The protection device is mainly used for differential protection of two winding main transformer, but if needed the three winding main transformer differential protection relay, you can choose the 9693 three winding main transformer differential protection relay of our company.
protection functions
Differential current instantaneous trip protection
Percentage differential protection (with second harmonic restraint, CT line-break locking)
CT line-break alarm
Y/△ turn on
Non-electric protection
slight gas protection – alarm
severe gas protection- tripping operation
Load slight gas protection-alarm
Load severe gas protection- tripping operation
Pressure release (turn on- tripping operation; turn off- alarm)
Temperature rise-alarm
Over temperature- tripping operation
Functions of measurement and control
High voltage current: IA、IB、IC；
Low voltage current: Ia、Ib、Ic；
Differential current: DIa、DIb、DIc；
Assistant functions:
Fault recording
Communication mode
485 communication
Ethernet communication
Fiber-optic communication
Protection Principle:
Pilot differential current instantaneous trip protection
Pilot differential current instantaneous trip protection is substantially reflected current difference on both sides of the transformer and makes quick action, to ensure to make quick action to get tripping operation, when the internal transformer has significant failure or external transformer on both sides between the CT happen short circuit.
Criterion of protective action: Icd>Isd
Icd is the actual differential current between the two sides of the same phase between CT, and the Isd is the setting value of the differential current instantaneous trip protection
Any one phase of the three phases satisfies Icd > Isd, differential protection means protector action exit jumps to all switches of main transformer.
In actual operation differential current = Ih * cosφ1 + IL*ＫLｊｘ*cosφ2
In that formula, ＫLｊｘ（low voltage side unbalance coefficient）= Ie2h（high voltage side twice rated current）/ Ie2l（low
voltage side twice rated current）
cosφ1 is the real angle of high voltage side；cosφ2 is the real angle of low voltage side.
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