8.2 Four step phase overcurrent protection OC4PTOC SEMOD129998-1 v78.2.1 IdentificationM14885-1 v5Function description IEC 61850identificationIEC 60617identificationANSI/IEEE C37.2device numberFour step phase overcurrentprotection 3-phase outputOC4PTOCTOC-REVA V2 EN-US51_678.2.2 Application M15335-3 v8The Four step phase overcurrent protection 3-phase output OC4PTOC is used in severalapplications in the power system. Some applications are:• Short circuit protection of feeders in distribution and subtransmission systems. Normallythese feeders have radial structure.• Back-up short circuit protection of transmission lines.• Back-up short circuit protection of power transformers.• Short circuit protection of different kinds of equipment connected to the power systemsuch as; shunt capacitor banks, shunt reactors, motors and others.• Back-up short circuit protection of power generators.If VT inputs are not available or not connected, setting parameterDirModex (x= step 1, 2, 3 or 4) shall be left to default valueNon-directional.In many applications several steps with different current pick up levels and time delays areneeded. OC4PTOC can have up to four different, individual settable, steps.The flexibility ofeach step of OC4PTOC is great. The following options are possible:Non-directional / Directional function: In most applications the non-directional functionality isused. This is mostly the case when no fault current can be fed from the protected object itself.In order to achieve both selectivity and fast fault clearance, the directional function can benecessary.Choice of delay time characteristics: There are several types of delay time characteristicsavailable such as definite time delay and different types of inverse time delay characteristics.The selectivity between different overcurrent protections is normally enabled by co-ordinationbetween the function time delays of the different protections. To enable optimal co-ordinationbetween all overcurrent protections, they should have the same time delay characteristic.Therefore a wide range of standardized inverse time characteristics are available: IEC andANSI. It is also possible to tailor make the inverse time characteristic.Normally it is required that the phase overcurrent protection shall reset as fast as possiblewhen the current level gets lower than the operation level. In some cases some sort of delayedreset is required. Therefore different kinds of reset characteristics can be used.For some protection applications there can be a need to change the current pick-up level forsome time. A typical case is when the protection will measure the current to a large motor. Atthe start up sequence of a motor the start current can be significantly larger than the ratedcurrent of the motor. Therefore there is a possibility to give a setting of a multiplication factor1MRK 505 363-UEN A Section 8Current protection131Application manual
