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What are Uninterruptible Power Supplies?

Uninterruptible Power Supplies, also known simply as "UPS" as well as a battery backup system, maintains a continuous supply of electric power to a building, or certain electrical devices within a building by supplying power from the UPS system whenever power is not available from the grid or utility company.

Typically,  Uninterruptible Power Supplies are located between the source of the normal power supply - such as the electric utility company - and the electric load the UPS system is protecting. When electric power from the grid fails - whether through a lightning strike, failed transformer, or a black-out occurs, the UPS will instantly recognize the loss or interruption of power from the grid, and switch from the grid power to UPS power. 

Uninterruptible power supply systems can be designed to protect small or large loads, including systems small enough to protect one or more computers, to critical life support systems that may be found in a home or hospital, to  telecommunications equipment where an unexpected power disruption could threaten life or health or serious business disruption or computer data loss. 

Small Uninterruptible Power Supplies systems can protect loads as small as just one computer to large UPS systems that will power and protect a company's entire data center or a building such as an office building or hospital.  These systems can be as large as 3-20 megawatts and typically work in conjunction with a genset or a cogeneration plant.

What is Frequency Regulation?

The electric grid, because supply and demand of electricity is always changing requires continuous and instantaneous balancing of supply and demand of electricity – this continuous and instantaneous balancing of supply and demand of electricity is known as "frequency regulation."

What are Flywheel Energy Storage systems?

Flywheel Energy Storage systems act as mechanical batteries that store power kinetically in the form of a rotating mass, or "flywheel." 

When the grid goes down, the power stored by the rotating flywheel is converted to electrical energy through the flywheel’s integrated electric generator. The system provides the DC energy to the Uninterruptible Power Supplies system until grid power is restored or the facility's back-up power generator can be started. Once either the utility is restored or the genset provides power to the input of the Uninterruptible Power Supplies, the Flywheel Energy Storage system will be re-charged by taking some current from the DC bus of the Flywheel Energy Storage until it is back up to full speed.

Flywheel Energy Storage Project Overview

This project demonstrates a flywheel energy storage system designed to respond to a regional transmission operator signal to quickly add or subtract power from the grid in a frequency regulation support mode. Using this concept, the flywheel recycles energy (store energy when generation exceeds loads; discharge energy when load exceeds generation) instead of trying to constantly adjust generator output.

The Purpose of the Flywheel Energy Storage Project

This project is being sponsored to determine the relative benefits of having faster responding generation resources. Additionally, understanding the response time of a flywheel storage system as compared to traditional generator response time will provide a better determination of the required sizing for flywheel and other fast response systems.

When aggregated to reach appropriate output/input levels there are many benefits that a flywheel energy storage can offer to the electric grid. The primary benefits are:

• Increased Available energy: Because present day generators need to be operated below their maximum capability to provide regulation, they are not available to provide their maximum power. Typically generators need to be below their maximum capacity by 2 times the amount of regulation in order to provide headroom for safe operation. If all regulation were accomplished by flywheel energy storage system, then there would be an additional 2-4 % generation capacity without adding new generators.

• Support Distributed Generation and Decentralized Energy projects with Local Voltage Support: Several Projects have already shown the benefits of using flywheels for local voltage support. This includes a project on the NY City transit system, where ten 1.6 KWh flywheels provide support between train stations. As flywheel storage increases, as will be demonstrated by this project, the feasibility of larger scale application of flywheel energy storage system for local voltage support will be more practical.

How Flywheel Energy Storage is Being Applied

The flywheel energy storage system consists of an array of flywheel energy storage modules and power conversion electronics packaged in a standard 12’ x 40’ shipping container. This mobile container would interface with the grid’s three-phase 480-volt cables via a step up transformer. This matrix is capable of storing and recycling 250 kWh’s of energy. The rated discharge rate of a matrix is 1 MW therefore each container will provide rated power for 15 minutes or lower power for an extended period.

