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  1. jhonsom

    Synchronous Motor starting sequence

    "A very smart GE engineer told me to synchronize at 2.4% slip for one project. I have seen a motor require energizing at 7% slip to allow it to actually reach the synchronizing speed" How to determine the choice of slip setting (range 0.5 to 10%), or can I set all motors high/low inertia to 3%...
  2. jhonsom

    Synchronous Motor starting sequence

    Please don't discourage me from understanding this. thanks!
  3. jhonsom

    Synchronous Motor starting sequence

    I have some low inetia motor, does it reluctance synchronize on no load? I'm not getting when this reluctance syc occurs... So for reluctance synchronize: I would first check if set speed is reached and then detect positive zero crossing every cycle, if no zero crossing is detected for a fixed...
  4. jhonsom

    Synchronous Motor starting sequence

    Lionel, Please let me know how you applied DC without breakers/contacts? Also if I close DC at positive zero crossing (or) if it had already locked before I apply the field (reluctance synchronism) 180 degree out of phase then when I apply DC at any rotor angle, I would slip a pole and run...
  5. jhonsom

    Synchronous Motor starting sequence

    Lionel, Thanks for your reply! Yes we have arrangements to do that. I understand slip settings are different for different motors, please elaborate me more on the choice of the slip % for a given motor. Also if we decide to pick positive zero crossing for all slip ranges, wouldn't the rotor...
  6. jhonsom

    Synchronous Motor starting sequence

    We have a few brush type synchronous motor of different HP used in our application. I'm thinking of bringing the motor to close to synchonous speed and then apply the DC field. Some manuals (GE-SPM) say after it reaches between 1- 10% slip (settings) and it should be closed on positive zero...
  7. jhonsom

    Minimum Contactor Closing Time for Generator Synchronization

    I see the SEL 700G relay has upto 1000ms and compensates for breaker close time.
  8. jhonsom

    How to determine the running state of Synchronous motor?

    Friends, Greetings! I'm trying to determine the running state logic of Synchronous Motor. I don't have field contactor breaker status and speed signal. The signals I have are stator current, 52A stator breaker status, rotor field current, rotor field voltage. This machine is started as...
  9. jhonsom

    Islanding detection scheme for Induction generator of wind turbine

    Would a simple Rate of Change of frequency Relay enough for detecting islanding condition for wind turbine application which uses Induction generators. Can we detect power mismatch in this application?
  10. jhonsom

    Switching between Synchronism voltage and 3V0 (polarization voltage)

    We have only one extra voltage input in the Relay other than the 3ph voltage input . Has anybody heard of any application where you can switch between two PT inputs ? one from VS PT( synchronism voltage) for doing 25 function and other from 3V0 PT (broken delta) for directional protection. We...
  11. jhonsom

    Design of Sudden Pressure Relay Blocking Scheme for Transformer

    How to design SPR blocking scheme using 63 and 50 Fast instantaneous over current element? Is SPR used for tripping the relay for internal faults only? How will it block tripping if 63 contacts are short because of transient? The logic I'm having in my mind is= 63A And not 63B not 87 not 50)...
  12. jhonsom

    Relay for high impedance grounded/ungrounded multiple machines

    1. Which Relay is the best for detecting fault in high impedance grounded/ungrounded multiple synchronous generators in parallel? What I think is voltage based ground fault detection is not very sensitive/selective for this type of ground. 59G, 64G (VN, VN3) are all good as backup protection...
  13. jhonsom

    reducing the skin effect

    As you strand the conductors the skin effect reduces, you find the formula in textbooks.
  14. jhonsom

    Phase to Phase votages in Metering

    Could you please explain this in detail as I didn't think from that angle " There are all sorts of voltage balance problems that can't be seen if only phase-phase voltages are available"
  15. jhonsom

    Phase to Phase votages in Metering

    Ya but what I want to know is it ok to show phase to phase voltage only despite of wye connected PT input to the relay. Is there customers who want to see phase to neutral voltages? Sorry about wrongly wording the previous post. We do over/under protection on both PP, PN like 27P,59P, 27PP...
  16. jhonsom

    Phase to Phase votages in Metering

    Do customers generally what to see phase- phase voltages (VAB,VBC,VCA) or Phase -Neutral voltages (VAN,VBN,VCN) in the Feeder Protection Relay Metering despite of delta or wye connected PT inputs ?
  17. jhonsom

    Autosynchronization of Hydro Plant

    Thanks for your response. The PLC doesn't change our pulse, it gives out what we give form our relay. We have compensation for breaker closing time. Breaker closing time is the time we calculate by giving close commant to the time we see voltage. How much frequency slip is allowed for hydro...
  18. jhonsom

    Automatic Synchronization of Generators using Relays

    Ariganello, Does your relay do Autosync for Hydro? Is hydro frequency control linear for Autosync ? Please reply to Autosync for Hydro thread. Thanks, Jhonsom
  19. jhonsom

    Autosynchronization of Hydro Plant

    I will get the PLC details soon, our relay didn't directly control the govenor, the plant has a PLC between the two. So is this PLC causing problem otherwise is it linear? I google and upload a old picture, the one in the field looks similar to this but has a motor...
  20. jhonsom

    Autosynchronization of Hydro Plant

    Here are the details: 1. Its a 67 FT, low head, 277 rpm, 2500HP, Hydraulic turbine ALLIS- CHAMBERS, MILWAUKEE-WIS and located in Minnesota. Sorry the field guy has not seen the valve and not sure whether it is a butterfly valve but he said it took more time for the water to come in and by the...

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