Rockwell Automation 1557 MEDIUM VOLTAGE AC DRIVE - Manual (Page 7)

INTRODUCTION CHAPTER 2
1557-UM050F-EN-P – June 2013
The Bulletin 1557 drive is a Pulse Width Modulated Current Source Machine side converter (PWM - CSI).
It is designed to supply 3 phase currents to standard induction motor loads. The Bul. 1557 MV (medium
voltage) drive converts 3 phase 50/60 Hz input power to an adjustable AC frequency current source for
speed control of AC squirrel cage motors.
The solid state technology used in the design is of proven reliability. A number of circuit implementation
techniques used are unique to the Allen-Bradley Bulletin 1557 drive.
The basic design philosophy emphasizes the isolation of single component failures, such that multiple
component failures do not occur. This leads to a low MTTR, (Mean Time To Repair), with extensive fault
diagnostic circuits and easy accessibility.
The basic design features of the Allen-Bradley Bulletin 1557 drive are as follows:
The three phase motor currents are sinusoidal with low total harmonic distortion.
The design uses isolated driver circuits, one per gate turn off thyristor (GTO), and
silicon controlled line side converter (SCR).
Two output phases are individually current sensed, ensuring protection and control.
The design is capable of producing smooth low speed torque with low harmonic current
to the motor.
A fuseless electronic protection scheme is used in the power circuit for normal fault
conditions. Power fuses provide back up protection and ensure safety.
Heatsinks are monitored with temperature sensors to detect overtemperatures.
(BUL 1557 Air-cooled units only)
The 1557 Drive uses a North American design base with all components readily
accessible from the front without need to extensively dismantle the unit.
The drive system logic is microcomputer based, thus eliminating numerous trimpots
for system calibration.
Fault and alarm indication is performed using an operator interface panel.