VALVE (EXHAUST) 8H1994 - Caterpillar

The UPS750 functions automatically, to supply AC electrical power to the critical load during certain conditions. There are several operation modes that allow the UPS to accomplish this task. Most of the operating modes have several states occurring within that mode. The current mode and state are displayed on the SIO User LCD Touchscreen display. The User LCD Touchscreen display is located on the front panel of the SIO cabinet. The UPS750 continually monitors internal systems and the incoming utility power. The UPS will automatically change between modes as required. The changes are accomplished without operator intervention. The detection and switching logic inside the UPS ensures that the changes in operating mode are automatic and transparent to the critical load. The operating modes are listed below:
On-line Mode
Discharge Mode
Bypass Mode
Automatic Voltage Regulation (AVR) Mode
Shutdown Mode
Manual Mode (Service only)
Calibration Mode (Service only)System Sub-Assembly Overview
A description of each of the UPS750 Flywheel Power Unit (FPU) subassemblies follows:Line Static Switch
The Line Static Switch in the SIO is a continuous-duty rated, phase-controlled, full-wave, three-phase, line-commutated electronic switch using Silicon Controlled Rectifiers (SCRs) as switching devices.The Line Static Switch turns off within one-half cycle of detecting an input voltage or frequency outside of preset limits.Phasing of the switch during normal operation inhibits reverse power flow from the output of the switch to the UPS input.Connection to the AC input through the switch is initiated when the phase difference between the input and output is within a few degrees. The connection is initiated then to reduce inrush currents when reconnecting to input power after a discharge.Flywheel Energy Storage Subsystem (FES)
The FES supplies ride-through energy for the UPS system is supplied by a FES in the FPU. The FES stores energy in the inertia of a rotating mass. The energy is immediately accessible, to support the critical load, without interruption.The heart of the FES is the rotating flywheel, with a stator, contained in a single housing all kept under vacuum.During normal operation, about 75 percent of the FES rotor weight is relieved on the flywheel bearings. The weight relief happens through magnetic suspension, provided by field coils mounted inside the FES housing.Normally, the flywheel rotor spins at 7,700 RPM. The complete FES can withstand the following fault conditions:
Sudden loss of vacuum.
AC short-circuits.
DC short-circuits.
Catastrophic bearing failure.
Over speed testing to 120% of rated speed.Bi-Directional Converters (BDC)
The FES is charged and discharged using an AC-to-AC BDC. The BDC is composed of two PWM AC-to-DC, four quadrant converters configured in a back-to-back arrangement.Each AC-DC converter uses a three-phase full wave PWM conversion technique, utilizing three Insulated Gate Bipolar Transistor (IGBT) converter stages. All stages in each AC-DC converter are identical and interchangeable have built-in short-circuit and overload protection.Failure or over-temperature of the converters is monitored and alarmed.Static Bypass
The static bypass switch consists of two SCRs per phase, arranged in a back-to-back configuration.The UPS automatically transfers to bypass. Transfers to and from bypass are synchronized and operate without interruption of load voltage or current.If Input power is available but synchronization has