Backup overcurrent
The 7SD80 features an overcurrent protection function which can be used as either backup or emergency
overcurrent protection. All elements are independent of each other and can be combined as desired.
The overcurrent protection has two overcurrent elements with definite trip time and one overcurrent protec-
tion element with inverse time delay for the phase currents and for the ground current. These elements
operate directionally or non-directionally.
One additional definite-time overcurrent protection element always operates non-directionally. It features an
additional release input and can act as emergency element if the other elements are used for backup
purposes.
The elements are independent of each other and can be combined in any way. Blocking by external criteria via
binary inputs is possible.
Operating Modes
Emergency Overcurrent Protection
The differential protection as a whole can only operate correctly if both devices receive the data of the respec-
tive other device properly. The emergency overcurrent protection in contrast requires only the local currents.
Acting as emergency overcurrent protection, it automatically replaces the differential protection as short-
circuit protection if data communication of the differential protection is faulty (emergency operation). The
differential protection is blocked in this case.
Backup Time Overcurrent Protection
If the overcurrent protection is set as backup time overcurrent protection, it will work independently of the
other protection and monitoring functions, i.e. also independently of the differential protection. The backup
overcurrent protection can also act as the only short-circuit protection if no suitable channels for the commu-
nication between the protection devices are available yet during the initial commissioning. It can be used as
busbar protection via reverse interlocking in combination with other protection devices or as backup protec-
tion function for protection device failure at continuing lines.
Non-directional Overcurrent Protection
Measured Quantities
The phase currents are fed to the device via the input transformers of the measuring input. The ground
current Ι
0
is calculated from the phase currents.
Definite Time High-set Element 50-1
Each phase current is compared with the setting value 50-B2 PICKUP after numerical filtering; the ground
current is compared with 50N-B2 PICKUP. A trip command is issued after pickup of an element and expira-
tion of the associated time delays 50-B2 DELAY or 50N-B2 DELAY. The dropout value is about 7 % below
the pickup value, but at least 5 % of the rated current.
Figure 2-26 shows the logic diagram of the 50-1 elements. They can be blocked via binary input
>BLOCK 50-
B2
. Additionally, the ground current element can be blocked separately via the binary input
>BLOCK 50N-B2
.
The binary input
>5X-B InstTRIP
and the evaluation of the indication “switch” (onto fault) are common to
all elements. They may, however, separately affect the phase and/or ground current elements.
Parameter 50-B1 DELAY (address 2618) determines whether a non-delayed trip of this element via binary
input
>5X-B InstTRIP
is possible (YES) or impossible (NO). This parameter is also used for fast tripping
before reclosing.
If parameter 50-B2 Inrush (address 2625) is set to YES, the element is blocked.
2.4
2.4.1
2.4.2
Functions
2.4 Backup overcurrent
72 SIPROTEC 4, 7SD80, Manual
E50417-G1100-C474-A2, Edition 02.2018
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