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    #16
    Originally posted by elec_eng View Post
    This confuses me a lot. Is the A-B-C (CCW) phase sequence/rotation the same as the A-C-B (CW)? By looking at the phasor diagram, I thought they are the same but I want to make sure.

    I have a utility with A-B-C (CW) phase sequence and I need to parallel generators that have A-C-B(CW) sequences. Here is what the generator phasor diagram says

    "When electrical energy is generated, the phasing is clockwise A-B-C"

    So Basically do they have the same phase sequence? I don't have to worry about swapping any phases in the field?
    No matter what the diagrams say, you should always field verify rotation.

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      #17
      Originally posted by Xptpcrewx View Post
      True but when speaking about system rotation it is purely electrical and not mechanical/physical. In other words, the direction of shaft rotation should already be fixed/specified/determined by the prime mover. The OP first needs to figure out which torque is being applied by the prime mover (CW or CCW), then we can talk about what electrical sequencing to expect for that machine. Once that is known, system rotation can later be discussed.
      Commissioning a new plant with over 100 drives I had the contractor confidently tell me that if you connect a motor L1 L2 L3 it will go clockwise looking at the shaft. Our drawing office hadn’t told him the whole works phase rotation was reversed. He wasn’t happy, even less happy when I wouldn’t let him reverse the drives at the MCC.
      [COLOR=#000000]The reports of my death are greatly exaggerated.[/COLOR]

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        #18
        Originally posted by Tony S View Post
        Commissioning a new plant with over 100 drives I had the contractor confidently tell me that if you connect a motor L1 L2 L3 it will go clockwise looking at the shaft. Our drawing office hadn’t told him the whole works phase rotation was reversed. He wasn’t happy, even less happy when I wouldn’t let him reverse the drives at the MCC.
        People struggle with the phasing/connection sequencing concept a lot. They think system rotation is just like a damn motor and it’s only a CW or CCW thing, so they look for the easiest physical place to start swapping phases. Then they get angry when you tell them swapping two phases there isn’t the solution and actually causes more problems....

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          #19
          On the Matter of the best Engineers.....

          Originally posted by Cow View Post
          I wish some degree of field experience was a prerequisite to getting an engineering license.

          I have nothing else to add here.
          The Best ones are those who do go into the field and lay hands on tools and systems.
          The best HVAC instructor I ever had was a Utility Electrical Engineer.
          The other class that has been referred to I find mostly insufferable. They might be called " Theoretical " Engineers.
          Also people who put things right in the " Field " can and should be classed as " Service Engineers." As is often the case, they see, deal with, and solve matters that designers have never considered and do not know about in real terms. This often times happens with the enlistment of " other " Engineers than the ones who have created the problem. This is a case of the best mechanics and the best on the university side getting things done that no one else is held accountable for.
          Microwave Radiation Dangers should be openly discussed

          Comment


            #20
            Originally posted by elec_eng View Post
            This confuses me a lot. Is the A-B-C (CCW) phase sequence/rotation the same as the A-C-B (CW)? By looking at the phasor diagram, I thought they are the same but I want to make sure.

            I have a utility with A-B-C (CW) phase sequence and I need to parallel generators that have A-C-B(CW) sequences. Here is what the generator phasor diagram says

            "When electrical energy is generated, the phasing is clockwise A-B-C"

            [COLOR=#ff0000]So Basically do they have the same phase sequence? I don't have to worry about swapping any phases in the field[/COLOR]?
            No, anytime you have two different AC power sources, there will always be two different phase sequences.

            Your generator could be running faster or slower that will have effect on the frequency of the output power.

            Besides, your generator prime mover-- being mechanical in nature-- whose speed could be unstable to provide sustainable synchronization-- especially when load is applied or removed.

            Your worries about what rotation would be needed in reference to the grid-- is just as important in terms of how important phase sequence is.

            There are four conditions that must be met in order to have a successful power synchronization set up.

            1. Phase Sequence

            2. Voltage Magnitude

            3. Frequency

            4. Phase Angle.

            Each power generation source should have the same characteristics.

            A synchroscope did help in synchronizing two power sources in the old days, but it requires human intervention. The operator has to throw the switch at the right moment when the synchroscope stops spinning CCW.
            Throwing the switch on at the wrong time and you could end up with a very expensive metal junk.

            All of the above problems were overcome by the arrival of inverters that convert DC to AC through the use of solid state HV thyristors.

            In today's technology, there is such a thing called asynchronous HVDC link back to back that is used to connect two different power sources of different voltages, frequencies, and phase angles. This is a technology that is getting popular worldwide. It involves tying regional grids to provide more reliable power source.

            We, Southern Californians have been using this technology for decades in our PACIFIC INTERTIE dc link from a hydro plant that provides supplemental power supply from station located 850 miles from an Oregon hydro-station.
            The station provides about 500 kilovolt -- 3100 megawatts of DC power to a substation nearby where I live.
            We need all the power we can get during the hot summer months.

            My references above may not collocate with your original query, nevertheless, they involve similar basic fundamentals as applied in synchronizing two dissimilar power set up.

            These principles can be applied also in lower voltages like yours.

            I suggest you read some abstract papers regarding power systems synchronization technology.

            You may need a lot of homework and not rely on mysticism.
            Save your career and even make more money.

            As a side note:
            I have posted a comment about this topic a while back on another thread that you may find helpful . . . try searching the archives.

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