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P740

NUMERICAL BUSBAR DIFFERENTIALPROTECTION

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MiCOM P740 Numerical Busbar ProtectionTechnical Presentation

June 2005

Bassam Gallalin

AREVA

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SUMMARY

USEFUL NOTATION - GENERAL

PRINCIPLE OF BUSBAR PROTECTION

INTRODUCTION

HARDWARE

CENTRAL UNIT - MAIN FEATURES

PERIFERAL UNITS - MAIN FEATURES

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Useful Notation -General

Current of Phase A,B or C in the feeder number i :

ii ii A, B o r CA, B o r C

Residual current in the feeder number i :

ii iiNN = 3 I= 3 I0 i0 i == ii iiAA ++ ii iiBB ++ ii iiCC

Any cur rent (phase or residual) in the feeder number i: ii ii

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Useful Notation -Conventional A lgorithms

Differential current (for a current node) = Sum of currents brought

in the node:

iidiffnodediffnode (t) = i(t) = i11 + i+ i22 +...+ i+...+ inn== II

Differential operating current = Absolute value of the sum:

iidiffdiff(t(t) =) = id(t)id(t)== ii

Bias current (Restraining current) = Sum of the absolute value:

iibiasbias(t(t) =) = ii 11 ++ ii22 + ... ++ ... + ii nn == ii

Minimum operating current of the bias characteristic:

IIss

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Slope of the bias characteristic:kk

Tripping authorisation :

iidiffdiff(t(t ) > IS + k x) > IS + k x iibiasbias(t(t))

Circuitry fault supervision threshold :

IIDD >1>1

ObjectifObjectif: Detect the loss of one current measurement: Detect the loss of one current measurement

Circuitry fault supervision alarm time delay :

ttDD>1>1

Differential overcurrent element threshold :

IIDD>2>2

ObjectifObjectif: Avoid any: Avoid any maloperationmaloperation due to the lost of thedue to the lost of the hightesthightest

loaded feederloaded feeder

Phase bias current threshold (for SEF use only) :

iibiasbias A, B, C >A, B, C >

(used for current control of internal sensitive earth fault)

Useful Notation -Conventional A lgorithms

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HV Application: Busbar Protection - 1

PRINCIPLEPRINCIPLE

OFOF

BUSBAR PROTECTIONBUSBAR PROTECTION

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HV Application:Busbar Protection

I1 = I2 + I3

I1 - I2 - I3 = 0

Kirchhoffs Principle applied to a healthy system

I1 I3I2

I = 0

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Kirchhoffs Principle applied to a system with a fault

I3

I1 I2 + I3I1 - I2 - I3 0 = IF

I1 I2

HV Application:Busbar Protection - 2

I 0

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Protection Relays June 200511 11

Ii1S1

Ii2S2

Ii3S3

Io1

Io2

Io3

Io4

Ii = Iin

Io = Ion

Ibias = Ii + Io

Idiff= Ii- Io

Import IiS

Simplified Substation Scheme

Export Io

Iin = Ion

Differential Bubar Protection

Principle

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Stability is entirely due to introducing a stabilising resistor in-

circuit.

It is a simple, reliable and circulating current scheme

(CT must have same ratio & must be high accuracy - class X)

The knee point voltage of the CTs needs to be relatively high

(Vk=2Vs)

Metrosil may be required (cross voltage must not exceed 3kV)

The CTs are usually not shared with other protection

The magnetising current can desensitise the scheme

The scheme is very fast

Isolator contacts are needed to switch the full CT secondary

current between the zones

Extending the scheme is quite simple

Buswire supervision can be offered with MVTP relays

High Impedance Principle

(MCAG & MFAC)

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Stability is entirely due to the bias characteristics of the scheme

CTs can have different ratios

Scheme bias characteristic can cater for lesser accuracy CTs (class 5P)

CTs with moderate knee point voltages can be used

Metrosils are never required

It is easier to share CTs with other protection

Number of // circuits does not affect the primary operating current

Tripping is fast

Isolator contact are not needed to switch heavy currents.

