4.7.1.2
Function block
V
1
I
1
78
TRIP
SWING_TRIP
DISABLE
SWING
BLOCK
I
2
OSB
OSB_Z2
GUID-169436AD-9E20-4D6E-9EF6-9DDEAF8F5901 V1 EN
Figure 340:
Function block
4.7.1.3
Functionality
The out of step protection function 78 detects out of step conditions by monitoring
impedance.
The protection uses two impedance measurement elements known as inner and outer
blinders on mho characteristics with a timer. The function calculates the impedance. If the
measured impedance stays between inner and outer blinder for a predetermined time and
moves farther inside the inner blinder, then an out of step condition is indicated. Trip is
generated if out of step is indicated and impedance moves out of mho characteristics. The
mho characteristic can be divided into two zones so separate trips can be generated based
on the zone. Tripping can also be selected to occur when the impedance is on the way into
the zone or for when the impedance is on the way out of the zone.
The function contains a blocking functionality. It is possible to block function outputs, the
definite timer or the function itself, if desired.
4.7.1.4
Operation principle
The function can be enabled and disabled with the
Operation
setting. The corresponding
parameter values are "Enable" and "Disable".
The operation of 78 can be described using a module diagram. All the modules in the
diagram are explained in the next sections.
BLOCK
Out of
step
detection
SWING_TRIP
TRIP
Blocking
logic
SWING
Impedance
calculation
I
1
V
1
t
Timer
DISABLE
I
2
OSB
OSB_Z2
GUID-60F5E154-F3C3-4D1D-9B33-A413F10526E8 V1 EN
Figure 341:
Functional module diagram
Section 4
1MAC059074-MB A
Protection functions
686
615 series ANSI
Technical Manual
Summary of Contents for Relion 615 series
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