Method and apparatus for protecting power transformers from large electro-magnetic disturbances

摘要

A protective system far a power transformer having a neutral line connected to ground where large currents can flow in the neutral line due to electro-magnetic disturbances. The system includes circuitry for: (a) sensing the current level in the neutral line and whether it exceeds a predetermined threshold for a predetermined period; and (b) sensing and processing the harmonic content of the load current and determining the existence of certain relationships of the “even” and “odd” harmonics. Signals, including alarms, indicative of excessive conditions are produced. The system may also include circuitry for sensing the load current level and generating a signal alarm if the load level is above a given value when the harmonics and the DC current have values in excess of certain predetermined values.

主权项

1. A system for protecting a transformer having: (a) an input winding, (b) at least one output winding intended to be coupled to a load, and (c) having a neutral line returned to ground, and wherein when the transformer is subjected to electro-magnetic conditions excessive currents can flow in the neutral line and cause the core of the transformer to saturate, the protective system including:
(a) circuitry for sensing the level of the current flowing in the neutral line, hereafter referred to as “IN”, and for determining whether the of level IN is above a predetermined value for more than a predetermined time period and for generating a first signal alarm when this condition occurs; (b) circuitry for sensing selected even and odd harmonics of the current flowing in the output winding coupled to the load and processing the selected harmonics to determine whether predetermined relationships pertaining to the harmonics indicative of core saturation are present for a preselected time duration and producing a harmonics status signal corresponding thereto; and (c) circuitry responsive to the first signal alarm and to the harmonic status signal for producing a second alarm signal.