Monitoring and data acquisition has been specified such that system availability and power/energy parameters will be accessible via the website. Any time the system is operated, the kilowatts supplied or absorbed by the storage unit and the total system efficiency will be viewable via graphical display by day, week, month, etc.

While performing Frequency Regulation, the flywheel energy storage system will receive two input signals from the System Operator.

1. Regulation Signal (RS): This will be the amount of regulation to be provided over the next time step. This value will be between (-)100KW and (+) 100KW. Minus refers to absorbing 100kW of power from the Grid. Plus refers to injecting 100 kW of power to the grid. The regulation signal refers to the amount of power being absorbed or injected relative to a base set point as described by signal 2. The amount of power being injected or absorbed will be as measured downstream of the flywheel energy storage system and upstream of the step up transformer. This regulation signal will be updated every 4 seconds.

2. Set Point (SP): This will be the nominal level of power being removed from the grid during the time on regulation. It will be a percentage of the full regulation signal and will be a variable during the demonstration phase of testing. This setting will remain constant over an agreed to time period – usually one to 24 hours. In addition to the set point and regulation signal the master controller will have input from the flywheel controller to know how much energy is in each flywheel. The system controller will then send a signal to the flywheel controllers, and load bank to control the power flow within and to and from the flywheel energy storage system based on these inputs.

The system will be installed and demonstrated at a location in San Ramon, California. It will be run for a period of six months to demonstrate its ability to interface with the ISO signals and grid. Data will be independently collected through funding provided by the U.S. DOE and used to estimate the system performance over time. 

The flywheel energy storage system will follow the regulation signal within a fraction of a percent. Unlike generation based Frequency Regulation, no fuel is consumed, and no emissions are generated. Analysis of presently used Frequency Regulation signals indicates that an energy storage module, which can store or deliver 1 MW for 15 minutes, would provide regulation services superior to services currently provided by generators. After development testing is completed the flywheel energy storage system and will be commissioned and put on automatic control.

 

What is "Power Factor" and "Power Factor Correction?"

Power factor is a measure of how efficiently, or inefficiently, that electrical power is used by a customer. For industrial customers, a low power factor is generally caused by inductive loads such as transformers, electric motors and high-intensity discharge lighting. Customers that do not use electrical power efficiently are being charged additional fees for the inefficient use of power by their electric utility company.  

An electric utility's power load on an electrical distribution system fall into one of three categories; resistive, inductive or capacitive. In most industrial facilities, the most common power usages are "inductive."  Examples of inductive loads include transformers, fluorescent lighting and AC induction motors. Most inductive loads use a conductive coil winding to produce an electromagnetic field which permits the motor to function. 

All inductive loads require two different types of power for the motor to operate:

Active power (measured in kW or kilowatts) - this power produces the motive force 
Reactive power (kvar) - this energizes the magnetic field of the motor.

The operating power from the distribution system is composed of both active (working) and reactive (non-working) elements. The active power does useful work in driving the motor whereas the reactive power only provides the magnetic field. Unfortunately, electric utility's customers are charged for both active and reactive power.

Example:  A customer's power factor drops, the system becomes less efficient. A drop from 1.0 to 0.9 results in 15% more current being required for the same load. A power factor of 0.7 requires approximately 40% more current; and a power factor of 0.5 requires approximately 100% (twice as much) to handle the same load. The answer to these problems is to reduce the reactive power drawn from the supply by improving the power factor.

If an AC motor were 100% efficient it would consume only active power. However, since most AC motors are only 75% to 80% efficient, they operate at a lower power factor. This means inefficient and even "wasteful" energy usage and cost efficiency because most electric utilities charge penalties for poor, inefficient power factor.

Simply installing capacitors will improve a commercial or industrial company's power factor and will result in savings on their electricity bill every month!

