Summer is hot! The elevator will also heatstroke, and these

1 Reasons for the temperature rise in the equipment room


1.1 The location of the building structure of the equipment room itself

    Most of the elevator rooms are on the top floor of the building. Some of the machine rooms are a raised room on the roof of the building. The roof and four walls of the machine room are all external structures. The external protective structure is also the external wall that we say as the saying goes. Its temperature is closely related to the greenhouse temperature, which affects the indoor temperature.


     In the high temperature weather in summer, the outdoor temperature is high, and the temperature of the external protection structure is also high, which leads to an increase in the indoor temperature of the machine room. For a room, the proportion of the outer guard structure occupying the entire maintenance structure is larger, and the indoor temperature is more affected by the outdoor temperature. Therefore, the position of the machine room determines that the machine room is affected by the ambient temperature and the sun exposure during the summer. room.


1.2 Heat emitted by the electrical system

    The main heating components of the electrical system of the equipment room are inverters, braking resistors and electric motors. Among them, the inverter and the motor consume a part of the electric energy and release it in the form of heat due to its own efficiency. The braking resistor is used to dissipate the electric energy generated by the elevator regenerative power and release it in the form of heat. Both of these heats are dissipated into the machine room, causing an increase in room temperature.


(1) Inverter

    The frequency converter consists of a main circuit and a control circuit. The main circuit is a power exchange part that supplies a voltage-regulating and frequency-modulated power supply to the motor, and is composed of a rectifier, a smoothing circuit and an inverter. Among them, the inverter component insulated gate bipolar transistor (IGBT) in the inverter is the most important heat source of the inverter. The heat generated by the IGBT is mainly concentrated at the moment of opening and closing. Therefore, when the switching frequency is high, the heat generated by the inverter becomes large. The frequency converter for the elevator needs to be started frequently, thus releasing a large amount of heat.


(2) Braking resistor

    The braking resistor itself is the energy consumed to be converted into heat. For example, when the elevator is idling up, the counterweight is heavier than the car, the rotor of the main engine rotates, and the magnetic field of the stator coil is cut to generate self-generation, so that the motor changes from the electric state to the power generation state. This regenerative energy is passed through the braking unit of the frequency converter and is eventually consumed by the braking resistor in thermal energy. In the past, there was a unit that did an experiment. Two elevators of the same frequency were used. One of the elevators used external power as the power, the elevator regenerative power was consumed by the braking resistor, and the other elevator used external power and power saving. The feedback device is powered, and the energy of the power-saving feedback device comes from the regenerative power generation of the elevator. After a period of operation, the external power consumption is 35% less than the other power consumption. It can be seen how much heat is generated by the braking resistor, which is about 1/3 of the elevator's power consumption.


(3) Motor

    The motor itself has a certain amount of power consumption. According to the motor's heat formula Q=I2Rt, the heat released during motor operation is proportional to the square of the current. The electric motor has the largest current during the starting and braking process, and the elevator, as a vertical transportation vehicle, frequently starts and brakes, and generates a large amount of heat.


2.1 Impact on electrical control systems


(1) High temperature is easy to cause abnormality of the microcomputer control board program

    The electronic device on the microcomputer control board or PLC is logically controlled by voltage and current comparison, and responds to external commands. Due to the material temperature characteristics of the electronic device, when the temperature is higher than the allowable temperature, the logic judgment of the electronic device may be wrong, the control panel of the microcomputer is unstable, the elevator is prone to failure, and the normal operation is affected (for example, the elevator is suddenly stopped during normal operation of the elevator, and the elevator is operated. If the door is not opened or closed, the elevator can not be changed to speed in the door area, and it is not easy to find the fault point when repairing.


(2) High temperature and easy damage to electronic components

(a) Inverter

    The fault rate of the inverter increases exponentially with the increase of temperature, and the service life decreases exponentially with the increase of temperature. The ambient temperature rises by 10 °C, and the service life of the inverter is halved.


