INTERACTION BETWEEN THE DISTRIBUTION NETWORK AND THE GENERATION DISTRIBUTED IN THE CASE OF SHORT-CIRCUIT IN THE MV NETWORK.

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Damian Pierce
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1 INTEACTION BETWEEN THE DISTIBUTION NETWOK AND THE ENEATION DISTIBUTED IN THE CASE OF SHOT-CICUIT IN THE MV NETWOK. Daniel CASTO, Eduardo BALMACEDA Energía San Juan S. A. - Argentina dcastro@energiasanjuan.com.ar; ebalmaceda@energiasanjuan.com.ar, INTODUCTION The main purpose of an electric network is to transfer electricity from the electric power generators to the clients. The distribution networks make the connection to the final clients and must satisfy the electricity service with an agreed quality level on watch in the applicable norm. In the case of the province of San Juan Argentina, it is Energía San Juan S.A. The combined development of the generation of the heat and of energy and the interest for the renewable energies (biomass, aeolian, solar, etc.) they can lead in the present to a growth of the supply of energy in small modules. As these generators can be connected in any point of the network, we can say that this is the evolution of the network with the introduction of the dispersed sources of generation were 2500 KW. However, the maximum power that can contribute the generator is around 350 kw. The geographic location of the feeder is shown in the Figure Nº1. Estación Transformadora enerador Also, the introduction of a generator in any point of the network can cause some complications with the coordination of the protections. This means that when the fault appears, now exits several ways of contribution from current to the place of the fault, causing generally problems between the protection elements that are not directional. Figure Nº 1 I1 Sistema Equivalenrte The present work states a strategy to achieve the coordination of protections in the MV of 13,2 kv, where it was connected a synchronous generator with a hydraulic turbine that generates approximately 350 kw (the considered load of the distributor is of around 2500 kw). This generator belongs to a private company and this located in a point near the main source of the feeder. 2. DESCIPTION AND MODELLIN OF THE NETWOK The present study was make for a substation transformation from 33 to 13,2 kv call Parque Industrial. It located in the industrial area of San Juan's city. It includes circuit breakers, two transformer of 10 MVA (T1) and four feeders with different characteristic as for the consumption type and longitude. The synchronous generator is connected from the feeder called Bonduel Sur. It is installed on a watering canal located to 1.6 kilometers of the substation. The feeder has 3000 residential clients and it has a global length of 5,5 kilometers. The maximum load of the feeder in the year Subestación MT/BT econectador Fusible MT Figure Nº 2 T1 I2 ET P. Industrial I3 I4 I5 Distribuidor Bonduel Sur I6 Central El Candil In the case of the transformer (T1) of the substation of power, it protected with overcurrent time protection relay (in the primary and secondary side). Also, the feeders are protected with overcurrent time protection relay in the

2 beginning of the line. Then, there are recloser in the middle of the line and fuses in their derivations. The structure of the system is shown in the Figure Nº DESCIPTION OF THE HYDAULIC POWE STATION The next graph shows the power injected by the generator (since the first days of October of the year 2003). In this case, we can observe that the injected maximum power reached 320 kw, and then in the months of winter its contribution decays until stopping to work. This situation is presented in times of cleaning of the watering canal. The synchronous generator is hydraulic and it is installed on a watering canal located to 1.6 kilometers of the substation transformer Parque Industrial. This power substation is called El Candil and it is connected to the network through two transformers ( and ), to convert the voltage to the rest of the system. Next, is given the detail of data about these transformers and generator. The synchronous generator: Demanda Inyectada en kw por la Central El Candil Power = 450 kw Voltage = 3200 V Connection group: /09/03 17/09/03 26/09/03 4/10/03 13/10/03 21/10/03 30/10/03 7/11/03 16/11/03 24/11/03 3/12/03 11/12/03 20/12/03 28/12/03 5/01/04 14/01/04 22/01/04 31/01/04 8/02/04 17/02/04 25/02/04 6/05/04 14/05/04 23/05/04 31/05/04 9/06/04 17/06/04 26/06/04 4/07/04 13/07/04 21/07/04 30/07/04 7/08/04 16/08/04 24/08/04 1/09/04 10/09/04 18/09/04 27/09/04 5/10/04 Transforme 2: Power: 500 kva Voltage = 3,3/0,396 kv UCC = 5,1 % Connection group: / Transforme 3 Power: 700 kva Voltage = 0,380/13,86 kv UCC = 5,1 % Connection group: The structure of the power station El Candil is shown in the Figure Nº 3. CENTAL EL CANDIL 3200 V Figure Nº4: Power injected by the generator. 3. STUDY OF SHOT CICUIT To establish the strategy of coordination of the protection, we make the studies of short circuit currents in the mentioned electric system. For this, the sequence circuits were analyzed and the value of short circuit current was calculated for different kind of faults in different points of the network. With these data, the maximum and minima values were obtained in the network. Maximum short circuit current: For the case that contribute to a fault (three phases) the system and the generator. Minimum short circuit current: In case of fault (one phase) with impedance of ground through a 40 Ohms impedance. 3.1 CICUITS OF SEQUENCE. Transformador 0,5 MVA Positive Sequence Circuit. 380 V Transformador 0,7 MVA V V ELE de Sobrecorriente Figure Nº 3 Figure Nº 5

