sensor inferared

خیص موانع به وسیله سنسورهای مادون قرمز

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  • دسته بندی: سنسور ها

امروزه ارزیابی كیفیت توان دارای اهمیت خاصی در مدیریت سیستمهای الكتریكی است . یكی از جنبه های ارزیابی كیفیت توان مطابقت آلودگی هارمونیكی با استاندارد صنعت برق ایران و استانداردهای بین المللی است . اغلب استانداردها مانند IEC61000-40-30 و IEEE519 نیاز به اندازه گیری هارمونیكها تا مرتبه 50 ام دارند .

سنسور كیفیت توان دستگاهی است بسیار ساده و با نصب آسان برویترانسهای ولتاژ خازنی و برای اندازه گیری با پهنای باند وسیع توسط CVT است . با نصب این دستگاه بروی CVT های در حال سرویس ، عملاً خللی در كار CVT یعنی نمونه گیری ولتاژ برای رله ها بوجود نمی آید و بطور همزمان برای مانیتورینگ كیفیت توان می تواند مورد استفاده قرار گیرد .

این دستگاه كوچك و ساده با دقت بالایی هارمونیك های ورودی به CVT را شناسایی و نمایش می دهد .مناسب نبودن پاسخ فركانسی CVT ها ناشی از ساختار داخلی آنها باعث شده كه دقت اندازه گیری ولتاژ اولیه تنها در فركانس اصلی قابل قبول باشد لذا اندازه گیری دقیق سطوح ولتاژ اولیه نیازمند پهنای باند بیشتر می باشد كه از طریق خروجی ثانویه امكان پذیر نیست .

با بررسی پلسخ های فركانس ترانسفورماتورهای ولتاژ آشكار می شود كه نسبت تبدیل در فركانسهای بالا خطاهای قابل ملاحظه ای دارد كه از حد اقل های  مقدار استاندارد بسیار بیشتر است . ترانسفورماتورهای ولتاژ خازنی بیشترین كاربرد را در سطح پستهای انتقال و فوق توزیع دارند همرا با قیمت مناسب و دقت در اندازه گیری خوب . اما از آنجا كه آنها تنها در فركانس های نامی تنظیم شده اند لذا به تنهایی قادر به اندازه گیری دقیق هارمونیكی نیستند . فن آوری جدید ABB یعنی ساخت دستگاه كوچك و كارا PQ Sensor این امكان را می دهد كه به راحتی هارمونیك ها را در سطح پستها اندازه گیری نمائیم .

 

PQSensor™

The PQSensor™ offers a unique, convenient and costeffective method of faithfully reproducing harmonic

content using Capacitive Voltage Transformers (CVT)without the need for Resistive-Capacitor Dividers (RCD)

− The PQSensor™ offers a practical and economical solutionfor wide bandwidth measurements using CVTs.

− Eliminates the need for special high voltage instrument transformers or wide bandwidth voltage dividers.

− Can be retrofitted to in-service CVTs or installed in new units.

− CVTs can continue to be used in normal ways to feed relays and other standard devices and at the same time to be used for power quality monitoring.

− It can be used to detect CVT internal ferroresonance.

General description

A power quality sensor is available to very accurately measure power quality parameters such as harmonics and flicker over a wide bandwidth from sub synchronous to high frequencies. The PQSensor™ current probes are installed in capacitor voltage transformers (CVTs) at the ground connection points in the secondary terminal box. The PQSensor™ signal-conditioning unit can be mounted on the CVT support structure making the retrofit nstallation simple.

Background

Power quality assessment has become an increasingly important requirement in the management of electric supply systems.

This recognition has led to the introduction of several standards for power quality measurement and monitoring. All standards such as IEEE 519, IEC 61000-4-30 and 61000-4-7 and UK Engineering Recommendation G5/4 require measurements up to the 50th harmonic. Flicker standard IEC 61000- 4-15 require measurement of modulating frequency between 0.5 Hz to 33 Hz.

Options for measuring harmonics

If utilities and users are to monitor ferroresonance oscillations, power quality and other wideband transients in high voltage systems, there is a need for cost effective and accurate means to do so. Sophisticated power quality monitors are now available from various manufacturers. The challenge, however, is to provide inputs to these monitors which accurately  eflect the phenomena occurring on the monitored system in a cost effective and safe way. The best performance from a conventional device in terms of a wide bandwidth frequency response is  ffered by a resistive-capacitor divider (RCD), which is very expensive, has a very limited output and would not normally be present ina substation environment and does not meet safety requirements for isolation between high voltage and low voltage parts. Most power quality monitors are currently receiving their inputs from wound or inductive type voltage transformers (VTs). The advantage with VTs is that they can also provide inputs into  onventional revenue meters and relays and therefore may already be present if harmonic measurement is being considered as an add-on. What is not well understood is that wound VT’s have a limited frequency range. Graph

1 shows the performance of typical wound VT (Reference: CIGRE Working Group 36). It can be seen that the frequency response becomes unacceptable around 500 Hz, well below the frequency limit established in the major standards. The upper limit increases for lower voltage class units but worsens for higher voltage class units.

Capacitor voltage transformers have become the dominant technology for voltage measurement at transmission voltage levels because they provide reliable and accurate performance at reasonable cost. CVTs, because they are essentially tuned to the system frequency, are not in themselves capable of harmonic measurement. Because of the prevalence and reasonable cost of this technology, much effort has been expended to add the functionality of harmonic measurement. There is a solution for employing CVTs for harmonic measurement. A power quality sensor, to be used in conjunction with CVTs, has been developed and patented which overcomes the  aforementioned objections. One of the important advantages of the technology, in addition to its cost   ffectiveness, is the speed of installation in in-serviImage

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