Gaahhrrrgh! I have been trying to learn more about Varialbe Frequency Drives and had a question regarding how the output of the drive functioned. 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. This is more a misunderstanding than a myth. Have a look at Page 9 (actually the 10th page), specifically Fig. Already a member? All quantities are normalised so that the rated or base value is 1.0. Required fields are marked *. Please let us know here why this post is inappropriate. However, VFDs provide not only a variable frequency output to the motor, they provide a variable voltage output as well. 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. However, this frequency conversion process causes 2% to 3% loss as heat in the VFD — caloric energy that must be dissipated. 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. The current however will follow the torque, so it will stay essentially the same (leaving losses out of it for the moment). So in your example, at 230V and 30Hz, you motor is outputting the same torque as it would at 460/60, but because the speed is half, so therefore is the shaft HP. See here for more details: https://www.emainc.net/2016/08/23/vfd-s-still-save-energy-a-lot-of-it/, Your email address will not be published. The equal harmonics tend to cancel each other, but the odd harmonics do not. By joining you are opting in to receive e-mail.

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. For a better experience, please enable JavaScript in your browser before proceeding. The drive's power factor was the part I was struggling with. Amperages on the output lines from the VFD supplying the blower are L1 11.0 amps, L2 10.2 amps, L3 11.0 amps.

At EMA we’ve been applying and servicing VFDs for over two decades now, and we’ve learned to trust the drive output readings. When under load the input current increases to about 200A, while the output current shoots up well over 300A. 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. 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. I have a 250HP VFD supplied with 472VAC. JavaScript is disabled. To summarise, Figure 4 shows how the input and output current of a typical AC drive vary as the speed and torque vary. However, VFDs provide not only a variable frequency output to the motor, they provide a variable voltage output as well. Click Here to join Eng-Tips and talk with other members! Thank you for helping keep Eng-Tips Forums free from inappropriate posts.The Eng-Tips staff will check this out and take appropriate action.

This is only possible because the current measurements are sampled rapidly and accurately. Copyright © 2020 VariableFrequencyDrive.net, All Rights Reserved. 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. 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. Why oh why can't we edit our posts?? Already a Member? Perhaps this is not a myth but a misunderstanding. Among, the. In most modern drives this is accomplished by using Pulse Width Modulation (PWM) . There is only a single line for the output current since it scarcely varies with speed. What's the FLA of a 5HP 230V motor? VFD Input vs Output Current. 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. I can only assume it may have something to do with the harmonic content of the conductors feeding the VFD as apposed to the … The 3 phase input voltages to a VFD are more or less static. 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? 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. 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.

VFDs manipulate the frequency of their output by rectifying an incoming AC current into DC, and then using voltage pulse-width modulation to recreate an AC current and voltage output waveform. Some Considerations for Using Variable Frequency Drive. From my understanding the input … 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. Myth No. 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. Is this normal?

You need to distinguish between two things: the torque that the motor is supplying to the load, and the torque that the motor is _capable_ of suppling to a load. For a VFD fed induction motor, a very rough approximation is that the current required depends upon the torque output. Errors actually exist in measuring current and power consumption with harmonic components by conventional instruments. 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. 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.

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.

The charts are dealing with other issues, but the idea is that the current will remain roughly the same. Please explain. (Power = Volts times Amps). 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. VFD Input Current Vs Output Current. How Does VFD Accelerate or Decelerate Motor? But, if you measure both currents, you will often see that the input current is much lower. Ozmosis' explanation helps a lot. See how the Generative Topology Optimization extension automatically delivers high-quality, lower-cost, manufacturable designs.

Scotty, I think you forgot to post a link. Keeping our warfighters safe and delivering them a competitive advantage is a key goal of departments of defense around the world. The POWER has dropped, i.e. The measurement methods are almost always considerably more precise and reliable than external measurements. 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. 15.2A. It doesn’t seem to align with the idea that the VFD should have some losses due to its own thermal component losses, so input should always be slightly higher that output. The process also yields overvoltage spikes and harmonic current distortions. Registration on or use of this site constitutes acceptance of our Privacy Policy. Thread starter blues; Start date Aug 9, 2012; B. blues Member. Consequently, one can find significant currents flowing at the 3rd and 5th harmonics especially (180 hz and 300 hz) and these currents can, if unmitigated, not only cause power line and equipment problems, but can result in erroneous power and current measurements. Is input current of VFD smaller than output current? While harmonics in the PWM output can easily be filtered by carrier-frequency-related filter inductance to supply near-sinusoidal currents to the motor load, the VFD's diode-bridge rectifier converts AC line voltage to DC voltage output by super-imposing non-linear half-phase current pulses thus creating harmonic current distortion, and hence voltage distortion, of the AC line input. ----------------------------------  If we learn from our mistakes I'm getting a great education! Amperages on the lines supplying power to a VFD for a blower are L1 19.1 amps, L2 9.2 amps, L3 19.2 amps.

The 3 phase input voltages to a VFD are more or less static. At frequencies below 60Hz, the output voltage from the VFD is below the line voltage. That is, at half speed, the output voltage is half, so the output current is double. Since VI in = VI out (or Power in = Power out, P in = P out), the output current must be higher than the input current.

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. 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. But to specifically answer your question, the torque remains the same in a Constant Torque application. !. *Eng-Tips's functionality depends on members receiving e-mail. This white paper shows how collaborative robots can play a role in helping companies succeed in the Covid-19 world: to help with social distancing, ramp up new lines quickly and reshore existing products due to interrupted supply chains. 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.

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