               ! "#$ %   ! & "#$ PERFORMANCE OF DIRECTIONAL RELAYS WITHOUT VOLTAGE SENSORS: IMPACT OF DISTRIBUTED GENERATION TECHNOLOGIES Trung Dung LE Marc PETIT E3S SUPELEC Systems Sciences – France E3S SUPELEC Systems Sciences – France trungdung.le@supelec.fr marc.petit@supelec.fr ABSTRACT Radial distribution networks are mainly protected with overcurrent relays, which are used for both earth and phase fault protection. Nevertheless, higher capacitive current of underground cables can cause false tripping problem for overcurrent relay of a feeder during a line-to-ground fault on the adjacent feeder. The contribution of distributed generation (DG) to the fault current during a line-to-line fault also leads to a similar situation. To solve this problem, a novel algorithm of directional relay has been proposed in a previous work [1]. Based on the symmetrical components method, the algorithm only uses current measurements to determine fault direction and thereby suppresses the cost of voltage sensors. This paper presents effect of distributed generators on the directional algorithm by comparing the cases of Inverter- interfaced Distributed Generators (IIDGs) in PV systems and of synchronous generators (SGs) in CHP plants. Results show good performances in both cases during earth faults. However, during line-to-line faults, this algorithm gives better results in case of IIDGs. INTRODUCTION To improve power quality of medium voltage (MV) distribution networks, the French DSO has adopted [2] a new structure for rural networks: underground cables for mainlines and overhead lines for laterals. As a result, earth fault protection relays, which can now measure a higher capacitive current, may trip the breaker during fault on an adjacent feeder (false tripping). To solve this problem, a directional earth fault relay (67N) can be installed. Symmetrical components method is widely used for power protection purpose. Based on this well-known method, a novel principle was proposed using only current measurements to detect fault direction (upstream or downstream of detectors) [1]. The I 2 /I 1(0) ratio was used to classify faults. This protection algorithm is advantageous in term of cost reduction compared to a traditional directional relay which needs both voltage and current sensors to operate. Therefore, the algorithm is particularly suitable for protections that are installed along feeder where voltage measurements are usually unavailable. It can also be considered as a back-up solution for traditional directional relay of feeder protection following voltage measurement failure. However, with the introduction of Distributed Generators (DGs) into MV grids, the contribution of DGs to current fault alters the ratio and consequently the performance of the algorithm. In a previous work [3], the influence of synchronous generators (SGs) was considered. The I 2 /I 0 ratio was used to determine the earth fault direction by creating two distinctive areas on the complex plane, for upstream and downstream faults. Recently, Inverter-interfaced Distributed Generators (IIDGs) have been growing not only in number but also in rated power. Although the contribution of this kind of DG to fault current is limited [4], a high power IIDG can still weaken the efficiency of our algorithm. Besides, line-to-line faults do not occur frequently but still need to be paid attention to: both SGs and IIDGs can cause false tripping for conventional overcurrent protections and phase directional relays may be necessary [3]-[5]. In Ref. [5], the authors have investigated the case of IIDGs for line- to-line faults with the “non-voltage-sensor” algorithm by using the I 2 /I 1 and I 2 /I 1 ratios, but case of SGs has not been covered yet. This paper shows the impact of SGs and IIDGs during both earth faults and line-to-line faults. In this study, simulations are done with Simulink/ SimPowerSystems for a radial grid. To estimate the fault direction, the I 2 /I 0 ratio is considered for earth faults while the I 2 /I 1 ratio is used for line-to-line faults. Based on Support Vector Machine (SVM) technique [6], optimal decision boundary is defined on the complex plane for upstream and downstream fault areas. INVESTIGATED GRID The investigated grid topology is shown in Figure 1: a radial network with three feeders, which consists of underground cables (C240) and overhead lines (L54). This network is grounded with the impedance Z n , whose value depends on neutral grounding method (compensative grounding or resistive grounding). Feeder 1 has two DGs connected in two sections that are protected by relays R1 and R2 respectively. The sum of rated power of the DGs is less than 9 MVA. As mentioned in previous section, two kinds of DGs are taken into account in the study: one is IIDGs and the other is SGs. Simulation model of the former is built as shown in [5]; whereas model of the latter is a built-in model of synchronous machine of Simulink Library. Detailed grid characteristics are given by APPENDIX.