Sag Sensitivity Research Articles

Sensitivity of Programmable Logic Controllers to Voltage Sags

This paper discusses the sensitivity of programmable logic controllers (PLCs) to voltage sags based on mechanistic analysis and numerous tests. First, the sag sensitivity caused by different values of rated working voltage is shown through an analysis of the power supply and discrete input/output modules of PLCs. Second, a detailed sag-tolerance experimental scheme is proposed, and PLC sensitivity curves that differ from early curves are established through several experimental tests. Experiments are conducted with nine typical PLCs. The sensitivity of the power supply and discrete input modules are researched first, and then, the effect of the key characteristics of voltage sag, namely, magnitude, duration, points-on-wave of sag initiation, odd harmonics, multiple sags, and continuous sags, is tested. The uncertain area of the PLC sag tolerance is identified after intensively processing the extensive experimental data and curve fitting. A more accurate sag influence assessment for PLCs can be made with the given curves compared to the early curves. Furthermore, experiments have revealed that certain PLCs may work in an uncertain status during voltage sags. The reason and the method of elimination with the proper choice of dc bus capacitance for PLCs are also analyzed.

A New Method of Evaluating the Sensitivity of Sensitive Load to Voltage Sag

This paper proposes a new method to evaluate the voltage sag sensitivity (VSS) of the sensitive load by the combination of several probability density function models, which can fully describe the randomness of load sensitivity. Firstly, five common probability density functions were respectively used to build the mathematical model of voltage tolerance curve (VTC) of sensitive load in uncertainty region. Secondly, the VSS of sensitive load was respectively evaluated by five models, and the weighted sum of five models’ results was calculated by unbiased variance method. In the end, the proposed method was verified to be rational according to an application example.

Power quality performance of energy-efficient low-wattage LED lamps

Light-emitting Diode (LED) lamps are more versatile and energy efficient compared with conventional light sources. This paper investigates two main problems related to power quality, namely, the harmonic generation from LED lamps and the effect of voltage sags on LED lamps. Laboratory tests on various LED lamps are conducted and the electrical characteristics of LED lamps are tapped under different conditions. Frequency domain analysis is then performed to investigate the generated harmonics. Then, voltage sag sensitivity analysis is performed by obtaining signals from a photo sensor, the different parts of a lamp ballast, and input voltage. The analysis includes the effects of varying sag depth and voltage sag duration. The findings are compared with the SEMI F47 standard curve, which predicts the effects of voltage sags on lamp performance. Experimental results show that the LED lamps produce a considerable amount of current harmonics. Moreover, different types of LED lamps were found to produce different levels of current harmonic depending on the ballast configuration. This harmonic distortion can be reduced by combining various types of LED lamps. Voltage sag tests show that all the tested lamps are sensitive to sag depth and sag duration.

Sensitive Equipment Failure Assessment Caused by Voltage Sags Using Interval Probability

It is difficult to assess the impact of voltage sags on sensitive equipment because of the complex uncertainties involved in voltage tolerance capability. Determining the distribution regularity of voltage tolerance capability is an important step in voltage sag sensitivity assessment. Computers’ voltage tolerance capability are obtained through laboratory tests. The point-value distribution function of voltage tolerance capability is calculated by Maximum Entropy Principle and then the interval probability distribution function is derived based on confidence interval, so as to derive an interval probability of equipment failure probability. The proposed model is finally verified in the IEEE-30 bus system. The results are compared with that of stochastic estimation method, showing that the proposed method can reflect actual conditions better and obtain accurate result.

현수교 PPWS 가설중 형상관리를 위한 PPWS 새그 및 장력민감도 산정법 개발

현수교 주케이블은 완성시 교량의 구조적 건전성을 나타내는 중요한 지표이다. 주케이블은 가설완료시 자유 매달림(free hanging) 상태의 형상이 되며 교량완성시 행어, 보강형 등의 고정하중을 지지하여 가설완료시 형상과는 차이가 발생한다. 따라서, 주케이블의 가설완료시 형상이 교량완성시 형상에 직접적인 영향을 미치므로 가설중 형상관리가 매우 중요하다. 주케이블의 가설중 형상관리는 중앙 및 측경간은 새그조정으로, 정착경간은 장력조정으로 수행된다. 새그조정은 새그조절량에 대한 스트랜드 길이 조절량을 나타내는 산정값인 새그민감도가 필요하며 장력조정은 온도변화에 대한 장력변화량을 나타내는 장력민감도가 필요하다. 이에 본 연구에서는 케이블 형상가정에 따라 유도된 기본식과 이로부터 도출된 미분 관계식으로부터 새그 및 장력민감도를 산정하는 방법을 제안하였다. 그리고, 다양한 새그변화 요인에 대해 현수선 기본식을 사용한 비선형 수치해석 새그민감도 계산 흐름도를 제안하여 미분관계식을 적용한 새그민감도 결과와 비교하였다. 또한, 각 새그변화 요인이 복합적으로 발생함으로 이를 고려하여 케이블의 최종 새그변화량을 산정하는 방법을 제안하였다. PPWS 공법으로 시공중인 실교량을 대상으로 PPWS의 길이변화 및 온도변화, 경간장변화 등의 다양한 시공여건의 변화에 따른 새그 및 장력민감도를 산정하였다. 본 연구내용이 주케이블 가설중 형상관리 방법에 대한 체계적인 지침이 되기를 바라며, 향후 실교 현장적용 및 실증에 의해 완성도를 높일 것이다. Main cable of a suspension bridge is the important member which shows the overall structure integrity at bridge completion. Configuration of main cable is a free hanging state at cable erection completion and is different from that at bridge completion supporting the dead loads such as hanger, girder, and so on. Accordingly, the configuration control under cable erection is considerably significant because the configuration at cable erection completion has direct influence on that at bridge completion. That is performed by sag adjustments at center, side span and tension adjustments at anchor span. The former needs the sag sensitivity which represents the control quantity of strand length corresponding to that of sag. The latter requires the tension sensitivity which shows the change of strand tension according to that of strand temperature. In this study, the fundamental equations of cable were derived with the assumption of either catenary or parabola shape, the differential-related equations using chain rule on horizontal tension were drawn from those and finally the estimation methods of the sag / tension sensitivity were proposed from both those. The nonlinear numerical analysis flow charts of sag sensitivity based on the catenary equations were proposed and the sag sensitivities grounded on the differential-related equations were compared with the results using them for various parameters of sag change. Also, considering the combinations of sag change parameters, the calculation method of the final variation for the cable sag was suggested. For the real suspension bridge under construction with PPWS method, the sag/tension sensitivity were estimated considering the construction conditions like the change of PPWS length, PPWS temperature, bridge span, etc.. We hope that this study will be a systematic guideline for the configuration control under main cable erection and improved highly by field verification in the real bridge site.