Abstract: As a typical unbalanced load, the traction load of electrified railway brings harmonic, negative sequence and reactive power quality problems to public power grid.
Ignore. Static Var Compensation Device (SVC) is an effective method to reduce or even eliminate power quality problems such as reactive power and harmonics. Stationary
Based on reactive power compensator, the comprehensive control of power quality of electrified railway is studied.
Keywords: electrified railway; Power grid; Power quality; integrated control
1 preface
The total mileage of electrified railways in China has exceeded 24,000 kilometers.
Ranked second in the world. Electrified railway has strong carrying capacity and fast running speed.
The advantages of rapid temperature rise, energy saving and less environmental pollution, etc., in the modern national economy,
It plays an important role in economic development.
However, due to the random fluctuation of traction load of electrified railway.
Dynamic and asymmetric, it brings to the public power grid such as negative sequence current,
Power quality problems such as harmonics and reactive power have also attracted great attention.
Attention. This paper studies how to control the traction load of electrified railway by effective means.
A series of power quality problems to ensure other power in the power grid.
The safe and economical operation of equipment is of great significance.
2 traction power supply system of electrified railway
2 1 overview
The voltage of power supply network in China is generally 1 10kV or
220kV is converted into 27 5kV by traction transformer as traction power supply.
Locomotive power supply. At present, the popular traction transformers mainly include
Single-phase traction transformer, Y-D 1 1 traction transformer, impedance matching traction.
Transformers, Scott Transformers, etc. China electrified railway adopts power frequency AC.
50Hz three-phase power supply and single-phase power consumption, and its load traction electric locomotive.
High power, frequent changes in speed and load conditions and asymmetric characteristics.
Traction power grid has low power factor, high harmonic content and negative sequence.
Large current and other characteristics, not only its own loss, but also to the public power grid and iron
Other power equipment along the way also brings serious harm, and the following measures must be taken.
Effective governance measures [1].
2.2 single-phase transformer traction power supply network
The topology of traction power supply system with single-phase traction transformer is as follows
Figure 1 display [2].
Single-phase wiring traction network adopts single-phase transformer for power supply.
It is divided into single-phase connection mode and V-V connection mode. Single phase wiring
The primary side of the transformer is bridged between two phases in a three-phase power system; Secondary edge
One end is connected with the traction side bus, and the other end is connected with the track and the grounding grid.
Traction transformer has high capacity utilization rate, but it is single-phase in power system.
The negative sequence current generated by traction load is large, and the catenary cannot supply power.
Realize bilateral power supply. So this kind of wiring is only suitable for the capacity of power system.
Large quantity, relatively developed power network, and three-phase load electricity can be used reliably.
Where the local power grid supplies power. In addition, the single-phase traction transformer shall
Designed and manufactured according to full insulation. Single-phase V-V wiring will be two single-phase transformers.
The voltage transformer is connected to each traction substation of the three-phase power system in a V shape.
They can all be powered by the two-phase line voltage of the three-phase system. Twice voltage conversion
One end of the secondary winding is connected to the two-phase bus of the traction substation.
And the other ends of them are connected to the steel rail to be led back in the form of male terminals.
Returns the row of the. At this time, the two arms are connected with a voltage difference of 60, and the current is not
The degree of symmetry decreases. This connection is usually called a 60 connection.
2.3 three-phase Y-D 1 1 transformer traction power supply network
Using three-phase Y-D 1 1 traction transformer to expand traction power supply system
The structure of the robot is shown in Figure 2.
The high voltage side of three-phase Y-D 1 1 connection traction transformer is introduced.
The lines are connected to 1 10kV or 220kV according to the specified sequence, which is higher in a three-phase power system.
Voltage transmission line; The angle C of the low voltage side of the transformer is connected with the track and the grounding grid.
Then, the other two corners A and B of the transformer are connected to phase A and phase B of 27±5kV respectively.
On the noninverting bus. The two-phase traction bus supplies power to the corresponding power supply arms on both sides respectively.
Power supply, the difference between the two arms is 60, which is also 60 connection. Therefore, in
Use a split-phase insulator between two adjacent catenary parts.
3 SVC static and dynamic reactive power compensation device
Development of 3 1 Static Var Compensator
Static dynamic reactive power compensation device SVC is an advanced high-speed reactive power compensation device.
