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3. Business Case
6. Success Factors
9. Next Steps
- Improving the efficiency of power transmission and distribution comes down to two choices: you can reduce the resistance of the wires by making them larger or using better materials (not a practical solution), or you can improve the effectiveness of the flow of electricity. To address the latter, it’s important to understand the difference between real and reactive power.
- Real power is what we use to run our lights, computers and production lines. It’s the power the “does the work.” Reactive power does not contribute anything to doing work, but it does cause conductors to heat up and it takes up a certain amount of “space” in the wires. The more reactive power flowing on a line, the less “room” there is for real power, and the less efficient the transmission and/or distribution system will be.
- So, to optimize the movement of electric energy, we would ideally like to eliminate reactive power flows, or at least minimize them. Utilities do this today on their local distribution systems using devices such as capacitor banks or special transformers, typically located at substations or on feeder. These devices work to keep reactive power flows down, making the full capacity of the conductor available for the real power that will be used by our lights, TVs and refrigerators. This process is known as volt/VAr control.
Historically, volt/VAr control devices have operated autonomously, independent of one another and without centralized coordination. This approach worked, but it left a good deal of efficiency on the table since actions taken by one device might have less-than-optimal results for another location on the grid or for the system as a whole.
- The current electric grid was designed to serve analog devices such as lights, motors and pumps, which work just fine despite varying electric loads. However, today’s personal computers and other smart digital devices with microprocessors inside are highly sensitive to variations in power quality due to voltage surges and sags and harmonic changes in the alternating electron flow.
- Almost all higher efficiency appliances, heating, ventilation, and cooling (HVAC) systems, consumer electronics, lighting, and other load devices are changing from being “resistive” (e.g., incandescent light bulbs) or “rotating” (as in motors) to “inverter based.” The transition of load from “resistive” to “inverter based” means that the overall system performance, especially with respect to power factor and reactive power needs, changes dramatically over time. Smart Grid technologies offer utilities increased monitoring of rapid power changes and help them adapt control schemes and deploy capacitors and other power-factor control devices—including power electronics-based devices in substations—to compensate.
- In the 1980s, electrical load from sensitive electronic equipment (e.g. computer chips) and automated manufacturing was limited. In the 1990s, electronic share grew to roughly 10%. Today, load from electronic technologies and automated manufacturing has risen to 40%, and the load is expected to increase to more than 60% by 2015.
- In power distribution, significant effort is made to control the reactive power flow. This is typically done automatically by switching inductors or capacitor banks in and out and by adjusting generator excitation. Electricity retailers may use electricity meters which measure reactive power to financially penalize customers with low power factor loads. This is particularly relevant to customers operating highly inductive loads such as motors at water pumping stations.
|Capacitive Load (i.e. Battery) Capacitors store electrostatic charges. Current leads voltage. Instanteous power is mostly positive|
|Inductive Load (i.e. Motor) - Inductors store power in magnetic field. Current (i) lags voltage (e). Instaneous power (p) is mostly positive|
|Resistive Load (i.e. Heater) - Voltage (e) and current( i) are coincident. Instantaeous power (p) is always positive|
- AC Power – Produced by an Alternator (commonly referred to as a generator) that functions by rotating an energized magnetic field adjacent to a coil of wire. The energized field has a flux around it. When the magnetic field cuts across the coil of wire, electrons are induced to flow and AC electricity is produced. (Therefore the name, Induction Generator) Since AC power has a varying voltage, efficient power systems must therefore vary the current in synchrony with the voltage.
- The polarity of the voltage across the wire coils reverses as the opposite poles of the rotating magnet pass by. When the direction of the AC voltage changes 60 times per second, it is called 60 Hertz (60 Hz) AC Power, the standard in North America
- System operators can adjust the output of “real” and “reactive” power at short notice to meet changing conditions.
- Numerically, the sine wave plot is:
Angle Sine (angle) in degrees
0 ............... 0.0000 -- zero
45 ............... 0.7071
90 ............... 1.0000 -- positive peak
135 .............. 0.7071
180 .............. 0.0000 -- zero
225 .............. -0.7071
270 .............. -1.0000 -- negative peak
315 .............. -0.7071
360 .............. 0.0000 -- zero
The height of the plot (Y Axis) represents the voltage being produced. The peak of the plot does NOT measure the voltage output. Because the voltage varies through the entire cycle, and even goes negative for 1/2 the cycle, output voltage is actually a calculation of the RMS of the Phase Angle. The procedure consists of squaring all the positive and negative points on a waveform graph, averaging those squared values, then taking the square root of that average to obtain the final answer. A shorter equation is to take the sine of the voltage at 45 degrees. Sine 45 = 0.7071. Therefore, the RMS voltage is about 70% of the peak voltage plot.
