In Electrical Power Systems that are used today, they have normally always followed a system of large central generators feeding electrical power through generator transformers to a high voltage transmission network. This system is used to transport power over fast distances which is then extracted from the transmission network, passed through distribution transformers and then to the customers. This has been the arrangement for over four decades. Recently however, there has been laws passed which recommend the need for connecting generation to the Distribution Network and this is called Distribution Generation. (DG) It is also known as on-site generation, dispersed generation and embedded generation among other things. Nowadays the developments of renewable technology with its energy sources are being promoted in countries by international energy policies. While new power plants are being built, they have to conform with their countries policies as well as the Kyoto Protocol. Most of these plants are from Renewable Energy Sources (RES) and combined heat and power (CHP) are connected to distribution networks. This form of DG poses permanent challenges with each step to the Distribution System Operators (DSOs).
Recently, research has been carried out by several universities and research institutes. They have been surveying and researching into different regulatory issues and ways of improvement of the DG in the Distribution Networks. The main issues were:
Current Regulation and DG Integration.
Impact of DG on Costs and Benefits for DSOs.
New business models and improvements to enhance integration.
In recent years, the increase of renewable energy sources increased dramatically. In 2002, it was calculated that 27.260 MW of electricity generating wind turbines were operating in fifty countries and that it was permanently increasing. Of these, 75% were in European Union countries, with the leading countries being Germany, Spain and Denmark. The major development that has allowed this is the micro-turbines and the novel energy storage technologies. The increasing penetration of DG goes back to the original technical implications that have occurred and has opened questions to whether the traditional methods of power systems are still adequate. This is true at least at the distribution level where the bulk of DG is connected.
1.2 Objectives/ Aims
The objectives of this paper is to:
Identify the components of the distribution network.
Study the nature and performance of distribution generations.
Recognize the necessity of DG in today power grid.
Investigate the reliability and security of distribution as are met of DG.
Discover the challenges to the distribution companies as a result of growth of the distribution generation.
1.3 Literature Review
The purpose of this essay is to study DG and its effects on the National Grid, as well as how other European Countries have integrated the energy into its systems. Currently there is many Papers, plans, and practical environments with the leading Doctors in the subject have researched and implemented the plans.
Many of the researchers have achieved high academia as well as furthering technology in the field and there for have a good reputation in the subject, providing proof of theories where needed as well as furthering research with in the field of DG and DN. Only European countries were investigated.
Much research has been instigated with improving the DSOs as they are needed to accommodate higher levels of DG.
1.3.1 Introduction
1.3.2 Main
1.3.3 Conclusion
2. Distribution Systems
2.1 History of the EU DG Systems
Today, the European Union countries have some of the highest penetration of wind power as well as small decentralised production units in the world. From Denmark who has such high penetration compared to the load demand that at times, the wind power generators can cover the entire load demand. To do this, it must have the traditional plants to run low to ensure stable operation.
In the United Kingdom, the government, as well as its predecessors, are working at aiming the UK to have renewable energy supply 10% of the UK electricity supplies by the end of 2010 with 10GW of CHP by the same date. Depending which load factor is assumed, it will approximately need up to 14GW of generation capacity installed throughout the UK. This has been successful as of Monday the 6th of September with Scotland supplying 4.7%. Wind Farms have generated just under 10% itself with other renewable sources such as hydropower generating a further 4%. The UKs plan is to increase gradually this percentage to approximately 30% produced from renewable sources of the UKs total consumption.
2.2 Distributed Generation
The purpose of implementing DG into network systems is to reduce the CO2 emissions caused by fossil fuel sources due to the damaging effects it has on the planet.
In the UK itself, it is connecting consumers to a transmission network by lower voltage networks that collectively are called the distribution network. These low and medium voltage networks are mostly connected to one another and connect to the transmission network at certain supply points. The resistance of the distribution lines over powers the reactance when lower voltages and lighter lines are placed at the extremities in the network. This affects the value of additional generation capacity which will be discussed further on.
