Protec Cio Introd 1

7/28/2019 Protec Cio Introd 1

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ProtectionsPrinciples


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PRINCIPLES

Introduction

General concepts of protection systems

Elements of a protection system

Relay types

Relay design and construction

Relay operating principles

Applying protective relays

LINES PROTECTION TRANSFORMERS PROTECTION

STATION BUS PROTECTION

AGENDA


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PRINCIPLES

Introduction



Relay types






AGENDA


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Introduction

Electric energy is one of the fundamental resources of the modern

industrial society

Electrical power is available to the user instantly, at the correct voltage

and frequency, at exactly the amount needed.

Yet the power system is subject to constant disturbances:

Random load changes

Faults by natural causes

Equipment or operator failure

The power system maintains its steady state mainly because of the

correct and quick remedial action taken by the protective relaying

equipment.


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Introduction

The response of the protection system must be automatic, quick, and

should cause a minimum amount of disruption to the power system.

To accomplish this is necessary:

Examine all possible types of faults

Analyze the required response and design the protective equipment

necessary

Provide for a back-up protective function to prevent failure of the protection

itself


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Possible types of faults

Overcurrent

Short - circuits Not wanted contact between phases or between phase and ground

Electrodynamic stress

Thermal stress

Overloads

Thermal stress

Ground faults

Fire hazard

Personal hazard

Overvoltage Switching

Temporary

Lightning strikes

Provoke isolation damage which could develop into short circuits


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Function of protective relaying

DETECT THE ELEMENT THAT STARTS TO OPERATE IN AN

ABNORMAL MANNER

REMOVE THIS ELEMENT FROM THE POWER SYSTEM AS

QUICKLY AS POSSIBLE

SIGNALING, LOGGING AND REPORTING


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PRINCIPLES

Introduction



Relay types






AGENDA


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Protective relays attributes

SENSITIVITY - Ability to detect deviations of the parametersinside the zone or element to protect

SELECTIVITY - Ability to discern when it must actuate, wait orblock, to remove the least number of elements

QUICKNESS - Minimum time in the process Detect- Select-Trip

RELIABILITY - Degree of certainty that an element will performas intended

SECURITY - Certainty that the relay will not operate incorrectly for anyfault

DEPENDABILITY - Certainty that the relay will operate correctly for

all the faults it is designed to operate

ROBUSTNESS (STRENGTH) - Ability to withstand over yearsthe adverse conditions at which they are submitted

BURDEN - minimum, so as not to oversize the instrumenttransformers


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Selectivity and zones of protection

Selectivity is defined in terms of regions of a power system (zones of

protection) for which a given relay is responsible.

The relay will be considered secure if it responds only to faults within its

zone of protection

A zone boundary is usually defined by a CT and a CB.

The CT provides the ability to detect a fault inside the zone

The CBs provide the ability to isolate the fault


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All power system

elements must be

encompassed by atleast one zone.

The more important

elements must be

included in at least two

zones

Zones must overlap to

prevent any element

from being unprotected.

The overlap must be

finite but small to

minimize the likelihoodof a fault inside this

region.

Such a fault will cause

both protections to

operate removing a

larger segment of thesystem from service

Selectivity and zones of protection


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PROTECTION REACH

ZONE OF PROTECTION

PROTECTION REACH

ZONE OF PROTECTION

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DEFINED REACH

CLOSED ZONE

PROTECTION

UNDEFINED REACH

OPEN ZONE

PROTECTION

Zones of protection


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Primary and back up protection

It is essential that provision be made to clear the fault by some alternate

protection system in case of the primary protection could fail.

These are referred to as back up protection systems

On EHV is common to use duplicate primary protection systems

Back up relaying may be installed locally, in the same substation, or remotelly

Remote back up are completely independent of the relays, CT, breakers,

etc.

Remote back up may remove more sources that can be allowed

Local back up use common elements an can thus fail to operate as the

primary protection


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REACH OF PROTECTION 21P

REACH OF PROTECTION 21B

21P

Back up protection locally at the same position

21B


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REACH OF PROTECTION 21

21

50/51

REACH OF PROTECTION 50/51 OF THE TRANSFORMER

REACH OF PROTECTION 50/51 OF BUS TIE BREAKER

A B

Back up protection locally at different positions


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REACH OF PROTECTION 21B

REACH OF PROTECTION 21A

21

Remote back up protection

21

SUBSTATION ASUBSTATION B


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87

Teletrip

TELETRIP

TELETRIP

86

1

2


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PRINCIPLES

Introduction



Relay types




LINES PROTECTION

TRANSFORMERS PROTECTION


AGENDA


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3

Elements of a Protection System

1

5

2.1

2.4

F.A.

