Delta MM300 Instruction Manual download pdf (Page 115)

6–28 MM300 MOTOR MANAGEMENT SYSTEM – INSTRUCTION MANUAL

PROTECTION ELEMENTS CHAPTER 6: SETPOINTS

The MM300 calculates the steady-state thermal capacity used according to the following

equation.

Eq. 3

In the above equation:

•TCU

represents the steady-state thermal capacity used expressed as a percentage.

• I

represents the equivalent motor heating current in per-unit values on an FLA base.

Refer to unbalance biasing for additional details.

• HCR represents the value of the

Hot/Cold Safe Stall Ratio setpoint expressed as a

percentage.

If a

Hot/Cold Safe Stall Ratio value of 100% is entered, the hot/cold biasing is defeated, and

unless RTD biasing is deployed, the thermal model will operate as if the motor was cold

prior to overload.

6.3.1.3 RTD biasing

The thermal model can operate based solely on measured current and the assumption of

rated ambient and normal motor cooling, as described earlier. However, if the ambient

temperature is unusually high, or motor cooling is blocked, the motor will have a non-

modeled temperature increase. The RTD biasing feature can correct for this by forcing the

Thermal Capacity Used register up to the value appropriate to the temperature of the

hottest stator RTD. Since RTDs are relatively slow, the rest of the thermal model is still

required during starting and heavy overload conditions when motor heating is relatively

fast. Thus the RTD bias feature does not prevent the thermal capacity used value from

rising above the value appropriate to the RTD temperature.

The value of the Thermal Capacity Used register appropriate to the RTD temperature is

determined by the straight line segmented curve shown in the following figure. This curve

is characterized by minimum, center, and maximum temperature values, and by the hot/

cold ratio value.

NOTE

NOTE:

The RTD bias feature alone cannot create a trip. If the RTD bias forces thermal capacity

used to 100%, the motor current must be above FLA before an overload trip can occur.

Figure 23: RTD bias curve

()

HCR%100TCU

-´=

853730A1.CDR

100%

80%

60%

40%

20%

500 100 150 200

Hottest stator RTD temperature (°C)

100% - Hot/Cold Ratio

Appropriate thermal capacity used

RTD Bia

-CenterT

RTD Bias - Minimum T

RTD Bia

s - Maximum T

1 2 ... 110 111 112 113 114 115 116 117 118 119 120 ... 166 167

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Delta MM300 Instruction Manual Page 115

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