CN103241138A - Low-frequency traction power supply system - Google Patents

Abstract

The invention discloses a low-frequency traction power supply system, which is composed of a traction substation and a traction network; the traction substation includes a traction transformer and a frequency converter; the primary side of the traction transformer is three-phase connected to the public power grid, and the secondary side is three-phase connected to the frequency converter; The traction side of the inverter output is single-phase and supplies power to the traction network through the single-phase traction bus; the power supply frequency f of the traction network satisfies the following formula: Traction network fault removal time limit TS (ms) = relay protection action time TR (ms) + half A cycle λ(ms), that is, f=500/(TS-TR), TS>TR, and between 5Hz and 16Hz; the traction network of each traction substation can be connected to implement through power supply; the traction substation is powered off When overhauling or traction side failure, shut down its frequency converter, and then operate the relevant circuit breaker. The low-frequency traction power supply system is widely applicable to the power supply of subways, light rails and trams in one line and one place, and the power supply of trolleybuses in double tram lines, and is easy to implement.

Description

A low-frequency traction power supply system

technical field

The invention relates to the field of transportation, in particular to a low-frequency traction power supply technology.

Background technique

Taking advantage of the single-phase traction power supply system's advantages of simple structure, low construction cost, and convenient operation and maintenance, the main line electrified railway generally adopts a relatively high voltage (27.5kV) single-phase power frequency AC system, while urban subways, light rails and railways Public transportation such as rails and trolleybuses generally adopt a lower voltage direct current system.

The electrified railway adopting the single-phase power frequency alternating current system directly draws power from the public grid, only uses low-cost and reliable transformers, does not use high-cost converters, and has the remarkable characteristics of large traction power and large transportation volume. However, there will also be negative sequence-based power quality problems that have a negative impact on the public grid and its own electrical phase separation (power supply breakpoint) problems, etc., which are difficult to control and costly. At the same time, the power frequency (50Hz in my country) In power supply, the voltage loss of the power supply system caused by reactance is much greater than the voltage loss caused by resistance. Obviously, the total voltage loss is much greater than that of the DC system.

Low voltage (750V and 1500V) DC traction power supply is generally used in urban subways, light rails and other rail transits. The voltage of rail and trolleybuses is lower, which has a small power supply voltage loss, and the traction network between substations can run through the following It has the advantages of avoiding power supply breakpoints, but there are inherent problems such as stray currents (earth stray currents), and DC arcs are not easy to cut off when faults occur. Stray currents will cause electrochemical corrosion to metal facilities such as the steel structure of the ballast bed, the steel structure in the tunnel, and the metal pipelines along the line, thereby affecting the safety and service life of these structures and metal facilities, making treatment and maintenance difficult and costly, and The stray current and its long-term corrosion effects cannot be fundamentally eliminated; the DC circuit breaker needs to cut off the DC arc, which is technically difficult, complicated in mechanism, short in service life, and high in cost, and my country has been relying on imports so far.

In the future, urban public transportation congestion and pollution will become more and more severe. Increasing transport capacity, improving efficiency, and reducing pollution are the fundamental solutions to the problem. In order to avoid the disadvantages of large one-time energy consumption and serious urban pollution of traditional urban public transportation, the use of electric traction is the most realistic choice. Therefore, it is very necessary and important to propose a low-frequency power supply system that is between the single-phase power frequency AC system and the DC system, can maximize strengths and avoid weaknesses, and can choose power supply frequency according to its own needs.

The low-frequency traction power supply system is widely used in the power supply of urban subways, light rails, and urban public transportation such as rails and trackless. At the same time, since the volume of the transformer is inversely proportional to the frequency, low-frequency power supply will increase the volume of the transformer and become extremely uneconomical. Therefore, it should be avoided to use transformers in low-frequency traction power supply systems. In other words, converters are widely used in public transportation vehicles Today, with the AC drive technology of the main circuit, the voltage of the low-frequency traction power supply system that directly supplies power to the vehicle will not be too high due to factors such as the withstand voltage level and economic performance of the converter (inverter), generally up to several thousand volts , but with the growth of traffic capacity demand and the development of converter technology and manufacturing technology, higher voltage may be used in the future to further increase power supply capacity.

