Parameters and properties
33
SIPROTEC PROFIBUS-DP - Communication profile
C53000-L1840-B001-03
2.2.2 Transformer tap change commands
A transformer tap change command is applied via two outputs viz. two bits, which are
defined with "01" = LOWER and "10" = RAISE (ref. to chap. 3.7).
Feed-back information is obtained as transformer tap position indication (ref. to
chap. 3.8)
The transformer tap change command is output when the relevant bit pair via PROFI-
BUS-DP changes its value (an edge) from: "Quiescent status" or RAISE to LOWER
and "Quiescent status" or LOWER to RAISE (a definition of the "Quiescent status"
value is given in chapter 3.7).
To execute a number of tap changes sequentially, the initiation via PROFIBUS-DP
must be with impulses due to the fact that the command execution is edge triggered.
• "Quiescent status" → RAISE → "Quiescent status" for raising the tap
• "Quiescent status" → LOWER → "Quiescent status" for lowering the tap
The impulse length must be greater than the maximum bus-cycle time.
Information regarding the maximum bus-cycle time (also referred to as data cycle
time) can be found under the bus parameter settings of the PROFIBUS-DP master
parameterization system.
2.2.3 Behaviour under special operating conditions
• A change of the switching device status which was not initiated by the PROFIBUS-
DP master (e.g. circuit breaker trip) is recognized by the PROFIBUS-DP master by
a change of the value of the switching device status in the corresponding bit posi-
tions of the input message.
If the PROFIBUS-DP master wants to reclose the locally switched off switching
device, then the current value (OFF) or "Quiescent status" must first be transmitted
via PROFIBUS-DP and then the switching device can be reclosed by setting the
must value (ON).
• A switching operation requested via PROFIBUS-DP, which cannot be executed
(e.g. because the control authority is set to LOCAL or the corresponding interlock
conditions in the bay are not fulfilled) is recognized by the PROFIBUS-DP master
from a discrepancy between the checkback signal of the double command or the
status of the single command in the PROFIBUS-DP input message and the
requested switching status, or because the expected transformer tap change
checkback indication is not received.
A checkback supervision time may be activated in the PROFIBUS-DP master.
Before starting a new switching attempt, first the current switching status as per the
input message or "Quiescent status" has to be transmitted again in the output mes-
sage via PROFIBUS-DP.
• The response in the event of disturbed communication is described in chap. 2.3.
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