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...
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.
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...
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...
I understand that the transformer nameplate impedance (Z%) is related to the nominal kVA.
I also understand that this impedance will change if we consider the full-load kVA of the transformer.
The result is that the short-circuit current delivered by the transformer is the same no matter which...
I know (as a rule of thumb) that the %Z of a transformer with multiple kVA ratings changes according to the kVA rating. For example if a transformer has a 2,000 kVA Nominal rating and a 2.500 Full Load kVA rating and the published %Z is 5.5% (at Nominal kVA rating) the %Z at Full Load kVA...
Does anybody know a detailed guide for polarization marks in current transformer relays?
I understand how the polarization marks work when the primary CT current ENTERS the primary CT and the polarization mark of the primary CT is at the entrance (begining of the coil. But I do not uderstand...
I am doing a coordination study and want to protect a medium voltage motor with a relay. To do this I need to know the damage curve of the motor.
If I would know this curve I can plot it. Where can I obtain standard motor damage curves for different types of motors?
Thanks.
RECS
