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  • Users: radug
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  1. radug

    Grounding switches in Gas Insulated Metal Enclosed switchgear

    Hello, One client is requesting for the incomer of a MV gas insulated metal enclosed switchgear (arc resistant), to include two grounding switches: one in the incoming cable connection side and another one being the usual 3-position-disconnector/grounding switch that is located between the...
  2. radug

    4-20mA to 110Vac

    Hello, I need to send the secondary 110Vac/sqrt(3)of a HV metering PT, to a remote location at around 5 km. I have found analogue to digital converters and signal transmission through fiber optic. However, for the remote end, I require also a 110Vac/sqrt(3) output, and I am only able to find...
  3. radug

    NEMA MG1 Motor frequency variation during starting

    Hello, NEMA MG1 is specifying a maximum 5% frequency variation during normal operation and also during starting: "Medium motors shall start and accelerate to running speed a load which has a torque characteristic and an inertia value not exceeding that listed in 12.54 with the voltage and...
  4. radug

    Use of a F/B motor as F/F

    Hello, If my understanding is correct, a motor with an insulation class F with a temperature increase B has a 25ºC margin for operating continously without affecting its design life. If this is correct, one could use a motor purchased as F/B with no risk at F/F. My question is: if the rated...
  5. radug

    MV cabinets busbar earthing switch

    Dear all, For the design of 6.6kV cabinets, an engineering subcontractor is recommending to add a cabinet with an earthing switch so that in case that maintenance work has to be done in the cabinets, the busbars can be earthed before performing the Works. Cabinets are metalclad type and all...
  6. radug

    Cables in piping racks or in cable trays. Short-circuits

    Good afternoon, A question has arisen among my workmates about piping racks foundations or supports sizing when carrying also for example ladder-type cable trays. Do the dynamic effects of short-circuits in cables need to be taken into account for sizing the supports? I usually only used...
  7. radug

    GSU Transformer energization

    Hello, I have a ST Generator (15.75kV) connected directly to a GSU Transformer by IPBs, and then in the HV side of the GSU Transformer is a circuit-breaker (33 kV). As usually transformer manufacturers specify in their commissioning manuals that the transformer must be energized with no load...
  8. radug

    Generator + GCB + GSU Transformer + 2 UAT reliability

    Hello, I have seen a tender for a power plant where the single-line diagram shows Generator + GCB + GSU Transformer + 2 UAT. The only way of feeding generator auxiliaries is through the UAT, as no station transformers of MV lines are available. The connection between Generator + GCB + GSU...
  9. radug

    Cast iron vs Aluminium

    Hello, I would like to know which are the differences between cast iron and aluminium squirrel cage motors in terms of performance, environment withstand,... When should be a cast iron motor used and not an aluminium motor? Thanks.
  10. radug

    Calculation of VFDs in parallel current harmonics

    Hello, I am trying to calculate which would be the total injected current harmonics spectrum of some VFDs connected in paralell to the same MCC. I have the harmonics spectrum of the individual VFDs. My problem is when calculating the total harmonics in the MCC as there seem not to be the...
  11. radug

    Dry-type transformer overloading

    Hello, I am trying to find some type of diagram or table for dry-type transformer overloading. I have found some diagrams for oil-inmersed type transformers but no luck with dry-type ones. I need a 110 kVA dry-type transformer which will be loaded for 30 seconds max (it will be a grounding...
  12. radug

    IEC 60909 motor contribution

    Hello, I have some questions that I think are related to thread238-289927 but it is closed. squasher, In your first post, shouldn't it be used Ith instead of Ik for short-time withstand current in 3 seconds? It is a question I have about IEC 60909 because if Ith should be used, then I do not...
  13. radug

    Grounding transformer suppliers

    Hello, I am looking for supliers of grounding gransformers, wye-open delta for high resistance grounding (10 A) of a 11 kV busbar. I have contacted different suppliers and have not been able to obtain anyone. Does anybody now about suppliers in Europe for this type of transformer? Thanks.
  14. radug

    Generator transformer connection: delta vs wye

    Hello, I have mainly seen MV synchronous generators connected to a generator transformer where the transformer generator side is in delta and the HV side in wye. Why not put the generator side of the transformer in grounded wye? Does anybody know of books or papers that discuss this topic...
  15. radug

    Ground grid as equipment grounding conductor

    Hello, I know that NEC 2011 explicitly forbids using the ground grid as an equipment grounding conductor while in NESC 2007 it is not explicitly covered. Let's say you have a large power plant where you have buried a mesh type grounding grid so that you have only one earth for both HV, MV and...
  16. radug

    Induction 60hz motor specifications catalogue

    Hello, I am looking for 480 V 60 hz ac induction motor technical catalogues with the following data for different rated powers: efficiency, power factor, starting current, speed (rpm), starting torque vs rated torque, max torque vs rated torque, inertia, starting power factor,... I have some...
  17. radug

    220 kV Outdoor substation layout. Distances between equipment

    Hello, I need information about how to calculate the minimum distances between current transformers, voltage transformers, surge arresters, power transformers and circuit breakers in outdoor 220 kV substations. I have done an insulation coordination study and have the minimum phase-to-earth...
  18. radug

    Isolated Phase Busduct grounding

    Hello, I have calculated the grounding grid of a power plant for one phase to earth faults and now I am concerned with the double phase to earth faults on isolated phase buses between generators and transformers. I have come across two pages of ABB about it but I have many concerns. -Should...
  19. radug

    NFPA 780 scope: what structures to protect

    Hello, I have been asked if in a parabollic-through thermal solar plant, the solar field containing only parabollic-through collectors should be protected against lightning according to NFPA 780. I am not familiar with USA regulations, it could be the first plant to be built there. I have just...
  20. radug

    Maximum allowable temperature in ecuation 41 of IEEE 80-2000

    Hello, When calculating the thermal rating for grounding conductors, Tm (maximum allowable temperature) must be entered in ecuation 41 of IEEE 80-2000. The standard gives fusing temperatures of different materials (for example 1084 degrees Celsius for soft-drawn copper). I asked some...

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