KTH ROYAL INSTITUTE OF TECHNOLOGY

EH2741 Communication and Control in

Electric Power Systems

Course Wrap-up

Lars Nordström larsno@kth.se

Course content

Pow

er System

Protection

Pow

er System

Instrumentation

Pow

er System

Operation/C

ontrol

Pow

er Com

munication S

ystems

Information S

ystem A

rchitecture

Information M

odeling

Pow

er System

Analysis

EH 2741 Communications & Control in Power Systems

Course philosophy

Open the door to future study •  EH2745/EH2751 advanced & project courses •  Degree projects Systems engineering approach Complement to Power Systems Applying theory and methods from several fields to real-world problems Engineering skills State of the Art technologies Industry involvement

Course map

The Power System

5

Power network structure

Transmission system –  all major generating stations and main

load centers –  voltage levels (typically, 230 kV and

above).

Sub-transmission system –  transmits the transmission substations

to the distribution substations.

–  Large industrial customers

Distribution system –  power to the individual customers –  between 4.0 kV and 34.5 kV

6

Transmission Grids

Meshed Long distances High Voltages Connects bulk generation

Meshed MV Grid (Distribution level)

Low Voltage Feeders

Transmission Substation

Gas Insulated

Open air, vaccum insulated

Distribution Substation

10 - 25 kV range Equipment housed in compartments Separate compartments for

• Disconnector • Breaker • Feeder • Measurement

Single Bus Configuration

Advantages: • Lowest cost • Small land area • Easily expandable • Simple in concept and operation Disadvantages: • Single bus arrangement has the lowest reliability • Failure of a bus fault causes loss of entire substation • Maintenance switching can complicate

Sectionalised Bus

Advantages: • Flexible operation • Isolation of bus sections for maintenance • Loss of only part of the substation for a breaker failure or bus fault Disadvantages: • Additional circuit breakers needed for sectionalizing, thus higher cost • Sectionalizing may cause interruption of non-faulted circuits

Main & Transfer Bus

Advantages: •  Maintain service and protection during circuit

breaker maintenance •  Reasonable in cost •  Fairly small land area •  Easily expandable Disadvantages: •  Additional circuit breaker needed for bus tie •  Protection and relaying may become complicated •  Bus fault causes loss of the entire substation

Ring bus configuration

Advantages: •  Flexible operation •  High reliability •  Double feed to each circuit •  No main buses •  Expandable to breaker-and-a-half

configuration •  Isolation of bus sections and circuit

breakers for maintenance without circuit disruption

•  Ring Bus Disadvantages: •  During fault, splitting of the ring

may leave undesirable circuit combinations

•  Each circuit has to have its own potential source for relaying

•  Usually limited to 4 circuit positions, although larger sizes up to 10 are in service. 6 is usually the maximum terminals for a ring bus

Breaker & a half configuration

Advantages: • Flexible operation and high reliability • Isolation of either bus without service disruption • Isolation of any breaker for maintenance without service disruption • Double feed to each circuit • Bus fault does not interrupt service to any circuits • All switching is done with circuit breakers Disadvantages: • One-and-a-half breakers needed for each circuit • More complicated relaying as the center breaker has to act on faults for either of the 2 circuits it is associated with • Each circuit should have its own potential source for relaying

Double breaker

Advantages: • Flexible operation and very high reliability • Isolation of either bus, or any breaker without disrupting service • Double feed to each circuit • No interruption of service to any circuit from a bus fault Disadvantages: • Very high cost – 2 breakers per circuit

Power System Instrumentation

19

The Current Transformer (CT)

Medium Voltage High Voltage

Bushing type Medium Voltage

CTs Accuracy

Voltage Transformers (VT)

Up

to 5

,5 m

eter

s Medium Voltage < 36kV

High Voltage

VT - Accuracy

Accuracy classes for measurement & revenue metering Accuracy classes for protection

A/D conversion

•  Accuracy determined by –  Bit resolution, Least Significant Bit –  Non-linearity due to imperfections. –  Sampling & Aliasing

Putting it all together

Purpose of the Protection System

•  Protect Equipment •  Protect People &

Property •  Separate Faulty

section from power system

•  Restore normal operation

Fundamentals of Protection

Protection System •  A complete arrangement of equipment that fulfills

the protection requirements Protection Equipment •  A collection of devices excluding CT, CB etc Protection Scheme •  A collection of protection equipment providing a

defined function.

Zones of Protection

By dividing the power system into protection zones the extent of disconnections can be limited

Over-Current Protection

Distance Protection

Differential Protection

Recap Common components

Intelligent Electronic Device(s) •  Implements functions Bay controller •  controls all devices related to a single bay Human Machine Interface •  Operator console for local control/configuration Communication bus(es) •  Connection between devices Upwards communication interface. •  To SCADA Remote Terminal Unit •  Telemetry and remote control device Merging Unit

Substation architectures IEC 61850 substation

Substation architectures The Merging Unit

IEC 61850 Information Model Modelling a substation

IEC 61850 Information Model Logical Nodes – Example

Recap Protocol basics

Recap Transition between layers

Computer Networking: A Top-Down Approach: International Edition (Kurose & Ross.) 1.5

IEC61968-100

IEC61968-100

IEC61850-8-1MMSTCPIP/AALATMTwistedpair

IEC61850-8-1MMSTCPIP/X.25LLC/RLC/MACGSMRadioFreq

IEC61850-8-1MMSTCPIPIEEE1901.1Powerline

SGAM model Communication Layer with OSI model

Protocols used in power systems IEC 61850-8-1

Protocols used in power systems IEC 61850-8-1

•  Horizontal communication

Protocols used in power systems IEC 61850-8-1

•  Vertical communication

The context– the Smartgrid Plane

Complete Reference architecture

Cybersecurity – what is it about?

48

NISTR mapping of communications

49

50

51

Countermeasures

52

How can the operator know the system?

62 MW

6 MW

The truth is out here!

Courtesy of ABB Ventryx

Network topology processing

Bus breaker model Bus branch model

State estimation process

State Estimator

Bad Data Processor

Observability Analysis

Topology Porcessor

Analog Measurements

Pi, Qi, Pf, Qf, V, I, θPseudo

Measurements

Breaker Position

s

V, θ

Power System Control Fundamentals

Load & generation balance

Match between electric load and generation Frequency is an indication Balanced system, 50/60 Hz Net power surplus , frequency increases Net power shortage, frequency decreases

Generation Load

ΔP Δf

58

Generator

Generation side Control Demand side control

Governor Δf

Primary Control

Δf

Secondary Control

AGC/LFC ΔPtie

Connection and Tripping of power

Operator

UFLS

UCT

UUFLS

USec

U pri

dfdt

Emergency Control

Power System

f

Frequency control actions

59

Voltage Control Hierarchy