These readings are with the VFD supplying the blower at 60 hertz. The equal harmonics tend to cancel each other, but the odd harmonics do not. 15.2A. The HP is changing with speed however. See how the Generative Topology Optimization extension automatically delivers high-quality, lower-cost, manufacturable designs. Have a look at Page 9 (actually the 10th page), specifically Fig. For a better experience, please enable JavaScript in your browser before proceeding. Your email address will not be published. However, VFDs provide not only a variable frequency output to the motor, they provide a variable voltage output as well. Scotty, I think you forgot to post a link. I can only assume it may have something to do with the harmonic content of the conductors feeding the VFD as apposed to the … Perhaps this is not a myth but a misunderstanding. (Power = Volts times Amps). Texas by the Gulf, geat crab, great shrimp. Although its not advised, most modern VFDs can take a phase to phase or phase to ground short, and trip off in time to save the output devices. When the VFD supplies the blower at 40 hertz, these are the readings: Input lines to VFD – L1 9.6 amps, L2 0.5 amps, L3 9.6 amps; Output from VFD to blower – L1 6.4 amps, L2 6.5 amps, L3 6.5 amps. Gaahhrrrgh! Amperages on the output lines from the VFD supplying the blower are L1 11.0 amps, L2 10.2 amps, L3 11.0 amps. As an analogy, think about the current that a transformer is supplying to operate a particular load, versus the current that the transformer is capable of supplying without overheating. Keeping our warfighters safe and delivering them a competitive advantage is a key goal of departments of defense around the world. Should have said that you can only get real power flow with current and voltage of the same harmonic order, so if you have a reasonably sinusoidal voltage then you can use a first order approximation that the active power transfer only takes place at fundamental frequency. Since the power being consumed by a VFD will always equal the power output of a VFD plus the internal drive losses, this means that if the output voltage is less than the input, then the amperes will be higher than the input. Login. Since VI in = VI out (or Power in = Power out, P in = P out), the output current must be higher than the input current. From what I have read it appears that as the drive changes the speed of the motor by adjusting the frequency, the drive will also adjust the voltage to maintain the appropriate voltz/hertz ratio, and constant torque. Why oh why can't we edit our posts?? Please explain. 6. Copyright © 1998-2020 engineering.com, Inc. All rights reserved.Unauthorized reproduction or linking forbidden without expressed written permission. When measuring VFD input current and output current some people become mystified with the current values read on the input side vs the output side. With Creo 7.0, you will be able to design the most innovative products faster than ever before, keeping you on the cutting edge of product design and ahead of your competition. This is more a misunderstanding than a myth. If I turn the speed to 50%, it is now a 5HP 230V motor. VFD Can Replace Regulating Valve and Air Damper, VFD Frequency is Difficult to Up-regulate Troubleshooting, Variable Frequency Drive On-load and Non-load Debugging Steps. They may vary by a small amount, but in general, a 2300 volt input is going to be relatively stable. I can only assume it may have something to do with the harmonic content of the conductors feeding the VFD as apposed to the conductors leaving the VFD once the line reactor has filtered out the harmonics to the pump. Drives, Soft Starters, and Harmonic Filters, https://www.emainc.net/2016/08/23/vfd-s-still-save-energy-a-lot-of-it/, Yaskawa’s new Z1000 HVAC VFD to replace the popular E7 VFD. !. Aug 9, 2012 #1 I would like to know why the input current of a VFD would be differnt than the output from the VFD to say a 200hp, 3ph, 480v motor load. The 3 phase input voltages to a VFD are more or less static. Often times, the output current will be higher than the input current! Commentdocument.getElementById("comment").setAttribute( "id", "afd0db00dc2eaa57428cc16f634e9acc" );document.getElementById("c01c2cc14d").setAttribute( "id", "comment" ); If you are a human, do not fill in this field. It’s a goal shared by embedded computing manufacturers like Abaco: we never forget who we serve.This case study describes how a major international contractor integrated an Abaco single board computer at the heart of its CAS/CSAR solution. For a VFD fed induction motor, a very rough approximation is that the current required depends upon the torque output. The process also yields overvoltage spikes and harmonic current distortions. VFD Myth #5: The Input Current of a VFD Should be Higher Than its Output Current. Input current of the VFD is related to the power required by the motor, the supply voltage, the efficiency of variable frequency