Modern Numerical Relay Design

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Design of Modern Numerical

Protective 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 ?

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Protective Relays

Why bother ?

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Source _Load

V

I

Protective Relay

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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 Relays

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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 Relays

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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 Relays

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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 Relays

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Protective Relay Technologies

Examples

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Protective Relay

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Analogue Inputs Analogue to Digital Conversion Power Supply Binary Outputs (Relays) Binary Inputs (Optos)

Signal Processing Communications

User Interface (HMI)

Additional I/O

Interconnection Bus

Protective Relay Design

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Protective Relay Design

- Analogue Inputs

Additional I/O

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10110111...

Analogue Inputs – Traditional Approach

Sequential Sampling

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Sequential Sampling

Advantages / Disadvantages

• Advantages

− Low cost solution

• Disadvantages

− Single data stream, sampling frequency

− Relatively slow

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V

I

10110111...

Analogue Inputs – New Technologies

Simultaneous Sampling

Buffering Re-sampling Re-sampling Data Transmission Buffering Re-sampling Re-sampling

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Simultaneous Sampling

Advantages / Disadvantages

• Advantages

− Multiple sampling rates

− Higher sampling frequencies

− Signal Pre-conditioning

• Disadvantages

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Analogue Inputs – Digital Substation

IEC61850 – 9.2LE Process Bus

Merging Unit Merging Unit

Switch Merging Unit Ethernet Communications IEC61850-9.2LE Conventional or NCIT Inputs CT / VT module replaced by Ethernet Communication card Time Synchronisation

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IEC61850 – 9.2LE Process Bus

Advantages / Disadvantages

• Advantages

− Lower installation cost (less wiring)

− Adoption of new technology transducers (better performance, size)

− Data sharing

− Supervision

• Disadvantages

− Higher complexity system

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Actual signal

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)

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Analogue to digital conversion n samples per cycle I V Anti aliasing Digital filter Anti aliasing I1 Mag, Ø I2 Mag, Ø Ix Mag, Ø V1 Mag, Ø Processed Data

Signal filtering

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Gain 1 0 f0 2f0 3f0 4f0 5f0 6f0 7f0 8f0 9f0 Alias of Fundamental H/W Low Pass Filter Fourier Filter

Frequency Response of 1 Cycle

Fourier Filter (8 Sample/Cycle)

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Protective Relay Design

Binary Inputs

Additional I/O

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• Wetting currents • Burden • Isolation • How many ? • How fast ? • Thermal dissipation • Safety

Binary Inputs

Considerations

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− Multiple variants

− Single voltage I/P

− Simple / low cost

− OK for Trip circuit

supervision applications

Binary Inputs

Circuit Designs

− Single variant

− Wide Range I/P

− Single threshold

− Power ן Voltage − Single variant

− Wide Range I/P

− Low Power − Multiple thresholds LPF 0,1 LPF 0,1 AUX PSU

Active Measurement Binary Input Circuit Constant Current Binary Input Circuit

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Protective Relay Design

Binary Outputs

Additional I/O

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• Contact rating • Isolation • How many ? • How fast ? • Thermal dissipation • Safety

Binary Outputs

Considerations

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− Op time ~10ms

Binary Outputs

Circuit Designs

− Op time ~4ms

− Op time <0.5ms

− High break capability

Static Assisted Output Circuit Accelerated Relay Circuit

Standard Relay Circuit

Data Data 20V 8V 12V 20V 8V

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Protective Relay Design

Additional I/O

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• Current Loop I/O

• Temperature Measurement (RTDs)

• Time Synchronization (IRIG-B)

• Protection Communications

− Current Differential

− Inter-tripping

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Protective Relay Design

User Interface

Additional I/O

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Protective Relay Design

- Computing Unit

Additional I/O

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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

Additional I/O

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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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Communications

Operating

Platform

Application

Software

B I O S

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 Unit

Performance

2005 2000 1995 1990 1980 MCGG 0.1 1 10 100 L Series Px40 Px40+ Px20 K Series Year

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Computing Unit

Example

• Microprocessor : 32 bit floating point

75 MIPS

• Memory

− (Flash) EPROM : 4 M bytes

− RAM : 2 M bytes

− NV RAM : 4 M bytes

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• Performance requirements

− International IEC 60255, ANSI

− National BS, DIN etc

• Mandatory requirements

− CE marking (Europe)

• LVD • EMC

Protective Relaying Equipment

Product Certification

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Numerical Relays

Physical Structure

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Additional

Features

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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

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Fault

Location

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16%

3.8 Ω

16km

10miles

Fault location

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Self Diagnostics &

Commissioning Tools

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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

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Programmability

& Customisation

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User programmable Timers Binary O/Ps LEDs Protection elements Fixed scheme logic Binary I/Ps Control & & 1 Gate Logic

Customisation :

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Trip Trip Binary I/P Trip coil 52a 52b Circuit breaker

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Trip Circuit Fail mapped to

Contact, LED and Alarm Indication

Trip Circuit Monitoring Using

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Off

-

_-

line Analysis

_{line Analysis}

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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

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A-GND Fault, Fault Inception

Trip Command

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Communications

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Digital Control Systems z Courier z Modbus z DNP3.0 z IEC60870-5-103 z. . .

Remote Communications

Traditional Solutions

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Remote Communications

Overall substation Communications

Switch Switch

LAN or

WAN

LAN or

WAN

• Ethernet Communications − IEC61850 − Tunnelling of traditional communications (DNP3…)

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Overall Substation Communications

IEC61850

• 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

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Overall Substation Communications

Redundancy

• Ring Topology

− Current - Areva Self Healing Protocol

− New - HSR (High

availability seamless ring)

Relay Relay Relay Switch PC Relay Relay Relay Switch Switch PC • Star Topology − Current - RSTP − New - PRP (Parallel Redundancy Protocol)

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Overall Substation Communications

Cyber 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

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Protection & Control Equipment

Looking 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

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Self Diagnostics & Commissioning Tools Instrumentation Bay Monitoring & Control Comprehensive Protection Fault Analysis Tools Programmability & Customization

Modern Numeric Protection

Benefits Summary

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