What is Constant-Wattage Autotransformer (CWA)

Horace He

Last Updated: December 26, 2023

What is Constant-Wattage Autotransformer (CWA)

A Constant-Wattage Autotransformer (CWA) is a type of ballast, specifically for high-pressure mercury lamps and high-pressure sodium (HPS) lamps. It provides the necessary starting and operating voltage for these types of lamps. A CWA ballast typically consists of input terminals for connection to alternating current lines, output terminals for connection across the lamp, and an autotransformer. The autotransformer has a primary winding connected to the input terminals and one output terminal, as well as a secondary winding connected to the other output terminal.

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In addition to the autotransformer, a CWA ballast may also include other components such as series capacitors and arc-sustaining capacitors. The series capacitor is usually connected in the connection to the output terminal, which helps limit or control the lamp current and improve the power factor of the load. The arc-sustaining capacitor, on the other hand, is connected to one of the input terminals in parallel with the secondary winding of the autotransformer. It is designed to resonate with the autotransformer, resulting in a fast rise in voltage at the output terminals during each alternating high cycle. This fast rise in voltage plays a crucial role in sustaining and stabilizing the arc in a high-pressure sodium lamp.