CN101702512B - Negative sequence impedance direction protection method for interior failures of stator winding of steamer generator - Google Patents

Abstract

The invention relates to a protection method for interior failures of a stator winding of a steam turbine generator, belonging to the technical field of main equipment relay protection of a power system. The protection method is characterized by comprising the following steps of: collecting three-phase voltage and three-phase current from the machine end of the generator, filtering fundamental wave negative sequence components of failure components of phase voltage and phase current, calculating the equivalence negative sequence impedance of the failure components of the machine end, and judging whether unsymmetrical failures are interior failures of a motor winding or exterior failures of the machine end according to the symbol and the size of the negative sequence impedance. Analysis for the calculation of all interior short-circuit failures and single-branch welding disconnection failures which possibly occur and the sensitivity in two typical steam turbine generators shows that the negative sequence impedance direction protection method for failure components has superior sensitivity and protection range for the interior asymmetrical failure (particularly a short-circuit failure among interior turns) of the rotor winding of the steam turbine generator to the other traditional protections, and can provide high-quality protection for interior asymmetrical failures of the steam turbine generator, the natural point side of which only leads out three terminals.

Description

Negative-sequence impedance directional protection method for internal faults of turbogenerator stator windings

technical field

The invention belongs to the technical field of relay protection for main equipment in a power system, and in particular relates to a method for protecting an asymmetric fault inside a generator stator winding based on the sign and magnitude of the fault component negative-sequence impedance.

Background technique

The internal asymmetrical faults of the generator stator mainly include the internal short-circuit faults of the windings and the single-branch disconnection faults, which are common and highly destructive faults. Large turbo-generator internal short-circuit faults will generate a large short-circuit current, while single-branch disconnection faults not only cause the normal branch current of the fault phase to increase significantly, but also generate a large current between the two branches of the non-fault phase. Circulating current, such a large current may burn the winding and iron core, and also generate destructive and serious electromagnetic force. The negative-sequence magnetic field generated by asymmetrical faults may greatly exceed the design allowable value, causing serious damage to the rotor. Therefore, my country's relay protection technical regulations clearly stipulate that large turbogenerators need to be equipped with phase-to-phase and inter-turn short-circuit protection for stator windings.

However, most of the existing turbo-generators have only three terminals on the neutral point side (see Figure 1), and cannot be equipped with zero-sequence current type transverse difference protection, incomplete longitudinal difference protection, and split-phase transverse difference protection. The inter-turn short-circuit main protection commonly used in generators, and the complete differential protection with installation conditions can only respond to the phase-to-phase short-circuit of the stator winding, and cannot act on the inter-turn short-circuit and single-branch disconnection faults inside the stator winding.

Turn-to-turn short-circuit protection for turbogenerators currently in use mainly includes longitudinal fundamental wave zero-sequence overvoltage protection and fault component negative-sequence direction protection, but both have relatively large action dead zones, and the latter generally cannot respond to single-branch disconnection Fault. In order to improve the safety and reliability of large turbogenerators, it is necessary to study new protection principles for internal asymmetric faults and put forward new protection criteria.

Contents of the invention

The purpose of the present invention is to provide a protection method for the asymmetrical fault inside the stator winding for the turbogenerator whose neutral point side only leads to three terminals.

In order to improve the safety and reliability of large turbogenerator operation, the invention proposes a new protection method for internal asymmetrical faults of stator windings. For a turbogenerator with only 3 terminals on the neutral point side, it is only necessary to collect three-phase voltage and three-phase current from the generator terminal, and filter out the fundamental negative-sequence component of the phase voltage and phase current fault components to form a negative sequence component. The characteristic quantity of sequence impedance directional protection (see Figure 2). The present invention is characterized in that the method is carried out in the computer according to the following steps:

