •  Availability of software development tools such as compiler, assembler and debugger.

        Transformer Oil Sampling / Testing : Video Training



        Oil testing in a transformer is just as a blood test in human body. A blood test provides a doctor with a wealth of information about the health of a patient. A sample of transformer oil, taken correctly, can tell service engineers a great deal about the condition of a transformer.

        Oil is used both to cool the transformer and to insulate internal components. Because it bathes every internal component, the oil contains a great deal of diagnostic information. So a laboratory analysis of a sample can provide advance warning of developing conditions such as tapchanger arcing.

        The oil tests can uncover several potential problems within a transformer. The same sample can contain evidence of soluble contaminants, dielectric contaminants, and acid materials present in the oil. With so much riding on transformer maintenance, it's important to conduct and complete all of the recommended tests.

        This is a video training series on transformer oil sampling or testing done by TxMonitor.

        Transformer Oil Sampling - Part 1: Introduction

        As always, safety first. We start our Transformer Oil Sampling series with a number of highlights on health, environmental and safety considerations when performing these tasks.

        Please these are only guidelines and do not replace adequate competency and skills. Always follow the relevant company and legislative requirements for your particular work context.


        Transformer Oil Sampling - Part 2: Bottle Sample

        There are some sampling techniques better suited for certain types of oil tests than others. 

        The techniques described in this video should be sufficient to sample oil when common chemical and physical properties are analysed, such as Breakdown Voltage, Interfacial Tension, Acidity (or Neutralization Number), Colour and Visual Inspection.


        Transformer Oil Sampling - Part 3: Glass Syringe

        A sampling technique proven to produce repeatable results when testing the Dissolved Gas content or Moisture (Water) Content in the oil is by sampling with a Glass Syringe.

        In this video we'll learn how to execute this technique.


        Transformer Oil Sampling - Part 4 : The Buchholz Relay

        In this video, the fourth and final of the Oil Sampling series, you'll learn how to extract a gas and oil sample from a Buchholz gas accumulation relay through a sampling device.




        Previous
        Editor's Choice