Basler Electric IFM-150 Interface Firing Module

Introduction

The Basler Electric IFM-150 Interface Firing Module receives a control signal from a DECS-400 or DECS

450 Digital Excitation Control System and calculates a phase-control firing angle that is synchronized with

the power transformer output. The IFM-150 then generates output pulses to drive the SCRs of an

excitation rectifier chassis.

The IFM-150 is available in two configurations that control either a single-phase rectifier module or a

three-phase rectifier chassis.

Three-phase IFM-150 modules can be user-configured to supply SCR firing pulses to a fully controlled or

half controlled (positive or negative) rectifier bridge. A fully controlled rectifier bridge requires that the IFM

150 supply six sets of firing pulses to drive the SCRs of the bridge. A half controlled rectifier bridge

contains three SCRs and three diodes. Positive control is used when the SCRs are connected to the

positive side (F+) of the field output. Negative control is used when the SCRs are connected to the

negative side (F–) of the field output.

A single-phase IFM-150 provides full control of a single-phase rectifier module. Four sets of firing pulses

are generated by the IFM-150 to drive the rectifier module SCRs.

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.

Control Power (DC+, DC– and AC1. AC2)

Operating power for the Firing Circuit Chassis is applied to the Control Power inputs. If dc operating power

is used, 125 Vdc should be applied to terminals DC+ and DC–. If ac operating power is used, 120 Vac

should be applied to terminals AC1 and AC2. Both inputs may be used if redundant control power is desired.

Bridge Control Voltage (COM, VC+)

This signal determines the firing control angle of the rectifier bridge SCRs. The Bridge Control Voltage

Input accepts a voltage range of –10 to +10 Vdc. The DECS must be programmed to supply the same

range of control voltage. Refer to Basler publication 9369700990 for information about DECS-400

configuration and Basler publication 9597100990 for information about DECS-450 configuration.

Synchronization Voltage

Voltage is applied to this input and passed through the synchronizing transformer. These voltage signals

are used to define the time reference for the rectifier chassis SCR control pulses. The voltages are also

used for generator voltage metering in applications where the rectifier chassis operating power is supplied

from the generator output (if the Internal mode of the generator voltage sensing is selected (for three

phase applications only)).

Terminal labeling for the synchronization voltage input varies according to the model of IFM-150 (single

phase or three-phase control).

The single-phase IFM-150 accepts synchronization voltage at terminals A1 and B or A2 and B. Terminals

A1 and B are used for synchronization voltage in the 240 Vac or 480 Vac range. Terminals A2 and B are

used for synchronization voltage in the 120 Vac range.

The three-phase IFM-150 accepts synchronization voltage at terminals A, B, and C.

Generator Voltage (B2. B3)

The dc output from the transducer, used to sense the generator voltage, is applied to this input. This

signal is used for generator voltage metering if the external generator voltage sensing mode is selected.

Gate Drive Block (BL+, BL–)

When a contact closure is sensed at this input, SCR firing is blocked and the IFM-150 output is disabled.

Full Invert (INV+, INV–)

The pulse outputs are forced to their maximum delay when a contact closure is sensed at this input. This

results in maximum negative voltage at the exciter output until the field current decays to nearly zero. The

Full Invert contact input is used only on full-control bridges.

Start/Stop (FS+, FS–)

A contact closure at this input initiates sampling of the synchronizing voltage (to determine phase

rotation) and calculation of the pulse generation time delay. Opening this contact input terminates the

firing pulses.

Terminal Voltage Limiter Enable (VTLIM+, VTLIM–)

The terminal voltage limiter is enabled when contact closure is sensed at this input. When enabled, the

terminal limiter will prevent the generator voltage from exceeding the limiter reference level.

Outputs

The following paragraphs describe the function of the IFM-150 outputs.

Firing Pulses

These outputs supply firing pulses to the gate trigger inputs of the Rectifier Chassis. The firing pulse

terminals used depend on the model of IFM-150. Installation illustrates typical firing pulse output

connections for single-phase and three-phase rectifier chassis applications.

Watchdog Relay (WTCHDG1. WTCHDG2)

The Watchdog Relay output closes to indicate a software execution problem within the IFM-150 or a loss

of power supply. This output remains closed for several seconds after the application of control power.

Alarm Relay (ALRM1. ALRM2)

The Alarm Relay output closes when the monitored synchronizing transformer frequency decreases

below the programmable level of the BESTCOMS Safe Mode Frequency setting. The output opens when

the frequency increases to 1 hertz above the Safe Mode Frequency setting. This output is disabled when

the Start/Stop contact input (FS+, FS–) is open.

Terminal Voltage Limiter Active Relay (LIMACTV1. LIMACTV2)

The normally-open Terminal Voltage Limiter Active Relay output closes when the terminal voltage limiter

activates due to high generator voltage. When the generator voltage decreases below the limiter

reference level, the terminal voltage limiter deactivates and the Terminal Voltage Limiter Active Relay

output opens.