Post By JST
Post By JST
VFD System Design - Filters, Reactors, Wire - Bridgeport 308 Rebuild/Retrofit
I didn't want to start another thread, but figured my question would be better answered in this section:
Taken from my BP 308 rebuild/retrofit thread:
While I have been away, I have been working out my electronics design. I am fairly new to VFD's (industrial controls for that matter) but have been trying to learn as much as I can in my free time. This post is more of a suggestions / what do you think type of request. I have decided to go with the AJAX CNC kit for 3rd party drives and will most likely us the CNC11 control system.
Little background on the machines operating environment. The power was checked at the breaker and if I remember correctly it was right around 237V. It is in a residential environment (3 phase on the poles outside) with the nearest industrial sites 10-15 miles away so the power does not fluctuate very much (assuming a pole doesn't get crashed into). In the garage there is a medium size drill press, contractor table saw, pedestal grinder, mini lathe, DC/AC TIG (near future), and miscellaneous other hand power tools that could be running at the same time. In the future it could be moved into a pole building with additional CNC/manual machining equipment located in close proximity.
The machine will use its existing 5HP 460V (not dual wound already checked) ATB inverter duty motor powered by a Hitachi (explain why below) inverter off a 15-20 KVA buck/boost transformer. I am keeping the original motor due to the cost of inverter duty motors and the much cheaper price of a transformer. Plus running at 460V will help the motor run a little bit cooler than a 230V motor. 3 phase is not an option, I have already set my mind on a single phase system. This is the reason for doubling the size of the VFD.
Hitachi SJ700-075HFUF2 10Hp | 380-480V 18A 3 Ph Input | 380-480V 16A 3 Ph Output
-I chose the hitachi for a few reasons: Phase loss detection disable, internal dynamic braking unit (adding external resistor), and encoder input card for orientation control (tool change/rigid tapping). The cable run from the VFD to the motor will be a max of 15' since the control cabinet will be separate from the machine on casters. I will be using Belden 29501 VFD cable to help avoid noise and preserve the signal. The motor itself has an encoder and there is a second encoder on the spindle for orientation.
With my power source and current/future workshop would I require all the AC line/load reactors and filters recommended by hitachi (see below). These accessories may be for a machine operating in a much nosier and power hungry enviroment or just Hitachis way of putting more money in their pocket. However, I do not want to skip a few hundred dollars now and blow a motor/VFD a year down the road.
Would running additional equipment off the same buck/boost transformer as the machine cause spikes in the power that would require the AC line reactor and filters to protect the VFD (in this instace the transformer would be larger than specified above)? Or should I keep the transformer as a dedicated unit to this machine (sized to the machines needs)?
Thank you in advance -B
well thought out post!
i will hit a few points I see before miller time here in OH.....
- buck boost xfmr fine for upping 230 to 460 no issue there
- well picked on 2x sj700 model 10hp for 1ph input
- nice you are going with shielded vfd motor cable
- the hitachi diagram shown is NOT to RECOMMEND you buy all that stuff (to put bucks in their - or our as distributor - pockete ) but just to show all the possible options.
- the ac input filter is more to protect the OTHER stuff on that power line, not to protect the vfd. that said, do you need it? prob not. the way you will find out is if you do power other stuff and that other stuff acts flaky from the vfd noise not filtered out by the added filter. I think if you took a survey you would find only 1-2% of folks on this forum add the input filter and their machines are powered directly from the 230v or 460v source that feeds other stuff too. I would say dont bother with it unless you have problems with the other stuff (not needed for the vfd)
- output reactor? hee hee, there is another thread here on that very topic right now. My vote: no way you need it for your setup.
Thanks Mike. I was under the impression the filter was to clean the incoming power to the VFD, rather than to protect other equipment on the same power source. Looks like I will just go with the line reactor.
I feel a good bit embarrassed about this, but we all make mistakes. I am not around the machine during the week and crossed the original VFD specs with the motor specs (the inverter was 460V 4KW 60Hz)!
