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  • Users: Guardiano
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  1. Guardiano

    Aternator current

    Hi, We are commissioning a 2000 k VA generator and the current on each phase is balanced. There are four single cores cables per phase but the current on each core is not balanced at all. The cables are run in trefoil. What could be the cause? Thanks Guardiano
  2. Guardiano

    Zonal Protection

    Hi forum members, I understand that class X CT is always used for differential protection because you don't want the protection to work for external fault. I have seen some applications where 5P20 CT is used for differential protection. Does this compromise the installation? Any comment is...
  3. Guardiano

    Motors in tandem

    Hi, We have two 5 MW 6.6 k V wound motors driving a crusher in tandem. We have always been running the crusher with the two motors powered. Now because of load reduction, only one motor is powered and the powered electric motor drives both the load and the second motor. We noticed a very strange...
  4. Guardiano

    Fixed MV Circuit Breaker

    Dear Forum Members, I understand that the only means to safely isolate a medium voltage circuit breaker is to take it out and padlocked it in the test position. What about fixed circuit breakers? Could the spring charged mechanism be used to safely isolate a fixed circuit breaker? A circuit...
  5. Guardiano

    Torque to be applied

    Dear Forum Members, I don't know if this is the right forum but I'm sure the gurus present would shed some light. We have a gearbox arrangement and the motor/gearbox assembly drives a shaft which itself drives a conveyor. The gearbox was removed for maintenance and now it has just been put into...
  6. Guardiano

    Hi Forum members, We experienced a

    Hi Forum members, We experienced a stainless steel basket failure on one of our sugar centrifugal machine. The basket spins at a maximum speed of 1100 RPM. I am attaching a picture of the tear. Any reason for the root cause ? Thank you...
  7. Guardiano

    Switching

    Dear Forum members, We noticed a strange phenomenon when we switched on a 5000 k VA 11 k V/ 690 V transformer on the grid. The grid was lightly loaded before switching and around 800 k W was imported.The grid metering showed export of some VA for a few seconds. Any explanation ? Thanks Guardiano
  8. Guardiano

    Dual driven generator

    Dear Forum members, We are working on a preliminary phase of a project which will include a 10 MW alternator driven by a steam turbine. The turbine will operate only for six months of the year and power will be supplied through a diesel driven generator for the remaining six months of the year...
  9. Guardiano

    Starting

    Hi everyone, I have a 250 kW compressor on site and due to lack of load, the compressor is recycling every 50 mins. The compressor is driving a compression chiller and is star/delta started. I understand that one restart every 45 minutes should not be a major problem but I presume that the...
  10. Guardiano

    VSD

    Dear forum members, I am having an issue with a 400 k W pump. The pump is driven by a variable speed drive.When the pump is started, it ramps well to rated speed and the current on the three phases are very well balanced at nominal speed. The pump pumps well and there is no issue with the pump...
  11. Guardiano

    Design

    Dear Forum memebers, I am having a discussion with a design engineer regarding the installation of two 3.0 MVA 400 V diesel sets. The sets will be used to feed the grid at 33 k V. The consultant is proposing fuses on the HV side of each 400 V/33 k V generator/transformer and a common 33 kV...
  12. Guardiano

    Motor Starting

    Hi, I have a 5 MW 6,6 k V wound asynchronous motor and the supply from the utility is at 22 k V. What's the minimum rating of the transformer that is required to start this motor ? The starting time of the load is around 15 seconds. Thanks Guardiano
  13. Guardiano

    Generator

    Hi forum members, I have a diesel engine running at 750 rpm but the aternator is only rated at 1500 rpm 50 Hz. The prime mover is rated at 1 MW and the alternator 1500 k VA. I understand that a multiplying gearbox will do the job but is there any other possible solution ? I understand that...
  14. Guardiano

    Transformer

    Hi, We had a breakdown of a cast resin tranformer, rated @ 3500 k VA 11 k V/ 415 V. The breakdown occured on one phase and the LV winding was shorted to ground. This transformer was working at a very high temperature, as do use to operate cast resin types,<= 115 deg C. I am having an argument...
  15. Guardiano

    Insulation breakdown

    Hi, Any reason about the cause of failure? The unit is a 250 k W compression chiller. Thanks Guardianohttp://files.engineering.com/getfile.aspx?folder=ae560a03-7132-41ed-b71d-14be30fcdfb8&file=Compressor.jpg
  16. Guardiano

    Spares

    Hi, The main board on my PDL microdrive is faulty and PDL/Scheneider no longer supports this product. Any idea where I may procure this card? Thanks for feedback. Guardiano
  17. Guardiano

    In rush current

    Hi, I am actually setting my protection relay on a 7.5MVA 22/11 kV transformer and would like to know if 12 times rated current is a safe setting for the inrush current. Thanks. Guardiano
  18. Guardiano

    Parallel Operation

    Hi, I am facing a dilemna.We are planning to operate our generator, a 5 MW steam turbine driven one,in parallel with the grid. The 5 MW plant is actually providing power to a cement factory. Our intention is to stay connected with the grid and import around 500-800 kW.Previously we were...
  19. Guardiano

    Torque measuring device

    Hi, I understand that this is not the right forum to ask this question but I am sure that I will find very clever responses form experts who are used to this forum. I am in the process of purchasing a torque measuring device and the specification outlines an acquisition frequency of 1000 Hz...
  20. Guardiano

    Inverter motor side

    Hi, Please find attached damage caused to one IGBT module on a ACS800, 250 kW 400 V regenerating drive. The drive is used to power a centrifugal machine. There are three IGBT modules in parallel but only one module is affected. I don't think the failure was caused by a surge, any guess ! Thanks...

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