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2 Functions
2.22.2 Setting Notes
Sensitive earth fault detection can only be effective and available if address 151 O/C
General
PROT. Iee> is set to Enabled during configuration. If one of the options with current
evaluation was selected during the configuration of the 90% stator earth fault protec-
tion (150 S/E/F PROT., see Section 2.2.2) the sensitive current measuring input of
the 7UM61 device is allocated. Note that sensitive earth fault detection uses the same
measuring input and thus accesses the same measured value. If sensitive earth fault
detection is not required, Disabled is set. Address 5101 O/C PROT. Iee> serves
to switch the function ON or OFF or to block only the trip command (Block relay).
Use as Rotor Earth
The sensitive earth current protection can be used to detect earth faults either in the
Fault Protection
stator or in the rotor winding of the generator. A precondition is that the magnitude of
the earth current alone is sufficient as a criterion. In very high-ohmic circuits or those
isolated from earth, sufficiently large earth currents must be ensured.
When for example earth fault protection is used as rotor fault protection, a system fre-
quency bias voltage (U
Rotor Earth Fault Protection in Section 2.22) must be applied to the rotor circuit.
Because of this bias voltage, with proper earth connection a current flows through the
earth capacitance, which can be used as a criterion for a closed measuring circuit (ad-
dress 5106 IEE<). Approximately 2mA is a typical pickup value. The monitoring stage
is ineffective is this value is set to 0. This can become necessary if the earth capaci-
tances are too small.
The earth current pick-up value 5102 IEE> is chosen such that isolation resistances
R
On the other hand, the setting value should be at least twice the interference current
caused by the earth capacitances of the rotor circuit.
The 5104 IEE>> trip stage should be dimensioned for a fault resistance of about 1.5
kΩ.
with Z
The 5103 T IEE> and 5105 T IEE>> tripping time delays do not include the oper-
ating times.
Use as Stator Earth
Please also refer to Section 2.21. For use as stator earth fault protection, the earth
Fault Protection
current must if necessary be increased by an ohmic load resistor at the earthing trans-
former. Instructions for dimensioning the earth current transformer and loading resistor
are contained in the publication "Planning Machine Protection Systems" /5/.
138
≈ 42 V, via 7XR61 series device in figure Application Case as
V
between 3 kΩ and 5 kΩ can be detected:
E
= Impedance of the series device at nominal frequency.
K
7UM61 Manual
C53000-G1176-C127-3
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