Design of Modern NumericalProtective Relay Equipment

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Lecture Outline

• What are protective relays and why do we need them?

• What technologies have been employed

• What are the additional benefits of modern protective relays

• What might the future hold

• Discussions

Design of Modern Protective Relaying Equipment

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What is a protection relay ?

A big expensive reusable fuse !

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Protective RelaysWhy bother ?

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Source Load

V

I

Protective RelayPrinciples of Operation

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ELECTROMECHANICAL (1950)

• Attracted armature or induction disc type elements to implement the protection functions.

• An electromagnetic force causes the mechanical operation of the relay.

Protective RelaysTechnologies Employed (1)

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STATIC (1970)

• Maturing of transistor technology

• Static implies that the relay does not have moving parts

• Discrete electronic components (generally analogue devices) used for creation of the operating characteristics.

• Trip output contacts would generally be of attracted armature type.

Protective RelaysTechnologies Employed (2)

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DIGITAL (1980)

• Used the then new microprocessor technologies

• Generally an analogue front end

• Protection function logic is implemented in the microprocessor.

• The only numerical states within the relay are high/low logic (logic one or zero) rather than mathematical algorithms

Protective RelaysTechnologies Employed (3)

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NUMERICAL (Today)

• Used exclusively in today’s protection relays

• Inputs sampled and converted into digital numerical data

• Complex mathematical algorithms generate the relay operating characteristics.

• The distinction from digital relays is that numerical relays use digital signal processing (DSP).

• Also characterised by the sophisticated communications facilities they offer.

Protective RelaysTechnologies Employed (4)

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Protective Relay TechnologiesExamples

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Protective RelayPrincipal Input/Output Interfaces

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Analogue Inputs

Analogue to

Digital Conversion

Power Supply

BinaryOutputs

(Relays)

BinaryInputs

(Optos)

Signal Processing CommunicationsUser Interface

(HMI)Additional I/O

Interconnection Bus

Protective Relay DesignKey Elements - implementation

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Protective Relay Design- Analogue Inputs

Analogue Inputs

Analogue to

Digital Conversion

Power Supply

BinaryOutputs

(Relays)

BinaryInputs

(Optos)

Signal Processing CommunicationsUser Interface

(HMI)Additional I/O

Interconnection Bus

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V

I

10110111...

Analogue Inputs – Traditional ApproachSequential Sampling

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Sequential Sampling Advantages / Disadvantages

• Advantages− Low cost solution

• Disadvantages− Single data stream, sampling frequency− Relatively slow− Signal Skew

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V

I

10110111...

Analogue Inputs – New TechnologiesSimultaneous Sampling

Buffering Re-sampling

Re-sampling

Dat

a Tr

ansm

issi

on

Buffering Re-sampling

Re-sampling

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Simultaneous SamplingAdvantages / Disadvantages

• Advantages− Multiple sampling rates− Higher sampling frequencies− Signal Pre-conditioning

• Disadvantages− Higher hardware costs

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Analogue Inputs – Digital SubstationIEC61850 – 9.2LE Process Bus

Merging Unit Merging Unit

Switch

Merging Unit

Ethernet CommunicationsIEC61850-9.2LE

Conventional or NCIT Inputs

CT / VT module replaced by Ethernet Communication card

Time Synchronisation

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IEC61850 – 9.2LE Process BusAdvantages / Disadvantages

• Advantages− Lower installation cost (less wiring)− Adoption of new technology transducers (better performance, size)− Data sharing− Supervision

• Disadvantages− Higher complexity system− Networks, network performance

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Actual signal

Apparent signal

Sample points

Sampling element

Analogue Sampling Basics- Aliasing effects

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10110111...

Dynamic Range, Quantisation Effects

Analogue Sampling Basics - Conversion errors

12 bit ADC equivalent to 4096 numbers

• For dynamic range of 64 In

• In = count 32

• Resolution - 30mA (In = 1A)

For 16 bit, resolution - 2mA

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Analogue todigital

conversion

n samplesper cycle

I

V

Antialiasing

Digital filter

Antialiasing

I1 Mag, ØI2 Mag, Ø

Ix Mag, Ø

V1 Mag, Ø

Vy Mag, Ø

Processed Data

Signal filtering

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Gain

1

0f0 2f0 3f0 4f0 5f0 6f0 7f0 8f0 9f0

Frequency

Alias of FundamentalH/W Low Pass Filter

Fourier Filter

Frequency Response of 1 Cycle Fourier Filter (8 Sample/Cycle)

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Protective Relay DesignBinary Inputs

Analogue Inputs

Analogue to

Digital Conversion

Power Supply

BinaryOutputs

(Relays)

BinaryInputs

(Optos)

Signal Processing CommunicationsUser Interface

(HMI)Additional I/O

Interconnection Bus

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• Wetting currents

• Burden

• Isolation

• How many ?

