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Introduction to STS2/PDU Operations
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8.0 INTRODUCTION TO STS2/PDU OPERATIONS
8.1 System Description
A STS2/PDU provides an automatic, seamless transfer between input power sources to an output
load. The STS2/PDU monitors the input sources, to ensure each source is operating within set param-
eters, as well as ensure that each source is within acceptable tolerances for a transfer between
sources to be completed.
The STS2/PDU contains two static transfer switches in one enclosure to allow the unit to transfer its
load between the two input sources without disruption to the output for longer than 1/4 of a cycle.
If a problem is detected with a primary (Preferred) input source and defined trigger points are
reached, the STS2/PDU automatically switches the input to the other (Alternate) input source. The
STS2/PDU continues to monitor both sources and can automatically transfer the load back to the pre-
ferred source, if so configured, when that source returns to acceptable operating parameters.
The system control logic automatically monitors the input sources and power output to ensure that
they are operating within acceptable tolerances. The system logic manages the transfer between
sources.
The STS2/PDU front panel contains a Color Graphical Display on an LCD touch screen display. The
Color Graphical Display provides a menu-driven operator interface and a display of system informa-
tion, status information, a one-line diagram (Mimic) of the STS2/PDU, active alarms and alarm his-
tory information.
The menu selections provide control of the preferred source, manual transfer initiation. Buttons pro-
vide for audible alarm silence and reset.
Through the touch screen, specific voltage, current and environmental parameters can be configured
to trigger events that can sound an alarm, write to a history log and either transfer sources or inhibit
a transfer.
Preferred input source selection, alarm reset and alarm silencing are done through buttons on the
touch screen display.
Communication options provide external communication with the STS2/PDU through a modem, a
network card, a programmable relay board, a contact isolator or an RS-422 port to Liebert’s SiteScan.
8.1.1 Redundancy
Redundancy within the STS2/PDU prevents one component from being a single point of failure,
should a problem occur. Redundant circuits and components are used to eliminate single points of
failure.
Since the STS2/PDU has two input sources, no single component failure can cause a loss of power to
the load. Redundant power supplies are provided which feed a DC dual-bus used throughout the unit
to prevent any single-point power supply failure modes.
Three separate redundant control logic modules are built into the system. Each contains the logic nec-
essary to run the STS2/PDU and control all transfers.
Redundant fans are provided if a primary fan fails. The redundant fans turn on to prevent overheat-
ing inside of the unit.
Should the front panel interface fail, the control logic continues to operate and the unit would transfer
should a problem be detected on the preferred source. Information on the monitoring parameters
would be available through the remote communication options, if available, or the DB9 (RS-232) con-
nector located next to the LCD behind the front door. See Figure 55 for details.