Self-healing networks come to the Netherlands

There is increased pressure on distribution network operators (DNOs) to maintain the integrity of the network. While huge investments are already being made in replacing aging infrastructure to minimize the probability of equipment failure, the chances of failure cannot be completely eliminated. Therefore, when network faults occur, it is necessary for DNOs to minimize the impact by reducing the outage time and number of customers without supply. To minimize the fault outage time, the Dutch DNO Stedin has started a project to introduce automation to its distribution network. The first phase of the project consists of installing intelligent fault passage indicators, while the next two phases use more advanced techniques such as remote-controlled ring main units (RMUs) and a completely self-healing distribution feeder

Integration of DG in MV-grids: challenges encountered by the grid operator

A major part of decentralised production in the Netherlands consists of Combined Heat and Power-plants (CHP). Especially in the horticultural sector small CHP-plants with a maximum rating of 2,5 MW are applied. In these areas the CHP-plants are connected to the Medium voltage grid which leads to a high penetration level of CHP-plants. The Dutch law obliges grid operators to connect CHP-plants to the grid in 18 weeks, and prohibits long term transportation restrictions. When dealing with multiple CHP-connection in a grid the legal obligations conflict with planning permissions and project times. The presentation describes a scenario based method, which enables Stedin to plan the grid expansion pro-actively. In the presentation the results of the case study in the Oostland area are presented

Effect of grid disturbances on fault-ride-through behaviour of MV-connected DG-units, in especially CHP-plants

In the near future a significant amount of the consumed electrical energy will be generated by distributed generation (DG). Because of the small size these units are normally connected to the local distribution grid [1]. Connection of DG changes the operation of the distribution grid. In order to minimize the effect of DG during grid disturbances some standards oblige immediate disconnection of DG-units. With an increasing number of DG-units this strategy can lead to a disconnection of a large amount of DG-units and jeopardize the security of supply. To prevent large unbalances between generation and load because of disconnection of DG-units some grid operators have defined fault-ridethrough requirements. These fault-ride-through requirements are especially applied for large wind parks which are connected to the transmission grid. In this paper the effect of disturbances in the transmission grid on the fault-ride-through behaviour of medium voltage connected DG-units is discussed. The examined grid is an existing transmission and distribution grid. To the distribution grid a large amount of combined heat and power (CHP) plants are connected. The CHP-plants are equipped with an under-voltage protection which switches-off the CHP-plant at a voltage level (dip) of 0,8 p.u.~100 ms. In the paper it is determined what amount of CHP-plants is disconnected due to transmission grid disturbances. It can be concluded that multi-phase faults as well as single-phase-to-ground faults result in a disconnection of a significant amount of CHP-plants. Voltage dips in the transmission grid below 0,6 p.u. lead to a disconnection of all CHPplants, between 0,6 and 0,7 p.u. lead to a partly disconnection of CHP-plants and between 0,7 and 0,8 p.u. to no disconnection at all. It is demonstrated that with a setting of 0,8 p.u.~200 ms most CHPplants stay connected and will not loose stability. Dynamic simulations have shown that the CHP-plants start to consume reactive power directly after fault clearing. This is due to armature reaction of the synchronous generator. The amount of consumed reactive power is related to the fault duration. The voltage recovery in medium voltage grids is delayed due to this reactive power consumption. This can lead to a disconnection of CHP-plants even when the fault is cleared within the clearing time of the under-voltage protection. The delay in voltage recovery has to be taken into account when fault-ride-through requirements for transmission grid faults are defined. © CIGRE2009

Influence of protection on transient stability of medium voltage grids including distributed generation

Due to the increase of distributed generation (DG) in the future it can become important to keep DG connected to the grid in order to maintain the balance between consumed and generated electrical power. Keeping DG-units connected to the grid during a disturbance, the dynamic behavior of the DG-units becomes important. Protection schemes based on definite and inverse over-current are simulated and transient stability of DG-units is investigated. The simulations have shown that there is no major benefit to apply inverse over-current relays in MV-grids with short feeder length and high short circuit power. With conventional grading of the protection in most cases the DG-units become unstable. The paper shows that reduction of the time grading is possible however, this reduction is not sufficient to guarantee stable operation. The best option is fast fault clearing of the complete feeder. It is shown that this is possible without loss of selectivity and with stable operation of the remaining DG-units

Effect of grid disturbances on fault-ride-through behaviour of MV-connected DG-units, in especially CHP-plants

