Abuja 3 Protection General

8/3/2019 Abuja 3 Protection General

1/66

yIntroduction to power

system protection:-AnOverview


2/66

Housekeeping and Climate setting


3/66

Components of power System

Generators

Transformers

Transmission LinesDistribution Networks

Loads


4/66


5/66

GenerationyAt power generating station (generating voltage) 11

20kV and frequency of 50 Hz

y Transform to higher voltage (transmission voltage) 132kV, 275kV 330kV and 500kV

y Transform to lower voltage (distribution voltage)

33kV or 11kV


6/66

Transmissiony To ensure the adequacy and reliability of supply

that are fundamental needs of modern society.y Provides the link between electricity suppliers and

electricity consumers.y Helps reduce energy prices since generation in

other regions which are cheaper can be channeledto customers.

y Transmission connects regional systems via inter-connectors to encourage cooperation for mutualbenefits.


7/66

Transmission Systemy Lines/transformers operating at voltages above 100 kV

are usually called the transmission system.

y Consists ofTransmission Line and Sub-stationsy Transmission network of 500kV, 330kV, 275kV and

132kV known as National Grid.


8/66

Transmission Line Components

yTransmission Line

y

OverheadL

inesyCable

y Underground Cables

y Submarine Cables

ySub-stations


9/66

Transmission Liney Components

y Tower support structure

y Cross-armsy Conductors

y Insulators

y Earth-wires


10/66

Sub-stationy Size of substation

y Depends on transformer size

y T

ypical sizesy 132kV; 2 x 30MVA, 3 x 45MVA, 2 x 90MVA

y 275kV; 2 x 180MVA, 3 x 180MVA, 2 x 240MVA

y Types of Sub-stationy Conventional outdoor

y Require bigger space

y GIS (gas insulated switchgear)y Less space

y Outdoor or indoor


11/66

Sub-station Components

yTransformer

y

Circuit Breaker / Switch GearyIsolator Switches

yBusbar

yProtection Relay & Control Equipment


12/66

Power Transformer


13/66

Circuit Breaker

Spark gap. In event ofa lightning strike on

the line, the currentcan jump the gapbetween that ball andthe protrusion on thetank, and make a pathto earth. This

prevents overloadingthe breaker.


14/66

Circuit Breaker


15/66

Distributiony Lines/transformers operating at voltages below 100 kV

are usually called the distribution system.

yPart of the electric utility system between the bulkpower source and the customer service entrances(loads).

y 33kV, 22kV, 11kV, 6.6kV, 415V and 240V


16/66

Distribution Sub-stationy Distribution Intakes (33kV, 22kV)

y Distribution Substations (22kV, 11kV, 6.6kV)

y Indoor substationy Outdoor substation

y Pole mounted substation

y Compact substation

y Underground substation

y Transformer capacityy 100kVA, 300kVA, 500kVA, 750kVA and 1000kVA


17/66

Distribution Transformer


18/66


19/66


20/66


21/66


22/66


23/66


24/66


25/66


26/66


27/66


28/66


29/66


30/66


31/66


32/66


33/66


34/66

Elements of a Protection System

1

The function of transducers (usually CT and VT) is to provide current and voltagesignals to the relays, to detect deviations of the parameters watched over.


35/66


36/66

3


1

2

4

Circuit breakersisolate the fault byinterrupting thecurrent.


37/66

3


1

5

2.1

2.4

F

.A.

A D

2.2

QP

2.3

2

4

Tripping power, aswell as power required

by the relays, isusually provided bythe station batterybecause is safer thanthe ac faulted system.


38/66

System Protection Flow

RelayInstr.Transfx.Fault

Occur

Circuit

Breaker

Fault

Clear

voltage or current rise from normal condition

voltage/current is reduced to match with relay rating

activate circuit breaker

circuit isolation


39/66

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 trip one ormorecircuit 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 circuitbreakers during faults can be monitored by verificationrelays.

Reclosing relays. Establish a closing sequence for a circuit breaker

following tripping by protective relays.


40/66


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 theprescribed limits.

Auxiliary relays. Operate in response to the opening or closing of theoperating circuit to supplement another relay or device. These includetimers, 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.


