Specifications

Liebert Static Transfer Switch
8 Guide Specification
The STS shall be equipped with 5 molded-case, plug-in, non-automatic circuit breakers. The breakers
shall be UL listed and IEC rated for use at the system voltage. The plug-in feature of the breaker shall
include interlock, which prevents the breaker from being unplugged without being in the “Off” (open)
position. Three of the breakers shall provide for total isolation of the solid-state switching devices with an
input breaker for each source and a load isolation breaker. Two of the breakers shall provide for
maintenance bypassing of the solid-state switching devices to either input source. Key interlocks shall be
provided on the breakers to prevent improper maintenance bypassing of the solid-state switch. A bypass
breaker can not be closed unless the solid-state switch is connected to the same input source and only one
bypass breaker can be closed at a time. All breakers shall be equipped with N.O. and N.C. auxiliary
switches for monitoring of the breaker positions. The two input breakers for the solid-state switching
devices also shall be equipped with 48 VDC shunt trips to allow for control by the STS logic.
2.2.2 Silicon Controlled Rectifiers (SCRs)
The STS consist of six pairs of SCRs connected in an AC switch configuration. The SCRs shall be brick-
type and rated to carry the full 100% rated load. The SCRs shall be rated to prevent hazardous device
failure in power systems with available fault currents listed in section 1.4.3.K.
2.2.3 Control Panel
The STS shall be provided with a microprocessor based control panel for operator interface to configure
and monitor the STS. The control panel shall be located on the front of the unit and can be operated
without opening the hinged front door. The display shall not be mounted to the front door so the door can
be easily removed for maintenance. A back-lit, menu-driven, full graphics, color touch-screen Liquid
Crystal Display (LCD) shall be used to display system information, status information, a one-line diagram
of the STS, active alarms, alarm history information, startup and bypass instructions. No mechanical
pushbuttons shall be used.
The mimic panel screen shall indicate the power flow, the status of all molded-case non-automatic circuit
breakers, the preferred source, and the STS position (connected to source 1 or 2) as well as active alarms.
Pop up boxes selected from the menu bar shall be provided for operator interface to the LCD control
panel for menu selection, control of the preferred source, manual transfer initiation, auto/manual
retransfer selection, and other system setpoints. In addition, by touching the screen you can silence and
reset the audible alarm. To facilitate STS operation, help test, step-by-step start-up, transfer, and
maintenance bypass procedures shall be displayed on the LCD screen. For manual transfers, a syncscope
shall display the leading or lagging real-time phase difference between the two input sources.
The control panel shall be equipped with an internal RS232 port and Flash memory to allow the STS
software to be upgraded by a factory trained customer engineer without shutting down the load.
To facilitate diagnostics, an event log of the last 512 alarm events shall be stored in non-volatile memory
and displayed on the LCD. Two history logs each having 64 frames of unit status frozen upon an alarm
condition designated, as a “freeze fault” will be stored in non-volatile memory and displayable on the
LCD. A frame shall be acquired every 4 milliseconds, with 40 frames before the fault and 23 frames after
the fault. Each frame contains metering data, active alarms/faults, and unit status. A system calendar and
real time clock shall be included to time-stamp all stored events. Monitored parameters shall be acquired
two times per 4-millisecond frame.
CAN bus shall be used to communicate between the logic and the control panel as well as the options.
For remote monitoring, a serial RS-232 port shall provide present switch status information, alarm history
information, and the history of status screens that are triggered upon a major alarm event.