PULLEY 4N4946 - Caterpillar

Introduction
Illustration 1 g01266139
The system is a three-phase Uninterruptible Power Supply (UPS). The system uses a flywheel to store energy mechanically in the form of a rotating mass. During normal operation, the flywheel will be rotating at a constant speed. The typical speed of the flywheel is 7700 RPM. The power from a utility will be delivered by the system to an external load. When power from the utility is interrupted, the system will convert the mechanical energy that is stored in the flywheel to electrical energy. This energy will be used by the external load. When the power from the utility is available again, the system will transfer the load back to the power from the utility.Diagram Overview of Components (UPS)
Illustration 2 g01254252
Diagram of Components (UPS) (1) Input node (2) Input contactor (3) Static switch (4) Bypass contactor (5) Inverter node (6) Output contactor (7) Output node (8) Field coil driver (9) Flywheel inverter (10) DC bus (11) Utility InverterIllustration 2 shows a simplified diagram of the system. The nodes that are shown in Illustration 2 are in the following list: Input Node (1) , Inverter Node (5) and Output Node (7) .The nodes determine the state of the system. The input node (1) and the output node (7) are externally available. These nodes are used in order to attach the system to a power source and to the load. The inverter node (5) is used internally by the system.The DC Bus (10) is also identified in Illustration 2. The DC Bus (10) is used as a power source for the field coil currents. The mode of the system determines one of the following:
If the bus is used as a power source for the flywheel
If the bus is used as a power source for the utility invertersThe main functional blocks are shown in Illustration 2. A description of each function is in the following list:Input Contactor (2) - A mechanical contactor that is used to control the flow of electricity into the systemStatic Switch (3) - The switch is a semiconductor device (thyristor). The Static Switch is used to isolate the system from the utility grid when an outage occurs.Bypass Contactor or Breaker (4) - A device that is used to connect electrically the input source to the load without going through the UPSOutput Contactor (6) - A mechanical contactor that is used to control the flow of electricity to the loadField Coil Driver (8) - The Field Coil Driver is a semiconductor device that is used to drive current through the field coils. The field coils are used to generate magnetic forces that act upon the flywheel. These forces are controlled in order to provide a lifting force on the flywheel. The force prolongs the life of the bearings.Flywheel Inverter (9) - The Flywheel Inverter is a semiconductor device that is used to convert the voltage from the DC Bus into AC signals. When the power from the utility is not available, the flywheel inverter will rectify AC