Convert Time into Parameters

I hope this isn't homework!

kt ≈ (9.6 x 10^-3 x time) + 0.05

From this:

time = 0.05 => kt = 0.05048,

time = 99 => kt = 1.0004,

time = 10 => kt = 0.146

Not exact, but quite close.

The reverse operation (for checking the results) is:

time ≈ (104.16 x kt) - 5.16

(I'm not going to explain how I did it, because if it is homework, you should work it out yourself ).

JohnDG:

This is not a homework and I am wondering where you take 9.6.

If the current: 120% to 200%

The real current in the system: 570 amps

Scale kt: 0.1 ~ 1

What if I want to set the kt is at 130% of the real curent?

Sorry, but you have lost me. You were asking about time in your first question - now it's changed to current. What is this about? Please explain.

JohnDG:

There are two cases. I am sorry not being clear at first. I am setting for the protection relay and I need to confirm.

Ok, for the current case:

What is the current corresponding to a trip value of 100%?

It is the real current of 570A.

I could give you the sums to find the answer mathematically, but it may be more practical for you to use the graphical method.

Take a sheet of graph paper (paper ruled with vertical and horizontal lines) and draw a graph like this:

The bottom left point is (kt=0.1,I%=120) and the top right point is (kt=1, I%=200).

If you look up the vertical axis to find 130%, you can read down to find the corresponding value for kt (0.21).

I'll show you the mathematical method if you want, but I think you'd be better using the graphical method - just get hold of some graph paper and plot it out.

Here's a close-up view of the region of interest:

Thank you for your time working out these graphs, it would be much helpful to me. If I need to explain to someone else, I will use the graphical method.

I am Ok now for the methematical method.