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Distributed Generation & Power Quality


Distributed Generation & Power Quality Wei-Jen Lee, Ph.D., PE Professor of Electrical Engineering The University of Texas at Arlington July 10, 2003 – PowerPoint PPT presentation

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Title: Distributed Generation & Power Quality

Distributed Generation Power Quality
  • Wei-Jen Lee, Ph.D., PE
  • Professor of Electrical Engineering
  • The University of Texas at Arlington
  • July 10, 2003

  • Perspectives on DG Benefits
  • End-User Perspective
  • Back Generation to Provide Improved Reliability
  • Reduce Energy Bill
  • Participation in the Competitive Power Market
  • Distribution Utility Perspective
  • Transmission Distribution Relief
  • Hedge Against of Uncertain Load Growth
  • Hedge Against Price Spike
  • Commercial Power Producer Perspective
  • Selling Power or Ancillary Service in the
    Deregulated Market
  • Integrated Resource Planning

  • Disadvantages of DG
  • Power Quality
  • Cost of Operation and Maintenance
  • Long Term Reliability of the Units
  • Interconnection


DG Technologies
  • Reciprocating Engine Genset
  • The Least Expensive DG Technology
  • High Nox and Sox Emission. This Severely Limits
    the Number of Hours the Units, Particularly
    Diesels, May Operate per Year.
  • Natural Gas-Fire Engine Produce Fewer Emission.
    However, the Natural Gas Price is Unpredictable.

DG Technologies
  • Reciprocating Engine Genset

DG Technologies
  • Combustion Turbine
  • Range from 1 to 10 MW
  • High Speed 8 12 kRPM
  • Microturbine
  • 30 75 kW
  • 10 100 kRPM
  • Efficiency 25 30

DG Technologies
  • Superconducting Magnetic Energy Storage

DG Technologies
  • Carbon Nanotube

DG Technologies
  • Fuel Cell

DG Technologies
  • Fuel Cell
  • Phosphoric Acid (PAFC)
  • PAFCs generate electricity at more than 40
  • Operating temperatures are in the range of 300 to
    400 degrees F (150 - 200 degrees C)
  • Existing PAFCs have outputs up to 200 kW, and 1
    MW units have been tested
  • One of the main advantages to this type of fuel
    cell is that it can use impure hydrogen as fuel.
    PAFCs can tolerate a CO concentration of about
    1.5 percent, which broadens the choice of fuels
    they can use. If gasoline is used, the sulfur
    must be removed.
  • PAFCs are the most mature fuel cell technology.

DG Technologies
  • Fuel Cell
  • Phosphoric Acid (PAFC)
  • Disadvantages of PAFCs include it uses expensive
    platinum as a catalyst, it generates low current
    and power comparably to other types of fuel
    cells, and it generally has a large size and

DG Technologies
  • Fuel Cell
  • Proton Exchange Membrane (PEM)
  • These cells operate at relatively low
    temperatures (about 175 degrees F or 80 degrees
    C), have high power density, can vary their
    output quickly to meet shifts in power demand,
    and are suited for applications, -- such as in
    automobiles -- where quick startup is required.
  • According to DOE, "they are the primary
    candidates for light-duty vehicles, for
    buildings, and potentially for much smaller
    applications such as replacements for
    rechargeable batteries.
  • This type of fuel cell is sensitive to fuel
  • Cell outputs generally range from 50 to 250 kW.

DG Technologies
  • Fuel Cell
  • Molten Carbonate (MCFC)
  • These fuel cells use a liquid solution of
    lithium, sodium and/or potassium carbonates,
    soaked in a matrix for an electrolyte.
  • They promise high fuel-to-electricity
    efficiencies, about 60 normally or 85 with
    cogeneration, and operate at about 1,200 degrees
    F or 650 degrees C.
  • To date, MCFCs have been operated on hydrogen,
    carbon monoxide, natural gas, propane, landfill
    gas, marine diesel, and simulated coal
    gasification products.
  • 10 kW to 2 MW MCFCs have been tested on a variety
    of fuels and are primarily targeted to electric
    utility applications.
  • A disadvantage to this, however, is that high
    temperatures enhance corrosion and the breakdown
    of cell components.

