ABB RELION REX640 Technical Manual page 1180

Protection related functions
Improper analog channel configuration causes a validation error if the analog
channels are not completely configured or they do not match with certain settings.
For troubleshooting, check the contents of this chapter and also the preprocessing
blocks in this document. The configuration can be written to the protection relay
once the mismatch is corrected.
5.4.5 Operation principle
The function can be enabled and disabled with the
corresponding parameter values are "On" and "Off".
PHIZ uses a multi-algorithm approach. Each algorithm uses various features of
earth currents to detect a high-impedance fault.
Although the PHIZ algorithm is very sophisticated, the setting required to operate
the function is simple. The
10, is set to strike a balance between the extremes of security and dependability
which together constitute the reliability of any system. The setting value "10" is
more secure than "1".
The higher the
but the system might miss out some genuine fault. On the other hand, a lower
setting would make the system operate more dependably for high-impedance
faults in the line, but the operation is more likely for other transients in the
system. There are events in electrical networks which can cause similar current
waveforms like high-impedance faults. These events could then be detected by
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.
Figure 670: Electrical power system equipped with PHIZ
1180
Security Level setting, with the setting range of 1 to
Security Level setting, the lower the probability of false detection,
Bus
Transformer
Feeder
Breaker
Ct
1MRS759142 F
Operation setting. The
Technical Manual
REX640