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KTH ROYAL INSTITUTE OF TECHNOLOGY
EH2741 Communication and Control in
Electric Power Systems
Course Wrap-up
Lars Nordström [email protected]
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