Additional potential benefits for correcting poor power factor include:

Reduction of heating losses in transformers and distribution equipment 
Longer equipment life 
Stabilized voltage levels 
Increased capacity of your existing system and equipment 
Improved profitability
Lowered expenses

What is Transmission and Distribution?

Electric power transmission and distribution is the bulk transfer of electrical energy from the electric power generation plants to substations that are located near the population centers or "load centers" that are the consumers of the electric power.  Electric power transmission voltage and wiring is very different from the "distribution" wiring and voltage.  Electric power transmission may be as high as 768 kV whereas the electricity distribution within the load centers may be at 144 kVa.

What is Energy Resource Planning?

The purpose of Energy Resource Planning (ERP)seeks to utilize and integrate the requisite analytical concepts and tools necessary to approach the problems of planning for an adequate energy supply and demand balance at the local, regional and national levels.  With a greater focus on reducing and eliminating greenhouse gas emissions, there is an increasing emphasis on "Carbon Free Energy" and "Pollution Free Power."  Renewable energy resources and renewable energy technologies are viewed as the preferred path forward for providing for energy supply and demand in conjunction with Demand Side Management.

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High Voltage Direct Current
www.HighVoltageDirectCurrent.com

What are the Advantages of "High Voltage Direct Current" Transmission Lines over standard AC Power Lines?

High Voltage Direct Current power lines have several distinct advantages over the typical AC power lines.  

High Voltage Direct Current, or "HVDC" power lines has the ability to transmit large amounts of power over long distances with lower capital costs and much lower electrical losses than typical AC power lines. 

Depending on the voltage level and construction details, losses for HVDC are about 3% per 1000 km. 

High-voltage direct current transmission allows use of energy sources remote from load centers.

In a number of applications High Voltage Direct Current, HVDC is more effective and efficient than AC transmission lines. 

Examples where HVDC is more effective, and efficient, than AC power lines, include the following:

*  Undersea cables, where high capacitance causes additional AC losses.

*  Endpoint-to-endpoint long-haul bulk power transmission without intermediate 'taps.'  

*  Increasing the capacity of an existing power grid in situations where additional wires are difficult or expensive to install. 

*  Allowing power transmission between unsynchronized AC distribution systems. 

*  Stabilizing a predominantly AC power-grid, without increasing maximum prospective short circuit current. 

*  Reducing line cost since HVDC transmission requires fewer conductors (i.e. 2 conductors; one is positive another is negative).

*  Long undersea cables have a high capacitance. While this has minimal effect for DC transmission, the current required to charge and discharge the capacitance of the cable causes additional I2R power losses when the cable is carrying AC. In addition, AC power is lost to dielectric losses.

*  High Voltage Direct Current transmission lines can carry more power per conductor, because for a given power rating the constant voltage in a DC line is lower than the peak voltage in an AC line. 

*  Increased stability of power systems - because High Voltage Direct Current transmission lines allow power transmission between unsynchronized AC distribution systems, it can help increase system stability, by preventing cascading failures from propagating from one part of a wider power transmission grid to another. Changes in load that would cause portions of an AC network to become unsynchronized and separate would not similarly effect a DC link, and the power flow through the DC link would tend to stabilize the AC network. The magnitude and direction of power flow through a DC link can be directly commanded, and changed as needed to support the AC networks at either end of the DC link. This has caused many power system operators to contemplate wider use of HVDC technology for its stability benefits alone.

Disadvantages of High Voltage Direct Current Transmission Lines

The required static inverters are expensive and have limited overload capacity. At smaller transmission distances the losses in the static inverters may be bigger than in an AC transmission line. The cost of the inverters may not be offset by reductions in line construction cost and lower line loss.

In contrast to AC systems, realizing multi-terminal systems is complex, as is expanding existing schemes to multi-terminal systems. Controlling power flow in a multi-terminal DC system requires good communication between all the terminals; power flow must be actively regulated by the control system instead of by the inherent properties of the transmission line.

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