Blackouts, brownouts and other power disturbances have always been with us, but now they affect us more severely and more often than ever before. At one time, flickering lights or temporary power losses were just inconveniences. Today, entire data files may be lost or equipment may malfunction as a result of these disturbances.
But don’t blame just the utility company¾ it is only one potential culprit. The equipment connected to the line today may be equally, or even more, at fault.
To provide the degree of power quality now demanded, standards have been established and adherence to them is gradually being enforced. These include the IEEE 519 guidelines for utilities which define several power-quality aspects at your facility’s electric-service entrance. Specifications IEC 555 and IEC 1000-3-2 set limits on allowable harmonics generated by the load, the equipment you plug into the wall outlet.
And IEC 100-3-3, a standard relating to EMC boundaries for induced voltage fluctuations and flicker, also limits perturbations that power supplies may cause. Compliance with these and other EMC directives became mandatory in EU countries this January and nonconforming equipment may not be sold in some European countries in the very near future.
But to what degree does the power provided at your facility or, even more importantly, the power supply you designed or integrated into your equipment comply with these specifications? Power-analysis tools can provide the answers and even suggest solutions to solve problems you may discover.
Several types of analysis tools exist, each equipped to solve a particular set of problems. Some of the audits and tests that can be performed with these are simple and common; others, such as fluctuating harmonics and flicker tests, may be lengthy and unique.
Typical Audits and Tests
Equipment power audits are performed to assure product qualification and market acceptance; facility audits are performed for economic and safety reasons. Typical facility audits and the required tests were described by Chuck Newcombe, Product Planner at the Service Tool Division at Fluke:
Determining whether a facility can provide power for additional loads. This merely requires measuring presently consumed true rms currents, adding anticipated further load currents and comparing the sum with the facility’s available power ratings. “If many electronic loads are present, individual harmonic current levels must also be measured to assure that transformers, power panels and wiring are properly sized for this type of load,” advised Mr. Newcombe.
Lowering utility costs. Power companies provide volt-amps (VA) but bill their customers for watts. If the equipment connected to the power line has a low power factor (pf), consuming substantially higher VAs than watts, many utilities impose surcharges. To eliminate these, pf measurements must be made and pf correction circuits added to the offending equipment.
Identifying power anomalies that cause equipment problems. The voltage quality and the power-system’s capability to supply peak loads are the issues in this case. Voltage-quality assessments include quantizing harmonics, noise and transients and determining the stability of the power line.
Types of Power-Analysis Tools
Power-analysis tools fall into four categories: power meters that measure instantaneous values, some storing selected results; power monitors that measure and record line behavior over extended periods; power analyzers, which perform a vast range of analysis functions; and power source/analyzer systems, which are most useful for determining electronic equipment power-supply performance.
All power meters indicate measured volts, amps, VAs and watts. But the instrument’s stated accuracy may be valid only for linear loads, those consuming sinusoidal current. Electronic equipment power supplies are not linear loads since they consume current during a short period of each sine wave.
To obtain accurate readings and to calculate the power factor (pf = W/VA), the meter must determine the true rms (heating equivalent) values of nonsinusoidal voltage and current waveshapes. Some power meters, such as the Fluke 39, measure not only pf, but also the crest factor (ratio of peak value to rms value) as well as individual harmonics and total harmonic distortion.
Power monitors are connected to the power line for extended periods of time. They typically measure and record brownouts, overvoltage, harmonic distortion, normal-mode and common-mode voltage spikes and noise, line phase shift and frequency changes. Multichannel monitors can also provide information on current and power consumption.
Some of these units do not require special setup or measurement skills. For example, “The Sherlock Power Analyzer plugs into a wall outlet, quantifies power problems and suggests potential problem causes as well as solutions,” said Red Redford of International Power Technologies. Data may be locally analyzed or sent via a modem to a central monitoring facility.
Multipurpose power analyzers combine the features of power meters and monitors and then add more. Most include four to eight input channels to facilitate single- as well as three-phase measurements. They provide direct readouts of all essential power and energy consumption-related quantities and evaluate up to the 50th, in some cases to the 99th, harmonic. Many also store and display multiple waveforms.
Some of these analyzers are programmable or are equipped with a PC interface to simplify operation, analysis and report preparation. “For instance, the Dranetz family of power analyzers can be preprogrammed to report only out-of-limit conditions,” said Paul Golden, the company’s Director of Product Marketing. Or all information may be fed to its Windows-based data analysis tool DRAN-SCAN™ 2000.
