- Slides: 23
The Smart Grid Enabling Energy Efficiency and Demand Response Clark W. Gellings Chapter 2: Electric Energy Efficiency in Power Production & Delivery Brevard Community College ETP 1400 Distributed Electrical Power Generation and Storage Bruce Hesher 433 -5779
Acronyms Note to students: Chapter 2 is loaded with acronyms. They are fair game for test questions!
Introduction There is a lot of effort going into end user energy efficiency, but what about the electric use efficiency of the power plant itself and of the distribution network? A measure of the efficiency of a power plant is the Btu input needed for a given KWH output. Power plant improvements include methods to improve overall efficiency. Power delivery system improvements include better efficiency transformers, better voltage control, and reactive power control (power factor correction on the source side)
Power Plant and Delivery System Improvements Condition monitoring and assessment uses sensors and communications to monitor plant and grid performance. Readings are compared to historic readings, theoretic models, and comparable plant performance. Some power plant operators subscribe to commercial databases that enable them to track and compare results. The objectives are to optimize performance and manage maintenance. Q: should the grid monitor the condition of power plants in addition to the delivery system and react accordingly?
Power Plant Electricity Use Power plants use electricity to drive pumps, fans, and conveyors. Motors are the largest use. 5 -7% of the energy generated by steam power plants (coal, biomass, gas, and nuclear) is used on-site. Hydro-power, Wind, and photovoltaic power plant use less. Pumps and fans must be adjusted for loading and climate conditions. Adjustable speed drive (ASD) motor controllers are used to improve efficiency. Controlling motors drives requires monitoring and communications.
Power Plant Lighting efficacy is a measure of a lights output in lumens divided by its energy input in watts (Lm/W). 683 Lm/W is theoretic maximum or 100% efficiency level. Most types of electric power plants are large facilities and use a lot of lighting. Power plants benefit in multiple ways by reducing their own power requirements: • They can sell the power instead of using it. • They can use less fuel to meet the demand. • They produce less CO 2 and other taxable pollutants.
Power Plant Space Conditioning and Domestic Water Heating There is a lot of energy in temperature. Making atoms vibrate faster requires lots of energy. Dense matter like water takes a proportionally larger amount of energy. Water is 800 times denser than air. While it requires less energy to heat air, space heating still uses a lot of energy due to the larger surface areas available to loose the heat/cool. Most space conditioning in power plants is used to cool.
Building Infiltration (outdoor air exchange) A major cause of energy loss in space conditioning is due to air entering or leaving a conditioned space. Infiltration results from temperature and pressure differences. While a sealed building with no outside air exchange would be good for heating and cooling costs, there are standards for indoor air quality that require some air exchange between indoor and outdoor air.
Energy Audit A professional energy auditor can examine and test your homes heating and cooling systems, insulation, windows, and etc. They test the AC ducts for leakage and the home for places where heat penetrates in summer or is lost in winter. A blower door test uses special fans to depressurize the home and pressurize the AC ducts to measure their performance and locate leaks. see: www. energyconservatory. com
See Where Heat is Penetrating Thermographic pictures or video are sometimes used by energy auditors while a blower door test running. The blower door helps exaggerate air leaking through defects in the building shell. Thermal cameras are expensive. They are a tool of the trade for energy auditors.
Attic and Exterior Wall Insulation Most homes in Florida do not have enough insulation. Inspect your attic. Fiberglass batting that is the depth of a 2 x 4 truss has about R-15. For R-30, run a second layer using care not to block soffit vent air flow. The DOE recommends that homes in zone 2 (Florida) have R-30 to R-60. Insulation improves both heating and cooling costs! Puncture the vapor barrier with a small pointed object like a nail, placing holes 2 -3 inches apart to prevent moisture build up between layers.
Motors Processes driven by electric motors typically consume 80% of the electricity used in electricity production. Implementing electric adjustable speed drives (ASD) on motors in power plants will improve their efficiency. Adjustable speed drives or variable-speed drive (VSD) are equipment used to control the speed of machinery. Steam generator water feed pumps, fuel supply pumps, cooling water pumps, and fan motors are all used in power plants. See http: //en. wikipedia. org/wiki/Adjustable-speed_drive
EPRI Demonstrations EPRI conducted research programs using ASD on the auxiliary motors of electric generating stations. By using modern electronic motor control to vary flow rates instead of valves, better efficiencies are achieved. EPRI conducted tests at the facilities of four utilities. They used ASDs that employed various electronic devices including Gate turn-off thyristors (GTOs) and Pulse Width Modification (PWM) controller integrated circuits. Two conclusions resulted: • The potential for energy savings by controlling process flow with motor speed is real. • Reliability of large ASDs is not an issue. See: TRIAC dimmer switch.