2.3 Benefits
There is several advantages with DG such as:
2.3.1 Losses
If generation is near points of demand, it can drastically reduce transmission losses as well as distribution losses, both caused by the resistance that power lines, cables and transformers. Most demands is on the DN and therefore connecting a generation source to a nearby on the load source on a DN will normally cause the least amount of losses, assuming generation doesn't exceed the local demand to greatly. When smaller plants are used closer to the loads, this is called Embedded Generation.
2.3.2 Plants
Combined Heat and Powers (CHP) plants are used to provide heat as well as electrical power. CHP plants are also used to provide head like conventional boilers as well as provide electrical power. Small scale CHPs run parallel to the grid as the power output is driven by the heat demand, rather than the electrical demand. The efficiency is greater than a unit that is solely for heating. This is because standard plants waste heat by dumping it into the air as well as water bodies, while CHPs harness the energy and use it to their advantage.
2.3.3 CO2 Reduction
CO2 reduction is a major issue due to the effects of Global warming, and most EU countries have made it a major agenda. To help with the reduction, governments have placed penalties to reduce the electrical industry from causing more CO2 emissions. Since the Renewable Obligations has come into effect, Power Providers have been forced to source a proportion of electricity from renewable sources. These are normally considered to have almost zero CO2 emissions and as they can be small and be located away from the transmission network, they can be cheaply connected at lower voltages. The supply of energy has always been from different fuels which have affected prices of different fuels. The main fuels in the UK are Coal, Oil, Gas and Nuclear. When the generation port folio is increased so that it absorbs sources that aren't reliant on the other fuels, it decreases the risk to the industry and the price increases for the consumers. With growth being demanded in the UK while the large generation plants are near the end of their estimated life times, there is an ever increasing demand for renewable energy which equals to more generation capacity to be required and built.
2.3.4 Security
With controlling and restraints, a distributed generator, can contribute to system security, very similar to larger generators that deliver system support for a larger network. DG can provide flexibility for reactive power suppers and the voltage and power flow services.
With real power balancing, DG can be limited with its availability to its renewable energy source with systems running control strategy and coordination with the other generation in both local and HV networks. As well as this, it may work the opposite way with DG improving system wide supply diversity.
2.3.5 Cost
The main advantage and disadvantages of DG is that to build a large generation plant, it can be a lengthy and expensive cost, due to rules and regulations, historical as well as natural reserves as well as community attitudes. Recently as far north as Caithness, many Wind Turbines have been built and were described as being "Ugly and appalling" and caused outrage amongst the community. If small plants are placed in locations that can be smaller, it can cost less as well as reduce the damage to the country side and land, as well as reducing planning costs and construction costs, compared to larger sites.
The capital cost, due to being smaller, of a small generation plant, has a lot lesser need for investment than a large one and there for has a lower financial risk. Small plants can be added and removed as required while large plants, eg: Nuclear, takes an extreme amount of planning as well as public enquiries. An extremely small amount of generation that is connected below 1kV would have extremely low connection costs compared to large and could generate up to 10% of average load. It is a lot cheaper to connect at lower voltages since the protection and switching equipment is cheaper for LV connection rather than HV connection. The costs of lines that are connected in rural areas will be cheaper as these are normally connected to the LV networks rather than the HV networks.
2.4 Types of DG plants
There are various types of plants that are delivering power in the UK. These are labelled by their effects on the DN and what the cons and pros are of DNOs.
The main type is a dispatchable power plant, which is where the output power is controlled. These are limited to small hydro, as well as thermal types. The source of the energy has to be available at all times for it to be a success. If it was a electricity storage plant, it would store electrical energy when there is excess energy generated. The speeds of these plants reactions change with the technology used. Another type uses voltage regulation. This is called Voltage Control. Voltage regulation can be automated using synchronous generators; however, it is normally achieved by changing the excitation of the synchronous generator. It is possible however to achieve this effect using power electronic converters. If it is not possible for voltage control to be used, it can be used to operate on power factors. If voltage control were used for smaller power plants, the voltage control method can lead to undesirable affects. It may become over excited such that over heating or under exciting can lead to problems this is normally the case for smaller types of plants. When this is used, smaller synchronous generators are used.
