ABB ret650 - Time Delay

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