Control-monitoring and protection of high voltage motors

Abstract

Unit power of rotating machines frequently exceeds 100 kW in industry and large tertiary. In such cases and/or if the length of the supply line is particularly long (voltage drops, losses…), use of high voltage motors is advantageous.

The purpose of this Cahier Technique is to analyse and compare these motors, their starting systems and the various protection devices which may be used, in order to simplify technical choices.

Reminder of the various types of AC motors

Both high and low voltage AC motors, offer a large variety of electrical, dynamic and technological characteristics. However, except for a small number of motors used for highly specific applications, they can be divided into three families, namely:

• asynchronous cage motors;
• asynchronous slipring rotor motors;
• synchronous motors.

They differ from each other in:

• starting current and torque values;
• speed variation in normal operation;
• power factor and efficiency values as
• function of load.

HV motors are supplied with a voltage rarely exceeding 7.2 kV, their power ranges from 100 kW to over 10 MW, with an average of 800 kW.

AUTHOR: Schneider Electric expert | J.Y. Blanc