The individual steps within the protection can be set as non-directional. When this setting is
selected it is then possible via function binary input BLKx (where x indicates the relevant step
within the protection) to provide external directional control (that is, torque control) by for
example using one of the following functions if available in the IED:
• Distance protection directional function
• Negative sequence polarized general current and voltage multi purpose protection function
8.5.7.4 Internal negative sequence protection structure
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The protection is internally divided into the following parts:
• Four negative sequence overcurrent steps
• Directional supervision element for negative sequence overcurrent steps with integrated
directional comparison step for communication based negative sequence protection schemes
(permissive or blocking)
Each part is described separately in the following sections.
8.5.7.5 Four negative sequence overcurrent stages
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Each overcurrent stage uses Operating Quantity I2 (negative sequence current) as measuring
quantity. Every of the four overcurrent stage has the following built-in facilities:
• Operating mode (
Disabled
/
Non-directional
/
Forward
/
Reverse
). By this parameter setting
the operating mode of the stage is selected. Note that the directional decision (Forward/
Reverse) is not made within the overcurrent stage itself. The direction of the fault is
determined in common “Directional Supervision Element” described in the next paragraph.
• Negative sequence current pickup value.
• Type of operating characteristic (Inverse or Definite Time). By this parameter setting it is
possible to select Inverse or definite time delay for negative sequence overcurrent function.
Most of the standard IEC and ANSI inverse characteristics are available. For the complete list
of available inverse curves, refer to Chapter
""
• Type of reset characteristic (
Instantaneous
/
IEC Reset
/
ANSI reset
).By this parameter setting
it is possible to select the reset characteristic of the stage. For the complete list of available
reset curves, refer to Chapter
""
• Time delay related settings. By these parameter settings the properties like definite time
delay, minimum operating time for inverse curves, reset time delay and parameters to define
user programmable inverse curve are defined.
• Multiplier for scaling of the set negative sequence current pickup value by external binary
signal. By this parameter setting it is possible to increase negative sequence current pickup
value when function binary input MULTPUx has logical value 1.
Simplified logic diagram for one negative sequence overcurrent stage is shown in the following
figure:
Section 8 1MRK 502 066-UUS B
Current protection
500
Technical manual
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