3 3.1.2 Negative Sequence Circuit. Figure Nº Zero Sequence Circuit. Figure Nº 7 4. STATEY OF POTECTION. The transformer of the power substation of 33/13,2 kv is protected against short circuit currents with overcurrent time protection relay (in the primary and secondary of the transformer). The normalised curves of adjustment are selected in function of the nominal current of the transformer. In the case of the feeders of 13,2 kv, they are protected by overcurrent time protection relay in the beginning of the line. The normalised curve of adjustment is selected in function of the nominal current according to the main section of the feeder. Also, each relay incorporates the function for instantaneous reclosing operation for different fault (one phase to ground or three phases). The main function, is the possibility to save the performance of fuses for transitory faults. Also, some feeders have reclosers due to the great problem of branches on the lines that we have in our city. 5. STUDY OF FAULTS IN DIFFEENT POINTS OF THE ELECTIC SYSTEM. We are going to analyse the most critical cases to establish and verify the selectivity of the protection. The graphic of the system study it shows in The Figure Nº 8, with the distribution of the short circuit currents for each fault in different points of the network. coordination between the switches of the feeder Bonduel Sur and the generator is not required. In that way, normalised temporised curves are selected to guarantee coordination between the switches (I5), (I2) and (I1). Also, as all the feeders have enabled the function of an instantaneous reclosing point for fault to one phase - earth or fault between phases, the relay of the generator is adjusted to send to the switch (I6) an instantaneous shot when its take a value above the threshold of overcurrent. This makes that every time that a fault appears in the point (1), they open in combined and instantaneous form the switches (I5) and (I6). After one second, the relay of the feeder sends a reclosing and it closes the switch (I5), without the contribution of the generator. In case of permanent fault, the feeder s relay sends a signal to open the switch (I5) according to the temporized curve. The Figure Nº 9, shows the adjustment of protection. It is necessary to clarify that the curves of the switches (I1) and (I2) are indexed at the level of 13,2 kv. Figures Nº 8 I Subestación MT/BT econectador Electrónico 5 T1 I1 Sistema Equivalenrte ET P. Industrial I3 I4 I5 4 I2 3 Fusibles MT 1 2 Distribuidor BonduelSur I6 CentralEl Candil 5.1 Fault in Point (1) In this case, the contribution to the faults is produced by the system and the generator. This makes that the value of the short circuit current is high reaching values of approximately 3,5 ka. Since the main function is highly commercial, we don t need that the generator operated in island. So the Fusible Figures Nº 9 Curva temp. I1 Curva temp. I2 Curva temp. I5 I6, I5 Instantánea t

