ni.com Sensor Measurement Fundamentals Series
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Sensor Measurement Fundamentals Series
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Voltage, Current, and Power Measurements
Doug Farrell
Product Manager
National Instruments
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Key Takeaways
• Power fundamentals
• Power derivation from voltage and current
• High-voltage and high-current measurements
• Requirements for a power measurement system
• Signal processing and software
• NI’s power monitoring solution
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Why Measure Power?
Facilities/Utilities
Machine Health
White Goods Testing
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The Benefits of Power Measurement
Measurement Action Benefit
Total energy consumption Verify with bill from utility Overpayment elimination
Submetering of energy Assign to cost center Focus on largest energy consumers
Demand prediction Run machines in shifts or alter
process control algorithm Avoid peak usage fees
Power factor Run machines in shifts or alter
process control algorithm Avoid fines from utility
Unbalance, RMS
trend/level, harmonics,
SAG/SWELL
Machine health monitoring Energy efficiency and predictive maintenance
(machine life, minimize downtime)
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What do we think of when we think of
measuring power?
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Two Measurements Needed for Power
Voltage Current
IVP *
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The Electricity/Water Analogy
Current = flow rate of water
(Amps)
Voltage = water pressure
(Volts)
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Turbine Generators
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Power Transmission
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Voltage Measurement
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Current Measurement
• Current transformers and transducers
• Split core versus solid core current transformers
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Instrumentation Considerations
• Simultaneous acquisition
• Resolution
• Anti-aliasing filters
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Synchronization
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Resolution
Time (ms)
100 200 150 50 0
0
1.25
5.00
2.50
3.75
6.25
7.50
8.75
10.00
Vol
tage
(V
olts
) 16-Bit Versus 3-Bit Resolution
(5 kHz Sine Wave)
16-bit
3-bit
000
001
010
011
100
101
110
111
| | | | |
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Improperly sampled Properly sampled
fN = fs/2 fs: sampling frequency
Anti-Aliasing Filters
• Shannon sampling theorem
• The maximum frequency (Nyquist frequency: fN) that can be analyzed is given by
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Measuring Waveform Data
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Voltage Measurement
NI 9225 “Supply”
White wire
Black wire
Connection made using spliced power cord
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Current Measurement
NI 9227
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Transformers and Transducers
• Output voltage or current
• DC or high frequency
• Split or solid core
• Mount or handheld
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Current Measurement
NI 9239
Exposed B, W, G wires
Black wire passes
through CT
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RMS (Root Mean Square) AC Equivalent of DC
3 Common Ways to Calculate
• True RMS
• Peak
• Average
Equation (True)
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Signal Processing
Features
• Voltage, current, power
• Instantaneous
• RMS
• Peak-peak
• Crest factor
• Fundamental frequency
• Power factor
• Power (reactive, apparent, real)
Events
• Sag
• Swell
• Interruption
• Flicker
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Interruption Swell Sag
Voltage Level (% of nominal)
10%<sag<90%*
Duration
Instantaneous 0.5-30 cycles
Momentary 30 cycles—3 seconds
Temporary 3 seconds—1 minute
Voltage Level (% of nominal)
110%<sag<180%*
Duration
Instantaneous 0.5-30 cycles
Momentary 30 cycles—3 seconds
Temporary 3 seconds—1 minute
Voltage Level (% of nominal)
110%<sag<180%*
Duration
Momentary 30 cycles—3 seconds
Temporary 3 seconds—1 minute
*Levels differ based on duration. Data pulled from IEEE 1159:1995. See standard for full data.
Power Quality Events
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Power Quality Events
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LabVIEW Electrical Power Suite
• Measure power quality and energy features
to IEC, EN, and IEEE standards
• Harmonics (IEC 61000-4-7)
• Flicker (IEC 61000-4-15)
• Sag/swell/interruption with standard or
custom levels (IEC 61000-4-30)
• Compatibility with the COMTRADE (IEEE
37.111) file format
Download the Evaluation Version: Search for “Electrical Power Suite” at ni.com
PN: 782071-35
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Hardware Demonstration
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Software Demonstration
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Types of Electrical Loads
Resistive Inductive Capacitive
In Phase Lagging Phase Leading Phase
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The Power Triangle Mathematical Analogy
(phi)
Apparent Power = V * I [VA]
Real Power = V * I cos () [Watts]
Reactive Power [Var]
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Power Factor = Real Power
Apparent Power
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The Power Triangle Mechanical Analogy
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Power Factor Correction
Circuit Connection
Contactors “Relays”
Bank of Capacitors
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Example Power Monitors
All power quality analyzers are compliant with IEC 61000-4-30 Class A
ENA440
ENA460
ENA450
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Power Monitoring Software ENA-Touch, ENA450 User Interface
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Case Study: Nucor Steel Corporation
• One of the largest steel producers in the United States
• Implemented grid power monitoring • Acted on grid power information
• Saved money and pollution
Monetary fines can be significant.
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NI C Series Platform
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NI Solutions for V/I and Power Measurement
USB-, Ethernet-, or WiFi-based system for 300 Vrms and 5 Arms
Three-phase monitoring, customizable analysis
Embedded system for 300 Vrms and 5 Arms
Deployable, rugged communication over Ethernet
High-channel-count isolated measurement system
Synchronized measurement on simultaneous channels
Choose DMM/switch combination for multiplexed measurements
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