Contents of the invention

The purpose of the present invention is to provide a low-frequency traction power supply system, that is, a system between the single-phase power frequency AC system and the DC system, which can make use of the strengths and avoid weaknesses of the single-phase power frequency AC system and the DC system, and can be used according to its own needs. Choose the low-frequency power supply system with power supply frequency; no longer use DC circuit breakers; the frequency converter can be used as an AC switch to cooperate with traction substation maintenance and traction side fault removal; it does not generate stray current and electrochemical corrosion like DC, nor does it Single-phase power frequency alternating current produces power quality problems dominated by negative sequence in the public grid and its own electrical phase separation (power supply breakpoint) problem; the traction network of each traction substation can be connected to implement through-through power supply, and greatly reduce Voltage loss in the traction network.

The present invention solves the technical problem, and the adopted technical solution is: a low-frequency traction power supply system, which is composed of a traction substation SS and a traction network OCS; the traction substation includes a traction transformer TT and a frequency converter UF; the primary side of the traction transformer The three phases are connected to the public power grid PS, and the three phases on the secondary side are connected to the frequency converter UF; the traction side output by the frequency converter UF is low-frequency single-phase and supplies power to the traction network OCS and vehicle L through the single-phase traction bus BB; the power supply frequency f of the traction network is 5Hz At a fixed frequency between 16Hz and 16Hz; the traction network of each traction substation can be connected to implement through power supply.

The single-phase traction busbar BB is divided into two feeders on the left and right, and feeder circuit breakers KL and KR are provided to realize the OCS segment of the traction network and the continuous power passing of the train. When the traction substation is powered off for maintenance or the traction side fails, its frequency conversion is turned off. device.

Considering factors such as cost, reliability and maturity, three-level inverters based on 1700V or 3300V IGBT circuits can be applied on a large scale, and the AC voltage of the traction network should be around 1200V-2000V. In the future, the AC voltage of the traction network output by similar five-level inverters can be increased to 4000V.

The working principle of the present invention is: a low-frequency traction power supply system, which converts the three-phase power-frequency alternating current of the public power grid into single-phase low-frequency alternating current on the traction side through the traction transformer and frequency converter in the traction substation to supply power to the traction network; The traction network of the substation can be connected to implement power supply; the power supply frequency f of the traction network is at a fixed frequency between 5 Hz and 16 Hz; the power supply frequency f of the traction network satisfies the following formula: the time limit for fault removal of the traction network TS (ms) = Relay protection action time TR (ms) + half cycle λ (ms), that is, f = 500/(TS-TR), TS>TR; when the traction substation is powered off for maintenance or the traction side is faulty, turn off its inverter .

For example, it is required that the traction network fault removal time limit TS=60ms, and the relay protection action time TR=20ms, then half cycle=40ms, that is, the traction network power supply frequency f=500/40=12.5Hz is selected; if the traction network fault removal time limit is required TS = 60ms, relay protection action time TR = 10ms, then half cycle = 50ms, that is, choose the traction network power supply frequency f = 500/50 = 10Hz. In other words, half a cycle is the minimum time limit for fault removal of the traction network.

Compared with prior art, the beneficial effect of the present invention is:

1. The present invention can overcome the inherent technical problems of stray current (earth stray current) in the DC system and its electrochemical corrosion to the metal facilities along the line, and the DC arc is not easy to cut off when a fault occurs, and avoid stray current management costs and DC circuit breakers. high investment.

2. The present invention utilizes the primary side three-phase current conversion technology of the frequency converter, and does not generate negative sequence and harmonics and reactive currents exceeding the requirements of the national standard in the public power grid; the isolation effect of the frequency converter on the public power grid and the traction side can make each traction The traction network of the substation is connected, and the power supply is implemented to eliminate the electric phase separation and power supply breakpoints existing in the industrial frequency AC electrified railway; under normal conditions, low-frequency power supply can greatly reduce the voltage loss of the traction network. It can reduce short-circuit current and its impact on power supply equipment.

