Category: Electrical Machines
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Common Causes of Failures of Power Transformers
As with most of electrical equipment, the key causes of failure of power transformers are either due to electrical failure or mechanical failure. These failures don’t occur that often as compared with other failures in other electrical equipment like switchgear… Read more
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Testing Power and Distribution Transformers
The typical practice for testing power and distribution transformers is to carry out a comprehensive set of tests at the manufacturer’s works. The number and nature of the tests depend on whether the transformer is the first of a new … Read more
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Fuses & Circuit Breakers vs. Overload Heaters for Industrial Motor Protection
A key component of any motor control circuit is some kind of device to detect a condition of excessive overload and interrupt the power to the motor before thermal damage occurs to it. An overload heater is a simple and … Read more
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Permanent Magnet DC Motors – Operation & Applications
Permanent magnet dc motors employ a permanent magnet instead of stationary field winding (as with the case of some other types of dc motors) for producing the required magnetic flux. These stationary magnets are normally fixed to the outer shell … Read more
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How to Perform a Brake Test on a DC Motor
Testing is usually performed on DC machines to establish efficiency and power losses. A brake test is a direct technique that involves applying a brake to a water-cooled pulley mounted on the motor shaft as demonstrated in Figure 1.0. This … Read more
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How solid-state soft starting of Induction motors is done
Solid-state soft starting is the most commonly used technique for starting induction motors. It provides a smooth build-up of current and torque; the maximum current and acceleration time are easily adjusted. The only problem with this technique over conventional starters … Read more
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Basic Features of Autotransformer Starter
A 3-phase autotransformer is typically employed where star or delta starting provides insufficient starting torque. Each phase of an autotransformer consists of a single winding on a laminated core. This incoming supply is connected across the ends of the coils, … Read more
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Types of AC Motors
Classification of AC Motors The AC motors works by rotating the stator field, they make use of the natural alternating nature of the AC wave to turn the field coils on and off sequentially. Generally, AC motors can be classified … Read more
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Direct-on-line (DOL) Starter
Let’s consider an illustration of a typical three-phase direct-on-line (DOL) starter below: Figure 1 Three-phase direct-on-line starter When the start button is pressed, the 415V contactor coil is energized, the main and auxiliary contacts close, and the motor starts. The … Read more
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How cycloconverter is used as a direct frequency converter
The cycloconverter provides direct ac to ac transformation with control over both the output voltage magnitude and output frequency. It employs phase-angle-controlled bridges to synthesize voltages. The most common form is the three-phase to three-phase converter illustrated below: … Read more