tolerances for 60-hertz (alternating current, AC) electric power systems above 100 volts and
through 230, 000 volts. Voltage operating ranges are recommended for two voltage categories:
1) the service voltage, typically the point of connection between utility and customer; and 2) the
utilization voltage, typically the termination point to equipment. The utilization voltage range
takes into account a voltage drop within the end user’s distribution circuits. ANSI C84.1
expects equipment to operate at service voltages between 95% to 105% with a utilization
voltage range of 87% to 106% (120V to 600V)
- An automatic power factor correction unit is used to improve power factor. A power factor correction unit usually consists of a number of capacitors that are switched by means of contactors. These contactors are controlled by a regulator that measures power factor in an electrical network. To be able to measure power factor, the regulator uses a current transformer to measure the current in one phase.
- Depending on the load and power factor of the network, the power factor controller will switch the necessary blocks of capacitors in steps to make sure the power factor stays above a selected value (usually demanded by the energy supplier), say 0.9.
- Inductive Load – Cause trouble for PF. Inductive loads such as transformers and motors (any type of wound coil) consume reactive power with current waveform lagging the voltage. Most loads are inductive, so we add capacitors to balance system.
- Capacitive loads - Such as capacitor banks or buried cable generate reactive power with current phase leading the voltage.
- Resistive Loads – (aka Linear Loads) Have very little effect on PF are 'resistive' such as heating coils and lighting (excluding lights that have ballast transformers). If a purely resistive load is connected to a power supply, current and voltage will change polarity in step, the power factor will be unity (1), and the electrical energy flows in a single direction across the network in each cycle.
For many power transformer applications, a supply interruption during a tap change is unacceptable, and the transformer is often fitted with a more expensive and complex LTC mechanism. On-load tap changers may be generally classified as either mechanical, electronically assisted, or fully electronic.
Historically, utilities have controlled the voltage level at the point of regulation, either at the load-tap changing transformer (LTC) or line regulator, so that the voltage at all points along the feeder is maintained within established standards
- Where the waveforms are purely sinusoidal, the power factor is the cosine of the phase angle (φ) between the current and voltage sinusoid waveforms. Equipment data sheets and nameplates often will abbreviate power factor as "cosφ" for this reason.
- Power factor equals 1 when the voltage and current are in phase, and is zero when the current leads or lags the voltage by 90 degrees. Power factors are usually stated as "leading" or "lagging" to show the sign of the phase angle, where leading indicates a negative sign.
- For two systems transmitting the same amount of real power, the system with the lower power factor will have higher circulating currents due to energy that returns to the source from energy storage in the load. These higher currents in a practical system will produce higher losses and reduce overall transmission efficiency. A lower power factor circuit will have a higher apparent power and higher losses for the same amount of real power transfer.
It is often useful to think of power quality as a compatibility problem: is the equipment connected to the grid compatible with the events on the grid, and is the power delivered by the grid, including the events, compatible with the equipment that is connected? Compatibility problems always have at least two solutions: in this case, either clean up the power, or make the equipment tougher.
The tolerance of data-processing equipment to voltage variations is often characterized by the CBEMA curve, which give the duration and magnitude of voltage variations that can be tolerated.
- Reactive Power is measured in 'kVAR' pronounced as 'kaye-VARs'
- Reactive power is particularly important for equipment that relies on magnetic fields for the production of induced electric currents (e.g., motors, transformers, pumps and air conditioning). It also must supply the reactive losses on transmission facilities.
- Reactive power can be transmitted only over relatively short distances, and thus must be supplied as needed from nearby generators. If reactive power cannot be supplied promptly and in sufficient quantity, voltages decay and, in extreme cases, a “voltage collapse” may result. The power grid needs enough reactive power to maintain reliable service.
- Reactive power is provided by generators, synchronous condensers or electrostatic equipment such as capacitors and directly influences electric system voltage. Examples of reactive loads include capacitors and inductors.
- If the load is purely reactive, then the voltage and current are 90 degrees out of phase and there is no net power flow. A practical load will have resistive, inductive, and capacitive parts, and so both real and reactive power will flow to the load.
- Increasing the device's field excitation results in its furnishing magnetizing power (kilovars) to the system.
