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Operating Instructions
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4.2.9 Abnormal Operations
Improper Transfer
Transfers can not be performed unless the OK TO TRANSFER LOAD (#) TO SYSTEM (#) light turns
on. This makes it difficult to begin an improper transfer.
The source feeding the UPS modules does not matter because the UPS inverter output is isolated
from the rectifier.
The logic permits transfers to and from a UPS system with the UPS modules running on Utility, Bat-
tery, or Engine-generator so long as the system accepting the load is running on inverter output.
Synchronization is verified by forcing the system to meet three independent criteria. First, all on-line
module oscillators must be synchronized. Second, the voltage zero crossings must be within tolerance.
Third, the instantaneous voltage differential between UPS system voltages must be within tolerance.
But, regardless of synchronization status, a critical load will not be allowed to transfer to a system
running on its bypass source. Transfers from a bypass source to a system on UPS is permitted.
Circuit Breaker Failure
If a “Close” or “Open” command to a circuit breaker fails to return a confirmation of completion within
an acceptable time period the Power-Tie logic initiates corrective actions based on the system’s initial
state and current state.
Loss of Tie Controls
Since UPS system independence has been stressed throughout the design of this Power-Tie configura-
tion, complete loss of Tie Controls will not affect either UPS system operating in any Momentary Tie
(Combined Loads Mode) configuration.
4.2.10 Trouble Recovery
While failures are extremely unlikely, the Power-Tie system has been designed to restart from any
system operating mode once the fault has been corrected. Refer to 1.5.5 - Modes of Operation for a
description of the operating modes.