2.5 Impacts with increasing the Distribution Generation
There are several impacts that can cause problems within the Network that are caused by DG which can alter the capacity of the system.
2.5.1 Bidirectional Power Flow
A situation can occur when part of the network which only had unidirectional power flow, where the sections that change from high voltage to low, changes direction. This is caused by the plant that is generating at the low voltage exceeds the demand that is needed. This is common when there is a low demand while generating high. This is a problem when designing DN.
The protection may not be able to offer the correct protection if this were to occur.
The transformer, especially ones with On Load Tap Transformers are normally assumed to be capable of unidirectional power flow. This will cause problems if the rations or tap settings are incorrect.
2.5.2 Connections of DG
The connection of DG may cause increasing voltages in local networks unless the reactive power can be absorbed. Another problem connected with changes in voltage levels is step voltages. When generating for a network, whether at the beginning, end or if it is suddenly removed from a network, it creates a step in the voltage level of the network. The voltage step size is dependent on the transfer of active and reactive between the network and the generator. If the generator is at unity power factor, (φ=0, cosφ=1), the size of the voltage step is linked to generator size. In the United Kingdom, the maximum step that is allowed is +/- 3%. Due to this, the generators are limited in size by the step voltage that can be caused.
Several types of generating plants can cause degradation in the voltage quality. This will be mentioned later on.
If the output of a generator is changed dramatically, this can cause changes in voltages. This is called Flicker. Wind turbines can cause flicker due to changes in wind speed, as well as the change in aerodynamics of a turbine blade when it passes by the tower structure that holds the blades.
2.5.3 Fault Levels
A problem that also has to be overcome is the fault levels. When renewable generating sources are connected, most are induction motors and if they are synchronous generators, they are converted and there for have a lower fault contribution. The induction motors are no longer exciting if the power output drops to zero which happens if there is a fault. This is different to synchronous generators being connected as this increases the fault level in networks nearer the connection.
DG can change how OLTC transformers act. The impedance of this is related to how the position of the tap is and there for the fault level of the network. If the flow of power was reversed since this can happen if the generation exceeds the demands, the voltage level will be increased. When this happens, the impedance of the OLTC is lower than if the generation was not involved and there for the fault level can be raised so that it can become dangerous. The tap positions can be edited so that it can vary the impedance in a transformer by 8-15% both positively and negatively of nominal impedance.
2.5.4 Current Carrying Capacity
The current carrying capacity of lines, as well as transformers is limited due to their own resistance. The resistance of these can cause losses in the form of heat. The limit of the current of a line is dependent on the type of line, such as what it is made from as well as the form of line, as well as the temperature of the surrounding air. This leads to different ratings depending on which period of the year it is as the temperature in the UK as well as Europe varies quite dramatically. Transformers also vary in construction and dissipate heat more efficiently in colder temperatures of air. The capacity limit is determined by the rate of losing heat and the maximum operating temperatures. With DG in in rural areas, if it were to be a radial distribution network, this would lead to a higher export of power either a network or substation, than the power that was originally being connected. Due to this reason, the output power from the generators is limited by ratings of the transformers as well as the lines that are used to connect the higher voltage network, minus the minimal local demand.
2.5.5 Protection Equipment
One of the problems with DG is being limited by the Protection equipment that is needed for the DG to be safe and efficient.
Generation cannot be connected when the local network is not connected to the network. It can be disconnected at times if there is a fault. Due to this, a loss of mains protection has to be installed if it isn't. This prevents power being used when the network is disconnected.
2.5.6 Frequency protection
Under, as well as over frequency protection always disconnects the generators and the feeders when there is either mismatch or deviation of the AC frequency. It is there for limited in ability to generate power which is to support networks during heavy demand. This can reduce the frequency of a local network.