A D

2.2P

2.3

2

4


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1

The function of transducers (usually CT and VT) is to provide current and

voltage signals to the relays, to detect deviations of the parameters watched

over.


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3


1

2.1

2.4

F.A.

A D

2.2P

2.3

2

Relays are the logic

elements which initiate

the tripping and closing

operations.


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3


1

2

4

Circuit breakers

isolate the fault by

interrupting the

current.


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3


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2.4

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2.2P

2.3

2

4

Tripping power, as

well as power

required by therelays, is usually

provided by the

station battery

because is safer than

the ac faulted

system.


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PRINCIPLES

Introduction General concepts of protection systems


Relay types




LINES PROTECTION



AGENDA


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Classification of relays

Relays can be divided into six functional categories:

Protective relays. Detect defective lines, defective apparatus, or

other dangerous or intolerable conditions. These relays generally tripone or more circuit breakers, but may also be used to sound an

alarm.

Monitoring relays. Verify conditions on the power system or in the

protection system. These relays include fault detectors, alarm units,

channel-monitoring relays, synchronism verification, and networkphasing. Power system conditions that do not involve opening circuit

breakers during faults can be monitored by verification relays.

Reclosing relays. Establish a closing sequence for a circuit breaker

following tripping by protective relays.


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Relays can be divided into six functional categories:

Regulating relays. Are activated when an operating parameterdeviates from predetermined limits. Regulating relays function

through supplementary equipment to restore the quantity to the

prescribed limits.

Auxiliary relays. Operate in response to the opening or closing of

the operating circuit to supplement another relay or device. Theseinclude timers, contact-multiplier relays, sealing units, isolating

relays, lock-out relays, closing relays, and trip relays.

Synchronizing (or synchronism check) relays. Assure that proper

conditions exist for interconnecting two sections of a power system.


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Classification of relays Performance Characteristics

Differential

Distance

Directional overcurrent

Inverse time

Definite time

Undervoltage

Overvoltage

Ground or phase

High or low speed Pilot

Phase comparison

Directional comparison

Current differential


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By design mode:

Electromechanical

Plunger type

Induction type

Thermal

Solid state

Computer type

By parameter controlled:

Current

Voltage

Power

Impedance (distance)

Direction

Frequency

By mode of Detection of

faults :

Level detection

Magnitude comparison

Differential comparison

Phase angle comparison

Pilot relaying

Harmonic content

Frequency sensing

By operating time:

Instantaneous

Time delay

Independent delay

Dependent delay



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Relay speed

Relays are generally classified by their speed of operation as follows:

Instantaneous These relays operate as soon as a secure decision is made.

No intentional time delay is introduced to slow down the relay response

Time delay

An intentional time delay is inserted between the relay decision time andthe initiation of the trip action

This time delay can be dependent on some parameter (usually inverse time

dependent) or independent

High speed

A relay that operates in less than a specified time (usually 3 cycles)

Ultra high speed

This term is not included in the Relay Standards but is commonly

considered to be operation in 4 milliseconds or less


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Analog/Digital/Numerical

Analog relays are those in which the measured quantities are converted into

lower voltage but similar signals, which are then combined or compared directly

to reference values in level detectors to produce the desired output.

Digital relays are those in which the measured ac quantities are manipulated in

analog form and subsequently converted into square-wave (binary) voltages.Logic circuits or microprocessors compare the phase relation-ships of the

square waves to make a trip decision.

Numerical relays are those in which the measured ac quantities are sequentially

sampled and converted into numeric data form. A microprocessor performs

mathematical and/or logical operations on the data to make trip decisions.


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PRINCIPLES



Relay types




LINES PROTECTION



AGENDA


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Protective relays for power systems are made up of one or more fault-

detecting or decision units, along with any necessary logic networks and

auxiliary units.

Because a number of these fault-detecting or decision units are used in a

variety of relays, they are called basic units.

