Plotting TCCs from transmission data sheet

[AHarb]

Hi,

I'm trying to verify that our circuit breakers coordinate with the substation bank protection by plotting the curves of each. We are sent data sheets with the protection settings from our transmission provider, but it seems like I'm missing a "time dial" setting when I try to plot the curve in CymeTCC. Is there a way to derive the time dial settings from the settings given (see image) or do I need more information from our transmission provider to plot the curves?



Thanks

 

[mayanees]

time setting

time setting

Yes, you can plot the device using the info given.

Note for the phase device they've given a time of 60 cycles @ 5X pu.
Plot out the device using all of the parameters given, and then vary the multiplier/time setting until the curve passes through the point (5X current pickup, 1 second)
The way I would do it in SKM is to assign a datablock to the device on the TCC that lists the test point 5X pickup and the resultant trip time, then vary the multiplier until the trip time is exactly 60 cycles.
PEPCO reports similarly at a 6X pickup. It seems a little crazy that they wouldn't just give you the multiplier, but then again it forces you to verify that your curve crosses the timing point.
John M

 

[jim dungar]

Time Dial is an electromechanical relay setting.
The confusion is more likely caused by the TCC plotting software that has a limited input menu, and therefore asks for a "TD setting" regardless of an electronic relay's characteristics.

 

[AHarb]

I'm pretty unfamiliar with mechanical relays and do not understand the time dial setting. I am trying the test point method as mayanees mentioned. There is an option in CymeTCC (TCC plotting software I'm using) to calculate the time dial value using a test point and it appears to be working correctly. When in input the test point (1350 A @ 1 second), it gives me a time dial setting of 0.296 and the curve crosses 1350 A at 0.9994 seconds.

Now I just have to convert the settings to 12.47 kV to match our circuit breaker settings and I should be able to compare the two. Thank you for the help.

 

[AHarb]

I'm now having trouble understanding how to input the test point. When I input the test point to calculate the time dial, it asks for a "Multiplier." Changing the multiplier value changes what the calculated time dial value will be. I think I just got lucky with the multiplier value when I plotted the phase curve. I'm not getting lucky with the ground curve though.

Also, there are 4 test points in the window. Any idea why there are 4 test points all with different multipliers (see image below)?

 

[jim dungar]

One of the ways to change the operting time of an electro-mechanical relay was to 'widen the gap' between the contacts. The movable contact was mounted on a dial, and the effect of rotating this dial was to shift the relay's operating curve resulting in different trip times for a given amount of current.

So by knowing a specific multiple of operating current and the corresponding operating time, you effectively have the results of a Time Dial setting.
This is why Mayanees said to start at the given point (5X @ 60cycles) and then adjust the TD setting until the trip curve intersects that point.

 

[mayanees]

I'm now having trouble understanding how to input the test point. When I input the test point to calculate the time dial, it asks for a "Multiplier." Changing the multiplier value changes what the calculated time dial value will be. I think I just got lucky with the multiplier value when I plotted the phase curve. I'm not getting lucky with the ground curve though.

Also, there are 4 test points in the window. Any idea why there are 4 test points all with different multipliers (see image below)?

View attachment 6754

Not completely understanding the "Compute TD and Test Points" screen, I suggest that it applies to a device that has a pickup point of 720 amps, and not the 270 amps you're interested in. This is apparent from Test Point (TP) 3 where the multiplier is 1 and the Check point is 720. Similarly for TP1, an 8 Multiplier translates to 8*720 = 5760.
So I suggest that if you change this screen to be looking at a device with the 270-amp pickup, enter a Multiplier of 5 and one (1) second for the Opening time to match the reported data - the "Compute Time Dial" button will calculate the TD settings, which as Jim points out, is a throwback to the electromechanical relays in terms of description, because it's actually the multiplier for the Very Inverse function for this SEL relay, and not a Time Dial at all.
The value to the presentation of these test points in your Report of Device Settings is that the test techs will use the Test Points to check operation of the relay. You don't necessarily need 4 test points, but it doesn't hurt to present them. I typically present three (3) in a Device Report.
John M

 

[AHarb]

I think I may be even more confused now. I was attempting to plot the ground curve along with the phase curve. The protection values are given at different voltages (phase at 115 kV and ground at 12 kV). I e-mailed CymeTCC support before posting here as well and they're going about a different way of plotting the curves. They're saying that those test point values are dependent upon the CT ratio. The "operation mode" I'm using to plot the curves has the C.T. ratio grayed out where I cannot change it.

They're suggesting using the "Tap with tap range" operation mode (see image below) to plot the curves. I was using the "Primary Amps" operation mode to plot the curves because I thought I did not have the necessary information to plot using the other modes. If I switch to that operation mode, it requires me to input "Tap Range" and "Tap L (long time)" which I have no idea what those are or what their values would be. Somehow in the e-mail, they came up with a tap range of 0.5/16.0 and a tap L (long time) value of 4.5.



Sorry for being so confused. I appreciate you trying to help.