7SR242 Duobias Description Of Operation
©2010 Siemens Protection Devices Limited Chapter 1 Page 2 of 52
Contents
Section 1: Introduction ..........................................................................................................................6
Current Transformer Circuits ............................................................................................................6
External Resistors.............................................................................................................................6
Fibre Optic Communication ..............................................................................................................6
Front Cover.......................................................................................................................................6
Section 2: Hardware Description........................................................................................................13
2.1 General ...................................................................................................................................13
2.2 Case........................................................................................................................................13
2.3 Front Cover .............................................................................................................................13
2.4 Power Supply Unit (PSU)........................................................................................................14
2.5 Operator Interface/ Fascia ......................................................................................................14
2.6 Current Inputs .........................................................................................................................16
2.7 Voltage Input...........................................................................................................................16
2.8 Binary inputs ...........................................................................................................................17
2.9 Binary outputs (Output Relays)...............................................................................................18
2.10 Virtual Input/Outputs ...............................................................................................................19
2.11 Self Monitoring ........................................................................................................................19
2.11.1 Protection Healthy/Defective......................................................................................19
Section 3: Protection Functions.........................................................................................................20
3.1 Current Protection: Differential Protection ..............................................................................20
3.1.1 ICT..............................................................................................................................20
3.1.2 Overall Biased Differential (87BD) .............................................................................21
3.1.3 87HS ..........................................................................................................................23
3.2 Current Protection: Phase Overcurrent (51, 50) .....................................................................25
3.2.1 Instantaneous Overcurrent Protection (50)................................................................25
3.2.2 Time Delayed Overcurrent Protection (51) ................................................................26
3.3 Current Protection: Derived Earth Fault (50N, 51N) ...............................................................27
3.3.1 Instantaneous Derived Earth Fault Protection (50N) .................................................27
3.3.2 Time Delayed Derived Earth Fault Protection (51N)..................................................28
3.4 Current Protection: Measured Earth Fault (50G, 51G) ...........................................................29
3.4.1 Instantaneous Measured Earth Fault Protection (50G) .............................................29
3.4.2 Time Delayed Measured Earth Fault Protection (51G)..............................................30
3.5 Current Protection: High Impedance Restricted Earth Fault (64H) ........................................31
3.6 Open Circuit (46BC)................................................................................................................32
3.7 Current Protection: Negative Phase Sequence Overcurrent (46NPS) ...................................33
3.8 Current Protection: Under-Current (37, 37G) .........................................................................34
3.9 Current Protection: Thermal Overload (49) ............................................................................35
3.10 Voltage Protection: Over Fluxing (24).....................................................................................37
3.11 Voltage Protection: Under/Over Voltage (27/59) ....................................................................39
3.12 Voltage Protection: Neutral Overvoltage (59N) ......................................................................40
3.13 Voltage Protection: Under/Over Frequency (81) ....................................................................41
Section 4: Control & Logic Functions................................................................................................42
4.1 Quick Logic .............................................................................................................................42
Section 5: Supervision Functions ......................................................................................................44
5.1 Circuit Breaker Failure (50BF) ................................................................................................44
5.2 Trip/Close Circuit Supervision (74TCS/74CCS) .....................................................................45
5.3 Inrush Detector (81HBL2) .......................................................................................................46
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