Basic units fall into several categories: electromechanical units, solid-

state units integrated circuits, and microprocessor architecture.

Combinations of units are then used to form basic logic circuits

applicable to protective relays.



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Four types of electromechanical units are widely used: magnetic

attraction, magnetic induction, D'Arsonval, and thermal units.

Plunger units have cylindrical coils with an external magnetic structure

and a center plunger.

When the current or voltage applied to the coil exceeds the pickup value,

the plunger moves upward to operate a set of contacts.

The force F required to move the plunger is proportional to the square ofthe current in the coil.

The plunger unit's operating characteristics are largely determined by the

plunger shape, internal core, magnetic structure, coil design, and

magnetic shunts.

Plunger units are instantaneous in that no delay is purposely introduced.

Typical operating times are 5 to 50 msec, with the longer times occurring

near the threshold values of pickup.

Electromechanical units. Plunger units


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The unit shown is used as a high-dropout instantaneous overcurrent unit.

The steel plunger floats in an air gap provided by a nonmagnetic ring in

the center of the magnetic core.

When the coil is energized, the plunger assembly moves upward,

carrying a silver disk that bridges three stationary contacts (only two are

shown).

A helical spring absorbs the ac plunger vibrations, producing goodcontact action.



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The more complex plunger unit shown is used as an instantaneous

overcurrent or voltage unit.

An adjustable flux shunt permits more precise settings over the nominal

four-to-one pickup range.

This unit is relatively independent of frequency, operating on dc, 25-Hz,

or nominal 60-Hz frequency. It is available in high- and low-dropout

versions.



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Clapper units have a U-shaped magnetic frame with a movable

armature across the open end.

The armature is hinged at one side and spring-restrained at the other.

When the associated electrical coil is energized, the armature moves

toward the magnetic core, opening or closing a set of contacts with a

torque proportional to the square of the coil current.

The pickup and dropout values of clapper units are less accurate thanthose of plunger units.

Clapper units are primarily applied as auxiliary or go/no-go units.

Electromechanical units. Clapper units


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Upward movement of the armature releases a target, which drops to

provide a visual indication of operation (the target must be reset

manually).

The ac unit operates as an instantaneous overcurrent or instantaneous

trip unit. It is equipped with a lag-loop to smooth the force variations due to

the alternating current input. Its adjustable core provides pickup

adjustment over a nominal four-to-one range.

Electromechanical units. Clapper units


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Polar units operate from direct current applied to a coil wound around the

hinged armature in the center of the magnetic structure.

A permanent magnet across the structure polarizes the armature-gappoles, as shown.

The nonmagnetic spacers, located at the rear of the magnetic frame, are

bridged by two adjustable magnetic shunts.

This arrangement enables the magnetic flux paths to be adjusted forpickup and contact action.

Electromechanical units. Polar units


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With balanced air gaps, the flux paths are as shown and the armature will

float in the center with the coil deenergized.

With the gaps unbalanced, some of the flux is shunted through thearmature.

The resulting polarization holds the armature against one pole with the coil

deenergized. The coil is arranged so that its magnetic axis is in line with the

armature, and at a right angle to the permanent magnet axis.



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Current in the coil magnetizes the armature either north or south,

increasing or decreasing any prior polarization of the armature, if as

shown in Figure b, the magnetic shunt adjustment normally makes thearmature a north pole, it will move to the right.

Direct current in the operating coil, which tends to make the contact end

a south pole, will overcome this tendency and the contact will move to

the left.

Depending on design and adjustments, this polarizing action can begradual or quick.

The left-gap adjustment controls the pickup value, the right-gap

adjustment the reset value.

Some units use both an operating and a restraining coil on the armature. The polarity of the restraint coil tends to maintain the contacts in their

initial position. Current of sufficient magnitude applied to the operating

coil will provide a force to overcome the restraint, causing the contacts to

change position.



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A combination of normally open or normally closed contacts is available.

These polar units operate on alternating current through a full-wave

rectifier and provide very sensitive, high-speed operation on very lowenergy levels.

The operating equation of the polar unit is

where K1 and K2 are adjusted by the magnetic shunts; K3 is a designconstant; is the permanent magnetic flux; Iop is the operating current;

and Ir is the restraint current in milliamperes


3

21

KIKIK rop


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There are two general types of

magnetic induction units:

induction disc

cylinder units.

