BENSHAW M2L 3000, User Manual, Page: 138 / 140

M2L 3000 Series VFD
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Look Ahead
The Inverter uses the Look Ahead circuit on the Precharge Board to determine
whether or not Medium Voltage DC is being supplied by the Front End before it at-
tempts to Precharge.
Loop Power Supply
A Loop Power Supply is a means of providing isolated Control Power to components
which may be exposed to Medium Voltage. A step-down transformer is used to drive
a high current through a loop of wire. The loop of wire passes through a current
transformer, which then supplies power to the component exposed to Medium Volt-
age. The distance between the loop of wire and the current transformer provides the
required amount of isolation.
Low Voltage
Per NEMA, Low Voltage refers to any voltage less than 1 kV.
Medium Voltage
Per NEMA, Medium Voltage refers to any voltage between 1 kV and 100 kV.
Precharge
The Power Cells in the Inverter contain capacitors that must be charged before it’s
able to run a motor. When the Inverter is energized, it prevents a large inrush of cur-
rent into the capacitors by executing a Precharge sequence. It first uses the Pre-
charge Board to connect the incoming Medium Voltage DC to the DC Bus Bars
through the Precharge Resistors. The resistors limit the current as the capacitors
charge. Once the capacitors are charged, the Inverter then closes its Main Contactor
and disconnects the Precharge Resistors.
VFD
A Variable Frequency Drive controls the speed of an AC motor by varying the fre-
quency of the voltage it supplies to that motor.