Benefits of Distributed Generation on Power Delivery System
Distribution Engineering
EE 5250
Rakesh Prasad
thDate: April 14 2006
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Contents
Chapter 1 Introduction
1.1 Distributed Generation………………………………..3
1.2 Why Distributed Generation……………………........4 Chapter 2 Advantages of Distributed Generation
2.1 Reliability…………………………………………....... 5-8
2.2 Power Quality……………………………………...…..8-12
2.3 Transmission Benefits.............................................….. 13
2.4 Environmental Benefits……………………………….14-15 Chapter 3 Conclusion………………………………………........16 References……………………………………………………….. 17
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Chapter 1 Introduction
1.1 Distributed Generation:
Distributed Generations are parallel and stand-alone electric generation units located within the electric distribution system at or near the end user.
[6]
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1.2 WHY Distributed Generation?
For the past 60 years, electricity production and supply has been performed by centralized, regulated electric utilities that owned and operated power generation facilities as well as the transmission and distribution lines.
Investor-owned utilities are regulated by state public utility commissions (PUCs), while cooperative and municipal utilities are governed by local jurisdictions. Since the 1970s, federal and state public policy has encouraged the opening of the electric power system to entities other than the electric utilities. This has created a competitive landscape for power generation and has opened the transmission system to access. A significant shift in the U.S. regulatory system began with the Energy Policy Act (EPAct) of 1992, which requires interstate transmission line owners to allow all electric generators access to their lines. Many states today are at various stages of electric utility deregulation.
Utility deregulation is one reason for the high level of interest in Distributed Generation. Other benefits associated with distributed generation
; Reliability
; Power Quality
; Transmission Benefits
; Environmental Benefits
Some well known types of Distributed Generation
; Fuel Cells
; Micro turbines
; Wind farm
; Photovoltaic Cells
; Internal Combustion Engine
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Chapter 2 Advantages of Distributed Generation
2.1 Reliability:
Power reliability is required for
？ Life-safety systems, such as emergency lighting or ventilation, which must
operate properly to prevent the loss of human life.
？ Systems that prevent damage to plant infrastructure (e.g., sump pumps at a
wastewater treatment plant), allow monitoring of other systems (e.g., supervisory
control and data acquisition, or SCADA, systems), or prevent the loss of vital data
during power failures (e.g., at bank data centers) or whose failure to operate could
significantly impact public health.
？ Processes that would cause sizeable financial losses if power outages occurred.
Power outages cause loss of quality control in batch processes—found at
microelectronic component manufacturing, food processing, chemical processing,
and oil refining facilities—and force owners to discard entire batches. In addition,
power losses to processes that operate 24 hours per day, seven days per week—
with no openings to recover lost production time—can lead to cancelled orders.
？ Equipment and processes for which operation is not time-critical. Operating this
type of equipment, such as a cooling system with a large, cool storage tank, can
be deferred to off-peak times; switched to an alternate source, such as an engine
generator; or switched to an alternate fuel, such as an electric heating system with
fuel-oil backup.
There are many ways to increase the reliability of power. Redundant power supplies do not always improve reliability. If two redundant feeders supply power to an industrial facility but originate at the same utility substation and are carried on the same set of power poles, reliability will be lower than if they originate at separate substations and travel to the site on different sets of power poles. The problem with redundant feeders carried on the same set of poles is that a single-point failure (e.g., a weather-related event, pole fire, or traffic accident) could cause simultaneous outages on both sources.
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To improve power reliability by installing standby generation, uninterruptible power
supplies (UPS), flywheels, or fuel cells.
Reliability is the most important feature of electric power distribution system.
Quantification of distribution system indices is the best indices of whether the system with distributed generation has increased reliability or not. The following indices are generally used by utilities (IEEE standard 1366, 2001) to
measure the reliability.
