|
|
|
|
Four
Quadrant operation of variable speed drive |
|
| |
|
A Four-quadrant
diagram can represent mode of operation of variable
speed drive. In Quadrant 1 the speed and torque
can be represented positive or forward direction.
This is consistent with a motor driving a load
taking power from the mains. Similarly in Quadrant
3, both speed and torque are in negative or
reverse direction.
This Corresponds
to a motor turning in the reverse direction,
driving a load and again taking power from the
mains. In Quadrants 2 and 4, the speed and torque
are in mutually - opposed directions, that is
to say, the torque of the motor is opposing
its rotation, giving a braking effect. It follows,then,
that mechanical and kinetic energy of the load
is being converted into electrical energy. The
motor is behaving as a generator and the system
as a whole is delivering power into the mains.
|
|
|
| |
This behavior
is known as Regeneration. After going, through
the mode of operation of VSDs, let us briefly discuss
about the various loading patterns. The characteristics
of the load are particularly important in the trouble
-Free operation of VSDs. Load refers essentially to
the torque output and the corresponding speed required.
Loads can be broadly classified as follows
- Constant torque
- Variable torque
- Constant power
CONSTANT TORQUE LOAD
Constant torque
load are those for which the output power requirement
may vary with speed of operation, but the torque does
not vary. Conveyors, rotary kilns and constant - displacement
pumps are typical examples of constant torque loads.
VARIABLE TORQUE LOAD
Variable torque
loads are those for which the torque required varies
with speed of operation. Centrifugal pumps and fans
are typical examples of variable torque loads ( torque
varies as the square of the speeds ).
CONSTANT POWER LOAD
Constant power
loads are those for which the torque requirements
are typically changed inversely with speed. Winders,
coilers are typically the examples of constant power
loads.
The largest potential
for energy savings with variable speeds drive are
generally in variable torque applications. For example,
centrifugal pumps and fans, where the power requirements
changes as the cubes of speed. Constant torque loads
are suitable for VSD application.
|
| |
|
| |
Top |
|
