Ensuring normal power supply under any circumstances is an important foundation of metallurgical industry. Therefore, in addition to the normal power supply of industrial power grid, UPS power supply system is also needed. UPS power supply is an important equipment to ensure the stability and continuity of power supply. Because of the high intelligence of its host, the energy storage equipment adopts maintenance-free batteries, and the maintenance and overhaul of the system are often ignored in operation. In fact, the quality of maintenance has a great influence on the life and failure rate of power supply. According to our specific situation and maintenance experience, this paper introduces the matters needing attention and daily maintenance requirements of UPS power supply.
Although the equipment model and system capacity of UPS power supply systems configured by various enterprises are different, their principles and main functions are basically the same. In the choice of UPS power supply type, all stations choose online. At this time, because the online UPS power supply system has zero-time switching for all kinds of power supplies, it can choose its own power supply time, which has the characteristics of voltage stabilization, frequency stabilization and purification.
When the UPS power supply system itself fails, it has the function of automatic bypass. When maintenance is needed, manual bypass can be used, so that maintenance and power supply do not affect each other. In terms of power supply selection, medium voltage power supply system is selected for medium and small bar production lines in Laigang.
Second, UPS power supply system
UPS power supply system consists of four parts: rectification, energy storage, conversion and switch control. The voltage stabilizing function of the system is usually completed by rectifier. The rectifier device adopts silicon controlled rectifier or high frequency switching rectifier, which has the function of controlling the output amplitude according to the change of external power supply, so that when the external power supply changes (the change should meet the requirements of the system), the rectified voltage with basically constant amplitude is output. The purification function is completed by the energy storage battery. Because the rectifier can't eliminate the interference of instantaneous pulse, there are still interference pulses in the rectified voltage. In addition to the function of storing DC direct energy, the energy storage battery is like connecting a large container capacitor to the rectifier, and its equivalent capacitance is proportional to the capacity of the energy storage battery. Because the voltage at both ends of the capacitor can't change suddenly, the smoothing characteristics of the capacitor are used to eliminate pulse interference and play a purification role, which is also called shielding interference. Frequency stabilization is completed by the frequency converter, which depends on the stability of the oscillation frequency of the frequency converter. In order to facilitate the daily operation and maintenance of UPS power supply system, the switching control of system working switch, automatic bypass switch after self-check failure of main engine and overhaul bypass switch are designed.
As shown in figure 1, when the grid voltage works normally, power is supplied to the load as shown in the figure, and the energy storage battery is charged at the same time; When there is a sudden power failure, the UPS power supply starts to work, and the energy storage battery worker provides the load with the power needed to maintain normal production (such as black body →); When the load is seriously overloaded due to production needs, the grid voltage is rectified and directly supplied to the load (as shown by the dotted line).
UPS power supply system is mainly divided into two parts, host and energy storage battery. The rated output power depends on the host part and the nature of the load, because UPS power supply has different driving capabilities for loads with different performances, and usually the load power should meet 70% of the rated power of UPS power supply. When the load power is determined, the capacity of the energy storage battery mainly depends on the length of its standby time, which varies according to the situation of each enterprise, and is mainly determined by the access time of the standby power supply, usually ranging from several minutes to several hours. Power failure is not allowed for small and medium bar production line in Laigang due to production needs. Therefore, UPS power supply system can start power supply by itself after detecting grid voltage interruption. With the slow discharge of energy storage battery, the capacity of energy storage battery will gradually decrease with time. Considering that there is still a certain margin when the capacity of the energy storage battery drops to 50% at the end of its life, the working time of the UPS power supply system in our factory is 2 hours when the energy storage battery is full, and the half capacity is 1 hour.
2. 1 working principle of power supply
2. 1. 1 AC DC conversion: AC power from the power grid is reduced by autotransformer, full-wave rectified, filtered into DC voltage, and supplied to inverter circuit. The AC DC input has a soft start circuit, which can avoid the impact on the power grid when starting.
2. 2. 2 DC- AC inverter circuit: High-power IGBT module full-bridge inverter circuit is adopted, with large power margin, extremely small output impedance in the output dynamic range and fast response characteristics. Due to the adoption of high frequency modulation current limiting technology and fast short circuit protection technology, the inverter can work safely and reliably regardless of power supply voltage transient, load shock or short circuit.
2.3.3 Control drive: Control drive is the core of complete machine function control. It not only provides detection, protection, synchronization and various switching and display driving signals, but also completes the control of SPWM sinusoidal pulse width modulation. Because of static and dynamic dual voltage feedback. The dynamic characteristics and stability of the inverter are greatly improved. The working principle block diagram of uninterruptible power supply is shown in Figure 2.
