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S700 MTIME + Goldline

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The S700 ASCII MTIME parameter maximum is 600 seconds while many of the goldline motors have a much longer thermal time constant. Our application uses a M-607-B motor with a 38 minute (2280 sec) TCT on an S772 amplifier.

What's the recommended practice for setting the MTIME parameter when the catalog TCT is significantly higher than the maximum parameter value?

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The S700 parameter MTIME is not actually the motor thermal time constant.  It is similar to the AKD parameter MOTOR.CTF0 (coil thermal constant) but is calculated differently.  It is used in the I^2*T algorithm.

 

MTIME = Thermal resistance (C/W) * 0.4 * mass of copper (kg) * Specific heat of copper (J/kgC)

(C = degrees C)

 

  • M-607-B motor has thermal resistance of 0.26 C/W
  • M-607-B motor winding contains about 5.03 – 5.47 kg of copper
  • Specific heat of copper = 385 J/kgC

 

MTIME = 0.26 (C/W) * 0.4 * 5.03 (kg) * 385 (J/kgC)

MTIME = 201 sec

 

MTIME = 0.26 (C/W) * 0.4 * 5.47 (kg) * 385 (J/kgC)

MTIME = 219 sec

 

So MTIME should be set to something around 201 to 219 seconds, or lower.

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Hi Dwern,

MTIME is used to calculate the I2t overload of the motor. This is equivalent to the constant thermal situation inside the motor. The expectation is that this is around the copper thermal time constant and much lower than the thermal constant of the manuals, as those numbers are the thermal situation on the surface.

Checking the current number in the data base for any existing motors shows the most common numbers are 16s to 40s. For bigger motors the thermal constant to surface (in minutes) is used as MTIME in s value. Following this logic  MTIME = 38 could make sense for your application.

If you set the number to low the I2t warning/fault triggers to early and you are not able to pull above nominal power with the motor for long enough. If the number is to high your able to burn the windings before even the surface gets really hot. So suggestion if you're unsure. Use a smaller value and validate if works for your setup.

Not the perfect answer but some guidelines.

Regards Martin Oxni GmbH

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Thank you Martin,

I'm concerned that setting MTIME to 38s will result in nuisance I2T faults. Can you share the formula(s) for calculating I2T so that we can run some simulations at different load cases and MTIME values?

I've only found a formula for the AKD drives at the link below. Is the S700 I2T computation method identical?
https://webhelp.kollmorgen.com/kas3.06/Content/UsersManual/Motor%20I2t%2...

Thanks again,
Daniel

dwern - Wed, 08/25/2021 - 08:04

As I don't have the formula implemented in the Servostar I can also only guess. Theoretical the formula could be identical but that someone from Kollmorgen should confirm.

I would go for a loop with Calculation Time Resolution increments:
MI2t = (MI2t^2 + (Icmd^2 - MI2t^2) / (Tau / Calculation Time Resolution)) ^ (0.5)
where Tau = MTIME / (2 * PI)
then scale the result with MICONT to get the the I2t percentage value

MartinRupf - Wed, 08/25/2021 - 09:01
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