FREQUENCY CONVERTER BASICS

WHY DOES A FREQUENCY CONVERTER COST SO MUCH ?

A lot of clients suffer “sticker shock” when looking to by a frequency converter.  It makes little difference if the frequency converter is a rotary unit (motor-generator set) or a solid state (electronic) unit.  And, in fact, the cost spread among vendors is surprisingly small.

So what makes frequency converters so expensive?  Well, it’s a law.  Specifically, the laws of physics.

Unlike voltage conversion, which only requires a rather passive transformer, a frequency converter must completely remake the power in order to change the frequency.  In a rotary converter, incoming electrical energy is converted to mechanical power in the drive motor.  That rotational power then feeds a generator, where the rotational energy is reconverted to electrical output.  Lots of moving parts, lots of hardware, lots of cost.

In a similar manner, a solid state frequency converter converts incoming AC power into DC, but use of a rectifier.  The DC energy is then reconverted into AC power by use of an inverter section.  Again, lots of parts, lots of cost.

One positive side benefit of either type of frequency converter is that any desired voltage conversion occurs “for free” as part of the frequency conversion process.  Unfortunately, this is often little consolation to our clients.

Sorry, it’s just the law.

DO I REALLY NEED A FREQUENCY CONVERTER? WELL … MAYBE NOT.

When potential clients are faced with buying a frequency converter, ours or those of our competitors,  they often find the cost to be a major impediment.  Do they really need the frequency converter?  Well, the answer lies in what type of load is being served.

Applications involving motor loads often need a frequency converter because the rotational characteristics, specifically revolutions per minute (RPM), are a direct function of the input frequency of the electricity.  A 60 Hz. Motor will spin at some multiple of 60, e.g., 1800 RPM.  Concurrently, a 50 Hz. Motor will spin at a multiple of 50, e.g. 1500 RPM.  Thus, when dealing with a motor load, especially in a multi-motor machine, it may be quite necessary to use a frequency converter to ensure that the motors spin in accordance to the original rotational design.

However, resistive loads, such a resistance heaters and some lights, don’t care what the frequency of the incoming power is.  So if the load is restive, no frequency conversion may be necessary.  The only caveat is that the voltage must be in the right range.  Even if only a major portion of the load is resistive, it may be more economical to split the load into parts, and only feed the frequency-dependent component with a converter.

It’s also wise to consider replacing motor(s) in the load to the proper frequency, as this may yield a less costly solution than using a frequency converter.

Georator application engineers are available to discuss these issues with you.  While we value your business, we don’t want to sell you something you don’t need.