ATB, UVF 100U/4R-12S, 2.2kW
330V Y 7A 50Hz
I am getting ready to order the correct size VFD required and want to make sure I get the smallest drive necessary. It took me a while to figure out how to deal with the 330V 50Hz specs, but I think I got it worked out. I want to try and maintain the V/f within a 10% variance when changing between 50 and 60Hz.
V/f @ 50Hz = 330/50 = 6.6 (10% variance: 5.94-7.26)
V/f @ 60Hz = X / 60 = 6.6, or X=396V (10% variance: 354-435)
The transformer I have is rated at 410V @ 22Amps. So, V/f = 410 / 22 = 6.83 or within 3.4% of 50Hz V/f. So would running the motor at 410V 60Hz be safe for the motor and VFD?
Is this an acceptable calculation for 50 to 60Hz power change: P(60Hz) = P(50Hz) * (60 / 50) or P(60Hz) = 2.2Kw * (60 / 50) = 2.64kW or 3.54hp.
Doubling this would give me a little over 7hp, so can I get away with a Hitachi SJ700 7.5hp VFD (output 14 amps)? Or is there something I am overlooking with the current?
gotta run so just quick reply: MOTOR cares about v/hz curve, VFD DOES NOT CARE. So, no issue with INCOMING power to the vfd!
your motor is rated 3hp: just buy a wj200-002HFU (double ck part no?) or equiv as it comes MADE for 1ph input and 3ph output WITH NO DERATE on 3hp model I believe!
Make sure you pick the "400 v class" high voltage vfd model since u will be supplying 410v
good write up!
I would not bother with an inductor - remind us again why you would add it?
The reason for the inductor (line reactor? - winding around iron core - making sure I'm following you correctly) is to protect the VFD. I'll pay a little over a $100 to avoid a spike that kills a +$700 VFD.
I believe I need a flux vector drive to allow for a true closed loop system, thus the SJ700 series. The flux vector will allow for the proper level of speed and torque control required for rigid tapping. My motor does have a shaft mounted encoder in addition to the spindle encoder.
Again, I am new to all this and still learning. Please correct any of my incorrect assumptions.
If it were MY machine, I would save the extra $100 and take my wife to a fine dinner instead; today's spike/short protection on vfd's is in my opinion 90% accurate - or higher - and I'd say the total times per year a spike/short will happen to you is maybe 1 time, so if you go to dinner instead of buying the inductor youi will be good for statistically 90 years before it will fail. (not sure on that math but it sounds good!)
For rigid tapping yes, sensorless vector is better choice. Know the SJ700 in small size is still being sold (3ph models), but really superseded by next gen model WJ200 (faster, better, cheaper) in your sizes.... consider it. also consider the 1ph input wj200 in 240v size for this motor.... but u have 410v xfmr...... interesting delemna on cost vs performance...... this would take some thinkin - maybe Jraef/others will jump in with their thoughts - I gotta run to finish WORK stuff now...... i'll think about it later.
I didn't realize that the spikes were that rare. I was under the impression it was something that was seen regulary. Its been a while since I went out to eat so I might just follow your advice.
The reason for my usage of 410V was mostly due to the motors 330V 50hz rating. I am trying to maintain the V/hz (50->60) variance below 10%, based on what I have read.
I'll look into the WJ200 series VFD's. I found the SJ700 on drives warehouse using the drop down menu, 7.5hp > 380-460V > Flux Vector. At this point the only thing I have ordered is the cable, so I am open to alternatives.
I dont want to confuse the issue of everyday all the time spikes and big spikes.... just the way the vfd works you will have about 700 v peak 'spikes' anytime it is running on 230v input or 1200-ish volt spikes anytime running on 460v.. when i said only a couple times a year spikes, I meant like ligthning strike nearby causing a 2000v or 3000v spike on our power system - at same time you are using the vfd..... so not very often likely...
how would you feel about having your motor capable of not 3hp but 240/330*3= 2.2hp instread?
if you bought the 1/2 price 240v wj200 3hp 1ph input 240v model instead, you could program it to be on same v/hz curve but stop at 240v point. so 240v@ 240/330*50hz= 36hz instead?