其中ΔU_a和

为a相电压故障分量的基波有效值和相角，ΔU_b和

为b相电压故障分量的基波有效值和相角，ΔU_c和

为c相电压故障分量的基波有效值和相角，ΔI_a和为a相电流故障分量的基波有效值和相角，ΔI_b和

为b相电流故障分量的基波有效值和相角，ΔI_c和

为c相电流故障分量的基波有效值和相角。(1) Sampling the three-phase voltage and three-phase current (according to the generator practice, see Figure 3) at the generator end, and the fault components of the three-phase voltage and three-phase current are obtained from the difference between adjacent sampling points The instantaneous value (for example, Δu _a (k)=u _a (k+1)-u _a (k), where u _a (k) is the k-th sampled instantaneous value of the voltage of phase a), and from the instantaneous value using Fourier The filtering algorithm calculates the fundamental phasor of the fault component of the three-phase voltage and three-phase current

where ΔU _a and

is the fundamental RMS value and phase angle of phase a voltage fault component, ΔU _b and

is the fundamental effective value and phase angle of the b-phase voltage fault component, ΔU _c and

is the fundamental RMS value and phase angle of the c-phase voltage fault component, ΔI _a and is the fundamental RMS value and phase angle of the fault component of phase a current, ΔI _b and

is the fundamental effective value and phase angle of the b-phase current fault component, ΔI _c and

is the fundamental RMS value and phase angle of the c-phase current fault component.

ΔU_b、

ΔU_c、和ΔI_a、ΔI_b、ΔI_c、

)，分解出故障电压的基波负序相量

和故障电流的基波负序相量

(2) According to the fundamental component effective value and phase angle of the above-mentioned three-phase voltage and three-phase current fault components (ie ΔU _a ,

ΔU _b ,

ΔU _c , and ΔI _a , ΔI _b , ΔI _c ,

), decompose the fundamental negative sequence phasor of the fault voltage

and the fundamental negative sequence phasor of the fault current

(3) Judging whether to start fault component negative-sequence impedance directional protection according to the magnitude of the fault current fundamental negative sequence phasor effective value ΔI ₂ : If ΔI ₂ is greater than 10% of the normal operating fundamental current, go to (4) and start the fault Directional protection of component negative sequence impedance; otherwise, go to (1) to continue sampling.

计算故障分量的负序阻抗

(4) From the fundamental negative sequence phasor of the fault voltage and the fundamental negative sequence phasor of the fault current

Calculate the negative sequence impedance of the fault component

的符号及大小描述的判据表达形式为：

(5) Based on fault component negative sequence impedance

The expression form of the criterion for the symbol and size description is:

If the above criteria are met, it is judged as an asymmetrical fault inside the generator stator winding.

The calculation and sensitivity analysis of all possible internal short-circuit faults and single-branch open welding and disconnection faults of two typical turbogenerators show that the fault component negative-sequence impedance direction protection proposed by the present invention has a negative effect on the internal asymmetry of the turbogenerator stator. The sensitivity and protection range of faults (especially for internal inter-turn short-circuit faults) are superior to other existing protections (including longitudinal fundamental wave zero-sequence overvoltage protection and fault component negative-sequence direction protection). High-quality protection is provided for internal asymmetrical faults of the turbogenerator leading out to 3 terminals. The action dead zone of fault component negative-sequence impedance direction protection is mainly the inter-turn short-circuit fault of the same phase and different branches with the same (or similar) distance from the two short-circuit points to the neutral point. The reason for the inability to operate is the fundamental negative-sequence phasor of the fault current Smaller, less than the threshold for starting negative sequence impedance directional protection. In fact, for the turbogenerator with only 3 terminals on the neutral point side, the sensitivity of the existing various protections to this kind of inter-turn short-circuit fault of different branches of the same phase is very low.

Description of drawings

Fig. 1 is a diagram of the traditional outlet mode and protection configuration of the turbogenerator in the present invention.

Fig. 2 is a schematic diagram of the protection in the negative sequence impedance direction of the turbogenerator fault component in the present invention.