In the near future a significant amount of the consumed electrical energy will be generated by distributed generation (DG). Because of the small size these units are normally connected to the local distribution grid [1]. Connection of DG changes the operation of the distribution grid. In order to minimize the effect of DG during grid disturbances some standards oblige immediate disconnection of DG-units. With an increasing number of DG-units this strategy can lead to a disconnection of a large amount of DG-units and jeopardize the security of supply. To prevent large unbalances between generation and load because of disconnection of DG-units some grid operators have defined fault-ridethrough requirements. These fault-ride-through requirements are especially applied for large wind parks which are connected to the transmission grid. In this paper the effect of disturbances in the transmission grid on the fault-ride-through behaviour of medium voltage connected DG-units is discussed. The examined grid is an existing transmission and distribution grid. To the distribution grid a large amount of combined heat and power (CHP) plants are connected. The CHP-plants are equipped with an under-voltage protection which switches-off the CHP-plant at a voltage level (dip) of 0,8 p.u.~100 ms. In the paper it is determined what amount of CHP-plants is disconnected due to transmission grid disturbances. It can be concluded that multi-phase faults as well as single-phase-to-ground faults result in a disconnection of a significant amount of CHP-plants. Voltage dips in the transmission grid below 0,6 p.u. lead to a disconnection of all CHPplants, between 0,6 and 0,7 p.u. lead to a partly disconnection of CHP-plants and between 0,7 and 0,8 p.u. to no disconnection at all. It is demonstrated that with a setting of 0,8 p.u.~200 ms most CHPplants stay connected and will not loose stability. Dynamic simulations have shown that the CHP-plants start to consume reactive power directly after fault clearing. This is due to armature reaction of the synchronous generator. The amount of consumed reactive power is related to the fault duration. The voltage recovery in medium voltage grids is delayed due to this reactive power consumption. This can lead to a disconnection of CHP-plants even when the fault is cleared within the clearing time of the under-voltage protection. The delay in voltage recovery has to be taken into account when fault-ride-through requirements for transmission grid faults are defined. © CIGRE2009

Transient stability of distributed generation in MV-ring networks

Due to the increase of distributed generation (DG) in the future it can become important to keep DG connected to the grid in order to maintain balance between consumed and generated electrical power. Keeping DG-units connected to the grid during a disturbance, the dynamic behavior of the DG-units becomes important. To guarantee after fault clearing stable operation of the DG-units, the protection scheme and settings have to be changed. In this paper conventional protection schemes of MV- ring networks are discussed as well as the additional measures that have to be taken to protect a MV-ring network including DG properly. It is found that it is not possible to find a proper relay setting to protect the MV-ring network in such a way that the fault clearing process is fast enough to maintain stability of the DG-units. In the paper it is demonstrated that the fault clearing process can be sped up by adding communication to the protection scheme

The effect of fault ride-through requirements on voltage dips and post-fault voltage recovery in a Dutch distribution network

In this paper the possibility to use Decentralized Generation (DG) units for voltage support in Distribution Networks during and after a Short Circuit (S/C) event is discussed. Two types of DG units will be examined, Combined Heat-Power (CHP) plants and Doubly-Fed Induction Generators (DFIG). Earlier approaches would oblige the disconnection of these units during grid disturbances, in order to avoid unwanted conditions such as interference with the protection system and islanding [1]. Newer grid codes for Transmission Networks like [2], taking into consideration the increased share of these units in energy production have set specific Fault Ride-Through (FRT) criteria which oblige them to stay connected during SC events when they are combined to large plants directly connected to the transmission grid, such as (off shore) wind farms.. If ever more DG is connected directly to distribution grids, the same reasoning leading to applying rault ride through criteria to DG connected in large groups to transmission grids, may be applied to DG connected to distribution grids, as a loss of a a large amount of DG connected to distribution grids has the same adverse effect as using DG connected directly to the transmission grid

Modeling, simulating and validating wind turbine behavior during grid disturbances

Due to the liberalized energy market Distributed Generation, DG, is increasing. At this moment, most of the power produced by DG, is generated by CHP-plants and variable speed wind turbines. Integration of wind turbines have impact on several aspects of power systems such as power system stability, protection and power quality. This paper focusses on the effect of wind farms on power quality phenomena during and after a grid disturbance. A dynamic model of a modern wind turbine will be presented in order to simulate grid disturbances. The results of the simulations are validated by measurements

Modeling, Simulating and Validating Wind Turbine Behavior During Grid Disturbances

Due to the liberalized energy market Distributed Generation, DG, is increasing. At this moment, most of the power produced by DG, is generated by CHP-plants and variable speed wind turbines. Integration of wind turbines have impact on several aspects of power systems such as power system stability, protection and power quality. This paper focusses on the effect of wind farms on power quality phenomena during and after a grid disturbance. A dynamic model of a modern wind turbine will be presented in order to simulate grid disturbances. The results of the simulations are validated by measurements

The long non-coding RNA SAMMSON is essential for uveal melanoma cell survival

Cancer Signaling networks and Molecular Therapeutic