- Its principal advantage is the ease with which the amount of correction can be adjusted; it behaves like an electrically variable capacitor. Unlike capacitors, the amount of reactive power supplied is proportional to voltage, not the square of voltage; this improves voltage stability on large networks.
- Synchronous condensers are often used in connection with high voltage direct current transmission projects or in large industrial plants such as steel mills.
difference, electrical pressure, or electromotive force (EMF). Symbol: E
- Voltage/VAR controls are a basic requirement for all electric distribution feeders to maintain acceptable voltage at all points along the feeder and to maintain a high power factor. Recent efforts by distribution utilities to improve efficiency, reduce demand, and achieve better asset utilization, have indicated the importance of voltage/VAR control and optimization. Utilities continue to face system losses from reactive load, such as washing machines, air conditioners. By optimizing voltage/VAR control great efficiencies can be realized. EPRI estimates 55% of the 566,000 distribution feeders will include voltage/VAR control by 2030, at an average cost of $258,000/feeder.
- Advances in automation and communications have laid the foundation to make centralized, coordinated voltage control possible and in fact applications to take advantage of it have been in the works for years. The problem lies in the fact that the computing requirements for such applications to generate useful solutions in near real time are staggering. However, new methodologies and today’s faster computers have converged to make volt/VAr optimization viable.
- VVO is an advanced application that runs periodically or in response to operator demand at the utility control center or in substation automation systems. Combined with two-way communication infrastructure and remote control capability for capacitor banks and voltage regulating transformers, VVO optimizes the energy delivery efficiency on distribution systems using real-time information.
- The real breakthrough is in the speed and quality of the computation. VVO uses advanced algorithms to identify the optimal operation strategy from millions, or even billions of possibilities. Arriving at that result fast enough to apply it in practice, in a day-to-day utility working environment, is a tall order.
- The result is improved efficiency that reduces the amount of power that must be generated and with it the emissions of CO2 and other pollutants associated with power generation. VVO also allows utilities to control costs better by getting the most out of their networks.A smart grid is needed at the distribution level to manage voltage levels, reactive power, potential reverse power flows, and power conditioning, all critical to running grid-connected DG systems, particularly with high penetrations of solar and wind power and PHEVs. Advanced voltage regulation, fault-detection, and system-protection practices need to be rethought as an increasing number of DG resources become available. This may require new equipment to identify and isolate DG resources in the event of a fault occurrence.
- During the daily operation, power systems may experience both over-voltage and under-voltage violations that can be overcome by voltage/Var control. Through controlling the production, adsorption, and flow of reactive power at all levels in the system, voltage/Var control can maintain the voltage profile within acceptable limit and reduce the transmission losses.
- Control of automated capacitor banks on distribution circuits and in substations can be greatly improved with better real-time information provided through the Smart Grid.
- The primary operating lever that utilities can use to affect the flow of reactive power is voltage control, which is accomplished through the use of various devices that inject, absorb, or force the flow of reactive power in the grid. These devices include: synchronous generators, synchronous condensers, shunt capacitors, shunt reactors, static VAR compensators (SVC), and STATCOM (Static Compensators). A Smart Grid will facilitate the application and monitoring of such devices. Similarly, a Smart Grid will enable opportunities to reduce distribution line losses through adaptive voltage control at substations and line drop compensation on voltage regulators and load tap changers (LTCs) to levelize feeder voltages based on load.
- ANSI standard C84.1, specifies a preferred tolerance of +/- 5% for 120V nominal service voltage to the customer meter, or a range of 114 – 126 V. Utilities tend to keep the average voltage above 120V to provide a safety margin during peak load periods. However, maintaining voltage on the upper end of the ANSI C84.1 band at all times, which most utilities do, wastes energy. A Smart Grid will allow utilities to place sensors at the ends of feeders to monitor and maintain voltage at 114 V, which minimizes energy losses without compromising the quality of delivered electrical service.
- Currently, the two primary modes of Volt-VAR optimization (VVO) under consideration are energy efficiency (EE) and demand response (DR). The energy efficiency mode would call for the system to be operated year-round at a near-unity power factor with the voltage as near as possible to the lowest ANSI allowable voltage. As determined in the EPRI’s Green Circuits project and other documented research, end-use equipment typically operates most efficiently at the lower end of the usual operating voltage band. Operation of the distribution system at the lowest ANSI voltage would increase the risk of power quality and reliability issues for customers, such as voltage sags and more sustained outages. Based on findings by Alabama Power in the Green Circuits project, system line and transformer losses only accounted for a percentage, typically less than 5 percent, of the overall energy reduction when VVO was implemented.
