Jan 29, 2021
UPS petrochemical industry application program
1 The necessity of UPS configuration for production equipment in petrochemical industry
Production in the petrochemical industry has the characteristics of high temperature, high pressure, flammability, and explosiveness. If the control instruments of important devices suddenly lose power, it may cause personal injury, major environmental pollution and large economic losses. SH/T3082-2003 "Petrochemical Instrument Power Supply Design Specification" clearly stipulates: "The electrical load of the instrument and control system is a particularly important load in the first class according to the provisions of SH3038 "Petrochemical Enterprise Production Equipment Power Design Specification". This type of load When the power supply is interrupted, in order to ensure safe shutdown and handle accidents, prevent equipment damage and personal injury accidents, and cause major economic losses, UPS must be installed."
The first level load includes:
Safety Instrumented (Interlocking) System (SIS);
⑵ Distributed control system (DCS) and related field instruments and control systems;
⑶ The key programmable logic controller (PLC) and related instruments provided by the equipment package manufacturer;
⑷ Instruments and automatic control systems for petrochemical production equipment, important common engineering systems and auxiliary production equipment;
⑸ Integrated compressor/turbine control system (ITCC) and safety instruments provided by key compressor and pump unit equipment packages;
⑹ Fire and combustible gas and toxic gas detection system (FGS);
⑺ Important online analysis instruments related to device operation and safety.
2 Sinopec Group's requirements for UPS system
Because there is no uniform configuration specification, enterprises and different projects in various regions have adopted multiple UPS configuration schemes. Most of the schemes are not standardized, resulting in frequent production shutdown accidents due to the interruption of the instrument power supply due to UPS system failure. Therefore, in 2005, the group company issued the "Technical Management Regulations for the Power Distribution System of Process Control Instruments for Production Equipment (Interim)", and in 2006 issued the IN212-2006 "Instrument Power Supply Design Regulations". The following requirements are put forward for the UPS power distribution system:
The power supply configuration schemes are generally: two power supplies, three power supplies, and inverter power supplies. The inverter power supply scheme is only applicable to thermal power stations and substations;
After the system is under normal operation of the load, it can perform UPS offline maintenance and regular maintenance of the battery;
The switching device of the power supply system should be able to realize disturbance-free switching;
The DC feed-out loop of the low-voltage bus bar needs to be equipped with isolation and voltage regulator;
The control instrument with two-way power supply should have the conditions for two non-synchronous power frequency AC power supplies to work at the same time.
Requirements for UPS:
When the online UPS is selected, when the power quality meets the UPS output standard, the inverter runs in the hot standby state, and its wiring is simple and reliable;
When the UPS capacity is less than or equal to 40kVA, single-phase output should be adopted; when >40kVA, three-phase output should be adopted. When using three-phase output, the UPS must have the ability to work normally in the short-term 100% imbalance of each phase;
Using stand-alone operation mode;
Using sealed valve-regulated lead-acid batteries, the standby time is generally (15~30) min;
The UPS capacity is configured at 1.5 times of the newly built system.
3 UPS system scheme design
3.1 System architecture
A typical two-power UPS architecture in the petrochemical industry consists of two power supplies, an isolation transformer, and a UPS. UPS adopts dual power circuit input, UPS main power supply is provided by power supply 1, UPS bypass power supply is provided by power supply 2. At the same time, UPS is set up with an offline maintenance bypass, allowing the system to still work normally when the UPS is repaired or replaced. At the same time, the load in the DCS system is divided into two levels, namely general load and important load. The important load (first-level load) is directly supplied by the UPS system, and the general load (third-level load) is supplied by the power supply 2 through the isolation transformer.
⑴ UPS working principle
UPS consists of rectifier, inverter, static bypass, manual maintenance bypass, and battery pack. When the mains power is normal, the UPS rectifies the AC power of the main circuit into DC power to charge the battery. At the same time, the inverter re-inverts the DC power to high-precision AC power with the same frequency and phase as the standby power supply to supply power to the load. When the mains power is abnormal or interrupted, the battery supplies power to the inverter, and outputs high-precision AC power to provide load work requirements.
⑵ Principle of isolation transformer
In the scheme, an isolation transformer is installed at the back end of the mains power supply 2, the input terminal adopts the delta connection method, the neutral wire is not introduced, and the output terminal adopts the Y connection method. Realize input and output neutral line isolation, reduce interference.
4 UPS selection
4.1 Basic parameter selection
After having a suitable system architecture, a suitable UPS must be selected according to the system architecture. According to the file requirements of the group company, UPS meets at least the following conditions:
Input power quality index:
Input voltage: three-phase 380V±15% or single-phase 220V±15%;
Input frequency: 50Hz±2.5Hz.
