[oxford]

I was looking at Ac drives and the their peripheral electronics.

What role do the magnetic contacts play?

Do you need a emf line filter?

Is it ok to step up 110V to 220V to meet drive voltage requirements?

Thanks

[Al_The_Man]

Not quite sure of the questions, but for VFD's often the manufacturer will recommend three phase chokes or reactors, in some cases I have fitted them on the input and output.
Most hobbiests do not bother it seems.
Magnetic contactors? These are uses to disconnect three phase power to the VFD input, never between VFD and motor.
They are usually picked up when the E-stop is released to put the VFD in the ready condition.
There is usually nothing wrong with raising the voltage by transformer for example, if the VFD warrants it, keep in mind the 120v current will be double the 240v current draw.
Al.

[oxford]

I think that answers the question.

Here is an image of the wiring of a drive that I was talking about

Thanks

[oxford]

Anyone know of a good source for magnetic contacts?

Thanks

[Al_The_Man]

You can pick up Telemecanique contactors off ebay, the DIN style DIN rail mount are nice and compact.
Other makes are Allen-Bradley and Square D etc.
Al.

[oxford]

How important is it for the contactors to have surge suppressors?

[Al_The_Man]

If you mean RC snubbers across the coil, I would recommend it for AC coils and reverse diode for DC coils.
Al.

[oxford]

Are there any type of Contactors that are not compatible with a RC snubber?

[Al_The_Man]

An RC snubber goes across any contactor coil if it is AC, A DC coil takes a reverse EMF diode.
Al.

[oxford]

Is the RC snubber type determined by ac voltage?


Thanks

[Al_The_Man]

Previous link.
http://cnczone.com/forums/showthread...hlight=snubber
The capacitor max voltage rating has to exceed the applied voltage.
The values can change according to the energy stored in the device.
The one shown is good for the average solenoid and most DIN style 3 ph contactors.
Al.

[oxford]

In the AC servo drive set up, there is a Molded Case Circuit Breaker before the Magnetic Contact. Is it possible to just use the right rated circuit breaker that can be found for cheap at the hardware store... The kind you find in your basement fuse box?

Thanks

[oxford]

How important is an AC reactor?

Thanks

[mactec54]

oxford

You should use the molded case circuit breaker, Fuji have a great one,(there are others as well that will do the job)I would not use the a magnetic contactor, Use solid state relay, in place of this, a lot less trouble, & cheaper in the end, nothing else is need if you use sheilded cable were you can,(IGUS cable) & twist all the wires were you can as well

[Al_The_Man]

How important is an AC reactor?

Thanks

Mitsubishi recommend using one for power factor correction, it also helps with preventing switching noise being imposed on the incoming line.
Most of these are three phase however. In which case you use the two outer sides.
You may not notice any appreciable difference in performance without it.
The three phase conductors from VFD to motor should be twisted together tightly.
And the ground should be run parallel to these, service ground to VFD and from there to the motor frame.
Al.

[oxford]

Thanks for the advice.

Will one AC reactor clean up the power line for multiple drives?

Are solid state relays not used in industry because of tradition?

[Al_The_Man]

Many companies are becoming conscious of the effect of power factor correction to lower the monthly power bill, but as well as power factor, harmonic distortion has to be measured in order for the correction to be effective, VFD's are one source of H.D.
So if line reactors are fitted, this lowers the cost of the correction equipment.
I usually fit one per VFD, and on occasion fitted them on the motor side of the VFD.
Up to 120hz, the reactance is fairly low, but high frequency energy spikes on the motor line are prevented from coming back and damaging the VFD electronics, if they can be suppressed first.
For a shop with one or two machines, the input side reactor may not show any saving, but it will help in suppressing harmonics getting back into the system that may affect other equipment.
Al.

[oxford]

Is the power factor related to the phase angle between the current and voltage?

[Al_The_Man]

Essentially yes, an ideal power factor reading is unity or 1. when the current is in phase with voltage, anything below .9 is considered correctable with cost saving.
There is a probably a vast number of sites that will give alot more information if you need it.
On line motors are a big contributor to poor power factor, in this case, capacitors are switched in as needed to bring the P.F. closer to unity.
Al.