4 5.2 Fault in Point (2) In this case, the short circuit current in this fault point is smaller than in point (1). According to the study, the maximum value of short circuit current (for faults between phases) is approximately (1,5 KA). Keeping in mind the strategy presented in the previous point (1) we maintain the coordination of the protection. Therefore, in the moment to appear a fault in the point (2), the instantaneous opening of the switches (I5) and (I6) take place. Then, the switch (I5) send the corresponding reclosing, having already disappeared the contribution of the generator. In case of permanent fault, the fuse of MV line burns. 5.3 Fault in Point (3) In this case, the contribution to the short circuit current in the point (3), is produced by the system and the generator. It is higher than the short circuit current in the previous points (1) and (2). According to the study, the short circuit current of three phase would be of approximately 4,5 ka. This is because the contribution of the system is higher than the contribution of the generator through the feeder Bonduel Sur. Keeping in mind the strategy presented in the previous points (1) and (2), we maintain the coordination of the protection. In this case, a fault in point (3) will cause the instantaneous opening of the switch (I6) or will open the switches (I5) and (I6), depending of the value of short circuit current. In that way, it will eliminate the contribution of the fault through the feeder Bonduel Sur. Then, the fault causes the opening of the switch (I2). After that, it is eliminated. It is important to mention that the instantaneous opening of the feeder's switch (I5) and of the generator (I6) reduce the possibility that the generator is works in island. This operation is not convenient because the minimum load of the feeder is bigger than the power able to inject the generator. a blockade sign to the feeder's relay Bonduel Sur in order to disable the instantaneous function for earth or between phases faults. 5.5 Fault in Point (5). In this case, the value of short circuit current contributed by the generator can be so small that it doesn't produce the open of the switches of the Bonduel Sur and generator. When we come closer to the power station, the short circuit current will be higher and the effect will be similar to the descriptions for point (4). It is important to mention that the are two recloser installed in series in this feeder. They have adjusted with two instantaneous tripping to stops the temporary faults and two time current curve timing to stop the permanent faults. In case of fault in the point (5), the recloser 2, send an instantaneous trip to stop the temporally faults. After two seconds, it sends a second instantaneous trip and it closes again. In the case of permanent fault, the fuse of the MV line eliminate it. 5.6 Adjustment of Protection System of 33/13,2 kv of the Power Station Parque Industrial. The Figure Nº 10, shows the real adjustment implemented in the studied system. This includes the temporized curves of the relay that protect the transformer of the power subtation and each feeder. Also, the curve of the fuse of MV (40 A) and the instantaneous and temporized adjustment of the two reclosers connected in series in one of the feeder. 5.4 Fault in Point (4) All the feeders have similar adjustments. When a fault appears in the point (4), the contribution of short circuit current takes place from the system and from the generator. Depending were the fault is located, the contribution of the generator can be very small. This fault produced the instantaneous opening of the switch (I3) or switches (I5) and (I6), depending of short circuit current. Then, the reclosing corresponding of the switch (I3) takes place without the contribution of the generator. In case of permanent fault, the switch (I3) will open. This situation causes an undesirable opening of the switches (I5) and (I6). To improve this situation, a system of blockades was implemented to cancel the instantaneous opening of the switch (I5). This way, when fault appears in anyone of the feeder (I3) or (I4), the protection relays sends Figure Nº10

5 6. CONCLUSIONS. The strategy of protection presented in this work allows to maintain the selectivity between the switches for almost all of the faults that can be presented in the studied system. Also, it maintained the instantaneous reclosing function for all of the feeders to different faults in order to save fuses in the network of MT for transitory fault. The only disadvantage in this strategy is when fault in point (3) appears, because it can cause not wanted openings of the switch of the generator. This situation can improve if we decided to adjust the curves of the protection relay of the feeder similar to the generator; for example, inverse time normalised curves. In this case, the fault in the point (3) will make an instantaneous reclosing in the feeder and then, in case of permanent fault, it will open definitive without cause the opens of the generator's switch. This is due to the difference of the contributions of short circuit current that will see each relay. In our case we decided to adjust the relay that protects to the generator with instantaneous trips for fault to one phase - earth or fault between phases. It was determined because in case of adjusting the relay with temporised curves, it will take a long time to open the switch. In that case, it will force to the generator to operate in island in a short time. Also, for any kind of fault, it could cause bigger mechanical demand in the generator and non-balance of voltage in the network of the system. It would affect the quality of service to the customers. We have to remember that the Bonduel Sur's minimum load is bigger than the capacity of power that can inject the generator. The study presented in this work allows you to achieve a good coordination of the protection to minimum cost. 7. EFEENCES 1] CIED 17ª International Conference on Electricity Distribution Barcelona [2] E. Orduña, Protección en Sistemas Eléctricos de Potencia Curso ama Estudiantil IEEE, UNSJ. San Juan Argentina, Octubre [3] SIEMENS Manual del elé de Sobrecorriente 7SJ

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