DISTRIBUTED GENERATION & POWER QUALITY

1. Planning & Operating
Electricity Network with
Renewable Generation

2. Distributed Generation & Power Quality

3. Introduction
• 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

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

5. Introduction
•

6. 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.

7. DG Technologies
• Reciprocating Engine Genset

8. 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 %

9. DG Technologies
• Superconducting Magnetic Energy Storage

10. DG Technologies
• Carbon Nanotube

11. DG Technologies
• Fuel Cell

12. DG Technologies
• Fuel Cell
– Phosphoric Acid (PAFC)
• PAFCs generate electricity at more than 40% efficiency
• 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.

13. 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
weight.

14. 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 impurities.
• Cell outputs generally range from 50 to 250 kW.

15. 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.

16. 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.

17. 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.

18. 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 reformer.
• 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 laptops.

19. 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
generation.
• 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.

20. 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 separators.
• 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.

21. 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. .

22. DG Technologies
• Wind Generation

23. DG Technologies
• Photovoltaic

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

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

26. Power Quality Issues
• Voltage Support and Ride Through

27. Power Quality Issues
• Voltage Support and Ride Through

28. Power Quality Issues
• Helping on Voltage Sags

29. Operating Conflicts
• Utility Fault-Clearing Requirements

30. 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.

31. Operating Conflicts
• Reclosing

32. Operating Conflicts
• Interference With Relay
– Reduction of Reach

33. Operating Conflicts
• Interference With Relay
– Sympathetic Tripping of Feeder Breaker

34. Operating Conflicts
• Interference With Relay
– Defeat of Fuse Saving

35. Operating Conflicts
• Voltage Regulation Issues

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

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

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

39. Operating Conflicts
• Harmonics

40. Operating Conflicts
• Islanding
Main Utility Grid
DG

41. Operating Conflicts
• Ferroresonance

42. Operating Conflicts
• Shunt Capacitor Interaction (Overvoltage due to
capacitor)

43. 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 Current

44. Operating Conflicts
• Transformer Connections
– D-Y Connection

45. Operating Conflicts
• Transformer Connection
– Delta-Delta Connection

46. Operating Conflicts
• Transformer Connection
– Grounded Y-D Connection

47. DG on Low-Voltage Distribution
Networks
• Spot Network Arrangement

48. DG on Low-Voltage Distribution
Networks
• Spot Network Arrangement
Underground Network
NPR
NPR
NPR
NPR
NPR
NPR
NPR

49. DG on Low-Voltage Distribution
Networks
• Arrangement of Network Protector Relay
Source
Network
Transformer
Network
Protector
Network

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

51. 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 normal

52. DG on Low-Voltage Distribution
Networks
• Tripping Characteristics of A Microcomputer Based
Network Protector Relay
0
o
90
o
270
o
180
o
Tripping
Region
Non-Tripping
Region
Non-Tripping
Region
Tripping
Region
Network
Phase Voltage
(Unity PF)
Current into
Network
Current into
Network
(Lagging PF)
(Unity PF)
Current out of
Network
Fault
Current
Max. Torque

53. DG on Low-Voltage Distribution
Networks
• Reclosing Characteristics of A Microcomputer Based
Network Protector Relay
0o
1V
2V
3V
4V
5V
6V
7V
8V
Phase Relay
Characteristic
Master Relay
Characteristic
Offset Voltage
Phase Relay
Reclosed
Region

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

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

56. DG on Low-Voltage Distribution
Networks
• Inverter Based DG on a Spot Network (Possible
Solution)

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

58. Siting DG
• DG to Relieve Feeder Overload

59. Siting DG
• DG to Increase Feeder Capacity

60. Siting DG
• DG to Provide Voltage Support & Reconfiguration

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

62. Interconnection of DG
• Simple Interconnection Protection Scheme for Small
DG

63. Interconnection of DG
• Interconnection Scheme
for Large Synchronous
DG