ABB UNITROL 1020 - Page 75

 Chapter 3 - Device Overview
UNITROL 1020 User Manual 3BHS335648 E82 67
interface. During DCH software operation, the Active channel sends the setpoints of the
current operation mode and the one for Manual mode through the CAN interface. These
two values are setpoints delayed and calculated out of the measurements of the Active
channel; the delaying method minimizes the influence of failures on the setpoint
calculation (e.g. wrong measurement due to PT failure) and improves the bumpless
characteristic at the moment of changeover.
At the moment of changeover, the Standby channel decides whether to take the setpoint
from the Active channel (over the CAN interface) or from its current measurements,
before it goes Active. The decision depends on the operation mode of both channels
according to the following:
 If operation modes on both channels are the same (except for OpenLoop), the
setpoint is taken from the Active channel, i.e. delayed setpoint over CAN.
 If the Standby channel has Manual mode enabled, the setpoint is taken from the
Active channel, i.e. delayed setpoint over CAN.
 If the Standby channel has Open Loop mode enabled, the setpoint after
changeover is set to zero.
 For all other possibilities not described above, the setpoint will be calculated from
the current measurements of the Standby channel; i.e. not from CAN. Under
these conditions, the setpoint is calculated based on delayed measurements from
the own channel; the delaying method minimizes the influence of failures on the
setpoint calculation and improves the bumpless characteristic.
A summary of the described cases is shown in Table 3-1
Table 3-3 Setpoint follow-up logic Note: SP = Setpoint.
Mode
Standby
AVR
Auto
Sync
VDC
Manual
PF
VAR
Openloop
Mode
Auto
Sync
VDC
Auto SP of
Active AVR
Manual SP
of Active
AVR
Calculated
from
Standby AVR
Measurements
Calculated
from
Standby AVR
Measurements
SP = 0%
Active
Manual
Calculated
from
Standby AVR
Measurements
Manual SP
of Active
AVR
Calculated
from
Standby AVR
Measurements
Calculated
from
Standby AVR
Measurements
SP = 0%
AVR
PF
Calculated
from
Standby AVR
Measurements
Manual SP
of Active
AVR
PF SP of
Active AVR
Calculated
from
Standby AVR
Measurements
SP = 0%
VAR
Calculated
from
Standby AVR
Measurements
Manual SP
of Active
AVR
Calculated
from
Standby AVR
Measurements
VAR SP of
Active AVR
SP = 0%
Openloop
Calculated
from
Standby AVR
Measurements
Manual SP
of Active
AVR
Calculated
from
Standby AVR
Measurements
Calculated
from
Standby AVR
Measurements
SP = 0%