Patent ID: 6998848

Claim:
A method for producing a fault signal indicative of a short to ground on a polyphase power transmission line after a short occurs on the power transmission line said method comprising: detecting phase currents on the power transmission line using current transformers to determine a sum current measured value, and producing a first short to ground suspicion signal if the sum current measured value is greater than a predetermined current threshold value; detecting the phase voltages on the power transmission line to form a residual voltage measured value and producing a second short to ground suspicion signal if the residual voltage measured value is greater than a predetermined voltage threshold value; producing a fault signal F indicating a short to ground if at least one short to ground suspicion signal is present; checking the current transformers for transformer saturation; and if transformer saturation is present in at least one current transformer, producing the fault signal F which indicates a short to ground only when at least the second short to ground suspicion signal is present.