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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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