2.3 power supply workflow
When the commercial power is normally 380Vac, the DC main circuit has a DC voltage, which supplies the DC AC inverter with a stable 220Vac AC voltage, and at the same time, the commercial power charges the current. When the power supply voltage is under-voltage or suddenly cut off, the battery pack supplies power to the DC circuit through the isolating diode switch. There is no switching time from grid power supply to battery power supply. When the battery energy is about to run out, the uninterruptible power supply will give an audible and visual alarm, and stop the inverter to give an alarm at the lower limit of battery discharge. Uninterruptible power supply also has overload protection function. When it is overloaded (150% load), it will jump to the bypass state and automatically return when the load is normal. When a serious overload occurs (exceeding 200% of the rated load), the uninterruptible power supply immediately stops the inverter output and jumps to the bypass state, at which time the front air switch may also trip. After troubleshooting, just close the switch and restart the machine to start working again. In order to make the uninterruptible power supply work fully and avoid overload or underload operation, the load capacity of the power supply is calculated before starting. The design load capacity of 80% resistive load of FR-UK uninterruptible power supply (nominal rated power) is estimated by the following formula:
∑I = 1nπ≤P
Where p is the output capacity (VA) of the uninterruptible power supply and p is the volt-ampere of the ith load.
Power of each PLC: 220V*0.5= 1 10VA.
Power of each operating station: 220V*2A=440VA.
IBM PC client and server: 220v *1.5a = 330VA.
Then the total power:10 *110VA+4 * 440VA+11* 330VA = 6490VA.
6490VA/0.8=8 1 12VA
Therefore, it is more suitable to use 10KVA uninterrupted power supply in this bar production line.
Third, the use and maintenance of UPS power system
1, UPS power system is turned on and off.
1. 1 First startup
(1) Turn on in the following order: energy storage battery switch → automatic bypass switch → output switch is turned on in turn.
(2) Press the "On" button on the UPS startup panel, the UPS power supply system will start slowly, and the "Inverter" indicator light will light up. After a delay of 1 minute, the "bypass" light goes out, and the UPS switches to the inverter power supply to complete the startup.
After no-load operation for about 10 minutes, start the load in the starting order of load power from small to large.
1.2 daily boot
Just press the "On" button on the UPS panel, and after about 20 minutes, you can turn on the computer or other instruments for use. Usually, the power switch of the load equipment can only be turned on after the UPS starts to work stably (note: the manual maintenance switch is "OFF" when the UPS is running normally).
1.3 shutdown
Turn off the computer or other instruments first, let the UPS idle for 10 minutes, and then press the "off" button on the panel after the heat in standby is exhausted.
2. Matters needing attention in using UPS power supply system
UPS power supply system adopts maintenance-free storage battery because of its high intelligence, which brings a lot of convenience to use, but many aspects should be paid attention to during use to ensure safety.
(1)UPS power supply host does not require high ambient temperature, and can work normally at +5℃ ~ 40℃, but it requires indoor cleanliness and less dust, otherwise dust and humidity will cause the host to work in disorder. Energy storage batteries need higher temperature. The standard working temperature is 25℃, which should not exceed+15℃ ~+30℃ at ordinary times. If the temperature is too low, the capacity of the battery will decrease, and its capacity will decrease by 1% every time the temperature decreases. Its discharge capacity will increase with the increase of temperature, but its life will decrease. If it is used at high temperature for a long time, the battery life will be reduced by about half for every increase in temperature of 10℃.
(2) The parameters set in the host computer cannot be changed at will during use. Especially for the parameters of the battery pack, it will directly affect its service life, but with the change of environmental temperature, the floating charge voltage should be adjusted accordingly. Generally, based on 25℃, if the ambient temperature rises or falls 1℃, the floating charge voltage should increase 18mV (relative to 12V battery).
(3) When the UPS power supply system has no external power supply, the UPS power supply should not be started with load. All loads should be turned off first, and then the load should be turned on after the UPS power supply system is started. Because the instantaneous power supply of the load will impact the battery, the impact current of multiple loads and the required power supply current will cause the UPS power supply to overload instantly, which will damage the converter in serious cases.
(4) The power margin of UPS power supply system is not large according to the use requirements. In use, it is necessary to avoid adding high-power additional equipment at will, and it is not allowed to run at full load for a long time. However, the nature of work determines that UPS power supply system runs almost continuously. Increasing the high-power load, even if it works in a basically full-load state, will lead to the failure of the main engine, and in serious cases, it will damage the converter.
(5) The output voltage, waveform, frequency and amplitude of the self-contained generator should meet the requirements of UPS power supply for input voltage, and the power of the generator should be far greater than the rated power of UPS power supply for a long time, otherwise any condition is not met, which will lead to the abnormal operation or damage of UPS power supply.
(6) Due to the high voltage of the battery pack, there is a risk of electric shock. Therefore, when loading and unloading the conductive connecting pieces and output wires, safety protection should be carried out, and insulation measures should be taken for tools, especially output contacts.
