DATAKOM DKG-705 User’s Manual
705_USER.doc
- 23 -
7.2 No Break Transfer
In this mode, the transfer will be made
without power interruption
. This implies that both of the
mains and generator contactors will be active during transfer.
The maximum duration that both contactors will be active is programmable. However this process
may be quicker with the use of one auxiliary contact at each contactor. Thus the changeover will be quite
instantaneous, preventing any excess or reverse power condition. Normally the digital input_6 (terminal
23
)
is used for mains contactor auxiliary contact and the digital input_7 (terminal
22
) is used for generator
contactor auxiliary contact.
To prevent a phase to phase short circuit below criteria must be met:
-The mains and generator voltages must be equal,
-The mains and generator voltages must have the same phase,
-The mains and generator voltages must have the same phase sequence order.
The DKG-705 will allow a
No Break Transfer
only if
all
of the below conditions are fulfilled:
-Mains phase voltages within the programmed limits,
-Mains frequency within the programmed limits,
-Genset phase voltages within the programmed limits,
-Genset frequency within the programmed limits,
-Mains phase order correct (or phase order check must be disabled),
-Genset phase order correct (or phase order check must be disabled),
-The difference between mains and genset frequencies not more than programmed limit,
-The voltage difference between phase R and phase U not more than programmed limit,
-The phase angle between phase R and phase U not more than programmed limit,
When a
No Break Transfer cycle
is initiated, the DKG-705 checks all the above criteria to be
satisfied. If any of the checks fail, then the unit reverts to a
Transfer with Interruption
.
If all conditions are met, the unit proceeds to the synchronization. The GOV output, if enabled,
acts to equalize the phase between the genset and the mains voltages. The AVR output, if enabled, tends
to equalize the genset and mains voltages.
It is also possible to make a
No Break Transfer
without
GOV
or
AVR
control. In this case the unit
will wait until the expiration of the
Synchronization Fail Timeout
(
P_A07
), to find a matching phase and
voltage. Normally with frequencies matching at +/- 2Hz and voltages matching at +/-10 volts an
uncontrolled No Break Transfer
will be successful if auxiliary contacts of the contactors are used. Also
note that most of the standard AVRs will accept external voltage matching, thus only a rough frequency
matching will be enough to succeed a
No Break Transfer
.
If matching is found before the expiration of the
Synchronization Fail Timeout
(
P_A07
), then
both contactors will be activated. If contactor auxiliary contacts are used, the other contactor will release
immediately. If contactor auxiliary contacts are not used, the other contactor will release after
contactor
timeout (P_A09)
.
