Power Measurement

The measurement of power and power quality includes the basic parameters of voltage, current, watts (kW, VA, VAR) or the basic parameters of energy (kVAh, VARh, kWh). When evaluating the power utilized in a system, there are many options when choosing what to measure and whether recording of the power system is required. Based on your individual goals, purpose and problems, you may desire to measure Power, Power Quality, Power Logging, Energy Management, Event Recording, Transients, Sags, Swells, or Waveforms. Many parameters must be considered when looking at power and power quality including AC or DC voltage, AC or DC current, watts, kW, VA, VAR, PF, THD, Harmonics, or energy including kVAh, VARh and kWh.

In addition to effectively performing basic tasks like measuring voltage, current, and power (wattage), power instrumentation varies considerably and you may consider ease of use, portability, and flexibility as well as capturing waveforms, event and parameter data logging and recording parameters.

One distinction to be made is the difference between Power Measurement and Power Monitoring. Measurement generally refers to real time/instantaeous readings, while Monitoring refers to recording/data logging.

Another distinction to be made is the difference between measuring and monitoring of Energy and Power. The requirements may have overlap but there are different resolution and accuracy needs:

• Energy. Generally measured in seconds with high accuracy, particularly for billing or billing disputes.
• Power Quality. Generally measured in microseconds. High accuracy is less important, though many instruments have revenue grade accuracy.
• Many Power Quality instruments can be used for energy measurement/monitoring, but not the reverse.

Each instrument may vary on capability, but the application and solution desired will dictate which instrumentation will be perfect for the application.

Here is a 1 hour recorded TEquipment.NET Webinar with Fluke covering the basics of Power Quality and Energy Measurements. Watch the video below:


1 hr Webinar Power Quality and Energy Measurement Practices to Reduce the Cost of Energy


Wiring Systems

There are many parameters needed to resolve most power issues and problems in commercial, industrial, and residential settings. The first consideration is always the wiring system in question. The following configurations are some of the most common wiring systems used for measurement of power and power quality with additional wiring configurations available in specific instruments, including a three phase four wire Delta and others.

Single Phase Three Wire
This is the most common residential service in North America. Line 1 to neutral and Line 2 to neutral are used to power 120 volt lighting and plug loads. Line 1 to Line 2 is used to power 240 volt single phase loads such as a water heater, electric range, or air conditioner.

Three Phase Four Wire Wye 
The most common commercial building electric service in North America is 120/208 volt wye, which is used to power 120 volt plug loads, lighting, and smaller HVAC systems. In larger facilities the voltage is 277/480 volt and used to power single phase 277 volt lighting and larger HVAC loads. In western Canada 347/600V is common.

Three Phase Three Wire Delta
Used primarily in industrial facilities to provide power for three-phase motor loads, and in utility power distribution applications. Nominal service voltages of 240, 400, 480, 600, and higher are typical.

The second consideration is the system itself and the type of Voltage and Current in the system. The following formulas are utilized for DC and AC circuits.

Power Measurement Formulas

For all DC Circuits and Resistive loads, P (power) is related to I (current) and V (voltage) and R (resistance) according to the following formula:
For all AC circuits, including the source, inductive elements and capacitive elements, the formula used for defining power is shown as: Where V_p is the peak voltage, I_p is the peak current, V_rms is the rms voltage, I_rms is the rms in amperes, and θ is the phase angle current and voltage. Cosθ is more commonly called PF, or Power Factor.
For balanced 3 phase circuits, total power can be simplified to But most real world applications are unbalanced loads, so the sum of the individual phases will be more accurate.
In AC circuits, elements such as inductors and capacitors alter the direction of energy flow. The portion of power flow that, averaged over one cycle of the waveform, is known as “real power” (also referred to as active power). That portion of power flow due to stored energy is known as "reactive power”.  In reality, most loads contain resistance, inductance, and capacitance, so both real and reactive power flows to the load. Apparent power is the vector sum of real and reactive power. Apparent power is the product of the root mean square of voltage and current and can be found displayed below in the Power Triangle.

