Correct Terminology to Describe Source "Stiffness"

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My reading on use of "stiff" in relation to electrical sources is related to maintaining regulated characteristics under varying load.

If the voltage drops off with increasing load, it is referred to as "droop". Stiffness is the absence of droop.

If you are working with a constant current source, then "stiff" would relate to the ability to deliver the constant current into varying resistance loads.
 
I second Bob's message. DROOP is in reference to the voltage being lost, so one can say 2% droop from no load to full load. STIFFNESS is in reference to the voltage being retained, so one can say 98% stiffness from no load to full load. Can't say, though, that I've ever seen a spec that used STIFFNESS; they all like to use DROOP.
 
A stiff utility source will have very high fault current.
for example in IEEE 519, ?Standard Practices and Requirements for Harmonic Control in Electrical Power Systems,? they determine the limits of harmonic content based on the value of Short Circuit current divided by the load current.
This is because a stiff source has high fault current as related to the load current.
 
A stiff voltage source would have a very low impedence or resistance.

A stiff current source would have a very high impedednce or resistance.
 
Stiffness is definded in IEEE Std 100-1996 (Electrical Dictionary) as:
The ability of a system or element to resist deviations resulting from loading at the output.
Click to expand...
Edit add: It is endorced by both the Power Engineering and Industrial Applications Societies. As such, it appears to be the term you are looking for.
 
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rbalex said:
Stiffness is definded in IEEE Std 100-1996 (Electrical Dictionary) as:
Edit add: It is endorced by both the Power Engineering and Industrial Applications Societies. As such, it appears to be the term you are looking for.
Click to expand...


It looks like "stiffness" is very similar to "voltage regulation", but I think I see one difference. The term "voltage regulation" is usually used when a source is intended to supply power at a constant voltage.

It sounds like "stiffness" is a better term to apply to a voltage that changes for reasons other than the loading. For example, voltages used to represent signals or measurements.
 
In my opinion, Steve has the idea. The impedance of a source can be defined by its capacity to not be affected by the load, as in maintaining voltage despite load variations. Also related is the ability of a source to maintain control over the load.

Similar to this is the term 'damping factor' used in audio amplifiers. Not only must an amplifier accelerate a speaker diaphragm upon a signal input or change, but it must also stop or alter that motion when the signal input stops or changes.

Remember, once excited into motion, a speaker voice coil, moving in the magnetic gap, becomes a generator. As with dynamic braking, the low source impedance of the amplifier must halt or alter the inertial movement of the diaphragm.

This ability is co-dependent on the sources current capacity as well as the impedance of the wiring between the source and the load, including everything in the conductive pathway. It's also why we must upsize wire for excess voltage drop.
 
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