DC Short Circuit Calculations 6

[DanDel]

Does anyone have a reference for DC Short Circuit calculations? IEEE/ANSI, similar to the 242 Buff Book possibly? I am mostly interested in how a rectifier would be modeled and what is used for the commutating reactance. I have the ETAP DC module, but I would like to check the results. Thank you.

 

[ruggedscot]

short circuit calculations in rectifier fed circuits are pretty complicated as there are several variables that need to be taken in.

1. Is current limitation involved ? Some dc circuits are fed from electronic based equipment and will have current limitation incorporated. If so you will find that you can not base on simple calculations for short ciruit currents.

2. Rectified dc if reservior capacitors are utilised then you will find that the ripple currents experianced by these will cause them to burst.

3. Thyristor pulsing with dv/dt characteristics causing the thyristor to breakdown leading to ac appearing on the output.

4. generally dc circuits can produce a lot of power especially those from batteries. AC derived can be limited by the impedance of the supply and rectification. Also with ac rectified supplies a complex waveform is developed feeding the short

 

[Modula2]

Ruggedscot, are you saying that batteries can feed back into ac system via the convertor such as thyristors? Would that normally require a detailed model of the power electronics or are simplifications possible.

 

[gordonl]

I'm sure there are newer articles out there, but if there isn't try and find this one:

S.C. Calculating Procedures for DC Systems

AIEE Paper No. CP 57-811
Published May 31, 1957
(OLD IEEE article)

 

[DanDel]

gordonl, thank you, but I can't find the CP 57-811 article on the IEEE website or by internet search. If possible, can you tell me where it can be found(or where you got it)?

 

[BJC]

I can offer a good reference but I can't tell you where to find it. General Electric use to publish a loose leaf notebook about 3" thick. It was call the "Industrial power systems book" of the Industrial power sytems data book"
Some of the material in the "Art and Science of Protcetive Relaying"

http://www.geindustrial.com/multilin/notes/artsci/index.htm

was in this book.
The section on short circuit studies for DC systems was very good and even thought dated (1940-50s for some articals, the last issue I saw was published in the &0s)I sure would help you a lot. I may hav a copy of the DC paper, I'll check tonight.
IF anyone has the GE book hang on to it. If you could get permission from GE it would be a great reference on CD

 

[stevenal]

The short answer is fault current at battery charger terminals is 150% of rated current. For longer answers, see IEEE 1375 and 946.

 

[gordonl]

The article has been around the office since original publication, to get a hold of a copy I would suggest trying a university library, and looking in the confrence proceedings for the 1957 summer meeting of the AIEE(IEEE).

 

[SidiropoulosM]

DanDel, it might be useful if you could describe your application somewhat. I suspect it's a low voltage application. In high voltage DC, the controls of DC converters are usually designed to limit their fault currents to values equal to or less than normal load current.

 

[DanDel]

Thank you, BJC and SidiropoulosM.
The application is 750VDC, with several 12 pulse rectifiers in the 3000kW range.

 

[Modula2]

Even in LV power electronics, the converters have software based protection against high currents. In the case of thyristors, this could, by stopping the gating, end the short circuit in a half cycle, but there could be a high peak even in that time. Fast acting current limiting fuses are also seen.

 

[milsad]

I think this standard will be very helpful..

IEC(EN)61660-1, short-circuit currents in D.C. auxiliary installations in power plants and substations