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Hi guys, interesting topic. Although i would like to ask something about LionelHutz example. I suppose you mean "after installing the breaker". Has the breaker to be a "current-limiting" breaker, being able to effectively limit SC Current...? If breaker is not current-limiting and 22 kA...

http://en.wikipedia.org/wiki/Power_line_communication

If 132 kV Side is not yet connected to the grid or can be easily isolated you may try this if you like. Isolate both GT3 and GT5 from 132kV grid. Force closure of "interconnector" and GT3 and GT5 breaker. Find a smart way to supply 480V AC to the primary side (132kV) of GT3 or GT5. You should...

Black Start Generators (BSG) are used in power plants to provide the "first" source for the auxiliaries subsystems of bigger engines/turbines to work. For sizing You need to know from customer what is the load/s that Generator is going to get, in how many steps. Also is good to know if the...

Generator datasheets refers that manufacturing of generator is according to NEMA MG 1-32. Part 32 of NEMA MG-1, section 32.13, NEMA Refers: Can somebody explain this .... with more details...? I admit is a little confusing term since 3ph short circuit capability of generators is described...

After some initial research: High impedance earthing (low current i.e 10A) needs special treatment by protection devices to ensure correct "understanding" of the fault current. For this reason some times low impedance (high current i.e 200Amps) is used, since higher currents can be picked up...

OK... If it is like that, this explains why the fault current coming from the generator side is 50% increased versus standalone operation. As well this proves that generator windings are in reality exposed to higher currents from what they can really produce (and most probably withstand). I...

Can you explain this a little bit more...I was expecting unfaulted phase windings of the generator to contribute to the faulted phase by a small fault current (calculated using the a operator). I wasn't expect unfaulted windings to carry grid contribution....

Hi odlanor, Did you check with Siemens the possibility to replace the trip unit?

LOL.... That sounded something like : Apply some impedance to your machine and stop posting questions! (just joking). I'm afraid math is correct. Calculations have been checked even by ETAP. Before to put my hand to my pocket to draw a lot of my company's money for applying neutral impedances...

Stupid Question : Since they have 690V-AC Circuit Breaker i assume it is 3 or 4 pole. No matter what is the trip unit, how a 3 pole CB deals with two poles of DC systems...?

Waross, for sure grid boosts the fault current using positive and negative sequence contribution , even if zero sequence of the grid is not able to reach the fault location due to the transformer delta. I can even understand the path you describe, if i draw the impedances using symmetrical...

Actually we talk about a Stamford Alternator equipped with an AVR (i.e MX321) combined with PMG.

Hi david, Actually in my configuration the utility (0) can't reach the fault location due to the existance of delta winding on LV side of the intermediate transformer. As a result, if you try to draw utility only fault circuit (i skipped this from my post) the fault current at LV bus 3 will be...

Hi guys, For one more time I need your opinion in a kind of strange issue, which escapes my understanding. Performing a single line to ground short circuit calculations (Low Voltage Side) in a simple Generator power plant using a step up to transformer, we can observe the two following facts...

Since the breaker you have can support up to 500V DC, it is ok for you. You don't need a specific breaker for 125 V DC. I guess what you really want in your case is a different trip unit to be fitted in the circuit breaker you already have. If i'm not wrong almost every circuit breaker gives...

Hi, Have a look in this pdf, page 12 of 30, chapter 9.14.2 I think you will find the answer there ;-) http://www.fecime.org/referencias/npag/chap9-122-151.pdf

In order to close this topic forever, the relavant standard which describes exactly what we are looking for is the following: IEEE std C37.013 - 1997: IEEE Standard for AC High-Voltage Generator Circuit Breakers Rated on a Symmetrical Current Basis, page 55/87, paragraph 7.3.5.1. Part of...

To all of you that you find this topic interesting: I just found a document by AREVA that refers to sizing of the Generator Circuit Breaker. I'm luck enough that this document describes GCB sizing to a system almost identical to my system. This AREVA document fully agrees with davidbeach and...

DavidBeach thanks for your info. Your consideration seems sensible, but my customer claims that correct sizing of the circuit breaker should be considering the total fault. PS: Offcourse there is a possibility my customer to be wrong, but since is a goverment company i would like to prove...