CN106227912A - Obtain and simplify the analysis method of maximum transient overvoltage under wind energy turbine set cable system asymmetry short circuit fault - Google Patents

Abstract

The invention discloses an analysis method for obtaining the maximum transient overvoltage under an asymmetric short-circuit fault of a cable system of a simplified wind farm, and belongs to the technical field of power system overvoltage. This analysis method is based on the characteristics of a large number of power cables used in offshore wind farms, and a simplified wind farm cable system simulation model based on PSCAD/EMTDC is established. This method proposes that, aiming at the factors that affect the transient overvoltage under asymmetric short-circuit faults: cable length, fault point, fault time, and fault type, the control variables are studied respectively, and the influence of the above factors on the transient overvoltage is analyzed, and finally obtained The maximum transient overvoltage when the short cable, the cable head, the peak voltage of the phase is faulty, and the single-phase grounding short circuit fault, so as to put forward a conclusion with certain reference value for the insulation protection of the cable system of the offshore wind farm.

Description

Obtaining the Maximum Transient Overvoltage of Simplified Wind Farm Cable System Under Unsymmetrical Short-Circuit Fault analysis method

technical field

The invention relates to the technical field of power system overvoltage, in particular to an analysis method for obtaining the maximum transient overvoltage under the asymmetrical short-circuit fault of a simplified wind farm cable system.

Background technique

In recent years, large-scale wind farms are moving from land to sea. According to the plan, my country's offshore wind power will grow by leaps and bounds in the next few years.

At the same time, more and more attention has been paid to the operation and maintenance of wind farms, especially transient overvoltage and equipment insulation failures caused by it. According to the characteristics of offshore wind farms, the power transmission of offshore wind power is completed through submarine cables. The power system of offshore wind farms is complex, the submarine cables are long, and the submarine environment is relatively harsh. Transient overvoltages may be generated due to asymmetrical short circuits. Overvoltage will cause harm to the cable collection grid system and its connected equipment (such as transformers, generators, etc.). Obtaining the maximum transient overvoltage of the wind farm cable system under an asymmetric short-circuit fault is helpful for selecting appropriate protection equipment and protection measures, and has practical significance for improving the safety and reliability of offshore wind farm operation.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art, and provide an analysis method for obtaining the maximum transient overvoltage under the asymmetrical short-circuit fault of the simplified wind farm cable system.

The object of the present invention is achieved through the following technical solutions:

An analysis method for obtaining the maximum transient overvoltage under an asymmetrical short-circuit fault of a simplified wind farm cable system, comprising the following steps:

S1, using PSCAD/EMTDC electromagnetic transient simulation software to establish a simplified wind farm cable system, the simplified wind farm cable system includes the following components: ideal power supply, transformer, circuit breaker, submarine cable, wind turbine;

S2. Set the parameters of each component in the simulation software to simulate the operation of a single fan;

S3. Simulating the transient overvoltage waveform and amplitude under the influence of different influencing factors of the asymmetrical short-circuit fault of the simplified wind farm cable system, the influencing factors including cable length, fault point, fault time, and fault type;

S4. On the basis of the conclusion obtained in the step S3, control the influencing factors affecting the transient overvoltage, and obtain the maximum transient overvoltage under the asymmetrical short-circuit fault of the cable system of the simplified wind farm.

Further, the step S3 includes:

Simulate and simplify the transient overvoltage waveform and amplitude under the influence of the cable length of the asymmetric short-circuit fault of the wind farm cable system, control the fault point, fault time, and fault type unchanged, and obtain the cable length and transient overvoltage by changing the cable length reasonably. voltage relationship.

Further, the step S3 includes:

Simulate and simplify the transient overvoltage waveform and amplitude under the influence of the fault point of the asymmetrical short-circuit fault of the cable system of the wind farm, and control the total cable length, fault time, and fault type unchanged. By setting two sections or The multi-section cable whose total length is equal to the original cable and whose parameters remain unchanged except the length is used when the equivalent fault point appears in different positions of the cable to obtain the relationship between the cable length and the transient overvoltage.

Further, the step S3 includes:

Simulate and simplify the transient overvoltage waveform and amplitude under the influence of the fault moment of the asymmetrical short-circuit fault of the wind farm cable system, control the cable length, fault point, and fault type, consider the specific point of the voltage waveform, adjust the fault time, and obtain the cable The relationship between length and transient overvoltage.