3. The frequency converter of the present invention can be used in conjunction with the circuit breaker on the traction side for the maintenance of traction substations and fault removal on the traction side; the life of the frequency converter has nothing to do with its switching (on and off) times, and the action speed is fast. Long life and low maintenance cost.

4. The traction network of the present invention implements through power supply, and the regenerative energy when the vehicle brakes can be used by the traction vehicle or returned to the public power grid nearby, which has good energy saving effect and is environmentally friendly.

5. The present invention can be widely used in city subways, light rails, and urban public transportation such as rails and trackless, and has good adaptability.

6. The system is advanced in technology, reliable, easy to operate, low in operating costs, and easy to implement.

The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

Description of drawings

Fig. 1 is a schematic structural diagram of a low-frequency traction power supply system according to an embodiment of the present invention.

Fig. 2 is a schematic structural diagram of a three-level inverter according to an embodiment of the present invention.

Fig. 3 is a schematic structural diagram of a single-phase one-line-one-ground traction power supply system according to an embodiment of the present invention.

Fig. 4 is a schematic structural diagram of a single-phase two-wire traction power supply system according to an embodiment of the present invention.

Detailed ways

Example

Fig. 1 is a schematic structural diagram of a low-frequency traction power supply system according to an embodiment of the present invention. The adopted technical scheme includes the traction substation SS and the traction network OCS; the traction substation SS obtains power from the public grid PS, connects to the primary side of the traction transformer TT through the three-phase AC switch MK, and then passes through the secondary side of the traction transformer TT The low-voltage three-phase AC switch LK is connected to the inverter UF. The traction side output by the inverter UF is a low-frequency single-phase and supplies power to the traction network OCS and the vehicle L through the single-phase traction bus BB. The single-phase traction bus BB is divided into two feeders on the left and right. Also set up feeder circuit breakers KL and KR to realize OCS segmentation of the traction network for maintenance and isolation of faults.

The working principle of the present invention is: in the traction substation, through the traction transformer and frequency converter, the three-phase power frequency alternating current of the public power grid is converted into the single-phase low-frequency alternating current on the traction side to supply power to the traction network; the power supply frequency f of the traction network is between 5Hz and 16Hz at a fixed frequency between them, and satisfy the following formula: traction network fault removal time limit TS (ms) = relay protection action time TR (ms) + half cycle (ms), that is, f = 500/(TS-TR ), TS>TR; for example, it is required that the traction network fault removal time limit TS=60ms, and the relay protection action time TR=20ms, then half cycle=40ms, that is, the traction network power supply frequency f=500/40=12.5Hz; if It is required that the fault removal time limit of the traction network is TS=60ms, and the relay protection action time TR=10ms, then half cycle=50ms, that is, the power supply frequency of the traction network is selected as f=500/50=10Hz. In other words, half a cycle is the minimum time limit for fault removal of the traction network. The traction network of each traction substation can be connected to implement through power supply, see Figure 3 and Figure 4. When the traction substation SS is powered off for maintenance or the traction network fails, its frequency converter UF is turned off, and then the relevant feeder circuit breaker KL or KR is opened.

Fig. 2 is a schematic structural diagram of a three-level frequency converter in a traction substation according to an embodiment of the present invention. In the traction substation, the secondary side of the traction transformer TT is connected to the frequency converter UF through a three-phase series reactor (which can be combined with the leakage reactance of the traction transformer). The obtained low-frequency single-phase alternating current of 5 to 16 Hz is output to the traction network; the traction side of the frequency converter UF is connected with a single-phase series reactor.

