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  Control hierarchy 
It is important that the user understand the meaning of the terms ‘control-right’ and ‘control-
hierarchy’ in connection with the functioning of the control and monitoring applications in the 
sub-station  automation  system  (SAS)  and  the  sub-station  control  and  monitoring  system 
(SCMS). For  instance, when  we wish  to operate a  device (such  as a  piece of switchgear  or 
others), the system has the device forbidden to operate if the system is unable to give a ‘control-
right’ for the device using the ‘control-hierarchy’. Figure 3.3-1 depicts the control-hierarchy; 
the control-hierarchy is made of three control-levels, two selector-switches, and three control-
points.  Either  control  command  of  three  control-points  is  permitted  so  that  the  other 
commands will be forbidden in the system. On this account, no collision of control-points exists 
within the system. 
Selector switch (43BCU‡ ) 
Control points and positions of selector switches 
ON/OFF operation on LCD(MIMIC) 
 
Figure 3.3-1 Control hierarchy and selector switches 
‡Note:   The    L|R    key on the IED is used for the 43BCU switch. The    L|R    key 
can be programmed during manufacture using the PLC function before shipment, 
but it can also be programmed by the user. 
§Note:   The user can implement a hierarchy by programming the PLC. For more 
details, see Chapter 
PLC function
.