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Trigger-3

For Exciter Rectifiers with the Motor Field and discharge resistor connected in series across the rectifier terminals.

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.

In order to improve the torque capability during starting of a Brushless Synchronous Motor, a discharge resistor can be used. The power developed in the discharge resistor increases the motor torque envelope.

Trigger-3 senses the motor condition during starting and will trigger an SCR to bypass the resistor during synchronous operation following the starting event. This maintains the synchronous motor’s superb efficiency.

The Schematic in Figure # 1 shows how Trigger-3 can be used with Trigger-1 to add a discharge resistor to a Trigger-1 Exciter circuit.

Figure # 1
Trigger-3 Application

For Exciter Rectifiers with the Motor Field and discharge resistor connected in series across the rectifier terminals.

Figure # 1 shows the application of Trigger-3 and suggests the possibility of adding a discharge resistor as an up-grade to the Trigger-1 circuit when starting conditions change. 

AC Motor Technologies has a dynamic analysis program which can analyze the motor’s starting performance. Much more data on the motor is required to do this - at least the rewind data used for coil replacement.

Trigger - 3 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. Figure # 2 shows a completed assembly.

The nominal operating voltage is 125 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.

Figure # 2
Trigger-3 Enclosure and label

The actual dimensions are 3 9/16 x 1 3/16 x 2 3/8 (Including terminal). Weight = 0.437 lb

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