UPS 750 Uninterruptible Power Supply Caterpillar

Illustration 1	g03686278
Line static switch assembly (1) Static switch snubber board (2) Static switch driver board (3) Line static switch thyristors

The line static switch assembly is composed of three discrete thyristor modules. One module is connected to each of the input phases. Each module has two devices. In the system, the devices are connected in parallel. However, the devices are connected in opposite directions. The functions of the static switch are as follows:

• Isolation of the input node during a discharge

• Synchronize signals of the inverter node to the signals of the input node upon restoration of the input signals after an outage

• Initial charge of the DC bus

One of the parallel sets of thyristors is turned on at a time. The thyristors for all three of the phases only conduct current when the thyristors are forward biased.

Line Static Switch Driver Board

Illustration 2	g03686093
(5) Line static switch driver board location

Illustration 3	g03686308
PWA Line static switch driver board (SSD)

The static switch driver (SSD) is located on the right, inside wall of the SIO cabinet on the line static switch assembly. The SSD acts as an interface between the UPS and the static switch.

Line Static Switch 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.

2. Disconnect thyristors gating leads.

3. Unplug connectors J1 (ribbon cable) and J3 (24 V).

   Note: Always practice electrostatic discharge (ESD) prevention when handling printed wire assemblies (PWAs).

4. Use the following steps to remove the board from the eight white plastic stand-offs.

   Note: The board must be removed from the stand-offs without bending the board.

5. Pinch the head of each stand-off so that the board is not locked but is still attached to the stand-off.

6. Remove the board by gently and evenly pulling the board from all stand-offs at the same time.

Line Static Switch Driver Board Installation

1. Position the board in the cabinet over the eight white stand-offs.

2. Push the board, gently and evenly, onto all the stand-offs simultaneously. Make sure that the board is fully seated and that all stand-offs are locked.

3. Plug in connectors J1 (ribbon cable) and J3 (24 V).

4. Connect all of the thyristor gating leads.

Line Static Switch Snubber Board

Illustration 4	g03686697
(6) Line static switch snubber board location

Illustration 5	g03686699
PWA line static switch snubber board (8) J3 connector (9) J2 connector (10) J1 connector

There are static switch circuit cards connected between the input and output of each of the three static switches. The snubber board prevents false signals that could turn on the static switches. False signals can be caused by voltage transients.

Line Static Switch Snubber 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.

2. Unplug the connectors from the J1, J2, and J3 board terminals.

3. Use the following steps to remove the board from the four white plastic stand-offs.

   1. Pinch the head of each stand-off so that the board is not locked but is still attached to the stand-off.

   2. Remove the board by gently and evenly pulling the board from all stand-offs at the same time.

Line Static Switch Snubber Board Installation

1. Position the board in the cabinet over the four white stand-offs.

2. Push the board, gently and evenly, onto all the stand-offs simultaneously. Make sure all stand-offs are locked in place.

3. Plug the wire connectors into the correct board connectors. Check the labels on each connector to ensure that each connector has been correctly installed.

Line Static Switch Thyristors

Illustration 6	g03686728
(15) Location of the line static thyristors

Illustration 7	g03686741
Line static thyristor

There are six thyristors located on the line static switch, two for each phase. The thyristors act as a static switch and allow rapid changeover when changing between the bypass and online states.

Installation

1. Position the thyristor in the appropriate location.

2. Install the 4 hex head screws that mount the thyristor to the SIO frame.

3. Install the bottom 3/4 inch bolt that attaches the thyristor to the bus.

4. Install top 3/4 inch bolt that attaches the thyristor to the bus.

5. Connect the "THY" lead to thyristor.