- On the other hand, the utility could choose to develop a DR program to utilize the VVO equipment during peak load periods. This mode of operation would control distribution devices in a manner that would maximize the demand reduction of the system. This type of operation might also result in a leading power factor at the substation; however, the excess VAR flow back to the transmission and generation systems should aid in the overall efficiency of the T&D system as a whole. This approach, as with the EE mode, would allow the utility to avoid building additional generation units, to defer capital improvement projects, and/or reduce demand charges from the generation supplier. However, the DR mode of operation would limit any loss of revenue and the potential for power quality issues since it would be used relatively few hours each year.
- A Smart Grid will also facilitate more intelligent controls on capacitors, optimizing their usage to reduce system losses further. A Smart Grid will also enable automatic reconfiguration to minimize losses during the day, which requires distribution state estimations, more sensors, and real time control.
- Reduce Distribution Losses - Up to a 30% reduction in distribution losses is possible from optimal power factor performance and system balancing. Grid efficiency comes down largely to “line losses,” the amount of power leaving a generation plant that is lost on the way to our homes and businesses. Losses in the transmission and distribution system of 6 to 8 percent are typical even in the world’s most advanced countries, and they can run even higher.
In 2006, a total of 1,638 billion kWh of energy was lost on the US power grid, with 655 billion kWh lost in the distribution system alone. To put this in perspective, consider that a 10 percent improvement in grid efficiency at the distribution level alone would have produced $5.7 billion in savings based on the 2006 national average price of electricity. It would also have saved over 42 million tons of CO2 emissions.
ERPI's Green Circuits found that Electric power transmission and distribution (T&D) systems typically have aggregate annual energy losses of 7–10%. The percentage losses across all U.S. T&D equate to approximately 300 million MWh based on a U.S. annual generation total of 4,157 million MWh according to the Energy Information Administration. Because these losses are inherent in the process, they cannot be reduced to zero but might be reduced significantly with present technology. Approximately two-thirds of these losses are incurred at the distribution voltage levels.
- Reduced Required Voltage - Reduce energy and carbon by precise dynamic voltage control. Reduce load while respecting given voltage tolerance (normal and emergency)While the impact of voltage reduction on energy consumption will vary from circuit to circuit based on resistive or reactive nature of the load, many studies have shown a 1% drop in voltage results in a close 0.8% drop in energy demand. On this basis, EPRI quantifies the savings range for a Smart Grid in reducing losses through voltage regulation as 3.5 to 28.0 billion kWh per year in 2030. Minimize kWh consumption at voltages beyond given voltage quality limit; ensure standard voltages at customer terminals.
- Reduced Reactive Power - Reactive power can be reduced by adding devices to compensate for poor power factor. If we know how much reactive power is needed, we can furnish systems to supply the reactive power and only take real power from the power company. This reduces the power company’s losses and reduces the power bill.
- Reduced Congestion - Reduced transmission congestion costs from increased transmission transfer capability without building additional transmission capacity. Minimize feeder segment(s) overload. Reduce or eliminate voltage violations on transmission lines. Reduce or eliminate overload in transmission lines
- Improve Reliability - Provide spinning reserve support
- Cost Savings - Minimize cost of energy
- Transmission Capacity – Extra VAR’s to supply reactive power fill up transmission lines. Extra wire to carry the reactive current.
- Circuit Overload - Poor PF can over-load electric circuits and cause trouble for the utility and the end-user. Circuits that are over-loaded heat-up and heat cause failures. Heated circuits draw more 'real' power and PF penalties billed by electric utilities can substantially increase monthly bills much higher than just the extra real power draw
- Harmonics – Typically causes power capacitor ratings to be exceeded. The effect is overheating and increased stress which results in premature failure.
- Overvoltage - The reactive elements can create voltage fluctuations and harmonic noise when switched on or off. They will supply or sink reactive power regardless of whether there is a corresponding load operating nearby, increasing the system's no-load losses. In a worst case, reactive elements can interact with the system and with each other to create resonant conditions, resulting in system instability and severe overvoltage fluctuations. As such, reactive elements cannot simply be applied at will, and power factor correction is normally subject to engineering analysis
- Communications - The ability to move large amounts of data from disparate points on the grid is the key to enabling the applications that will in turn facilitate the widespread adoption of distributed generation and maintain (or even improve) the level of service customers expect.
- ABB - Cary, NC - Smart Grid Portal
- Cooper Power System – Waukesha, WI - Engineers and manufactures medium- and high-voltage electrical equipment, components, and systems that deliver reliable electric power to homes, industries, businesses, and institutions worldwide.
