Compensation of the Skin Effect in Low-Frequency Potential Drop Measurements
Compensation of the Skin Effect in Low-Frequency Potential Drop Measurements
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DOI：
10.1007/s10921-016-0374-4
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发表时间：
2016-10
影响因子：
2.8
通讯作者：
J. Corcoran;Peter B. Nagy;Peter B. Nagy
中科院分区：
文献类型：
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作者：
J. Corcoran;Peter B. Nagy;Peter B. Nagy
潜在液滴测量通常用于部件完整性的无损评估。电位降测量使用直流（DC）或交流（AC），后者将具有优越的噪声性能，由于能够执行相敏检测和减少闪烁噪声。然而，交流测量受到趋肤效应的影响，即电流在电磁上收缩到元件表面。不幸的是，集肤效应是磁导率的函数，在铁磁性材料中，磁导率对包括应力和温度在内的许多参数都很敏感，因此原位阻抗测量可能不稳定。提出了采用准直流测量法进行电站构件蠕变原位测量的建议，准直流测量法具有较好的噪声性能，但更倾向于集肤效应独立的直流测量法。不幸的是，准直流测量将只倾向于直流分布，因此对趋肤效应的一些残余灵敏度将保留。本文将对使用足够低的频率不能充分抑制对趋肤效应的残余灵敏度的情况进行修正；特别感兴趣的应用是电站部件蠕变应变的现场监测。校正使用测量的相位角来近似集肤效应的影响，并允许恢复电阻的直流渐近值。修正的基础，即电位降测量是最小相位，提出并说明了两种情况；实际感兴趣的蠕变应变传感器和导电棒是另一个常见的例子来说明普遍性。在一个组件上，通过应用一系列弹性应力来操纵趋肤效应，实验证明了这种校正。
Potential drop measurements are routinely used in the non-destructive evaluation of component integrity. Potential drop measurements use either direct current (DC) or alternating current (AC), the latter will have superior noise performance due to the ability to perform phase sensitive detection and the reduction of flicker noise. AC measurements are however subject to the skin effect where the current is electromagnetically constricted to the surface of the component. Unfortunately, the skin effect is a function of magnetic permeability, which in ferromagnetic materials is sensitive to a number of parameters including stress and temperature, and consequently in-situ impedance measurements are likely to be unstable. It has been proposed that quasi-DC measurements, which benefit from superior noise performance, but also tend to the skin-effect independent DC measurement, be adopted for in-situ creep measurements for power station components. Unfortunately, the quasi-DC measurement will only tend to the DC distribution and therefore some remnant sensitivity to the skin effect will remain. This paper will present a correction for situations where the remnant sensitivity to the skin effect is not adequately suppressed by using sufficiently low frequency; the application of particular interest being the in-situ monitoring of the creep strain of power station components. The correction uses the measured phase angle to approximate the influence of the skin effect and allow recovery of the DC-asymptotic value of the resistance. The basis of the correction, that potential drop measurements are minimum phase is presented and illustrated on two cases; the creep strain sensor of practical interest and a conducting rod as another common case to illustrate generality. The correction is demonstrated experimentally on a component where the skin effect is manipulated by application of a range of elastic stresses.