Yes Exactly, confirming the above. Up to 3250A (about 70MVA)we have used off-the-shelf 40, 50, and 63KA circuit breakers, over and over and over. Beyond that (6300 and 8,000A) we apply GCB's such as ABB HGI-3's. The only thing 'special' that the supplier is talking about would be the surge...
Mr Roobarb:
Late reply, but the 'cheapest way' would be to add a series, iron-core current limiting reactor with a bypass contactor. (A resistor would be too big and expensive and doesn't give you di/dt advantage). The bypass contactor can either be timer, or current sensing switched. Generally...
Mr. Wonderchi:
The transient analysis gives you the data to use for selection of the proper close and latch capability of the circuit breaker. Remember, circuit breakers not only interrupt faults, but they can also close on faults, or, selectively, let faults through. The initial asymmetrical...
This sounds like a brushless synchronous machine. If it is, the sequence is simple. Start the motor. Apply the field. If and when it reaches about 95 to 97% speed, the motor will apply its internal field and pull in on its own. If you have regulation, turn it on after the motor is in synch...
iigp2006:
I don't know if these are 'apart from the obvious' or not, but here are a few, anyway...
1. Interruption medium: Gas or Vacuum? What's the state of the art? What gives you the interrupting ratings that you need. Do all three on your list of suppliers offer both?
2. Insulation medium...
One more thing...
if you get too carried away with 'turns' without credible calculations, you might end up with a resonnant circuit. Ideally, LC should be tuned to a fractional harmonic that does not exist (like 150Hz on a 60Hz system).
Furthermore...
Metalclad switchgear has metal barriers between cable and main bus compartments with no intentional openings in between (usually the equivalent of 11Ga), also barriers between cable compartments.
And to answer the original question: all else being equal in terms of good equipment...
Mr. Selec:
You would be on the correct path if you were referring to the time inverse curve and not the instantaneous. If you set the time inverse curve of the 469 as you stated, then the R-rated fuses will perform their duty to clear the fault above the contactor interrupting rating. The trick...
Mr. Mora2:
Before you start changing your circuit breakers you must consider, among other things, the switching surge issue, and insulation coordination. Oil circuit breakers, inherently, have very limited switching surges. On the other hand, and whereas you can purchase now-a-days low surge...
Mr. Engcan:
On the micro-level...,
Spinning motors at full speed have built-up emf's that will not go away (decay) until a couple of hundred power cycles. Re-application of power within 3 seconds of removal will cause inrushes up to 20 times FLA, guaranteed.
Also, energized transformers have...
Mr. Antenna2001:
You might want to consider investing in a micro PLC for a couple of hundred dollars, and a few toggle switches and control relays and program your circuits from your digital logic in the PLC. Some PLCs actually talk boolean. This way you can simulate your circuits, test them...
...are designed to handle the starting of the motor, period. No matter what means you use, they will have endured the same amount of heating due to i**2t. Why? because one acceleration from stand-still to full speed requires the same amount of energy to mechanically bring the motor up to speed...
It is possible to securely detect faults down to 0.1A using a machine differential relay such as an ABB 87M or GRD. You need not worry about the ratios, the sensors are dedicated, and are available from ABB in multiple dimensions.
