The elevator is afraid of heat and will suffer from heat stroke. Please cool it down in time to reduce frequent failures

2018-06-14 00:00:00 雷曼电梯有限公司 Viewd 23

The reason why the temperature of the computer room is rising
The location of the building structure of the computer room itself

Most of the elevator machine rooms are on the top floor of the building, and some machine rooms are a special raised room on the top of the building. The roof and four walls of the machine room are external protective structures. The outer protective structure is what we call the outer wall as the saying goes. Its temperature is closely related to the temperature of the greenhouse, thus affecting the indoor temperature. In the hot summer weather, the outdoor temperature is high, and the temperature of the outer protective structure is also high, which leads to an increase in the indoor temperature of the equipment room. For a room, the larger the proportion of the outer protective structure in the entire maintenance structure, the greater the indoor temperature is affected by the outdoor temperature, so the location of the computer room determines that the computer room is greatly affected by the ambient temperature and solar radiation in summer. Room.              

 

1. Heat dissipated by the electrical system

The main heating components of the electrical system in the computer room are frequency converters, braking resistors, and motors. Among them, the frequency converter and the motor consume part of the electric energy due to their own efficiency and release it in the form of heat; the braking resistor consumes the electric energy generated by the elevator regeneration and releases it in the form of heat. Both parts of the heat are dissipated into the equipment room, causing the room temperature to rise.

(1) Inverter

The inverter consists of the main circuit and the control circuit. The main circuit is the power exchange part that provides voltage regulation and frequency regulation power to the motor, and consists of three parts: rectifier, smoothing circuit and inverter. Among them, the inverter element insulated gate bipolar transistor (IGBT) in the inverter is the main heat source of the inverter. The heating of the IGBT is mainly concentrated at the moment of opening and closing. Therefore, when the switching frequency is high, the heat generation of the inverter becomes larger. The inverter used in elevators needs to be started frequently, thereby releasing a lot of heat.

(2) Braking resistor

The braking resistor itself consumes energy and converts it into heat. For example, when the elevator goes up with no load, the counterweight is heavier than the car, the rotor of the main engine rotates, and the magnetic line of force of the cutting stator coil moves to generate self-generating power, so that the motor changes from the electric state to the power generation state. , and this regenerative energy will pass through the braking unit of the inverter, and finally be consumed by the braking resistor in the form of thermal energy. In the work, a unit once did a test, two elevators with the same operating frequency, one elevator uses an external power supply as power, the elevator regenerative power is consumed by the braking resistor, and the other elevator uses an external power supply and power saving The feedback device is the driving force, and the energy of the power-saving feedback device comes from the regenerative power generation of the elevator. After running for a period of time, the external power consumption is 35% less than the power consumption of the other one. It can be seen how large the heating value of the braking resistor is, which is about 1/3 of the electric energy consumption of the elevator.

(3) Motor

The operation of the motor itself has a certain power consumption. According to the heat formula Q=I²Rt of the motor, the heat released during the operation of the motor is proportional to the square of the current. The motor has the largest current in the process of starting and braking. As a means of vertical transportation, the elevator has to start and brake frequently, which will generate a lot of heat.

2. Impact on electrical control system

(1) High temperature can easily cause abnormality in the program of the microcomputer control board . Due to the material temperature characteristics of electronic devices, when the temperature is higher than the allowable temperature, the logic judgment of the electronic devices will be wrong, the microcomputer control board will be unstable, the elevator is prone to failure, and the normal operation will be affected (for example, the elevator suddenly stops and shuts down people during the normal operation of the elevator, and the elevator runs The door does not open or close the door, the elevator cannot change the speed when it runs to the door area, etc.), and it is not easy to find the fault point during maintenance.

(2) High temperature is easy to damage electronic components

(a) Inverter
The failure rate of the inverter increases exponentially with the increase of temperature, and the service life decreases exponentially with the increase of temperature. When the ambient temperature rises by 10°C, the service life of the inverter is halved.

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

(3) Braking resistor

When the ambient temperature is too high, it is easy for the braking resistor to dissipate heat for a long time. If the elevator runs frequently, the heat of the braking resistor will accumulate for many times, which will eventually lead to the damage of the braking resistor due to the high temperature, and even cause safety accidents such as fire.

(4) Other electronic components

When electronic components such as contactors, relays, and transformers are working, resistance losses are generated due to current passing through conductors and coils; in AC circuits, eddy current and hysteresis losses are generated in the magnet due to the action of alternating electromagnetic. Almost all of these losses are converted into heat energy, part of which is dissipated into the surrounding medium, and part of which remains in the appliance, increasing the temperature of the appliance. At this time, if the ambient temperature is too high, the heat dissipation of each electronic component will be poor. First, the reliability of the electronic component will be greatly reduced; second, the service life of the electronic component will be reduced, and even the electronic component will be damaged. Statistics show that the reliability of electronic components decreases by 10% when the temperature of electronic components rises by 2°C.  

