42 Eaton Static Transfer Switch 2000A 3-Pole Installation and Operation Manual 164001127—Rev 01
• The automatic retransfer to the Preferred Source can be disabled by an authorized user with administrator,
service, or Eaton PDI level privileges, by setting Retransfer = No.
• If Retransfer = No, there is no affinity to the Preferred Source, except at startup. The logic will transfer the
load from the failing source to the “good” source and will remain on that source even after the Preferred
Source returns to acceptable limits. The only effect of specifying a Preferred Source is to specify the
source used at STS startup.
• Retransfer = No also allows the operator verify the power source prior to reapplying the critical load. After
verifying power reliability on the Preferred Source, the operator can force a manual transfer back.
88..11..33 MMaannuuaall TTrraannssffeerrss
Manual transfers can be made in three ways:
1. In Normal Mode, from Home screen, switching the Preferred Source to the other source will manually
transfer the load to the other source if:
a. Preferred Source = Current Source, and
b. the new Preferred Source is within acceptable voltage limits and phase tolerances. The selected
transfer algorithm, VSS or POG, is used.
2. In Normal Mode, toggling the SOURCE SELECTOR momentary toggle switch on the ROI panel is an
alternative way to set the Preferred Source. Transfer behavior is the same as in (1.) above.
3. In Redundant Mode, from the ROI panel, toggling the SOURCE SELECTOR momentary toggle switch
directly transfers the load to the other source, if not already on that source and the other source is within
specification. The SAS logic board controls the transfer, not the Monitor logic.
88..11..44 SSppeecciiaall TTrraannssffeerr SSiittuuaattiioonnss
To keep power flowing to the output load, STS logic responds to several special circumstances:
• Excessive transfers. If transfers between sources become excessive, the logic dynamically adjusts
certain transfer parameters to minimize thrashing between sources until one or the other power source
stabilizes.
• Excessive load current. If the load current exceeds an adjustable preset level, automatic transfers are
disabled until load current falls below that level, even if the voltage on the selected source exceeds the
transfer limits.
• Shorted power switching element. Shorted SCRs cannot be opened and the load must remain on or be
transferred to the side with the shorted SCR to avoid cross-currents. Hence,
– If there is a shorted SCR on the non-conducting side, the load is transferred to the non-conducting
side and retransfer is inhibited. The input switch or circuit breaker on the previously conducting side is
opened. An alarm is sounded and recorded with a date-and-time stamp in the Event Log.
– If there is a shorted SCR on the conducting side, transfer is inhibited and the input switch or circuit
breaker on the non-conducting side is opened. An alarm is sounded and recorded with a time/date
stamp in the event log.
• Open power switching element. If there is an open SCR on the preferred or alternate side, the load will
either remain or transfer to the “good” side, and retransfer is inhibited.
• Cross currents. If cross currents between sources are detected, the STS logic will transfer the load to the
non-conducting side and lock on that source.
• Failure of both sources. If both sources fail, the logic locks on the last available source for 100ms. After
100 ms, the logic will transfer the load to the first available source that returns to acceptable operating
limits.
Example A:
Operational Modes
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