ABB RELION REX640 Technical Manual page 597

1MRS759142 F
Touch voltage estimation
After estimate for earth-fault current is calculated and its validity confirmed, then
conversion of fault current estimate
derived using equations below:
Effective earth potential rise estimate:
with
Where
Setting
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 effective earth potential rise is used:
Setting
which determines operation speed of IFPTOC:
• In case
earth potential rise.
• In case
part of earth potential rise. In this case the value of setting
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).
REX640
Technical Manual
(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.
Equation 115 Equation 117
,
Maximum earthing Ris is a user defined maximum earthing resistance
Reduction factor enables down scaling of the estimated earth potential rise,
Reduction factor = 1, it is assumed that touch voltage equals 100% of
Reduction factor < 1, then it is assumed that touch voltage equals only
into earth potential rise estimate
can also be written as:
Protection functions
is
(Equation 117)
(Equation 118)
, the estimate of
(Equation 119)
Reduction factor
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