Siemens SIPROTEC 7SK80 Manual page 25

Frequency Protection 81 O/U
• Monitoring on underfrequency (f<) and/or overfrequency (f>) with 4 frequency limits and delay times that are
independently adjustable;
• Insensitive to harmonics and abrupt phase angle changes;
• Adjustable undervoltage threshold.
Thermal Overload Protection 49
• Thermal profile of energy losses (overload protection has total memory capability);
• True r.m.s. calculation;
• Adjustable thermal alarm level;
• Adjustable alarm level based on current magnitude;
• Additional time constant setting for motors to accommodate the motor at standstill;
• Integration of the ambient temperature or coolant temperature is possible via internal temperature detection
or an external thermobox.
Monitoring Functions
• Reliability of the device is greatly increased because of self-monitoring of the internal measurement circuits
as well as the hardware and software.
• Fuse failure monitor with protection function blocking.
• Monitoring of the current transformer and voltage transformer secondary circuits using summation and sym-
metry monitoring with optional protection function blocking.
• Trip circuit monitoring;
• Phase rotation check.
Ground Fault Detection 50N(s), 51N(s), 67N(s), 59N/64
• Displacement voltage is measured or calculated from the three phase voltages;
• Determination of a faulty phase on ungrounded or grounded systems;
• Two-element Ground Fault Detection: High-set element 50Ns-2 and overcurrent element 50Ns-1.
• High sensitivity (as low as 1 mA);
• Overcurrent element with definite time or inverse time delay;
• For inverse time overcurrent protection, a user-defined characteristic is available.
• Direction determination with zero sequence quantities(I
tion;
• A sector characteristics can be set as directional characteristic.
• Any Element can be set as directional or non-directional — forward sensing directional, or reverse sensing
directional;
• Optionally applicable as additional ground fault protection.
SIPROTEC, 7SK80, Manual
E50417-G1140-C344-A4, Release date 08.2010
, V ), wattmetric ground fault direction determina-
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Introduction
1.3 Characteristics
25