Maximum Slip Frequency - ABB RES670 Technical Manual

Section 7
Impedance protection
7.2.7.3
164
right to left in case of a generator and in the opposite direction in case of a motor.
Another requirement is that the travel across the lens takes no less than a specific
minimum traverse time, typically 40...60 milliseconds. The above timing is used to
discriminate a fault from an out-of-step condition. In
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 fault with low fault resistance: 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. Figure 42
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.

Maximum slip frequency

A pole-slip may be detected if it has a slip frequency lower than a maximum value
fsMax. The specific value of fsMax depends on the setting (parameter) PickupAngle
(which determines the width of the lens characteristic). A parameter in this calculation
routine is the value of the minimum traverse time, traverseTimeMin. The minimum
traverse time is the minimum time that the travel of the complex impedance Z(R, X)
through the lens, from one side to the other, must last 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:
1000
[ ]
≅
fsMax Hz
traverseTimeMin ms
ANSIEQUATION2319 V1 EN-US
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
The maximum slip frequency fsMax for traverseTimeMin = 40 ms is:
shows two pole-slips. Figures like

PickupAngle
⋅
 
1 000 . -
[ ]
180

1MRK 511 408-UUS A
Figure 42, some important points
Figure 42 and Figure 44
GUID-1311529F-21F8-40A0-8D01-0296BD9B4F00 v5
[ ]

°
 
[ [ ]
°

(default 110°)
Phasor measurement unit RES670 2.2 ANSI
Technical manual
are
(Equation 7)