TSC 900 TRANSFER SWITCH CONTROLLER
PM 151 REV 1 15/10/08 Thomson Power Systems
4.10. PHASE UNBALANCE PROTECTION ALARM RESET
When the TSC 900 is programmed with Phase Unbalance protection enabled, should a
transfer occur due to an out of limit phase unbalance condition, an alarm message will be
shown on the TSC 900 GHC display “UTILITY (or GEN) UNBALANCED”. The Phase
unbalance feature may be user programmed to provide two different re-transfer operating
sequences (i.e. AUTO or MANUAL RETRANSFER). When the “AUTO” re-transfer mode is
selected, the load will be automatically re-transferred back to the original source and does not
require operator intervention. When the “MANUAL” retransfer mode is selected, a re-transfer
back to the original source will not occur until the ALARM RESET button is pressed by ATS
operator. For further details on phase unbalance programming refer to Section 5.
NOTE: When in the MANUAL RETRANSFER mode, if the alternate source fails, the alarm
lockout will not be bypassed inhibiting the load to re-transfer back to the original source even if
within limits. The reason the re-transfer is inhibited is phase unbalance is generally only
detected when load is applied to the source and the condition will appear to clear when the
load is removed, as such allowing a re-transfer to the failed source previously determined to
have a phase balance fault will only result in multiple unnecessary transfers of the load
between sources. Retransfer is set to lockout and requires operator intervention.
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