2.5.7Voltage Protection
Under voltage, and over voltage protection is needed and can at times disconnect the feeders and/or generators connected at the distribution level when voltages of the bus change and go to + or - 3% of its nominal voltage. This can limit the generation that is part of the voltage support section of the network.
This the DNOs responsibility to provide the correct protection. The power ratings must never go beyond the limits of the equipment as this could cause failures in the network and disconnect the loads. The protection is always designed to prevent a major disconnection of consumers and is used to minimise the loss of power to a major section of the network.
2.6 Quality Issues
With DG on power quality of a DN, it depends on different factors like the type, the size of the unit of DG, what its operation mode is, the output fluctuation, the DG relative load capacity at the interconnection point and the voltage regulation practice. Normally, DG is installed to generate a backup power source on site that improves the power quality of the system but isn't necessarily the case all of the time. There are issues when the generators and technologies of different types are connected to DN. The main issues are Voltage Regulation, Voltage flicker, Voltage dips, sustained interruptions, harmonics and a contrasting interference with existing utilities used for protecting the current system setup.
2.6.1 Voltage Regulation
VR problems occur when DG is introduced to DN for a number of reasons, these being: Intermittent nature of the wind turbines, fuel cells and CHP, Interference occurring with synchronous generators that are capable of supplying both active, as well as reactive power with the voltage regulators such as SVRs and LTC, the use of induction generators and inverters with grid connection that are not suitable for VR since they are unable to create reactive power, the use of DG units that are to small since it cannot regulate the voltage, a breakdown of large DG units that are used for VR, when DG units are have minimal communication and co ordination, a high amount of turn on/turn off times with a high number of small DG units, reversing power flow than can happen when the ouput DG is in excess of a downstream feeder load.
Voltage Flicker
Voltage flicker is caused by energy fluctuating from the generation, normally as energy levels change suddenly.
Voltage Dips
This is normally caused during the start up of a synchronous motor, due to the magnetisation process absorbing the reactive power. This can also happen during short circuiting or the generators are switched away.
Sustained Interruptions
There are cases where a back up has been unable and due to this, if generation fails due to an interruption in the circuit or even a break down in the system, this would fail to provide power to the loads.
Harmonics
This was originally caused by thyristor based line commutated inverters. However, modern methods are connected to networks through converters and are insulated gate bipolar transistors. The converters use pulse width modulation and this causes fewer harmonics, but they care still caused if the system uses induction generators, or synchronous generators. This changes the response of the system networks and in turn the harmonic impedance by changing to other harmonic sources. It can also be caused by capacitors that are used for the induction generators during excitation. This can cause resonances.
.Voltage Unbalance
This is normally caused due to the integration of single phase DG into DN.
2.7 Protection Issues
There are four methods to protect the network as a change in the current level occurs when DG is connected to DN. This change has a high probability of changing the device discrimination as well as reduce the reach of the over current, cause a tripping affect, cause unintentional islanding and autoreclosures failing. As mentioned before, depending where the fault is, bi direction flow and voltage profiles are also affected.
With DG and DN, there is a necessity to have the correct relay position, fuses and other protective equipment to ensure safe connections.
2.7.1 Modifying the fault level
Due to previous research done before myself, it is known that fault current increases when a connection is made between DG and DN. The current increases to its peak between the load and connection.
2.7.2 Protection by blinding
Feeder over current relays can be altered by the introduction of DG. The fault levels of the relays decrease even though the fault levels of the DN increase. This is because the DG is normally located between fault points and feeding stations. The introduction of DG however affects the switching time of the relays.
2.7.3 Sympathetic Tripping
There are situations where the DG itself is responsible for faults on the feeder if it is fed from the same station. It can also cause faults at higher levels of the voltage which can cause isolation of a healthy feeder which is not needed.
