IPC402x-UM-2209-1-2.x.x (en)
Ensto Protrol AB
Phone: +46 31 45 82 00
Alfagatan 3
internet: www.protrol.se
431 49 Mölndal, SWEDEN
41
e-mail: [email protected]
8 Detector Functions
8.1 General
IPC402x contains the following detector functions:
▪
Overcurrent - detects short circuit or overload
▪
Earth fault Protrol - patented method for sensitive detection of solid and intermittent earth faults
▪
Earth fault non-directional
–
residual current based detection
▪
Phase break - for detection of the loss of a phase
The fault detector measures the phase currents. Isolation between detector and the secondary current
circuit of the primary current transformer is provided by current transformers. The sampling frequency of
the phase currents is 2 kHz.
Protrols method for earth fault detection is of transient measuring nature, which means that it is both fast
and sensitive. Fast means that the method works safely for both high impedance as well as transient and
arcing faults. The method is based on analysing the change of the phase currents when an earth fault
occurs. Detection of an earth fault means that the fault is downstream of the measuring point in a radial
network, or that a fault current has passed the measuring point, i.e., true fault pass-through detection.
Indirectly, this means that the direction of the fault can be identified by measuring phase currents only,
without the need of polarizing zero-sequence voltage.
The method works very safely for all types of networks from directly grounded to isolated. In particular, this
means that for an impedance grounded network, the compensation degree has no significance, and for an
isolated network, the natural unbalance between the phases in principle can be infinite. It works just as
well.
8.2 Detection states
The earth fault detection sequence goes through discrete states. These states can be seen in the transient
fault recording (chapter 10). For each state, an evaluation is made if certain conditions are met to proceed
to the next state. If these conditions are not met, a controlled return to the basic state is made.
0 IDLE
–
This is the basic state. The detector continuously evaluates any changes in the residual current, I
N.
2 TRIG
–
An earth fault somewhere in the network is triggered by detecting a sudden change of I
N
. The size
of the change is related to the sensitivity, the smaller the change, the higher the impedance of the earth
fault. During a short period after TRIG, the nature of the error is evaluated. Depending on the result, the
state changes to either RESET, EVAL-T, or EVAL-A.
3 EVAL-T
–
In this state, supplementary calculations are made especially for high impedance faults. From
this state, the detector always continues to EVAL-A.
4 EVAL-A
–
State to determine whether the detector should go to START or RESET.
5 START
–
Here, a timer for the set time delay is started. The detector proceeds to the DETECT or TRIP
states if the changed I
N
exists after the set time. The state will return to RESET if the condition is not met.
6 DETECT/TRIP
–
This state means that a fault has been detected. Controlled return to IDLE via RESET will
follow.
8 REIGNITION
–
This state means the same as DETECT but indicates that the fault is reigniting or arcing.
