9.2.7.2
Time delay
The time delay for step 1 can be either definite time delay (DT) or inverse time delay
(IDMT). Step 2 is always definite time delay (DT). For the inverse time delay three
different modes are available:
•
inverse curve A
•
inverse curve B
•
inverse curve C
The type A curve is described as:
k
t
U U
U
=
- >
æ
ö
ç
÷
>
è
ø
IEC09000051 V1 EN
(Equation 81)
The type B curve is described as:
2.0
480
0.035
32
0.5
k
t
U U
U
×
=
-
-
>
×
-
>
æ
ö
ç
÷
è
ø
IECEQUATION2287 V1 EN
(Equation 82)
The type C curve is described as:
3.0
480
0.035
32
0.5
k
t
U U
U
×
=
+
-
>
×
-
>
æ
ö
ç
÷
è
ø
IECEQUATION2288 V1 EN
(Equation 83)
The highest phase (or phase-to-phase) voltage is always used for the inverse time
delay integration, see
. The details of the different inverse time
characteristics are shown in section
"Inverse time characteristics"
.
1MRK 502 048-UEN A
Section 9
Voltage protection
267
Technical manual
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