FRT and islanding 2

[xernoxian]

if an inverter supports a power system by feeding it reactive current during a fault, doesn't that inhibit the anti-islanding feature of the inverter? please help me understand FTR(fault ride through) and anti-islanding!!

 

[waross]

If a system includes reactance then the current will have a reactive component. If a system is purely resistive a fault current will only have a reactive component if the source has has an inductive component.
For a short circuit at a transformers terminals the only induction in the circuit is the transformer itself and reactive current flows as a result.

Bill
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"Why not the best?"
Jimmy Carter

 

[Adam1980]

A fault ride through (FRT) requirements for inverters is required today due to the vast use of power electronics grid interface devices with generation from renewable resources, wind and PV in particular. The most common FRT requirements are the low voltage ride through (LVRT) as opposed to high voltage ride through (HVRT) which is still in development and not always required.

The LVRT requirements could be summarized in the following:
- The generation unit should stay connected to the grid during a certain period of low voltage of a certain depth (ex. 125 ms for a voltage drop of 100%)
- The generation unit should support the grid during the period of voltage drop by injecting reactive (capactive) current into the source of the dip.
- As a consequence the generation unit should be stable in the post event operation.

The requirements of FRT are different from country to country and they are stated in the grid code of each transmission system operator (TSO) and usually they are also used when generation is connected to the distribution level. around 8 years ago there was no such requirement since generation connected to the grid through inverters was only a negligible part of the system and their disconnection or islanding during a voltage dip would not have affected the corresponding system. However today with 500 MW wind farms connected all over the network these wind farms should remain connected and provide support during a voltage dip.

 

[bacon4life]

FRT requirements apply during the fault(usually less than 0.125 seconds), but Anti-islanding protection usually operates in the 0.2 to 2 second time frame. FRT requirements are intended to ensure that protective devices have enough current to operate, and to keep everything except the faulted portion of the system in service. Anti-islanding protection is intended to de-energize sections of the distribution grid after the section has been isolated by an upstream protective device opening.

 

[xernoxian]

thank you all very much.

 

[xernoxian]

could anyone suggest some reading materials or videos that can help me get a better understanding of FRT? thanks