ABB Relion 670 Series Technical Reference Manual page 430

Section 7
Current protection
7.5.2.3
7.5.2.4
7.5.2.5
7.5.2.6
424
Then the phasor of the total polarizing voltage VTotPol is used, together with the
phasor of the operating current, to determine the direction to the fault (Forward/Reverse).
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 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
Base quantities within the function
The base quantities must be entered as setting parameters for every function. Base
current (IBase) must be entered as rated phase current of the protected object in
primary amperes. In line protections the primary rated current of the CT is chosen.
Base voltage VBase must be entered as rated phase-to-phase voltage of the protected
object in primary kV. In line protections the primary rated voltage of the VT is chosen.
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.
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 (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
1MRK505222-UUS C
Technical reference manual