Case unselective tripping

In a power grid, protection relays are critical components which are supposed to detect and disconnect faulty feeders. Unfortunately, they do not detect all faults. For example, the relay protection systems can be incorrectly configured or not sensitive enough for certain intermittent earth faults, why a faulty feeder may not be disconnected in a proper way leading to a high displacement voltage tripping the whole substation. The problem of unselective tripping is a hot topic of discussion and, among others, Vattenfall has drawn attention to the problem in a thesis which can be read here.

dInsight Analytics Platform from dLab consists of different applications and services, and one of those applications, dAnalyzer, is based on unique patented algorithms that automatically analyze and categorize even the smallest deviations in the distribution grid. Harnessing this data, operations will get early warnings for imminent faults, making it possible to work proactively fixing the root-cause before an outage appear. Moreover, the information from dAnalyzer facilitates for a substantially faster fault investigation, and in many cases the system is even used to monitor the relay protection system making sure it works as desired.

One important aspect is the possibility for dAnalyzer to effectively identify which feeder is faulty, which is one key in solving the unselective tripping.

dAnalyzer is more sensitive compared to most protection relays and detect faults earlier, but normally it acts as a decision support system and no actions are taken actively by the application. However, dLab also provides dProtection which can be described as a dAnalyzer on-the-edge with the ability to send digital signals and thus commanding the circuit breakers directly, or indirectly via the protection relays, to operate. With dLab’s patented algorithm for detecting directional and intermittent earth faults, dProtection ensures that only the faulty feeder is disconnected in case of a fault, and not the entire busbar.

Read more about our customer Olofström and their use of dAnalyzer and dProtection here: New order: Olofström Kraft AB takes another step together with dLab.  

In case dProtection isn’t installed and an unselective tripping occurs, dAnalyzer will still provide critical information. In the figures below, one real example is presented of an earth fault occurring unnoticed by the substation’s actual protective relay in “Outgoing feeder 14”. Eventually, the neutral point overvoltage protection, trips the whole busbar. But as made evident in the first figure, dAnalyzer has correctly identified the faulty feeder and, if dProtection had been installed, would have disconnected that feeder six seconds earlier and before the neutral point overvoltage protection did. In the current- and voltage plots, the red line marks the point in time where dAnalyzer indicated trip for the outgoing feeder.

This information is very useful for the ones working in operations to quickly take correct actions.

Furthermore, with dLab’s dXport application, this information can be exported to for instance a network information system (NIS) where the faulty feeder will be pointed out directly in the NIS interface as well.