Siemens 6MD85, Manual

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Parameter:
Power criterion
,
Phi (power criterion)
,
Min. current (power crit.)
•
Default setting
(_:18121:103) Power criterion
=
yes
•
Default setting
(_:18121:106) Phi (power criterion)
=
-5°
•
Default setting
(_:18121:104) Min. current (power crit.)
=
0.050 p.u.
The power criterion evaluates the power-flow direction as a blocking criterion for the protection stages.
•
With the
Power criterion
parameter, you configure whether to apply the power criterion or not.
If a feeder can deliver active power towards the busbar, or if the medium-voltage busbar can deliver
active power to the high-voltage busbar, Siemens recommends using the power criterion to exclude the
feeder or the medium-voltage busbar from being shed under this condition. If a feeder or the medium-
voltage busbar is always consuming active power, the power criterion is not required.
•
With the
Phi (power criterion)
parameter, you decide whether the protection stage is blocked or
released in the case of low active-power flow. If the active-power flow is low, the determined active
power-flow direction is not always reliable.
For
Phi (power criterion)
≤ 0, the protection stage is released for a clear forward active power-
flow direction. If the active power-flow direction is not reliable, the protection stages are blocked. For
Phi (power criterion)
> 0, the behavior is the contrary.
The
Phi (power criterion)
parameter can be set depending on your philosophy.
•
With the
Min. current (power crit.)
parameter, you set the minimum positive-sequence current
threshold to achieve a reliable active-power criterion result. The
Min. current (power crit.)
parameter is set as a per-unit value related to the rated current of the connected current measuring
point. Siemens recommends using the default setting.
Parameter:
df/dt-rising blk. criterion
,
df/dt-rising blk. threshold
,
df/dt-falling blk.
criterion
,
df/dt-falling blk. threshold
•
Default setting
(_:18121:107) df/dt-rising blk. criterion
=
no
•
Default setting
(_:18121:108) df/dt-rising blk. threshold
=
1.0 Hz/s
•
Default setting
(_:18121:109) df/dt-falling blk. criterion
=
no
•
Default setting
(_:18121:110) df/dt-falling blk. threshold
=
3.0 Hz/s
If the change rate of df/dt is too high, the Underfrequency load shedding function may not be applicable
anymore.
With the parameters
df/dt-rising blk. criterion
and
df/dt-falling blk. criterion
, you
determine whether to check the df/dt-rising blocking and the df/dt-falling blocking.
With the parameters
df/dt-rising blk. threshold
and
df/dt-falling blk. threshold
, you set
the threshold rates of df/dt-rising and df/dt-falling.
Parameter:
df/dt measuring window
•
Default setting
(_:18121:111) df/dt measuring window
=
5 periods
With the
df/dt measuring window
parameter, you optimize the measuring accuracy or the pickup time of
the function.
The default setting provides the maximum measuring accuracy. If you do not have specific requirements for a
decreased pickup time, Siemens recommends using the default setting.
For a non-sensitive setting (high threshold value), you can set the
df/dt measuring window
parameter to
a value which is smaller than
5 periods
.
Parameter:
df/dt dropout differential
•
Default setting
(_:18121:112) df/dt dropout differential
=
0.1 Hz/s
With the
df/dt dropout differential
parameter, you define the dropout threshold of the parameters
df/dt-rising blk. threshold
and
df/dt-falling blk. threshold
.
Protection and Automation Functions
7.20 Underfrequency Load Shedding
840 SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017