Efficiency in Power delivery p 43 Transmission and distribution accounts for losses of about 7%. Transmitting electricity at high voltage reduces the fraction of energy lost to resistance. For a given amount of power, a higher voltage reduces the current and thus the resistive losses in the conductor. Raising the voltage by a factor of 10 reduces the current by a factor of 10 and therefore the I 2 R (resistive) losses by a factor of 100. At extreme high voltage (>2 MV) coronal discharge losses are large. Hollow conductors with large diameters and stranded cables help reduce these losses. As of 1980, the longest cost-effective distance for DC electricity was 7, 000 km (4, 300 mi) (4, 000 km (2, 500 mi) for AC), although all present transmission lines are considerably shorter.
Power Factor Correction In AC, reactances can cause losses due to the phase mismatch between the power signal and the load. Many large loads are inductive (motors). Electrical loads that are not purely resistive, have a load impedance that is at a phase angle. They do NOT consume more energy because of it. They do however cause more current to be cycled back and forth between the power source and the load thereby causing greater losses in the system. When the load is inductive (motors), the current in the circuit will lag the voltage.
Apparent Power Work is done by the Real Power (Watts) but, the power source and load cycle some power back and forth. This is the Reactive Power (VAR). The power supply and wiring must be large enough for the resulting Apparent Power (VA). This large amount of energy transfer between the source and load causes larger energy consumption. The Power Factor (PF) is the ratio of W/VA or the cosine of the phase angle. note: This is why UPSs are rated in VA not Watts.
Reducing Power Factor Losses If a capacitor with a reactance equal to the reactance of the inductive load (motor) is place in series with the load, the net reactance is 0! Calculating the size of the capacitor is left to other courses or the manufacturer of the motorized equipment. This topic is covered in EETC 1025. If the losses due to the energy cycled back and forth are reduced, smaller gauge wire can be used, less heat is created, equipment can last longer, and energy is saved. Power Factor Correction is typically only done when there a lot of inductive loads.
Conservation Voltage Reduction p 43 Keeping tight voltage control also reduces power losses. therefore, some utilities have implemented conservation voltage reduction (CVR) techniques. If the voltage is dropped the current also drops and the product of voltage and current (power) drops a lot. Keeping the voltage on the low end of the acceptable range saves power. CVR factor is defined as the percentage in power reduction that results form a 1% reduction in voltage. Utilities often reduce the voltage during critical peak periods (CPP). Sensitive loads such as computers may not operate reliably with lower line voltages.
Distribution Transformer Efficiency Developments in transformer technology can also save power. There are 3 classes of transformers used in power distribution: • Low voltage, dry transformers up to 600 V. • Medium voltage dry transformers 601 -34, 500 V. • Liquid-immersed for voltages up to 2. 5 MVA. Liquid filled transformers are the most efficient with losses of only about 0. 25%. Medium voltages have losses of about 5% and Low voltage losses are about 2%. Individual transformer losses are small, but with over 25 million installed transformers in the distribution grid they constitute the largest total losses.
Transformer Losses There are 2 types of significant losses in transformers: Core losses result from magnetizing and de-magnetizing the transformer core during normal operation. Amorphous core transformers can reduce these losses by up to 80% but are more expensive. But there higher cost is coming down and wider adoption is expected. Winding losses are due to the resistance of the winding material (copper or aluminum). Newer more efficient transformers use copper windings.
Solid State Intelligent Universal Transformers (IUT) p 49 Act like power supplies for entire buildings providing the various voltages and frequencies needed. Energy Efficiency: The existing transmission systems supply more power through the same wires. Flexibility: Able to reliably deliver diverse power such as 400 Hz service, DC service (for hybrid electrical systems) and three phase power from a single phase line. Power Quality: Sag correction and harmonic filtering can be built in to the IUT. Configurable: Because one device can be used in many configurations, inventory, spare parts, and maintenance costs can be reduced. Environmental Concerns: Contain no hazardous liquid dielectrics, such as conventional transformers. The hazards and costs of spills and cleanups will be avoided. See: http: //www. siliconpower. com/_Documents/IUT-Applications. pdf
Advanced Distributed Automation (ADA) p 50 The IUT is one component in a broader strategy called ADA. Traditional Distributed Automation (DA) automates control of basic distribution switching functions. ADA is concerned with complete automation of all of the controllable equipment and functions in the distribution system to improve its strategic operation. Inoperability. communication, and control to improve various aspects of the systems is the intent. Advanced Distribution Automation is a term coined by the Inteli. Gridsm project in North America to describe the extension of intelligent control over electrical power grid functions to the distribution level and beyond.
Conclusion p 51 The smart grid as a concept must extend from power production through delivery to end-use. Concepts of functionality employing sensors, communications, and computational ability can be effectively used to reduce energy consumption, reduce emissions from power production, and to improve reliability in the frontend of the electricity value chain.