60 to 50 Hz · 50 to 60 Hz · 60 to 60 Hz
Isolation · 50/60 to 400 Hz
Rotary Design Considerations
Rotary Vs. Solid State Design
In general, the advantages of rotary design over solid state design
1. Price-- In sizes over 12KVA, 3ph., rotary is about 50%
of the price compared to the same KVA size in a solid state design.
Rotary has the ability to start more then twice the horsepower motor
vs. a solid state design of the same KVA rating which often means
that you are comparing a 12KVA rotary with a 25KVA or larger solid
state unit because you need the motor starting capability of the
rotary design--which further increases the rotary price advantage.
2. Longevity and Repairability-- our rotary units are designed
(class H insulation, brushless) to operate for 30 years of continuous
(24hr/day) operation with minimum maintenance (50,000 hour permanently
lubed bearings are typical). Bearing changeover can be done in any
motor repair shop by two men in 6 hours using worldwide standard
available bearings. The weakest link is the solid state voltage
regulator which, like most solid state power devices, is subject
to failure after 8 or 9 years. Spare regulators are relatively inexpensive
and always readily available as a package device from our factory
stock or Basler Electric, Highland, IL, the worldwide leader in
such devices (components change but device function remains constant).
Downtime on rotary units rarely exceeds two days and any downtime
is uncommon (once in 10 years, maybe). Our solid state units, like
all other manufacturers, are subject to component failure (often
due to repeated spikes on the input utility line) after 8 or 9 years
(and sometimes much sooner). Replacement boards will have to be
ordered from us and a technician will have to trouble shoot the
unit over the phone using the schematic(often a language problem
overseas)--or the unit could be shipped back to us for service.
Either way, there will be more time down. Another factor is obsolescence--solid
state power design and the components used change very rapidly.
Components commonly used today are phased out in a few years and
start becoming hard to find. We try to ensure that we maintain a
stock of any component used within the last 10 years sufficient
to cover any repair needs but this is a constant problem. We can
always repair and replace parts, if obsolete, for our solid state
units if returned to the factory but that takes time.
For those rare instances where in shop repair is required, we have
a worldwide list of qualified repair shops. For warranty repairs
only, we pay freight to and from such a shop.
Quite simply, which do you expect to last longer -- your VCR or
3. Operating Noise Level-- The main
advantage of solid state design in a 3phase unit is low noise level.
The 3 phase solid state units are not totally quiet (which I define
as below 60 dBa@3ft.) but they are relatively quiet (all are under
80dBa and most are under 73dBa). All our data sheets on rotary units
show the operating noise level. Obtain the data sheet for the unit
you are considering and click here for a comparison of dBa level
with commonly heard sounds. Generally, sound levels under 80 dBa@3ft
are not a problem in an industrial plant. Levels over 83 dBa are
an OSHA problem for 8 hour exposure.
There are three approaches to controlling the sound level of rotary
Put the rotating component skid in another room with other equipment
such as compressors etc. The totally noiseless control panel would
be the only thing the operator would see and this allows him access
to the Stop-Start pushbuttons, meters, output voltage adjust,
output circuit breaker, etc. There is no charge for this but it
does add a little to installation wiring cost.
Enclose the rotary equipment skid in a ventilated, enameled
steel outdoor enclosure and place the skid outside on a pad with
the control panel on the inside of the wall. All outdoor units
are furnished with anti-condensation heaters in the motor and
Specify an optional indoor, quietized enclosure which is lined
with an acoustic foam that will drop the sound level by 10dBa.
These come in horizontal and vertical configurations. The vertical
adds cost but cuts the footprint by almost 50%. To see photo click here.
4. Noise Immunity-- Rotary units can be designed to handle
"difficult loads" such as those which consist in large part
of SCRs, triacs, welders, etc. and motor starting surges. Be sure
to contact our application engineers and discuss the nature of the
load if you suspect it may involve such devices.
5. Consider our Solid State 3phase IGBT Design when:
Any electric motor in the load constitutes less than 25% of
the full load.
SCRs, triacs, welders etc. that feed distortion back into the
supply line (which will be the frequency converter in this case)
constitute less than 20% of the load or have input filtering or
A 50% or more cost adder is acceptable (vs. rotary design) primarily
to achieve the desired operating sound level after considering
the three alternatives for rotary and finding them unacceptable
under the circumstances.
An English speaking electrical technician capable of using an
oscilloscope is available for out of warrantee repairs or:
The unit can easily be shipped back to the factory (it is
in the U.S., Canada or Mexico).
For out of warrantee repairs, the owner is willing to pay
our travel, labor, parts and expenses.
Sizing The Converter-- In general, the converter must be
rated at the higher of:
The starting surge of the largest motor (or motors that start
simultaneously). This involves the KVA rating of the generator
portion of the set only- i.e. starting surge is at very low power
factors and is "seen" by the generator only, not the
converter motor or other converter components. It is important
to know if the motor load is started "across the line"
(as is usually the case with motors that cycle on and off line)
or uses a "soft start" or reduced voltage starter which
minimizes the starting surge. In this regard, it helps to know
the LRA or locked rotor amps. of the motor (or the design code-not
the insulation code). If the LRA is not easily determined we will
assume a figure of 6X the full load current of the motor.
The total amperage of all the devices in the load.