drive and the power factor. But to specifically answer your question, the torque remains the same in a Constant Torque application. There is only a single line for the output current since it scarcely varies with speed. Some VFD users check their output and input currents with a current clamp meter or by using VFD display monitors and find that the input current is much lower than the output current. VFD Input power vs. output power. Click Here to join Eng-Tips and talk with other members! Jump to Latest Follow 1 - 8 of 8 Posts ... my output current is about 80 amps and measured output voltage is about 370V while my input current is approximately 35 amps. In most modern drives this is accomplished by using Pulse Width Modulation (PWM) . In other words, to produce full torque at half speed requires the same current as producing full torque at full speed. VFD Input vs Output Current. the kW (which is the HP) so the energy use (kWh) is going to be less, but of course, that's because you are doing less work. The 3 phase input voltages to a VFD are more or less static. What's the FLA of a 5HP 230V motor? Due to the non-sinusoidal currents, the input voltage can be distorted by currents flowing at frequencies other than the power line 60 hz. For example if 480V motor is operating at 60hz and is then slowed down to a frequency of 30hz the drive will compensate by proportionally dropping the output voltage to 240V. Electric motors & generators engineering Forum, Solutions Brief - Protecting and Rescuing On-Ground Personnel, White Paper - Cobots vs Covid: Today's Manufacturing Reality and Tomorrow's New Normal, Datasheet - Creo Generative Topology Optimization Extension. ---------------------------------- If we learn from our mistakes I'm getting a great education! When under load the input current increases to about 200A, while the output current shoots up well over 300A. When the VFD is running, the input and output currents contain higher harmonics, it’s difficult to measure the phase angle and errors occur in traditional measurement methods. Required fields are marked *. Think of it this way just using the NEC motor FLA charts; If I have a 10HP 460V motor, the FLA is 14A. The drive protection circuits in modern drives are excellent, which is why output device failures are very low given the fact that they routinely switch large currents. I have a 250HP VFD supplied with 472VAC. EMA can supply your VFDs, we can repair your existing VFDs, and troubleshoot VFD problems.. we work on both low voltage and medium voltage VFD s. Call your nearest EMA office as listed below, or use our contact page to email us. Please let us know here why this post is inappropriate. This non-linear amp draw can be mitigated somewhat by using phase shifted input bridges, which have become common in high horsepower VFD equipment, but nonetheless, it remains non-sinusoidal. If I know the output current rating of a generic 6-pulse PWM VFD, is there a good rule of thumb for determining the input current (rms) to achieve this output into a typical induction motor? VFDs do not draw sinusoidal current from a power line, they draw pulsating currents, which can appear to many measuring instruments as DC currents. For example if 480V motor is operating at 60hz and is then slowed down to a frequency of 30hz the drive will compensate by proportionally dropping the output voltage to 240V. The charts are dealing with other issues, but the idea is that the current will remain roughly the same. This doesn't seem right to me. VFD Input Current Vs Output Current. However, this frequency conversion process causes 2% to 3% loss as heat in the VFD — caloric energy that must be dissipated. How Does VFD Accelerate or Decelerate Motor? A blower is a variable torque load, so based on the affinity laws, the power consumed should drop exponentially based on the speed of the load. Logic dictates that, because a VFD should lose current due to its own thermal component losses, a VFD’s input current should be slightly higher than its output current. JavaScript is disabled. Yes this is normal for a blower. Among, the. Close this window and log in. RE: Determining VFD Input current ScottyUK (Electrical) 22 Jan 08 14:27 Should have said that you can only get real power flow with current and voltage of the same harmonic order, so if you have a reasonably sinusoidal voltage then you can use a first order approximation that the active power transfer only takes place at fundamental frequency. As an analogy, think about the current that a transformer is supplying to operate a particular load, versus the current that the transformer is capable of supplying without overheating. At 1400rpm (full running speed), and no load, my output current is about 80 amps and measured output voltage is about 370V while my input current is approximately 35 amps.
Gyumri Population, Right Through Me Marnix Emanuel Lyrics, Steward Health Choice Address, Dte Dinosaur Quest, Samson Kayo Age,