Introduction to Protection

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basics related to protection of power system

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INTRODUCTION TO POWER SYSTEM PROTECTION R&D Deptt. Protection & Control Division R.J.Phansalkar 1

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What is Protected? Why protection is needed ? What is Power system & What are its basic elements ? Principle elements of Protection system including Circuit breakers, Relays, CTs & PTs Relay & Fuse comparison. What are Faults & why they occur ? Types of Relays & Digital relay Advantages & Enhancements Basic requirements of the Protection schemes Any Queries from the Audience Discussion Points 2

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Protection of the equipments Protection of the personnel Protection of the property Protection of the protecting elements What is Protected ? 3

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Power System includes: Generation System Electrical Power is obtained either by Thermal, Hydro, Nuclear, Solar, Wind Energy Transmission System Why transmission of Power? What are different voltages of power transmission? Overhead OR Underground? Distribution System All types of Electrical Loads Motors, Furnaces, Lights, Domestic appliances What is Power System ? 4

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Power System Protection includes a series of devices, whose main purpose is to protect persons and primary electric power equipment from the effects of faults. Relays are like the “Sentinels” What is Protection System ? 5

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There is no ‘ Fault Free ’ system. It is neither practical nor economical to build a ‘ Fault Free ’ System. Electrical system shall tolerate certain degree of faults. Usually faults are caused by breakdown of insulation due to various reasons: system aging, lighting etc. Why the system needs Protection ? 6

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Cost of Damage because of Electrical Faults is directly proportional to the Square of the Fault current and is also directly proportional to the time for which Fault current flows. In addition to the direct losses there will be huge production losses if the fault is allowed to damage and power is not provided. SO PROTECTION OF THE POWER SYSTEM FROM THE FAULTS IS EXTREMELY IMPORTANT Why Protection ? 7

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Damage to Main Equipment 8

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http://video.google.com/videoplay?docid=7703052748770170847# Video showing severity of damage 9

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I t I n I md Damage Curve Short-Circuit Current Damage Time Rated Value Electrical Equipment Thermal Damage 10

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Whenever current flows in the unwanted device or unwanted place we call it a Fault Any undesired thing in the system such as Overvoltage or under voltage condition Or Over / Under frequency Condition we call it fault What is Fault? 11

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Single-Phase-Ground : 70–80% Phase-Phase-Ground : 17–10% Phase-Phase : 10–8% Three-Phase : 3–2% Typical short circuit faults in the distribution system 12

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Overload Insulation breakdown because of aging or over voltages External objects /Animals/Birds Mal operation of the Relays leading to system instability Rains/Moisture/Snow fall/ other external calamities WHAT ARE THE CAUSES OF FAULTS ? 13

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Fuses Protective Relays Circuit Breakers Current & Voltage Transformers Communications Channels DC Supply System Control Cables Protection System Elements 14

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Relays Circuit Breakers Fuses Acquisition Detection Activation Actuation Protective Devices Comparison 15

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Relays are electrical switches that open or close another circuit under certain conditions. What are Relays ? 16

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Isolate controlling circuit from controlled circuit. Control high voltage system with low voltage. Control high current system with low current. Logic Functions Relays Purpose 17

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Electro-Mechanical Static Microprocessor based Microcontroller based Intelligent relays which can communicate with other devices Types of protective Relays ? 18

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Electromagnetic Relays (EMRs) EMRs consist of an input coil that's wound to accept a particular voltage signal, plus a set of one or more contacts that rely on an armature (or lever) activated by the energized coil to open or close an electrical circuit. Solid-state Relays (SSRs) SSRs use semiconductor output instead of mechanical contacts to switch the circuit. The output device is optically-coupled to an LED light source inside the relay. The relay is turned on by energizing this LED, usually with low-voltage DC power. Microprocessor / Microcontroller based Relays Use microprocessor for switching mechanism. Commonly used in power system monitoring and protection. Relays Types 19

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Fuses Vs. Relays Relays have different settings and can be set based on protection requirements. Relays can be reset. Fuses only have one specific characteristic for a individual type. Fuses cannot be reset but replaced if they blow. Protective Device Comparison 20

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DC Tripping Circuit 21

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Circuit Breaker 22

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Very High Voltage CT Medium-Voltage CT Current Transformers 23

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Medium Voltage High Voltage Note : Voltage transformers are also known as potential transformers Voltage Transformers 24

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Protective Relays 25

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What happens if protection fails ? What is Primary Protection ? Back-Up Protection Coordination Primary & Backup Protection 26

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Primary Protection 27

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Backup Protection 28

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Single-Phase-Ground : 70–80% Phase-Phase-Ground : 17–10% Phase-Phase : 10–8% Three-Phase : 3–2% Typical Short circuit type Distribution 29

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Why Faults occur 30

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Protection Zone B Protection Zone A To Zone B Relays To Zone A Relays 52 Protection Zone B Protection Zone A To Zone B Relays To Zone A Relays 52 Primary Protection Zone Overlapping 31

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When a fault takes place, the current, voltage, frequency, and other electrical variables behave in a peculiar way. For example: Current suddenly increases Voltage suddenly decreases Frequency suddenly drops Relays can measure the currents and the voltages and detect that there is an over-current , or an under voltage , or a combination of both Many other detection principles determine the design of protective relays How do Relays detects faults ? 32

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Reliability Dependability Security Selectivity Speed System stability Equipment damage Power quality Sensitivity High-impedance faults Dispersed generation Main Protection requirements 33

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Balanced System Unbalanced System Balanced Vs Unbalanced Conditions 34

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Decomposition of an Unbalanced system 35

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Over-current (50, 51, 50N, 51N) Directional Over-current (67, 67N) Distance (21, 21N) Differential (87) Power line protection principles 36

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How a Relays Works ? 37

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Solid State Relays 38

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Multifunctional Compatibility with digital integrated systems Low maintenance (self-supervision) Highly sensitive, secure, and selective Adaptive Highly reliable (self-supervision) Reduced burden on CTs and VTs Programmable Versatile Low Cost Advantages of Digital Relays 39

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THANKS 40