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Thanks Mark. Machine already has 400kg flywheel. But obviously this is not enough. Thanks again for your advice!!!

The best way to flatten the load demand, is to add a large flywheel. Any device you add to try to flatten the load will not work well. You may be able to change the way the saw works perhaps, but a reciprocating saw is going to have a modulating torque demand and this will cause an equal variation in the electrical demand. A flywheel acts as a mechanical capacitor to reduce the torque variations on the motor. Best regards, Mark.

Thanks for the reply marke! I am coming to pretty much same conclusion. Maybe only solution will be to install VFD (oversize it) with DC resistor and cope with energy loss. Or maybe put some sort of reactive filter on the line. But then I guess it will have to be tuned somehow to frequency of this energy sloshing around. I did not find any ready made solution. And I don't have enough expertise on the matter to design myself. Another thing that comes to my mind maybe isolation transformer? Delta star or star delta? Would that help maybe?

It sounds to me as though the "power" demand of the motor is very erratic with both positive and negative power flow where the motor is both driving the cutter and breaking the cutter (slowing down). This can be due to a concentric load where the cutter system is not properly balanced. Where there is an issue with the balance of the load and the motor is both driving the load and the load is driving the motor, then yes I would expect to see voltage disturbances on the supply. The magnitude of these disturbances is a function of the supply impedance. Adding a VFD will not fix this problem, and can make it worse due to the inability of the VFD to feed energy from the load back into the supply. Adding braking resisters may help to stop energy being fed back into the DC bus, and this may keep the machine running, but you now have considerable energy being wasted as heat. An active front end drive will prevent the motor from tripping on over-voltage, but will still enable the energy to be fed back into the supply and in addition, will add common mode switching current to the network and potentially cause additional issues. Do I have a solution? No. If the load current is unstable, a VFD will probably make it worse and trip. Slowing the cutter down, will reduce the load and you could get down to a load where it does not affect the supply, but the work rate will be severely reduced.

Hi all! My first post here. I have above mentioned inverter that I tried installing on a 30kW motor for stone cutting machine. Original problem is that when machine is cutting it is inducing garbage back into the line, causing all lights to flicker. This is due to linear movement of the cutting blade. Since rotation is converted to linear forward / backward motion, load on the motor keeps oscillating. As one of the solutions for this was reccommended, install a VSD. VSD was sourced from a friend that had one as a spare, so that is what I'm stuck with for now. When trying to run the motor, it starts and ramps up to 37 Hz (for a 50Hz target speed) and then following fault comes on: Main circuit overvoltage (OV) The DC voltage of the main circuit exceeded the overvoltage detection level (approx. 400 V for 200-V class models and approx. 800 V for 400-V class models). The deceleration time setting is too short and regenerative energy from the motor is excessive. → Increase the deceleration time or connect the Braking Resistor Unit. A surge is imposed when the phase advance capacitor is switched. → Insert an AC reactor into the power input side of the Inverter. The voltage of power supply to the Inverter is too high. → Lower the voltage within the rated power supply voltage. I can also see that kW reading on the drive is also going into negative reading. So drive probably can not absorb that much energy from the motor as it's load is variying, also going into braking due to zig zag motion of the blade. This drive doesn't have provision for braking resistor so I can not try that. My questions are: Is there any alternative for this problem? Solution wihout the resistor? If anybody has enough experience, will drive of this size be able to cope with this problem if another model with braking resistor is chosen? Or bigger drive need to be installed? At 35Hz, we tried cutting, and there was no lights flickering. So we are sort of half way to the solution. Thanks!!!

The Control Word is set by serial communications from the PLC. These are the values to insert into the control word to RUN Forward, RUN Reverse, STOP and RESET the drive over the Modbus TCP network. // Run Forward If ((RunForwardIn = True) and (RunReverseIn = False)) then ControlWord := 16#047C; End_If; // Run Reverse If ((RunForwardIn = False) and (RunReverseIn = True)) Then ControlWord := 16#847C; End_If; // STOP If ((RunForwardIn = FALSE) (*And (RunReverseIn = False)*) And (ResetIn = False)) then ControlWord := 16#043C; End_If; // RESET If ((RunForwardIn = FALSE) (*And (RunReverseIn = False)*) And (ResetIn = True)) then ControlWord := 16#04BC; End_If; Sample Horner PLC code in CScape 10 SP1 attached. tcp demo.csp