Further, the step S3 includes:

Simulate and simplify the transient overvoltage waveform and amplitude under the influence of the fault type of the asymmetrical short-circuit fault of the cable system of the wind farm, and control the cable length, fault point, and fault time unchanged. Obtain the relationship between cable length and transient overvoltage.

Compared with the prior art, the present invention has the following advantages and effects:

1. The wind farm system involves a lot of equipment and has high requirements for reliability and safety. Through experiments or actual measurements, the overvoltage cost of the wind farm cable system under asymmetrical short-circuit fault is relatively high, and the feasibility is poor. In the present invention, by inputting engineering parameters for simulation, relevant conclusions on the insulation protection of the cable system of the wind farm can be obtained more conveniently;

2. The cable system of the wind farm is relatively complicated. The present invention simplifies it scientifically and equivalently, and builds a model composed of an ideal power supply, a transformer, a circuit breaker, a single-section submarine cable, and a wind turbine, which is relatively simple and clear, and can also facilitate Obtain the relevant law of transient overvoltage under asymmetrical short-circuit fault of wind farm system;

3. The present invention uses the idea of control variables to study the influence of the four main factors of cable length, fault point, fault time, and fault type on the transient overvoltage under asymmetrical short-circuit faults, which is relatively comprehensive and scientific;

4. By comprehensively analyzing the influence of the above four factors on the overvoltage, the maximum transient overvoltage per unit value under asymmetrical short-circuit fault of the wind farm cable system under certain engineering parameters can be obtained by simulation as 3.237, which provides protection for the insulation protection of wind farm equipment. Important reference.

Description of drawings

Figure 1 is a model diagram of a simplified wind farm cable system;

Figure 2 is a schematic diagram of equivalent three-core cable parameters;

Figure 3 is a diagram of the relationship between cable length and transient overvoltage;

Figure 4 is a schematic diagram of the equivalent setting of the fault point;

Figure 5 is a diagram of the relationship between the fault point and the transient overvoltage;

Figure 6 is a diagram of the relationship between fault time and transient overvoltage;

Figure 7 is a waveform diagram of a single-phase ground short circuit occurring near the peak moment of a certain phase voltage;

Figure 8 is a diagram of the relationship between fault types and transient overvoltages;

Fig. 9 is a flow chart of the analysis method of the maximum transient overvoltage disclosed in the present invention.

detailed description

In order to make the object, technical solution and advantages of the present invention more clear and definite, the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Example

Please refer to FIG. 9 . FIG. 9 is a flowchart of a method for analyzing the maximum transient overvoltage in this embodiment. The present invention will be further described below in conjunction with the accompanying drawings. An analysis method for obtaining the maximum transient overvoltage under an asymmetrical short-circuit fault of a simplified wind farm cable system disclosed in this embodiment specifically includes the following steps:

S1. Using PSCAD/EMTDC electromagnetic transient simulation software, establish a simplified wind farm cable system with not less than the following components: ideal power supply, transformer, circuit breaker, submarine cable, and wind turbine, as shown in Figure 1.

S2. Setting the parameters of each component in the simulation software to simulate the operation of a single fan.

Among them, the infinite power grid is equivalent to an ideal power supply, and then stepped down by a 220/35kV transformer; the cable part adopts the structural parameters of a 3*400 26/35kV cable from a certain company, and arranges three single-core cables in a zigzag shape to be equivalent to three core cable, as shown in Figure 2. The frequency-dependent (phase) line model based on the frequency characteristics proposed by J.Marti in PSCAD/EMTDC is used, as shown in Table 1:

Table 1. Frequency-dependent (phase) line model parameters considering frequency characteristics

Travel Time Interpolation: On Curve Fitting Starting Frequency: 0.5Hz Curve Fitting Starting Frequency: 1.0E6Hz Total Number of Frequency Increments: 100 Maximum Order of Fitting for Yc: 20 Maximum Fitting Error for Yc: 0.2% Max. Order per Delay Grp. for Prop. Func. 20 Maximum Fitting Error for Prop.Func. 0.2% DC Correction: Disabled Passivity: Disabled

Finally, the 4MW fan is connected after stepping down again at 35/0.69kV. The model of the wind turbine in the event of a fault is equivalent to an inductive load. The choice of reactance is based on the rated current of the transformer, which is 0.379mH in this example.

