ABB SPAD 346 Stabilized Differential Relay

ABB SPAD 346 Stabilized Differential Relay

Design

The feeder protection relay is provided with  six energizing inputs for phase currents and  inputs for residual or neutral currents. The  relay is also equipped with nine output relays  for CB control, signalling, etc.

The differential relay consists of three protection relay modules, i.e. a differential relay  module, an earth-fault relay module and a  combined overcurrent and earth-fault relay  module. The modules are withdrawable as are  the power supply module and the I/O relay  module located behind the system front  panel.

Differential relay module  SPCD 3D53

The differential relay module includes three  protection units, i.e. a stabilized differential  current unit, an instantaneous differential current unit and a circuit-breaker failure protection unit. In addition, the module contains a  disturbance recorder unit.

The stabilized differential current unit constitutes the main differential protection. The  unit is provided with second and third harmonic restraint, selectable transformer vector  group, zero-sequence current elimination,  numerical correction of CT ratios and flexible  configuration of tripping, blocking and control signals.

The instantaneous, non-stabilized differential  current unit functions as an ultra-fast protection unit with an operate time less than 30 ms  at heavy faults. The circuit-breaker failure protection unit is  activated by the main trip signal of the other  protection units and it provides a second trip  signal to be routed to a back-up circuit  breaker if the main CB fails to operate.The differential relay module also incorporates a digital disturbance recorder module.  The module continuously monitors the object  protected and stores pre- and post-fault network information, which can be used for  post-fault analysis.

Earth-fault relay module  SPCD 2D55

The earth-fault relay module measures the  neutral current and/or residual current on both  sides of the object protected. The earth-fault  protection can be implemented by four different principles, i.e. the high-impedance principle, the numerical stabilized differential  current principle, the residual overcurrent  principle or the neutral overcurrent principle.  Both sides of the object can be protected  independent of each other, which means that  the protection principle on one side does not  have to be the same as that of the other side.

The circuit-breaker failure protection unit is  activated by the main trip signal of the protection units and it provides a second trip signal to be routed to a back-up circuit breaker if  the main CB fails to operate.  The earth-fault relay module also incorporates a digital disturbance recorder module.  The module continuously monitors the object  protected and stores pre- and post-fault network information, which can be used for  post-fault analysis.

Application

The stabilized differential relay SPAD 346 C  is designed for protecting two-winding power  transformers and generator-transformer units  against winding short-circuit, interturn fault,  earth fault and short circuit, and generators  and motors against interwinding faults and  pole short circuit. In addition, the relay can be  used for the protection of three-winding  power transformers, provided 75% of the  short circuit power to the power transformer  is supplied from the same direction, and for  the protection of compensating chokes and  short cable lines.

No interposing transformers are needed for  the protection of two-winding power transformers, as the relay allows the vector group  matching, the elimination of the zerosequence component of the phase currents  and the CT ratio corrections to be carried out  numerically

FEATURES

• Integrated three-phase differential relay,  three-phase overcurrent relay and multiconfigurable earth-fault relay 

• Alarm channels activated by normally open  or normally closed contact 

• Stabilized differential relay module providing winding short-circuit and interturn fault  protection for two-winding power transformers and generator-transformer units,  and interwinding short-circuit protection for  generators 

• Earth-fault relay module providing protection for transformer HV and LV side according to the principle selected: stabilized  differential current principle, high-impedance principle, residual current principle or  neutral current principle 

• Three-stage overcurrent module providing  protection for power transformers and generators and two-stage back-up earth-fault  protection 

• Short operate time even at partial saturation of the current transformers 

• Operation characteristic of differential relay  module easily adapted for different applications 

• Stabilized against unwanted operations at  faults occurring outside the protected area  and at transformer inrush currents 

• Second harmonic restraint for prevention of  unwanted relay operations at transformer  inrush currents 

• Fifth harmonic restraint for prevention of  unwanted relay operations at transformer  overexcitation. The fifth harmonic restraint  can be aborted if the ratio of the fifth harmonic and the basic frequency component  rises too high at dangerous overvoltages