Fig. 3 is a schematic diagram of the reference direction of the turbine generator terminal voltage and current in the present invention (generator convention).

Figure 4 is the fundamental negative-sequence equivalent circuit and negative-sequence fundamental phasor diagram when the grid is symmetrical and the generator is asymmetrical.

Figure 5 is the negative-sequence fundamental wave phasor diagram when the grid is symmetrical and the generator is asymmetrical.

Figure 6 is the fundamental negative sequence equivalent circuit when the generator is externally asymmetric.

Figure 7 is the negative-sequence fundamental wave phasor diagram when the generator is externally asymmetric.

Fig. 8 shows a kind of inter-turn short-circuit fault between different branches of the same phase with the same number of turns between two short-circuit points and the same number of turns that may actually occur in No. 1 turbogenerator (300MW, 54 slots in the stator).

Fig. 9 is a schematic diagram of the reliable action ranges of various protections of the turbogenerator against the inter-turn short circuit fault of the same phase.

Figure 10 is a schematic diagram of the reliable action ranges of various protections for turbogenerators against phase-to-phase short-circuit faults.

Fig. 11 is a program block diagram of the present invention.

Detailed ways

Firstly, the principle of the present invention will be described in conjunction with the accompanying drawings.

与电流的参考方向规定为发电机惯例)，负序电流

滞后于负序电压

机端负序等值阻抗Z₂的阻抗角

在0°至90°之间，而且由于实际系统中X_t＞r_t，

应接近于90°；当发电机定子绕组本身对称而外部发生不对称故障或者发电机带不对称负荷运行时，负序量来源于电网(负荷)，负序功率由电网流向发电机，负序等值电路如图6所示(图6中R₂和jX₂代表发电机的负序等值电阻和电抗(实际值))，基波负序相量图如图7所示(图7中电压

与电流

的参考方向仍规定为发电机惯例)，负序电流

领先于负序电压

机端负序等值阻抗Z₂的阻抗角

在-180°至-90°之间，而且由于实际系统中X₂＞＞R₂，

应接近于-90°。When the three-phase generator operates symmetrically, the voltage and current have only symmetrical positive-sequence fundamental wave components, while asymmetrical faults (or asymmetrical operation) will cause negative-sequence and zero-sequence quantities. If the generator has an internal asymmetric fault and the grid is still symmetrical, then the negative sequence quantity comes from the generator, and the negative sequence power flows from the generator to the grid. The negative sequence equivalent circuit is shown in Figure 4 (r _t and jX _t in Figure 4 Represents the total resistance and leakage reactance (actual value) of each phase converted from the three-phase symmetrical grid transmission line and transformer to the generator side, and the fundamental negative sequence phasor diagram is shown in Figure 5 (the voltage in Figure 5

with current The reference direction is specified as the generator convention), the negative sequence current

lagging behind the negative sequence voltage

The impedance angle of the machine terminal negative sequence equivalent impedance Z ₂

between 0° and 90°, and since X _t >r _t in practical systems,

should be close to 90°; when the generator stator winding itself is symmetrical and an asymmetrical fault occurs externally or the generator operates with an asymmetrical load, the negative sequence quantity comes from the grid (load), and the negative sequence power flows from the grid to the generator. The equivalent circuit is shown in Figure 6 (R ₂ and jX ₂ in Figure 6 represent the negative-sequence equivalent resistance and reactance (actual value) of the generator), and the fundamental negative-sequence phasor diagram is shown in Figure 7 (in Figure 7 Voltage

with current

The reference direction is still specified as the generator convention), the negative sequence current

Leading the negative sequence voltage

The impedance angle of the negative sequence equivalent impedance Z ₂ at the machine terminal

Between -180° and -90°, and since X ₂ >>R ₂ in the actual system,

Should be close to -90°.

