Application - ABB RELION 620 Series Technical Manual

1MAC504801-IB E
4.7.2.5
620 series ANSI
Technical Manual
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.

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
impedance stays between the blinders for a predetermined time, the function declares a
power swing condition and asserts an output that can be used to block the distance
protection. However, if the impedance passes the inner blinder and exits on the other side
of the mho characteristics (that is, the resistive component of impedance has opposite sign
as at the time of point of entry) an out of step tripping is issued by the function.
gives an example of out of step detection.
Section 4
Protection functions
Figure 243
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