Functions
2.3 Overcurrent protection (optional)
SIPROTEC, 7VK61, Manual
C53000-G1176-C159-3, Release date 05.2009
67
2.3
Overcurrent protection (optional)
The 7VK61 features a time overcurrent protection function with four independent stages that can be combined
freely with one another.
2.3.1
General
For the overcurrent protection there are in total four stages for the phase currents and four stages for the earth
currents as follows:
• Two overcurrent stages with a definite time characteristic (O/C with DT),
• One overcurrent stage with inverse time characteristic (IDMT),
• One additional overcurrent stage which is preferably used as a stub protection, but which can be applied as
an additional normal definite time delayed stage. With the device variants for the region Germany (10th digit
of ordering code = A) this stage is only available if the setting
126
TOC IEC /w 3ST
is active.
These four stages are independent of each other and are freely combinable. Blocking as well as release of in-
stantaneous tripping (e.g. by an automatic recloser) by external criteria is possible via binary inputs. During en-
ergisation of the protected line onto a fault it is also possible to release any stage, or also several stages, for
instantaneous tripping. If not all stages are needed, the unneeded ones can be disabled by setting their pickup
value to
∞
.
2.3.2
Functional Description
Measured values
The phase currents are fed to the device via the input transformers of the measuring input. Earth current 3·
I
0
is either measured directly or calculated depending on the ordered device version and usage of the fourth
current input
I
4
of the device.
If
I
4
is connected to the starpoint of the current transformer set, the earth current will be available directly as
measured quantity.
If the fourth current input
I
4
is not connected as earth current transformer, the device will calculate the earth
current from the phase currents. This requires, of course, all three phase currents from a set of three star-con-
nected current transformers to be available and connected to the device.
Definite time high set current stage
I
>>
Each phase current is compared with the setting value
Iph>>
after numerical filtering; the ground current is
compared with
3I0>> PICKUP
. Currents above the associated pickup value are detected and signalled. After
expiry of the associated time delays
T Iph>>
or
T 3I0>>
a trip command is issued. The dropout value is
approximately 5% below pickup value, but at least 1.5% of the nominal current, below the pickup value.
The figure below shows the logic diagram of the
I
>> stages. The stages can be blocked via a binary input
„>BLOCK O/C I>>“
. Binary inputs
„>O/C InstTRIP“
and the function block „switch-onto-fault“ are common
to all stages and described below. They may, however, separately affect the phase and/or earth current stages.
This is accomplished with the following setting parameters:
•
I>> Telep/BI
(address
2614
)determines whether a non-delayed trip of this stage via binary input
„>O/C
InstTRIP“
is possible (
YES
) or impossible (
NO
) and
•
I>> SOTF
(address
2615
)determines whether during switching onto a fault tripping shall be instanta-
neous(
YES
) or not (
NO
) with this stage.
Summary of Contents for Siprotec 7VK61
Page 8: ...Preface SIPROTEC 7VK61 Manual C53000 G1176 C159 3 Release date 05 2009 8 ...
Page 14: ...Contents SIPROTEC 7VK61 Manual C53000 G1176 C159 3 Release date 05 2009 14 ...
Page 316: ...Literature SIPROTEC 7VK61 Manual C53000 G1176 C159 3 Release date 05 2009 316 ...
Page 328: ...Glossary SIPROTEC 7VK61 Manual C53000 G1176 C159 3 Release date 05 2009 328 ...