Engineers, building managers, and consultants are concerned with apparent power, even though the current measured as reactive power does no work; it heats the system wiring, causing energy losses as well as possible heat and component failures. Energy and Power is costly. Wasting Power and Energy is not a goal for any user or owner of any system. Once problems are found, wiring systems, components, and generation equipment must be sized properly to handle all the current produced.

The Power Triangle
 
These three types of power -- true, reactive, and apparent -- relate to one another in what is referred to as the power triangle. The relationship between true power, reactive power, and apparent power is shown below as vectors.

• True Power is the horizontal vector. P (watts) = V*I*PF
• Reactive Power is the vertical vector. VAR = V*A*sin(θ)
• Apparent power is the hypotenuse of the right triangle below. The angle between the hypotenuse and the base of the triangle is the impedance phase angle. VA = V*I
• Power Factor PF = cos(θ)  =  Watts/VA

Power Meters Glossary      Power Quality Overview
 

• IEEE 1159 and IEC 61000-4-30Power Quality
• IEEE 519 and IEC 61000-4-7 Harmonics
• IEEE 1453 and IEC 61000-4-15 Voltage Flicker

Power Energy Logging

Power and Energy Loggers measure and save (data log) important parameters, i.e., Voltage, Current, Frequency, Harmonics, Watts, VARS, VA and Energy (kWh and kVAh, kVAh), Power Factor and Displacement Power Factor (DPF), Crest Factor, THD, and waveforms.
 
In these modern days, rising costs of most goods and services force us to continually evaluate and modify our purchasing habits in order to obtain the greatest efficiencies. Having and maintaining this information at our finger tips allows us to react and plan. It is also understandable that as Power and Energy costs increase, we need a mechanism to be able to evaluate our needs and power and energy use. Understanding what is needed and what is being used gives us greater insight into the manner in which we may react and plan our use. The measurement of “how much and when” regarding power and energy is vital and the instruments used are Power and Energy Loggers.

Power loggers are chosen on the basis of information desired and report capability as well as parameters required, length of time for recording values, hand-held, portable, bench top, with or without displays, wiring system (single phase or three phase), and related problems in the system. Many loggers, both Energy and Power, may be programmable and chosen based on the environment capability. There are many alternate displays that may be chosen. Below are examples “only” of a digital display as well as a graphical display. Many Instruments offer both utilizing existing display panels as an integral part of the Instrument as well as software used with a laptop or PC.

Here are examples of a graphical display of a Harmonic distribution. Certainly helpful in determining system problems and establishing a mitigation plan.

• Load Studies. Understanding the system or circuit load capacity before attempting to add increased loads
• Energy Assessments. The ability to evaluate energy used before corrections and after corrections have been made. The establishment of an Energy Profile is required when looking at system data
• Harmonics Measurements. Harmonics existence can be dangerous and damaging. Understanding the existence and possible mitigation required is an advantage
• Voltage Event Capture. Seeking any information that will aid in system evaluation, i.e. surges, sags, swells, transients. etc.

One of the primary factors to consider is the time base and total length of recording for each value. It is common to consider whether the information being recorded is available in real time or in recorded intervals. Data may be collected from a time reference from every second to days and even months. This selection is based on existing problems, intermittent or average values, and costs. Utilizing a logger system offers a comprehensive picture of the Power and Energy Systems and is now available to evaluate and solve Power and Energy problems.

Applications for Power Energy Logging

• Measurement and recording of power system quality (kW, VA, VAR)
• Energy metering (kVAh, VARh, kWh)
• In plant troubleshooting of power distribution panels and individual machinery
• Monitor pad mount transformers
• Determine harmonic problems originating from source or load
• Monitor phase unbalances
• Determine transformer K-Factor
• Setup and troubleshoot variable frequency drives and UPS systems
• Verify correct operation by measuring key power quality parameters
• Harmonics measurements- Uncover harmonic issues that can damage or disrupt critical equipment
• Inrush capture. Check start-up current where spurious resets or nuisance circuit breaker tripping occurs
• Load studies. Verify electrical system capacity before adding loads
• Energy Audits
• Predictive maintenance
• Long Term Intermittent Analysis

Here are additional examples of display options. On the left, the wiring and phase choice are shown, On the right, the details of Voltage, Current and Phase angles are shown on the Phasor Diagram.
 
