Short circuit

[MacKow]

Hello, this is my first forum post. I have a question regarding the photo below. How was the IR (2) current (with DG) calculated? What does this impedance formula result from? Thanks for any help. The photo comes from the article "Impact of Distributed Generation on
Distribution Protection and Power Quality ''.

 

[waross]

This may be helpful.

What is the difference between subtransient and transient reactance?

Sri Krishna Sharma
, BE (Hons.) Electrical Engineering & Trained in SQC , TQM, Six Sigma, ISO Audits,Vendor Audits, University of …
Answered 2 years ago · Author has 2K answers and 2.3M answer views

Sub transient reactance

The period immediately after a short circuit on the generator and lasting up to 2-3 cycles, is called sub transient period. The current during this period is highest and is determined by sub transient reactance.

The value of sub transient reactance is about half of the leakage reactance. Considering a leakage reactance of 0.2 p.u., sub transient reactance can be taken as 0.1 p.u. Thus the fault current during sub transient period would be 10 times the normal rated current.

Transient reactance

After the elapse of sub transient period, we have transient period which lasts till the fault current settles to a low value (less than normal current).

During transient period, fault current is determined by transient reactance which is nothing but leakage reactance of the generator.

Considering a transient reactance of 0.2 p.u., the fault current during transient period would be five times the normal current.

Note that during sub transient period and transient period, armature reaction is absent. Finally when armature reaction comes into play, current settles to a value determined by synchronous reactance which is normally less than the full load rated current.

Link

Bill
--------------------
Ohm's law
Not just a good idea;
It's the LAW!