Relay Settings in the "Overcurrent" Room – Part 2
After specifying a “Stage” for the relay characteristic curve, it is possible to specify the characteristic curve time and current range limits in “Range limits” section. To do this, you need to activate this section by checking “Active” option and enter the required ranges in according fields. For example, here, “I min” equals 1.2 times “lref” and “l max”, 100 times “Iref” is entered. At the right side of this window you can see that the characteristic curve of the relay is specified to be between 1.2 and 100 times of the reference current which is the same as “Iref” or “CT” secondary. Also, the minimum time is entered in “t min” field and here “1.5” second is entered. In “t max” field, on the other hand, the maximum time is entered which, here, is 40. Now you can see the effect of these changes on the characteristic curve.Moreover, for relays that act in “Definite Time” mode from currents higher than a specific amount, “Limit t from I” option can be used. For example, for relays that act from 1.1 time of the determined “Pickup” current and act in “Definite Time” mode from 20 times of the “Pickup” current, the settings are entered as can be seen.
In “Reset Characteristic” section, you can specify the setting related to “Drop out” characteristic curve of the relay which is set at “Off” by default. This means that as soon as the fault current falls below the relay “Drop” current, the pickup contact must be removed from the relay. By selecting “Definite time”, “tr” field is activated and you can specify a time for “Drop out” of the relay. For example, if 1.5 second is entered here, when the fault current falls below the specified value, the pickup contact must be removed from the relay after 1.5 second. Also, by selecting “Inverse time”, “R” and “T” fields are opened and it is made possible to specify an “Inverse” curve for “Drop out” time of the relay according to the formula displayed in “Formula” section and by specifying “R” and “T” values. Note that it is possible to manage “Reset Characteristic” and “Range limits” sections from “manage / select characteristic” page as well.
If the characteristic curve of the relay comprises of multiple “Stages”, it is necessary to use “Add” button to specify the required number of “Stages” and by specifying their parameters, test the intended relay. For example, here, another “Stage” of “Time Definite” type is created and the pickup current is set at 1.5 times “I ref” and its operation time is set at 200 milliseconds in “Time” column. You can see that by clicking on any “Stage”, its corresponding characteristic curve is displayed in the right side window. Now, in “View Resulting Characteristic” tab, it is possible to view the final characteristic curve created. You can see that this curve is the result of both “Stages” specified in the table on this window. In “Color” column, a color is selected for each “Stage”. In “Active” column, it is possible to activate or deactivate any intended “Stage” by using “Yes” and “No” options. For example, here, the second “Stage” is deactivated and removed from the characteristic curve.
By using “Save as User-defined” option from “Manage / select characteristic” window, it is possible to add the characteristic curve created in each “Stage” in “User defined” folder and use when necessary. For example, here, the first “Stage” is selected and by clicking on “Save as User-defined”, the “Manage / Select Characteristic” window opens. Then, by clicking on “Ok” button and returning to this window, you can see that this curve and its setting are added to this folder with the name of IEC Normal Inverse2.