Originally, induction disc units

were based on the watt-hour

meter design. Modern units,

however, although using thesame operating principles are

quite different. All operate by

torque derived from the

interaction of fluxes produced by

an electromagnet with those frominduced currents in the plane of a

rotable aluminum disc.

Magnetic induction units


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The E unit, in Fig, has three poles on one side of the disc and a common

magnetic member orkeeper on the opposite side.

The main coil is on the center leg. Current I in the main coil produces flux,which passes through the air gap and disc to the keeper. (A small portion

of the flux is shunted off through the side air gap.)

The flux T, returns as L, through the left-hand leg and R through the

right-hand leg, where T = L + R. A short-circuited lagging coil on the left

leg causes L to lag both R and T, producing a split-phase motor action.

Magnetic induction units. Induction disk


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Flux L induces voltage Vs, and current Is flows, essentially in phase, in

the shorted lag coil. Flux T, is the total flux produced by main coil

current, I. The three fluxes cross the disc air gap and induce eddycurrents in the disc. These eddy currents react with the pole fluxes and

produce the torque that rotates the disc. With the same reference

direction for the three fluxes as shown, the flux shifts from left to right and

rotates the disc clockwise, as viewed from the top.



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There are many alternate versions of the induction disc unit.

The unit shown, for example, may have a single current or voltage input.

The disc always moves in the same direction, regardless of the direction

of the input. If the lag coil is open, no torque will exist.

Other units can thus control torque in the induction disc unit.

Most unusually, a directional unit is connected in the lag coil circuit.

When the directional unit's contact is closed, the induction disc unit hastorque; when the contact is open, the unit has no torque.


M i i d i i I d i di k


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Induction disc units are used in power or directional applications by

substituting an additional input coil for the lag coil in the E unit

The phase relation between the two inputs determines the direction ofthe operating torque.

A spiral spring on the disc shaft conducts current to the moving contact.

This spring, together with the shape of the disc (an Archimedes spiral)

and design of the electromagnet, provides a constant minimum operating

current over the contact travel range.

A permanent magnet with adjustable keeper (shunt) dampens the disc,

and magnetic plugs in the electromagnet control the degree of saturation.

The spring tension, damping magnet, and magnetic plugs allow separate

and relatively independent adjustment of the unit's inverse-time currentcharacteristics.


M ti i d ti it C li d it


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The operation of a cylinder unit is similar to

that of an induction motor with salient poles

for the stator windings. The basic unit used for relays has an inner

steel core at the center of the square

electromagnet, with a thin-walled aluminum

cylinder rotating in the air gap.

Cylinder travel is limited to a few degrees bythe moving contact attached to the top of

the cylinder and the stationary contacts.

A spiral spring provides reset torque.

Magnetic induction units. Cylinder unit

M ti i d ti it C li d it


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Operating torque is a function of the product of the two operating

quantities applied to the coils wound on the four poles of the

electromagnet, and the cosine of the angle between them. The torqueequation is

where K and are design constants; I1 and I2 are the currents through

the two coils; 12 is the angle between I1 and I2; and Ks is the

restraining spring torque. Different combinations of input quantities canbe used for different applications, system voltages or currents, or network

voltages.

sKIKIT 1221 cos

Magnetic induction units. Cylinder unit

DA l it


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In the D'Arsonval unit, a magnetic structure and

an inner permanent magnet form a two-pole

cylindrical core. A moving coil loop in the air gap is energized by

direct current, which reacts with the air gap flux

to create rotational torque.

The D'Arsonval unit operates on very low energy

input, such as that available from dc shunts,bridge networks, or rectified ac.

The unit can also be used as a dc contact-

making milliammeter or millivoltmeter.

DArsonval unit

Th l it


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Thermal units consist of bimetallic strips or coils that have one end fixed

and the other end free.

As the temperature changes, the different coefficients of thermal

expansion of the two metals cause the free end of the coil or strip to

move.

A contact attached to the free end will then operate based on

temperature change.

Thermal units

AGENDA


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PRINCIPLES



Relay types




LINES PROTECTION



AGENDA

L l d t ti O t l


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This is the simplest of all relay operating principles.

The relay operates for values of the parameter above or under what iscalled pick up setting.

