Function Block - ABB 615 series Technical Manual

Section 4
Protection functions
4.7.1.2
4.7.1.3
4.7.1.4
686

Function block

78
V TRIP
1
I SWING_TRIP
1
I SWING
2
DISABLE OSB
BLOCK OSB_Z2
GUID-169436AD-9E20-4D6E-9EF6-9DDEAF8F5901 V1 EN
Figure 340: Function block
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.
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.
I
1
Impedance
calculation
V
1
I
2
DISABLE
Blocking
BLOCK
logic
GUID-60F5E154-F3C3-4D1D-9B33-A413F10526E8 V1 EN
Figure 341: Functional module diagram
TRIP
Timer
SWING_TRIP
Out of
t
step SWING
detection
OSB
OSB_Z2
1MAC059074-MB A
615 series ANSI
Technical Manual