PSS test and analysis in Hanfeng Power Plant

2022-08-05
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PSS test and analysis of Hanfeng Power Plant

tangjianhui 1, mengyu'e 2, Li Yanxue 2 (1. Hebei electric power test and Research Institute, Shijiazhuang 050021, Hebei; 2. Hanfeng Power Plant, Handan 056200, Hebei)

1 concept and function of power system stabilizer

power system stabilizer (PSS) is generally used as an additional function of excitation system. The natural damping of the whole system decreases due to automatic excitation regulation, which will lead to the decline of system stability. The function of PSS is to generate damping torque in phase with the speed in the control link to compensate for this adverse effect. Generally, PSS is added at the inlet of automatic voltage regulator. There are two main situations in power system where PSS is required to enhance the stability effect due to low power transmission oscillation: one is that a unit or a plant unit is far away from the system, with weak connection and relatively heavy transmission power, that is, a unit oscillates to the infinite bus system after passing through the transmission line, which belongs to the type of "local oscillation", and its oscillation frequency is about 0.8 ~ 1.8 Hz; The other is that a group of units in the system oscillates with another group of units through the tie line, which belongs to "Interval Oscillation". Since there are many oscillating units, the oscillation frequency is low, about 0.2 ~ 0.5 Hz. PSS link can play a certain leading compensation role in a frequency range to suppress low-frequency oscillation

2 PSS test of Hanfeng Power Plant

generator transformer unit wiring is adopted for unit 2 of Hanfeng Power Plant, and the outgoing line is 500 kV Hanlin III line, as shown in Figure 1. The excitation system is a self shunt fast excitation mode, which has the potential problem of underdamping. At the same time, the system connection is weak, which has the hidden danger of low-frequency oscillation. 2.1 test purpose and test method

according to the guidelines provided by the manufacturer, the field test method is developed

the purpose of the field test is to verify the function of the PSS link of this set of regulation system and find the best frequency of the PSS link. The test can be conducted only when the unit is in parallel operation and the load is greater than 80% of the rated load, that is, the load is greater than 500MW

use a low-frequency signal generator to input a disturbance signal at the regulator reference voltage. The signal is a sine wave with frequencies of 0.2 Hz, 0.3hz, 0.4 Hz, 0.5 Hz, 0.6 Hz, 0.7 Hz, 0.8 Hz, 0.9hz, 1.0 Hz, 1.1 Hz, 1.2 Hz, 1.3 Hz, 1.4 Hz, 1.5Hz and 2.5 Hz respectively. The amplitude increases from 0 until the change of active or reactive power reaches 3% of the rated value

the monitored outputs are active power P, reactive power Q, magnetic field voltage UF, magnetic field current if, PSS output and voltage deviation signal E. All output signals are provided with measuring points on the device, which are directly connected to the recorder to record the frequency. The contact of long chain molecules will produce entangled molecular rigid bundles of 1 kHz

during the test, each frequency is injected continuously to observe the effect of PSS link at each frequency, and finally find out the frequency with the most obvious effect of PSS link of the machine

2.2 test process

during the test, inject the sine wave signal with frequency of 1 Hz, do not input PSS first, and gradually increase the amplitude to observe the changes of each output; Then put the PSS link into operation, repeat the above process, and observe the effect of PSS

2.3 test results

from the output results under different frequencies, when the frequency of disturbance is closer to 1 Hz, the effect of PSS link is more and more obvious, and when the frequency is 1 Hz, the effect is the most obvious. When the frequency is 1.0 Hz, under the same disturbance, after PSS is put into operation, the magnetic field voltage fluctuation and power fluctuation caused by disturbance can be significantly suppressed to maintain the stable operation of the unit. In addition, the baud diagram is drawn according to the test curve, as shown in Figure 2. It is obvious from the baud diagram that the closer to 1.0 Hz, the more obvious the role of PSS link

3 analysis of test results

the PSS mathematical model recommended by China Electrical Engineering Society is shown in Figure 3. This is a double lead lag link. T5 is the filtering time constant of the input signal sensor. TS is the straight time constant, when the input signal is Δω or Δ F, take the larger value; When the input signal is Δ PE, take the smaller value. T1 ~ T4 are the lead and lag link time, so they have advantage constants in product development and marketing, which are generally determined through calculation. Δ UT and Pe0 are the given values for cutting off PSS links. When the absolute value of generator voltage deviation exceeds Δ When ut or generator power deviation is less than Pe0, PSS output is 0

siemens, especially the production material with high requirements, did not provide the specific transfer function of PSS link, but only provided a calculation block diagram as shown in Figure 4. From the principle of the block diagram, it is roughly the same as the transfer function recommended by the Electrical Engineering Society of China, but the algorithm is relatively simple. After the field test, each parameter suggests that with the gradual expansion of the power system and the continuous improvement of the single machine capacity, more stringent requirements are put forward for the stability. At present, most excitation systems adopt the design method of PID + PSS. The former is designed to improve the static and dynamic performance of the generator, and the latter is mainly used to suppress the low-frequency oscillation of the power system in the current global pattern of plastic machinery. Putting PSS into operation is an effective method to improve the stability of power system without increasing one-time investment. PSS is now a mature advanced technology to improve the stability of power system. The relevant standards of China's power system stipulate that large generators, especially fast excitation (such as self shunt excitation system), should be equipped with PSS. Therefore, the application of PSS is an important subject at present

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