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  1. electrolitic

    4 or 2 diodes

    itsmoked It is not a question of ground reference. It is simply a way that makes a connection between two points and simply doubles the rated output voltage. To lose all the connected instrumentation it is not a simple failure.
  2. electrolitic

    4 or 2 diodes

    Diodes on both the negative and positive. Thanks LionelHutz but if you have an electrical connection between the positive output of power supply #1 and the negative output of power supply #2 (both grounded, as an example-it is not a short circuit because some diodes are blocked) you will double...
  3. electrolitic

    4 or 2 diodes

    It is an old question, still unclear: Why some designers apply 4 blocking diodes, instead of 2, when connecting two DC power sources in parallel. There is a risk of, under certain circumstances, the output voltage be the sum of the two sources. Is there a reason that justifies this risk?
  4. electrolitic

    Capacitors discharge

    After all these years, sometimes my wish is to leave this forum. I suppose that is absolutely clear when a thread is written by someone that is not fluent in English. Most of answers are educated and respectly sent. Others don't. I had received answers explaining the risk of re-start after few...
  5. electrolitic

    Capacitors discharge

    Thanks all of you. The concern is related to a 4,16kV system, induction motor 4,0kV,low inertia load, capacitors bank connected to the motor terminals, DC control power from batteries and AC undervoltage relay not fast enough to detect a deep grid peak. It makes sense this concern related to...
  6. electrolitic

    Capacitors discharge

    High voltage capacitors connected in parallel with induction motor needs a dedicated discharge circuit before next motor starting? Thanks.
  7. electrolitic

    Brushless excitation

    waross and SkottyUK.thanks. Simple and direct as your answers.
  8. electrolitic

    Brushless excitation

    So, considering the rotary compensator, the field forcing can provide a faster response and a better regulation performance when field weakening becomes necessary. Am I right? Thanks waross.
  9. electrolitic

    Brushless excitation

    Even new synchronous machines, specially Rotary Compensators, still use brushes/rings for field winding excitation current instead of brushless system. Probably the possibility of field polarity reversion is the reason. When/why is this reversion necessary? Thanks.
  10. electrolitic

    Blocking diodes

    It is an old question : some important switchgear designers apply 4 blocking diodes when connecting two control DC power supplies in parallel. Others, 2 just at positive leads. It is well known the risk of serious continuous overvoltage ( 2 times Vnom) at load, under certain fault conditions...
  11. electrolitic

    Metering CT for protection

    I am not sure if costs more. I will check it. Accuracy is better, no need of high dynamic and thermal capabilities, possibility of very low setting points (less than 10% of CT nominal current), less weigth and reduced dimensions. Really, is the only place, I guess, that I could use metering CTs...
  12. electrolitic

    Metering CT for protection

    I think that a metering CT can be connected to a protection ground relay if installed at HRG circuits of transformers and generators. I can see some pros and no cons. Am I right? Is this feasible/usual? Thanks.
  13. electrolitic

    Dahlander motor - high to low speed

    This subject was discussed recently. It was explained the reason of a time delay during high speed to low speed switching. The example of Panter (to see above) 2MW motor, Dahlander connection, it means "0.5MW/2,0MW motors" (1 to 4 power ratio if variable torque/Y-YY connection)L/H speeds...
  14. electrolitic

    Rotary frequency converters

    As Waross had said:Thanks for the chance to share memories. "My" 60Hz/50Hz Rotary Converter is now clear, a synchronous motor stator turning some degrees to compensate generator load angle. A hidraulic cilinder doing it, a set of directional valves, a set of blocking valves to withstand short...
  15. electrolitic

    Is time delay required when switching from LO to HI speed on 3 phase, two winding motor?

    Itsmoked. Sorry, really doesn't work. Please try : circuit diagrams 2 speed, 1 winding:2 speed. It is a typical Dahlander diagram from ABB. Sorry again.
  16. electrolitic

    Is time delay required when switching from LO to HI speed on 3 phase, two winding motor?

    Sirs. I wrote time delay between high speed and low speed (only at this order) considering Dahlander "Variable Torque" connection and centrifugal loads as fans, pumps (an eventual high inertia and the power ratio 4/1). Please see www.abbsales.com/pdfs/circuit/ diagrams-winding, at Google. It...
  17. electrolitic

    Is time delay required when switching from LO to HI speed on 3 phase, two winding motor?

    Sir. Probably it is a Dahlander connection. I think this name is not frequently used in US. Anyway this two-speed with commutating pole windings is the most used AC motor 2 speed system.Speed ratio is 2:1.It can be connected as "Constant Torque":torque is constant on both speeds, power ratio is...
  18. electrolitic

    Rotary frequency converters

    Recently I took notice of an old (50's) but still running electric equipment. Two MG sets, 20 MW each, (60 Hz Synchronous Motor driving a 50Hz Synchronous Generator). One of the sets has an special sliding cradle that permits the turning (+/- 20 degrees) of the complete SM stator (hidraulic...
  19. electrolitic

    Residual VT

    Even out of prime time: 1.The residual 59N from the 60’s is well known: 3Ph VTs with 1ry,2ry and 3ry windings. 1ry windings wye connected and 3ry windings broken delta connected including V0 voltmeter and damping resistor at delta terminals and an incandescent lamp paralleling each delta...
  20. electrolitic

    Residual VT

    Mr Davidbeach The question is considering only two primary windings connected phase to ground (simply 2/3 of a conventional wye connection). So, zero sequence voltage at tertiary is feasible, I suppose. When the phase not connected to VT is grounded the summation voltage at tertiary windings...

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