Expending the scheme is simple

Self supervision and breaker fail protection is easier to integrate

Numerical scheme offer many fault, event and recording capabilities

Low Impedance/Biased Principle

(MBCZ, DIFB CL, DIFB)

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Large CTs to avoid saturation & ensure stability

Difficult to apply if system topology is dynamic

Busbar

S1S1S1 S1P1

P2 S2 S2 S2 S2

Bias voltage image of the crossing current Differential elements

Flow control

CTs with different ratios

I1 I2 I3 I4

Interposing CTsrequired

Ud Rd

Ur

Differential Busbar Protection

Merz-Price Principle

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INTRODUCTIONINTRODUCTION

Numerical Busbar ProtectionP740

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Introduction

Modular

Communication between modules is via fibre optic connections

Numerical technology

Universal topol ogy processing

Biased differential principl e

Multiple criteria for tripping

High speed operation for internal faults

Stability maintained under external fault condi tions

Continuous monitoring of plant and protection circui ts

P740 - Busbar Protection

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Busbar

Protection

Overcurrent

ProtectionCB Failure

Protection

CB & Isolator

Supervision

Measurements

Disturbance

Recorder Event &Fault Records

Programmable

Scheme Logic

Dead Zone

Protection (*)

Continuous

monitoring

CT

Supervision

Numerical Busbar ProtectionP740 - Features

(*) : Coupling CB or feeder

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Single Busbar Application

Peripheral Units

BB2BB1

Fibre Optic

P742

P742 P741P742

P742P742

P742

Central Unit

P742

Fibre Optic

P742

P742P742

P742

P742

P742

Peripheral Units

P742 P742

P742P741

Zone 1 Zone 2Virtual Zone

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Double Busbar Application

Central UnitPeripheral Units

P742 P743P742P742

BB5

BB4

BB3

BB2

BB1

Optical Fibre

P742 P742 P742 P743 P741

2 P742 or

2 P743

P741

The transfert bar should be considered as a particular feeder

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Double Busbar ApplicationGlobal View

BB3BB1

BB4

Peripheral

Units

P743

P743

P742

P742

P742

P742

P742

P742

Central

UnitPeripheral

Units

P742 P743P742P742

BB5

BB2

Fibre Optic

P742 P743 P741P742 P742

2 P742 or

2 P743

P741

Fibre Optic

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Module Interconnection

Facilitates either a centralised or decentralised scheme.

Each Peripheral Unit has a sing le Transmit and Receive fibre.

Each Central unit can accommodate up to 32 pairs of fibr es from Peripheralunits

The fibre used must be Duplex Multimode 850nm, ST connectors wit h max

attenuation of 7dB/km.

The distance between the Central Unit and the Peripheral Unit, if

distribu ted, therefore cannot exceed 1km.

P743

P742

Feeder 1

P743

Feedern

P741P741

Scheme

Peripheral Units

P742

Module interconnection is done via fibre optics

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Numerical Busbar ProtectionP740

HARDWAREHARDWARE

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Numerical Busbar ProtectionP740

8 Optically isolated logic inputs

8 Relay ouputs

8 Communication boards

4 Peripheral Units per communication board

1 Main Processor board - 1p DSP-TMS320C-32 bits-40 Mhz

1 Coprocessor board - 1

p DSP-TMS320C-16 bits-100 Mhz

12 LEDs

Back lit liquid crystal display Extended outpu ts possible using a P742 or P743 (withou t current

inputs, normally used for buses including disconnectors)

Central Unit Hardware - Size 19 inches - 4U

P741 Central Unit

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Numerical Busbar ProtectionP740

Peripheral Units Hardware - Size 8 or 12 inches - 4U

Logic inputs: 16 for P742 (2 boards) and 24 for P743

Universal Opto inputs - programmable battery voltages

Relay ouputs: 8 for P742 and 21 fo r P743

Current inputs : 3 phase + 1 residual current inputs

Dual r ated current inputs (1/5A, externally connected)

1 Main board - 1p DSP-TMS320C-32 bits -40 Mhz

1 Coprocessor board - 1p DSP-TMS320C-16 bits-100 Mhz

12 LEDs

Back lit liquid crystal display

P742 & P743 Peripheral Units

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