Phase Converters

In today’s market field of phase converters, you will see a wide selection of different types. Below, you will find a list and a brief
description of each one. The static and the rotary converters are the most popular ones in the market today.

Static-Phase Converters:

These are the first phase converters and have been around the longest. The uses are limited, and if you have a smaller motor or one motor, these may do the job. Remember that static-phase converters do not convert one-phase power to three-phase power, nor do they generate three-phase power. The static-phase converter will not power any type of machinery with  three-phase circuitry. Static-phase converters operate by producing a  third-phase of power for only a few seconds during the startup of electrical motors.

Rotary-Phase Converters:

A rotary-phase converter is designed to power larger equipment and higher HP motors, and a single unit can provide a continuous reliable source of three-phase power to more than one machine. These converters are a popular choice when a continuous source of three-phase power is needed. A typical rotary phase converters consists of a three phase motor and a bank of capacitors wired together to act as a single large capacitor. Two of the leads to the motor are connected to the single-phase power source and the third lead of the motor is connected in series with the capacitor bank to either one of the single phase inputs. The output leads for the phase converter are connected across the three motor terminals. The electrical interaction between the capacitor bank and the free-running phase converter motor generates a voltage on the third motor terminal which approximates the voltage needed for a balanced three-phase system.

Capacitors can be added and/or removed to provide balanced three phase power for a given load. However, with varying loads, power from the rotary converter will become imbalanced which adversely impacts both the performance and the life of the motor.

Digital-Phase Converters:

These are the newest of the phase converters. They are all electronic in nature and non-mechanical, and they produce and maintain a balanced load. Another benefit of digital-phase converters is that they are very quiet. The downside of the digital-phase converter is that they are expensive; and due to their sensitive complex electronic nature, they are easily damaged
by power surges.

VFD-Phase Converters:

Variable frequency drives are designed primarily to control the speed of AC motors but can be adapted to function as phase converters. A variable frequency drive is an adjustable speed drive; it balances the speed of an AC motor and frequency of the AC power supply. A VFD is a system for controlling the speed rotation of an alternating current (AC) electric motor by
controlling the frequency of the electrical power supplied to the motor. Variable frequency drives are the newest technology in developing more efficient ways to vary the frequency of the currents supplied to special AC electric motors.

Applications for variable frequency drives use equipment that requires speed control such as conveyors, large pumps, and boiler fans. Due to modern-day advances in solid-state electronic technology, variable frequency drives were developed. This new technology made it possible to switch large current levels at high-kHz rates by developing insulated gate bipolar transistors, which lead to pulse-width-modulated inverter drives. These units have high operating efficiency, are compact, and are relatively low in distortion.

Pulse-width-modulated inverters control the kHz-chopping rate of a wave. They vary envelope voltage and fundamental frequencies and control motor acceleration and running of the induction motor. Where resonance in the mechanical equipment and structural supports might be excited to levels that could cause damage to the motor, these drives can accelerate and operate the electric motor to skip critical frequencies and avoid harm that might have occurred otherwise.

CNC-Phase Converters:

The CNC-phase converters provide balanced voltage for computer operated and voltage-sensitive machines. These converters have a power conditioning to produce lower harmonic distortion and a smooth sine wave. These converters have excellent power quality but are quite expensive.

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