基于等值回路平衡方程的变压器保护原理

Study on Transformer Protection Principle Based on Equivalent Circuit Equilibrium Equation

利用在正常运行及励磁涌流状态下,由原副边绕组回路方程得到的回路平衡方程值为零,而在内部故障状态下回路平衡方程值不再为零这一特征,构成了基于回路方程的变压器保护原理,并推导出应用于单相变压器、三相Y/Y、 Y/△接法变压器的保护动作方程。由于变压器绕组漏感参数难以求取,且在运行过程中绕组变形将会导致漏感参数发生变化,文中采用最小二乘算法对变压器漏感参数进行实时在线估算,以提高算法灵敏度。动模试验表明:该算法原理清晰,能够不受励磁涌流的影响,快速可靠地识别变压器各种故障,且特征明显,其动作门坎有较大的裕度。

The value of equilibrium equation is zero derived from the equivalent circuit equation of the primary and second winding during normal operation conditions, magnetizing inrush and external fault. It is not equal to zero during an internal winding fault, ground fault and phase fault. A new transformer protection algorithm based on the equivalent circuit equilibrium equation is described in this paper. For a single-phase and a three-phase Y/Y transformer, the criterion functions are derived from the principle. For a transformer with delta winding, the differences of the circuit equation between the two phases are calculated to use the line currents. Because of the accuracy of winding parameter influencing the sensitiveness of protection algorithm, the least square is adopted to identify and correct the parameter value. Compared to a conventional harmonically restrained differential relay, the algorithm is independent of core characteristics and system condition, Test result indicates that the algorithm can successfully discriminate between internal fault and all other operation conditions.