Examples of this type are over-current relays and under-voltage relays

Level detection. Over-current relays

L l d t ti O t l


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The operating characteristic of an overcurrent relay can be presented

as a plot of the operating time vs. the current.

Level detection. Over-current relays

This figure represents the operating

time for an independent delay time

overcurrent relay.

It will operate always at the same time

for currents over the pick up setting

This relays are defined by the pick up

current, as number of times the normal

current, and the operating time

Coordination of different protections of

this type is achieved by time delaying

and pick up setting

It must be a minimum of 0,3 sec. to

permit operating of the first breaker

t

iIn n*In

t 0

Rel tiempo independ.

50 (ANSI)

O t l D d t ti d l


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This type of relay will have an operating time depending on the value

of the current, generally with an inverse characteristic, that is to say ,

the bigger the current, the shorter the time.

Over-current relays. Dependent time delay

This characteristic permits a

reasonable coordination between

protections just changing the pick

up setting.

These relays will be defined by the

pick up setting and the type of

tripping curve, which can be

adjusted

There are three or five types ofcurves, Normal (NI), Very inverse

(VI) and Extremely inverse (EI)

t

iIn n*In

Curva trafo

Rel tiempoinverso

t 0

Rel tiempo independ.

50/51

O t t ti


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The working principle of an inverse time overcurrent relay is depicted in

this figure.

Overcurrent protection

The current to be controlledfeeds a coil with multiple taps

which allow the pick up current

setting.

The generated magnetic field

makes the disc rotate with aspeed proportional to the

current.

A timing dial allows the

adjustment between contacts

and hence sets the op. time.

The braking magnet lessens the

rotating speed and acts as an

opposing force to the rotation.

Varying the magnetization,

different tripping curves can be

achieved.

Current

taps

Induction

disk

Lagging

coil

Timing

dial

Braking

2 4 6

1

2

Directional o erc rrent protection


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It is triggered when the current exceeds the reference value and also

the energy or power flow has the determined direction.

An overcurrent element controls the current magnitude

A directional element controls the direction of the power flow

Directional overcurrent protection

V

I

Cylinder

Magnetic

core

IV

IIII

IV

I

V



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One coil is fed with voltage and

the other one with the current.

The rotating torque will be

proportional to the product of

both magnitudes (hence to

power) and will invert if any of

the aforementioned magnitudesalso inverts.

The torque will peak when the

phase angle between both fields

is 90.

The rotation will only be allowedin one direction (corresponding

to the selected one) closing a

contact which allows the

functioning of the overcurrent

unit.

V

I

Cylinder

Magnetic

core

IV

IIII

IV

I

V

The working principle of a directional unit is shown in the figure.




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Given that the maximum rotating torque is reached when the fields

owing to the current and the voltage have a phase angle of 90, it is

necessary to ensure that, in case of fault, the measured values have a

phase angle close to the aforementioned value.

An internal phase angle is usually introduced to ensure the previously

stated.

When a fault occurs, the voltage of the affected phase can be

significantly reduced, so it is recommended to measure the line to line

voltage of the other phases, in order to avoid an incorrect performance

of the protection.

I

Abrir

V

VI

Cerrar

IV

L.P.N

L.P.M (+)L.P.M (-)

L.P.M. : Lnea Par Mximo

L.P.N. : Lnea Par Nulo

= 90

L.P.M (-)

I

V

V

I

IV

L.P.N

L.P.M (+)




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This operating principle is based upon the comparison of one or more

operating quantities with each other.

A current balance relay may compare the current in one circuit with the

current in another circuit, which should have equal or proportional

magnitudes under normal operating conditions.

The relay will operate when the current division in the two circuits varies by

a given tolerance

Differential relaying for transformer protection


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87With internal fault Id > 0 Trip

With external fault Id = 0 No trip

It compares the current entering the transformer with the current

leaving the element.

If they are equal there is no fault inside the zone of protection

If they are not equal it means that a fault occurs between the two ends

Differential relaying for transformer protection



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Alternatively one could form an algebraic sum of the two currents

entering the protected element, which could be termed as differentialcurrent (Id), and use a level detector relay to detect the presence of a

fault.

In general this principle is capable of detecting very small

magnitudes of fault.