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

3. Effects on mechanical systems

The mechanical system of the elevator machine room is mainly the traction machine, which is usually composed of a motor, a brake, a reduction box, a traction sheave, a guide wheel, a frame, and a cranking handwheel. (Source WeChat public account: Elevator)
(1) Influence on the traction motor
When When the ambient temperature exceeds the allowable temperature of the machine room, it will seriously affect the heat dissipation of the traction motor. Due to the frequent starting and braking of the motor, the motor itself will release a lot of heat, and the high temperature of the machine room cannot be removed in time, so the motor continues to run in a high temperature environment. , it is easy to burn out the coil and damage the motor. Although the structural design of the motor, careful consideration has been made to strengthen the heat dissipation of the stator core. For example: some products are designed to be supported by end caps, eliminating the need for traditional machine bases, making the iron core an open structure, and enhancing the cooling effect; strengthening the arrangement of the circumferential ventilation passages of the stator and rotor iron cores; increasing the ventilation volume design of the hood holes, etc. , but the motor of this structure is used less. Most of them adopt an attached cooling fan, which is controlled by a thermal switch set on the surface of the stator core. When the surface temperature of the iron core reaches about 60°C, the thermal switch will act, and the fan will be turned on to force ventilation and cooling of the traction motor. (Source WeChat public account: Elevator) Forced cooling In the case of high temperature in the machine room, the cooling effect is not obvious. Considering that when forced cooling fails and cannot cool down, the temperature of the motor will continue to rise. Some motor products have thermistors embedded in each phase winding. When the temperature of the motor rises to 155°C, the resistance of the internal thermistor increases sharply, and the thermal protection relay of the external circuit is controlled to act. The control circuit forces the elevator to stop and open the door at the nearest landing at a speed change, until the motor cools down before restarting. Start running. Although this method can play a role in protecting the motor, the high temperature weather in summer is long and frequent stop protection occurs, which seriously affects the normal operation and use of the elevator.

(2) Influence on the reducer

The reduction box is composed of a worm gear and a worm. The worm is generally made of materials with high hardness and rigidity. At present, most of them are made of nickel-chromium alloy steel or silicon-manganese alloy steel, and are 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 from phosphor bronze, tin bronze or copper-tin-nickel alloy with low friction coefficient. Since the thermal expansion coefficients of various materials are different, and the thermal expansion coefficient of the worm gear is about 1/2 of the thermal expansion coefficient of the worm, when the temperature of the machine room is higher than 40 ℃, the heat in the air and the heat generated by the rotation and friction of the various parts in the reduction box , the two together, the temperature in the reduction box will be higher, and the continuous high temperature will cause the thermal expansion of the parts, which will destroy the production accuracy of the worm gear and worm in the reduction box, and reduce the axial clearance of the turbine shaft and the worm shaft. Small, the meshing surface increases, which increases the frictional force of the friction surface and accelerates the wear. In severe cases, it will affect the comfort of elevator operation, and will also produce abnormal noise and damage the worm gear (for example: when you take the elevator, you will hear the elevator machine room. There is a rumbling sound, and there will be abnormal vibration in the car, etc.). At the same time, the continuous high temperature in the reduction box will also reduce the viscosity of the lubricating oil, which is not conducive to the formation of the lubricating oil film, and will also accelerate the oxidation of the lubricating oil, which will affect the lubricating effect of the worm gear and increase the wear of the worm gear.


 

 

How to control the temperature of the computer room

building structure

The elevator machine room is treated with heat preservation of the maintenance structure to reduce the influence of the outdoor temperature on the indoor equipment in the high temperature weather in summer.

(1) Install ventilation and cooling equipment

In the state of natural ventilation, to install ventilation equipment to meet the temperature requirements of the equipment room, it is necessary to install air conditioners. When installing ventilation equipment (such as exhaust fans), it should correspond to the ventilation openings (such as shutters) in the equipment room, so that air convection is generated, so as to improve the ambient temperature of the equipment room.

(2) Adopt energy-saving device

The thermal energy of the braking resistor in the control cabinet is converted into electrical energy and stored in the battery or fed back to the power grid, which can not only eliminate the heat source, but also play a role in energy saving. In the elevator operation, the elevator inevitably has a power generation process. When the elevator goes up with no load and goes down with rated load, the motor rotor is dragged by external force or maintained by the inertia of the load itself, so that the actual speed of the motor is greater than the synchronous output of the inverter. At this time, the motor is in the power generation state, and 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's normal work. Usually, the way to deal with this part of the energy is to increase the braking unit or braking resistor, and this part of the energy is consumed in the resistor as heat energy and wasted. The use of energy-saving devices can completely replace the braking unit and braking resistor, and this part of the energy can be fed back 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 grid voltage of the inverter, and then inverts the DC voltage of the DC link in the inverter into an AC voltage with the same frequency and phase as the grid voltage through the processor and inverter. After the link, it is connected to the AC grid, so as to achieve the purpose of energy feedback to the grid.

User units and maintenance units should arrange full-time personnel to strengthen management

The maintenance unit should regularly check whether the cooling equipment is working properly, and regularly check the operation of heat sources (such as frequency converters, braking resistors, and motors). For units that use multiple elevators, they should operate alternately in high temperature weather in summer to avoid using only one elevator for convenience or other reasons, increasing the operating burden of elevators in high temperature weather. In addition, the user should equip each elevator machine room with a fire extinguisher.
Conclusion: The continuous improvement of the intelligence of the elevator control system cannot completely eliminate elevator failures. The trend of frequent failures due to the ageing of elevators in use will not change. . However, through the discussion and analysis of the building structure, electrical control system and mechanical system of the elevator machine room, and taking targeted measures to effectively control each link, it can ensure that the temperature of the elevator machine room is within the normal range in high temperature weather in summer, and ultimately eliminate or Reduce various faults caused by high temperature, ensure that the elevator operates in a safe, stable and reliable environment, and better serve users.