SCR is given for machines. We have sequence impedances- typical- for most network components. Quite a lot depends on the shorting point. and the type of fault too I suppose
Dear Sudha Balagopalan Madan,
I am interested to know the maximum fault current values.
A dead short at machine terminals is the worst and the short circuit levela are easily obtained using SCR and voltage levels. As the THE DEAD SHORT PROGRESSES further away from the machine, impact is reduced by the transformer and line impedance, all of which have empirical values, or a real system spec can give you. But you know all this. What am I missing?
When using the line commutated converter (LCC), for example at the point of common coupling (PCC) between the HVDC line and AC grid, to control the frequency and voltage. The short-circuit ratio (SCR) in AC/DC link (or at the PCC) has to be maintained higher to ensure strong link. At about the value of 3 for a high SCR or 2 for a critical SCR.
Note that the LCC based inverter or rectifier use thyristors with firing angle control. The commutation of thyristors/gates depends on the AC network. If the AC/DC link is weak e.g. SCR=1 (low SCR), the commutation becomes vulnerable. Therefore, a reactive power compensator is needed in the AC/DC junction to maintain the SCR high..
There are many factors that affects the short circuit levels in a power system, such as, network configuration, generators operation point, transformers and line impedances, motors connected in busbars, fault location, fault types (single phase, two phase, three phase short circuit) and so on. commonly the generators busbars have the higher levels for three phase short circuit.
The IEC 60076-5 standard gives a typical values for three phase short circuit (see the attached table)
SO Mam you are saying Grid is not having a Short circuit MVA rating???
You can also check the IEC - 60076-5 which talks about the ability to withstand short circuit . in page 14 an 15 of this IEC standard, you can find the " Short-circuit apparent power of the system ", both for European and North American Networks. It's valid and you can apply it to your calculations.
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