Load Sharing Application - Toshiba G3 Workbook

Applications workbook

Table of Contents

The following application is a description of two G3 Plus Packs on a mining coal conveyer where the

drive is required to load share two 300HP motors using separate drives.

300 HP

MOTOR

MAIN DRIVE

ROLL

The conveyer is 4000'-6000' long underground and has two drive rolls within 10 feet of each other pulling

on the bottom of the 48" belt. Belt speed is 650 FPM at 60Hz.

This application is best served by one drive running both motors. In this case, the customer demands a

48" height on the drive skid, a separate drive on each motor and very high breakaway torque. A 390KVA

REDA design chassis was installed sideways in a special enclosure.

Problems with this application:

1. Surface speed of the belt on the two motors does not stay constant as irregularities such as splices pass

over one roll. During one pass of the belt, either drive may trip over-voltage fifteen or twenty times

because it was pulled too fast from the other motor. Common DC bus is recommended for this

application but was not allowed by the user (for perceived safety reasons). Surges in speed are so fast,

the pump jack software was not effective in all cases although it did reduce tripping.

2. This conveyer is hanging from the ceiling of the mine and motors are bolted to the rock floor.

Between 52 and 58Hz, a resonance occurs that causes the two drives to motor and regenerate

exchanging energy at a very fast rate that also causes tripping. Programming critical frequency jump

avoids that condition.

3. The company called Line Power designed and built a low profile input transformer with a high

resistance grounding circuit. Main power shunt trips when the drive is applied to the transformer.

Trip levels were raised to prevent the nuisance but it is higher than the customer liked. They claimed

it would not meet IMSA codes. Have you been in a mine when all the lights go out?

For additional assistance, please contact Toshiba Adjustable Speed Drive Marketing Dept. at (800) 872-