Hello, I understand that photovoltaic plants are able to disconnect very quickly if there is a fault in the grid (cause power electronics), while synchronus generators cant disconnect due to his inertia and synchronism. So is this good charasteric of the photovoltaic plants (or any renewable energy which depends of power electronics), because it will reduce the shortcircuit current, or no? Im wondering this because there exists the synthetic inertia for this kind of systems, so why would I like to keep feeding this fault?. Thanks in advance.
Hi Giovanni,
As you say, this is certainly a good characteristic of the photovoltaic plant, particularly when the PV plant is working in isolation on a networked system of loads (say, an islanded system that is totally PV based).
However, when the network has conventional generators connected as well, the PV based generators must have steady state, transient, and dynamic compatibility with the system as a whole. In such situations, the synthetic inertia feature is often useful.
Think of a situation where under some dynamic disturbance, all the connected inertias are swinging in real time. If the PV unit (which need not swing by default) is made to swing in a manner that the electromechanical oscillations are better damped, then that certainly helps !
Cheers !
-Sanjay
Most standard fault detection scemes depend on a high current jump for the algorythms usually trigger on a high dI/dt, which the intia of a heavy generator rotor can deliver.
My guess would be that the 'synthetic inertia' of an converter can be increased by increasing the inner capacities. But there will be a limit on cost and the switches itself, too .
I‘m not an expert in short circuit detection, but if the short circuit current is not much higher than the rated normal current (due to PV plant switching off extremely fast), I’d guess short circuit detection in other parts of the network may be difficult (as Karsten Backhaus basically said). Also, if there are fuses they might not melt in this case.
the disconnection of a synchronous motor from the network in the event of a short circuit depends very much on the sensitivity of the protections of this machine. compared to my experiences, I believe that there are very powerful and ultra fast digital relays (tripping) and which protect the synchronous machine connected to the network especially if these short circuits take place very close to the terminals of the machine. as far as photo voltaic cells are concerned, I think that their protection is also fast but they are often considered as negative charges when they are connected to the networks because they do not participate in maintaining the inertia of the network machine set. since they are static.
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