Thyristor switching circuits are used on all Brushless Exciters for Synchronous Motors to provide a current path for the reverse current portion of the induced, ac, motor field current during across-the- line starting. These circuits use voltage sensitive devices to trigger Thyristor(s) into conduction above a particular voltage level, allowing the reverse current to flow without damaging the exciter or motor components.

At this time, the high voltage Zener diodes, originally used to provide this function, are no longer available. Alternative circuits, offered by manufacturers as replacements, have a long lead time and a high price.

Trigger – 1 represents an alternative which is readily available and sells at approximately ½ the cost of these other devices.

Trigger – 1 comes in a small, rugged package, simply mounted, which can be easily integrated into a rectifier assembly. The circuit is potted and enclosed in a cast aluminum case. A barrier terminal strip provides for rectifier connections.

Trigger – 1 is equivalent to the original Zener diode arrangement with the extra features of reverse voltage protection and Thyristor gate current limiting.

The nominal triggering voltage is 250 vdc but can be provided in voltages up to 360 vdc.

Complete instructions are included for a simple means of rectifier assembly testing to ensure correct operation of the exciter rectifier.
Elastic Stop Nuts are supplied with each unit and can be used for the recommended mounting, with the proper length bolts

Trigger-1 Enclosure and label

Trigger-1 side view of terminal strip

The actual dimensions are 3 9/16 x 1 3/16 x 2 3/8 (Including terminal).

Weight = 0.437 lb