DG Technologies
  • Fuel Cell
  • Solid Oxide (SOFC)
  • This type could be used in big, high-power
    applications including industrial and large-scale
    central electricity generating stations.
  • Some developers also see SOFC use in motor
    vehicles and are developing fuel cell auxiliary
    power units (APUs) with SOFCs.
  • A solid oxide system usually uses a hard ceramic
    material of solid zirconium oxide and a small
    amount of ytrria, instead of a liquid
    electrolyte, allowing operating temperatures to
    reach 1,800 degrees F or 1000 degrees C.
  • Power generating efficiencies could reach 60 and
    85 with cogeneration and cell output is up to
    100 kW.

DG Technologies
  • Fuel Cell
  • Alkaline
  • Long used by NASA on space missions, these cells
    can achieve power generating efficiencies of up
    to 70 percent. They were used on the Apollo
    spacecraft to provide both electricity and
    drinking water.
  • Their operating temperature is 150 to 200 degrees
    C (about 300 to 400 degrees F).
  • They typically have a cell output from 300 watts
    to 5 kW.

DG Technologies
  • Fuel Cell
  • Direct Methanol Fuel Cells (DMFC)
  • These cells are similar to the PEM cells in that
    they both use a polymer membrane as the
    electrolyte. However, in the DMFC, the anode
    catalyst itself draws the hydrogen from the
    liquid methanol, eliminating the need for a fuel
  • Efficiencies of about 40 are expected with this
    type of fuel cell, which would typically operate
    at a temperature between 120-190 degrees F or 50
    -100 degrees C.
  • This is a relatively low range, making this fuel
    cell attractive for tiny to mid-sized
    applications, to power cellular phones and

DG Technologies
  • Fuel Cell
  • Regenerative Fuel Cells
  • Still a very young member of the fuel cell
    family, regenerative fuel cells would be
    attractive as a closed-loop form of power
  • Water is separated into hydrogen and oxygen by a
    solar-powered electrolyser. The hydrogen and
    oxygen are fed into the fuel cell which generates
    electricity, heat and water. The water is then
    recirculated back to the solar-powered
    electrolyser and the process begins again.
  • These types of fuel cells are currently being
    researched by NASA and others worldwide.

DG Technologies
  • Fuel Cell
  • Zinc-Air Fuel Cells (ZAFC)
  • In a typical zinc/air fuel cell, there is a gas
    diffusion electrode (GDE), a zinc anode separated
    by electrolyte, and some form of mechanical
  • The GDE is a permeable membrane that allows
    atmospheric oxygen to pass through. After the
    oxygen has converted into hydroxyl ions and
    water, the hydroxyl ions will travel through an
    electrolyte, and reaches the zinc anode. Here, it
    reacts with the zinc, and forms zinc oxide. This
    process creates an electrical potential.

DG Technologies
  • Fuel Cell
  • Protonic Ceramic Fuel Cell (PCFC)
  • This new type of fuel cell is based on a ceramic
    electrolyte material that exhibits high protonic
    conductivity at elevated temperatures.
  • PCFCs share the thermal and kinetic advantages of
    high temperature operation at 700 degrees Celsius
    with molten carbonate and solid oxide fuel cells,
    while exhibiting all of the intrinsic benefits of
    proton conduction in polymer electrolyte and
    phosphoric acid fuel cells (PAFCs).
  • The high operating temperature is necessary to
    achieve very high electrical fuel efficiency with
    hydrocarbon fuels. PCFCs can operate at high
    temperatures and electrochemically oxidize fossil
    fuels directly to the anode. This eliminates the
    intermediate step of producing hydrogen through
    the costly reforming process. .

