1 Introduction
10
7UM62 Manual
C53000-G1176-C149-3
•
Measurement of displacement voltage at the machine via the neutral transformers
or earthing transformer or by calculation from phase-to-earth voltages;
•
Highly sensitive earth current detection, optional with or without directional
determination with zero sequence components (I
0
, U
0
);
•
With adjustable slope of directional characteristic;
•
Discrimination of the earth-faulted phase.
Sensitive Earth
Current Protection
•
Two sensitive earth fault instantaneous overcurrent elements: I
EE
>> and I
EE
>;
•
Pickup currents are adjustable and can be set very sensitive (as low as 2 mA);
•
Can be used for stator earth fault or rotor earth fault detection;
•
Measured circuit monitoring when used for rotor earth fault protection.
100–%–Stator Earth
Fault Protection
with 3rd Harmonics
•
Detection of the 3rd harmonic of the voltage at the starpoint or open delta winding
of an earthing transformer;
•
In addition to the 90-%-stator earth fault protection there is a protection of the entire
stator winding (protective range 100 %).
100–%–Stator Earth
Fault Protection
with 20 Hz Voltage
Injection
•
Evaluation of the 20 Hz measurement (7XT33 and 7XT34);
•
Warning and trip stage R< and R<<;
•
Trip stage with earth current;.
•
High sensitivity also at large stator earth capacitances.
Rotor Earth Fault
Protection
•
100 % protection for the entire excitation circuit;
•
Symmetrical capacitive coupling of a system-frequency AC voltage into the
excitation circuit;
•
with consideration of operational earth impedances and brush resistances;
•
Calculation of the fault resistance from the total impedance;
•
Alarm stage and tripping stage directly adjustable in Ohms (rotor-earth resistance);
•
Measurement circuit supervision with alarm output.
Sensitive Rotor
Earth Fault
Protection with
1 to 3 Hz Square
Wave Voltage
Injection
•
Evaluation of the 1 to 3 Hz square-wave voltage injected into the rotor circuit
(7XT71);
•
Warning and trip stage R< and R<<;
•
High sensitivity (max. 80 K
Ω
);
•
Integrated test function.
Motor Starting Time
Supervision
•
Current dependent tripping based on an evaluation of the motor starting current;
•
Blocked rotor protection.
Restart Inhibit for
Motors
•
Rotor temperature is calculated based on the stator currents;
•
Start-up is permitted only if the rotor has sufficient thermal reserves for a complete
start-up;
•
Calculation of waiting time (till automatic reclosure is available);
