UPS 750 Uninterruptible Power Supply Caterpillar

Excitation Coil Driver Board

Illustration 1	g03694079
Excitation coil driver board assembly (1) Excitation coil driver board

Illustration 2	g03694080
PWA excitation coil driver

The insulated gate bipolar transistors (IGBT) for the field coil are connected to the DC bus. The excitation coils are used to generate magnetic fields in the flywheel which perform the following functions:

• Provide a lifting force on the rotor in order to prolong bearing life

• Generate an electromotive force that enables the flywheel to spin during start-up

• Generate an electromotive force during discharge that provides energy to the bus

The excitation coil driver assembly is located on the far right side of the cabinet. The excitation coil driver assembly is made up of an excitation coil driver PWA, a heat sink, and IGBT.

Note: The right, outside wall of flywheel cabinet must be removed to access the excitation coil driver board.

Removal

1. Refer to Systems Operation, Test and Adjust, UENR4695, "Internal Component Pre-Removal Steps". Perform the internal component pre-removal procedure to shut down the system and to gain access to internal components.

   Note: The flywheel cabinet must be de-energized before removal steps can be performed.

2. Disconnect J1, J3, TB1-1, TB1-3, TB2-1, and TB2-3 connectors from the excitation coil driver (FCD) PWA. The cables are labeled to help identify the correct location. Verify that all of the labels exist and are legible.

3. Be sure to support the weight of the assembly to prevent damage. Loosen the left bolt that holds the assembly to the top of the flywheel cabinet.

4. Loosen the right bolt that holds the assembly to the top of the flywheel cabinet.

5. Slide the assembly forward and down off the loosened bolts to remove the assembly from the cabinet.

Installation

Note: Be sure to support the weight of the assembly to prevent damage.

1. Position the two mounting holes at the top of the ECD under the two loosened bolts at the top of the flywheel cabinet.

2. Move the assembly up and back onto the mounting bolts.

3. Tighten the two mounting bolts.

4. Torque the bolts to appropriate specifications.

5. Connect J1, J3, TB1-1, TB1-3, TB2-1, and TB2-3 connectors to the PWA. Check to confirm that all of the cable connectors are in the correct location.