If the “Adaptive” option is selected and an OSB condition is not detected, but the
impedance enters the mho circle after remaining between the inner and outer blinders for
greater than 1.5 cycles, the function assumes a severe swing and assert the TRIP output.
The drop out delay for TRIP output can be set by Trip dropout time setting.
If the polarity of the voltage signal is opposite to the normal polarity, the correction can be
done by setting Voltage reversal to “Yes”, which rotates the impedance vector by 180
degrees.
The DISABLE input can be used to coordinate the correct operation during the start-up
situation. The function is blocked by activating the DISABLE signal. Once the DISABLE
signal is deactivated, the function remains blocked (outputs disabled) for additional time
duration as set through the setting Disable time.
Blocking logic
There are three operation modes in the blocking function. The operation modes are
controlled by the BLOCK input and the global setting in Configuration/System/Blocking
mode which selects the blocking mode. The BLOCK input can be controlled by a binary
input, a horizontal communication input or an internal signal of the protection relay's
program. The influence of the BLOCK signal activation is preselected with the global
setting Blocking mode.
The Blocking mode setting has three blocking methods. In the “Freeze timers” mode, the
operation timer is frozen to the prevailing value, but the TRIP output is not deactivated
when blocking is activated. In the “Block all” mode, the whole function is blocked and the
timers are reset. In the “Block TRIP output” mode, the function operates normally but the
TRIP output is not activated.
4.7.1.5 Application
Out of step protection functions detect stable power swings and out of step conditions
based on the fact that the voltage/current variation during a power swing is slow compared
to the step change during a fault. Both faults and power swings may cause the measured
impedance to enter into the operating characteristic of a distance relay element. The
apparent impedance moves from the pre-fault value to a fault value in a very short time,
a few milliseconds, during a fault condition. However, the rate of change of the impedance
is much slower during a power swing or out of step condition than during a fault depending
on the slip frequency of the out of step. The impedance measurement should not be used
by itself to distinguish between a fault condition and an out of step condition from a phase
fault. The fundamental method for discriminating between faults and power swings is to
track the rate of change of the measured impedance.
The function measures the rate of change of the impedance using two impedance
measurement elements known as blinders together with a timing device. If the measured
Section 4 1MAC059074-MB A
Protection functions
692 615 series ANSI
Technical Manual
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