S3. Simulate and simplify the transient overvoltage waveform and amplitude under the influence of four factors: cable length, fault point, fault time, and fault type of asymmetrical short-circuit faults in the wind farm cable system;

To carry out insulation protection on the cable system in engineering, it is necessary to obtain relevant data of transient overvoltage. Therefore, this method considers, simulates and simplifies the transient overvoltage waveform and amplitude under the influence of four factors of cable length, fault point, fault time, and fault type in the asymmetric short-circuit fault of the wind farm cable system.

For the convenience of expression, the end close to the ideal power supply side is called the cable head end, and the end close to the wind turbine side is called the cable end.

The step S3 includes: simulating and simplifying the transient overvoltage waveform and amplitude under the influence of the cable length of the asymmetric short-circuit fault of the cable system of the wind farm. It is necessary to control the fault point, fault time, and fault type unchanged. By changing the cable length reasonably, Obtain the relationship between cable length and transient overvoltage.

In the specific application, the control fault point is the first end of the cable, the fault time is 0.0175s, and the fault type is a single-phase ground short circuit. By adjusting the cable length reasonably, the overvoltage value of the high-voltage side of the transformer at the end of the wind turbine under different cable lengths is obtained. The results are shown in Figure 3.

The step S3 also includes: simulating and simplifying the transient overvoltage waveform and amplitude under the influence of the fault point of the asymmetrical short-circuit fault of the cable system of the wind farm. It is necessary to control the total cable length, fault time, and fault type. In PSCAD/EMTDC, it is necessary to set two or more sections of cables whose total length is equal to that of the original cable and whose parameters remain unchanged except for the length. This is used when the equivalent fault point appears in different positions of the cable, and the cable length and transient overvoltage can be obtained. Relationship.

In the specific application, the simulation simplified the transient overvoltage waveform and amplitude under the influence of the fault point of the asymmetric short-circuit fault of the cable system of the wind farm. The total cable length is controlled to be 3km, the fault time is 0.0175s, and the fault type is single-phase ground short circuit. As shown in Figure 4, a 3km cable is split into two sections of the same cable except for the length, and by continuously changing the length of the two sections of cable, the equivalent transient overvoltage situation where the fault point appears at different positions of the cable is obtained. At different distances from the fault point to the cable head end, the overvoltage value of the high-voltage side of the transformer at the end of the wind turbine is shown in Figure 5.

The step S3 also includes: simulating and simplifying the transient overvoltage waveform and amplitude under the influence of the fault moment of the asymmetrical short-circuit fault of the cable system of the wind farm. point, adjust the fault time, and obtain the relationship between cable length and transient overvoltage.

In the specific application, the simulation simplified the transient overvoltage waveform and amplitude under the influence of the fault moment of the asymmetric short-circuit fault of the wind farm cable system. The length of the control cable is 3km, the fault point is the cable head end, and the fault type is single-phase ground short circuit. Considering a specific point in the voltage waveform, adjust the time of fault occurrence, and obtain the overvoltage value of the high-voltage side of the wind turbine terminal transformer at different fault times. The results are shown in Figure 6 and Figure 7.

The step S3 also includes: simulating and simplifying the transient overvoltage waveform and amplitude under the influence of the fault type of the asymmetrical short-circuit fault of the cable system of the wind farm. It is necessary to control the length of the cable, the fault point, and the fault time. Short-circuit and two-phase-to-ground short-circuit to obtain the relationship between cable length and transient overvoltage.

In the specific application, the simulation simplified the transient overvoltage waveform and amplitude under the influence of the fault type of the asymmetrical short-circuit fault of the wind farm cable system, the total cable length is controlled to 3km, the fault point is the cable head end, and the fault time is 0.0175s. Single-phase ground short circuit and two-phase ground short circuit are two types of asymmetric short circuit faults, and the overvoltage value of the high voltage side of the wind turbine terminal transformer under different fault types is obtained. The results are shown in Figure 8.

S4. On the basis of the conclusion obtained in the step S3, control the factors affecting the transient overvoltage, and obtain the maximum transient overvoltage under the asymmetrical short-circuit fault of the cable system of the simplified wind farm.