DG Technologies
  • Wind Generation

DG Technologies
  • Photovoltaic

Interface to the Utility System
  • Synchronous Machine
  • Asynchronous Machine
  • Electronic Power Inverters

Power Quality Issues
  • Sustained Interruptions
  • Voltage Regulation
  • Voltage Ride Through
  • Harmonics
  • Voltage Sags
  • Load Following
  • Power Variation
  • Misfiring of Reciprocating Engines

Power Quality Issues
  • Voltage Support and Ride Through

Power Quality Issues
  • Voltage Support and Ride Through

Power Quality Issues
  • Helping on Voltage Sags

Operating Conflicts
  • Utility Fault-Clearing Requirements

Operating Conflicts
  • Reclosing
  • DG Must Disconnect Early in the Reclose Interval
    to Allow Time for the Arc to Dissipate.
  • Reclosing on DG, Particularly Those System Using
    Rotating Machine Technologies, Can Cause Damage
    to the Generator or Prime Mover.

Operating Conflicts
  • Reclosing

Operating Conflicts
  • Interference With Relay
  • Reduction of Reach

Operating Conflicts
  • Interference With Relay
  • Sympathetic Tripping of Feeder Breaker

Operating Conflicts
  • Interference With Relay
  • Defeat of Fuse Saving

Operating Conflicts
  • Voltage Regulation Issues

Operating Conflicts
  • Voltage Drops Along the Feeder if the DG is
    Interrupted (Determine the Max. Capacity of DG)

Operating Conflicts
  • Excess DG Can Fool Reverse Power Setting on Line
    Voltage Regulator

Operating Conflicts
  • Varying DG Output can Cause Excess Duty on
    Utility Voltage Regulation Equipment

Operating Conflicts
  • Harmonics

Operating Conflicts
  • Islanding

Main Utility Grid
Operating Conflicts
  • Ferroresonance

Operating Conflicts
  • Shunt Capacitor Interaction (Overvoltage due to

Operating Conflicts
  • Transformer Connections
  • Grounded Y-Y Connection
  • No Phase Shift
  • Less Concern for Ferroresonance
  • Allow DG to Feed All Types of Faults on the
    Utility System
  • Back Feed of the Triplen Harmonic
  • Should Insert Ground Impedance to Limit the

Operating Conflicts
  • Transformer Connections
  • D-Y Connection

Operating Conflicts
  • Transformer Connection
  • Delta-Delta Connection

Operating Conflicts
  • Transformer Connection
  • Grounded Y-D Connection

DG on Low-Voltage Distribution Networks
  • Spot Network Arrangement

DG on Low-Voltage Distribution Networks
  • Spot Network Arrangement

DG on Low-Voltage Distribution Networks
  • Arrangement of Network Protector Relay

DG on Low-Voltage Distribution Networks
  • A Microcomputer Based Network Protector Relay

DG on Low-Voltage Distribution Networks
  • Operation of A Microcomputer Based Network
    Protector Relay
  • Network protector relays are used to monitor and
    control the power flow of low voltage AC to
    secondary network systems
  • The purpose of the network protector is to
    prevent the system from backfeeding and initiate
    automatic reclosing when the system returns to

DG on Low-Voltage Distribution Networks
  • Tripping Characteristics of A Microcomputer Based
    Network Protector Relay

DG on Low-Voltage Distribution Networks
  • Reclosing Characteristics of A Microcomputer
    Based Network Protector Relay

DG on Low-Voltage Distribution Networks
  • Network Primary Feeder Fault

DG on Low-Voltage Distribution Networks
  • Fault Current Contribution From Synchronous Local

DG on Low-Voltage Distribution Networks
  • Inverter Based DG on a Spot Network (Possible

DG on Low-Voltage Distribution Networks
  • Adjustable Reverse Power Characteristics

Siting DG
  • DG to Relieve Feeder Overload

Siting DG
  • DG to Increase Feeder Capacity

Siting DG
  • DG to Provide Voltage Support Reconfiguration

Interconnection of DG
  • Typical Voltage and Frequency Relay Setting for
    DG Interconnection for a 60 Hz System

Interconnection of DG
  • Simple Interconnection Protection Scheme for
    Small DG

Interconnection of DG
  • Interconnection Scheme for Large Synchronous DG
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