ERL L-PRO 4000, Руководство пользователя

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4 Protection Functions and Specifications
4-12 L-PRO 4000 User Manual D02706R02.30
The positive-sequence calculation determines the angle between the measured
positive-sequence impedance (based on measured current, and the memory
voltage output of the ring filter) and the positive-sequence line impedance an-
gle entered in settings. To perform the positive-sequence impedance calcula-
tion, the directly measured positive-sequence current must exceed 0.2 A
secondary, and the memorized positive-sequence voltage must exceed 2 V sec-
ondary.
There may be some rare circumstances where there may not be sufficient volt-
age or current, using the negative, zero, and positive sequence components, for
the directional element to make a valid directional decision. The most likely
circumstance where this may occur is a 3-phase bolted fault near the line VTs,
that is not cleared in an appropriate amount of time. It takes approximately 30
cycles, after the measured 3-phase system voltage drops to 0, for the ring filter
voltage to decay such that the Vpos_mem is less than 2 V secondary. For this
circumstance, or for any other fault case where there are insufficient sequence
component quantities for any of the directional calculations to operate, the di-
rection is set to “forward”. Setting the directional element to forward explicitly
sets the direction to forward for the distance elements, and for the 50N/67N-F
and 50N/67N-R elements in the communications aided tripping schemes (ef-
fectively blocking the 50N/67N-R element), and allows all other directional
controlled elements to operate non-directional.
Directional
Element
Outputs
The output of the directional element asserts when the direction is determined
to be “forward”. This output is used internally by protection functions directly
supervised by the element, and is also available as the “Directional Element”
indication in ProLogic equations. The directional element also provides the
“Directional Valid” output for use in ProLogic equations. This output asserts
when any one of the active sequence impedance calculations has sufficient in-
put quantities to make a valid direction determination, regardless of the actual
direction. The “Directional Valid” output will always be asserted, except in the
rare case where system voltage has gone to 0 for more than 30 cycles, as pre-
viously described. The 2 outputs can be combined in a ProLogic equation to e
a secure reverse directional output from the relay, for example.
Figure 4.10: Directional Element
Directional
Element
Settings
The default setting of the directional element in the relay should be correct for
most applications. The default settings enable both the negative-sequence and
zero-sequence calculations, with the minimum sensitivities as described. There
are some applications where it may be advisable to change the sensitivity
thresholds for the negative-sequence or zero-sequence calculations, or it may
be desirable to disable one or both of these elements.
Selecting “Directional Element Override Enabled” allows user settings for the
negative-sequence and zero-sequence directional elements.
Directional Element
Directional Valid
Reverse Fault