Power and Energy Loggers may have a multitude of displays and may be chosen using a variety of formats including Analog Data, Digital Data, Digital Graphics, Multiple Screen, Single Waveform, Multiple Waveforms, General Report generation, and Specific Report generation.  It is important to realize that Power and Energy Loggers may also be chosen for building and system monitoring, as well as residential and overall energy audits. For most data logging systems, all important power and energy data is measured, recorded, and possibly analyzed. This will allow you to understand utility costs, improve efficiency, install energy savings devices, and explore alternative energy solutions. For a complete review of the choices you have, please call one of our Power and Energy Specialists for assistance.

Energy and Energy Management

The kWh is a unit of energy and is the cost representing power over time. Energy Management instruments designed to measure and display and calculate costs will display both KWh and dollars (if incorporated).

 
Energy and Energy Management is the use of instrumentation in monitoring, displaying, recording, and conserving costs. Energy is expressed as KWh’s and expressed in dollars as a cost to the user by the utility. This is the cost of operating your building or residence and is an accumulation of individual costs of power for all the machinery and equipment in the building.
 
Energy (electricity) costs may vary depending on a variety of parameters including peak demand, time of day, the state and county the facility is operating in, the rules specific to any given utility, and any applicable charges from that utility as well as machinery used and instrumentation and applicable electronics in the system. For example, the energy costs might be based on a peak demand, KWh, within a 15 minute period on any weekday between 8AM and 4PM in the summer. Charges may be based on a one time occurrence. It is the purpose of any Energy or Energy Management system to allow measurement and evaluation of the building energy dynamics to be considered and possibly modified. Instrumentation allows information to be evaluated and corrected.          

• Safety Machinery Concerns
• Reduce Energy Waste
• Optimizing Machinery Use
• Conserve Energy
• Quantifying Load Capacity
• Identifying Financial Energy savings
• Documenting Hazardous Conditions and Wasted Electrical Energy
• Performing Load Studies
• Reducing Energy Costs
• Taking Advantage of Utility Rebates
• Power Factor Correction

 

Power Displays

Power Displays contain parameters for Power (kW, VA, and VAR) and Energy (kVAh, VARh, kWh), if required, and may be analog, digital or graphical with bar-graph included.
 
There are many varieties of Displays that incorporate the following parameters. The display is user chosen.

• Apparent Power (kVA)
• Reactive Power (kVAR)
• Active Power (kWh)
• Power Factor
• Phase Angle
• True Power
• AC Current
• AC Voltage
• Frequency
• Harmonics
• Harmonic Distortion
• Phase Rotation

RF / Microwave Power Meters

RF / Microwave Power Meters are compact power sensors/meters that deliver fast, accurate RF and microwave power measurements. A broad range of CW and pulse modulation measurements are available, depending on the series you choose. Each meter comes with Windows Power Meter application software for controlling the meter, displaying readings, and recording data. The combination of the sensor/meter and PC provides a complete solution, eliminating the need for a separate, dedicated meter mainframe.

No Meter Mainframe Required

With the included power meter application software, familiar meter controls are available at the click of a mouse and readings are presented right on your PC screen. Familiar Windows pull-down menus provide additional controls. Data is immediately available on the PC for further analysis and documentation. The meters communicate with the PC using standard USB 2.0 protocols and cables for plug-and-play ease of use.

Integrate High-speed Power Measurements Into Your Testing

Tektronix PSM Series power sensors feature the industry’s fastest measurement speed (2000 readings/s). This can significantly reduce test times and provide dynamic power measurement information that was previously unavailable. An included High-speed Logging Application provides a mechanism for getting this data into your PC for analysis. For custom test applications, you can communicate with the sensors using LabVIEW, or using a fully documented API. Example programs are provided for the most commonly used development environments. The communications library allows your program to communicate with up to 12 sensors, eliminating the need for costly switches.Tektronix real-time signal analyzers, arbitrary waveform generators, and oscilloscopes that use the Windows operating system can also be used to control the PSM Series sensor/meter and give you quick access to accurate power measurements. To allow synchronization with other measurement equipment all models include Trigger In and Trigger Out TTL signals. High-speed measurements, extensive programming tools, and synchronization features make these sensors versatile additions to your test setup.

