7x24 Exchange

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7x24 Exchange

• Power Quality Troubleshooting
• Dallas, May 5th 2005

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What is Power Quality ?

• Power The ability to do something
• Quality The degree of excellence

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What is Power ?

• Major utility company had a faulty electrical
  switch and had to open the branch while under
  load.
• Note that one of the air switches, refused to
  disconnect immediately.
• Watch the result!!!

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How is your Power today?

• Is it good?
• Is it bad?
• Is it getting better?
• Is it getting worse?
• Where is it getting worse?
• Why is it getting worse?

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Expensive Downtime

• Semiconductor Manufacturer 3,000,000 per
  event
• Intel, Motorola, AMD
• Telecom Switch 50,000 per minute
• Bell, Sprint, MCI
• Data Center 20,000 to 1,000,000 per min
• EDS, Fidelity, American Express
• dot.com IBX centers
• Car Manufacturer 25,000 per minute
• General Motors, Ford

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PQ Troubleshooting tools

• Voltage logger.
• Single phase. voltage
• Transient capture
• Sags, swells

• Hand held portable.
• Single phase power
• In-Rush current
• N-G bonding

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PQ Troubleshooting tools

• Power Quality.
• 3 phase. Voltage, current
• Transient capture
• Sags, swells, Harmonics
• Unbalance

• Power Quality.
• 3 phase power
• Cycle by Cycle
• Full Disclosure capture

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PQ Troubleshooting Philosophy

• Start at the scene of the crime
• Examine the victim (the load)
• Take time to visually inspect
• What is the business cycle?
• Ask questions?

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PQ Troubleshooting Bottom-up

• Example High harmonics everywhere
• Load location
• Problem location, most likely causes
• Monitoring issues

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PQ Troubleshooting Getting Started

• Make a simplified as-built one-line
• Do a walk-around
• Interview witnesses

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Power Distribution System
3. Feeder loads
1. Branch circuit and service panel

• 2. Distribution Transformer

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Receptacle Line to Neutral Voltage
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The Case of the Rural Transformer Failure

• Scene of the crime
• Rural area surrounded by farmland and open space
• Enigma
• Utility transformer failure occurred in location
  where power quality problems are rare
• Risk
• Loss of power

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Utility Electrical Engineers Notes
Load consists of 3 end-users
What happened during the day of the transformer
failure?
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Single Phase Measurements
Battery chargers are non-linear loads that
generate harmonic currents
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Utility Electrical Engineers Notes

• Problem
• All three end-users experienced peak loads at the
  same time (5 7pm)
• Residential peaks occur at dinnertime with use of
  TV sets, stoves, dishwashers, etc.
• Addition of the large battery charger load on the
  day of the golf tournament caused the transformer
  to overheat

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Utility Electrical Engineers Notes
Solution

• Golf club supervisor agreed to use careful load
  management
• Restrict number of chargers connected at one time
• Avoid use of chargers during peak times

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Takeaways

• Transformers can overheat and fail if heavily
  loaded with harmonic currents
• Battery chargers are non-linear loads that
  generate harmonic currents
• Golf clubs and marinas are vulnerable to sudden
  large battery charger loads
• Timing was important in solving this case history
  always ask for timing info
• Careful load management can usually avoid
  overloads

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Power Quality TroubleshootingService Panel
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Feeder Current
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Feeder Phase Balance
ØA
ØB
ØC

• How much current do you expect on the feeder
  neutral?

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Neutral Current
3rd harmonic 37.35A
Fundamental 3.71A

• Neutral current
• 180 Hz waveform
• 40.57A

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3rd Harmonic
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The Case of the 5th Harmonic Resonance

• Scene of the crime
• A small city gets its water from a mountain lake
  30 miles away
• A pumping system at the lake brings water through
  a pipeline that feeds the citys water
  distribution system
• Enigma
• Under generator power, the backwash filtering
  system suddenly shuts off
• Risk
• Interruption of water supply to the city

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Water Plant Electrical Engineers Notes
Diagram of the water plant
Utility System has no problem when utility power
is connected
Generator Backwash pump shuts off partway
through the start sequence
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Water Plant Electrical Engineers Notes
Generator Why does the backwash pump shut off
partway through the start sequence?

