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14 Lectures on Programmable Logic Controllers (PLC)

A PLC is a user-friendly, microprocessor based specialized computer that carries out control functions of many types and levels of complex...

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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;
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
}   //
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.

      IEC 61850 - Features and Advantages

      Communication plays an important role in the real time operation of a power system. In the beginning, telephone was used to communicate line loadings back to the control center as well as to dispatch operators to perform switching operations at substations. 

      With the entry into a digital age, we needed the technology to cater to the hot requirements, which are;

      • High-speed IED to IED communication
      • Multi-vendor interoperability
      • Support for File Transfer
      • Auto-configurable / configuration support
      • Support for security

      Given these requirements, work on next generation communication architecture began with the development of the Utility Communication Architecture (UCA) in 1988.

      The result of this work was a profile of “recommended” protocols for the various layers of the International Standards Organization (ISO) Open System Interconnect (OSI) communication system model. 

      The concepts and fundamental work done in UCA became the foundation for the work done in the IEC Technical Committee Number 57 (TC57) Working Group 10 (WG10), which resulted in the International Standard – IEC 61850 – Communication Networks and Systems in Substations.

      Today, IEC 61850 is a standard for the design of electrical substation automation and it has been defined in cooperation with manufacturers and users to create a uniform, future-proof basis for the protection, communication and control of substations. 

      IEC 61850 meets the requirements for an integrated Information Management, providing the user with consistent Knowledge of the System on-line rather than just Gigabytes of raw data values. IEC 61850 defines standardized Information Models across vendors and a comprehensive configuration standard (SCL – System Configuration Language).

      Features of IEC 61850:

      Some of the features of IEC 61850 are given below.
      • Data Modeling: Primary process objects as well as protection and control functionality in the substation is modeled into different standard logical nodes which can be grouped under different logical devices. There are logical nodes for data/functions related to the logical device (LLN0) and physical device (LPHD).
      • Reporting Schemes: There are various reporting schemes (BRCB & URCB) for reporting data from server through a server-client relationship which can be triggered based on pre-defined trigger conditions
      • Fast Transfer of events: Generic Substation Events (GSE) are defined for fast transfer of event data for a peer-to-peer communication mode. This is again subdivided into GOOSE & GSSE.
      • Setting Groups: The setting group control Blocks (SGCB) is defined to handle the setting groups so that user can switch to any active group according to the requirement.
      • Sampled Data Transfer: Schemes are also defined to handle transfer of sampled values using Sampled Value Control blocks (SVCB)
      • Commands: Various command types are also supported by IEC 61850 which include direct & select before operate (SBO) commands with normal and enhanced securities.
      • Data Storage: Substation Configuration Language (SCL) is defined for complete storage of configured data of the substation in a specific format.

      Advantages of IEC 61850

      The main advantages of using IEC61850 include:
      • Offering a complete set of specifications covering all communication issues inside a substation.
      • Meeting the requirement for an integrated information management providing the user with consistent knowledge of the system on line, rather than just gigabytes of raw data.
      • Inter-operability between various manufacturers’ IED’s, thus forming an integrated system.
      • Substation Configuration Language(SCL)
      • Lowering installation and maintenance costs, with self-describing devices that reduce manual configuration.
      • Support for functions difficult to implement otherwise.

      How to Make a Digital Lock Using Arduino?

      Digital code locks are most common on security systems. An electronic lock or digital lock is a device which has an electronic control assembly attached to it. They are provided with an access control system. This system allows the user to unlock the device with a password. The password is entered by making use of a keypad. The user can also set his password to ensure better protection.

      In this project major components include a keypad, LCD and the controller Arduino. This article describes the making of an electronic code lock using arduino.

      Components Required

      The following components are required for making the digital code lock
      1. Arduino Uno
      2. 16x2 LCD Display
      3. 4x4 keypad
      4. Relay
      5. 1K Resistors Qty. 3
      6. BC548
      7. LEDs

      Digital Code Lock Circuit

      Code lock circuit is constructed around Arduino Uno, using LCD and keypad. 

      LCD and keypad forms the user interface for entering the password and displaying related messages such as “Invalid password”, “Door open”, etc. 

      Two LEDs are provided to indicate the status of door whether it is locked or open. To operate latch/lock we are using Relay which can be connected to the electronic actuator or solenoid.

      Program Code for Arduino Digital Code Lock

      Program is constructed using two libraries “LiquidCrystal” and “Keypad”. 

      Program have different modules, Setup, Loop, Lock. 

      In setup we initialize all the IO connections and LCD, Keypad. 

      In main loop we are taking pressed keys in array “code[]”, Once the four digits are entered we stop accepting keys. 

      We are using numeric keys and ‘C’ , “=” key. ‘C’ key is used to lock or clear the display incase wrong password is entered. 

      We can hide the entered password by putting Star character ‘*’.

