Siemens 6MD85, Manual

Page: 838 / 1256

For
Phi (power criterion)
≤ 0, the power criterion is checked as follows:
•
When the positive-sequence current I1 falls below the
Min. current (power crit.)
, the current
criterion is not fulfilled and the
I1< blocking
indication is issued. Therefore, all the protection stages
are blocked and the power-angle criterion is not considered.
•
When I1 exceeds the
Min. current (power crit.)
and the power angle is out of the release area,
the
Power crit. blocking
indication is issued and all the protection stages are blocked.
For
Phi (power criterion)
> 0, the power criterion is checked as follows:
•
When I1 falls below the
Min. current (power crit.)
, all the protection stages are released and
the power-angle criterion is not considered.
•
When I1 exceeds the
Min. current (power crit.)
and the power angle is out of the release area,
the
Power crit. blocking
indication is issued and all the protection stages are blocked.
df/dt Blocking
If the change rate of df/dt is too high, the Underfrequency load shedding function may not be applicable
anymore.
The df/dt blocking comprises the df/dt-rising blocking and the df/dt-falling blocking.
The df/dt-rising criterion and the df/dt-falling criterion can be individually switched on or off. These 2 df/dt
criteria are operative only when the magnitude of the positive-sequence voltage V1 is greater than the
Minimum voltage
:
•
The df/dt-rising blocking takes place when the df/dt-rising value exceeds the setting value of the param-
eter
df/dt-rising blk. threshold
. It is signaled via the indication
df/dt-rising blocking
.
•
The df/dt-falling blocking takes place when the df/dt-falling value exceeds the setting value of the param-
eter
df/dt-falling blk. threshold
. It is signaled via the indication
df/dt-falling
blocking
.
Activating/Deactivating Protection Stages
The mechanism of exclusive stage activation is described in section Exclusive Stage Activation, Page 842 .
Functional Measured Value
Value Description
df/dt Calculated rate of frequency change
Application and Setting Notes
Parameter:
Minimum voltage
•
Default setting
(_:18121:101) Minimum voltage
=
0.700 p.u.
If the magnitude of V1 is smaller than the
Minimum voltage
, all protection stages are blocked.
The
Minimum voltage
parameter is set as a per-unit value related to the rated voltage of the connected
voltage measuring point. Siemens recommends using the default setting.
Parameter:
Positive power direction
•
Default setting
(_:18121:115) Positive power direction
=
inv. to CT neu.pnt sett.
With the
Positive power direction
parameter, you define the positive active-power flow direction of
the function in relation to the standard forward direction of the protection functionality.
7.20.3.2
Protection and Automation Functions
7.20 Underfrequency Load Shedding
838 SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017