Industry-leading Performance for Demanding Designs

Tektronix power sensors/meters come fully calibrated over their entire operating temperature range. Sensor zeroing and meter reference calibration have been eliminated, reducing setup time and helping to avoid inaccurate results. These meters provide accuracy you can count on for general-purpose CW, peak, pulse, and other modulated power measurements. Whether doing installation or maintenance on a wireless base station, production testing, or R&D for wireless components, the PSM Series products serve these needs with a wide dynamic range (–60 dBM to +20 dBm) and frequencies ranging from 10 MHz up to 26.5 GHz.

Select the Performance/Features to Meet Your Needs

PSM5000Series power sensors/meters provide the same measurements as the PSM4000, and add pulse profiling capability for signal viewing and characterization in pulsed RF and microwave systems.

A Broad Range of Pulse Envelope Measurements

Tektronix PSM5000 Series products feature an easy-to-use, high performance, pulse profiling, pulse (modulation), and CW power meter and sensor in one. The PSM5000 Series product is specifically designed for applications requiring time domain analysis of constant-envelope, repetitive pulsed signals. It performs time domain pulse measurements such as rise/fall time, overshoot, and droop that have typically required costly signal analyzers. PSM5000 Series sensors use an equivalent time-sampling technique to reconstruct repetitive, pulsed input signals. Repetitive pulses with video bandwidths up to 10 MHz can be measured with an effective sample rate of up to 48 MS/s.

Solar Analyzer

While separate instruments can be used, a Solar Analyzers are instruments specifically designed for solar panel analysis and installation applications.
 
Solar Power Meter also called Pyranometers and Irradiance Meters
 
A solar power meter is a type of analyzer used optimize the placement of solar systems and verify window efficiency. Solar Power Meters measure solar output that is used to calculate overall energy, efficiency and placement of solar systems.
 
Applications for Solar Power Meters

• Windows performance – calculation and verification of the heating or heat reduction caused by direct sunlight
• Solar radiation measurements
• Solar power research for solar powered water heaters and solar panels, including location, roof tilt and orientation
• Physics and optical laboratories
• Meteorology
• Agriculture

Voltage Event Recorders

Voltage Event Recorders display, record and report voltage anomalies. These may include Sags, Swells, Spike and Transients. The units are offered from as simple as supplying a non-display alarm with software report capability to complete recordings of waveforms, transients, sags and swells. Typically they have come supplied with a line cord to plug directly to an AC mains outlet (110 VAC, 220-240 VAC)
 
Here is a typical graphical voltage display as well as a tabular view of events
 

Watt Meter

Watt Meters, or Wattmeters, measure single and three phase power usage (kW).
 
These units may also have data logging, memory of minimum and maximum values, memory hold and peak hold functions. They are primarily used for measurement of single phase and three phase Energy and Power. They can measure and display many of the following parameters using either a single or three phase wiring system.

• Apparent Power (kVA)
• Reactive Power (kVAR)
• Active Power (kWh)
• Power Factor
• Phase Angle
• True Power
• AC Current
• AC Voltage
• Frequency
• Harmonics
• Harmonic Distortion
• Phase Rotation

Here, a discussion of the Power Triangle follows:
There are three types of power -- true, reactive, and apparent -- relate to one another in what is referred to as the power triangle. The relationship between real power, reactive power and apparent power is shown below as vectors. P, Real power (true power, watts) is the horizontal vector and Q, reactive power (VAR) is the vertical vector. S, apparent power, (VA), is the hypotenuse of the right triangle below. The angle between the hypotenuse and the base of the triangle is Z, the impedance phase angle.