Dynamic power factor compensation device for voltage network. By increasing the power factor
Save a lot of electric energy, at the same time, reduce the harmonics of the power grid and stabilize power consumption.
Pressure, improve the quality of power grid (environment). In the 1970s,
To thyristor controlled reactor (TCR) and thyristor switching capacitor.
Device (TSC) and its mixing device (TCR+TSC), etc.
Static Var Compensator (SVC) composed of formulas has developed rapidly. Switched virtual circuit
It can be regarded as a reactance element with adjustable susceptance, which depends on electricity.
The sub-device switch realizes reactive power regulation. SVC can be used as system compensation.
Continuously adjust and exchange reactive power with the system, and also have
The response speed is fast and the terminal voltage can be kept constant.
Working principle of 3 2 SVC and its application in power grid
The basic topology of TCR+TSC SVC is shown in Figure 3. It includes
1 TCR, 2 TSCs and 2 passive filters. Actually,
In the system, the number of TSC and passive filter groups can be set as needed.
The working principle of TCR is to connect with the phased reactor through control.
The phase shift trigger pulse of the anti-parallel thyristor pair is used to change the reactor equivalent value.
The size of the susceptance, so as to output continuously variable reactive power. In fig. 3
The two thyristors are respectively changed according to the single-phase half-wave AC switch.
Changing the control angle α can change the current through the inductor. α is measured based on
Based on the voltage zero-crossing point, α can be partially turned on between 90 ~ 180.
When the conduction angle increases, the fundamental component of the current decreases, which is equivalent to the increase of reactance.
Reduce the reactance of fundamental reactive power. The conduction angle is 90 ~ 180.
In the process of continuous adjustment, the current also changes continuously from rated value to 0, and TCR increases.
The supplied compensation current contains harmonic components [3].
The working principle of TSC is based on the change of inductive reactive power of load.
The capacitor is cut off or put into operation by the anti-parallel thyristor pair. Here,
Unlike thyristors in TCR, thyristors are only used as switches.
Act in stages. In practical systems, each capacitor bank should be connected in series.
A damping reactor to reduce the abnormal operation of the crystal.
Surge current value of brake pipe, while avoiding resonance with the system. Use crystal
When switching capacitor banks, the peak voltage of the system is usually selected or
Zero crossing is a necessary condition for switch action. Due to TSC
The capacitor only switches between two extreme current values, so it does not
It will produce harmonics, but its compensation for reactive power is gradual.
The joint operation principle of TCR and TSC is as follows: When the system voltage is low,
When setting the operating voltage, it should be put into operation according to the reactive power that needs compensation.
When the number of capacitor banks is slightly positive (overcompensated), this
Then TCR is used to adjust the output inductive reactive power to offset this part.
Overcompensated capacitive reactive power; When the system voltage is higher than the set voltage, it will be turned off.
Except for all capacitor banks, only TCR is still running.
Comprehensive control and management of power quality in power grid
4 1 Harmonic Suppression and Reactive Power Compensation
Application of SVC dynamic reactive power compensation device in traction power supply system
The key to comprehensive control of harmonics and reactive power is the maximum reactive power compensation of SVC.
Determination of compensation and design of filtering branch [3].
The maximum reactive power compensation Qsvc should be the negative value of design line traction.
The load should be adapted to the maximum traction load of electrified railway.
Active power demand and power factor at the installation site after compensation or maximum.
The maximum voltage loss during power surge can be determined by the following formula
According to formulas (1) and (2).
QSVC =(tanφ 1-tanφ2)Pmax( 1)
Where φ 1 and φ2 are the measured power before and after 1 10kV power supply compensation, respectively.
Factor angle; Pmax is the maximum active demand of electrified railway load.
QSVC = Qfmax-δU % Xs(2)
Qfmax is the maximum reactive power influence on the installation site; Δ δU% is installed.
Maximum voltage loss requirements on site; Xs is the system impedance.
In order to achieve ideal harmonic suppression effect, FC must be considered comprehensively.
The design of filter branch should not only ensure the safe operation of the device, but also realize it.
The expected ideal effect. In actual design, firstly, according to the power supply
Harmonic components contained in the arm are used to determine the composition of FC filter branches. pass by
Among the harmonics of electric traction load, the third, fifth and seventh harmonics account for a large proportion.
