presentation on relays and circuit breakers

8/2/2019 Presentation on Relays and Circuit Breakers

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PRESENTATION ONRELAYS AND CIRCUIT

BREAKERS


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Click to edit Master subtitle style

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INTRODUCTION OFSWITCH GEAR.

TYPES OF SWITCH GEAR EQUIPMENT:-

1. CIRCUIT BREAKER2. BUS BAR3. FUSE4. PROTECTIVE RELAY


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CHARACTERISTICS OF

PROTECTION SYSTEM 1. RELIABILITY2.SENSTIVITY

3.SELECTIVITY4.DISCRIMINATION5.SPEED

6.SIMPLICITY7.ECONOMY


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RELAYS

The function of protectiverelaying is to cause the promptremoval from service of any

element of a power system whenit suffers a short circuit, or whenit starts to operate in any

abnormal manner that mightcause damage or otherwiseinterfere with the effectiveoperation of the rest


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REQUIREMENTS OFPROTECTIVE RELAYS

1.SENSITIVITY : The relay shallbe sensitive to operate forminimum quantity of

operating parameter.

2.SELECTIVITY: The

relay/scheme should be ableto select the faulty sectionand isolate.


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REQUIREMENTS OFPROTECTIVE RELAYS

4.STABILITY : The Relay should

be stable.

5.RELIABILITY: The relay/scheme

should operate for all typesof faults with repeatabilityand reliability.


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Basis of Classifications

Quantity of response: Voltage,current, frequency, power etc.

Function: Detection, time-delay,tripping, alarm, signaling, flag,

contact multiplication etc

Construction: Electromagnetic,

Static or Numerical


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Basic Types Based onOperating Principle

Attracted Armature

Moving Coil

InductionThermal

Motor-Operated

Mechanical

Static

Numerical


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OPERATING PRINCIPLES

1. Electromagnetic attraction:Electromagnetic attraction relays operateby virtue of a plunger being drawn into a

solenoid, or an armature being attracted to the poles of an electromagnet. Suchrelays may be actuated by dc or by acquantities.

2. Electromagnetic induction:Electromagnetic-induction relays use theprinciple of the induction motor whereby

torque is developed by induction in a


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IMPORTANT TERMS

Pick-up current - It is the minimumcurrent in the relay coil at which therelay starts to operate.

Current setting It is oftendesirable to adjust the pickup currentto any value. This is know as current

setting and is usually achieved bythe use of tapping on the relay coil.

Pickup current = Rated secondary

current of CT x Current setting


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IMPORTANT TERMS

Plug setting multiplier (P.S.M) Itis the ratio of fault current in therelay coil to the pick up current.

Time setting multiplier- Thisfeature allows the adjustment ofrelay operation time.

Actual time of operation = timesetting multiplier X time in seconds.


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CIRCUIT BREAKER

Circuit Breaker is a device which canmake or break circuit under normalconditions either manually or through

remote control. Break circuit automatically under

faulty conditions.

Make or break circuit under faultyconditions either manually or throughremote control.

CIRCUIT BREAKER VERSUS


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CIRCUIT BREAKER VERSUSFUSE

Fuses are used for low and highvoltage circuits of moderate tohigh capacity where frequentoperations are not expected.Circuit breakers are used whereslight overload occurs or whereheavy currents are to be broken.Moreover a circuit breaker "trips"to break the circuit and may bereset, while a fuse melts andm t r l .


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WORKING PRINCIPLE OFCIRCUIT BREAKER

A Circuit breaker consists of fixedand moving contacts touching eachother under normal conditions.Whenever a fault occurs the tripcoil get energized ,the movingcontacts are pulled by somemechanism and therefore circuitbreaker is opened and circuit isbroken.


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ARC EXTINCTIONWhen a current is interrupted, an arc

is generated. This arc must becontained, cooled, and extinguished in acontrolled way, so that the gap betweenthe contacts can again withstand thevoltage in the circuit. Different circuitbreakers use vacuum, air, insulatinggas, or oil as the medium in which the

arc forms. Different techniques are usedto extinguish the arc including:

Lengthening of arc .

Division into partial arcs .


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FAULT CLEARING PROCESS1- Fault Occurs. As the fault occurs, the

fault impedance being low, the currentsincrease and the relay gets actuated.

The moving part of the relay move becauseof the increase in the operating torque. Therelay then closes its contacts.

2 - Relay contacts close the trip circuit ofthe Circuit

breaker and trip coil is energized.

3 - The operating mechanism startsoperating for the opening operation andcontacts separate.

4 - Arc is drawn between the breaker


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TRIP CIRCUIT


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BREAKERS Low Voltage Circuit Breakers

Oil Circuit Breakers

(i) Bulk Oil Circuit Breakers

(ii) Minimum Oil Circuit Breakers() Air Blast Circuit Breakers

()

Vacuum Circuit Breakers() Sulphur Hexa Fluoride Circuit

Breakers


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Low Voltage CircuitBreakers

These breakers are made for directcurrent (DC) applications and lowvoltage A.C applications and are

commonly used in domestic,commercial, and industrial fields.Miniature circuit breakers (MCB) and

molded case circuit breakers (MCCB)are some common types of lowvoltage circuit breakers.


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MINIATURE CIRCUITBREAKER


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COMPONENTS OF MCB

1. Lever

2. Mechanism

3. Contacts4. Terminals

5. Bimetallic strip

6. Calibration Screw

7. Solenoid

8. Arc Chute


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OIL CIRCUIT BREAKERS

Such circuit breakers utilize dielectricoil (transformer oil) for arc extinction.In bulk oil circuit breakers, the

contacts are separated inside a steelfilled with dielectric oil. In minimumoil circuit breakers, the contacts are

separated in an insulation housing(interrupter)filled with dielectric oil.


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AIR BLAST CIRCUITBREAKER

In air blast circuit breakers, thecontacts are surrounded bycompressed air. When the contacts

are opened the compressed air isreleased in forced blast through thearc to the atmosphere extinguishing

the arc in the process. A compressorplant is necessary to maintain highair pressure in the receiver.

AIR BLAST CIRCUIT


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AIR BLAST CIRCUITBREAKER

VACUUM CIRCUIT


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VACUUM CIRCUITBREAKERS

Vacuum circuit-breakers does not

require an interrupting or insulationmedium. In fact, the interrupters donot contain ionizable material.

During the separation of current-carrying contacts, contact pressurereduces, real contact surface reduces

and the temperature of contactsincreases to melting temperature.

This produces metal vapors whichinitiates and supports the vacuumarc, maintainin until the next


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VACUUM CIRCUITBREAKERS

SULPHUR HEXA FLUORIDE


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SULPHUR HEXA FLUORIDECIRCUIT BREAKERS

Sulfur hexafluoride (SF6) gas is analternative to air as an interruptingmedium. SF6 is a colorless nontoxicgas, with good thermal conductivity

and density approximately five timesthat of air. SF6 is chemically inert upto temperature of 150 C and will not

react with metals, plastics, and othermaterials commonly used in theconstruction of high voltage circuitbreakers.


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ARC EXTINCTIONPHENOMENON


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presentation on relays and circuit breakers

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