• How fast ?

• Thermal dissipation

• Safety

Binary InputsConsiderations

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− Multiple variants− Single voltage I/P− Simple / low cost− OK for Trip circuit

supervision applications

Binary InputsCircuit Designs

− Single variant− Wide Range I/P− Single threshold − Power Voltage

− Single variant− Wide Range I/P− Low Power− Multiple thresholds− Measurements− Settable− Complex / higher cost

LPF0,1

LPF0,1

Signal Processing Voltage

MeasurementorStatus + Settings

AUXPSU

PWM Measurement

Circuit

Active Measurement Binary Input Circuit

Constant Current Binary Input Circuit

Passive Binary Input Circuit

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Protective Relay DesignBinary Outputs

Analogue Inputs

Analogue to

Digital Conversion

Power Supply

BinaryOutputs

(Relays)

BinaryInputs

(Optos)

Signal Processing CommunicationsUser Interface

(HMI)Additional I/O

Interconnection Bus

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• Contact rating

• Isolation

• How many ?

• How fast ?

• Thermal dissipation

• Safety

Binary OutputsConsiderations

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− Op time ~10ms

Binary OutputsCircuit Designs

− Op time ~4ms

− Op time <0.5ms− High break capability

Static Assisted Output Circuit

Accelerated Relay Circuit

Standard Relay Circuit

Data

Data

20V8V

12V

Data

20V 8V

12V

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Protective Relay DesignAdditional I/O

Analogue Inputs

Analogue to

Digital Conversion

Power Supply

BinaryOutputs

(Relays)

BinaryInputs

(Optos)

Signal Processing CommunicationsUser Interface

(HMI)Additional I/O

Interconnection Bus

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• Current Loop I/O

• Temperature Measurement (RTDs)

• Time Synchronization (IRIG-B)

• Protection Communications− Current Differential− Inter-tripping

Additional I/O

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Protective Relay DesignUser Interface

Analogue Inputs

Analogue to

Digital Conversion

Power Supply

BinaryOutputs

(Relays)

BinaryInputs

(Optos)

Signal Processing CommunicationsUser Interface

(HMI)Additional I/O

Interconnection Bus

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User Interface

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Protective Relay Design- Computing Unit

Analogue Inputs

Analogue to

Digital Conversion

Power Supply

BinaryOutputs

(Relays)

BinaryInputs

(Optos)

Signal Processing CommunicationsUser Interface

(HMI)Additional I/O

Interconnection Bus

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Computing Unit - Hardware

• Microprocessor(s)

• Memory− (Flash) EPROM− RAM−NV RAM

• Time synchronization

• Communications drivers

• Battery back-up

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Protective Relay Design- Computing Unit

Analogue Inputs

Analogue to

Digital Conversion

Power Supply

BinaryOutputs

(Relays)

BinaryInputs

(Optos)

Signal Processing CommunicationsUser Interface

(HMI)Additional I/O

Interconnection Bus

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• Control of analogue acquisition

• Process raw data in magnitude & phase

• Sample of plant binary I/Ps

• Execute protection algorithms

• Combine protection outputs and plant status to control outputs (scheme logic)

• Control user interface

• Implement remote communications protocols

• Log events and disturbances

Computing Unit - S/W Processes

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CommunicationsOperatingPlatform

ApplicationSoftware

B I O S

Hardware

Protective Relay Software Design

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• Microprocessor requires sufficient power to− Process samples in real time before next sample is taken− Run the protection algorithms often enough to meet the

requirements for speed of operation− Service communications tasks− Ensure background tasks have sufficient priority (ie user

interface)

• Typical maximum processor loading <70% quiescent, <90% during faults

Computing Unit - Requirements

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Computing UnitPerformance

2005

2000

1995

1990

1980MCGG

0.1 1 10 100

L Series

Px40

Px40+

Px20

K SeriesYea

r

Millions of Instructions per second (MIPS)

