System Operation; Autonomous Operation - GE PACSystems RX3i User Manual

System Operation

Autonomous Operation

GFK-2749
The PSM digitizes the voltage and current input waveforms from Grid 1 and Grid 2, storing
the results into internal memory buffers. Data is updated every power line cycle.
Therefore, the data is updated every 20ms on a 50Hz power grid, or every 16.67ms on a
60Hz power grid.
While background processes analyze a set of waveforms stored in one memory buffer,
the next set of waveforms is captured and stored in another buffer. In this way,
calculations are performed on each waveform with the DSP processing the data in about
two-thirds of a power line cycle.
The PSM is a semi-autonomous module running on the RX3i backplane. If the PLC goes
to Stop Mode, or the CPU is lost due to over temperature or a watchdog timeout, the PSM
continues to operate with the last directive received from the CPU. If the CPU had
requested the synchronization of Grid 1 and Grid 2, when all sync parameters are met, the
PSM will assert RelayCloseOK and close its relay output contacts, even when the PLC is
in Stop Mode. Care must be taken to leave the Sync request in a known state when
transitioning to stop mode.
When Grid 1 and Grid 2 are synchronized, the PSM cannot be reset or cleared, and it
will not accept a new hardware configuration from the CPU. Once synchronized, the PSM
can only be cleared in preparation for receiving a new configuration by first commanding
the PSM to release the grid synchronization (simultaneously set %Q offset 16 to 1, and
clear %Q offset 32 to 0), or by removing power from the PSM module. Mission Critical
applications must have a redundant PSM system to take over the grid synchronization
from the Primary PSM if the primary controller can no longer perform its function.
Chapter 1 PSM Module Description and Specifications
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