Handbook of Energy Storage for Transmission or ... - W2agz.com

More documents

Recommendations

Info

EPRI Proprietary Licensed Material cycles. The rotor is subject to fatigue effects due to the cyclical application and stress during charge and discharge. The most common failure mode for the rotor is the propagation of cracks through the rotor over a period of time. Crack propagation can be difficult to detect in steel rotors, and hazardous failure modes are possible in which large chunks of steel break off from the rotor during operation. Appropriate design and operation precautions must be taken in order to ensure safe operation (see Safety, below). In graphite rotors, cracks tend to propagate longitudinally, or result in de-lamination of the concentric layers of material. This phenomenon causes the rotor to gradually deviate from normal operation. Thus, monitoring of suitable operating parameters will ensure that the device can be removed from service before a hazardous failure mode occurs. Recharge Time Like electrochemical capacitors and SMES, flywheels have the advantage of relatively quick recharge times. Recharge times are comparable to discharge times for both power and energy flywheels designs. High-power flywheel systems can often deliver their energy and recharge in seconds, provided that adequate recharging power is available. Bi-directional power conversion facilitates this two-way action. On the other hand, in stabilizer applications the controls may be designed to provide a negative feedback where the rate of charging and discharging depend on voltage or frequency. In this case charging may occur quickly and discharge slowly or vice versa and most of the time no charging or discharging is required. Standby Power Loss Flywheel systems may have both intrinsic and parasitic power losses which cause the energy stored to be gradually used up. A certain amount of power must be applied to maintain a high level of charge if the flywheel is used in a standby mode. The magnitude of the power loss is dependent on the design of the flywheel, and may have both intrinsic and parasitic components. Intrinsic power losses include friction and other forces that cause the rotor to slow down, and are common to all flywheel designs. Intrinsic power losses can be reduced through the use of techniques such as vacuum containment and magnetic bearings, but can never be reduced to zero. Parasitic power losses include power provided to active magnetic bearings or cooling for superconducting bearings. Unlike intrinsic losses, parasitic power losses are independent of the speed of the flywheel. Not all flywheel systems have parasitic power losses. Electrical Interface The electrical interface, where the flywheel mechanical or kinetic energy is converted to electrical energy, and vise versa, can vary greatly with different flywheel types and applications. There are a number of rotating machine technologies that can be used in flywheels for generating (during discharge) and restarting (after discharge). These include permanent magnet alternators as well as dc, synchronous, wound-rotor induction, and written-pole motors and generators. Additional variety comes when these various machine technologies are mixed with different forms of power electronic and electromagnetic frequency conversion technologies. Also in the mix are application- Flywheels Page 12
EPRI Proprietary Licensed Material specific filtering or conditioning, paralleling, isolation, transfer, and back up generator equipment. This results in the practical reality that no two-flywheel systems on the market in 2002 use exactly the same electrical interface. The parameters that determine electrical interface design are flywheel speed (high, medium or low), electrical loading (ac or dc), response time (seconds or fractions of a second), parallel or series connection, need to interface with an alternate source, and the need for high power or high energy. With all these variables the variety in electrical interface is understandable. Still, in all cases, energy loss is a critical parameter that must be minimized, partly through electrical interface design. Thus, the interface design of most of the flywheels on the market allow suppliers to claim above 90% overall system round trip efficiency with standby losses of less than 3%. Table 2 provides an overview of the combinations of equipment that are typically used in the flywheel electrical interface. Table 2 Typical Combinations Of Electrical Interface Equipment In Flywheels Size Rotor Mech. To Electric Frequency Load Recharge Eff. Range Speed Converter Converter Type Starter % 1 MW Low Rectifier/Inve AC Synchronous 96 WR Alternator rter. Motor/ASD 2 1 The permanent magnet (PM) machines are preferred in high-speed applications because they are more durable than electrical winding under mechanical forces on the spinning rotor. 2 An adjustable speed drive (ASD) allows speed matching between the power source moving magnetic field (MMF) and the machine rotor poles. In the case of a PM alternator or synchronous machine, the machine only produces torque when the source MMF matches the rotor pole speed. This is not the case in induction machines, which produce torque (for starting) at zero rotor speed. 3 Wound rotor (WR) machines are preferred in low speed applications where larger structures are needed to obtain high energy. A good example of the application influence on the flywheel electrical interface is the bridge power system. In this application, when prime power is lost the flywheel system takes over and must operate as a standalone generator, with load following, voltage and frequency control until an alternate power source is available. At that point the flywheel system electrical interface synchronizes and transfers the load to the alternative source and begins the recharging sequence. This interface is typical for systems that have an integrated diesel engine or other backup generation. Flywheels Page 13
Page 1:
Handbook of Energy Storage for Tran
Page 4 and 5:
DISCLAIMER OF WARRANTIES AND LIMITA
Page 7:
EPRI Proprietary Licensed Material
Page 10 and 11:
Vanadium Redox Battery 2
Page 12 and 13:
Page 14 and 15:
Page 16 and 17:
Page 18 and 19:
Page 20 and 21:
Page 22 and 23:
Page 24 and 25:
Page 26 and 27:
Page 28 and 29:
Page 30 and 31:
Page 32 and 33:
Page 34 and 35:
Page 36 and 37:
Page 38 and 39:
Page 40 and 41:
Page 42 and 43:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50:
Page 51 and 52:
Page 53 and 54:
Regenesys Electricity Storage Techn
Page 55 and 56:
Page 57 and 58:
Page 59 and 60:
Page 61 and 62:
Page 63 and 64:
Page 65 and 66:
Page 67 and 68:
Page 69 and 70:
Page 71 and 72:
Page 73:
Page 76 and 77:
Page 78 and 79:
Page 80 and 81:
Page 82 and 83:
Page 84 and 85:
Page 86 and 87:
The status of sodium sulfur batteri
Page 89 and 90:
Page 91 and 92:
Page 93 and 94:
Page 95 and 96:
Page 97 and 98:
Page 99 and 100:
Page 101 and 102:
Page 103:
Page 107 and 108:
Page 109 and 110:
Page 111 and 112:
Page 113 and 114: EPRI Proprietary Licensed Material
Page 145: EPRI Proprietary Licensed Material
Page 151: EPRI Proprietary Licensed Material
Page 215 and 216:
Page 217 and 218:
Page 219 and 220:
Page 221 and 222:
Page 223 and 224:
Page 225 and 226:
Page 227 and 228:
Page 229 and 230:
Page 231 and 232:
Page 233 and 234:
Page 235 and 236:
Page 237 and 238:
Page 239 and 240:
Page 241 and 242:
Page 243 and 244:
Page 245 and 246:
Page 247 and 248:
Page 249 and 250:
Page 251 and 252:
Page 253 and 254:
Page 255 and 256:
Page 257 and 258:
Page 259 and 260:
Page 261 and 262:
Page 263 and 264:
Page 265 and 266:
Page 267 and 268:
Page 269 and 270:
Page 271 and 272:
Page 273 and 274:
Page 275 and 276:
Page 277 and 278:
Page 279 and 280:
Page 281 and 282:
Page 283 and 284:
Page 285 and 286:
Page 287 and 288:
Page 289 and 290:
Page 291 and 292:
Page 293 and 294:
Page 295 and 296:
Page 297 and 298:
Page 300:
About EPRI EPRI creates science and
show all

Handbook of Energy Storage for Transmission or ... - W2agz.com

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?