| 摘要 |
PURPOSE:To eliminate a transient phenomenon, and to prevent a malfunction of a combined relay, by dividing only an iron core, and not dividing a winding and a shielding, in each current transformer installed to each phase of a 3 phase electric circuit. CONSTITUTION:In current transformers CT-1-3 provided on each phase of a 3 phase electric circuit, they are formed by dividing only an iron core of the current transformers CT-1-3, taking an air-gap, and not dividing a winding and a shielding. As for division of said iron core, for instance, when piling up 4 pieces, they are scarcely influenced by the external magnetic field by shifting the divided surface by 45 deg. each. Magnetic flux density of the iron core is set to <=1,000 gausses. When sums of burden resistance and winding resistance of the current transformers CT-1-3 are denoted as R1, R2 and R3, and inductance seen from a secondary side in case when a primary current is as shown in the expression II is denoted as L1, L2 and L3, a sensitivity current of the current transformer is set to <= a value decided by the expressionI. In this way, a transient phenomenon is eliminated, and a zero-phase current of high sensitivity can be detected. |