Other companies also provide programs to complement or control their analyzers. Voltech introduced the VPAS Visual Power Analysis Software, which includes measurement, graphing and cycle-by-cycle analysis modes. Valhalla Scientific provides a GPIB interface and includes a LabVIEW software driver with its multifeatured D6000 Wideband Spectral Power Analyzer.
Combined Power Sources/Analyzers
In addition to an analyzer, a controllable low-impedance, low-distortion voltage source is needed to power equipment undergoing IEC conformance tests. Consequently, companies such as California Instruments, Pacific Power Source and Elgar have combined the two pieces of equipment into a single unit. According to Herman vanEijkelenburg, Product Marketing Manager at California Instruments, this arrangement offers you several advantages:
A single-instrument solution eliminates interface problems often encountered when interconnecting multiple units.
Phasing or timing errors between the source and the analyzer are avoided. This is particularly important when performing fast digital Fourier transforms.
A single-vendor system simplifies hardware/software integration.
Power Factor, Harmonics and Flicker
Electronic power supplies draw current only during the time the unfiltered rectified voltage exceeds the smoothing capacitor voltage. During this short period, it replenishes the charges drawn off during the previous line-voltage cycle. The resultant current flow is pulse-shaped, which means it is composed of a fundamental plus many odd-order harmonics (Figure 1).
Poor power factors are caused by phase shifts between the source voltage and the load current, as is the case for motors or other inductive loads, or by distorted waveshapes. Phase shifts are easily correctable; waveform distortion is not. Converting a pulse-shaped current into a single-frequency current requires electronic circuitry or filtering.Fortunately, low-power electronic equipment (<600 W with special wave shape) does not have to exhibit a pf of exactly 1, but limits for harmonics apply as established in IEC standards. To demonstrate compliance, it is essential to measure all harmonics and compare their magnitudes with established limits. This may be accomplished with many of today’s power analyzers(Figure 2).
In addition to a steady-state harmonics test, the IEC 1000-3-2 standard requires a fluctuating harmonics test. “This demand is based on the recognition that many loads do not draw constant power, but have fluctuating needs. This, in turn, affects the harmonic distortion they generate during a given period,” explained Mr. vanEijkelenburg.
Another relatively new test¾ a flicker and voltage fluctuation measurement¾ is demanded by IEC 1000-3-3. Fluctuation of luminance (flicker) occurs when your equipment causes lamps connected to the same supply to pulsate. A flicker meter simulates the eye-brain response as defined in IEC 868. Using filters and statistical analysis, two values are generated: a short-term flicker severity factor (minutes) and a long-term flicker severity factor (hours).1
“These newer harmonics and flicker tests can be technically challenging and time-consuming if an assortment of conventional test equipment were used,” remarked George Smith III at Pacific Power Source. But some of the newer instruments and the combined source/analyzers contain the flicker meter facilities needed to automatically carry out the IEC 1000-3-3 tests.
1. “International Electrotechnical Commission, Harmonic and Flicker Testing,” Valhalla Scientific, March 1996.
Power Analyzer Products
Monitor Records Events,
The Power Investigator PI-500 plugs into a wall outlet and records up to 65,000 power events. Events include spikes, sags, surges, noise, voltage and frequency changes, half-cycle dropouts, power failure and hot/neutral wiring reversal. After monitoring, the PI-500 may be connected to a printer for a hard copy printout. Reports include disturbance events, cause-and-effect information and a solutions guide with site-specific recommendations. Models operate at ranges from 80 V to 300 V and 40 Hz to 70 Hz. $495. PowerTronics, (603) 483-5876.
Power Source/Analyzer Tests
For IEC 1000-3 Compliance
The 4801iL is comprised of a precision AC power source, a digital harmonics analyzer, an IEC 868-compliant flicker meter and a line impedance network. It operates in a standard AC source analyzer mode or, when used with the Windows-based Harmonic Flicker Test System software, in the IEC mode. Software runs tests automatically and processes all measurement data for display, analysis and reporting. Harmonics and flicker data are displayed in color bar charts, and graphical and tabular formats. $21,400. California Instruments, (619) 279-8620.
Hand-Held Analyzer Measures
The Power Platform® 4300 features four voltage and four current channels, allowing measurements on single- or three-phase service. It displays volts, amps, watts, VA, VARs, power factor, voltage and current harmonics, crest factor, K factor, demand and energy. In the Scope ModeÒ , it enables real-time graphical waveform viewing of as many as eight inputs simultaneously. Measurement functions can be changed or upgraded by replacing a TASKCardÒ . Features include harmonic reports to the 50th and eight-channel transient capture. $3,995. Dranetz Technologies, (908) 287-3680.
