GE 469 Instruction Manual

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Contents

Application Example469Motor Management RelayGetting Startedhttp://www.GEindustrial.com/multilin1–22 GE Multilin• Stator RTDsSet the RTD trip level at or below the maximum temperature rating of theinsulation. The data available shows class F insulation (temperature rating of155°C), therefore the Stator RTD Trip level should be set to between 140°C to155°C, with 155°C being maximum. The RTD alarm level should be set toprovide a warning that the motor temperature is rising. For this example, 135°Cwould be appropriate since this motor is designed for class B rise, 130°C is it'snormal hot operating temperature.• Bearing RTDsThe Bearing RTD alarm and trip settings will be determined by evaluating thetemperature specification from the bearing manufacturer.• Unbalance bias of thermal capacityEnable the Unbalance Bias of Thermal Capacity so that the heating effect ofunbalance currents is added to the Thermal Capacity Used.• Unbalance bias K factorThe K value is used to calculate the contribution of the negative-sequencecurrent flowing in the rotor due to unbalance. It is defined as:(EQ 1.1)where: R r2 = rotor negative-sequence resistanceR r1 = rotor positive-sequence resistance.A formula based on empirical data states that K is equal to 230 divided by theper-unit locked rotor current squared.From the data sheet, the locked rotor amps = 631% FLA or 6.31 × FLA.Therefore,(EQ 1.2)• Hot/cold curve ratioThe hot/cold curve ratio is calculated by simply dividing the hot safe stall timeby the cold safe stall time or use the motor thermal limits curve. For thisexample, both are available. Using the data sheets the, safe stall time H/C orhot/cold curve ratio is given as 16/18 = 0.89• Enable RTD BiasingThis will enable the temperature from the Stator RTD sensors, to be included inthe calculations of thermal capacity. This model determines the thermalcapacity used based on the temperature of the Stator and is separate from theoverload model for calculating thermal capacity used.RTD biasing is a back up protection element, which accounts for such things asloss of cooling or unusually high ambient temperature. This measuredtemperature is used to bias or modify the thermal capacity value stored in therelay.RTD BIAS MINIMUM: Set to 40°C, which is the ambient temperature, obtainedfrom the data sheets.RTD BIAS MID POINT: The center point temperature is set to the motor's hotrunning temperature and is calculated as follows:Temperature Rise of Stator + Ambient TemperatureThe temperature rise of the stator is 80°C (class F rise by resistance) + 10%hot spot allowance, obtained from the data sheets. Therefore, the RTD Centerpoint temperature is set to 90°C + 40°C or 130°C.RTD BIAS MAXIMUM: This setpoint is set to the rating of the insulation or slightlyless. A class F insulation is used in this motor which is rated at 155°C, so thesetting should be “155”.K R r2R r1---------=K 230(per-unit locked rotor amps) 2----------------------------------------------------------------------------------------- 2306.31------------- 6≈= =