    When the ambient temperature exceeds the allowable temperature, the parameter turn-on time and turn-off time of the inverter device in the inverter inverter circuit will change, resulting in one device being turned on during the alternation process, and the other device will be turned off in the future. Broken, causing "straight through" between the upper and lower devices of the same bridge arm, so that the part is in an instantaneous short-circuit state, the inverter is instantly damaged immediately, and the inverter cannot work normally. At the same time, the insulation performance of the inverter will be greatly reduced, which will easily lead to damage to the inverter and cause elevator failure.


(b) Braking resistor

    When the ambient temperature is too high, it is easy to make the braking resistor heat dissipation time too long. If the elevator runs frequently, the heat of the braking resistor accumulates many times, eventually causing the braking resistor temperature to be too high and damaged, and even causing fire and other safety accidents.


(c) Other electronic components

    When electronic components such as contactors, relays, and transformers work, resistance loss occurs due to current passing through the conductor and the coil; in the AC circuit, eddy current and hysteresis loss are generated in the magnet due to the action of alternating electromagnetic. Almost all of these losses are converted into heat, some of which is lost to the surrounding medium, and some of which are trapped in the appliance, causing the temperature of the appliance to rise. At this time, if the ambient temperature is too high, the heat dissipation of each electronic component is poor. First, the reliability of the electronic component is greatly reduced; second, the service life of the electronic component is reduced, and even the electronic component is damaged. Statistics show that for every 2 °C increase in temperature of electronic components, the reliability is reduced by 10%, and the lifetime at 50 °C is only 1/6 of the temperature rise of 25 °C.


    When the ambient temperature exceeds the allowable temperature of the equipment room, it will seriously affect the heat dissipation of the traction motor. Due to frequent starting and braking of the motor, the motor itself will release a large amount of heat, and the high temperature of the equipment room cannot be eliminated in time. The motor continues to be in a high temperature environment. Running, it is easy to burn the coil and damage the motor.


2.2 Impact on mechanical systems

    The mechanical system of the elevator machine room is mainly a traction machine. The traction machine is usually composed of an electric motor, a brake, a reduction gear box, a traction sheave, a guide wheel, a frame, a hand wheel and the like. (Source WeChat public number: elevator circle)


(1) Influence on traction motor

    When the ambient temperature exceeds the allowable temperature of the equipment room, it will seriously affect the heat dissipation of the traction motor. Due to frequent starting and braking of the motor, the motor itself will release a large amount of heat, and the high temperature of the equipment room cannot be eliminated in time. The motor continues to be in a high temperature environment. Running, it is easy to burn the coil and damage the motor. Although the structural design of the motor has been carefully considered in strengthening the heat dissipation of the stator core. For example, some products are designed to support the end cover, eliminating the traditional frame, making the iron core an open structure, enhancing the cooling effect; strengthening the arrangement of the circumferential air passages of the stator and rotor core; increasing the ventilation design of the windshield hole, etc. However, the motor of this structure is used less. Most of the attached cooling fans are controlled by a thermal switch located on the surface of the stator core. When the surface temperature of the iron core reaches about 60 ° C, the thermal switch operates, and the fan is turned on to forcibly ventilate and cool the traction motor. (Source WeChat public number: elevator circle)


    When the forced cooling is high in the machine room, the cooling effect is not obvious. Considering that forced cooling fails to cool down, the motor temperature will continue to rise. Some motor products have a thermistor embedded in each phase winding. When the temperature of the motor rises to 155 °C, the internal thermistor resistance increases sharply, and the external circuit thermal protection relay operates. The control circuit forces the elevator to stop at the nearest station, and the door can be opened until the motor is cooled. Start running. Although this method can protect the motor, the high temperature weather in the summer is long, and the parking protection is frequently seen, which seriously affects the normal operation and use of the elevator.


