The SGF-25 is an accurate and sensitive ground fault protection device. The SGF-25 utilizes a microprocessor to provide a wide range of functionality and employs various sophisticated techniques to improve accuracy and provide a high degree of nuisance trip immunity.
The SGF-25 monitors both insulation resistance and ground leakage-current. Before the circuit is energized, the resistance- monitoring feature is continuously “looking ahead” for a low-resistance condition and may be programmed to monitor resistances from infinity down to the trip setting which may be set to values from 100K ohms up to 10 megohms. Measured resistances below the trip setting will be classified as a resistance fault, and will cause the relay coils of the resistance control contacts to de-energize.
Once the circuit contactor is energized, the SGF-25 will enter the ground-current monitoring mode and begins monitoring the load circuit for a ground-fault condition. The SGF-25 may be programmed to monitor ground-fault currents from zero up to the trip setting which can be set from 25 mA up to 500 mA, with a trip delay from 0 mSec (instantaneous) up to 250 mSec. Measured ground-current that is above the trip setting and that lasts longer than the programmed trip-delay will cause a current fault trip, which will cause the relay coils of the current control contacts to de-energize.
Be sure to limit set point and time settings as required by the installation for proper protection.
Note: Both current and resistance control contacts operate in a fail-safe mode, since the relay coils are energized during non-fault conditions
The SGF-25 supports two optional devices for displaying real-time information.
The first devices that may be used are standard analog meters. The SGF-25 has meter outputs for both current and resistance measurements.
The second device that may be used is the SGF-25 remote display device. The remote display is a full-featured device that is able to display actual current and resistance measurements in real time, and also has the ability to remotely reset SGF-25 fault trips. The SGF-25 trip settings may be changed from the remote display, and the display maintains a fault log that records the date, time and source of the last fault as well as previous faults that have occurred.
The CT’s used with the SGF-25 to sense the ground leakage-current have been designed for maximum noise immunity and for high-tolerance of off-center and asymmetrical cable positioning through the CT window.
The high-voltage coupler used to look ahead into the load circuit has also been designed for maximum noise immunity and high-voltage isolation.