the magnitude of polarizing voltage must be bigger than a minimum level defined by
setting UpolMin.
Note that –U2 is used to determine the location of the fault. This ensures the required
inversion of the polarizing voltage within the function.
8.5.7.3 External polarizing for negative sequence function
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 BLKSTx (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
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
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 (Off/ 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
""
1MRK502052-UEN B Section 8
Current protection
383
Technical manual
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