Lecture 06 介質功率因數絕緣試驗測試
檢驗目的 介質功率因數測試最主要之目的為協助客戶判斷設備絕緣優劣。 介質功率因數試驗 交流電壓加於絕緣體時會產生全電流超前電壓充電電流I1,其中δ稱之為介質損失角,表示絕緣體之損失, 若絕緣體之絕緣良好時δ角較小,反之絕緣體不良則δ角必較大,因此δ角之大小可判斷絕緣體良好與壞。 所有絕緣材料並不是一種完全介質的絕緣物質,在外加AC電壓、電流I流經不完全介質絕緣材質,會產生一 介質損失,除位移電流I1外,還有損失電流I2與電壓同相。當絕緣材質愈良好,R的電阻愈大,I2洩漏電流 損失愈小,δ稱為介質損失角,通常絕緣材料的介質損耗因數tanδ的百分率表示絕緣材料的性能, tanδ=I2/I1介質損耗因數簡稱D.F(Dielectric Dissipation Factor)若損失電流I2很小,則位移電流I1幾乎 等於總電流。因介質電力因數(Dielectric Power Factor) ∵cosθ=I2/I, tanδ=I2/I1 → I1 ≒I ∴ cosθ≒tanδ 因此以cosθ代替tanδ,以cosθ的百分率表示絕緣材料的絕緣性能。 PF=cosθ*100%介質損失Watt=V*I2=VIcosθ∴cosθ=I2/I
Influences of tan delta Stray capacitance Surface currents and leakage currents Environmental conditions (temperature, Humidity) Magnetic fields Influences of the power supply, filters and non linear elements could influence the null instrument
電介質損耗發熱消耗能量並可能引起電介質的熱擊穿,因此在電絕緣技術中,特別是當絕緣材料用於高電場強度或高頻的場合,應儘可能採用tanδ較低的材料。 介質功率因數測試方法: 1. Schering Bridge 被側絕緣物 In this diagram: C1 = capacitor whose capacitance is to be determined, R1 = a series resistance representing the loss in the capacitor C1, C2 = a standard capacitor, R3 = a non-inductive resistance, C4 = a variable capacitor, R4 = a variable non-inductive resistance in parallel with the variable capacitor C4. HV
The Schering Bridge is balanced if: Real part Imaginary part The balance equation is independent of frequency.
2. Direct Current Measurement Reference capacitor High voltage
高壓變壓器介質功率因數測試
OCB 介質功率因數測試 OCB OFF 測試 OCB ON 測試
高壓電纜 介質功率因數測試