21. Grid connection of wind power

welcome to this session my name is Paul Johnson and I'm professor in wind power integration and control and in this session I will talk about good connection of wind turbines and wind power plants to the power system the learning objectives of this session are the following first to be able to distinguish between four different main types of electrical concepts that we have of modern wind turbines and secondly to describe a typical electrical layout of a wind power plant and finally to explain how wind turbines and wind power plants are typically connected to different voltage levels in the grid and also how we can use DC as an alternative to AC connections the first type of wind turbines is type called type 1 and it is based on an asynchronous generator which connects the wind turbine to the grid the advantage of this concept is that it is very simple and very robust the a synchronous generator rotates with a rotor speed which is determined by the frequency in the grid and it does not need to be controlled this concept also includes a gearbox because the rotors rotational speed of the a synchronous generator is much faster than what we want to have in the rotor of the wind turbine and we also are using a capacitor bank and the reason for this is that the a synchronous generator is consuming reactive power and if we are not compensating for this consumption of reactive power then we may experience problems keeping the voltage at the terminals of the wind turbines finally we have in most modern wind turbines there is a built in transformer this is transforming the voltage from the low voltage level to a medium voltage level indicate where we connect the wind turbines type two is a symbol extension of the taiwan wind turbine but this makes it possible to control the rotor speed of the type two wind turbine the idea is to use a variable rotor resistance which is seen here and by changing the resistance in this in the rotor we can change the rotational speed of the wind turbine this offers the opportunity to vary the speed typically with ten percent but there is also some heat loss in the variable rotor resistance which is not advantageous the next concept type three is utilizing the energy and is also much more controllable than the type two this is connecting instead of available resistance to the rotor we are connecting the rotor through a back-to-back converter and by this connection we can be able to utilize the energy which we were burning in this resistor and we can also control the speed in a much higher wider range the rotor speed of the generator and on top of that we can also use this converter to control active and reactive power flow out of the wind turbine and that is why we don't see the capacitor bank here anymore because we don't need it because we can control the reactive power coming out of the stator by controlling this back to back converter finally we have the type 4 where we have a full a converter here which is transmitting all the power stepping back to the type 3 it's only about 30% max 30% of the power that is passing through the converter so the advantages that the converter is much smaller here whereas the main power is flowing this way through this data but in the type 4 case all the power is going through the converter meaning that the converter must be larger on the other hand we have good isolation from the grid which is and can be an advantage in the case that we have disturbances from the grid side the cost of this is added cost for power electronics the next slide shows that a typical layout of wind power plant there is a power collection system in the wind power plants which is collecting the power from all the wind turbines and it is connecting them to the point of connection to the grid which is typically in the transformer station and typically at the lower voltage side of the transformer station the point of connection can also depending on which country behind it can also be in the high voltage side of the grid some times it is necessary not only to have wind turbines but also to have some liquor ciliary equipment like reactors or s VCS which are serving to compensate for reactive power the wind turbines are capable of controlling reactive power but maybe the capacity is not sufficient to what is required from the grid and that is why in some in many cases we also use axillary equipment now we will talk about connection of wind turbines to the different voltage levels in the grid and the idea is that we want to of course connect the wind turbine to as close as possible to where we are building the wind turbine and generally speaking we can say that the lower voltage levels they are available in the vicinity like 0.4 kilo volts whereas there can be longer distances to the transmission weight so we are only connecting at higher voltage levels if we need to depending on the size of the wind turbine small wind turbines they are typically connected to the low-voltage squid here if we have larger with groups of wind turbines we often connect them this way we can connect them directly to the 10 kilovolt grid but we can also choose to build a dedicated radial cable where we are transmitting the power into the transformer station so that we are disturbing less the consumers connected to the 10 kilovolt grid here and finally having large offshore typically offshore but it cannot definitely also be onshore wind farms we will connect to the transmission grid at the voltage levels above one hundred kilovolts in some cases when we go offshore we are moving further and further away from land when we are connecting with wind power plants or wind farms and if we exceed say one or two hundred kilometers distance then we have an issue with stable transmission of the power from the wind plant to the onshore quit this cannot be done with conventional alternating current technology without compensations on the way to land and this is because there is a large consumption of our last generation of reactive power in the cables so we need to compensate for this generation the alternative which is used today already is to to transmit the power with direct current from the wind plant to the onshore and to do that we need the wind plant is still working in alternating with alternating currents then this alternating current is converted to direct current and transmitted to shore and then it is converted again to alternating-current often when we are connecting wind plants this way the DC converter or the HVDC connection system that we have here is serving not only one wind plant but several wind plants with which soft can have different owners also so to summarize this lecture what we have learnt is we have been familiar with the four types of with turbines that we have seen from an electrical point of view we have also looked at a typical electrical layout of a wind power plant or a wind farm and finally we have looked at how wind turbines and wind power plants are connected to the different voltage levels in the AC systems and also that we can use DC for transmission over long distances offshore you

Channel: DTU Wind and Energy Systems

Views: 120,313

Keywords: Coursera, MOOC, Coursera online course in wind energy, wind energy, DTU, DTU Wind Energy, DTU Vindenergi, vindenergi, education, educational video, sustainable energy

Id: -HljEywnEf0

Length: 10min 22sec (622 seconds)

Published: Wed Feb 24 2016