Alstom MiCOM P545 - 1.37 Frequency protection

P54x/EN OP/La4 Operation
(OP) 5-98 MiCOM P543, P544, P545 & P546
OP
1.37 Frequency protection
The relay includes 4 stages of underfrequency and 2 stages of overfrequency protection to
facilitate load shedding and subsequent restoration. The underfrequency stages may be
optionally blocked by an undervoltage level (setting CB FAIL & P.DEAD/POLEDEAD
VOLTAGE/V<). All the stages may be enabled/disabled in the "F<n Status" or "F>n Status"
cell depending on which element is selected.
The logic diagram for the underfrequency logic is as shown in Figure 69. Only a single stage
is sh
own. The other 3 stages are identical in functionality.
If the frequency is below the setting and not blocked the DT timer is started. Blocking may
come from the Undervoltage level (selectively enabled for each stage) or the underfrequency
timer block.
If the frequency cannot be determined, the function is also blocked.
Underfrequency
1
All Poles Dead
Freq. Not Found
Underfrequency
Timer Block
Underfrequency
Start
P1640ENa
&
1
&
(DT)
Underfrequency
Trip
Figure 69 Underfrequency logic (single stage)
The functional logic diagram is for the overfrequency function as shown in Figure 70. Only a
singl
e stage is shown as the other stages are identical in functionality. If the frequency is
above the setting and not blocked the DT timer is started and after this has timed out the trip
is produced. Blocking may come from the All_Poledead signal (selectively enabled for each
stage) or the overfrequency timer block.
Overfrequency
1
All Poles Dead
Freq. Not Found
Overfrequency
Timer Block
Overfrequency
Start
P1641ENa
&
1
&
Definite Time
Overfrequency
Trip
Figure 70 Overfrequency logic (single stage)