Dictionary of Electrical Engineering
Commonly used terms in the Electrical industry.

D'Arsenval meter

a permanentmagnet movingcoil instrument with a horseshoe form magnet. It measures direct current only.

damper winding

an uninsulated winding, embedded in the pole shoes of a synchronous machine, that includes several copper bars shortcircuited by conducting rings at the ends, used to reduce speed fluctuation in the machine by developing an inductiontype torque that opposes any change in speed.

damping

a characteristic built into electrical circuits and mechanical systems that prevents rapid or excessive corrections that may lead to instability or oscillatory conditions.

damping coefficient

electrical torque component in phase with the rotor speed.

dB

See decibel

dBc

ratio of the signal power (p) to a reference signal power (p_{ref}), usually the modulation carrier signal, expressed in decibels referenced to a carrier (dBc). Thus a harmonic signal that is 1/100th of the power in a desired fundamental signal is at 20 dBc.
P_{dBd} = 10 log_{10} ( p / p_{ref} )

dBm

Power ratio in decibels referenced to 1 milliwatt.

dBW

ratio of the signal power in watts (p watts)to a 1W reference power, expressed in decibels referenced to 1 W (dBW). Thus
1 watt signal power is equal to 0 dBW, and 30 dBW is equal to 0 dBm.

DC

direct current
See DC voltage

DC block

A circuit simulation component that behaves like a capacitor of infinite value.