Output power quality index:
Output voltage: 220V±5%;
Output frequency: 50Hz±0.5Hz;
Output waveform distortion rate: less than 5%.
The instantaneous power-off time of the output power should be less than or equal to 20ms.
The instantaneous output voltage drop is less than 10%.
Output harmonic distortion rate: THD<3%.
The above parameters are very easy to implement for the current UPS technology.
At present, some UPS can meet the following technical specifications:
Input power quality index:
Input voltage: three-phase 380V±25%.
Input frequency: 50Hz±5Hz.
Output power quality index:
Output voltage: 220V±1%.
Output frequency: 50Hz±0.1Hz.
Output waveform distortion rate: less than 3%.
The instantaneous power-off time of the output power should be 0ms.
The instantaneous output voltage drop is less than 5%.
Output harmonic distortion rate: THD<3%.
When choosing a UPS, the larger the input range, the better. A UPS with a wide input voltage range can better adapt to the complex grid environment of the enterprise and reduce the battery discharge times of the UPS. The higher the accuracy of output range selection, the better. At the same time, the output voltage transient time must be considered. The more sophisticated the instrument, the short transient may cause equipment malfunction or data error, which is a fatal danger. Therefore, UPS should choose a model with high output accuracy and zero instantaneous interruption.
4.2 Other feature selection
At present, the concept of energy conservation and emission reduction, and green environmental protection are increasingly valued in various domestic industries. As a large energy consumer, the petrochemical industry is particularly important to shoulder the task of energy conservation and emission reduction. Due to the characteristics of the industry, the petrochemical industry is currently focusing more on power frequency machines when choosing UPS, but the structure of the rectifier and inverter during power frequency operation determines that the efficiency of the UPS is low and the power factor is low. , A lot of harmonics will be generated when working at the same time. Therefore, when choosing a UPS, it is advisable to consider selecting a UPS host with high efficiency and supporting ECO mode. At the same time, harmonic suppression measures should be considered.
4.2.1 Introduction to UPS ECO Operation Mode
In the "Technical Management Regulations for Power Distribution System of Production Equipment Process Control Instrumentation (Interim)" of the Petrochemical Group Company, it is clearly mentioned: "When the quality of the power grid meets the UPS output standard, its inverter runs in a hot standby state." The hot standby state referred to here refers to the economic operation mode (ECO) of the UPS. That is, when the mains power is normal or meets the set conditions, the mains power is directly supplied. At this time, the inverter works, but the inverter static switch is not turned on and is in a hot backup state; when the mains power is abnormal or exceeds the preset range, the UPS The inverter static switch is turned on, and the inverter supplies power to the load. When adopting ECO mode, the rectifier and inverter consume almost no energy, and the whole machine basically has only the power consumption of the fan. Therefore, the efficiency of the whole machine can be increased from about 93% to over 97.5%. According to a 100kVA UPS calculation, it can save nearly 25,000 kilowatt-hours of electricity a year, and based on the annual life expectancy, it can save hundreds of thousands of electricity bills, which is equivalent to the direct purchase amount of several UPSs.
It should be noted that the traditional ECO mode control uses an asynchronous switching method. When the phase difference or transient voltage difference between the bypass voltage and the inverter output voltage is too large, the circulating current may be too large at the moment of the switching operation. Causes accidents, such as burning the SCR of the static bypass or the IGBT and drive module in the inverter; or the switching time is too long during the switching process. According to actual load characteristics and with SCR forced commutation control, design the best conversion method. When the UPS phase locks and produces a phase difference, it will immediately switch to the inverter for power supply to avoid the phenomenon of no phase lock.
4.2.2 Power factor and harmonic improvement measures
When the UPS is working, the input must be rectified. The petrochemical industry generally uses 6-pulse or 12-pulse rectifier UPS. When it works, it will reduce the input power factor and produce larger current harmonics. At the same time, the power grid environment of petrochemical plants and UPS peripheral equipment are generally precision instruments, which are more sensitive to current harmonic interference, and the harmonics are large, which directly affects the accuracy of equipment sampling, resulting in poor equipment control accuracy, and affecting product quality and production safety. In addition, the existence of harmonics will increase the burden on the company in terms of transformers, distribution capacity, and wiring diameter. Therefore, when choosing a UPS, it is necessary to consider the corresponding power factor and harmonic improvement measures. The current mainstream UPS improvements mainly include phase shifting, passive filters, active filters, and hybrid filters. Among them, the phase shift means that on the basis of the 6-pulse rectifier, adding a phase-shifting transformer and then adding a 6-pulse rectifier can suppress harmonics.