      After entering password ‘=’ key acts as ok. If password is correct door is kept unlocked for few seconds. If it is incorrect message will be displayed.

      /* Digital Code Lock Demo */
      #include <Keypad.h>
      #include <LiquidCrystal.h>
      // initialize the library with the numbers of the interface pins
      LiquidCrystal lcd (9, 8, 7, 6, 5, 4);
      const byte ROWS = 4; //four rows
      const byte COLS = 4; //four columns
      //define the cymbols on the buttons of the keypads
      char hexaKeys [ ROWS ][ COLS ] = {
      byte rowPins [ ROWS ] = {3, 2, 19, 18}; //connect to the row pinouts of the keypad
      byte colPins [ COLS ] = {17, 16, 15, 14}; //connect to the column pinouts of the keypad
      //initialize an instance of class NewKeypad
      Keypad customKeypad = Keypad ( makeKeymap ( hexaKeys ), rowPins , colPins , ROWS ,
      COLS );
      const int LED_RED =10; //Red LED
      const int LED_GREEN =11; //Green LED
      const int RELAY =12; //Lock Relay or motor
      char keycount =0;
      char code [4]; //Hold pressed keys
      // SETUP
      void setup (){
      pinMode ( LED_RED , OUTPUT );
      pinMode ( LED_GREEN , OUTPUT );
      pinMode ( RELAY , OUTPUT );
      // set up the LCD's number of columns and rows:
      lcd . begin (16, 2);
      // Print a message to the LCD.
      lcd . print ("Password Access:");
      lcd . setCursor (0,1); //Move coursor to second Line
      // Turn on the cursor
      lcd . cursor ();
      digitalWrite ( LED_GREEN , HIGH ); //Green LED Off
      digitalWrite ( LED_RED , LOW ); //Red LED On
      digitalWrite ( RELAY , LOW ); //Turn off Relay (Locked)
      // LOOP
      void loop (){
      char customKey = customKeypad . getKey ();
      if ( customKey && ( keycount <4) && ( customKey !='=') && ( customKey !='C')){
      //lcd.print(customKey); //To display entered keys
      lcd . print ('*'); //Do not display entered keys
      code [ keycount ]= customKey ;
      keycount ++;
      if(customKey == 'C') //Cancel/Lock Key is pressed clear display and lock
      Lock (); //Lock and clear display
      if(customKey == '=') //Check Password and Unlock
      if(( code [0]=='1') && ( code [1]=='2') && ( code [2]=='3') && ( code [3]=='4')) //Match the
      password. Default password is “1234”
      digitalWrite ( LED_GREEN , LOW ); //Green LED Off
      digitalWrite ( LED_RED , HIGH ); //Red LED On
      digitalWrite ( RELAY , HIGH ); //Turn on Relay (Unlocked)
      lcd . setCursor (0,1);
      lcd . print ("Door Open ");
      delay (4000); //Keep Door open for 4 Seconds
      Lock ();
      lcd . setCursor (0,1);
      lcd . print ("Invalid Password"); //Display Error Message
      delay (1500); //Message delay
      Lock ();
      // LOCK and Update Display
      void Lock ()
      lcd . setCursor (0,1);
      lcd . print ("Door Locked ");
      delay (1500);
      lcd . setCursor (0,1);
      lcd . print (" "); //Clear Password
      lcd . setCursor (0,1);
      keycount =0;
      digitalWrite ( LED_GREEN , HIGH ); //Green LED Off
      digitalWrite ( LED_RED , LOW ); //Red LED On
      digitalWrite ( RELAY , LOW ); //Turn off Relay (Locked)

      Basic Relays - Electromagnetic Attraction and Induction Relays

      Most of the relays used in the power system operate by virtue of the current and/or voltage supplied by current and voltage transformers connected in various combinations to the system element that is to be protected. 

      Through the individual or relative changes in these two quantities, faults signal their presence, type and location to the protective relays. 

      Having detected the fault, the relay operates the trip circuit which results in the opening of the circuit breaker and hence in the disconnection of the faulty circuit.

      Most of the relays in service on electric power system today are of electro-mechanical type. They work on the following two main operating principles :

      1. Electromagnetic attraction 
      2. Electromagnetic induction

      Practically, a relay is an amplifier, since it is able to control a high power output through a low power input. They were first invented in 1835 by Joseph Henry, the man who also discovered electromagnetic induction and whose name is currently being used for the SI unit of inductance.

      Electromagnetic Attraction Relays

      Electromagnetic attraction relays operate by virtue of an armature being attracted to the poles of an electromagnet or a plunger being drawn into a solenoid. Such relays may be actuated by DC or AC quantities. 

      The important types of electromagnetic attraction relays are:
      • Attracted armature type relay
      • Solenoid type relay
      • Balanced beam type relay

      Induction Relays

      Electromagnetic induction relays operate on the principle of induction motor and are widely used forprotective relaying purposes involving a.c. quantities. 