Single-Phase Power Analyzer
Has DC to 250-kHz Bandwidth
The PM100/300 Analyzer measures all power parameters, including power factor, crest factor, inrush current, frequency to the 50th harmonic and THD. Voltage/current accuracy is +0.2%; power accuracy is +0.4%. A high-resolution backlit LCD presents alphanumerics, waveforms and bar graphs, and facilitates cursor measurements. Integration enables measurement of time-dependent variants. Floating isolated inputs allow direct connections for current measurements. Optional plug-in interface modules provide IEEE 488.2, RS-232 serial, parallel printer and chart recorder/alarm outputs. PM100: $1,575; PM300: $3,495. Voltech, (508) 655-2550.
Meter Provides 3f Readout
From Single Phase Measurement
The Model 39 Power Meter measures voltage, current, frequency, phase, power, power factor, crest factor and harmonic distortion. Measured signals can be viewed as a waveform display, a bar graph or as numeric values. Readings are updated three times/s. A three-phase readout is automatically calculated and displayed based on single-phase measurements. A record mode measures data over time, logging minimum, maximum and average values. True rms measurements ensure accurate readings on circuits that supply electronic loads. $995. Fluke, (800) 44-FLUKE.
Power Quality Monitored Via
The Sherlock Power Analyzer records the date, time, duration and magnitude of brownouts, blackouts, dropouts and overvoltages. It measures line noise (>2 V peak-to-peak) and surge impulses (to 1,000 V) and indicates in which part of the sine wave the noise or surge is located. It logs voltages and surge impulses detected between neutral and ground as well as changes in average line voltage, frequency and phase. Graphical and text reports are available via a printer, PC or modem connection.$1,795. International Power Technologies, (800) 944-0356.
Spectral Power Analyzer
Features up to Six Channels
The D6000 Series Wideband Spectral Power Analyzer displays multiple waveforms and uses digital signal processing and 16-bit ADC technology for measuring harmonics (up to the 99th). It also measures flicker and the telephone harmonic influence factor for IEC 1000-3-2, -3, and ANSI/IEEE C57.12 tests. The display indicates watts (f A, f B, f C and total watts), Hertz, pf (any f ), VA, VARs, kWHrs, inrush current, crest factor, harmonics, THD, peak, true rms or average levels, efficiency, phase angle, impedance and flicker. The bandwidth extends from DC to 1.0 MHz. Typical price: $16,995. Valhalla Scientific, (619) 457-5576.
Performs IEC Compliance Tests
The TMX Series AC Power Source and Analyzer includes a dual-channel spectrum analyzer and flicker meter. Source and load may be simultaneously monitored, facilitating compliance testing per Annex A.2 of IEC 1000-3-2 and section 6.3 of IEC 1000-3-3. The equipment also features selectable lumped parameter as well as programmable digitally synthesized networks. Test software running under WindowsÒ 3.1 or WindowsÒ 95 provides test setup, test control, data analysis and presentation of pass/fail results.Tabular and graphical test results are presented. From $12,500. Pacific Power Source, (800) 854-2433.
Analyzer Meets IEC 555,
IEC 868 Requirements
The 2503AH Three-Channel Power Analyzer measures and displays V, A, VA, VAR, true power, inrush current, form factor, power factor, crest factor, THD and flicker per IEC 555, and performs harmonic and spectrum analysis. Input voltage ranges from 15 V to 1,200 V rms and current from 50 mA to 40 A rms for frequencies from DC to 500 kHz. Resolution is better than 0.05% of the full-scale range. Three input channels have separate digital signal processors. Digital and analog I/O is provided. $5,500 to $15,000. Xitron Technologies, (619) 458-9852.
Power Meter Has
The Model 2402A Digital Power Meter is a benchtop instrument featuring true rms measurements on complex waveforms with crest factors up to 50. Measurement bandwidth is DC to 50 kHz. Four LED front-panel readouts display load volts, amperes, watts and power factor. The load range is 440 V at 20 A; external potential/current transformers can extend range. An RS-232 interface is standard. $1,995. OakTec, (513) 299-5047.
Compact Digital Power Meters
Feature Memory, Comparators
The WT110/130 Power Analyzers feature a bandwidth of DC and 10 Hz to 50 kHz, accuracy of 0.25%, and harmonic analysis to the 50th order. Inputs (to 600 Vrms and 20 A) are floating and isolated. The display is comprised of three rows of seven-segment LCDs. An internal memory stores up to 600 measurements. RS-232 or IEEE 488 interfaces are included. D/A outputs and four-channel comparators for go, no-go testing are optional. From $2,160. Yokogawa Corp. of America, (800) 258-2552.
Copyright 1996 Nelson Publishing Inc.