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Computing UnitExample

• Microprocessor : 32 bit floating point75 MIPS

• Memory− (Flash) EPROM : 4 M bytes− RAM : 2 M bytes− NV RAM : 4 M bytes

• Software : >700 000 lines code

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• Performance requirements− International IEC 60255, ANSI− National BS, DIN etc

• Mandatory requirements− CE marking (Europe)

• LVD

• EMC− UL (US, Canada)

Protective Relaying EquipmentProduct Certification

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Numerical RelaysPhysical Structure

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Additional Additional FeaturesFeatures

Numerical Relays

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• Additional features found in numerical relays− Multiple functions in same relay− Fault location− Self diagnostics & commissioning tools− Programmable scheme logic / customization− Intelligent Communications− Fault recording− Re-configurable inputs and outputs− Monitoring and control of circuit breakers− Instrumentation

• Reliability, repeatability, ….

Numerical Relays - what are the benefits ?

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FaultFaultLocationLocation

Numerical Relays

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16% 3.8Ω16km10miles

Fault location

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Self Diagnostics &Self Diagnostics &Commissioning ToolsCommissioning Tools

Numerical Relays

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Self Diagnostics & Commissioning

•Self diagnostics− Power-on diagnostics− Continuous self-

monitoring− Condition based

maintenance

•Commissioning features available to user

− Input states− Output states− Internal logic status− Measurements

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Programmability Programmability & Customisation& Customisation

Numerical Relays

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User programmable scheme logic

Timers

Binary O/Ps

LEDs

Protectionelements

Fixed scheme

logic

Binary I/Ps

Control

&

&1

Gate Logic

Customisation :Programmable Scheme Logic

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Trip

Trip

Binary I/P

Tripcoil

52a

52b

Circuit breaker

Trip Circuit Monitoring

Binary I/P

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Trip Circuit Fail mapped to

Contact, LED and Alarm Indication

Trip Circuit Monitoring Using Programmable Scheme Logic

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OffOff--line Analysisline Analysis

Numerical Relays

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Prefault Postfault

Disturbance Records

•8 Analogue channels

•32 Binary I/O channels

•Sample 12 times per cycle

•Configurable trigger source

•Variable trigger point•Up to 20 Records can be stored

•The duration of each record can be up to 10.5s

•Battery backed memory

•Extended recording time

•MiCOM S1 saves file in the COMTRADE format

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A-GND Fault,Fault Inception

Trip Command

Disturbance analysis software

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CommunicationsCommunications

Numerical Relays

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Digital Control Systems

CourierModbusDNP3.0IEC60870-5-103. . .

Remote CommunicationsTraditional Solutions

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Remote CommunicationsOverall substation Communications

Switch

Switch LAN or WAN

LAN or WAN

• Ethernet Communications− IEC61850− Tunnelling of traditional

communications (DNP3…)

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Overall Substation CommunicationsIEC61850

• Peer to Peer Fast I/O Communications− GOOSE (Generic Object Orientated Substation Events)

• Sampled Analogue Values− IEC61850-9-2

• IEC61850 Data Model− Status Monitoring− Event Reporting (Un-buffered / Buffered)− Control Services (CB Tripping/Closing)

• Time Synchronisation− SNTP (Simple network Time Protocol)− IEEE1588 (Precision Time Protocol)

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Overall Substation CommunicationsRedundancy

• Ring Topology− Current - Areva Self Healing

Protocol− New - HSR (High

availability seamless ring)

Relay

Relay

Relay

Switch

PCRelay

Relay Relay

Switch Switch

PC

• Star Topology− Current - RSTP− New - PRP (Parallel

Redundancy Protocol)

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Overall Substation CommunicationsCyber Security

• Standards− NERC (North American Electric Reliability Corporation)− IEEE1686 – Security of relays and substations− IEC62351 – Security of communications

• Security− Defined password schemes− Password blocking− Password encryption− Unused port disabling

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Protection & Control EquipmentLooking Forward

• Requirements− Protection enhancements− Greater Integration (Protection, Control & Monitoring)− Digital Substation solutions− Programmability and customization− Off-line analysis− Communications− Security− Expert systems / Smart Grids

• Implementation− More processing power− Higher sampling / multiple sampling− More I/O− Increased communications capabilities

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Self Diagnostics& Commissioning

Tools

Instrumentation

Communications

Bay Monitoring& Control

ComprehensiveProtection

FaultAnalysis Tools

Programmability& Customization

Modern Numeric ProtectionBenefits Summary

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