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  • Users: genhead
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  1. genhead

    Lightning Protection

    Hello all, I have attached details of a lightning protection device that a customer has asked us to fit to some mobile equipment which has a steel mast. The equipment is on rubber tyres and there is no grounding conductor. 1. How does it work? 2. Does it work? Thanks
  2. genhead

    Current Transformer Question

    I have a generator control unit on a 500kva 415v generator. The control unit has short-circuit protection settings, but short-circuit protection is covered by a circuit breaker with an electronic trip unit. The current transformers feeding the control unit are 800/5 metering CTs, so they are...
  3. genhead

    Overcurrent protection on only one phase

    I have a 3-phase, y-connected generator, 400volt. Overcurrent protection is provided in one phase only. Does this provide adequate protection? Any comments?
  4. genhead

    Multiple Generators Onto Single Transformers

    A client has a temporary installation of 4 x 600kw 400v generators connected to a 400/11,000v 3MVA step-up transformer. The generators are self-contained mobile units, each with its own circuit breaker. Each generator is cabled from the load-side of its circuit breaker to the LV terminals of...
  5. genhead

    IEEE-142-2007 Grounding of Industrial Systems

    Could somebody please help me in my understanding of this section from IEEE-142-2007 Green Book, regarding generator earthing. "If the generator is rated for solidly grounded service, the neutral may be connected directly to the grounding circuit conductor. If a standard generator is used, a...
  6. genhead

    Neutral Grounding Reactors

    Resistance/reactance grounding of low voltage generators is new to me. A number of 400v generators are supplying a stand-alone (island) 400v 4-wire system, a lot of which is single-phase load. Normally the neutral bus would be solidly grounded at one point, but the plant owner has asked for...
  7. genhead

    Generator Step-up Transformer

    There are several 400v generators connected to a 400/11,000v YnYn transformer. The 11kv system supplies some industrial plant. It is a separate system with no utility. The 11kv transformer neutral is solidly grounded. The generator neutrals are connected to an LV neutral bus, with one...
  8. genhead

    11kv Generator Grounding

    A 2mva 11kv generator is to be added as stand-by to an existing 11kv substation. The generator will operate in island mode when the utility supply fails. It will operate in parallel with the utility supply for peak shaving. The incoming transformer is grounded via a neutral-grounding resistor...
  9. genhead

    Cable Fault Current

    Where multiple low voltage generators are connected in parallel (say, 4 x 1.5MW, 400v) the fault current obviously gets extremely high. Whilst switchgear is available to cope with these high fault levels, how is the cable protected? If the protection settings are sensitive enough to keep the...
  10. genhead

    Generator Transient & Subtransient Reactance

    When calculating fault currents for a generator (400 volt 1250kva for example), I thought that we would use the subtransient reactance, X"d. However, I have just read a paper on short circuit currents that states "for salient pole alternators, subtransient reactance is negligible". Can anyone...
  11. genhead

    Liquid resistance starter

    Hi all, A 3.5MW 11,000V motor has a liquid resistance starter. I don't have any more information at the moment, but I'm assuming that it will be driving a crusher or mill. Does anyone know what kind of starting characteristics I can expect. I know that it will vary considerably, depending on...
  12. genhead

    Generator/transformer circuit breaker

    We have a 415v 2Mva generator connected via a circuit breaker to a 415/6.6kv transformer. The complete unit is trailer-mounted. We intend to use it to temporarily supply some 6.6kv plant. What protection is required on the 6.6kv outgoing supply?
  13. genhead

    Circuit Breaker trip caused by utility fault?

    A commercial building is supplied through a 630amp 415v circuit breaker. On two occasions this circuit breaker has tripped (overcurrent or short circuit) after utility faults have occurred nearby. One of the faults was caused by a vehicle hitting a power pole, I'm not sure about the other one...
  14. genhead

    11kv GENERATORS NEUTRAL-GROUNDING

    8 X 2MW 11kv generators will be connected to an 11kv switchboard, as the sole source of supply. Is it acceptable to leave the generator neutrals open, and use a zig-zag transformer and NGR connected to the switchboard, to ground the neutral ?
  15. genhead

    Earthing of Gensets During Factory Testing

    We are a supplier of new and used low voltage (415v)generators. During factory testing before despatch, how should the gensets be earthed ? My main concern is operator safety. Most of the gensets don't have earth leakage protection. The neutral is connected to the main earth terminal in the...
  16. genhead

    Earth/Ground Fault Protection

    A small (3MW), remote area power station consists of several generators at 415v (wye) stepped up to an 11kv (delta) distribution system. The 11kv grounding is via an grounding transformer and resistor (10 amp). If an earth leakage relay was installed with its CT over the 11kv neutral conductor...
  17. genhead

    PARALLEL TRANSFORMERS - LOAD/IMPEDANCE CALCULATIONS

    I want to parallel two transformers with the same voltage ratios, kva rating, and vector group. Can anyone tell me how to calculate the load carried by parallel transformers with difference impedances. In this case 5.97 and 6.1 % What aout transformers with different kva ratings ?
  18. genhead

    Taiyo alternator

    I need to know the winding pitch of a TAIYO alternator. I don,t have a model number, but it's 415volt, 1500rpm, around 550kva, somewhere round about 15 years old.
  19. genhead

    GENERATOR EARTH FAULT PROTECTION

    I have 2 x 1MW 6.6kv diesel generators (paralleled), connected to the delta winding of a 6.6/11kv step-up transformer. A grounding (zig-zag) transformer is also connected here, with grounding via a resistor. There is no earth-fault ct at this neutral-point, and access is very difficult. The...
  20. genhead

    WYE-DELTA AS A GROUNDING TRANSFORMER

    How is a wye-delta transformer connected as a grounding transformer. I have only used zig-zag previously.

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