Time Overcurrent Characteristics and Constants Data

[VARS]

Happened across this site today and found a topic posted by ckrueger, re: formula on calculating time current plots on curves.

I am familiar with the formula that ABB and Basler show for calculating the time current curve plots for various points along the time dial curves shown in their microprocessor based relaying instructions.

My question, related to testing electromagnetic, solid state and microprocessor protective relays, where can I get photo-copies or materials that define the type of curve used, formula and constants tables for overcurrent and/or other functions on current, voltage relays?

Many times I want to prove by manually ploting the points, for comparative analysis. Many curves are referenced to IEEE, ANSI or IEC curves but ploting off a "old" photo-copy curve is not accurate enough given the time-error percentages of +/- 3% to 5%.

Ther must be a standardized set of equations and constants somewhere to define EM, Solid-State and Microprocessor based relay systems.

Can anyone help?

Thanks,
VARS

 

[bigamp]

If you check out the Alstom T&D website and download the technical manual for their Micom P121 or P141 overcurrent & earth fault relays you will find tables with the information you seek, for the various curves (formulas and constants).

The various generatons of Alstom microprocessor based relays (Midos, K series and Micom series) follow the curves defined by the mathematical expressions. You then calculate sufficient points to be able to manually draw a curve with the aid of a flexicurve.

I have found that electromechanical relays do not exactly follow the same curves as given by the formulas. For these relays, it was traditional to use templates to plot the curve, or alternatively to get sufficient points from a good photocopy of the curve and then plot off that. There is some inaccuracy with this method, but this is compensated for by using slightly higher grading margins between relays.

Regards

 

[busbar]

See IEEE Std C37.112-1996 ...Inverse-Time Characteristic Equations for Overcurrent Relays

The standard is described at

http://standards.ieee.org/reading/ieee/std_public/description/relaying/C37.112-1996_desc.html

and is available [for online purchase] as a pdf at

http://shop.ieee.org/store/

 

[dpc]

You will need to get the equation for each relay from each individual relay manufacturer.