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Lecture 29
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ECE 528 – Understanding Power Quality
Paul Ortmann [email protected] 208-733-7972 (voice) 208-736-3248 (fax)
http://www.ece.uidaho.edu/ee/power/ECE528/
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Today…
- Finish long duration voltage variations
- Power quality and reliability benchmarking
- Definitions
- Motivation
- Issues
- Trends
- RMS Voltage variations
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End-user mitigation of
Long-duration voltage variations
- Ferroresonant transformers
- Very constant voltage output over a wide range of voltage input
- Must be oversized
- Best for relatively constant load – not suitable for motors
- Inefficient
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End-user mitigation of
Long-duration voltage variations
- Electronic tap-changing transformers or
regulators
- Use solid-state switches to quickly switch between taps
- Can provide voltage in a narrower range than supplied by the utility - One example: - Input: +10% to -20% of nominal - Output: +/- 2.5% of nominal
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Power Quality and Reliability Benchmarking:
Defining terms (PSQ Ch. 8)
- Aggregation
- Grouping events within a time period or only considering the worst event in the time period
- Benchmark
- A standard against which performance is measured
- Benchmarking
- The process of evaluating performance against some standard level of performance
- Uses one or more defined indices or metrics
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Defining terms
- Index or metric
- A specific measured parameter
- For each index or metric, we need to know:
- What is measured and how
- How often it’s measured
- The benchmark for that index
- The target for that index
- Target
- Goals for specific indices based on benchmarks, local constraints, and specific objectives
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Motivation – why benchmark?
- Benchmarking helps drive improvement
- Under-performing areas can be identified
- “Best practices” can be determined
- Helps ensure fact-based decision making
- The power quality may seem good or bad, but is it?
- How good or bad is it, specifically?
- Benchmarking helps establish a common set of measurable expectations - Regulators, utilities, and customers can agree to, and document indices and benchmarks
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The value of a common set
of measurable expectations
Energy Consumer
Energy Provider Perceptions
Receivables & Deliverables
Rights & Duties
Rights & Duties
Delivered Products & Services
Received Products & Services
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4
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Benchmarking issues
- Not reasonable to expect the same
performance across all transmission and
distribution systems
- Geography
- Weather
- System density/feeder length
- Underground/overhead
- Protection scheme
- Animals/vehicles/vegetation
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Trends
- Standards have been and are being
developed which combine power quality
and reliability indexes and benchmarks
- In Europe, EN 50160: “Voltage
characteristics of electricity supplied by
public distribution systems”
- In the US – Work is underway to establish
“Service Quality Indices”
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EN50160 (pg 292)
- Sets limits for:
- Frequency
- Voltage sags
- Interruptions (short and long (>3 min))
- Voltage unbalance
- Voltage harmonics, and more
- Generally specifies acceptable limits, measurement interval, length of recording, and acceptance percentage.
- Example: Voltage sampled every 10 minutes for a week will be within 10% of nominal 95% of the time.
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US Service Quality Benchmarking
- A Service Quality Index combining power quality and reliability measures has been proposed. - Not adopted yet
- Purpose is to reflect customer quality and reliability requirements and expectations
- EPRI project 1010199
- IEEE paper “Quantifying Reliability and Service Quality for Distribution Systems” – by Mark F. McGranaghan, 2007
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Applications of RMS variation indices
(see pg. 90+ for reliability indices)
- SARFIx, STARFIx, SMARFIx, and STARFIx
can be determined for the system and for
individual feeders or areas
- Feeders with below-average values can be
targeted for improvement
- Feeders with above-average values can be
studied for best practices
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Next time…
- More power quality and reliability
benchmarking
- Harmonic indices
- Looking at real-world data
- Read chapter 8
