The 2nd operation uses the delayed curve which is coordinated with the fuse characteristic curve.The means to achieve this range from the simplest and cheapest systems to the most complex and expensive schemes.Among these, overcurrent protection is often the simplest and the most inexpensive to employ.
The concept of overcurrent coordination ensures that only a minimum portion of the power system is interrupted from a fault or overload condition. Our understanding of time-current curves was supplemented through a discussion of Coordination Time Intervals (CTIs). The example is taken from the book Protective Relaying Principles and Application by J. Blackburn. You can refer to this link to review the basic elements and toolbars available in the software, and the step-by-step process of modeling. This is a straightforward procedure that involves selecting and connecting the power system devices in a single line. ![]() ![]() To verify that you are in the coordination module, your Study Mode Toolbar located on the right side of your screen should look like the figure shown in figure 5. In addition, type T (slow-acting) fuse-links were selected for lateral taps since they coordinate well with distribution transformer fuses which generally use the fast-acting type K. An E-rated fuse is selected to provide current limiting protection. The transformer through-fault damage curve is shifted to the left considering that the 115 kV side protection sees only 57.7 of the current resulting from a line-to-ground fault in the 13kV side. The transformer is sufficiently protected from thermal damage. The fuse characteristic curve is located to the left of the shifted transformer damage curve. The phase overcurrent minimum operating current or pick-up value is set to more than twice the maximum load, at 560 A, to provide security for cold-load transients. On the other hand, the ground overcurrent minimum operating current or pick-up value is set at 50 of the phase pick-up to 280 A. The time multiplier for the phase overcurrent is set to establish a coordination time interval (CTI) of at least 0.12 s with respect to the fault level at the downstream 100 A Type T fuse. This is configured in ETAP through the Controller tab of the recloser. For this controller, the delayed curve is configured as TCC 2. In this case, a time multiplier of 0.7. This translates into a CTI of 0.435 s at 1.346 kA with respect to the downstream 100 A Type T fuse. An instantaneous high current trip setting is also enabled for ground overcurrent with k 1.2 x fault 4 (see figure 1) or 1.615 kA which is equivalent to 5.77 times the ground overcurrent pick-up setting. The fast curve is set with the same pick-up level as the delayed curve (TCC 2) but is set to operate instantaneously in order to avoid fuse operations for transient faults. This scheme is particularly known as the Fuse Saving scheme.
0 Comments
Leave a Reply. |
Details
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |