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Logic diagrams for relays help

  1. May 26, 2015 #1
    Good morning,

    I'm looking at some logic diagrams for relays and have encountered something that I've never seen before. I haven't looked on the internet extensively since I thought the folks here at the forums would be able to answer my question more quickly. My experience with logic is limited (I'm more of a Power guy) so I've not looked at much outside of classes on the subject; so if anyone could explain to me what this little thing in the picture below does, I'd be much obliged.

    Thanks for your help.
  2. jcsd
  3. May 26, 2015 #2


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    What picture?
  4. May 26, 2015 #3
    Last edited: May 26, 2015
  5. May 26, 2015 #4

    jim hardy

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    From what industry does that symbol come ?

    Instrument Society of America's standard symbols are in 5.4 table 3 here

    and yours rather resembles a converter block, element 20 on page 25 of the pdf.

    Surely there are some cryptic clarifying notes nearby ? Can you scan and post the page ?
  6. May 27, 2015 #5

    High Power Transmission Protection and Controls. I have someone at work that should be able to explain it to me, but they won't return 'till tomorrow. In the mean time, there aren't any notes around, but the full logic may help someone come to an explanation. I've spent some time analyzing the logic so as to gain some understanding of how these circuits are behaving with various inputs, but I'm at a cross-roads of understanding.

    Here's the component in a circuit for context...

    As you can see, the circuits aren't really that difficult to understand; but without knowing exactly what this piece does, it's difficult for me to say I understand it completely.
  7. May 27, 2015 #6

    jim hardy

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    Would it make sense for it to be a memory element, to provide the lockout ?
  8. May 27, 2015 #7
    Thanks for your replies Jim! I was able to contact someone who knew a little more about this stuff than I did.

    I think that memory would be an accurate description, but timer might be a little better. I found out that the SV stands for Schweitzer Variable. If you have one in a circuit where the input to the SV is RELAY ALARM + !TRIP COIL MONITOR + STATION DC NOT GOOD and one of these inputs goes to high for, lets say, 130 cycles; then the SV will allow current to flow. If the SV has "0" as its set value (as in the example in the picture), then it will allow complete transparency between the input and output sides. I suppose it's there only to set a timer if it's needed in any particular application. This signal will pass through several other gates that provide inputs to an SR latch. The output of this latch will let the relay know if a HOT LINE TAG has been applied. Meaning the breaker will go straight to lockout if a limb hits the line or there's some other type of ground fault (it'll also make the relay more sensitive to ground disturbances).
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