ABB RELION RET670, Applications Manual

Page: 611 / 1016

Inverse time delay characteristic of the NS2PTOC (46I2) function is represented in the
equation
2
2
I t K
=
, where the K1 setting is adjustable over the range of 1 – 99 seconds.
A typical inverse time overcurrent curve is shown in Figure 293 .
Negative sequence inverse time characteristic
Negative sequence current
T
im
e d
el
ay
I2
tMax
tMin
IEC08000355-2-en.vsd
1
10
100
1000
10000
0.01 0.1 1 10 100
IEC08000355 V2 EN-US
Figure 293: Inverse Time Delay characteristic, step 1
The example in figure 293 indicates that the protection function has a set minimum trip
time t1Min of 5 sec. The setting t1Min is freely settable and is used as a security
measure. This minimum setting assures appropriate coordination with for example line
protections. It is also possible to set the upper time limit,
t1Max .
9.16.3.2 Pickup sensitivity
GUID-1D038486-7086-466F-A92F-30E1A47D0298 v3
The trip pickup levels Current I2-1> and I2-2> of NS2PTOC (46I2) are freely settable
over a range of 3 to 500 % of rated generator current IBase . The wide range of pickup
setting is required in order to be able to protect generators of different types and sizes.
After pickup, a certain hysteresis is used before resetting pickup levels. For both steps
the reset ratio is 0.97.
1MRK 504 163-UUS A
Section 9
Current protection
Transformer protection RET670 2.2 ANSI 605
Application manual