Energy losses in transient modes
In electric drives, in which the dynamic mode is the main (EP of rolling mills, cranes, planing machines), it is necessary to take into account energy losses in transient processes .
If the permanent losses do not change during the transient process , the energy losses due to the permanent losses are:
The energy loss component due to variable power losses is
It is difficult to determine D-4, since it is required to know the change in current in time. If we express power losses through mechanical quantities (M/and ), a simpler calculation is obtained.
Energy losses during the operation of unregulated power supplies without load (M with = 0), taking into account transient modes.
There is a power loss in the DCT anchor
where is the relative speed difference.
Then the energy loss in the anchor of the DPT
When starting DPT idle then
With dynamic braking
When braking by opposing , whence , the energy losses are equal to
that is 3 times higher than the energy loss during dynamic braking.
With the reverse and energy loss
that is, they are equal to the sum of the losses during braking by opposing and starting.
Energy losses A A n = A /), are determined by varying power losses for DFT.
The power losses in the rotor circuit of the AD are
When starting, opposing and reversing the AD, is defined similarly to DFT.
Energy losses in the BP stator depend on the Joule losses Then
Total energy losses in blood pressure are equal to
Thus, the losses in the AD rotor do not depend on its resistance, and the losses in the BP stator are inversely proportional to
Energy losses in the operation of unregulated power supplies with a load (taking into account transient modes). Energy loss in the rotor AD
we express through and
where - energy loss at - energy losses caused by the img src="images/image1122.jpg">
With a load of energy loss in the stator,
Total loss in blood pressure
Assuming that M does not change in transient modes and is , , the - corresponds to the start, + - braking. Then
The - in the equation shows that the energy losses during operation with a reactive load increase in comparison with the energy losses during idling in the start-up mode and decrease in the braking mode. When braking, some of the stored kinetic energy is expended to overcome the moment of the load, therefore less energy will be released in the form of losses in the engine.
Energy losses in a regulated electric drive in transient conditions
If you smoothly change the speed of ideal idling changing the voltage using thyristor voltage converters (TPN) or frequency converters (IF), you can significantly reduce energy losses in transient processes.
If there is a linear change in time of ideal idle speed
then the energy losses during the transient process are added from the losses in two stages:
1) with a linear change in the speed with.
The energy losses in the rotor BP The total loss of blood pressure
We define the energy loss in the linear velocity changes when starting the engine idles during the
Usually , so the energy loss at start-up with a linear
the increase in voltage (frequency) is much less than when starting with a constant voltage (frequency). Therefore, in order to reduce energy losses in controlled electric drives, one should strive to reduce the ratio of
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