TROUBLESHOOTING FOR H.V. MOTORS PART 2

TROUBLE SHOOTING FOR H.V. MOTORS PART1

TROUBLE SHOOTING FOR H.V. MOTORS PART 2

Limit Of Induction Motor's Temperature Rise

The limit of temperature rise (temperatures at various parts minus ambient temperature) is prescribed by NEMA Standard MG1-20, 40 for each insulation material as shown in Table 1-2. The values given in table 1-2 show the temperature limits when the ambient reference temperature is 40ºC or lower. In case that the ambient temperature exceeds 40º C, the limit of temperature rise is to be reduced by the difference between the actual ambient temperature and 40º C.


The observable temperature rise under rated-load conditions of each of the various parts of the induction motor, above the temperature of the cooling air, shall not exceed the values given in the following table. The temperature of the cooling air* is the temperature of the external air as it enters the ventilating openings of the machine, and the temperature rises given in the table are based on a maximum temperature or 40ºC for this external air. Temperatures
shall be determined in accordance with the latest revision of IEEE Std 112, Test Procedure for Poly phase Induction Motors and Generators.

Table 1-2 NEMA Standard MG1-20,40 Temperature Rise

Item	Machine Part	Method of Temperature Determination A	Temperature Rise. Degrees C Class of Insulation System
			A	B	F	H
1	Insulated windings a.      All horsepower ratings b.      1500 horsepower and less. c.      Over 1500 horsepower  1.  7000 volts and less.   2. Over 7000 volts.	Resistance Embedded detector Embedded detector Embedded detector	60 70 65 60	80 90 85 80	105*1 115*2 110*3 105	125 140 135 125
2	Cores, squirrel – cage windings and mechanical parts, such as collector rings and brushes, may attain such temperatures as will not injure the machine in any respect.

For totally-enclosed water-air-cooled machines, the temperature of the cooling air is the temperature of the air leaving the coolers. See Note 1



Embedded detectors are located within the slot of the machine and can be either resistance elements or thermocouples. For motors equipped with embedded detectors, this method shall be used to demonstrate conformity with the standards.






NOTE :- Totally-enclosed water-air-cooled machines are normally designed for the maximum cooling water temperature encountered at the location where each machine is to be installed. With a cooling water temperature not exceeding that for which machine is designed.


a.      On machines designed for cooling water temperature up to 30ºC-the temperature of the air leaving the coolers shall not exceed 40 ºC.


b.      On machines designed for higher cooling water temperature-the temperature of the air leaving the coolers may exceed 40ºC provided the temperature rises of the machine parts are then limited to values less than those given in the table by the number of degrees that the temperature of the air leaving the coolers exceed 40ºC.


NOTE :- For motors which operate under prevailing barometric pressure and which are designed not to exceed the specified temperature rise at altitudes from 3300 feet (1100 meters) to 13000 feet (14000 meters). The temperature rises as checked by tests at low altitudes, shall be less than those used in the foregoing table by 1 percent of the specified temperature rise for each 330 feet (100 meters) of altitude in excess of 3300 feet (1000 meters).


NOTE :- Temperature rises in the foregoing table are based upon a reference ambient temperature of 40ºC. However it is recognized that induction motors may be required. to operate in an ambient temperature higher than 40ºC. For successful operation of the motors in ambient temperatures higher than 40ºC. It is recommended that the temperature rises of the motors given in the foregoing table be reduced, as indicated below, for the ranges of ambient temperature given. (Exception-for totally-enclosed water-air-cooled machines. see NOTE I.)

Ambient Temperature Degrees C	Values by which Temperature Rises in the Foregoing table Should be Reduced in Degrees ºC
Above 40 up to and including   30 Above 50 up to and including   60	10 20

For 190 KW, 200 KW & 230 KW L.V.
motors For 570 KW, 6.9 KV Horizontal Motors.
For 2620 KW & 1420 KW, 6.9 KV Vertical Motors

Caution:-

Since the motor temperature would rises until the heat produced by copper loss, iron loss and mechanical loss is balanced with the heat dissipated by ventilation, the ventilation system requires special attention. Particularly, it must be noted that an obstacle close to the ventilating part or narrowing of the part by accumulated dust when the motor is used in a dusty place will cause the abnormal temperature rise of the motor. Each motor, when delivered, is accompanied by a test report showing the temperature rises of the coil, core and other parts at the time of the shop test. it is necessary to measure the actual temperature of the motor from time to time to ascertain that the measured values are not much different from those obtained in the shop test.

TROUBLE SHOOTING FOR H.V. MOTORS PART 3 ....SOON