Final Thoughts

It is a well-known fact in the protection, automation and control industry that optimal performance of the PAC systems can be achieved based on advanced technology and engineering tools. The impact of the DERs on the performance of the PAC system has to be evaluated as part of the short circuit and protection coordination studies.

 

And this is where the problem is. Today we can say (and I am sure everybody will be very happy if someone proves that what I say here is not correct) that the tools that we typically use for fault analysis and protection settings calculation do not support the proper simulation of the impact of the different types of DERs on the protection devices.
The situation is a little better when we think about the impact of the wind turbines/generators.

There are some existing generic positive sequence models for the main four types of wind generators, however they are not sufficient when we need to calculate the protection function settings for the more common single-phase-to-ground faults.
Approximate models can be a solution, but it may be useful only when the impact of the DER on the fault currents is minimal in comparison to the fault contribution of the grid. But this is definitely not the case when large wind generators are connected to a distribution feeder.

Then the fault contribution of the wind generator can be a factor that needs to be considered for the protection settings coordination.

Another issue is the impact of the inverter based DERs, such as photovoltaic systems.
The inability to properly model inverter-based generation in utility industry analysis tools can be a significant obstacle to the further penetration of DERs, due to the difficulties of protection settings calculation and coordination.
An alternative to the approximate simulation in steady-state fault analysis tools is the more precise simulation in electromagnetic transients programs.

The problem in this case is first that the number of users of such tools in the protection and control departments of many utilities is limited, but also that the correct model of a specific wind turbine generator depends on a detailed hardware and control model which in most cases is not available from the suppliers of the DERs.

Some of the things we need to do to solve these problems are first to require from DER suppliers accurate models that can be used for transient simulation, as well as to push the industry to develop adequate models that should be quickly implemented in the steady state fault analysis and protection coordination tools.

Power. Flexible. Easergy.
BeijingSifang June 2016