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  1. CuriousElectron

    Ventilated Dry type transformer inside a building

    Hello, Are large dry-type transformers installed inside industrial facilities typically of a ventilated design(versus non-ventilated which would typically be installed outdoors)? Also, do these units require proper clearance for air flow, especially if they come with AA/FA rating? Would one...
  2. CuriousElectron

    Power Transformer Rating

    What if this is a GSU transformer sizing exercise for a big generator? Would you match the GSU rating to Generator rating but provide a bit more MVA capacity on the GSU to account for any future unit uprate as a result of a unit rewind and to compensate for higher-than-average summer...
  3. CuriousElectron

    Power Transformer Rating

    Greetings, What determines whether we go with single forced cooled rating, or natural cooling/first stage cooling/second stage cooling for oil filled, power transformers above 100MVA rating? Is this evaluation based on engineering judgement/industry best practices, or? Thanks, EE
  4. CuriousElectron

    VFD(VSD) on sluice gates

    Thank you for the explanation, Mr.waross!
  5. CuriousElectron

    VFD(VSD) on sluice gates

    Hi All, I had a question - I'm seeing Variable frequency drives or variable speed drives being used on sluice gates (vertical slide gates) to drive gate motor actuator. Why is the reason behind it? Why not use a standard FVNR starter instead. These gates are rated at 3 HP to 5 HP. I see they are...
  6. CuriousElectron

    MV Switchgear - Switching multiple sources

    Hi All, I've seen low-voltage switchboard being used to automatically transfer from Source A to Source B(double-ended unit substation). Can a Medium Voltage switchgear be designed to switch between 2 or 3 medium voltage sources? I don't see why not, but wanted to get other opinions. In this...
  7. CuriousElectron

    Transformer impedance

    Hi All, When specifying 1MVA transformer or above, do you usually specify its impedance based on short circuit-study performed to determine what the impedance should be, or do you go with OEM recommended standard value for the size transformer and then specify appropriate kAIC and protective...
  8. CuriousElectron

    Doble Tests of Power Transformer

    Hi All, Are Doble tests effective in evaluating health of GSU transformer windings? Does a transformer need to have its oil drained prior to performing a test(Doble or Megger) to focus on winding insulation, since oil would act as an insulator? Thank you for your thoughts. EE
  9. CuriousElectron

    Testing of Medium-Voltage Circuit Breakers

    Greetings, Per IEEE 37-013, manufacturer of HV CBs are required to perform extensive numbers of tests, including short-circuit test, withstand test, etc. How are they able to comply with the standard/spec, and demonstrate that their products meet those requirements considering the high magnitude...
  10. CuriousElectron

    GCB in the 15,000 Amp range

    Hi All, Does anyone know what interrupting medium technology is used for high ampacity generator circuit breakers? I know for 5,000Amps and below typically vacuum is employed, but for high amperage applications, not sure if vacuum is still employed or perhaps SF6 or air blast technology? Thanks, EE
  11. CuriousElectron

    Altitude de-rating of Turbocharged standby generator

    Greetings, all I had a question - does a turbocharged propane engine driven generator needs to be derated for high altitude? I understand the need for derating for high altitude, since the air is less dense at higher elevations and it loses its effectiveness to cool down the engine. But for...
  12. CuriousElectron

    Space heater for Totally Enclosed Fan Cooled(TEFC) Motors?

    Hello All, Does a TEFC type motor require electric heaters to keep it warm and dry when the motor is idle? Does it depend upon environment and if the area has high humidity. If there is high humidity, then higher chance of condensation? Thanks for your thoughts.
  13. CuriousElectron

    Eutectic Alloy vs E100 Solid State Overload

    Hello All, What are uses and pros/cons of Alloy type O/L versus Solid state O/L for a single speed motor in the range of 20 HP? Does it depend on environment where a motor is installed? Cost? Any thoughts on where you'd use either one would be appreciated. My understanding is that both types are...
  14. CuriousElectron

    Standby Generator Starting kW

    Greetings All, What is typical ratio between skW and rated kW of a gas generator? I know that gensets are capable of providing higher starting kVA for motor starting, but do they also provide higher skW for limited time? What is the limiting factor here.. is it the temperature rise on alternator...
  15. CuriousElectron

    Battery Charger for a Standby Generator

    Hello All, Has anyone used a DC to DC converter in the past as battery charger to charge 12VDC battery on a genset? The project I'm working on doesn't have a reliable 120vac supply on site, but there is battery bank that can be used to maintain charge on the generator battery. Looking for 24VDC...
  16. CuriousElectron

    Life expectancy of a current transformer

    Hello, For a CT installed indoors in a powerhouse, what is the "typical" or rule-of-thumb life cycle of a CT? What are factors affecting the life expectancy and is it common to see a CT fail in service? Typically, CT's are not maintained, so I was wondering what could be leading up to a...
  17. CuriousElectron

    Current Transformer Thermal Factor

    Hi Gents, I had a question - is the thermal factor rating on a current transformer refer to continuous or overload capability of an instrument to carry increase in current? For example, if 1000:5 CT has TF of 2.0 at 40 degree C ambient, does this mean that this device can carry 2000Amps...
  18. CuriousElectron

    Pressure Transducer reporting a negative value

    Hello Gents, I'm looking at a trend in PI for a water level value and the value is fluctuating below 0 feet and above 0 feet. To me that is strange, I'd expect the trend to be above 0 feet. What can I infer from this trend? When the sensor is reading & reporting a negative value, is that...
  19. CuriousElectron

    Why Delta-Delta Transformers used in Full Static Exciter System

    Hello Gents, I notice that in Full Static Excitation schemes, a delta-delta connected PPT is utilized. Why delta-delta type? My thoughts are that to provide higher reliability - if one phase fails, you can still supply AC power to your power bridge converter via open delta connected PPT. Also, a...
  20. CuriousElectron

    PT Burden Tests

    Greetings, Has anyone done offline Potential Transformer burden testing? Is offline PT burden testing more challenging to do than an online testing? Just wanted to hear from your experience. Thanks, EE

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