What causes the phase shift in a delta-wye transformer, is it the way the transformer is connected or the way the transformer is built? Will varing the voltages in each of the windings give a different phase shift? What would a manufacturer have to do to build a transformer with a special...
Does anyone know why it is a good practice to turn off a generator's excitation system as soon as the generator breaker is opened and the driver is still running? It seems like it would make no difference if excitation remains on since there is no load.
We have 3 generators rated 30MW running in parallel not connencted to the grid. They are run in reaactive droop mode and not in speed droop. What does reactive droop actually mean. If one generator would trip, the load, both real power and var would increase on the other two generators. What...
Does anyone know how the primary taps ratio on a transformer work. Is a +2.5% tap apply to the full voltage accros the primary or to the number of turns on the primary? To raise the secondary voltage does one connect to the + or the (-) taps?
We have 4-13MW, 13.8kV generators that are cabled to a 13.8kV switchgear. Each generator has its own breaker. The generators are grounded via a resistor rated at 200a for 10s. The problem comes in sizing the cable from the star point at the generator to the resistor located outside the...
I posted this in the NFPA forum and no one replied! Any takers here?
Vessels in a refinery which are tall and slim are usually not required to have lightning protection since they are constructed of metal of at least 3/16" in thickness and are electrically conductive. However, what if the...
Vessels in a refinery which are tall and slim are usually not required to have lightning protection since they are constructed of metal of at least 3/16" in thickness and are electricall conductive. However, what if the vessel is covered with insulation, top to bottom. Normally the cladding...
Can someone explain why an LCI drive topology can be used with synchronous motors only. I understand a VSI type drive can be used with both induction and synchronous.
Does anyone know which NEMA, ANSI, IEEE or UL standard applies to UPS system design that covers EMC requirements in the US. In the IEC there is 62040-2, but does the US have one?
I work for a company that has two main air compressors powered by 2 36KW synchronous motors. They are soft started by a medium voltage VFD and placed on an 11KV run bus that has vacuum type contactors. Over the past several years lightning strikes has caused two of the surge packs in the motor...
Does anyone know of any manufacturer of a variable voltage/ variable frequency soft starter in the medium voltage range, 5.5, 6.6kV? Are there more advantages in using a 50% rated VFD for soft starting duties than using a real soft starter that varies the voltage and limits the current?
KJvR,
See my post 1May06. I too am looking for information on this topic. I have the the IEC 60287 standards but do not have the ERA 60-30 part 3 report. You are correct that most of the IEC cable companies prefer to invoke the ERA report and say that it is based on the IEC 60287 standards...