[wildwestpat]

Hi Oxford

You have recieved a lot of good advice since you started this thread in the fall of last year. The best advice is to treat the VFD and motor leads as capable of generating severe radio frequency interference. The VFD should be well screened inside but the leads to the motor should be kept as short as prtactical and if possible mount the VFD on the motor. The leads should be screened either using special cables or using metal conduit that is well bonded at each joint to the erath pin of the VFD at one end and the motor frame at the other.

The VFD is an electronic bundle of tricks that takes the incoming public mains supply converts it to DC and then chops up the DC into three phase alternating current at a variable frequency. The chopping action takes place under electronic control at very high frequency. It is these high frequencies that give rise to the need to both screen the motor leads and to use a filter (reactor). The closer the filter (reactor) is fitted to the VFD the better. But the interference producing potential of VFD motor controls is leading to widespread adoption of VFD modules that have the filter (reactor) built into the VFD. It is worth checking to see if your VFDs have filters built in. The filters are now mandated in Europe. There is an increasing class of variable drive motors that have integral VFD as the VFD part of the overall cost is falling also the need to match the motor to the VFD is assured.

The power factor of the VFD should be close to unity and will have been compensated for by the VFD manufacturer. Large industrial concerns get hassel from the generating companies if they draw power that has a poor power factor. Power factor correction is normally seen in lighting circuits where flourescent lamps are used for industrial / commercial buildings. Large capacitors are connected between neutral and live to correct for the phase difference between current and voltage thus avoiding difficulties with the electricity supply company as well as making sure that the cost is minimised. (Power = volts multiplied by current multiplied by the power factor, For example a power factor of 0.8 means you would be paying 20% more. Conecting capacitorsaccross the load, or more rarely inductances in series, which themselves consume negligable power but ensure that the cost of energy billed is reduced by bringing the voltage and current into phase which is what is meant by unity power factor correction.)

The motor should be turned on and off during normal operation with the VFD control wires or if the VFD does not have an on/off comand then by switching the public mains supply to the VFD. Never ever switch the motor leads between the motor and the VFD with the VFD live. To do so can wreck the VFD electronics.

The use of an electro mechanical or electronic switch depends on several factors. The local health ans safety regulations will stipulate if emergency switches are required and may stipulate that electro magnetic switches (contactors) are used. Many industrial installations will have a single emergency stop system probably with a number of prominently located push for off switches that break the hold on current in the main workshop contactor. To prevent accidental restarting the reset switch is normally a key switch or is in the supervisors office. Most machines in addition have an E-stop which should be within reach of the operator - as they get wound into the machine? Where there are computer controls and other sources of power than the basic electricity supply then the emergecy stop arrange ments can become very complicated. A simple example is a power hoist where simply cutting the motive power may not operate the brake that prevents the load decending. A search of the web will produce charts that show the requirements. For my own part I like to fit a single electro mechanical contactor that will isolate the entire workshop leaving the overhead lighting on. The perimeter of the workshop is fitted with emergency stop buttons with the reset being a key switch. The contactor on key switch is held by the supervisor who alone has the responsibility for reseting the contactor. The contactor is not wired with auxiliary contacts as a volts trip as this function has to date been provided on each individual machine. Each individual machine has its own E-stop which in some cases does not stop the machine but moves the machine into a safe null state.

Just one further point each VFD should have its own filter (reactor) taking into account the need for screened leads / enclosure if the VFD does not contain the required filter. There are installations where multiple VFDs are placed in a metal screened cabinet along with other control circuitry and here it is common to find that a single filter (reactor) has been used.

Looking back through the thread I ask are you thinking of multiple motors and saving cost by having just one VFD. If so there are multipole plug and sockets that would permit you to interlock the three VFD motor feed wires to the incoming mains supply contactor. The requirement would be to ensure that normally the VFD is isolated from the mains by interlock switch on the mains supply before the motor can be disconnected. There are availabble enclosures that have a mains isolator switch built into the cabinet locking handle. Place the VFD and motor change-over arrangenents inside the cabinet. That way the VFD is powered down by removing its mains supply pror to getting at the motor to VFD wiring. These interlocked enclosures are available for DIN rail mounted contactors and many VFDs are also DIN rail mounted.

The use of a domestic portable radio is a great test for satisfactory shielding of the wiring and efficient filter no matter where you stand on the music while you work question.

Hope this helps.

Regards

Pat