BENSHAW M2L 3000, User Manual

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M2L 3000 Series VFD
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Converter
The Converter, or Input Stage, consists of a medium voltage trans-
former and full-bridge rectifiers that convert the incoming AC mains
voltage to a fixed source of DC. Individual 3-phase bridge rectifiers
are connected in series, as shown in Figure 5, to produce the re-
quired DC voltage for the inverter.
The Converter does not contain any capacitors for energy storage.
Energy storage in the drive is distributed among identical power
modules in the drive’s Inverter. The distributed capacitive energy
storage greatly reduces arc flash potential and substantially im-
proves reliability.
The transformer is a standard rectifier grade transformer consisting
of a single 3-phase primary winding, with three (3) secondary wind-
ings, appropriately phase shifted to yield an 18-pulse current wave-
form in the primary for low harmonic distortion. The total harmonic
distortion (THD) of the primary current is typically ~2.3% for a 1000
hp, 4160 VAC drive operating at full power, which easily complies
with IEEE 519 distortion requirements.
Figure 5: M2L 3000 Converter
Typically, the primary voltage of the transformer is identical to the AC
operating voltage of the motor; however, the M2L 3000 can accom-
modate voltages that differ from the motor voltage. For example, a
customer application may require that a 4160 VAC induction motor
be operated from a 2300 VAC or 13.8k VAC source. In this case, the
primary winding would be specified to be 2300 VAC or 13.8 kVAC.
The secondary winding voltages have been selected to generate the
DC voltage needed to synthesize AC waveforms for 4160 VAC at its
output terminals.
Two typical size Converter enclosures (small and large frame) are
shown in Figure 6, with all electrical components contained within the
enclosures. The enclosure design allows for top or bottom entry of all
cable connections between the AC mains and the Inverter.
The Converter is forced-air cooled. Cooling air is drawn through fil-
ters on the front of the enclosure by multiple blowers mounted on the
top. The Converter is designed to function with “N-1 Redundancy”
(for example only 2 of 3, or 4 of 5 blowers operating), providing re-
dundant protection and high operating availability. Filter elements are
provided in series on the front of the enclosure, to block the ingress
of dirt and dust particulates. The filter assembly mounts over a pro-
tective screen, welded to the enclosure, that prevents inadvertent
contact with the resident high voltages when the filter media is re-
moved for cleaning or replacement.
The enclosure also contains internal baffles that route air flow
through critical areas of the transformer, and across the rectifier as-
semblies. Thermal sensors are located in the input air stream to the
blowers, to detect over temperature conditions. The standard Con-
verter enclosure is rated for NEMA 1 applications. Enclosures with
other environmental ratings are available.
Figure 6: 300 Amp Converter