Harmonics
Harmonics With the increasing use of power electronics and non-linear loads such as variable-speed drives, computers and other IT equipment, uninterruptable power supplies, or arc welding for example, the power system is getting more and more polluted. This is causing power quality problems such as harmonic distortion, low power factor, unbalance and flicker among other disturbances. The focus of this article is harmonic distortion. Power electronic and non-linear loads draw distorted currents due to the switching nature of the equipment. The distorted current is composed of a...
Read MoreVariable Speed Drives
What is a variable speed drive ? A variable speed drive varies the motor’s frequency and voltage to control its speed. The basic schematic of a variable speed drive system is shown in Figure 1. It normally consists of an AC/DC converter and an output DC/AC PWM controlled three phase output. When using a variable speed drive correctly one can obtain very accurate speed control of the electrical motor leading to: better process control, less wear in the mechanical equipment, less acoustic noise and, significant energy savings. Harmonics in Variable Speed Drive Systems: Variable...
Read MorePower Factor Correction
Power Factor Correction? Most loads employed in industry such as induction motors, transformers, light ballasts and induction heating furnaces are predominantly inductive. Such loads draw two kinds of power: Active power (kW) to perform work Reactive power (kVAr) to build the magnetic field. The active and reactive power make up the total power – apparent power measured in kVA. Reactive power is considered as wasted energy as it does not contribute to useful work. The relationship between the three power quantities can be explained using the power triangle as shown in Figure 1. The...
Read MoreMotor Energy Efficiency
Energy Efficiency in Electrical Motors Motor energy efficiency is a measure of the effectiveness with which a motor can convert electrical energy into output mechanical energy on its shaft. The motor efficiency is defined as the ratio of motor power output to electrical power input at the terminals. The difference between the input and output power is due to electrical and mechanical losses. Electrical motors of higher power rating have higher energy efficiency ratings, however this does not mean that one should use a higher rated motor for a given operating power. On the other...
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