Timer Current Curve pickup

[mbrooke]

I think you need have actual fault conditions to know exact pick up values. Have you got those data to work out exact pick up values?

I'd rather know ahead of time- and that is the point. You need to know what you are telling the relay to do as the desired response is known and often must be within very tight tolerances.

 

[Sahib]

I'd rather know ahead of time- and that is the point. You need to know what you are telling the relay to do as the desired response is known and often must be within very tight tolerances.

Well, let us forget for a moment timer and take an inverse over current relay. What is the least pick up value for it? I think it is same for your inverse timer also.

 

[Ingenieur]

Is this for all microprocessor relays or just SEL?


You are indeed correct, it is equation based. Does this mean I follow the equations in the manual and ignore the time current curves? And if so, then why have these time current curves in the first place? Unless they are just generics?

they are not generic (they have curves for ansi, iec, etc)
the curves are plots of the equation(s)
they try to cover the various national standards
the mfg will usually have a chart or subgraph for the low end of the curve

attached is an example of the chart

 

[mbrooke]

they are not generic (they have curves for ansi, iec, etc)
the curves are plots of the equation(s)
they try to cover the various national standards
the mfg will usually have a chart or subgraph for the low end of the curve

attached is an example of the chart

But how do I know what I have hear?

 

[mbrooke]

Well, let us forget for a moment timer and take an inverse over current relay. What is the least pick up value for it? I think it is same for your inverse timer also.

I'd like my curve to start timing at exactly 850 amps primary on a 1000:5 CT. The goal is so that I trip in X time when I exceed my STE rating. I know its not always done, but I am a big believer in overload (thermal protection) on equipment and feeders.

 

[rian0201]

@mbrooke,

In my opinion, this is the reason why relays are tested, to get the actual starting point. You can always looked at the curves, but manufacturers declare certain tolerances.

I always test the relays to get the actual starting point or pickup value.

Sent from my vivo 1606 using Tapatalk

 

[mbrooke]

@mbrooke,

In my opinion, this is the reason why relays are tested, to get the actual starting point. You can always looked at the curves, but manufacturers declare certain tolerances.

I always test the relays to get the actual starting point or pickup value.

Sent from my vivo 1606 using Tapatalk

Have you determined at what point SEL relays will pickup on their 51 elements?

 

[rian0201]

It is still range of values.. By still within specifications of SEL.

Sent from my vivo 1606 using Tapatalk

 

[Ingenieur]

But how do I know what I have hear?

look at the relay?
test the relay? ramp i up until it starts timing

 

[Smart $]

S$ -
I have not heard of the term "window plot". The paper is "Log-Log" - logarithmic on both axis. Doesn't matter what "window" one picks, neither axis will ever get to zero. But I'm thinking you already knew that.
...

Window is quoted because it is not a conventional term that I'm aware of. Consider a large plot of data lines without the graph (aka grid) and an opaque overlay with a transparent rectangle in it (aka the 'window') smaller than the entire plot behind it. What you see of the plot is a 'window' plot. This combination is then overlaid on a to-scale graph. Thus a 'window' plot.

You are correct about log graphs not having a zero axis, but for example, elapsed time (Δt) must have a zero data point.

 

[mbrooke]

look at the relay?
test the relay? ramp i up until it starts timing

Easier said then done. Knowing ahead of time is key before building or commissioning anything.

 

[mivey]

I'd like my curve to start timing at exactly 850 amps primary on a 1000:5 CT. The goal is so that I trip in X time when I exceed my STE rating. I know its not always done, but I am a big believer in overload (thermal protection) on equipment and feeders.

Again, picking up at 850A is one thing but tripping in a reasonable time is another. You can set the SEL 51 pu at 850 amps but it is actually a limit and will pick up when the current exceeds 850A.

If you pick up at 850.01A then you might not trip for hours so is that OK? Probably makes more sense to determine where you want to trip in the cycles to minutes time frame.

Thermal overload can be checked with a thermal sensor. You can also set an SEL logic timer to close a contact based on time and load and create a thermal pickup if you want. This would be like a 50 pickup with a minimum time or torque equation.

 

[mivey]

Have you determined at what point SEL relays will pickup on their 51 elements?

For the 51 curves it is as soon as you exceed the pu limit.

 

[mivey]

But how do I know what I have hear?

Section 9 of the manual has the curve equations.

 

[mivey]

Easier said then done. Knowing ahead of time is key before building or commissioning anything.

The manual has the curve equations and logic diagrams you need.

If you want an overload pu then consider intgrating a 50 setting with timer logic to speed up the response before you get to what might be a long time on a 51's inverse curve. You could have it set to cover a range from the overload pu to whatever amp value you want to swap to the 51 inverse curve.

You could even stack in a faster (flatter) 51 curve on the front end but torque it so it will not pick up until something like 2X before the more inverse curve comes into play, then the inverse curve will cross it and pick up faster for high faults. For that matter you could torque a single 51 curve like that. The torque control will get rid of the steep, long time part of the inverse curve.

 

[mbrooke]

Again, picking up at 850A is one thing but tripping in a reasonable time is another. You can set the SEL 51 pu at 850 amps but it is actually a limit and will pick up when the current exceeds 850A.

If you pick up at 850.01A then you might not trip for hours so is that OK? Probably makes more sense to determine where you want to trip in the cycles to minutes time frame.

Thermal overload can be checked with a thermal sensor. You can also set an SEL logic timer to close a contact based on time and load and create a thermal pickup if you want. This would be like a 50 pickup with a minimum time or torque equation.

All sounds reasonable and easily. But why do those curves make it look like the pickup starts at 125% of the entered value?

 

[mbrooke]

The manual has the curve equations and logic diagrams you need.

If you want an overload pu then consider integrating a 50 setting with timer logic to speed up the response before you get to what might be a long time on a 51's inverse curve. You could have it set to cover a range from the overload pu to whatever amp value you want to swap to the 51 inverse curve.

You could even stack in a faster (flatter) 51 curve on the front end but torque it so it will not pick up until something like 2X before the more inverse curve comes into play, then the inverse curve will cross it and pick up faster for high faults. For that matter you could torque a single 51 curve like that. The torque control will get rid of the steep, long time part of the inverse curve.

This forum needs a "like" thumbsup button :happyyes:

 

[mivey]

All sounds reasonable and easily. But why do those curves make it look like the pickup starts at 125% of the entered value?

Because that is how the old EM curves were drawn and they were duplicating the historic curves.

The EM relays were not considered consistent below 1.5X (even though you test them to within 3% of pickup). The digitals are computer consistent down to the pickup setting.

 

[mbrooke]

Section 9 of the manual has the curve equations.

Is this the equation you have in mind or am I way off?

 

[mbrooke]

Because that is how the old EM curves were drawn and they were duplicating the historic curves.

The EM relays were not considered consistent below 1.5X (even though you test them to within 3% of pickup). The digitals are computer consistent down to the pickup setting.

Ok- that would make more sense then. It was those curves that were throwing me off. So when I hit 801 amps (primary) from an 800amp (primary) set point, the relay will indeed start timing, albeit it will take some time to produce a trip output.