DESCRIPTION : 

The 7SG14 Duobias-M has an established history as a transformer protection relay going back to the fundamental development of biased differential transformer protection. It is capable of providing all necessary protection and alarm functions for protecting a 2 or 3 winding transformer. The main protection function is current differential with load bias and second harmonic restraining characteristic. This is supplemented with a number of additional functions to provide a comprehensive transformer protection management package.

FUNCTION OVERVIEW : 

Standard Functionality

• Biased differential current protection with even harmonic restraint (87). 
• Instantaneous differential highset (87HS). 
• Integral current amplitude and vector group compensation.
• Variants for 2 or 3 sets of current transformers. 
• E8, E12 or E16 case.
• Trip circuit supervision.
• LEDs for alarm functions removes the need for flag repeat relays, Buchholz etc Compatible with communications software Reydisp Evolution.
• Metering of external and internal signals for both magnitude and phase angle aids commissioning Settings stored in EEPROM, logic schemes in FLASH memory Flash upgradeable firmware Expandable I/O of up to 27 binary inputs and 29 output contacts that can be programmed from the relay front fascia Continuous self monitoring

Optional Functionality

• High Impedance Restricted Earth Fault per winding (87REF)
• Circuit Breaker Fail per winding (50BF)
• Instantaneous / definite time overcurrent phase fault and derived earth fault per winding (50 and 50N)
• Inverse definite minimum time phase fault and derived earth fault per winding (51 and 51N)
• Instantaneous/definite time measured earth fault per winding (50G)
• Inverse definite minimum time measured earth fault per winding (51G)
• Overexcitation protection Volts/frequency (2 x DTL + 1 x IDMTL) (24)
• Transformer thermal overload (49)
• 4-stage under/overvoltage(27/59)
• 4-stage under/overfrequency (81)
• 2-stage NPS overcurrent (46)