Modern Numerical Relay Design

Design of Modern Numerical Protective Relay Equipment

Design of Modern Protective Relaying Equipment

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

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What is a protection relay ?

A big expensive reusable fuse ! - -P3

Protective Relays Why bother ?

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Protective Relay Principles of Operation

I

Source

V

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Load

Protective Relays Technologies Employed (1)

ELECTROMECHANICAL (1950) • Attracted armature or induction disc type elements to implement the protection functions. • An electromagnetic force causes the mechanical operation of the relay.

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Protective Relays Technologies Employed (2)

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.

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Protective Relays Technologies Employed (3)

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

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Protective Relays Technologies Employed (4) 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.

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Protective Relay Technologies Examples

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Protective Relay Principal Input/Output Interfaces

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Protective Relay Design Key Elements - implementation

Power Supply

Binary

Binary Outputs

Inputs

(Relays)

(Optos)

Analogue to Digital Conversion

Analogue Inputs

Interconnection Bus

Additional I/O

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Signal Processing

User Interface (HMI)

Communications

Protective Relay Design - Analogue Inputs

Power Supply

Binary

Binary

Outputs

Inputs

(Relays)

(Optos)

Analogue to Digital Conversion

Analogue Inputs

Interconnection Bus

Additional I/O

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Signal Processing

User Interface (HMI)

Communications

Analogue Inputs – Traditional Approach Sequential Sampling

V 10110111...

I

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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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Analogue Inputs – New Technologies Simultaneous Sampling

Buffering

V

Re-sampling Data Transmission

Re-sampling

I Buffering

Re-sampling Re-sampling

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10110111...

Simultaneous Sampling Advantages / Disadvantages

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

• Disadvantages − Higher hardware costs

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Analogue Inputs – Digital Substation IEC61850 – 9.2LE Process Bus

Time Synchronisation Conventional or NCIT Inputs Merging Unit

Ethernet Communications IEC61850-9.2LE

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Merging Unit

Switch

Merging Unit

CT / VT module replaced by Ethernet Communication card

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 − Networks, network performance

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Analogue Sampling Basics - Aliasing effects

Sampling element

Actual signal

Apparent signal Sample points - - P 20

Analogue Sampling Basics - Conversion errors 10110111...

Dynamic Range, Quantisation Effects

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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Signal filtering

Processed Data

Anti aliasing

I1 Mag, Ø Analogue to digital conversion

I

Digital filter

Anti aliasing V

I2 Mag, Ø

n samples per cycle

Ix Mag, Ø V1 Mag, Ø Vy Mag, Ø

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

H/W Low Pass Filter

1

Alias of Fundamental

Fourier Filter

0 f 0 2f0 3f0 4f0 5f0 6f0 7f0 8f0 9f0 Frequency - - P 23

Protective Relay Design Binary Inputs

Power Supply

Binary

Binary

Outputs

Inputs

(Relays)

(Optos)

Analogue to Digital Conversion

Analogue Inputs

Interconnection Bus

Additional I/O

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Signal Processing

User Interface (HMI)

Communications

Binary Inputs Considerations

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

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Binary Inputs Circuit Designs Passive Binary Input Circuit LPF

0,1

Constant Current Binary Input Circuit LPF

0,1

Active Measurement Binary Input Circuit AUX PSU PWM Measurement Circuit

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Signal Processing

− − − −

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

− − − −

Single variant Wide Range I/P Single threshold Power ‫ ן‬Voltage

− − − − − − −

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

Voltage Measurement or Status + Settings

Protective Relay Design Binary Outputs Power Supply

Binary

Binary

Outputs

Inputs

(Relays)

(Optos)

Analogue to Digital Conversion

Analogue Inputs

Interconnection Bus

Additional I/O

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Signal Processing

User Interface (HMI)

Communications

Binary Outputs Considerations

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

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Binary Outputs Circuit Designs Standard Relay Circuit − Op time ~10ms

Data Accelerated Relay Circuit

20V 8V − Op time ~4ms

Data Static Assisted Output Circuit

Data - - P 29

12V

20V 8V

12V

− Op time