Hello marcellosalas Welcome to the forum. You have asked an interesting and potentially contentious question. There is a lot of myth and intrigue when it comes to energy saving and the VFD has been promoted very strongly as the means to solve the energy and the carbon crisis of the planet. I would answer : The VFD increases the losses in the motor by a very small amount due to the frequency components in the waveform. These comprise switching components and harmonics. The claims are that the VFD will improve the efficiency of the motor and that is wrong. Energy can be saved in some instances by slowing the machine down where full speed is not required, but the work output will drop also and often to achieve the same total work output, you can slow down and run for longer! In the case of circulation fans in say a cool store, energy can be saved as less air needs to be moved when product is down to temperature and the store remains sealed. Likewise, circulation pumps just circulating water in a pond will reduce energy consumption where less circulation is required. Transferring water between sumps can save energy where the maximum capacity (throughput) is not required all the time. Reducing the flow will reduce the frictional losses, but will result in longer pumping times. Applications where the motor is oversized, but still needs to run at full speed, will not save energy. Applications where the speed is constant and the coupling means has been designed for full motor speed, will not save energy. Pumping applications with steep curve pumps and variable flow demands can save energy where they are operating under constant pressure conditions. Pumping applications with flat curve pumps with the impellor selected/machined for design pressure at full speed will not save energy under constant pressure control. Commonly, the VFD has losses in the order of 2.5 - 3%. If harmonic mitigation is required, you should expect another 3% losses. The myth that you can use a high efficiency motor, but must add a VFD to a low efficiency motor to improve the motor efficiency is totally incorrect!

Hello everyone, I am exploring ways to enhance energy efficiency in our industrial motors and came across Variable Frequency Drives (VFDs). I understand they help control motor speed, which can potentially reduce energy consumption. However,, I have a few questions ::- What is the actual impact of VFDs on energy savings for different motor loads, especially in variable vs. constant torque applications: ?? Are there specific conditions or motor types where VFDs may not provide significant efficiency benefits: ?? How challenging is it to integrate VFDs with existing older motor systems, and what should we consider for a seamless installation: ?? Any insights from those with VFD experience in industrial setups would be very helpful !! Also; if anyone has seen noticeable ROI improvements after VFD implementation, I would love to hear about your results. Thanks in advance !! With Regards, Marcelo Salas

Hello Ewan If we apply a variable frequency variable voltage waveform to a three phase induction motor, the rotor will try to spin at the frequency of the applied voltage. - The induction motor is a pseudo-sychronous device. If the rotational speed of the magnetic field is higher than the motor speed, there will be an acceleration torque that will accelerate the motor up to synchronous speed. The motor will draw energy from the VFD. - current will flow from the DC bus, through the inverter to the motor. The DC bus will be charged by the applied rectifier and supply. If the frequency applied to the motor is less than the motor speed, there will be a breaking torque to slow the motor to synchronous speed (speed of applied waveform) This will cause the motor and the driven load to slow down. As the motor and load is slowed down, we are reducing the rotational kinetic energy. This energy is transferred to the DC bus and will cause the DC bus to rise. There is only a small amount of allowable DC bus, so we apply a Brake Chopper that pulses a connection to a large discharge resister. The excess energy from the rotational kinetic energy, is dissipated in the break resistor. The sizing of the resister is important. The resistance of the brake resister must be low enough to soak up the energy at a fast enough rate, but must be high enough to limit the discharge current to less than the maximum current of the brake chopper transistor. The resister must be large enough to absorb the total excess energy without overheating.

Hi Marke, I've got a question regarding Dynamic Braking. How does the Dynamic brake actually stop the motor from rotating? I understand that Dynamic Braking is the process of converting the kinetic energy of the rotating motor into electric power, then applying a resistor bank to that power to dissipate it as heat to allow the energy to be dumped into a brake resistor. With DC injection braking, a counter force is exerted on the rotor when the magnetic fields are aligned (N to S and S to N) as it rotates through the static stator flux. My understanding is clear with DC injection braking as I understand what's actually happening with the rotor & stator fields. I lack the understanding of Dynamic Braking. Could you please kindly shed some light if possible of how the Dynamic brake actually stops the motor from rotating? Thanks again Marke, Kind regards, Ewan