2.7.4 Reducing the Distance Relay Reach
There are types of relays called Distance relays which settings make the relay operate in specific times in case any faults occur. These are set to activate in zones in relation to the transmission lines or distributions feeders. A problem with this when DG is initiated is that it may not operate to the set settings. When a fault occurs past the bus bar when DG is connected, the impedance of a relay that is further up the stream will have a higher fault current than the real fault impedance. This can affect settings and can there for alter the operation times. This, in a worst case scenario, can cause the relay to fail completely.
2.8 Summary
3. Losses: Active and Reactive
A problem with the transmitting and distributing of energy in electricity form is that it will always lead to Active Power Losses. When studying the losses, it is determined into 2 categories, technical, and non-technical losses. The technical losses are the electrical to heat conversion of energy. This is divided further into load dependant and load independent losses. Load dependant losses are when there are series losses, given by I|2·R with R being the series resistance of overhead lines etc. However an unbalanced loading of distribution cables will have a higher loss than a balanced one, as you would expect from the quadratic function. Load independent losses are commonly known as shunt losses. This is given by V|2·G. G is the shunt conductance where the shunt losses of the system are independent of loading when the voltage change is created by a load change. The reason there are losses is that it is in relation to eddy currents and hysteresis from the iron cores in transformers, as well as dielectric losses in cables. There are also some losses related to the operating constraints with cooling or switching gear among other things.
The non technical losses are the energy that is consumed where the companies do not get money from. This could be inaccuracies from readings, or connections that are illegal. Non technical issues have a higher rate of happenings in third world countries where theft is common and monitoring of the systems is primitive.
With AC systems, a transfer of electricity can lead to a type of loss known as reactive power loss. The difference with Active Loss is that the inductive reactive power losses can be positive as well as negative. This cannot be from the user end of the circuit like the active energy. It does however have similar losses as it is divided into two categories. These being load dependent series losses and load independent shunt losses. These given by |I|2*X with X being X being the reactance of the series, and -|V|2*B, where B is the shunt susceptance, respectably.
3.1 Estimation of Losses
There is two different ways to calculate the losses. The first is to calculate the losses as the different between the generation and consumption. Using this method doesn't require the parameters but unfortunately, while being simple, needs all information about the measurements of consumers as well as the producers. The losses are smaller than loads flows, so small inaccuracies can create huge inaccuracies in the estimates of loss.
To achieve increased accuracy, losses can be gained by estimating the load flows, which is achieved my models of the network, an estimation of the states and measuring of the power. This method if dependant by the measuring accuracy as problems can occur if the losses aren't measured accurately. This method however can give the information of where the losses of the network will happen which can be useful.
3.2 Allocation of Losses
Knowing where the losses are going to occur can be essential in the modern market due to saving costs.
With the allocation of losses, especially in the current economic market, it is necessary to discover where the losses are occurring to save future investments. An issue that has to be overcome is the separation of the cause of losses with the losses that correspond to current from a source that connects in parallel. There are other loss allocation methods where they are detected by viewing the total power that is flowing through the system to the loads. This is known as Tracing. Tracing involves finding the inflows of a bus bar and the outflows and detecting the difference.
In the UK
3.3 Summary
Of all losses, most of these occur on the distribution network. 6% average of the energy that is generated is lost compared to a quarter of that energy being lost on the transmission network.
With loss allocation, there are requirements in place to help allocating losses easier and used for optimum efficiency. There are several which are most important. These are that the losses have to be located to show the true cost so that there is no cost of losses for the companies. The location of the losses must be accurate and true, as to reduce the wasted cost of false results. There must be in place, an exact measurement to discover the true cost and location and the system of the losses allocation must be simple to put into place so that the method is easy to understand and put into place.
4. Stability of DN with DG
With AC power systems, it is essential to the system that the frequency as well as the voltage magnitudes are permanently close to their chosen values all of the time. The frequency and voltage control has been managed normally by large plants.
The types of stability that were looked at were Frequency stability, oscillatory stability, transient stability and voltage stability. These were looked at various penetrations to gain a further understanding of the difficulty of High Penetration.
