Overview

Static transfer switches help maintain power to critical loads by monitoring AC sources and transferring the load when the active source moves outside specified tolerances. The STSREG31 is a three-phase input-selective static voltage regulation system. It is supplied by a three-phase AC grid and selects the most suitable phase to provide a continuously regulated single-phase AC supply to critical loads.

The system consists of four main sections:

Three-Phase Input Selector

Operating across an input range of 50–300 VAC, the selector evaluates the three-phase AC supply and sends the most suitable phase to the input of the single-phase static voltage regulator. If the selected phase moves outside the specified tolerances, the system automatically transfers to the most suitable available phase.

Single-Phase Static Voltage Regulator

This thyristor-controlled AC voltage regulator accepts an input range of 90–280 VAC and corrects the output to 220 VAC ±3% within 20 milliseconds.

Manual Bypass

For maintenance, the bypass switch connects a selected grid phase between the input and output:

• Position 0: No load is connected to the STSREG31.
• Position 1: The STSREG31 is bypassed and input phase L1 is connected to the output. This is the normal operating position.
• Position 2: The regulated STS output is connected to the load.

Automatic Bypass and Switch Output

If the static regulator unit in the STSREG31 fails, the static switch output is automatically connected to the final output channel.

General Features

• LCD alphanumeric panel for easy monitoring and operation
• DSPIC-based control
• Convenient front access
• Input sources protected by thermal fuses
• Three-position bypass selector
• Password-protected parameter changes
• Circuits can be fully de-energized during maintenance bypass
• Transfer delay adjustable up to 3 seconds
• SCR fault detector