Limiting temperatures windings

The temperature of the windings and other parts must not exceed the limiting temperature specified in Table 7.5, even if the motor, after a prolonged operating period, remains energized in a stalled condition, for a specified time of fg seconds while /g will not be less than 5 seconds. 

This is the time taken by the stator or the rotor, whichever is less, to reach the limiting temperature rise, as specified in Table 7.5, when the starting current /s, is pas.sed through the stator windings after the motor has reached thermal equilibrium, underrated conditions. For increa.sed safety motors, this time should not be less than 5 seconds (preferably 10 seconds or more). 

The above methods assume that all superheated liquids can flash explosively, yet this may perhaps be the case only for liquids above their superheat-limit temperatures or for pre-nucleated fluids. Furthermore, the energies of evaporating liquid and expanding vapor ate taken together, while in practice, they may produce separate blasts. Finally, in practice, there are usually structures in the vicinity of an explosion which will reflect blast or provide wind shelter, thereby influencing the blast parameters. 

If the motor operates at temperatures above 40 °C, it will heat up beyond its maximum permissible temperature at its rated power, which can lead to destruction of the motor. For this reason, a derating (power reduction) must be provided for. That means that a more powerful motor has to be used which is not loaded to its power rating and thus never reaches its limit temperature, even at increased ambient temperature. The maximum temperature of a motor is mainly determined by the temperature stability of the insulating paint on the winding. Several classes are distinguished here. The most common classes are ... 

Pressurized motors and generators are not subject to special requirements for temperature limitations concerning windings and rotor, there are no stringent... 

R = resistance, T = thermometer, ETS = measurement with electric temperature sensors Note The original tables in EN 50019 and IEC 60079-7 indicate the limiting temperatures for insulated windings (and not the limiting overtemperatures). To enable an easier comparison, these values are transformed to overtemperatures taking into account an ambient temperature of +40°C. 

An essential point considering e-motors is their thermal behaviour. For the simple case of permanent operation at rated power, the windings shall exceed neither the temperature limit of the corresponding temperature class (T1. .. T6) nor the limiting temperature due to the thermal class of insulating material given in Table 6.13, Part A. 

Table 6.20 Limiting temperatures for insulated windings (for stalled motors) (referring to an ambient temperature of +40°C, and to the end of time fE). Method of temperature measurement resistance...

For a short time, the limiting temperature for insulated windings given in Table 6.13, Part A, may be exceeded up to increased values (Table 6.20). 

Field residues, if below the toxicological limit (acceptable daily intake), are used to set the legal limit. The residues of pesticides in the field experiment are affected by the environmental conditions such as temperature, wind, rain, solar irradiance etc. For this reason, residues limits (MRLs) can vary between countries because of the different climatic conditions, leading to EU trade difficulties. 

The pesticide residues are affected by environmental conditions, such us temperature, wind, rain, and solar irradiance. Consequently, MRLs can vary between countries because of the different climatic conditions. Currently, the EU is working for the harmonization of MRLs for raw food, but no limits are fixed for transformed foods. In Italy, when there is no legal limit for transformed food, the amount of raw food for a transformed food unit (e.g., 1.5 kg of grape to produce 1L of wine) and the incidence of technological process should be taken into account. Unfortunately, in the absence of specific data on changes of the residue occurring with the transformation, the only reference data is the MRL of raw food. Some countries, such as the United States, adopt the same MRL of grape for wine (Cabras and Caboni, 2008). 

For a higher ambient temperature, the end temperature of the winding will exceed the permissible limit by the amount the ambient temperature is higher. For example, for a class E motor, an ambient temperature of 30°C will cause the end temperature to reach I25°C as against 115°C permissible by the resistance method. For details refer to Sections 9.1 and I 1.3.2. 

Surface temperature should not exceed the ignition temperature noted in Table 7.6 for a particular temperature class under any conditions of operation. There is no limit to the temperature rise to the permissible limits for a particular class of insulation of windings or other parts of the machine, except the limiting surface temperature as in Table 7.6. For such an application, a normal 1P 55 enclosure may also be employed. 