4.1 Oscillatory Stability
To date, oscillatory stability is becoming more and more efficient to use due to the electrical power networks being under continuous disturbances and permanently operating near the stability limits. Due to this, it is becoming more and more explored and used. The oscillations occur normally due to insufficient damping of the electro mechanical oscillations. Stability of oscillatory stability in electrical power networks is permanently being analysed to discover more efficient methods. With each penetration level, which adds up to the seven levels of the DG units, a power flow calculation is worked out to confirm the operation conditions of the network. This is normally done using model analysis.
4.2 Frequency Stability
Frequency changes in networks due to large disturbances in systems from imbalances caused by electromagnetic and mechanical torques on generators, as well as a huge imbalance between generated power as well as with load demands. Frequency stability is a reference to how capable electrical power systems maintain a fixed frequency level after being severely disturbed. The change in frequency is not a problem with stability if the levels between generation and the load are returned back to the maintained level. This would need a high generation backup and a fast response from the control systems. If severe disturbances affect the units and it cannot be corrected, units will be tripped and stability will be lost.
4.3 Transient Stability
The problems with transient stability, often called "first swing stability" is considered one of the most important concerns that are in planning as well as power system operations. Transient stability, when the angle stability is under large disturbances, is increasing in importance due to the security of the system. This is labelled as the ability of the system to correct and maintain synchronism when put under disturbances of either short circuiting or loss of loads or generation. This type of stability is dependent on initial conditions of the system as well as with the types and severity of disturbances. The normal method of to assess the stability is to use the time domain simulations and analyse the transient energy function which are related to the extended equal area criterion which are used under some assumptions.
4.4 Voltage Stability
This is labelled due to its ability of the systems power maintaining the voltages at the nodes (that are in the limits) instantly after a disturbance. The instability of the voltage is from the sudden lowering of sudden rising of voltages that can cause losses in loads or transmission lines. Reactive power consumptions would increase if the induction motors are used to restore power if the slips were adjusted. If the consumption of power required increases to above the generators capacity, it results in voltage instability. The controller units are normally near the load centres, and there for the performance are improved, specifically during short circuit scenarios.
4.5 Summary
5. OLTC Study
5.1 Tap Changing
To conform that the operation and time life of components are correct, voltages in the systems must be kept at the correct levels and values. With distribution systems in the UK, it has been ensured by the EU that the 10 minutes average RMS voltage at medium and low voltages must be 10% above or below the nominal 95% voltage of the time to reduce and stop damage as well as wear from the equipment. With Low Voltage Busses over 400Volts, they are maintained to be within 6% either way, and for 400v busses, +10% and -6%. This responsibility is from the DNO.
Power goes to the distribution network at a point known as the GSP, a Grid Supply Point. This is a transformer, or in some cases, a parallel formation of several transformers which usually feed a 33kV busbar. The high voltage side is then kept within its limits by the actions of the plant that is connected to the transmission network. The other side of the voltage, which is on the distribution side, is maintained by the transformers which are OLTCs. This voltage is automatic and has predictable local control, which is achieved through good design and onsite manual switching. The DNOs normally connect generators to the DN and thus control the voltages in the network. If the generators are connected, they are also maintained to be used as a frequency supporter and can provide real power to local demands. The most used voltage controller in the United Kingdom OLTCs.
The OLTC is used for stepping up or stepping down voltages between Medium Voltage circuits and High Voltage circuits, or Medium Voltage circuits and Low Voltage circuits. It can also be used to have direct contacts between High Voltage and Low Voltage as well. The purpose is actuated by an Automatic Voltage Controller Relay (AVC). Due to this configuration, the busses connected to the OLTCs voltage can be controlled. Similarly, an autotransformer can also be used to control voltages between bus bars of similar nominal voltages.
OLTCs can perform various operations such as a similar role to a step down transformer and this is situated at the GSP. The AVC controls the lower voltage bus voltage. The other role it maintains is to step up voltages from generating plants. AVC acts as a limiter and keeps the voltage to the correct level.