The demonstration shows that considering factors such as cost, reliability, and maturity, the three-level inverter based on the 1700V or 3300V IGBT circuit can be applied on a large scale, and the AC voltage of the traction network on the traction side is selected to be around 1200V-2000V. should. In the future, the AC voltage of the traction network output by similar five-level inverters can be increased to 4000V.

Fig. 3 is a schematic structural diagram of a single-phase one-line-one-ground traction power supply system according to an embodiment of the present invention, where three traction substations are taken as examples. The partition substation SP is set between the adjacent traction substations, and K12 and K23 are circuit breakers in SP1 and SP2 respectively, and the circuit breakers K12 and K23 are normally closed to connect the traction networks of each traction substation. Implement pass-through power supply. When a ground fault occurs in the traction network between the traction substation SS1 and the divisional substation SP1, the frequency converter UF1 of the traction substation SS1 should be shut down first, and then the feeder circuit breaker KR1 of the traction substation SS1 and the divisional substation SP1 The circuit breaker K12 is opened to remove the fault, and then the frequency converter UF1 is turned on to restore the normal power supply in the fault-free section.

The single-phase one-line one-ground power supply method is widely used in the power supply of subways, light rails and trams, that is, the traction network is composed of catenary and return rail (ground). The advantage is that the traction network has a simple structure, saves investment, and is easy to maintain. The disadvantage is that once the human body contacts, it will form a circuit with the catenary and the return rail (ground), which has great potential safety hazards. Therefore, closed circuits are often used, and unrelated personnel are not allowed to enter.

Fig. 4 shows a schematic structural diagram of a single-phase two-wire traction power supply system according to an embodiment of the present invention, still taking three traction substations as an example. Between the adjacent traction substations SS, a divisional substation SP is set up. K11 and K12 are the circuit breakers in the divisional substation SP1, and K22 and K23 are the circuit breakers in the divisional substation SP2. K11 and K12, K22 and K23 are normally closed. In order to connect the traction network of each traction substation to implement through power supply. When a ground fault occurs on the uplink (or downlink) traction network between the traction substation SS1 and the district substation SP1, the inverter UF1 of the traction substation SS1 should be shut down first, and then the uplink (or downlink) of the traction substation SS1 should be turned off. ) feeder circuit breaker KR11 (or KR12) and the uplink circuit breaker KL21 (or KL22) of SP1 of the partition station, cut off the uplink (or downlink) fault, and then open the frequency converter UF1 to restore the normal power supply in the fault-free section. The single-phase two-wire traction power supply method is widely used in the power supply of trackless and tram cars, that is, the traction network is composed of double tram lines (catenary). The advantage is that the double tram lines and between the double tram lines and the ground are insulated from each other. Once the human body touches it, it will not cause the human body to form a loop between the tram line and the ground, and the safety performance is good; the disadvantage is that the structure of the traction network is complex and maintenance trouble. It is suitable for urban public transportation where people are easily accessible.

Claims (3)

1. low frequency tractive power supply system is characterized in that: the low frequency tractive power supply system is made up of traction substation SS and traction net OCS; Traction substation comprises traction transformer TT and frequency converter UF, the former limit three of the traction transformer utility network PS that is connected, the inferior limit three frequency converter UF that is connected; The traction side of frequency converter UF output is that low frequency is single-phase and power for traction net OCS and vehicle L by single-phase traction bus BB; The traction net of each traction substation can UNICOM, implements to connect power supply; Traction net line frequency f is on a certain fixed frequency between 5Hz and the 16Hz.

2. a kind of low frequency tractive power supply system according to claim 1; it is characterized in that: traction net line frequency f is obtained by following formula: traction net failure removal time limit TS (ms)=relaying TR opening time (ms)+half cycle (ms); be f=500/(TS-TR), TS〉TR.

3. a kind of low frequency tractive power supply system according to claim 1, it is characterized in that: two feeder lines about described single-phase traction bus BB divides, and establish feeder line circuit breaker KL and KR, realization traction net OCS segmentation and train do not cut off the power supply and pass through, when traction substation interruption maintenance or traction side fault, turn-off its frequency converter.

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