Patent ID: 6529858
Filing Date: 2003-03-04
Classification: H01H,H02P

Abstract:
A method of monitoring a tap changer comprising the steps of:(a) during an actuation of a tap changer in a switchover process, substantially continuously measuring values of current, voltage and phase angle of an electric drive motor of a motor drive provided for actuating the tap changer; (b) calculating from said values an actual power draw of the drive motor; (c) determining from the power draw and a motor characteristic of the drive motor, an effective torque thereof by the steps of: (c1) with each switchover process (x=1,2,3, . . . ) of the tap changer from values for a torque at the drive motor (MxPw1 . . . MxPw8) selecting characteristic values (Mx PwA, Mx PwB) of motor torque at two previously established time points (tA, tB) which are the same for each switchover process and stored, (c2) calculating from magnitudes of the characteristic values of motor torque at the drive motor (MxPw1 . . . MxPw8) the calculated values for torque at the tap changer (MxSt1 . . . MxSt8) in accordance with the relationship MxSt1=MxPw1Â·mx30 nx, . . . ,MxSt8=MxPw8Â·mx+nx, â€ƒand monitoring said calculated values and comparing said calculated values with previously established threshold values, whereby the values for mx and nx are calculated for a torque at the drive motor (Mxâˆ’1PwA,Mxâˆ’1PwB) and at the tap changer (Mxâˆ’1StA, Mxâˆ’1StB), each at the respective one of the two time points (tA,tB) according to the relationships Mxâˆ’1StBâˆ’Mxâˆ’1StA Mxâˆ’1PwBâˆ’Mxâˆ’1PwA â€ƒand nx=Mxâˆ’1StAâˆ’mxÂ·Mxâˆ’1PwA, â€ƒand (c3) selecting and storing from the magnitudes of these calculated values for the torque at the tap changer (MxSt1 . . . Mx St8) the characteristic values at two previously established time points (tA,tB) for the torque at the tap changer (Mx StA, Mx StB).