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    #16
    Originally posted by Jraef View Post
    that's where the line reactors help. They slow down the rise time of the surges and if the drive is running
    They slow down di/dt. For spikes, the concern is dv.

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      #17
      Originally posted by Besoeker3 View Post
      They slow down di/dt. For spikes, the concern is dv.
      Yes, the current through a series inductor is the integral of the voltage across it (plus a constant) and so it will slow down the rate of rise (and the rate of fall) of the current. Of course if you wanted the highest protection level you would add a surge protector in front of a line reactor to clamp any large voltage spikes before the inductor can store much energy from a voltage spike.
      It would be interesting to know what the stray capacitance is across a typical reactor inductance due to the interwinding capacitance. That would limit how much it could slow down fast rising voltage spikes

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        #18
        Originally posted by Besoeker3 View Post
        They slow down di/dt. For spikes, the concern is dv.
        His concern is "tripping out", which unless he returns and discloses the meaning of that, means it is all speculation at this point. But as a general rule, I recommend line reactors on almost all VFD applications, they are cheap insurance.
        __________________________________________________ ____________________________
        Many people are shocked when they discover I am not a good electrician...

        I'm in California, ergo I am still stuck on the 2014 NEC... We'll get around to the 2017 code in around 2021.

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          #19
          Originally posted by Jraef View Post
          Yes, line reactors. What a line reactor does mainly for a VFD is to slow down the rise time of any transients on the incoming line side, so that they don't cause the dc bus to spike up and either trip the drive, or damage the capacitors and diode bridge. I call them "cheap insurance" fro expensive drives.
          They also limit fault current.

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            #20
            Originally posted by Besoeker3 View Post
            They also limit fault current.
            And there we get to the purpose of a line reactor. If you have a small drive on a big transformer it cannot handle the available current. It can also block harmonics (the “rabbit ears” current pattern).

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              #21
              Originally posted by paulengr View Post

              And there we get to the purpose of a line reactor. If you have a small drive on a big transformer it cannot handle the available current. It can also block harmonics (the “rabbit ears” current pattern).
              but that available current isn't flowing unless something in the drive front end fails, at that point there is nothing left to protect as it has already failed, all the reactor will do is limit how spectacular the failure may be to watch.

              I live for today, I'm just a day behind.

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                #22
                Originally posted by kwired View Post
                but that available current isn't flowing unless something in the drive front end fails, at that point there is nothing left to protect as it has already failed, all the reactor will do is limit how spectacular the failure may be to watch.
                From what I understand the LR also limits the flow of current to the capacitors as they are first charged.
                Tom
                TBLO

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                  #23
                  Originally posted by ptonsparky View Post

                  From what I understand the LR also limits the flow of current to the capacitors as they are first charged.
                  It does. Some also have precharge resistors.
                  I live for today, I'm just a day behind.

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                    #24
                    The fact that the VFD tripping is happening more often during thunderstorms makes me think that they may be tripping due to voltage sags (dips) than a transient of some sort. But fault codes should help clear up the cause of the trips. Do the VFD's trip any other times besides thunderstorms?

                    Line reactors are a great investment for VFD's. They help reduce trips due to utility capacitor switching transients, and help reduce harmonic current distortion.

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                      #25
                      The problem with MOVs is that they are 'sacrificial--' every time they swallow up a transient, a little bit of them gets eaten away-- until (as someone said) they end up as an open or short circuit. I'm familiar with the 'home version' of line reactors-- the Zero Surge / Brick Wall surge protectors, with 'reactors' (ie coils of wire with iron cores and capacitors) inside them, which 'absorb' a surge and release it slowly (NOT to the ground line!).

                      I've had 4 Zero Surge units for years, and (knock on wood) have not had issues with power surges. I have heard the one guarding my computer HUMMMmmmm during storms, so there's hope they're still working properly!

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