Powerohm Type
NR Neutral Grounding Resistors are used in industrial power systems for resistance
grounding of wye-connected generators and transformers. A neutral grounding resistor
limits the fault current to a value which is sufficient enough to operate protective
relays, and prevents unwanted fault damage.
The Powerohm Type SF Sinewave Output Filter
is used where variable frequency drives are installed that require extremely long
motor leads, such as a submersible downhole pump motor. Since voltage wave reflection
is a function of the voltage rise time and the length of the motor leads, there
is an impedance mismatch at both ends of the cable. Due to the impedance mismatch,
a portion of the waveform high frequency leading edge is reflected back in the
direction from which it arrived. When the reflected leading edges encounter other
waveform leading edges, their values add, and cause voltage overshoots. As the
carrier frequency increases, there are more leading edges present, causing higher
and higher voltage overshoots. This condition leads to premature motor failure,
halting critical processes. The Type SF Sinewave Output Filter uses a specially
designed RLC network to minimize and nearly eliminate these damaging voltage overshoots.
AC variable frequency drives are commonly used
with a general purpose AC induction motors to form a reliable variable speed drive
system. For applications that require faster deceleration rates, or where motor
speeds are exceeding the synchronous speed set by the output frequency of the
drive (an overhauling load condition), a braking resistor is required. Braking
resistors increase the braking torque capability of a variable frequency drive,
producing faster and more controlled braking. The resistor dissipates regenerated
power to keep the bus voltage from exceeding the rated limit of the drive.
Motor control is one of the most common applications
of power resistors. Resistors are used to control the torque and speed characteristics
of AC and DC motors, and to limit inrush currents.
This
section provides a basic understanding of how resistors are used for motor control,
and the information required to design a resistor configuration. To order a resistor
assembly, simply obtain the data needed for your motor type and either enter it
into the appropiate quote Navigator or call the factory. Our engineers will design
a package that best suits your needs.
