Introduction of Crest Factor in Electrical Power System

 

Definition of crest factor

Crest factor (CF) is defined as the ratio of the peak amplitude of a waveform to its RMS value. It is a numerical value without units. When inputting a Sine voltage to a non-linear load, its current waveform will be distorted and the CF value will be more than 1.414. For example, the CF value of current to computer may be up to 2.4-2.6.

Crest Factor reflects the electronic instrument's performance from another view. The bigger its crest factor is, the more rush current will be needed for powering, and the heavier damage will be made to the power grid.

Upk: peak value of the waveform

Urms: rms of the waveform

To measure crest factor of Sine

The crest factor of Sine without distortion is . Let's measure it using Suin SA2200 power quality analyzer. Firstly input a 230V/500A/50Hz Sine signal to SA2200 through a calibrator, waveform in scope mode will be shown as Figure 1.

Figure 1

Then voltage and current CF result without distortion will be seen in Volts/Amps/Hertz interface as Figure 2 shown and they are separately 1.41 and 1.42.

Figure 2

To measure crest factor of other waveforms

Besides Sine waveform, SA2200 can also measure other waveform's crest factor. Let's take Square as example to see its waveform and crest factor as Figure 3.

Square waveform and its crest factor

 

Figure 3

 

Bigger current crest factor not only makes extra consumption and other bad effects to the instrument, the generated current waveform distortion can also make pollution to the power grid. So the crest factor of an alternating instrument is as same important as its rms value, and one of the most important parameters to evaluate instrument's performance.

 

Suin SA2200 power quality analyzer has the basic measuring function of voltage, current and their crest factor. Besides this, it can also measure other parameters, such as dips & swells, harmonics, power & energy, flicker, etc. If you want to know other measuring functions, please kindly contact us.

 

Brief introduction On How to Select Power Quality Analyzer

The definition of power quality - is the deviation of voltage, current, or frequency that lead to electric equipment’s breakdown or abnormal work, which contains: frequency deviation, voltage deviation, electromagnetic transient, power supply reliability, waveform distortion, three-phase imbalance, voltage fluctuation, flicker and so on.

The power quality analyzer is a portable device that could test and analyze the running quality of the power grid. It could provide harmonic and power quality analysis during power processing, and also are able to offer a long-time data collection and monitoring. Meantime, with help of matched PC software, it could analyze the data uploaded to the PC.

For the past few years, because of the impact of the frequency converter and variable load on the power grid, the difference of power quality in grid become huger, so more and more industrial clients would like to select and buy power quality analyzer to carry out self-assessment of power quality and prevention.

Then how to select a suitable power quality analyzer?

 

Firstly, select ones which can meet international and national standards according to the actual requirement. International Electrotechnical Commission abbreviated IEC especially issues the IEC61000-4-30 standard for power quality. Referring to IEC standard and to meet China actual situation, we classify this standard and issue national power quality standard GB/T 12325/15945/15543/12326. Meanwhile, due to the electronic instrument limit, even if the same data is tested by one test instrument, there will be deviation in the result. And if a serious deviation occurs, it will lead to bad results during issue verified report. Considering this factor, IEC makes the IEC62586 standard which defines strictly the uncertainty requirement for instrument repeat testing. Therefore, the power quality analyzer which is designed as IEC61000-4-30 standard and already passes IEC62586 certification will be the best choice for the user.

   

 

Secondly, proper voltage range and accuracy could selectable for user according to the actual measured voltage and current. Currently, the main voltage limitation in market is 1000V or 600V, while current selection based on the different current clamps or rogowski coil configuration and range 10A, 500A, 3000A or 6000A will be popular ones.

 

 

Thirdly, the convenience of matched PC software is also very important. Because a lot of test points are referred and larger data volume to be processed, strictly speaking, it is required to test one week for each point. So how to issue a standard conformity report, analyze the default point in detail and set the trigger mode, will affect the operator’s working volume and difficulty level to solve problem. Therefore, the convenience of PC software attracts greater attention from manufacturer of power quality analyzer to increase device’s competition.

 

 

Fourthly, the application scene of power quality analyzer should specify clearly before purchase. The common frequency setting is 50Hz when use power quality analyzer. While 400Hz setting will be needed when use power quality analyzer carry out measurement for avionics and shipboard systems. At this time, the power quality analyzer compatible both 50Hz and 400MHz will be best choice.

In addition, most instruments in the market reach to IP50 protection grade only in dustproof protection, while measurement performed in heavy humidity area, power quality analyzer with higher protective level IP65 which contains both dustproof and waterproof will be considered.

Product Recommendation

Suin power quality analyzer SA2100/SA2200 totally conforms to IEC61000-4-30 standard,

separately meet Class S or Class A accuracy according to different usage. They can measure and calculate flicker, voltage dips and swells, interruption, transient, unbalance, harmonic, interharmonic, signal voltage, RMS, power, power factor and energy, etc. With characteristic of high quality, portable, convenient software, IP52 grade and 400Hz measurement, they are also good choice for user when buy power quality analyzers.

                   

They can help engineers and electronic technicians to quickly find and analyze all power quality parameters in fields of power grid, machine manufacturing, electronic manufacturing, process industry, metallurgy and petrochemical, rail traffic, construction, energy saving, etc., so that to guarantee safe production, energy saving and cost reduction.

How to Select A Suitable Stopwatch Calibrator

 

Types of stopwatch

A stopwatch is a time measuring device that’s commonly used in our everyday life, usually, it is divided into three types - digital, mechanical, and electrical. And currently, the most common ones we can see in the market are 401/405/407/408 pointer electrical stopwatch, 411 digital millisecond meter, 415/417/417B digital electrical stopwatch.

Tips to select a stopwatch calibrator

Instruments that can calibrate stopwatches are named stopwatch calibrators, usually working together with a fixture. It can make a stopwatch start, stop or return to zero adopting the control circuit and output circuit, with OCXO as the standard time source, so as to achieve the aim of calibrating stopwatches. Here are some tips to select stopwatch calibrators as follows for your reference:

1. National standard

SF2002 Stopwatch Calibrator is totally designed according to China JJG237-2010 Standard. If you need another national standard, please firstly compare it with this.

2. High accuracy OCXO

OCXO is built in the stopwatch calibrator and it is important for time intervals. The higher accuracy it has, the better it is. SF2002 Stopwatch Calibrator adopts 10MHz OCXO with accuracy≤5×10-8, which is higher than the one specified in JJG237-2010 Standard. In addition, it has excellent second stability and aging rate, which is more helpful for long time calibrating.

3. External frequency standard

Although the OCXO in a stopwatch calibrator is very accurate for calibrating stopwatches or timers, sometimes higher accuracy is still needed in the actual calibrating job, therefore, a stopwatch calibrator with an external frequency standard will be a better choice.

Fortunately, the SF2002 stopwatch calibrator reserves a 10MHz input terminal in the rear panel to meet this requirement. Please switch the Nominal Frequency at the rear panel to EXT, and input a 10MHz signal with 0V-0.5V (Low)& 3.3V-5V(High) amplitude, then SF2002 can make higher accuracy calibration.

4. To calibrate more kinds of timer/stopwatch

This is a very important factor for users to consider when selecting a suitable calibrator. The following pictures will take you to see the real working status when SF2002 calibrates different stopwatches.

① To calibrate mechanical stopwatch

 

 

 

② To calibrate digital stopwatch

 

③ To calibrate pointer electrical stopwatch -405 timer

 

If you need more specification or technical support for this product, welcome to contact Suin. As a specialist in electrical test and measurement instruments, Suin team will do its best to meet all of your needs.