Power of a motor given as in a producers specification is actual for work without breaks by nominal power supply and frequency in temperatire of environment maximum 40°C at heigth 1000m. In case of different environment conditions, the power of motor should be changed according to data in the table.
If the temperature and heigth vary at the same time, proper values should be multiplicated by values given in % in the in table.
Temperature of environment °C<30° power % = 106
Temperature of environment °C 40° power % = 100
Temperature of environment °C 45° power % = 97
Temperature of environment °C 50° power % = 93
Temperature of environment °C 55° power % = 90
Temperature of environment °C 60° power % = 87
Heigth <1000 : power % = 100
Heigth 1500 : power % = 97
Heigth 2000 : power % = 93
Heigth 2500 : power % = 90
Heigth 3000 : power % = 87
Heigth 4000 : power % = 79
Simultaneously with changes of power are changing features like Ma/Mn.
If power will decrease more than 15% then a special winding should be used.
Usually motors are equipped with F Class insulation, for which standards let for 105oK temperature increase (because of overload). In outside environment if temperatutr is not higher than 40oC and heigth is 1000m
Impregnation is made of high quality resin – Class H (whole 180oC). Due to this winding is resistant against moisture and high temperature.
Wires made of copper, Class H insulation are covered with polyester enamel, that increases more the termal winding safety
Caution: Motors can incessantly work even if voltage differs from the nominal by 5%, but the frequency must be the same as nominal.
Technical data characterize relationship between Ia/In, Ma/Mn i Mmax/Mn for direct start-up at nominal voltage.
For the star-delta start-up this relationships come down about 30%.
Direct start-up:
It is used if there’s no limits for power supply and the machine tolerates without damages big amount of steam during start-up.
His kind of start-up is often used with machines which are started-up with full duty (load) and for which moment of force is stable
but the speed varies (conveyor belts, lifts)
Star-delta start-up:
This kind of start-up can be used when moment of force is 50% smaller than nominal motor’s power. It is used usually with centrifugal machines (fans, pumps).
Warmth produced at start-up is independent on used system only in case of a little moment of force, otherwise during star-delta start-up bigger amount of warmth is produced and it results in bigger overheating than at direct start-up.
During frequent start-ups or high inertia moment of the load the thermal protection of control meters is often not sufficient. In cases like this one the machine can be equipped with motors with thermal protection.
The thermoprotecotor is placed in winding according to one of following systems:
Thermoprotector with bimetal disc
When winding’s temperature reaches the same temperature as excitation temperature of bimetal transmitter, its contact (which is usually closed)
opens and directly breaks coil of control meter, what results in its opening.
Thermoprotecotor with thermistor (PTC)
When excitation temperature grows then inner resistance suddenly increases. It results in break of meter coil and its opening. It happens by agency of “detaching device” – we don’t have it our offer.
Thermal protection for motors is useful in following cases
Exciting temperature of thermoprotectors depends on kind of motor insulation:
155oC for „F” Class, 180°C for „H” Class.