Fault circuit indicators are used to detect earth faults in medium voltage net: a change-over contact is used to remote the over-current tripping while a local LED indicator is used to select the faulted area of the net. The high sensitivity of earth fault indicators allow to use them in the most typical application.
Connection between tripping device and earth current sensor is made by electrical cables suitable to be used in tropical environments.
Device is normally energized by 230-240Vca aux while the energy to trip the remote indication relay and manual reset is stored by internal li-ion battery (10 years is the estimated life time).
A diagnostic test can be performed locally by pressing a push-button. Reset con be performed locally by a second push button or by a remote command.
The device keeps the remote fault indication during the whole timing before reset The local flag indicator always lasts the whole timing before reset.
The operating points for earth fault are adjusted with a threshold level electronic. When the current exceeds the pre-adjusted threshold level, a signal is sent to the reading instrument for evaluation. Automatic reset is possible either after elapsing of internal timer or after AUX restoring; a system to prevent false indication due to inrush current (after AUX restoring), disable sensing circuit for some seconds.
Minimum impulse adjustment: the reading instrument is equipped with a setting for minimum impulse duration The impulse picked up from the sensor is evaluated for its duration. If the impulse length is shorter than the adjusted value for the minimum impulse duration, no fault will be indicated. If the impulse duration is longer than the pre-adjusted duration, an earth fault circuit wil be indicated.
Test: a push button on front panel allows to verify all the functions are ready to run. Pressing “test” also the remote relay will change state. Test can be done only if start-up “smile” indication appears on flag indicator. Reset: the reset of the earth fault or short circuit can be done over:
