Emerson Liebert Static Transfer Switch - Manual (Page 70)

Theory of Operation
62
Hardware
• The Liebert STS2 operator interface in the Color Graphical Display unit is designed to provide all
of the information required to configure and monitor the unit’s operation.
• The control logic performs automatic operations with minimal operator interface.
• Each Liebert STS2 unit is equipped with either a color LCD touch screen or a panel of LEDs and
push buttons.
• The Liebert STS2 can have optional communication ports installed. See 6.0 - Options and 12.0 -
Communication Interfaces on page 76 for more information on communication options.
• On LED Display units, the RS-232 interface is used for configuration and status and event log
monitoring. The RS-232 interface can also be used with the Color Graphical Display units, if nec-
essary.
Firmware
The operator interface enables you to monitor the Liebert STS2, to configure set points for transfers,
monitor system parameters and access event and history logs. The firmware is accessible through the
LCD touch screen (if installed) or the RS-232 interface. The firmware includes:
• View and set the preferred source.
• View and configure setpoints.
• View alarms, faults and status.
Additionally, the Color Graphical Display unit provides:
• The mimic graphical representation of the systems operation.
• Menu driven monitoring and configuration.
• Step-by-step instructions to assist you in the start-up, shut-down and bypass operations.
• Help on event messages.
• Touch screen alarm reset and silence buttons.
Events in the system, both faults and alarms, are detected and displayed on the LCD. See 11.0 -
Alarm and Faults on page 71 for more information on events.
• A set of event masks can be configured through the LCD to trigger a system response to an event.
See 11.1 - Event Mask.
• Report event conditions from other components of the system.
• Monitor and report changes in event condition states. If the event condition’s state changes from
inactive to active, a new event is detected. If the transition is from active to inactive, the event con-
dition has cleared.
• Process new faults and alarms, and clear inactive alarms.
• Provide the alarm reset and silence options.
9.2.2 Circuit Breakers
Three circuit breakers provide total isolation of the solid-state switching devices with an input
breaker for each source and a load isolation breaker. Two breakers provide for maintenance bypass-
ing of the solid-state switching devices to either input source.
All switches in the Liebert STS2 are plug-in types, which allows any switch to be replaced without de-
energizing the output bus. The Merlin Gerin breakers have an interlock in the plug-in base, which
prevents the switch from being withdrawn in the CLOSED position. The switch trips OPEN before it
disconnects from the plug-in base.
See 15.2.5 - Circuit Breakers for specifications and more information pertaining to the circuit
breakers. See Figure 14 to Figure 19 for circuit breaker locations. The circuit breaker schedule is
provided in Figure 20.
9.2.3 SCRs
Brick-type SCRs are used rated to carry the full 100% rated load. Because the unit is a fuseless design
with non-automatic circuit breakers, overcurrent protection is provided by upstream circuit breakers.