Emerson Mentor MP Advanced User's Manual page 84

Parameter
Menu 5
structure
This assumes that the maximum allowed field temperature is produced by 1.05 * field rated current and that τ is the thermal time constant of the point
in the motor that reaches it maximum allowed temperature first. τ is defined by Pr 5.81. The estimated motor temperature is given by parameter 05.82
as a percentage of maximum temperature. If the Pr 5.81 has a value between 0.0 and 1.0 the thermal time constant is taken as 1.0.
When the estimated temperature reaches 100% the drive stops the motor and then trips on F.OVL.
The time for some action to be taken by the drive from cold with constant field current is given by:
T = -(Pr 5.81) x ln(1 - (1.05 x Pr 5.70 / Pr 5.56)
trip
Alternatively the thermal time constant can be calculated from the trip time with a given current from
Pr 5.81 = -T / ln(1 - (1.05 / Overload)
trip
For example, if the drive should trip after supplying 120% overload for 60seconds then
Pr 5.81 = -60 / ln(1 - (1.05 / 1.20)
The thermal model temperature accumulator is reset to zero at power-up and accumulates the temperature of the field whilst the drive remains pow-
ered-up. Each time Pr 11.45 is changed to select a new motor, or the rated current defined by Pr 5.70 or Pr 21.24 (depending on the motor selected)
is altered, the accumulator is reset to zero.
5.82 Field overload accumulator
Bit SP
Coding
0 to 100.0%
Range
Update rate Background write
See Pr 5.81.
84
Keypad and
Parameter x.00
display
2
)
2
)
2
) = 41
FI DE Txt VM DP ND
1 1
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Parameter description Advanced parameter
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1
Mentor MP Advanced User Guide
Performance
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