Motor Temperature Ratings

A oftentimes misunderstood subject related to electric forces is withdrawal configuration and temperature ratings. This paper tries to describe, in basic terms, the temperature relationships that are meaningful in standard AC induction gets. Some of the same information female genitalia be applied to DC repulses but DC motors are more(prenominal) specialized and some of the ratings are slightly different. Perhaps the best government agency to start is to define the commonly used terms.MOTOR SURFACE TEMPERATURESMotor surface temperature is patronisely of concern.The motor surface temperature will never exceed the internal temperature of the motor. However, depending upon the anatomy and cooling arrangements in the motor, motor surface temperature in modern motors earth-closet be high enough to be very uncomfortable to the touch. grow temperatures of 75 to 95 C can be found on T hurtle motor designs. These temperatures do not necessarily foreshadow overload or impending motor failure.OTHER FACTORSInsulation demeanor is affected by many factors aside from temperature.Moisture, chemicals, oil, vibration, fungus growth, abrasive particles, and mechanical abrasion created by frequent starts, all work to shorten insularism life. On some applications if the direct environment and motor load conditions can be properly defined, satisfactory means of winding protection can be provided to obtain fair motor life in spite of external disturbing factors.OLD AND stream STANDARDSU frame 184 through 445U frames, were designed based on using affiliate A insulation. Temperature establish was not precisely defined by the protection method.Temperature rise by thermometer for Class A, open drip proof motors was 40 C. This was mostly thought to be equivalent to approximately 50 C by resistance. U frame motors were the industry standard from 1954 to 1965 and are nonetheless preferred in some industries and plants. T frame, 143T through 449T motors are generally designed based on using Class B insulation with temperature rises by resistance of approximately 80 C. Production of T frame motors started in the mid-sixties and they continue to be the industry standard at this time.SUMMARYA key ingredient in motor life is the insulation strategy used in the motor.Aside from vibration, moisture, chemicals, and other non-temperature related life-shortening items, the key to insulation and motor life is the maximum temperature that the insulation system experiences and the temperature capabilities of the system components. duck 1 shows the temperature ratings, temperature rise allowances and calorific spot allowances for various enclosures and service factors of standard motors. Table 2 shows a listing of temperature related life-shortening factors along with symptoms and cures. You may name this table useful.TABLE 1Insulation System ClassABFHTemperature range in Degrees Centigrade105130155180 Temperature Rise Allowance by Resistance (Based on 40 C Ambient Temperature) All Motors with 1. 15 Service Factor (Hot Spot Allowance)70 *90 *115 * Totally enfold Fan Cooled Motors (Hot Spot Allowance)60 (5)80 (10)105 (10)125 (15) Totally Enclosed Non- ventd Motors (Hot Spot Allowance)65 (0)85 (5)110 (5)135 (5) Motors other than those listed supra (Hot Spot Allowance)60 (5)80 (10)105 (10)125 (15) * When operating at service factor loading the live(a) spot temperatures can actually exceed the insulation rating resulting in shortened motor life.TABLE 2Temperature Related Life-Shortening FactorsPROBLEMS SYMPTOMS CURESLow VoltageOverload light-headed richly current Short motor lifeCorrect power sum or match motor to actual power supply potentiality rating. High VoltageOverload scant(p) High current Short motor lifeCorrect power supply or match motor to actual power supply potential difference rating. Unbalanced VoltageUnbalanced phase currents Overload trippingDetermine why voltages are unbalanced and correct. OverloadOverload Tripping High current Short motor lifeDetermine reason for overload. Increase motor size or decrease load speed.High Ambient TemperaturesShort motor life* Rewind motor to higher class of insulation.Oversize motor to reduce temperature rise. Ventilate area to reduce ambient temperature. Blocked VentilationShort motor life Runs hot Amperage o. k. Clean lint and debris from air passageways or use proper motor enclosure for application. Frequent StartsShort motor life** Use a reduced voltage starting method. Upgrade class of insulation. High Inertia LoadsShort motor life Overload tripping during startingOversize motor frame. Use higher class of insulation * Use a reduced voltage starting method. * heading lubrication must also be matched to high operating temperature. **Reduced voltage starting method and motor characteristics must be matched to the load requirement. supplementTemperature Rise by Resistance Method Degrees C Rise = Rh Rc/ Rc (234. 5 + T) Where Rc = Cold Winding Resista nce in Ohms R h = Hot Winding Resistance in Ohms T = Cold (ambient) Temperature in Degrees Centigrade Note This formula assumes that the ambient temperature does not change during the test. Example A small motor has a cold temperature of 3. ohms at 25 C (77 F) ambient temperature. After operating at full load for some(prenominal) hours, the resistance measures 4. 1 ohms and the ambient has increased to 28 C.Calculate the temperature rise Apparent rise = 4. 1 3. 2/3. 2 (234. 5 + 25) = 73 C Correcting for 3 C increase in ambient effective rise = 73 3 = 70 C Centigrade Fahrenheit(postnominal) Conversions essential Temperatures To change Fahrenheit to Centigrade C = (F 32) 5/9 To change Centigrade to Fahrenheit F = (C x 9/5 ) + 32 Rise set Only Degrees C Rise = F (Rise) x . 56 Degrees F Rise = C (Rise) x 1. 8