It is an old question, still unclear: Why some designers apply 4 blocking diodes, instead of 2, when connecting two DC power sources in parallel. There is a risk of, under certain circumstances, the output voltage be the sum of the two sources. Is there a reason that justifies this risk?
Even new synchronous machines, specially Rotary Compensators, still use brushes/rings for field winding excitation current instead of brushless system. Probably the possibility of field polarity reversion is the reason.
When/why is this reversion necessary? Thanks.
It is an old question : some important switchgear designers apply 4 blocking diodes when connecting two control DC power supplies in parallel. Others, 2 just at positive leads. It is well known the risk of serious continuous overvoltage ( 2 times Vnom) at load, under certain fault conditions...
I think that a metering CT can be connected to a protection ground relay if installed at HRG circuits of transformers and generators.
I can see some pros and no cons. Am I right? Is this feasible/usual? Thanks.
Recently I took notice of an old (50's) but still running electric equipment. Two MG sets, 20 MW each, (60 Hz Synchronous Motor driving a 50Hz Synchronous Generator). One of the sets has an special sliding cradle that permits the turning (+/- 20 degrees) of the complete SM stator (hidraulic...
Condition: single phase fault on an unearthed neutral 3-phase system
Question: Can I obtain 59N protection using just 2 single phase VTs connected in open delta configuration?
Thanks
On LV isolated network Schneider recommends a surge limiter (Cardew C) to discharge overvoltages to earth, normally connected between neutral and earth.
In case of unavailable neutral the catalog shows just one surge limiter connected between one of the three phases
and earth. Is this enough or...
Do I need to consider the calculated short circuit asymmetrical factor in case of arc fault in a MV system?
For bolted faults I already need to provide a zero crossing delay for safe breaker opening.
Thanks.
Recently I had started a thread: If a CT originally designed to be applied at 50 Hz circuit is installed at 60Hz which would be the influence over the secondary saturation voltage?
The answers were perfect but one doubt remained if related to the accuracy threshold at low current settings...
If a CT originally designed to be applied at 50 Hz circuit is installed at 60Hz which would be the influence over the secondary saturation voltage?
Thanks
Can I consider Pt100 sensors at induction motor stator windings a good protection against overheating caused by unbalance currents (max unbalance voltage=5%).RTD has a relatively slow reaction time. Can it respond adequately to the heating process? Thanks
All papers that I could find describes gen stator ground fault (over 80-90% of stator winding) protection for unit-connected generator (connected to a step transformer). Is it possible to protect generators connected in parallel? Thanks.
I connect a 3,5MVA transformer, Z=7%, 11.0kV/3.3kV to a 2,5 MW induction motor, Is=6 In. Circuit breakers at primary and secondary. Can I suppose around 30% of reduction voltage at starting, Is reduction to aprox. 4,0 In as it was a reator starting (70%) without additional breakers and bump...
10P20 CT it means a protection CT with composite error of +/- 10% and that error will be maintained up to 20 times the rated primary current of the CT. Is it correct? Is it constant?
More and more current measurements/monitoring using the modern protection relays instead of dedicated...
Sirs
Can I connect two 5,0kW VFD (diode front end) to a selectable (open transition) AC 3ph or a DC from battery bank?
Fuse protection and blocking diodes at DC entry. If yes, which should be the DC voltage compared to AC?
Could the built-in precharge be used for both supplies? Control power to...
If I have a VFD in a HRG system the ground fault is difficult to be detected. It depends where the fault occurs. Can be at AC entry side, DC bus or drive output, sometimes running at very low output frequency. Expensive microprocessor based relay reading a CT at neutral resistor circuit can...
I received an electric single line diagram drawn in USA where it appears two small circles close to a low voltage circuit breaker. Inside one circle is written EO. Inside the other, DO. What do they mean?
Thanks.
Rotary blade saw, 125kgm2,running at 1200rpm, driven by AC induction motor 610kW, 1780rpm. Motor starting torque 1.8 times Tn, motor max torque 2,7 times Tn.
VFD for no-load starting up to nominal speed. During open transition (applied VFD cannot run in parallel with the grid) a high peak...
