Siemens 7SK80 Manual page 25

Load Step Function
• Detection of mechanical or thermal overload of the rotor.
Frequency Protection 81 O/U
• Monitoring of falling below (f<) and/or exceeding (f>) with 4 frequency limits and time delays that are inde-
pendently adjustable
• Insensitive to harmonics and abrupt phase angle changes
• Adjustable undervoltage threshold.
Thermal Overload Protection 49
• Thermal profile of energy losses (overload protection has full memory capability)
• True r.m.s. calculation
• Adjustable thermal warning element
• 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
• Increased reliability due to monitoring of the internal measurement circuits as well as the hardware and soft-
ware
• Fuse failure monitor with protection function blocking
• Monitoring of the current transformer and voltage transformer secondary circuits using sum and symmetry
supervision with optional protection function blocking
• Trip circuit monitoring possible
• 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-current 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(I0, V0), wattmetric ground fault direction determina-
tion.
• A sector characteristic 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-A5, Release date 11.2012
Introduction
1.3 Characteristics
25