In a specific application, analyze the specific conclusions of each sub-step in step S3, and set the control total cable length to 3km, the fault point to the cable head end, the fault time to 0.0175s, and a single-phase ground short circuit to finally obtain a simplified wind farm cable system The maximum transient overvoltage per unit value is 3.237.

To sum up, this embodiment discloses an analysis method for obtaining the maximum transient overvoltage under an asymmetric short-circuit fault of a cable system of a simplified wind farm, which belongs to the technical field of overvoltage of a power system. This analysis method is based on the characteristics of a large number of power cables used in offshore wind farms, and a simplified wind farm cable system simulation model based on PSCAD/EMTDC is established. This method proposes that, aiming at the factors that affect the transient overvoltage under asymmetric short-circuit faults: cable length, fault point, fault time, and fault type, the control variables are studied respectively, and the influence of the above factors on the transient overvoltage is analyzed, and finally obtained The maximum transient overvoltage when the short cable, the cable head, the peak voltage of the phase is faulty, and the single-phase grounding short circuit fault, so as to put forward a conclusion with certain reference value for the insulation protection of the cable system of the offshore wind farm.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention.

Claims (5)

1. obtaining and simplify an analysis method for maximum transient overvoltage under wind energy turbine set cable system asymmetry short circuit fault, it is special Levy and be, comprise the following steps:

S1, employing PSCAD/EMTDC electromagnetic transient simulation software, set up and simplify wind energy turbine set cable system, described simplification wind energy turbine set Cable system includes elements below: ideal source, transformator, chopper, submarine cable, Wind turbines；

S2, the parameter of each element is set in simulation software, the ruuning situation of simulation separate unit blower fan；

S3, to emulate the transient state under the influence of the different affecting factors of described simplification wind energy turbine set cable system asymmetry short circuit fault the most electric Corrugating and amplitude, described influence factor includes cable length, trouble point, fault moment, fault type；

S4, according to conclusion in described step S3 on the basis of, control affect the influence factor of transient overvoltage, obtain simplification Maximum transient overvoltage under wind energy turbine set cable system asymmetry short circuit fault.

The most according to claim 1 acquisition simplifies maximum transient overvoltage under wind energy turbine set cable system asymmetry short circuit fault Analysis method, it is characterised in that described step S3 includes:

Emulation simplifies the transient overvoltage waveform under the influence of the cable length of wind energy turbine set cable system asymmetry short circuit fault and width Value, controls trouble point, fault moment, fault type constant, by rationally changing cable length, obtains cable length and transient state mistake The relation of voltage.

The most according to claim 1 acquisition simplifies maximum transient overvoltage under wind energy turbine set cable system asymmetry short circuit fault Analysis method, it is characterised in that described step S3 includes:

Emulation simplifies the transient overvoltage waveform under the influence of the trouble point of wind energy turbine set cable system asymmetry short circuit fault and amplitude, Control joint current length, fault moment, fault type are constant, by arranging two sections or many in simulation software PSCAD/EMTDC The cable that Duan overall length remains unchanged equal to former cable, other parameters of being outside one's consideration except length, occurs in cable not for equivalent fault point Situation during co-located, obtains the relation of cable length and transient overvoltage.

The most according to claim 1 acquisition simplifies maximum transient overvoltage under wind energy turbine set cable system asymmetry short circuit fault Analysis method, it is characterised in that described step S3 includes:

Emulation simplifies the transient overvoltage waveform under the influence of the fault moment of wind energy turbine set cable system asymmetry short circuit fault and width Value, controls cable length, trouble point, fault type constant, it is considered to the specified point of voltage waveform, adjusts fault moment, obtain electricity Cable length and the relation of transient overvoltage.

The most according to claim 1 acquisition simplifies maximum transient overvoltage under wind energy turbine set cable system asymmetry short circuit fault Analysis method, it is characterised in that described step S3 includes:

Emulation simplifies the transient overvoltage waveform under the influence of the fault type of wind energy turbine set cable system asymmetry short circuit fault and width Value, controls cable length, trouble point, fault moment constant, by contrast single-line to ground fault and two-phase grounding fault, obtains electricity Cable length and the relation of transient overvoltage.