System Average Interruption Duration Index (SAIDI):
Customer interruption duration，SAIDI；
Total no of customer served
Customer Average Interruption Duration Index (CAIDI):
customer interruption duration，CAIDI；
Total no of customer interruption
System Average Interruption Frequency Index (SAIFI
Total no of customer interruption
SAIFI；
Total no of customer served
Customer Average Interruption Frequency Index (CAIFI)
Total no of customer interruptions
CAIFI；
Total no of customer interrupted
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The following is a short example taken from [7]. The system is a two 22 KV feeders as the main incoming feeders in the station, followed by two 10 MVA, 22KV/11KV transformers. Both the transformers share the total load of about 2 MW with around15000 customers 22 KV Incoming
22 KV Incoming
TR 2 10 MVA,22/11KVTR 1 10MVA 22/11KV
TR 2 10 MVA,22/11KVTR 1 10MVA 22/11KV
11 KV Bus BarFeeder 1Feeder 211 KV Bus BarFeeder 1Feeder 2
Rest of NetworkRest of Network
Rest of NetworkRest of Network
Society 2Society 1
Society 2Society 1
Customer 327 Customer 220 Customer 327 Customer 220
System without DG System with DG If there is a fault on feeder 1 all 327 customer of society 1 attached to it get affected, if
the fault leads to sustained interruption then there is no alternate feed is for these customers. In such situations a strategically placed DG will be able to take care of all these 327 customers of society 1 in the event of fault in feeder 1, the same will be true in the event of fault in feeder 2 catering to 220 customers of society 2.
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The following are data’s obtained from TATA POWER COMPANY.
Total no of Sum of No of affected customers Total no of customers served interruption customer duration in interruption minutes Without Without With With DG DG DG DG
Feb-03 2020 74537 2018 1691 12336 12663
Aug-03 6106 241012 4334 4007 15101 15428
Dec-03 5012 66983 4916 4589 15497 15824
CAIFI SAIFI SAIDI
Without Without Without With With DG With DG DG DG DG DG
Feb-03 1 1.194 0.163 0.159 6.042 5.886
Aug-03 1.409 1.523 0.404 0.396 15.96 15.62
Dec-03 1.02 1.09 0.323 0.316 4.322 4.233
The above results show that by optimally placing DG, the reliability indices have improved. The improvement may have been significant in the case of DG supplying a larger part of the network.
2.2) Power Quality Power Quality of any power system can be judged by the voltage profile and line losses. The index VPII and LLRI gives the result of benefits of the system with DG in comparison to system without DG.
[4]
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The above fig shows the single line diagram of 12 bus system used to obtain VPII and LLRI. The system consists of three conventional generators at bus 1, bus 5 and bus12 with ratings of 1.0, 0.75 and 0.625 respectively. Total load of 2.013 pu located unevenly on every bus is assumed. The resistance and reactance of all the distribution and transmission lines are assumed to be 0.000625 pu/km and 0.000375 pu/km. The lengths of the distribution lines are as below
[4]
Simulations of following four cases were done
Case (1): D.G located at bus 9.
Case (2): D.G located at bus 10.
Case (3): 50% DG located at Bus 9 and 50% DG located at Bus 4.
Case (4): 50% DG located at Bus 9 and remaining 50% located at Bus 10.
VPII: Voltage Profile Improvement Index
It is defined as the voltage profile index of the system with DG to the voltage profile of the system without DG
VPw/DGVPII； VPwo/DG
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Is voltage profile of the system with DG VPw/DG
Is the voltage profile of the system without DG VPwo/DG
NN
VP；VLk With k；1，iii，ii；1；1i
Is the voltage magnitude at bus i in per unit. Vi
Is the load at bus i in per unit. Li
Is the weighting factor for load bus i. ki
Is total number of Load bus. N
The weighting factors are chosen based on the importance and criticality of different
Loads
[4]
To study the impact four sets of bus weighing factor set 1 through 4 as listed above were
selected. The results thus obtained are shown below.
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