      They are not used with d.c. quantities owing to the principle of operation. 

      An induction relay essentially consists of a pivoted aluminium disc placed in two alternating magnetic fields of the same frequency but displaced in time and space. 

      The torque is produced in the disc by the interaction of one of the magnetic fields with the currents induced in the disc by the other.

      The following three types of structures are commonly used for obtaining the phase difference in the fluxes and hence the operating torque in induction relays :
      • shaded-pole structure
      • watthour-meter or double winding structure
      • induction cup structure

      Solid State Relays (Static Relays)

      What is a Static Relay?

      There are two basic classifications of relays - Electromechanical Relays and Solid State Relays. One main difference between them is electromechanical relays have moving parts, whereas solid state relays have no moving parts. 

      Solid State Relay (Static Relay) is an electrical relay in which the response is developed by electronic/magnetic/optical or other components, without mechanical motion of components.

      A solid state relay is composed of both static and electromechanical units in which the response is accomplished by the static units. Therefore solid state relays are also called as static relays.

      In static relays, the measurement is performed by electronic/magnetic/optical or other components without mechanical motion. However additional electromechanical relay units may be used in output stage as auxiliary relays. A protective system is formed by static relays and electromechanical auxiliary relays.

      Working of Solid State Relay

      Figure shows the essential components in a static relay. The output of CT's or PT's or transducers is rectified in rectifier.

      The rectified output is fed to the measuring unit. The measuring unit comprises comparators, level detectors, filters, logic circuits. The output is initiated when input reaches the threshold value.

      The output of measuring unit is amplified by Amplifier. The amplified output is given to the output unit which energizes the trip coil only when relay operates.

      In conventional electromagnetic the measurement is carried out by comparing operating torque/force with restraining torque/force. The electro-mechanical relay operates when operating torque/fence exceeds the restraining torque/force. The pick-up of relay is obtained by movement of movable element in the relay. In a static relay the measurement is performed by static cincuils.

      A simplified block diagram of single input static relay is given in the above figure. In individual relays there is a wide variation. The quantities: voltage, current. etc. is rectified and measured. When the quantity to be measured reaches certain well defined value, the output device is triggered. Thereby current flows in the trip circuit of the circuit-breaker. 

      Figure below gives a block diagram of a microprocessor based digital, programmable static relay.

      Static relays can be arranged to respond to electrical inputs. The other forms of inputs such as heat, light, magnetic field, travelling waves etc. can be suitably converted into equivalent analogue or digital signals and then fed to the static relay.  multi-input static relay can accept several inputs. The logic circuit in the multi-input digital static relay can determine the conditions for relay response and sequence of events in the response.

      A programmable protection and control system has a microprocessor or microcomputer in its circuit. With the help of the logic circuits and the microprocessor the integrated protection and control system can perform several functions of data acquisition, data processing, data transmission, protection and control. Earlier, for each of these functions, separate electromechanical or static units were used along with complex wiring.

      Protective Zones in Power Systems

      A protective zone is the separate zone which is established around each system element. The significance of such a protective zone is that any fault occurring within cause the tripping of relays which causes opening of all the circuit breakers within that zone. 

      The circuit breakers are placed at the appropriate points such that any element of the entire power system can be disconnected for repairing work, usual operation and maintenance requirements and also under abnormal conditions like short circuits. Thus a protective covering is provided around rich element of the system. 

      The various components which are provided with the protective zone are generators, transformers, transmission lines, bus bars, cables, capacitors etc. No part of the system is left unprotected. The figure below shows the various protective zones used in a system.

      Why Protection Zones are Overlapped?

      The boundaries of protective zones are decided by the locations of the current transformer. In practice, various protective zones are overlapped. 

      The overlapping of protective zones is done to ensure complete safety of each and every element of the system. The zone which is unprotected is called dead spot. The zones are overlapped and hence there is no chance of existence of a dead spot in a system. For the failures within the region where two adjacent protective zones are overlapped, more circuit breakers get tripped than minimum necessary to disconnect the faulty element. 

      If there are no overlaps, then dead spot may exist, means the circuit breakers lying within the zone may not trip even though the fault occurs. This may cause damage to the healthy system. 

      The extent of overlapping of protective zones is relatively small. The probability of the failures in the overlapped regions is very low; consequently the tripping of the too many circuit breakers will be frequent. The figure shows the overlapping of protective zones in primary relaying.
      Figure shows Overlapping zones in primary relaying. It can be seen from the figure that the circuit breakers are located in the connections to each power system element. This provision makes it possible to disconnect only the faulty element from the system. 

      Occasionally for economy in the number of circuit breakers, a breaker between the two adjacent sections may be omitted but in that case both the power system are required to be disconnected for the failure in either of the two. Each protective zone has certain protective scheme and each scheme has number of protective systems.
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