41/66


In addition to these functional categories, relays may be classified byinput, operating principle or structure, and performance characteristic.The following are some of the classifications and definitions described inANSI/ IEEE Standard C37.90 (see also ANSI/IEEE C37.100 Definitions forPower Switchgear):

Inputs Current, Voltage, Power

Pressure, Frequency

Temperature

Flow Vibration

Operating Principle or

Structures Current balance Percentage

Multirestraint

Product

Electromechanical Thermal

Solid state

Static

Microprocessor


42/66

Classification of relays Performance Characteristics

Differential

Distance

Directional over current

Inverse time

Definite time

Under voltage

Overvoltage

Ground or phase

High or low speed

Pilot

Phase comparison

Directional comparison

Current differential


43/66

Analog/Digital/Numerical

Analog relays are those in which the measured quantities are converted into lowervoltage but similar signals, which are then combined or compared directly toreference 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. Logiccircuits or microprocessors compare the phase relation-ships of the square waves tomake a trip decision.

Numerical relays are those in which the measured ac quantities are sequentiallysampled and converted into numeric data form. A microprocessor performsmathematical and/or logical operations on the data to make trip decisions.


44/66

Zones ofProtection

To limit the extent of the power system that is disconnected when a fault occurs,protection is arranged in zones

Zones of protection should overlap, so that no part of the power system is leftunprotected

Location of the CT connection to the protection usually defines the zone Unit type protections have clear zones reach e.g Diff. Relay, REF relay

Zone reach depends on measurement of the system quantities e.g OC , EF,distance relays . The start will be defined but the extent (or reach) is subject to

variation, owing to changes in system conditions and measurement errors.


45/66

Zones ofProtectiony For fault anyway within the zone, the protection

system responsible to isolate everything within thezone from the rest of the system.

y Isolation done by CB

y Must isolate only the faulty equipment or section


46/66

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 zoneof 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


47/66


48/66


49/66


50/66


51/66


52/66

REACH OF PROTECTION 21B

REACH OF PROTECTION 21A

21

Remote back up protection

21

SUBSTATIONASUBSTATIONB


53/66


54/66


55/66

a b c Phase sequence a-b-c

AC Bus

51-N

51-A51-C 51-B

52

51: Time overcurrent relay52: AC circuit breaker

Prote

cted

Line

a

c

b

CT

AC Elementary Diagram


56/66


AC Bus

51-N

51-A51-C 51-B

52

51: Time overcurrent relay

52: AC circuit breaker

Protected

Line

a

c

b

CT


TOC phase relays51-A, 51-B, and 51-Cshould send trip signal

to breaker 52


57/66


AC Bus

51-N

51-A51-C 51-B

52

51: Time overcurrent relay

52: AC circuit breaker

Protected

Line

a

c

b

CT


TOC ground relay51-N (set sensitively)should send trip signal

to breaker 52


58/66

Relay operating coil

Relay contacts

51-A

51-A51-A

s

s

52

52a

51-B

51-B51-B

s to 51-Cand 51-N

s

TC

DC Elementary Diagram


59/66

Remarksy The elementary diagrams are drawn for

electromechanical relaysy The auxiliary relay marked with s is the seal-in or

contact switch

y This is not usually needed with solid-state relays, butthe relay must latch in the trip position


60/66

Conventional contact positionsy Convention: contacts are shown in the de-

energized or non-operated position

y 52a is auxiliary contact that is in same position as thebreaker

y 52b is auxiliary contact that is in the oppositeposition as the breaker


61/66


Relay contacts

51-A

51-A51-A

s

s

52

52a

51-B

51-B51-B

s to 51-Cand 51-N

s

TC


Shows the operated condition for a faultproducing a trip signal to the breakertrip coil 52 TC


62/66


Relay contacts

51-A

51-A51-A

s

s

52

52a

51-B

51-B51-B

s to 51-Cand 51-N

s

TC


Shows the operated condition for a faultproducing a trip signal to the breakertrip coil 52 TC, with relay latched


63/66


Relay contacts

51-A

51-A51-A

s

s

52

52a

51-B

51-B51-B

s to 51-Cand 51-N

s

TC


After breaker trips, 52a opens, whichunlatches the circuit, when relay no longersees the fault, 51-A and 51-B will open


64/66


65/66


66/66

Documents

Abuja 3 Protection General