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milliseconds. (To require that the impedance Z(R, X) travels through each of the two
halves of the lens, for example, in 25 milliseconds, results in a tendency to miss the 1st
pole-slip, that one immediately after the fault has been cleared.) The above timing is used
to discriminate a fault from an out-of-step condition. In
, some important points
on the trajectory of Z(R, X) are designated. Point 0: the pre-fault, normal load Z(R, X).
Point 1: impedance Z under a three-phase, low-resistance fault. Z lies practically on, or
very near, the Z-line. Transition of the measured Z from point 0 to point 1 takes app. 20
ms, due to Fourier filters. Point 2: Z immediately after the fault has been cleared.
Transition of the measured Z from point 1 to point 2 takes approximately 20 ms, due to
Fourier filters. The complex impedance then travels in the direction from the right to the
left, and exits the lens on the opposite side. When the complex impedance exits the lens
on the side opposite to its entrance, the 1st pole-slip has already occurred and more pole-
slips can be expected if the generator is not disconnected.
shows two pole-slips.
Figures like
are always possible to draw by means of the analog
output data from the pole-slip function, and are of great help with eventual investigations
of the performance of the out-of-step function.
7.4.7.3
Maximum slip frequency
The maximum slip frequency
fsMax
in Hz where a pole-slip can be detected when using
a specific value of the setting (parameter)
PickupAngle
(which determines the width of the
lens characteristic) is as follows. A parameter in this calculation routine is the value of the
minimum traverse time,
traverseTimeMin
. The minimum traverse time determines the
minimum time, the complex impedance Z(R, X) must travel through the lens from one
side to the other, in order to recognize that a pole-slip has occurred. The value of the
internal constant
traverseTimeMin
is a function of the set
PickupAngle
.For values of
PickupAngle
<= 110°,
traverseTimeMin
= 50 ms. For values
PickupAngle
> 110°,
traverseTimeMin
= 40 ms. The expression which relates the maximum slip frequency
fsMax
and the
traverseTimeMin
is as follows:
fsMax Hz
traverseTimeMin ms
PickupAngle
[ ]
≅
[ ]
⋅
°
[ ]
°
1000
1 000
180
.
-
[[ ]
ANSIEQUATION2319 V1 EN
(Equation 40)
The maximum slip frequency
fsMax
for
traverseTimeMin
= 50 ms is:
PickupAngle = 90° → fsMax = 20 ⋅ 0.500 = 10.000 Hz
PickupAngle = 100° → fsMax = 20 ⋅ 0.444 = 8.888 Hz
PickupAngle = 110° → fsMax = 20 ⋅ 0.388 = 7.777 Hz
(default 110°)
The maximum slip frequency
fsMax
for
traverseTimeMin
= 40 ms is:
1MRK 502 048-UUS A
Section 7
Impedance protection
183
Technical manual
Содержание 650 series
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