Nasir Khan & Oumar FallELEN281-Fall’13

Tittle: What Makes a Transmission Grid Smart ?Authors: A. Edris (aedris@quanta-technology.com)Affiliation: Quanta Technology USA Presented: Bologna Italy 2011 (Conference)

Content Introduction

Definition of Smart Grid Characterizing features making a grid “Smart Grid” Smart Transmission Grid

o Key characteristics to qualify a transmission grid to be “Smart”o Road-map ideas for smart transmission grid

Smart Transmission Technologies and concepts Power Electronics-Based Transmission Controllers Monitoring Dealing with the cause not the effect approaches

Q/A

Introduction Electricity is fundamental to the world civilization

Conveys energy and information (with no emission at point of use)

Provides an increasing array of innovative products and services Electric power system by all measures is a very

complex “machine”. Traits of this complexity are: Inadequate power flow control and reactive power management Power angle and voltage instabilities Inadequate planners/operators training, inefficient use of data

Vital to continuously develop “smart” technologies Improved performance for reliable and quality power delivery “Smartening” of power system is an evolutionary

process, not a one-time event.

Smart Grid Definition: Integrated array of grid technologies,

devices, and controlling systems that provide and utilize digital information, communications, and controls to optimize the efficiency, reliability and security of electric power delivery. Puts information and communication technology into

electricity generation, transmission, and consumption making systems cleaner, safer, more reliable and efficient.

Smart Grid Characterizing Features

Auto-balancing and self monitoringo Integrate any resource of energy (e.g. renewable resources)o Provide enhanced physical and cyber security

CO2 emissions reduction supporting environment protection Adept of self-mechanism of relieving transmission

bottleneckso Prevent cascading failures

Enable real-time communication between consumer & suppliero Informed participation by customerso Optimized energy usage based on environmental/ price

preferences

Smart Transmission Grid Key characteristics:

Self-adapting and self-healing: It prevents power disturbance and breakdown via self-diagnosis and fault location.

Consumer friendly: Empowers and incorporates consumer equipment and behavior in grid design and operation.

Security: Tolerant of attacks; grid which mitigate and resilient to physical and cyber attack.

Quality: Provides power quality for the range of needs.o Power quality consistent with consumers and industry.o Varying grades (and prices) of power.

Renewable energy integration: Accommodates variety of resources.o DR, combined heat and power, wind, photovoltaic and end-use efficiency.

Economical energy usage: Fully enabling and is supported by competitive markets.

Road map ideas Generation of electrical energy is presently the largest

source of CO2 emissions, making a significant contribution to climate change.

To alleviate the consequences of climate change, the current electrical system needs to endure significant adjustments.

Adjustments must meet four requirements: Capacity: Satisfying increasing demand for electrical energy. Reliability: Satisfying quality and reliability & availability of

electricity. Efficiency: Production to consumption energy has to be saved. Sustainability: Integration of low carbon energy sources.

Road map ideas To achieve the adjustments it is vital to have a grid that:

Has ability to sense overloaded areas and re-route power flows to reduce overload and prevent a potential outage and cascading failures.

Enables real-time communication between consumer and utility, allowing the consumer to optimize energy usage based on environmental and price preferences.

Is capable of auto-balancing supply and demand. Accepts any energy resources with a robust transformation of these energy

resources into consumer end use with minimal human intervention. Will allow unlimited use of renewable energy sources aiming at minimizing

carbon footprint.

“Smart” transmission technologies & concepts Basic limitations of power flow are line impedance, thermal rating, angle,

and voltage stability. Limitations result in underutilization of transmission assets.

o Scheduled power transfer levels can be far below 20%- 50% lower than the “inherent” thermal capacity.

Strengthening of the transmission network with new lines is not a reasonable solution due to high cost, regulatory, & environmental constraints.

What is the solution then? “Smart” technology solutions and concepts overcome limits and inflexibility of existing transmission grid.

Transmission Controllers Flexible Alternating Current Transmission Systems

Systems used for the dynamic control of voltage, impedance & phase angle of high voltage AC transmission lines

High Voltage Direct Current System used for transmitting or exchanging electrical power by means of direct

current. FACTS and HVDC technologies: provide flexibility, controllability,

reliability, and accessibility for transforming a transmission grid. They provide: Increased transmission capacity Relieving transmission bottlenecks Improved flexibility and controllability of transmission grid Bulk power transmission over long corridors (GW range) Grid access of renewable power plants (CO2 emission reduction) Increased robustness and reliability of transmission grid

Transmission Controllers Convertible Static Compensator (CSC): relieves transmission bottleneck and increases capacity.

Consists of two 100 MVA converters; one shunt transformer, series transformer, and a set of motor operated switches.o Relief of major transmission bottlenecko Strong dynamic voltage support resulted in increase of

transmission capacity by about 200 MW (~200,000 US homes).

o Exceptional “Smart” controllability and flexibility in grids

Transmission Controllers Unified Power Flow Controller (UPFC): improves reliability and efficiency of power

delivery.Increase of power transfer capability by 100 MW (Inez substation in AEP )Frees up transmission capacity for years of load growth on AEP’s transmission system.Reduction of real power losses by more than 24 MW, which is equivalent to a reduction of CO2

emissions by about 85,000 ton/year.

Transmission Controllers Segmentation and Grid Shock Absorber : prevents cascading

failures & improves reliability of grid. Limit the wide spread of disturbances & faults

o VSC BtB connecting electrically separated transmission segments o VSC BtB provides a four-quadrant real and reactive power control o BtB acts as a firewall stopping propagation of a disturbance

Prevents cascading failures o Tested on the EI (experienced a major blackout in August 2003)

Segmented into four segmentso Interconnection between the respective segments is replaced by a VSC BtB , where

the power transfer levels between the respective segments are kept the same as with AC interconnections

Monitoring Monitoring and data integration play an important role in making a transmission grid smart.

Weather condition and tension of overhead transmission lineo Improvement in transmission capacity by 10%-15%.

Synchrophasor: synchronized phasor data collected from optimally located Phasor Measurement Units (PMUs) on the transmission grid. o Data is used for wide area protection, control, and security assessment.

Dealing with the cause not the effect

“Smart” solutionSubsynchronous Resonance (SSR) problem: Undesirable energy exchange between the

electrical and mechanical sides of turbine-generator sets at frequencies below the power frequency.o Phase imbalance created by adding series resonance circuits, tuned to power frequency, on phase a and

phase b.

Dealing with the cause not the effect First-swing stability issue: Synchronous generator

can lose its synchronism with the connected grid as a result of a major fault when clearance time is longer than the critical time to ensure first swing stability of the generator.

o Concept is based on extending the inherent braking capability of the generator to an extent of completely counter balancing the accelerating energy during fault.

o Achieved through the use of “high-speed phase shifting transformer”, controlling phase angle of generator voltage in step with the generator power angle.

Equal-area criterion without phase shifter and with phase shifter changing phase shifting angle α in step with the power angle δ.