Thyristor controller reduces harmonics

Dean Palmer reports on a unique power control technology for voltage, current or power regulation that reduces harmonics and provides a smoother proce


A new power controller has been developed that employs novel technology that results in a significant reduction in harmonic distortion and provides a smoother process.

Reo's 'Reotron MEW 700/50 2S' controller operates on the phase angle principle but, unlike traditional systems, reduces harmonics (power factor) and can be used for voltage, current or power regulation.

The device produces two output voltages simultaneously. One is adjusted by firing the thyristors at a variable phase angle, whilst the other is permanently on full conduction but at a lower voltage level. This avoids abrupt switch-on of current at the firing angle. The two outputs are combined by interposing a transformer (with two primary windings) between the controller and load.

The standard Reotron controller is built as a module with bus bar, snap-on connections and a digital control panel for setting up operating parameters. The controller can also be provided with a choice of fieldbus interfaces for applications where a number of control stations are being run and monitored from a central, supervisory system such as a PLC.

The controller may offer customers a solution for situations where a cost effective power regulation method is required but without undesirable harmonic voltage distortion on the mains supply and a power factor which is close to unity. Potential applications are many and varied but include water treatment, lasers, PCB manufacture, UV generators, heat treatment, smelting and electroplating.

John Symonds, UK MD at Reo, commented: "Traditional power controllers cause harmonic distortion which leads to voltage distortion of the power supply. The problem is, there are often no accessories provided by the supplier to combat this distortion. However, because these controllers are cost effective, customers continue to use them, especially in applications over 1,000A.

"We decided to turn the thyristor design on its head and create a two-stage controller that provides two voltage outputs, a conventional phase angle and a continuous underlying voltage. Reotron therefore achieves two things: first, voltage is always applied to the load but with underlying voltage control."

Symonds said that customers can use several Reotron controllers on a bus bar with fieldbus interfaces including most of the major suppliers (InterBus, Profibus, etc). Remote monitoring is also an option.

Typically, the new controller outperforms traditional units and Symonds suggested a power factor improvement from 0.81 for a traditional controller to 0.96 for Reotron, which is almost unity.

He concluded: "First, customers benefit from reduced harmonics distortion which will help them meet the G5/4 recommendations which are becoming more rigorous. Second, the improved power factor means the customer can use less expensive control gear, protection devices, smaller cables, and so on.

"Also, you get a lower current draw which is cost effective if the output voltage needs to be stepped up or down using transformers. Reotron therefore provides a smoother process, is energy efficient and offers reduced installation costs."


* The power controller works on the phase angle principle but, unlike traditional controllers, significantly reduces mains harmonics

* Power factor improvement is 0.96 compared to an average of 0.81 for traditional controllers

* End users benefit from reduced installation costs, since the improved power factor means that less expensive control gear, protection equipment and smaller diameter cabling

Tom Shelley

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We always use phase angle firing controls in our vacuum furnaces .A method of reducing harmonics and improving the power factor is greatest a achievement .Please let us have details on primary phase angle controlled transformer and secondaries to resistive furnace loads.

Comment V K V Raju, 03/03/2020

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