Measurement and control system of the hottest 300k

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After the maintenance of 300kW Cummins diesel generator set, its performance must be tested. The test process is generally to adjust the load of the unit, make it operate stably at different power points for a period of time, and test whether the unit parameters are abnormal in real time. The load of diesel generator set is usually simulated in the following ways: first, water resistance; Second, for resistance; Third, the power of the diesel generator set is fed back to the power grid in parallel. Compared with using dry resistance as load, using water resistance as load has the following advantages: low price and continuous load regulation. However, due to the rise of water temperature during the test, the load changes greatly. In order to maintain the stability of the load, it is necessary to adjust the draught of the polar plate or supplement cold water in time to maintain the constant water temperature. Therefore, overflow and charging devices must be provided. The dry resistance is relatively stable in load, but it is expensive. Although the third method can save energy, it is limited by the power license. If the quasi synchronous method is adopted, the voltage amplitude, frequency and phase of the electric side and the unit to be merged need to be detected, and some protective devices such as reverse power need to be added. The system is relatively complex. Therefore, using water resistance is an economic and reasonable scheme

using water as the load is to insert three-phase plates vertically at an interval of 120 ° in a circular container containing water, as shown in Figure 1. In order to ensure uniform three-phase load, each group of plates is divided into three phases a, B and C, and the spacing between plates is d. The test shows that the size of the load is directly proportional to the surface area s of the plate and the conductivity of water, and inversely proportional to the distance d between the plates. In order to adjust the size of the load, an AC asynchronous machine for lifting the plate is set on the top of the circular container. When the asynchronous machine rotates forward, the plate drops and the power increases; When reversing, the plate rises and the power decreases. Fuji frequency converter fvr022g7s-2 is used for speed control of asynchronous machine

1. Measurement and control system

Figure 2 is the schematic diagram of the measurement and control system. Pc586 system microcomputer is used as the main controller, programmed with C language, 32-channel 12 bit a/d plus a 12 bit d/a board, which is used to sample analog quantities and control the frequency of frequency converter; Timing/counter board, used to measure frequency and set start sampling time; The 16 channel input/output i/o board mainly controls the start and stop of the diesel engine, idle/rated speed operation, loading, load reduction, on/off alarm of the load circuit breaker, alarm, as well as the monitoring of the state of the generator winding temperature being too high and the upper and lower limits of the pole plate displacement; They all adopt ISA bus standard

the main parameters to be tested are: three-phase voltage rating 400/230v, three-phase current rating 580A, power rating 300kW, excitation ≤ 30V, oil temperature 82~107 ℃, water temperature ℃, oil pressure 3.53~4.97ks/cm2 (1kvcd=9.807kpa), inlet air pressure ≤ 3kg/cd, exhaust temperature ≤ 800 ℃, ambient temperature 0~50 ℃, and diesel engine speed (1500 ± 15) r/min

the microcomputer samples the analog quantity in sequence according to the above order, processes and archives the detected data, analyzes the results, and diagnoses the faults in real time. This paper mainly introduces its measurement and control part

1.1 times number detection and conversion circuit

in order to measure the voltage waveform, the tracking AC voltage sensor is used to sample the phase voltage of the generator, and the current signal is changed from the primary side current to 5A by CT. The range refers to the current of compounds with a relative component of more than 10000 and repeated structural units, which are mainly composed of many atoms or atomic groups combined by covalent bonds, which is sampled through a small resistance, and then sent through the precision detection circuit and amplification circuit ν D board, as shown in Figure 3. The speed of the diesel engine is calculated by frequency measurement. Other signals are connected to the input channel of a/d board after the transmitter cuilixin changes into appropriate DC after investigating the national and global markets

1.2 synchronization signal

a-phase voltage sensor signal turns into a square wave as shown in Figure 4 after passing through the zero comparator, and is connected to the PC interrupt controller irq10 after passing through the optical barrier. Its rising edge applies for interrupt to the PC as the system synchronization signal. In the system, it has the following functions: ① it provides a reference point of reference, which makes the sampled voltage waveform display stable; ② When used together with 8253 on the timing/counting board, it is easy to measure the voltage and frequency; ③ After introducing the synchronous signal, it is convenient to measure the analog quantity with n (n ≥ 1) whole cycles, and the influence of interference signal can be effectively eliminated

1.3 analog sampling

8253 channel 2 on the timing/counting board works in mode 0 to set the sampling period. When the rising edge of the synchronization signal causes an interrupt for the first time, start the timer to work, and then synchronize every four cycles, as shown in Figure 5. When the timing time expires, select a filter suitable for establishing a high-level mutual access mechanism, its out2 outputs a jump signal from low to high, applies for an interrupt through irq12, and samples the analog quantity in turn in the interrupt service subroutine. In order to shorten the code of the interrupt service program and reduce the execution time of the interrupt service program, only data is collected in the interrupt service program, and the conversion of sampling code, data storage and other processing work are carried out outside. Therefore, a public array a[] is set, in which the sampling code of interrupt collection is placed. The current position of storing data is indicated by the pointer PA, and the pointer after storing a data is increased by 1, The interrupt service program maintains the pointer of group a[] and restarts the timer after 14 analog quantities are sampled. The format of data storage is shown in Figure 6

in order to eliminate the influence of system frequency fluctuation and improve the measurement accuracy of the system, the filtering method of moving average value of four whole cycles is adopted. When the 4th synchronization signal arrives, the value of PA pointer is assigned to pa_ End pointer, and then PA points to the initial position, so that the actual sampling points m of each analog quantity can be calculated as

1.4 voltage effective value calculation

according to the definition, the true effective value of AC voltage is

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