Study of Starting Process of Pumped Storage Machines by Static Frequency Converter

ZHANG Yu-zhi Information and Control Engineering College, Weifang University

261061 Weifang, China e-mail: zhangyuzhi2010@126.com

Abstract—For the pumped storage machines started by static frequency converter (SFC), the mathematical model of multi-circuits is established considering actual arrangement of the damper bars based on the multi-circuits theory of the electrical machines. On the basis of this mathematical model the process of static frequency converter starting were analyzed on simulation and analysis of the naturally operational phase. Meanwhile the rules of current, torque, rotational speed were given and several factors influencing starting were analyzed as well. The results show that, then the excitation current will rise quickly with the excitation control added, which can reach 4 times the rated value in 10 seconds, so it is necessary to control the excitation current by the excitation section in the inverter.

Keywords-pumped storage machine; starting; static frequency converter; damper bar; naturally operational phase

I. INTRODUCTION (HEADING 1) Pumped-Storage Hydroelectric Station, also known as

the storage hydropower station, uses the power when the electrical load is the lowest to pump water to upper reservoirs and to lower reservoirs when the electrical load reaches the peak. The world's first pumped storage power station was Natra Pumped-Storage Hydroelectric Station, built in 1882 in Zurich, Switzerland, 515KW of capacity, 153m. of head of delivery. Pumped storage in China started late. The first plant unit was built by Japanese manufacturers in Gangnan Reservoir, in 1968, single 110MW. According to the National Pumped-Storage Academic Symposium held in Nov, 2007, the installed capacity has increased from 1500MW to current 5725MW in the past 10 years; the present scale under construction which has increased from 4050MW from 10 years ago, to the present 12576MW, is expected to reach 18300MW in 2010[1-3].

One of the pumped storage power station unit’s important features is that it starts and stops frequently and mode converts quickly. It adjusts the peak and fills in the valley. Daily boot and stop are at least twice for regulations. Frequent starting and stopping threat the reliability of the motor running. Researching on the distribution of current and loss on each damper bar in the starting process, thus, to calculate the change of temperature on damper bars is quite meaningful[4]. Static frequency converter starting is a popular starting method, for the issue of static frequency converter starting of pumped storage motor, there are some literature at home and abroad[5-6].

This text has established mathematical model of the static frequency converter while the damping of current is not considered mathematical model, carrying out a specific[7-10]

analysis and calculation of the starting of the static frequency converter of pumped storage motors to draw the conclusion of law of change of current, torque, speed and loss, etc.

II. THE PRINCIPLE AND STRUCTURE OF PUMPED-STORAGE ELECTRIC STATIC FREQUENCY CONVERTER STARTING The way of static frequency converter starting is to

connect the synchronous motor to be starting with static frequency, provided an adjustable frequency power supply by the inverter; synchronous motor provides appropriate excitation, when the frequency of the inverter rises gradually from zero to rated frequency , the synchronous motor will gradually rise to the rated speed from stationary state. The starting of synchronous motor is a static frequency converter-controlled frequency control system, mainly composed of synchronous motor, inverter, rotor position detector PS and control unit.

The main loop of inverter is composed of bridge rectifier, inverter bridge and the smoothing reactor Ld, which is different from a general sense of thyristor AC-DC-AC current inverter, with no forced commutation capacitor and series diodes, relying on synchronous motor back-EMF to commutate. When starting, the three-phase 50Hz AC is commutated into DC by the rectifier bridge, and then is transformed into a certain-frequency three-phase AC power by the inverter, input to synchronous motor to be starting.

Control unit's primary role is to analyze signals from the rotor position detector, identify the actual rotor position and speed and produce control signals according to a certain control strategy to control the inverter to output a three-phase current (voltage) frequency, amplitude and phase, reaching the purposes of motor speed tracking the rotor speed.

III. THE MATHEMATICAL MODEL OF MULTI-CIRCUITS IS ESTABLISHED

By motor practice, regarding the input current as positive, the electromotive force and voltage’s positive direction as being consistent with the current’s positive direction, and the positive current creates positive magnetic chain, as shown in figure 1.

