ABB RELION REX640 Technical Manual page 1090

Section 5
Protection related functions
1084
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.
Bus
Transformer
Feeder
Ct
GUID-210F3A10-C3F1-4C23-B43D-E05455D314DE V1 EN
Figure 583: 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.
GUID-9938E840-E126-463D-9BF7-4EEDE9007AA7 V1 EN
Figure 584: Block diagram of PHIZ
PHIZ is based on algorithms that use earth current signatures which are considered
non-stationary, temporally volatile and of various burst duration. All harmonic and
Breaker
1MRS759142 C
REX640
Technical Manual