You would get 2.2hp instead of 3, base speed would become 36hz instead of 50, base speed would be at 240v instead of 330v, and base speed would be 1500*36/50 or 1080rpm instead. then you can go upto 72hz for 2160rpm max or maybe higher before you run out of torque....
just an idea.
i looked at your motor nameplate just now and see why it is 330v@50hz - it is to allow voltage to continue upto 400 or 480 at higher speed to get to 8000rpm top speed! did you plan to run to 8000rpm? cuz if you did you probably need 480vac input....
ck price of 1ph input sj700 or wj200 or teco etc to see price savings to see if it makes sense...
The biggest reason for line reactors is to reduce the huge capacitor charging current surge that occurs twice per cycle per input phase. Basically a power factor improvement that helps the rectifier.
Originally Posted by EdwardsB
Thank you both for the help and information.
I have a lot of research to do yet. I underestimated this as a "my motor is X rated hp, I need a VFD of 2*X hp". Not completely following you on how I can reach 8,000 RPM. It would be a nice feature to have. I was under the impression that the VFD output a constant voltage, and varied the frequency. I dont think I fully understand the relationship between voltage and frequency between the motor and VFD. And how my choice in voltage will effect the speed of the motor.
My understanding was I need the VFD to output a voltage of Z (determine by V/f between the motors 330V and 50hz to 60 hz), and the frequency would be varied between 0-X hz by the VFD. This would then change the motor speed based on Speed = 60*Freq/# poles.
I must be misunderstanding some relationship between frequency and voltage and how they relate to motor speed. Also, I dont think I fully understand how you interpret the motors nameplate when applying it to a varying speed VFD application. If it was a single speed VFD application it makes sense to me, but throw the varying speed/VFD in and not so much. I just want to make sure I do not burn my motor/VFD up by not choosing the correct operating ranges.
Not asking any of you to spoon feed me everything. This weekend I'll have time to go through and figure this stuff out. If you can direct me to a good article or thread where my questions are already answered I would really appreciate it.
OK... any motor has a relation between voltage and frequency... A 60 Hz 240V motor has 4 "volts per Hz", since 240/60 = 4.
So what.....? here's what..... the motor wants that volts per Hz to always be the same. If you set the VFD to 30 Hz, the voltage should be 120V.......... at 15 Hz, it should be 60V, and so forth. That may be "adjusted" a bit to compensate for losses, but it is basically true. It keeps teh current flow essentially constant at any load over frequency.
If you gave it too much voltage, excess current would flow, and the motor would overheat, etc.
OK... The constant current produces constant torque, but the lower speed reduces total power in proportion to speed (rpm).
To get constant power, the current would need to go up as speed went down, but the motor cannot take that.
Going ABOVE 60 Hz, you probably "run out of voltage", the VFD is limited by input voltage, so while you can RUN at say 120 Hz, the voltage is too low by half (your 240V motor would need 480V) , and so you get less torque (due to less current) but more speed.... leading to approximately constant power.
Now if you used a 480V VFD, you could set it for constant V/Hz all teh way to 480V, and your 240V motor might be capable of double rated power..... same current and torque, double voltage and speed, which means double power.
a 1 HP 240V motor at 60 Hz is 1 HP. At 30Hz, it is 1/2 HP, at 15Hz, about 1/4 HP. At 120Hz with a 240V VFD, it is probably close to 1 HP.
Go really slow, like 10 Hz or so, and the motor may not cool well because the fan is weak at slow speeds. Fans tend to drop output by the speed reduction cubed, but motors don't lose much dissipation with lower rpm.