Functional Description

Introduction

The IFM-150 Interface Firing Module receives a control signal from the DECS-400 or DECS-450 Digital

Excitation Control System and then calculates a time delay based on the zero crossing of each phase of

voltage from the synchronizing transformer. At the end of the time delay, the IFM-150 produces the

properly synchronized sets of pulses to drive the SCRs of the excitation system rectifier chassis. As the

DECS control signal increases (or decreases), the time interval between the zero crossing of each phase

voltage and the start of its next output pulse will decrease (or increase). This results in an increase (or

decrease) in the rectifier chassis output voltage.

A terminal voltage limiter within the IFM-150 can be enabled to monitor the generator voltage through the

synchronizing transformer or external voltage transducer and compare the measurement with a user

adjustable reference level. If the generator voltage exceeds the reference level for a user-adjustable

amount of time, the IFM-150 will modify the SCR firing pulses and limit the generator voltage.

Inputs

The function of each IFM-150 input is described in the following paragraphs.