In August 2011, Cooper Power Systems was selected to provide advanced volt/VAR control for Public Service Company of Oklahoma, part of American Electric Power. It will become harder and harder for utilities to ignore voltage optimization as the trend gains visibility and as regulators come to believe it is a viable way to save energy.
On May 21, 2012, Eaton Corp., the power and control systems giant, announced Monday that it would acquire Cooper Industries, catapulting the 90-year-old Eaton into a new class of smart grid competition.
Terms of the transaction announced Monday set a value of $72 per share of Cooper stock in cash and shares in the new company, for an equity value of $11.8 billion, one of the biggest M&A deals of the year so far. Eaton has secured a $6.75 billion bridge financing commitment from Morgan Stanley and Citibank to finance the cash portion of the acquisition.
The combined companies had a collective $21.5 billion in 2011 revenues, The deal, to close in the second half of 2012, will create a company headquartered in Ireland and tentatively titled “Eaton Global Corporation Plc
- CURRENT Group Germantown, MD - Provides intelligent voltage and current sensing integrated with a variety of open IP real-time communications solutions to provide the distributed analysis and communications necessary for a Smart Grid. Sensors may be installed at selected locations identified as key monitoring and control locations, at network trouble spots, or may be broadly deployed for comprehensive monitoring of the full distribution grid. Sensors are designed and tested to utility-grade standards and contain analysis capabilities to detect a variety of events on the grid as well as configurable data logging and alarms.
- DC Systems, Pleasanton, CA - A leading developer of Smart Grid software for utilities and large energy users. Founded in 1990, the company has pioneered solutions that provide powerful architectural advantages by combining distributed intelligence SCADA computing with centralized data management. Customers worldwide use the DC Systems RTscada™ family of products to put intelligence where it is needed—in hundreds of locations such as substations, control centers, and power generation sites—while centralizing configuration, administration and monitoring at the enterprise level.
- Silver Spring Networks Redwood City, CA - Launched a new application in May 2011 that lets utilities monitor power quality across the grid and gain insights into potential problems before they can affect service. UtilityIQ Power Monitor uses the distributed intelligence in Silver Spring networking devices to help utility companies keep an eye on key power quality metrics throughout their service territory. Silver Spring clients can use smart grid devices already deployed, combined with distributed polling, to improve vital grid efficiency applications such as Conservation Voltage Reduction (CVR) and Volt/VAR Optimisation (VVO).
The new application provides Silver Spring clients with proactive notification of meter locations where voltage levels exceed or fall below expected levels. UtilityIQ Power Monitor works with Silver Spring’s UtilOS firmware to expand the capabilities of meters and other devices distributed throughout the grid, without requiring modification to any hardware or a field visit.
The Silver Spring ecosystem now includes leading providers of Volt/VAR Optimization (VVO) and Conservation Voltage Reduction (CVR) software, including ABB/RCCS, CURRENT Group, DC Systems, and Open Systems International (OSI.)
8. Next Steps
- Smart Inverters - Inverters, which convert DC to AC, are required for
all PV systems. Inverters are now “software-driven” and have some amazing capabilities to shift their output:
- They can manipulate Watts (energy) output (as long as they remain within the capabilities of the PV system)
- More importantly, they can manipulate VArs
- Can provide capabilities like volt-var control, frequency-watt control, and dynamic grid support as part of low voltage ride through
- Inverters can sense local conditions, such as voltage and frequency, and respond with autonomous actions These pre-set reactions will improve power system efficiency and delay the need for distribution upgrades and can help avoid outages and system black-outs
- Inverter manufacturers are already adding these functions for the European market
- Expensive communications between utilities and these inverters are not immediately necessary
- Smaller inverters may never need communications
- Medium inverters may need to respond to broadcast commands
- Larger inverters or those on more “sensitive” circuits may need more interactive communications
- Intelligrid Architecture - Distribution Operations - Voltage and Var Control (VVC) Function
- A Review of Voltage/VAR Control M. Lin, R. K. Rayudu and S. Samarasinghe Centre for Advanced Computational Solutions Lincoln University
- Power Factor Correction Whitepaper
- EERE - REDUCING POWER FACTOR COST
- Power Factor Java Applet Demo
- Volt/VAR Optimization Reduces Losses, Peak Demands By: Xiaoming Feng, ABB Corporate Research and William Peterson, ABB Power Systems Raleigh, North Carolina