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

EPRI Proprietary Licensed Material
“Reassessment of Superconducting Magnetic Energy Storage (SMES) Transmission
System Benefits”, Power Systems Engineers, EPRI Report 1006795, March 2002.
A summary of applications from this report is summarized below.
System Stability-Damping
Large power systems may experience instabilities associated with the delivery of power over
long distances when there are abrupt changes in operating conditions, e.g., when a large load is
applied or when a generator or line is lost. Perhaps the best-known case of this type of instability
is in the north-south power corridor on the West Coast of the United States. A great deal of
power (several thousand Megawatts) is generated in the Pacific Northwest and is delivered to
middle and southern California via multiple transmission lines. One characteristics of the system
in this region is that a north-south power oscillation can occur with a frequency of about 0.3 Hz.
That is, power flow increases and decreases with a period of about 3 seconds. These oscillations
are generally insignificant. Under certain conditions, however, the system has exhibited
oscillatory power flow with amplitudes of 300 MW, as shown in Figure 8.
Load levelling
Demands for electric power vary both randomly and with predictable variations. Perhaps the
most significant variation of power demand is the diurnal change associated with the functioning
of an industrial society. Both commercial and residential demands are greater during the day
than at night. On the other hand, many power plants operate most efficiently and have longer
lives if they operate continuously near their maximum power output. One method of
accommodating users’ power demands and the characteristics of these plants is to install an
energy storage system that can accept energy at night and can deliver it back to the grid during
periods of high demand. The value of this type of storage is based on the difference in marginal
cost of off-peak power and the price paid for power during the peak. An additional impact of
diurnal storage is that it can replace the installation of extra generation capacity.
Transient Voltage Dip
Major disturbances on power systems, such as loss of generation or of a line or, in some cases an
abrupt increase in load, can cause transient voltage dips that may last for 10-20 cycles.
Typically, control of this effect is accomplished today by limiting power transfer. If this is
required on critical power lines then they must operate well below their thermal limits.
Reduction of this effect on the grid to can defer construction of transmission lines.
Dynamic Voltage Instability
Dynamic voltage instability is a condition that can occur when a loss of generation or
transmission line and insufficient dynamic reactive power is available to support voltages. As a
result, line voltage in all or part of the system will degrade. This process may occur over a
period of minutes and result in voltage collapse.
Spinning Reserve
Operating guidelines for major power systems demand that some excess power capacity is
available for immediate power delivery in case of loss of a major generator or transmission line.
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