(2) Impact on the gearbox

    The reduction gearbox is composed of a worm gear and a worm. The worm is generally made of a material with high hardness and rigidity. At present, most of the nickel-chromium alloy steel or silicon-manganese alloy steel is used, and it is also forged with carbon steel with a carbon content of 0.4%-0.55%. The surface of the worm must be hardened by quenching or carburizing. The worm wheel rim is machined by a low friction coefficient phosphor bronze, tin bronze or copper tin nickel alloy. Since the thermal expansion coefficients of various materials are different, and the thermal expansion coefficient of the worm wheel is about 1/2 of the thermal expansion coefficient of the worm, when the temperature in the machine room is higher than 40 ° C, the heat in the air and the heat generated by the rotation and friction of the various components in the reduction gear box When the two are added together, the temperature inside the gearbox will be higher, and the continuous high temperature will cause thermal expansion of the components, thereby destroying the manufacturing precision of the worm gear in the reduction gearbox, and reducing the axial clearance of the turbine shaft and the worm shaft. Small, the meshing surface is increased, the frictional friction of the friction surface is increased, the wear is accelerated, and the comfort of the elevator operation is seriously affected, and the noise is also generated, and the worm gear is damaged (for example, the elevator machine room is heard when the elevator is taken) There is a rumbling sound, there will be abnormal vibrations in the car, etc.). At the same time, the continuous high temperature in the gearbox will also reduce the viscosity of the lubricating oil, which is not conducive to the formation of the lubricating oil film, and will accelerate the oxidation of the lubricating oil, affecting the lubricating effect of the worm gear and worm, and increase the wear of the worm gear.


3 How to control the temperature of the equipment room


3.1 Building structure

    The elevator machine room is used for maintenance structure insulation treatment to reduce the influence of outdoor temperature on indoor equipment in high temperature weather in summer. At the same time, it cannot ignore the insulation of maintenance structure and reduce the thickness of maintenance structure because it is equipment room.


3.2 Installation of ventilation and cooling equipment

    In the natural ventilation state, install ventilation equipment to meet the temperature requirements of the equipment room, and install air conditioners. When installing ventilation equipment (such as exhaust fans), it should correspond to the ventilation openings of the equipment room (such as blinds) to make the air convection, thus improving the temperature of the equipment room.


3.3 Adopt energy-saving devices

    Converting the thermal energy of the braking resistor in the control cabinet into electrical energy and storing it in the battery or feeding it back into the power grid can eliminate the heat source and save energy. In the elevator operation, the elevator will inevitably have the power generation process. When the elevator is no-load up and the load is descending, the motor rotor is driven by external force or the load's own inertia is maintained, so that the actual motor speed is greater than the inverter output synchronization. Rotating speed, when the motor is in the power generation state, the electric energy generated by the motor will be stored in the filter capacitor in the inverter. If this part of the electric energy is not consumed, the DC bus voltage will rise rapidly, affecting the inverter. normal work. The usual way to handle this part of the energy is to increase the braking unit or braking resistor, and this part of the energy is dissipated as heat energy is wasted.


    The energy-saving device can completely replace the braking unit and the braking resistor, and can return this part of the energy to the power grid to achieve the purpose of green, environmental protection and energy saving. The energy-saving device automatically detects the DC bus voltage and the grid voltage of the inverter, and inverts the DC voltage of the DC link in the inverter into an AC voltage of the same frequency as the grid voltage through the processor and the inverter, and filters the multiple noises. After the link, it is connected to the AC grid to achieve the purpose of energy return to the grid.


3.4 The use unit and maintenance unit should arrange full-time personnel to strengthen management

    Maintenance units should regularly check whether the cooling equipment is working properly, and regularly check the operation of the heat source (such as inverter, braking resistor, motor). For units with multiple elevators, in the hot weather in summer, they should be alternately operated to avoid using only one elevator for convenient ride or other reasons, increasing the running load of the elevator in hot weather. In addition, the use unit should be equipped with fire extinguishers for each elevator room.


4 Conclusion

    The increasing intelligence level of the elevator control system can not completely eliminate the elevator failure, and the trend of frequent failures of the elevators in use is not changed. However, through the discussion and analysis of the building structure, electrical control system and mechanical system of the elevator engine room, the targeted measures are taken to effectively control the various links, which can ensure that the temperature of the elevator room in the summer high temperature weather is within the normal range, and finally eliminate or Reduce various faults caused by high temperature, ensure the elevator operates in a safe, stable and reliable environment, and better serve the users.