If a 3-phase, 3-Wire (no Phase to neutral loads), Y-G, 480V system has several phase-to-phase loads unbalancing the system.
I would like to provide GF protection at the service disconnect and a second level at the feeder.
All 600 A frame breakers I have seen (Eaton, GE, and Square D) have GF...
According to NEMA MG 1-2011 section 32.13, generators can withstand a maximum short-circuit current equal to the three phase fault current at its terminals for at least 30 seconds (unless otherwise specified by the manufacturer) when operated at rated kVA and power factor and with a maximum of...
Lets assume that we have a 10,000 kVA 138 kV to 12.47 kV transformer with a primary FLA of 41.8 A.
The short-circuit available at the secondary side of the transformer is 5.76 kA which referred to the primary side is 520 A.
Assuming this CT feeds a typical electromechanical 50/51 relay (CO...
Does anybody knows of a software that can draw and calculate steady state single phase electrical circuits? I have SKM but is not what I want. SKM is an excellent program but it can't draw the single phase schematic diagrams, including phase, neutral, and equipment grounding conductors and then...
The NEC allows for transformer protection to go to the next standard size. It is very clear how to apply this rule for low voltage circuit breakers. But what are defined the medium voltage or high voltage breaker standard sizes?
In standard MEMA MG 1-2011 Section IV Part 32 the title shows the following:
"Synchronous Generators (Exclusive of Generators Cover By ANSI Standards C50.12, C50.13, C50.14, and C50.15 Above 5000 kVARatings".
Then in the scope section establishes that this part 32 covers synchronous generators...
Thank you for your responses. But I might not have clear on the purpose of my question.
I understand and agree with all what you wrote. But the questions is:
Why the IEEE determines that a Voltage-Restrained relay (not a Voltage-Controlled Relay) is advisable when the time constant of the...
In IEEE Std. C37.102-2006 related with generator protection, it is recommended to use voltage-restrained back-up protection when the following condition is present (Section 4.6.1.2 Overcurrent Type Backup, page 77): Short, short-circuit time constant. The actual wording is:
"On units that have...
UL 1066 and ANSI C37.13 are recognize standards for Low Voltage Power Circuit Breakers (LVPCB).
Are these standards equivalent, in other works, did ANSI or UL adopted one of these standards from the other organization?
If different, what are the main differences?
Thanks.
I would not use an ESE device to provide proper lightning protection. As told, in spite of a ferocious war waged by specialized lightning air terminals suppliers, NFPA and IEEE did not find any credible evidence that they work, on the contrary. But they have an excellent marketing machine...
I only affix one worst case label to a transformer.
I model the transformer with a bus at the primary and a bus at the secondary (i.e. TR-1-P and TR-1-S).
I then run the arc flash and these two locations will be together and easy to compare which is the worst case.
When I print the labels I...
I want to correct an error with the previous statement. When the relay curves tend to converge in a lower value of time as current values increases, you may have that the momentary duty results in a lower CTI than the CTI obtained by the lower interrupting duty.
I agree that the momentary asymmetrical duty (RMS or Crest depending of the rating of the CB's) should the one to use because is higher than the interrupting duties (Symmetrical or Asymmetrical depending on the CB's).
But if you have two relay TCC's growing apart from each other as current...
When performing a coordination study on a MV system, we can use many types of short-circuit currents in the TCC curves.
If we use the ANSI C37 standard for calculation, we have many types of short-circuits to show in the TCC. Some of these are:
1. Momentary: Calculated using the first-cycle...
7anoter4
Thanks so much for your help. I kind of understood the first kindly response of Mr. davidbeach, but an example is the equivalent to a thousand words.
Thanks again.
RECS
IEEE Std. 242 2001 in page 314 describe how to obtain the overload curves (i.e. intermediate zone characteristics) for cables. this is the zone between the continues load capability and the short-circuit capability. It says:
"Intermediate zone characteristics of medium-voltage cables and 75...
RC Wilson:
You are a good teacher and communicator. Thanks for your step by step explanation .... I got it!!!!!! I am slow but not totally retarded.
Thanks all for your patient comments and responses.
For some stupid reason, (all mistakes are) I though that the "calculated ohmic value"...
DPC:
Your are right, I should have read your response more carefully.
The whole discussion that I started with my first post, was not about the "actual ohmic impedance", but the Z%. Please review my first post. But now that you mentioned this "actual ohmic impedance", I realized that I have...
DPC:
Thanks for your prompt answer.
Actually, the Z% impedance does change when the full-load kVA is used instead of the nominal kVA. If it would not change, the short-circuit delivered by the transformer would be greater when using the full-load kVA instead of the nominal kVA.
The Z% is the...
