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

EPRI Proprietary Licensed Material
Proceedings of the International Seminars on Double Layer Capacitors and Similar
Energy Storage Devices Volumes 1 through 11. Available through Florida Educational
Seminars, Inc., Boca Raton, Florida (1991 – 2001)
Y. Kobayashi, Acceleration Coefficient of the Molded Electric Double Layer Capacitor,
NEC Corporation
Websites: www.faradnet.com, www.POWERSOURCES.net, manufacturer websites are
listed in Table 3.
Glossary
Asymmetric capacitor – See type III capacitor and type IV capacitor
Electrochemical capacitor, double layer capacitor, electric double layer capacitor,
supercapacitor, ultracapacitor – common names for the type of capacitor in which
electrical energy is stored in an electric double layer by means of separation of charge at
an interface between a solid electrode and electrolyte. Ultracapacitor and supercapacitor
are trademarked names.
Energy, Capacitor - The ideal (maximum) value of the electrical energy stored in a
capacitor. For the first-order model of a capacitor, it is equal to ½ CV 2 where C is the
capacitance and V is the working voltage on the capacitor.
Energy, Specific – Energy per unit mass usually expressed as Watt-hours/kilogram or
kilojoules/kilogram.
Energy density - Energy per unit volume, usually expressed as Watt-hours/liter or
kilojoules/liter.
Equivalent series resistance - The value of the resistance element when a capacitor is
modeled as a series RLC circuit. ESR can be measured using current interrupt methods
or by AC impedance techniques. It contributes to dynamic losses in the capacitor, that is,
losses experienced only during charge or discharge. ESR is a lumped element value that
arises from the leads, current collectors, electrodes, separators, contacts, and other
resistance elements.
Impedance (Z) – The ratio V/I of a capacitor where V is a voltage (periodic in time)
applied to the component and I is the resultant current. Z is a complex quantity, having
real and imaginary parts. It represents the current flow response to an applied timedependent
voltage.
Leakage current - The steady-state current drawn by a capacitor after being charged. It is
responsible for static energy losses . The leakage current is established by resistor R p
, the
equilavent resistance in parallel with the capacitor which is sometimes referred to as the
self-discharge resistance. The leakage current is time dependent when the capacitor is
held at a constant voltage and the current required to maintain this voltage decreases with
time as the capacitor comes to an equilibrium-charge state.
Power (maximum) - The ideal (maximum) value of the power that can be delivered by a
capacitor. For the first-order model of a capacitor, it is equal to V 2 /4R where V is the
working voltage on the capacitor and R is the equivalent series resistance.
Electrochemical Capacitors 54