(fundamental frequency magnitude). Positive value means that fault is
seen inside the protected feeder, negative value means that fault is seen
outside the protected feeder.
Touch voltage estimation
After estimate for earth-fault current is calculated and its validity confirmed, then
conversion of fault current estimate
into earth potential rise estimate
is
derived using equations below:
Effective earth potential rise estimate:
(Equation 117)
with
,
can also be written as:
(Equation 118)
Where
Setting
Maximum earthing Ris is a user defined maximum earthing resistance
value encountered in the earthings located at the protected feeder. Higher earthing
resistance results in higher earth potential rise and touch voltage during the fault.
For estimating the hazardous touch voltage at fault location,
, the estimate of
the effective earth potential rise is used:
(Equation 119)
Setting
Reduction factor enables down scaling of the estimated earth potential rise,
which determines operation speed of IFPTOC:
• In case
Reduction factor = 1, it is assumed that touch voltage equals 100% of
earth potential rise.
• In case
Reduction factor < 1, then it is assumed that touch voltage equals only
part of earth potential rise. In this case the value of setting
Reduction factor
depends e.g. on actual reduction effect in the return path of earth-fault current
and properties of earthing systems in the protected feeder.
Magnitude of estimated touch voltage is given in Recorded data:
•
Touch voltage (fundamental frequency magnitude)
•
Touch voltage rms (rms-value).
In Monitored data the magnitude of estimated touch voltage is given in as:
•
TCH_VOLTAGE
(fundamental frequency magnitude)
•
TCH_VOLT_RMS
(rms-value).
1MRS759142 F
Protection functions
REX640
Technical Manual
597