• Backwash pump shuts off partway through the start
  sequence due to a stop signal from the
  protection circuit

• Fluke 43B showed 5th harmonic distortion rising
  to 80 of the fundamental prior to the stop
  signal

• Distortion caused by high resonance current at
  the 5th harmonic flowing between the motor
  inductance and the PF correction caps

• Harmonic current flowing into the generator
  impedence caused enough voltage distortion to
  produce a stop signal

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Water Plant Electrical Engineers Notes
Solution
Move the capacitors to the utility side of the
transfer switch so that the capacitors are out of
the circuit when the generator is operating
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Takeaways

• System operation on generator power should be
  tested for all load combination
• Voltage distortion is usually higher when
  operating on a generator due to higher impedance
  of the generator
• Power factor correction caps can make the system
  resonant near the 5th harmonic
• Semiconductor soft start circuits are often not
  compatible with PF correction caps
• Common test equipment is not adequate for
  harmonic analysis.

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Voltage Severity ITIC
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Voltage Severity ITIC
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Selected Event
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Why Worry About Sags?
Sags are the most prevalent event

• Voltage quality was monitored at the wall outlet
  at 112 North American locations from 1990-1994
• Sags average 27.9 per month with an average sag
  amplitude of 99.3Vrms.
• The median sag duration is 260ms (4.3 cycles)

2-10cycles
10c-1s
1-10s
gt1min
10s-1min
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6
11

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RMS Inrush Measurement

• Half cycle rms value of the r.m.s. current
  measured over each half-period
• Inrush current begins when the half-cycle rms
  current rises above the inrush threshold, and
  ends when the half cycle rms current is equal to
  or below the inrush threshold minus a
  user-selected hysteresis value. The measurement
  should be the half cycle rms values. Each
  half-cycle interval is contiguous and
  non-overlapping.

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Inrush Current
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Transients

• Causes of Transients

• Utility transformer tap switching
• Capacitors switching on.
• Lightning
• Motors switching off (Elevators)
• Switch and relay contact bounce

• Effects of transients

• Damage semiconductor junctions
• Couple into adjacent circuits because of high
  frequency (fast rise times)
• Corrupt data signals

• Protection TVSSTransient Voltage Surge
  Suppressors

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Case Study Re-active decision

• Large European Wafer Plant
• 5,000 employees
• Serious failure condition
• No monitoring
• Costly downtime
• Installed equipment to prevent similar incident

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Case Study Pro-active decision

• Major US bank
• Central HQ for ATM and On-Line customer
  transactions
• Failure of UPS system
• SCR misfiring
• Bank identified problem
• Corrective action in place

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New ways of thinking

The old way Did anything happen? What
happened? What is the cause? The new way What
will happen next? When will it happen again? How
can I prevent it?
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FULL DISCLOSURE MONITORING

• BREADTH OF MEASUREMENTS
• DEPTH OF MEASUREMENTS

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BREADTH OF MEASUREMENTS

• Power Quality
• Power Consumption
• Harmonics
• Flicker
• Imbalance
• Ground loops
• Oscilloscopes

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DEPTH OF MEASUREMENTS

• Cycle by Cycle measurements RMS, harmonics,
  THD, W, VA, VAR, PF, etc.
• Power Quality No thresholds set limits
  after the fact use power tolerance curve use
  indices to track conditions

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Power Quality Index
PQ Index 100
PQ Index 100
PQ Index 0
PQ Index 0
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time
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1250 1000 750 500 250 0
1250 1000 750 500 250 0
Atlanta Power Quality Index Peak 270 Mean
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(No Transcript)
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7x24 Exchange

• Thank you for attending
• john.carroll_at_fluke.com