Substation Comms Intro

Substation Communications:

Introduction

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”)

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

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

Prot oco ls / F orm ats

Language

Digital Communications : Definitions

_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 11101010 00001101 Receiver

_SYNCHRONOUS

 Bit periods controlled by synchronizing the clocks at the transmitter 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

_{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

Data Security

Noise corruption of data

 Parity bit check

 Checksums

 Cyclic redundancy check

Unauthorized access – “cybersecurity”

 Password protection

 Modem dial back

 Firewalls

 Encryption

_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/Slave

but can have multiple Clients!

IED IED Engineering Engineering Station Station Modem Modem Modem Modem Laptop Laptop IED IED

Transmission Definitions : Point to point

LOCAL LOCAL

REMOTE REMOTE

Ethernet Standard - 30/05/2012 - P 11

Bus Network/Multidrop Token Ring Network Topology

Star Network Topology

Network An interconnected group of nodes or

stations linked by communication channels

Node The interface point where one or more

functional units are connected

LAN Local area network (<5km)

WAN Wide area network

Network topology Pattern of nodes and their interconnection

Gateway Equipment which makes data from a separate subnetwork available to primary network

_{CARRIER SENSE METHODSCARRIER SENSE METHODS}

 CSMA (Carrier Sense Multiple Access) /CD (Collision Detection)

 Medium Access Control (MAC)

_{TOKEN ACCESS METHODTOKEN ACCESS METHOD}

 The device that has the Token has access to transmit

_{RESERVATION METHODRESERVATION METHOD}

 Each device has a predefined time slot to transmit

IED IED

* IED _Computer Laptop Gateway Modem SCADA Client Substation HMI Modem DNP3.0 Level 3 DNP3.0 Level 2 DNP3.0 Level 2 EIA232 Front Engineering Station Modem Modem EIA485 EIA485 EIA485 Gateway

Network Topology (serial communication)

IED IED * IED Gateway Gateway IEC61850 Laptop Computer SCADA Client Substation HMI EIA232 Front Engineering Station Terminal Server Ethernet EIA485 _Ethernet WAN Ethernet Switch EIA232 Terminal Server

Network Topology (Ethernet communication)

Open System Interconnection (OSI)

7 Layer Model

Data link Data link Physical Physical Data link Data link Physical Physical Physical transmission medium

Physical transmission medium Application

Application _{Application Application} 7 7 6 6 5 5 4 4 3 3 2 2 1 1 7 7 6 6 5 5 4 4 3 3 2 2 1 1 Presentation Presentation Session Session Transport Transport Network Network Presentation Presentation Session Session Network Network Transport Transport Application Specific Protocols

Application Specific Protocols Message Format, Language Message Format, Language

Flow Control, Message sequence Flow Control, Message sequence

Dialog Between Processes Dialog Between Processes

Packets (Routing) Packets (Routing) Error Detection, Frames Error Detection, Frames

Tx

Protocols: Analogy

ZG9948

Postal network

SCADA SCADA

Within the substation Within the substation

Standard/independent:

Standard/independent:IEC60870-5-103,IEC60870-5-103, DNP3, MODBUS, Profibus, etc.

DNP3, MODBUS, Profibus, etc.

Proprietary:

Proprietary:Courier, SPA-Bus, etc.Courier, SPA-Bus, etc.

Master / Slave Master / Slave Speed 1200bps to 64 kbps Speed 1200bps to 64 kbps IEDs IEDs RTU / Bay RTU / Bay Computer / Computer / Gateway Gateway

Outside the substation Outside the substation

Standard/independent:

Standard/independent:IEC60870-5-101,IEC60870-5-101, DNP3, MODBUS, etc.

DNP3, MODBUS, etc.

Proprietary RTU protocols Proprietary RTU protocols Master / Slave

Master / Slave

Speed 9.6 to 64 kbps + Speed 9.6 to 64 kbps +

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

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

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 complex concepts

 For example, Object Oriented Design enabling the re-use of existing software modules

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

_{…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}