Siemens siprotec 7SA6 User Manual

Functions
6-2677SA6 Manual
C53000-G1176-C156-2
Example:
Belted cable 10 kV 150 mm
2
Permissible continuous current I
max
=322A
Current transformer 400 A/5 A
Setting value
K-FACTOR = 0.80
Time Constant τ
The thermal time constant τ
th
is set under the address 4203 TIME CONSTANT.This
is also provided by the manufacturer. Please note that the time constant must be set
in minutes. Quite often other values for determining the time constant are stated which
canbeconvertedintothetimeconstantasfollows:
• 1–s current
• permissible current for application time other than 1 s, e.g. for 0.5 s
• t
6
–time; this is the time in seconds for which a current of 6 times the rated current
of the protected object may flow
Example:
Cableasabovewith
permissible 1–s current 13.5 kA
Setting value
TIME CONSTANT = 29.4 min
Alarm Stages By setting a thermal alarm stage Θ ALARM (address 4204)analarmcanbeoutput
before the tripping temperature is reached, so that a trip can be avoided by early load
reduction or by switching over. The percentage is referred to the tripping temperature.
The current overload alarm setpoint
I ALARM (address 4205) is stated as a factor of
the rated device current and should be set equal to or slightly below the permissible
continuous current k ·
I
N
. It can also be used instead of the thermal alarm stage. In this
case the thermal alarm stage is set to 100 % and thus practically ineffective.
Calculating the
Overtemperature
The thermal replica is calculated individually for each phase. Address 4406 CALC.
METHOD
decides whether the highest of the three calculated temperatures (Θ max)or
their arithmetic average (
Average Θ) or the temperature calculated from the phase
with maximum current (
Θ @ Imax)shouldbedecisiveforthethermalalarmandtrip-
ping stage.
k
322 A
400 A
----------------
0.805==
τ
th
min
----------
1
60
------
perm. 1-s current
perm. contin. current
-------------------------------------------------------------
èø
æö
2
⋅=
τ
th
min
----------
0.5
60
--------
perm. 0.5–s current
perm. contin. current
-------------------------------------------------------------
èø
æö
2
⋅=
τ
th
min
----------
0.6 t
6
⋅=
τ
th
min
----------
1
60
------
13500 A
322 A
-----------------------
èø
æö
2
1
60
------
42
2
29 4,=⋅=⋅=

Siemens siprotec 7SA6 Specifications

General

Brand	Siemens
Model	siprotec 7SA6
Category	Relays
Language	English