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IV. SIMULATION AND ANALYSIS OF THE NATURALLY OPERATIONAL PHASE

As the motor accelerates, its port voltage amplitude will increase gradually, and the frequency will speed up correspondingly but also because the resistance torque in the no-load starting process of the water pump, so, shortly after pump starts, excitation current begins to fall to the rated excitation current. About 9 seconds later when the pumps start, that is, the rotating speed increased to 5Hz, the inverter control system ended the operational phase of pulse, switching to the terminal voltage commutation of the natural

commutation phase. If the transition process in pulse phase and naturally operational phase is not considered, in the whole operational phase, excitation current will be a constant value.

A. Simulation analysis of the naturally operational phase without considering the impact of the harmonic wave

As the modulation current which is rectified and inverted through the inverter, containing a large number of harmonic components, these harmonics will be induced a high-frequency current in the damper winding, resulting in pulsating torque and affect the motor running. When analyzing natural simulation of operational phase, first take a look at the ideal state, that is, the variation of every quantity of state when the power supply is by full sinusoidal fundamental, in order to compare with subsequent analysis.

As can be seen from figure 4, current in the damping bar is basically 0 without considering the harmonic influence.

a) Speed curve

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b) field current curves

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B. Simulation analysis of the naturally operational phase considering the impact of the harmonic wave

t(s) a) Speed curve

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Figure 3. Simulation results considering harmonic influence

By comparing figure 4 with figure 5 we can find that in the static frequency converter starting process, the current in damping bar is mainly aroused by the harmonics which is input from the inverter to stator, and electromagnetic torque

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is mainly generated by the reciprocity of stator armature current and excitation current that damper winding has a low influence on electromagnetic torque.

V. CONCLUSION Pumped-storage motor starting process is a rather

complex process. Its internal electromagnetic field and temperature changes are complicated. This text, mainly researched on the starting process of static frequency converter of pumped storage motor, calculated the saturation parameter of pumped-storage motor, and analyzed the starting rules of pumped storage motor. Aiming at the operational phase of pulse in the starting process of pumped-storage motor, the simulation and calculation have been carried out respectively, with or without the excitation control. The results show that, then the excitation current will rise quickly with the excitation control added, which can reach 4 times the rated value in 10 seconds, so it is necessary to control the excitation current by the excitation section in the inverter.

REFERENCES [1] B. J. Ge, Y. L. Li and B. Li, “Study of starting process of pumped

storage machines by static frequency converter”. Electric Machines and Control, Vol. 6, No. 3, pp. 200-203, Dec. 2002.

[2] B. J. Ge, B. Li, F. H. Li et al, “Analysis of partial frequency startup process of synchronous machine”. Proceedings of the CSEE, Vol. 25, No. 5, pp. 93-97, Dec. 2005.

[3] B. J. Ge, Z. T. Wang, X. R. Huang et al, “Full frequency starting analysis of synchronous machine”, Proceedings of the CSEE, Vol. 19, No. 4, pp. 63-67, Dec. 1999.

[4] B. J. Ge, Y. L. Li, “Study of starting of starting pumped storage machines by static frequency converter with field current controlled”. Electric Machines and Control, Vol. 7, No. 3, pp. 187-190, Dec. 2003

[5] Y. G. Sun, X. H. Wang, L. Gu et al, “Transient calculation of stator’s internal faults in synchronous generator using fem coupled with multi-lop method”. Proceedings of the CSEE, Vol. 24, No. 1, pp. 163-141, Dec. 2004.

[6] HARAN K, CHUNTING M I. Improving the Starting Performance Of Large Salient-Pole Synchronous Machines [J]. IEEE Trans on Magnetics, 2004, 40(4): 1920-1928.

[7] H. M. Ahmed, R. E. Gabr and M. Kadahy, et al, “A New Method for Data Acquisition and Image Reconstruction in Parallel Magnetic Resonance Imaging”. Proceedings of the 2008 IEEE, CIBEC'08, No. 9, pp. 1-2, Dec.2008.

[8] G. S. XU. Linear Array CCD Image Sub-pixel Edge Detection Based on Wavelet Transform[C]. The Second International Conference on Information and Computing Science, No. 2, 2009, pp.207-210.

[9] G. S. XU. Sub-pixel Edge Detection Based on Curve Fitting [C]. The Second International Conference on Information and Computing Science, No. 2, 2009, pp.373-375.

[10] G. S. XU. The Study on Real-time Data Processing Based on CCD Scanning and Detecting Device on FPGA [C]. 2009 IEEE International Conference on Intelligent Computing and Intelligent Systems., No. 2, 2009, pp. 81-84.

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