This test is intended to determine the temperature rise in different parts of the motor windings while running at rated conditions and the permissible temperature rise limits are specified in Table 11.1. While preparing for the temperature rise test the motor should be shielded from currents of air coming from adjacent pulleys, belts and other components to avoid inaccurate results. Sufficient floor space should be left between the machines... 

Note The embedded lemperalure deleclor melhod is inappropriate for stator windings, which have only one coil side per slot, in such ciises the resistance melhod must be used with the same limits of temperature rise. For checking the temperature of such a winding in service, an embedded detector at the bottom of the slot is of little use because it would give mainly the temperature of the iron core. A detector placed between the coil and the wedge will follow the temperature of the winding much more closely and is, therefore, better for check tests, although the temperature there may also be a little less than the actual one. 

The limiting secondary resistance is required to determine the secondary limiting e.ni.f. which is = (FS) x rated secondary current x VA X resistance of secondary windings at 90°C or the highest operating temperature as in Table 14.5, where... 

Other data, gathered primarily once each day by cooperative observers, consist mostly of temperature and precipitation readings. These are of limited usefulness for air pollution analysis because wind data are generally lacking. 

The temperature limits inside a building are mostly within the variations of the temperature outside, and the heat resistance requirements on the building materials inside are the same as the requirements on materials used outside. There could be some additional requirements on outside materials depending on rain, snow, wind, sunshine, etc. When the temperatures inside, whether higher or lower than outside, will be used because of the process, the building materials must be chosen with these requirements taken into account, especially when heat radiation is a factor. This should not be confused with demands on temperature and humidity insulation. 

For windings immersed in either hydrocarbon oil or synthetic liquids the coil insulation is usually a Class A material. For oil-immersed transformers BS 171 specify two maximum oil temperatures 60°C for sealed-type transformers for those fitted with conservators and 55°C for transformers without either. In the case of air-insulated, air-cooled transformers, the class of insulation used, i.e, limits the maximum permitted temperature rise ... 

Infrared thermometers or spot radiometers are designed to provide the actual surface temperature at a single, relatively small point on a machine or surface. Within a predictive maintenance program, the point-of-use infrared thermometer can be used in conjunction with many of the microprocessor-based vibration instruments to monitor the temperature at critical points on plant machinery or equipment. This technique is typically used to monitor bearing cap temperatures, motor winding temperatures, spot checks of process piping temperatures and similar applications. It is limited in that the temperature represents a single point on the machine or structure. However when used in conjunction with vibration data, point-of-use infrared data can be a valuable tool. 

Many physical and process constraints limit the cycle time, where cycle time was defined as the time to the maximum exotherm temperature. The obvious solution was to wind and heat the mold as fast and as hot as possible and to use the polymer formulation that cures most rapidly. Process constraints resulted in a maximum wind time of 3.8 minutes where wind time was defined as the time to wind the part plus the delay before the press. Process experiments revealed that inferior parts were produced if the part gelled before being pressed. Early gelation plus the 3.8 minute wind time constrained the maximum mold temperature. The last constraint was based upon reaction wave polymerization theory where part stress during the cure is minimized if the reaction waves are symmetric or in this case intersect in the center of the part (8). The epoxide to amine formulation was based upon satisfying physical properties constraints. This formulation was an molar equivalent amine to epoxide (A/E) ratio of 1.05. 

Another consideration when planning field fortification levels for the matrices is the lowest level for fortification. The low-level fortification samples should be set high enough above the limit of quantitation (LOQ) of the analyte so as to ensure that inadvertent field contamination does not add to and does not drive up the field recovery of the low-fortification samples. Setting the low field fortification level too low will lead to unacceptably high levels of the analyte in low field spike matrix samples if inadvertent aerial drift or pesticide transport occurs in and around where the field fortification samples are located. Such inadvertent aerial drift or transport is extremely hard to avoid since wind shifts and temperature inversions commonly occur during mixer-loader/re-entry exposure studies. 

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