Patent ID: 7561396
Filing Date: 2009-07-14
Classification: H02H

Abstract:
1. A method for determining opening of secondary terminals of a current transformer and preventing an accidental opening comprising; preventing false operation of a protecting relay connected to the secondary terminals caused by and over voltage generated by an accident other than opening of the secondary terminals of the current transformer; setting a secondary delay time that the protecting relay can operate and allowing operation after a prescribed time; setting by a user a desired set value by setting said secondary delay time variously by a Dual In-line Package (DIP) switch; determining whether the second terminals of the current transformer are open by the over voltage generated temporarily when the normal operation of various loads including motor starting, by setting in advance expected over voltage values according to characteristics of the load; letting the user choose the over voltage value suitable for the characteristics of the load according to necessity; allowing an apparatus to operate when greater voltage than the value set by the user is inputted to the current transformer; and indicating an operating state by using one or more warning indicators when an open signal of the secondary terminals of the current transformer is detected.