使用非晶質鐵心改善低電流比之套管型比流器精度之探討

The Study of Using Amorphous Metal Core to Improve the Accuracy of Low Current Ratio Bushing Type Current Transformer

林順濂(Shun-Lian Lin)

指導教授 ： 何金滿

中原大學/工學院/電機工程研究所/碩士(2009年)

https://doi.org/10.6840/cycu200900162

摘要

電力變壓器因造價不斐且有安全性上的考量，故皆裝置有套管型比流器（Bushing Current Transformer, BCT）以提供必須的檢測訊號。比流器的誤差與一次安匝成反比，因此採用較大的一次安匝才得以設計出較高精度之比流器。然因套管型比流器其一次安匝是固定的，當遇有一次次電流甚小時，因無法增加一次匝數以提高一次安匝，故難以實現較高的準確級。
本篇論文利用非晶質鐵心之低鐵損、低激磁伏安特性來改善此一問題，使其準確度提高而符合規範要求，進而使電力變壓器的保護裝置皆能接收正常訊號，避免誤動作或不動作情形產生；也因而提升電力系統的安全性。從套管型比流器的工作原理得知，只有當激磁電流等於零時，二次電流乘以額定電流比才等於一次電流；但實際上則不然，激磁電流總是存在著，所以二次電流乘以額定電流比將不會等於一次電流，於是將產生誤差；據此另輔以ATPDraw軟體來模擬套管型比流器並以MathCAD撰寫精度計算程式，驗證非晶質鐵心套管型比流器之精度，以提高設計之準確度，減少開發失敗之成本費用；依此可供設計者作為參考。
最後由實測數據證明非晶質鐵心對於低電流比之套管型比流器確有改善的效果，且精度提升效果大。

關鍵字

ATPDraw ； 精度 ； 比流器

並列摘要

The reasons to install the bushing current transformer (BCT) on the power transformer for signal detection are to protect expensive equipments and to meet safety consideration. The current ratio error of the BCT is in inverse proportion to the Ampere-turn product of the primary side of the BCT. In order to design a BCT with high accuracy, a primary with larger Ampere-turn is selected to achieve the demand. However, since the primary on the BCT is fixed only one turn, the higher accuracy of current ratio cannot be achieved easily for very small current occurred on the power transformer.
This paper describes how to use the low core loss and exciting power characteristics of the amorphous alloy to improve the ratio accuracy to meet the requirement of the standard and the protection device of the transformer will receive the signal accurately to avoid malfunction. It will increase the safety of the power system. From the theorem of the BCT, we learn that only under the exciting current is zero, the current in secondary side multiples the rated current ratio is equal to the current in primary side; however, in fact the exciting current is always exists, so the error is occurred. In addition, the ATPDraw software is adopted as the supplement tool to simulate the performances of the BCT. The MathCAD programming software is also adopted for accuracy calculation to verify the actual accuracy of the BCT to improve the design accurately and reduce failure cost spent in development. The designer can adopt as a reference.
Finally, the remarkable accuracy improvement with low current ratio by amorphous metal core BCT is approved from the tested data.

並列關鍵字

ATPDraw ； Accuracy ； BCT

參考文獻

[17] 游宏益，二次變電所主變壓器停電時未切離負載下逕行所內轉供之暫態分析，中原大學電機工程學系碩士班碩士學位技術報告，2008年1月。

[3] O. Xu, A. Refsum, and R.Watson, “Application of External Compensation to Current Transformers”, IEEE Proceedings-Measurement and Technology, Vol. 143, No. 2, pp. 147-150, 1996.

[4] A. T. Johns, “An Algorithm for Compensation Secondary Currents of Current Transformers”, IEEE Transactions on Power Delivery, Vol. 12, No.1, pp.116-124, 1997.

[7] M. Kezunovic, C. W. Fromen and F. PhiLLips, “Experimental Evaluaton of EMTP-BASED Current Transformer Models for Protective Relay Transient Study”, IEEE Transactions on Power Delivery, Vol. 9, No. 1, pp. 405-413, 1994.

[10] Intemational Electrotechnical Commission, Instrument Transformers – Part 1: Current Transformers, International Standard IEC-185, pp. 55-61, 1987.