近年來由於科技的進步與生活品質的提昇，工業界與家庭使用的非線性設備激增，如整流器、轉換器、變頻器、截波器、等非線性負載，使得原本應為正弦波的電流發生畸變而含有大量諧波，並流入系統中造成電力品質不良而影響其他用戶，即為諧波污染。本文針對諧波對差動電驛影響加以分析探討，首先對比流器的操作頻率加以探討，利用EMTP所建構的數學模型進行分析並建立實測環境，再加以檢討分析比較。變壓器差動保護須考慮的因素甚多，在規劃及運用上很容易發生錯誤，本文只針對諧波對差動電驛的影響現象做分析，忽略了變壓器的激磁湧流和比流器的飽和現象，施予不同工作頻率、不同諧波之作用下，差動電驛始動時間變化情況。藉由本研究之分析，期能提供有價值的參考依據，以期協助差動電驛的應用及發展。

　　　　　The use of nonlinear devices such as rectifiers, converters, power supplies and other devices utilizing solid state switching have been increased in the industry during recent years. The power quality has been deteriorated by these equipments. This deterioration causes the increasing of power loss, resonance problem, insulation deterioration, and even safety problem of system apparatuses.This paper aims at analyzing and probing into the influences of harmonics on a differential relay. First it probes the operation of a CT in frequency domain. Then, it analyzes and compares the mathematic model, which is constructed by using EMTP, and the real test results.There are many factors, which must be considered in transformer differential protection design and application. This paper only analyzes the influential phenomena of harmonics to differential relay.The results of this research can be valuable references and for applying and designing differential relay.