Its only drawback is that it requires currents from the extremitiesof a zone of protection




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A B

IA IB

Internal fault = IA e IB are in phase reversal = Trip

External fault = IA e IB are in phase = No trip


Circuit breaker failure protection


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The breaker may have a mechanical failure if it is not able to open any

of the poles when it is ordered to do so, or even an electrical failure if

although open, is not capable of breaking the current, which will keepon flowing as an arc.

This implies a current flow that keeps on feeding the fault which

can be used to detect the breaker failure itself.

In those applications which even though the mechanical failureexist, the current could not be high enough to be detected, the

opening must also be verified by means of breaker auxiliary

contacts.



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87B+FI


21I falta

A tripping order for thecircuit breaker initiates

the time delay count

down for the protection.



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87B+FI

TELEDISPARO

21

I falta

T 250 ms

Once the time delay is

over , if the breaker is

not yet open, theprotection sends a

tripping order to all the

adjacent breakers,

including those at the

end of the lines if

necessary.

Sometimes two time

delays are used, the

first one to repeat the

tripping order for the

breaker itself, and thesecond for the other

breakers.


AGENDA


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PRINCIPLES



Relay types




LINES PROTECTION



AGENDA

Factors Influencing Relay Performance


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Factors Influencing Relay Performance

Relay performance is generally classed as

(1) correct,

(2) no conclusion

(3) incorrect.

Incorrect operation may be either failure to trip or false tripping.

The cause of incorrect operation may be (1) poor application, (2)

incorrect settings, (3) personnel error, or (4) equipment malfunction.

Equipment that can cause an incorrect operation includes current

transformers, voltage transformers, breakers, cable and wiring, relays,

channels, or station batteries.

Incorrect tripping of circuit breakers not associated with the trouble area

is often as disastrous as a failure to trip. Hence, special care must be

taken in both application and installation to ensure against this.

Noconclusion is the last resort when no evidence is available for a

correct or incorrect operation. Quite often this is a personnel

involvement.

Protective relaying systems and their design


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Protective relays or systems are not required to function during normal

power system operation, but must be immediately available to handle

intolerable system conditions and avoid serious outages and damage. Thus, the true operating life of these relays can be on the order of a few

seconds, even though they are connected in a system for many years.

In practice, the relays operate far more during testing and maintenance than

in response to adverse service conditions.

In theory, a relay system should be able to respond to an infinite number

of abnormalities that can possibly occur within the power system.

Protective relaying systems and their design


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The first step in applying protective relays is to state the protection problem

accurately.

Although developing a clear, accurate statement of the problem can often bethe most difficult part, the time spent will pay dividends particularly when

assistance from others is desired.

Information on the following associated or supporting areas is necessary:

System configuration

Existing system protection and any known deficiencies

Existing operating procedures and practices, possible future expansions

Degree of protection required

Fault study

Maximum load, current transformer locations and ratios

Voltage transformer locations, connections, and ratios Impedance of lines,

transformers, and generators




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System configuration is represented by a single-line diagram showing the

area of the system involved in the protection application.

This diagram should show in detail the location of the breakers, busarrangements, taps on lines and their capacity, location and size of the

generation, location, size, and connections of the power transformers

and capacitors, location and ratio of ct's and vt's, and system frequency.

Transformer connections are particularly important. For ground relaying,

the location of all ground sources must also be known




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The existing protective equipment and reasons for the desired change(s)

should be outlined.

Deficiencies in the present relaying system are a valuable guide toimprovements.

New installations should be so specified.

As new relay systems will often be required to operate with or utilize parts of

the existing relaying, details on these existing systems are important.

Whenever possible, changes in system protection should conform with

existing operating procedures and practices.

Exceptions to standard procedures tend to increase the risk of personnel error

and may disrupt the efficient operation of the system.

Anticipated system expansions can also greatly influence the choice ofprotection.




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An adequate fault study is necessary in almost all relay applications.

Three-phase faults, line-to-ground faults, and line-end faults should all be

included in the study.

Line-end fault (fault on the line-side of an open breaker) data are

important in cases where one breaker may operate before another.

For ground-relaying, the fault study should include zero sequence

currents and voltages and negative sequence currents and voltages. These quantities are easily obtained during the course of a fault study

and are often extremely useful in solving a difficult relaying problem.


Protec Cio Introd 1

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Transcript of Protec Cio Introd 1