the PHIZ algorithm causing unnecessary detections. Normally, electrical network
operator does not know the existence of these events well and those can also be
happening very randomly. The effect is also always dependent on event location
compared to protection relay measurement location. All these facts make the
PHIZ algorithm operation in certain electrical networks quite hard to measure and
forecast beforehand. There is not any direct formula which can calculate the exact
right setting based on known electrical network parameters.
It is hence recommended to set the value midway to “5” initially. Based on
experience and confidence gained in a particular application, the setting can be
moved either side. In many cases, it would be a good practice to use PHIZ as
an indicative function during a piloting phase, until enough experience has been
gathered and a suitable setting found.
Transformer
Feeder
Bus
Ct
Breaker
Figure 432: Electrical power system equipped with PHIZ
Power system signals are acquired, filtered and then processed by individual high-
impedance fault detection algorithm. The results of these individual algorithms
are further processed by a decision logic to provide the detection decision. The
decision logic can be modified depending on the application requirement.
Figure 433: Block diagram of PHIZ
1MRS757644 H
Protection related functions
620 series
Technical Manual
821
