Requirements for marine propulsion motors
The requirements for the propulsion motor are not only determined by the characteristics of the marine propulsion motor, but also the environmental conditions such as seawater, salt spray, mold, etc., and the tactical and technical conditions such as the influence of tilt, sway and impact, etc. when the ship is working, and also consider the requirements of the cabin layout, external structure size, weight and other requirements.
The basic requirements for a propulsion motor are as follows:
1. High reliability. The requirement for high motor reliability is a comprehensive concept that determines many structural features of the motor. The high reliability of the motor can usually be understood as follows:
(1) The motor can work uninterrupted for a long time, and only needs to stop working in a short time during maintenance, that is, to replace the parts that need to be repaired, such as the brush of the DC propulsion motor, the power module of the mechatronic propulsion motor, and the bearing lubricating oil, and it will not stop working for a long time when the dust on the motor is removed;
(2) The propulsion motor is installed on the ship, requiring all the most important structural components to be easily maintained regularly;
(3) Moisture resistance and water resistance of winding insulation. Under the action of normal marine air humidity, the motor can still maintain good insulation performance. Even if the motor immersed in seawater is washed with fresh water after the seawater is discharged from the tank, and after short-term baking and drying, it can still work for a short period of time;
(4) Mechanical strength of the motor. It has the ability to withstand the mechanical stress generated during normal operation and when the ship performs tasks, and can withstand large shocks and vibrations;
(5) Ensure that the motor can work reliably under heeling, pitching and rolling;
(6) The independence of the motor from the auxiliary machinery, that is, within a limited time interval, the motor does not lose its ability to work independently and vitality due to the abnormality of auxiliary machinery (such as fans, oil pumps for bearing oil and other auxiliary machinery);
(7) Ensure the safe operation of the motor cooling system.
2. It is best to use forced ventilation for the propulsion motor to reduce the volume and weight and avoid overheating when the ship is braking or reversing. Water cooling can also be used for motors with excessive power.
3. Depending on the conditions of the ship, either a separate ventilation system or a general ventilation system can be used, but it is better to use a separate ventilation system.
4. Motors with forced ventilation should be able to withstand low load operation without forced ventilation.
5. In order to prevent the internal condensation of water after the motor is stopped, and to improve the insulation of the motor, an electric heater should be installed inside the motor to keep the temperature in the motor 2~3°C higher than the temperature of the surrounding medium. For this purpose it is also permissible to use the field winding of the electric motor as a heater.
6. The insulation resistance of the propulsion motor, before and after the withstand voltage test, should be corrected to the insulation resistance value at 25°C (corrected by doubling the insulation resistance for every 15°C decrease in temperature), which should not be lower than the following values :
Field winding (B, F, H class insulation): 50MΩ;
Armature circuit (B, F, H class insulation): 25MΩ;
Electric heater: 25MΩ;
7. The motor should be able to withstand the test of overspeed operation. The motor should be able to withstand 125% of the rated speed and run at no-load overspeed for 5 minutes without damage or harmful deformation. When 125% of the rated speed is less than 120% of the maximum working speed, the test should be carried out at 120% of the maximum working speed.
8. REVERSE. For reversible motors, they should be able to operate normally under the reversing conditions specified in the product technical specifications.
9. Effective measures should be taken for the motor to prevent the shaft current from harming the bearing. Generally, the peak-to-peak value of the shaft voltage should not exceed 1V. Higher shaft voltages are permissible if the bearings are electrically insulated and the shaft current circuit is disconnected.
When taking bearing insulation measures, at least the non-drive end bearing of the motor should be electrically insulated, and the metal oil pipes, metal cooling pipes and other conductive connectors connected to the insulated bearings should be electrically insulated.
10. Bearings and lubrication of the propulsion motor. Within the allowable inclination range of the motor, it should be ensured that the bearings can be well lubricated and work normally. Lubricating oil (grease) cannot leak or overflow from the bearing.
11. The propulsion motor should use sliding bearings as much as possible.
12. When the propulsion motor adopts rolling bearings, it should be considered:
(1) The rolling bearings can be replaced smoothly on the ship;
(2) Set the bearing oiling cup (hole) and set the oil discharge channel; correctly select the lubricating oil to ensure the bearing is well lubricated; 3) The service life of the rolling bearing should be no less than 20000h.
13. When the propulsion motor adopts sliding bearing, it should be considered;
(1) Bearing temperature measurement, oil level observation and over-temperature alarm devices should be installed in obvious parts;
(2) If pressure lubrication is used, sufficient oil pressure or oil level must be maintained to ensure continuous oil. If splash-type sliding bearings are used, bearing oiling cups (holes) should be provided to replenish lubricating oil;
(3) The propulsion motor with sliding bearing must be equipped with a rotor lifting device to facilitate the replacement of bearing bushes.
14. The diameter of the rotor of the propulsion motor should be as small as possible to reduce the moment of inertia, reduce the transition time during reversal or speed regulation, and improve maneuverability.
15. Where necessary, overspeed protection of the propulsion motor shall be installed to prevent exceeding the speed limit for which the motor is designed under maneuvering and fault conditions.
16. In the specified operating mode and emergency control mode, the regenerative power shall not cause any alarm of the propulsion system.
17. The propulsion motor excitation circuit protection shall not cause an open circuit unless the armature circuit is simultaneously disconnected.
18. For motors with one field winding or two armature windings, the failure of one armature circuit shall not cause an open circuit of the field circuit.
19. There should be a device to detect the internal temperature of the motor and the lubrication of the bearing, and the signal should be reflected on the control panel.
20. For propulsion motors powered by static frequency converters, the influence of harmonics in the power supply should be considered in the design.
21. The export of heat from the motor in the cabin. The cabin space of the ship is very limited, and the heat discharged by the large-capacity propulsion motor has a great impact on the living conditions on the ship and the normal working conditions of the maintenance personnel. Therefore, the heat dissipation of the motor in the cabin is very important. Marine propulsion motors generally use a closed circulation ventilation cooling system with a water-cooled air cooler or a water-cooled system.
22. Meet the requirements for marine use. Marine propulsion motors must be moisture-proof, mildew-proof and salt-fog proof.