10.4. Configuring the non-direction overcurrent protection
By default, added overcurrent protections are non-directional, as shown in the following picture:
Selecting the “Characteristic” drop-down menu, the user can select one of IEC or IEEE standard tripping curves: definite time, normal inverse time, very inverse time, extremely inverse time and long-time inverse time.
“Direction” drop down menu defines the direction of the overcurrent protection. It can be non-directional, directional forward or directional reverse.
Check box “Connected curve” enables the option to connect different overcurrent protection stages into one curve, as shown in Figure 9.13 .
“Relay time setting” defines protection time setting. Minimum value is 20 ms.
“Relay current setting” defines protection current setting in primary values.
The table shown earlier depicts protection sensitivity values of each short-circuit type calculate in relation to the “Relay current setting”. Sensitivity coefficient formula:
Isc in this equation is min short circuit current. Bigger setting current means smaller ksens value. It is recommended to have sensitivity value not less than 2, this assures that protection will react to short circuit current. If sensitivity is less than 2, table cell turns red.
