substation comms intro

8/10/2019 Substation Comms Intro

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Substation Communications:Introduction


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Communications : Why use it ?

Why would utilities/industry use communications to substation

equipment? To get power system data into a remote SCADA / DCS system

To set IEDs, aid commissioning and extract data for analysis (local

access)

Remote control of plant


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Communication Requirements

Retrieval

Measurements Plant status Trip information Fault location Setting files Fault, event & disturbance records Maintenance information

Change settings

Plant control (CB, disconnector, Tap Position, etc.)

Peer-to-peer communications


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PROTOCOL:

Rules and procedures that communications networks

use to communicate on the communications medium

HARDWARE CONNECTIONS

Physical shape

Electrical characteristics

DATA FLOW

Control transmitter/receiver rate

Detection of data corruption

DATA CODING

Code information

Protocols / Formats

Language

Digital Communications : Definitions


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SIMPLEX

Transmission in one direction only

HALF DUPLEX

Two way means of transmission but data can

only travel in one direction at a time

FULL DUPLEX

Transmission in both directions simultaneously

Serial Transmission : Definitions

Transmitter Receiver11101010 00001101

SERIAL TRANSMISSION


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SYNCHRONOUS

Bit periods controlled by synchronizing the clocks at thetransmitter and at the receiver

Framing bits are added to blocks of data

ASYNCHRONOUS

Tansmitter and Receiver clocks run at approximately the

same rate Framing bits are added to raw data bits

Transmission Systems


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EIA 232 - 9/25 pin D connector

(was RS232) - Maximum data rate ~19200 bps

- Maximum distance 15m

EIA 485 - 2 or 4 wires

(was RS485) - Maximum data rate ~19200 bps

- Maximum distance 1000m

Optical fibre - Immunity to electrical interference

- Advantages in distance and speed

Ethernet - Electrical and fibre media

- Data rate 10Mbps, 100Mbps

Transmission Medium


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MASTER/SLAVE

Slave (IED) can only send when it receives a

request from the Master (e.g. RTU)

Slave sets flags to indicate functions need servicing

by the Master

CLIENT/SERVER

same relationship as Master/Slavebut can have multiple Clients!

Transmission Definitions : Client/Server


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IED

Engineering

Station

Modem

Modem

Laptop

IED

Transmission Definitions : Point to point

LOCAL

REMOTE


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Ethernet Standard - 30/05/2012 - P 11

Bus Network/MultidropToken Ring Network TopologyStar Network Topology

Transmission Definitions : Shared Access


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CARRIER SENSE METHODS

CSMA (Carrier Sense Multiple Access) /CD (Collision

Detection) Medium Access Control (MAC)

TOKEN ACCESS METHOD The device that has the Token has access to transmit

RESERVATION METHOD

Each device has a predefined time slot to transmit

Transmission Definitions : Network Access


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IEDIED * GatewayIED LaptopComputer

Modem SCADA

Client

Substation

HMI

Modem

DNP3.0 Level 3

DNP3.0Level 2

DNP3.0

Level 2

EIA232Front

Engineering

Station

Modem

Modem

EIA485

EIA485

EIA485

Gateway

Network Topology (serial communication)

* proprietary protocol


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Protocols: Analogy

ZG9948

Postalnetworkservice


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SCADA

Within the substation

Standard/independent: IEC60870-5-103,

DNP3, MODBUS, Profibus, etc.Proprietary: Courier, SPA-Bus, etc.

Master / Slave

Speed 1200bps to 64 kbps

IEDs

RTU / Bay

Computer /

Gateway

Outside the substation

Standard/independent: IEC60870-5-101,

DNP3, MODBUS, etc.Proprietary RTU protocols

Master / Slave

Speed 9.6 to 64 kbps +

Serial Communications Protocols


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Serial protocols : limitations

Designed 5-20 years ago to:

minimise the communication bandwidth

minimise the processor/memory load make it implementable for non-communication expert

Few standards

Slow communication: need for multiple links

Difficult connection of a third party application - gateway

Database absolute address, not flexible, no modelling

Master-slave: long recovery time in case of master failure

Peer-to-peer communication usually not possible


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Need for Standardisation

Lack of commonality between vendors

Lack of standard SCADA / DCS protocols

Existing industry protocols (e.g. Modbus, Profibus,..) not well

suited to protection communications

Cost of interface / gateway solutions

Global market


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Changes in Technology

Processor speeds have been multiplied by 30 (at least) in 15 years

Cost of Memory has dropped considerably

Ethernet is widely available

100 Mbit/s, 1 Gbit/s, etc.

Software technology allows easier implementation of complexconcepts

For example, Object Oriented Design enabling the re-use ofexisting software modules


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Recent Developments

UCA2

EPRI ( USA utilities ) project

Not tied to any particular vendor

Use of some existing standards (MMS protocol, Ethernet

medium)

IEC 61850

Based on UCA 2 concepts

International Standard issued 2004

Edition 2 now partly issued

Hundreds of substations commissioned


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the ability of two or more IEDs or applications from the

same vendor, or from different vendors, to exchange

information and use that information for correct execution

of specified functions

the goal of IEC 61850

Communications Interoperability is...

substation comms intro

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