Transformers that are in networks that were examined are unique as it is dependent on the number of turns on the high voltage winding coil that is connected. In most cases, if the high voltage side has less turns, then the tap ratio is lowered and there for the voltage is raised on the lower side. Connecting a higher voltage will raise the tap ratio and this will lower the voltages on the lower side.
Due to the transformer having two winding sides, if the number of turns were reduced from the high voltage side, this is referred to as tapping up. A tap up is only when the LV voltage is raised and vice versa with the lowering of LV voltage. P36
Due to this being a mechanical device, this takes time to operate and can cause a short circuiting without protection, however, a diverting inductor is placed in series with the taps to stop short circuiting.
5.2 Considerations
While technology has developed, so have the controllers of the OLTC.
5.2.1 Digitalised Control
The original OLTCs were analogue but with Programmable logic circuits with microprocessors, they have increased the efficiency of the transition of different taps. With modern control designs to increase efficiency further, it is necessary to have digital controllers.
5.2.2 Automatic Communication Networks
Units for control can be linked to control stations to create automatic adjusting of the taps. This can be an advantage due to achieving possible controlling that was previously impossible. Due to communication networks, it also speeds up the notice of errors and alarm signals, as well as information to the control station.
5.3 Summary
6. Voltage Control
6.1 Introduction
To confirm correct operation and to maximize the life time of the components, voltages are kept in the safe and correct parameters given. The EU laws state that is must have, within the 10 minute average RMS voltage between medium and low voltages, must be within the +/- 10% of the nominal voltage level at 95% of the time. This is to reduce wear and damage occurring at both the user equipment and the distribution side. To date, the voltage control is maintained differently in transmission systems compared to distribution systems due to the transmissions system having a higher X/R ratio where the voltage magnitude is maintained by the reactive power flows. There are various methods to compensate the difference caused by imbalanced such as shunt capacitors and reactors, as well as HVDC units, and synchronous condensers, these both can provide reactive power and short circuit power.
6.2 Compensation Strategies
With medium voltage, it is controlled by OLTC where the X/R ratio is lower than the transmission systems which mean that the power flow affects the voltage drop. To compensate with voltages rising and dropping, a booster transformer is placed in the circuit. However no active power injection is performed at the medium or low voltage levels due to it being difficult to detect if the area was not part of the main grid. Also, voltage control confuses the OLTC of the transformers which could cause problems and the sensitivity of the voltage to the power interjections isn't high when the X/R ratio is small at the connections.
6.3 Constraints
6.4 Summaries
Through previous research done by various engineers, it has been proved that DG can improve stability in power systems, depending on the type of Generation and the position of the power plant. With oscillatory stability, DG can improve the dampening of the electromechanical positions as well as increases the frequencies. To use the maximum potential of using DG units, the stability needs to be improved to create a correctly functional stable network.
7. Model Simulation
7.1 Software
7.2 Method
7.3Errors and Correction
8. Results and Conclusions
8.1 Summary
8.2 Strengths to this Approach
8.3 Weakness to this Approach
8.4 Suggestions of Further Work
8.5 Conclusions
In a research article regarding Distribution Generation, Víctor H. Méndez Quezada, Juan Rivier Abbad and Tomás Gómez San Román, states "In all the situations, annual energy losses variation as a function of the penetration level of DG shows a U-shape trajectory. Losses start to decrease with low DG penetration levels, whereas after a minimum value, they start to increase with higher DG penetration levels."
9. Bibliography
Embedded Generationby Nick Jenkins et al. IET © 2000 (273 pages) CitationISBN:9780852967744
http://www.renewableenergyfocus.com/view/12387/wind-power-delivers-near-10-of-uks-electricity-/
http://www.ewea.org/fileadmin/ewea_documents/documents/publications/WD/WD25i_focus_grid.pdf
http://www.powergenworldwide.com/index/display/articledisplay/307887/articles/cogeneration-and-on-site-power-production/volume-8/issue-5/features/challenges-for-dg-integration-in-europe-status-and-potentials-vary-by-country.html
http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=00822093
