Distributed photovoltaic (pv) grid protection for power system what is the effect

Distributed photovoltaic power generation system is connected to the power distribution network, power distribution network is no longer a pure single power supply, the radiant power supply network. At this point, if the line fails, the size of the short circuit current in power distribution network, the flow, distribution and behavior of reclosing can be

access to distribution network distributed photovoltaic power generation system, power distribution network is no longer a simple single power supply and radiation power supply network. At this point, if the line fails, the distribution of the size, direction and distribution of short-circuit current and reclosing behavior may be affected by distributed photovoltaic (pv). Distributed photovoltaic behavior also can affect system operation and protection. Although the contribution of the short circuit current by a single photovoltaic cell is different, but many small photovoltaic cells or large photovoltaic cells comprehensive contribution may change the short-circuit current level, resulting in failure of C fuse over-current protection, coordination and fuse operation and fault detection. In this case, the circuit breaker must increase capacity, protection device must be upgraded. ( 1) Results in the decrease of the line protection sensitivity, refused to run. ( 2) In the line protection misoperation. ( 3) Lead to adjacent lines of the instantaneous speed of protection failure, loss of selectivity. ( 4) Cause the reclosing is not successful. After connection of distributed photovoltaic (pv), the line on both sides of the connection of two power supply. When the circuit failure occurs, if only the system side protection tripping, photovoltaic power generation didn't disconnect, pv will continue to provide short circuit current to the point of failure, failure point is still in a state of freedom. If the system is focused on closing, will inevitably with the current state overlap, lead to the failure reclosing. In order to ensure the success rate of the reclosing must ensure that distributed photovoltaic system before system focused on the feed motion has stopped or removed from the distribution network. ( 5) Lead to standby power automatic switch device can't work normally. In the traditional distribution network, standby power automatic devotion device is often used to improve the reliability of important load power supply. Distributed photovoltaic after introduction, is likely to affect the automatic standby power supply input device to the master work power if there is a fault judgment, thus unable to accurately implement to cut off the fault of power supply and enter standby power supply operation. ( 6) Distributed photovoltaic directional protection equipment should be. Distributed photovoltaic (pv) grid makes distribution network for more than a power supply system, trend by one-way trend into a two-way trend. Therefore, directional protection equipment requirements. Using directional element instead of all the fuse in power distribution network and automatic reclosing is not feasible in economy. In order to solve this problem, there are two solutions: as solutions and island. The first is mainly used in China. By the scheme is to point to in the case of any failure, disconnect all distributed photovoltaic system, and the original protection measures. The downside of this approach is to reduce the quickness and reliability of protection, at the same time also brought time coordination problems. Islands plan refers to the use of distributed generation to independently to the part of the distribution system power. If power failure, distribution network will be converted into several islands. As far as possible with distributed photovoltaic power, reduce the blackout area, improve the efficiency of power generation. However, the plan calls for distributed photovoltaic configuration and build a micro grid energy storage equipment to ensure the stability of the system voltage and frequency.