ABB ret650, Technical Manual, Page: 219 / 670

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 73)
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 74)
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 75)
The highest phase (or phase-to-phase) voltage is always used for the inverse time
delay integration, see
Figure 94 . The details of the different inverse time
characteristics are shown in section "Inverse time characteristics" .
1MRK 504 135-UEN A
Section 9
Voltage protection
213
Technical manual