The timer calculates the start duration value START_DUR, which indicates the
percentage ratio of the start situation and the set operating time. The value is
available in the monitored data view.
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
OPERATE
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 OPERATE output" mode,
the function operates normally but the
OPERATE
output is not activated.
4.2.2.5
Directional earth-fault principles
In many cases it is difficult to achieve selective earth-fault protection based on
the magnitude of residual current only. To obtain a selective earth-fault protection
scheme, it is necessary to take the phase angle of Io into account. This is done by
comparing the phase angle of the operating and polarizing quantity.
Relay characteristic angle
The
Characteristic angle setting, also known as Relay Characteristic Angle (RCA),
Relay Base Angle or Maximum Torque Angle (MTA), is used in the "Phase angle"
mode to turn the directional characteristic if the expected fault current angle does
not coincide with the polarizing quantity to produce the maximum torque. That is,
RCA is the angle between the maximum torque line and polarizing quantity. If the
polarizing quantity is in phase with the maximum torque line, RCA is 0 degrees. The
angle is positive if the operating current lags the polarizing quantity and negative if
it leads the polarizing quantity.
Example 1
The "Phase angle" mode is selected, compensated network (φRCA = 0 deg)
=>
Characteristic angle = 0 deg
1MRS757644 H
Protection functions
620 series
Technical Manual
393