(7) Whether in the floating charging working state or in the charging and discharging maintenance test state, it is necessary to ensure that the voltage and current meet the specified requirements. Excessive voltage or current may cause thermal runaway or water loss of the battery, and too small voltage or current may also cause it.
Lack of electricity will affect the service life of the battery, and the former has a greater impact.
(8) In any case, short circuit or deep discharge of the battery should be prevented, because the cycle life of the battery is related to the depth of discharge. The deeper the discharge depth, the shorter the cycle life. During capacity test or discharge maintenance, it is usually enough to discharge 30% ~ 50% of capacity.
(9) Avoid charging and discharging the battery with large current. Although large current can be accepted during charging, it should be avoided as far as possible in actual operation, otherwise it will cause the expansion and deformation of the battery plate, lead to the shedding of the active material of the plate and increase the internal resistance of the battery. The higher the temperature rise, the lower the capacity and the premature termination of life.
3, daily maintenance and repair
(1) Under the normal use of UPS power supply, there is little maintenance work for the host, mainly dust prevention and regular dust removal. Especially in dry areas, there are many dust particles in the air, and the wind in the machine will bring dust into the machine for deposition. When the air is humid, it will cause the control disorder of the main engine, which will lead to the abnormal work of the main engine and inaccurate alarm. A lot of dust will also cause poor heat dissipation of equipment. Generally, it should be thoroughly cleaned once every quarter. Secondly, during dust removal, check whether the connectors and joints are loose.
(2) Although maintenance-free batteries are used for energy storage batteries at present, this only saves the previous work of regular ratio measurement, proportioning and adding distilled water. However, the influence of external working conditions on the battery has not changed, and the influence of abnormal working conditions on the battery has not changed. This part of the maintenance and repair work is still very important. A lot of maintenance and repair work of UPS power supply system is mainly in the battery part.
A the energy storage battery works in a floating state. In this case, it should be discharged at least once a year. Before discharging, the battery pack should be charged evenly to achieve the balance of the whole battery pack. It is necessary to know the backward batteries in the battery pack before discharging. If one of the batteries reaches the discharge termination voltage during discharge, it should stop discharging and continue discharging after eliminating the backward battery.
B. To check the discharge, we should not first pursue the percentage of discharge capacity, but pay attention to finding and handling backward batteries, and then do the inspection and discharge experiment after handling backward batteries. This can prevent accidents and prevent the reverse battery from deteriorating into a reverse battery during discharge.
C at ordinary times, each battery pack should have at least 8 labeled batteries as a reference to understand the working condition of the whole battery pack, and the labeled batteries should be measured and recorded regularly.
D. Items that need to be checked frequently in daily maintenance include: cleaning and detecting the voltage and temperature at both ends of the battery; Whether there is looseness and corrosion at the joint, and detect the pressure drop of the connecting strip; Whether the battery appearance is intact, whether there is shell deformation and leakage; Whether there is acid mist escaping around the pole and safety valve; Whether the host equipment is normal.
E. maintaining maintenance-free batteries is not nonsense. From the standpoint of generalized maintenance, we should make the operation and daily management thoughtful, meticulous and standardized to ensure that the equipment (including the host equipment) maintains a good running state, thus prolonging the service life; Ensure that the DC bus always maintains qualified voltage and battery discharge capacity; Ensure the safety and reliability of battery operation and personnel. This is the purpose of battery maintenance, and it is also the content and rules contained in the battery operation regulations.
(3) When the UPS battery system fails, the reason should be found out first, and the load and UPS power supply system should be distinguished; Is it a mainframe or a battery pack? Although the UPS host has the function of fault self-checking, it does the opposite and it is very convenient to replace accessories. However, repairing the fault point still needs a lot of analysis and testing work. In addition, if the self-test part fails, the displayed fault content may be wrong.
(4) If the main engine fails, the fuse blows or the equipment burns out, the reason must be found out, and it can only be restarted after troubleshooting, otherwise the same failure will occur one after another.
(5) When batteries with reverse voltage, large voltage drop, large pressure difference and acid mist leakage are found in the battery pack, corresponding methods should be taken to restore and repair them in time. Those that cannot be restored and repaired should be replaced, but batteries with different capacities, different performances and different manufacturers cannot be connected together, otherwise it may bring adverse effects to the whole battery pack. Battery packs that have passed the service life should be replaced in time to avoid affecting the host.
Four. Concluding remarks
Even the best equipment will have all kinds of faults, but good maintenance can prolong the life and reduce the occurrence of faults, which is the same as people's life and death. Don't neglect the maintenance work that should be carried out because of high intelligence and maintenance-free. Prevention is an important guarantee for safe operation at any time.