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Power Quality on Transportation
and Isolated Systems (Panel)
An Overview of Power Quality Problems In
Transportation and Isolated Power Systems
Paulo F. Ribeiro
Calvin College / BWX Technologies, Inc
Grand Rapids, MI USA
Vancouver
July 18, 2001
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General Considerations
- Power Quality issues associated with isolated, transportation,
stand alone, or decentralized power systems are becoming more
complex and requiring additional consideration as more
advanced generation and load-controlled techniques are utilized.
- Due to the typically low inertia and short-circuit levels,
frequency/voltage variations, unbalances and harmonics tend to
be amplified.
- These systems also provide an ideal environment for the
investigation of both the nature of the generation and impact of
power quality deviations.
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Definition
Isolated, transportation/dedicated, stand-alone or decentralized
power systems are systems that by nature (operational necessity
or design) have reduced or optimized generation and/or
transmission-distribution topologies in order to maintain an
adequate/compatible power quality performance / stable and an
economically sustainable operation.
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New Environment
- From a utility perspective, the construction and maintenance of ever increasing
interconnected grids are becoming both economically and environmentally less attractive.
The operational and administrative costs associated with providing power from remote
locations may not compensate the gains of bulk production.
- Utilities may back away from grid expansion and large scale, centralized generating
plants towards decentralized small-scale generation near the load centers. The
opportunity to optimize resources and reduce costs can be significant. Moreover,
deregulation of the power industry did not run the successful course of the
telecommunication industry. These facts have created a new situation in which large
scale centralized systems may become less prevalent even in developed countries.
- From a utilization perspective (transportation, remote locations, or weak transmission
systems), optimization is the objective. Thus, as more advanced generation and load
controlled techniques are implemented in order to increase efficiency and reduce costs,
the power quality issues isolated or decentralized power systems require more attention.
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New Conditions and Problems
- Relatively low inertia and short-circuit levels system and/or load
variations tend to produce higher levels of power quality deviations.
- These include harmonics, reactive power supply and voltage
regulation, voltage unbalance, and frequency variations.
- The current trend toward advanced power electronics (PWM, etc) in
connection with renewable sources and electronically controlled loads
and power factor correction devices add to the complexity of the system.
- For example, isolated systems operating mainly on solar and or wind
power plants may have difficulties in maintaining normal system
frequency. Also weak or optimized power systems have low tolerance to
load unbalance and or variations due to low short-circuit levels.
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New Modeling and Simulation Requirements
- In the past, performance of an isolated power system could be
simply and effectively evaluated from simple expressions based on
short-circuit levels and generation capacity / load variation
parameters.
- Presently, the sophistication of the generation and utilization
techniques requires a much more detailed analysis. Voltage unbalance
can no longer be determined simply by the ratio of the equivalent
single-phase load over the short-circuit power, or similarly the voltage
variation by the maximum load complex load step variation over the
short-circuit power.
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New Opportunities For Investigation
1 - Evaluating Power Quality Generation, Propagation Mechanisms and
Interactions
2 – Evaluating the Impact of PQ Deviations on Sensitive Loads
Power quality standards have been established mainly by empirical
methods and based on utility systems.
3 - Evaluating Integration of New Technologies and Control Issues.
4 - Evaluating the Adequacy of Power Quality Standards for Isolated
Systems.
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Conclusions
• Transportation or isolated power systems provide a unique and
valuable way for engineers to better understand the behavior and
determine better models for describing and predicting the
performance of these common types of power systems.
• This knowledge will enhance our understanding of control,
interaction and power quality issues as new generation and utilization
technologies make isolated, stand alone, decentralized, or better
defined optimized systems, more and more complex. This knowledge
could also be used to help better predict, analyze and control power
quality issues in large utility systems.
• Other papers on this panel session will develop some of the details
related to the new problems encountered with isolated power systems
and the integration of technologies, monitoring, modeling and
simulation.
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