Solutions and alternative protective systems

Installing small generation in the distribution grid has become popular since the mid eighties and the protection problems caused by DG has been studied accordingly (Dugan et al., 1984; Rizy et al., 1985). In the literature for the problems mentioned in the previous section a wide pallet of solutions is offered. These solutions vary between a simple change in relay settings to a complete new adaptive protective system. In this section an overview of possible solutions is given.

2.1 Prevention of detection and selectivity problems

Fault detection problems do have a relation with the amount of generation connected to the distribution grid and the local short-circuit power. To prevent fault detection problems a first attempt is to modify the relay settings of the relays and reclosers (Baran & El-Markabi, 2004; Hadjsaid et al., 1999; Kumpulainen et al., 2005; Maki et al., 2004). The generator contribution leads to a reduction of the grid contribution to the fault current hence the pick-up current of the relays has to be reduced. However, fault detection problems might be solved by reducing the pick-up current, the sensitivity and security of the protective system is decreased and might lead to false tripping in case of a fault in an adjacent feeder. In (Maki et al., 2004) an example of a weak network is given where blinding of protection occurs due to the connection of a small wind farm. By reducing the pick-up current blinding of protection is solved but at the same time it introduces for faults in a certain area false tripping. A proposed solution is to install protection devices with an additional time delay to give the feeder including the wind farm a longer fault clearing time. These type of solutions also discussed in (Deuse et al., 2007). Another example of changed protection settings is discussed in (Baran & El-Markabi, 2004). Here an adaptive overcurrent relay is proposed which decreases the pick-up current as the output of the local generation increases. This is also studied in (Vermeyen, 2008) where it is stated that a continuous adaptation of the pick-up current as function of the generator output results in less superfluous disconnection of the feeder.

Updated: September 26, 2015 — 9:24 am