Therefore, the FC filter branch is generally filtered by single tuning for 3, 5 and 7 times.
Wave device.
When the maximum reactive power compensation capacity and the composition of the filter branch are determined,
How to allocate the reactive power capacity to each filter branch reasonably is as follows.
A very important question. If the capacity allocation of each filter branch is inconsistent
On the one hand, it will make the total capacity of equipment installation larger, on the other hand, it is possible.
Because the compensation power of a filter circuit is too small and overload occurs, the filter circuit is set up.
For safe operation.
The algorithm adopted by some famous electric companies is as follows [6]:
For example, the reactive power compensation of Siemens is allocated according to formula (3).
Qc(h)=QSVCIh/h∑Ih/h(3)
Where Qc(h) is the compensation capacity allocated by the H filter branch; Ih
It is the h-th harmonic current of the power supply arm.
BBC electric company distributes reactive power according to formula (4)
Qc(h)=QSVC∑Ih(4)
AEG Power Company allocates reactive power according to Formula (5).
Qc(3)∶Qc(5)∶Qc( 1 1)∶Qc( 13)= 2∶2∶ 1∶ 1(5)
Where Qc(3), Qc(5), Qc( 1 1) and Qc( 13) are 3, 5, 1 1 respectively.
13 compensation capacity allocated by filter branch.
4.2 Negative sequence current compensation
A large amount of negative sequence current generated by traction electric locomotive is given to others in the power grid.
It has great influence on the safe and economic operation of power equipment. SVC static
Static reactive power compensation device has the function of compensating negative sequence and terminal voltage.
When efficient. In engineering application, we can choose power grid system and load.
SVC[5] is installed on both.
SVC is installed at the system end of power grid to compensate negative sequence current.
The principle is to refer to steinmetz's law. Regardless of mining
What kind of traction transformer is used, and the realization of negative sequence compensation is divided into the following two steps:
(1) power factor correction. By installing capacitor devices, each
The phase loads are all resistive.
(2) see steinmetz's law), AB phase ab.
Resistive load G and capacitive load G/ 3 of BC phase and CA
The inductive loads G/ 3 of each phase are symmetrical to each other.
The current loop diagram and phase diagram are shown in Figure 4 and Figure 5 respectively:
As can be clearly seen from fig. 5, that line current i. a, i. b and i. c are symmetrical.
And the impedance load between BC phase and CA phase can also be realized.
Similar symmetry, so all negative sequence currents in the system can be compensated.
Compensation and elimination.
The key problem now is how to keep up with the fluctuation of traction load.
Capacitors and inductor groups required for compensation are effectively controlled. Desperate for digital signals
Fixed capacitor (FC) of DSP and reactor controlled by thyristor.
The combination of (TCR) is widely used, as shown in Figure 6. Benefit from
DSP can quickly process data information and compensate the required capacitance and inductance.
Parameters can be calculated quickly and accurately.
5 Conclusion and prospect
Based on static and dynamic reactive power compensation devices, a static and dynamic reactive power compensation device is proposed.
Principle and application of comprehensive control and management of power quality in electrified railway traction network
This scheme has important engineering significance. The power quality of electrified railway is
A prominent and severe subject and problem requires us to constantly explore new ones.
On the basis of comprehensive compensation method, the influence of power quality is comprehensively controlled and treated.
Reactive power, harmonics, negative sequence and other factors, in order to improve the power quality of the power grid and ensure the use of electricity.
Network security and economic operation.
refer to
[1] Li Qunzhan. Comprehensive compensation for parallel connection of electrified railways and its application [M]. Beijing: China Railway.
Press, 1993.
[2] TB/ 10009-2005 Code for Design of Railway Electric Traction Power Supply [S].
Wang Zhaoan. Harmonic suppression and reactive power compensation [M]. Beijing: Machinery Industry Press, 1999.
[4] Electrification Survey and Design Institute of Electrification Engineering Bureau of Ministry of Railways. Electrified railway design manual
Power supply system [M]. Beijing: China Railway Publishing House, 1988.
[5] An Peng, Zhang Lei, Liu Yutian. Influence of electrified railway on safe operation of power system
Policy [J]. Shandong Electric Power Technology, 2005, (4): 16- 19.
Ma liqian Application of dynamic reactive power compensation device in traction substation [J]. Electrified railway
Tao, 2008(4).