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Introduction

1 Introduction

This manual is intended to help users of variable speed drives successfully install and utilize Siemens Standard Drives.

It includes an introduction to drives, which may be informative to first time users.

Detailed technical information and complete parameter descriptions are available in the Reference Manual and the Parameter List.

INTERNET Address:

http://www.siemens.de/micromaster

These sites will allow access to handbooks, application and training information, as well as Frequently Asked Questions. (FAQs).

1.1What is a Variable Speed Drive?

A Variable Speed Drive (VSD) consists of a Motor and some form of controller. Early electric VSDs consisted of AC and DC motors combinations which were used as rotating controllers. The first electronic controllers used Thyristor (SCR) Rectifiers which controlled the voltage, and therefore the speed of DC motors. These DC VSDs are still widely used and offer very sophisticated control capability.

However, the DC motor is large, expensive and requires periodic brush maintenance. The AC induction motor is simple, low cost, reliable and widely used throughout the world.

In order to control the speed of an AC induction motor a more complex controller, usually called an inverter is required.

In order to understand how an inverter works, it is necessary to understand how an induction motor works.

An induction motor works like a transformer. When the stator (the fixed, outer winding) is connected to a three-phase power source, a magnetic field is set up which rotates at the frequency of the supply.

Figure 1-1 shows a simplified cross-section of an induction motor.

 

 

Stator Windings

 

1

 

3

 

Air Gap

 

2

2

 

Rotor

 

3

 

1

Shaft

 

 

Figure 1-1 Induction Motor. Simplified Cross Section

MICROMASTER Applications Handbook

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