本文利用不平衡電橋法給出了一個較為精確的，用于電網直流系統計算正負母線絕緣值都出現降低的情況下的正、負絕緣電阻的公式。同時提出了一種主—從式的絕緣監測小系統的設計方案。即用一個絕緣主模塊來測量主回路的絕緣電阻，而用專門的支路模塊來判斷出現絕緣降低的那條支路，并且在實際應用中取得了很好的效果。
關鍵詞：不平衡電橋；主—從式； 絕緣監測。
Abstract：By unbalant electricity bridge ,this article educed a accurate formulation with which the insulation resistance can be calculated when both the plus insulation resistance and the minus insulation resistance decend in DC system. Moreover it bring forward a design project of small insulation monitoring system named master-slave type.Namely measured insulation resistance of main road with main insulation module,and measured which road’ insulation resistance decended with branched insulation module.And obtained good result in use.
Key Words：Unbalant electricity bridge； Master-slave type； Insulation detecting.