According to the above principles, it can be judged whether the asymmetrical fault is an internal fault of the motor winding or an external fault of the motor according to the sign and magnitude of the equivalent negative sequence impedance at the machine end. In order to avoid the misjudgment caused by the original asymmetry of the grid voltage, it is necessary to adopt the fault component processing method, that is, the fault component of the fundamental negative sequence voltage and negative sequence current constitutes the characteristic quantity of the negative sequence impedance criterion.

In order to verify the performance of the above-mentioned fault component negative-sequence impedance directional protection, the following two turbogenerators (main parameters are shown in Table 1) are taken as examples, and the "multi-loop analysis method" is used on the basis of a comprehensive internal fault simulation calculation. Its action performance is analyzed and calculated, and its performance is compared with the existing turn-to-turn short-circuit protection of turbogenerators (including longitudinal fundamental wave zero-sequence overvoltage protection and fault component negative-sequence directional protection).

Table 1 Main parameters of the two turbogenerators

According to the stator winding connection diagram provided by the motor manufacturer, the types and numbers of all internal short-circuit faults (including same-slot faults and end faults) that may actually occur in the two turbogenerators can be analyzed, as shown in Table 2.

Table 2 The same slot and end faults that may actually occur in two turbogenerators

For the rated load operation status of the network, Tables 3 to 5 respectively count the fault component negative-sequence impedance directional protection proposed by the present invention and the existing longitudinal fundamental zero-sequence overvoltage protection and fault component negative-sequence directional protection of the turbogenerator. The number of failures of the action and their nature. It can be seen that for these two turbogenerators, the fault component negative-sequence impedance directional protection proposed by the present invention cannot operate for only six types of inter-turn short circuits in different branches of the same phase, and the dead zone of action is far smaller than that of the other two existing protections. .

Table 3 The number of faults and their properties that the fault component negative-sequence impedance directional protection cannot operate under the rated load operation state of two turbo-generators connected to the network

Table 4 The number of faults and their properties that the longitudinal fundamental wave zero-sequence overvoltage protection cannot operate under the rated load operation state of two turbogenerators connected to the network cannot operate reliably)

Table 5 Under the rated load operation state of two turbogenerators connected to the network, the number and nature of the faults that the fault component negative sequence direction protection cannot operate (the operating value is set to 1% of the rated capacity of the generator, and the protection is considered to be sensitive to faults with a sensitivity < 1.5 cannot operate reliably)

Further analysis shows that the fault component negative-sequence impedance directional protection proposed by the present invention cannot act on inter-turn short-circuit faults in different branches of the same phase, and the distance between the two short-circuit points and the neutral point is the same number of turns. For example, the No. 1 steam turbine generator shown in Figure 8 (stator with 54 slots, each branch is composed of 9 coils in series), the lower side of the first branch of the phase a, the No. 8 coil (counting from the machine end) and the phase a The turn-to-turn short circuit occurs at the end intersection of the upper side of the No. 8 coil of the second branch. The number of short-circuit turns is 2 turns, and the short-circuit point of the two branches is only 1 coil away from the neutral point. In the network rated load operation mode, calculate the effective value and phase of each camera terminal voltage, current and steady-state fundamental current of each branch as follows:

It can be seen from this calculation example that for this kind of inter-turn short-circuit fault of the same phase and different branches with the same or similar number of turns between the two short-circuit points and the neutral point, since the normal potentials of the two short-circuit points are relatively close, although the current of the short-circuit circuit is very large, the The short-circuit current with a large value mainly causes the circulating current between the two fault branches of the fault phase, but has relatively little influence on the three-phase voltage and three-phase current at the machine terminal. Therefore, the current and voltage are mainly positive-sequence components of the fundamental wave, and the negative-sequence and zero-sequence components are very small (U ₀ =139.8V, U ₂ =187.9V, I ₂ =758.5A), and the longitudinal fundamental wave zero-sequence overvoltage protection and the sensitivity of fault component negative-sequence direction protection are relatively low, and although the scope of the negative-sequence impedance angle of the fault component negative-sequence impedance direction protection proposed by the present invention satisfies the action criterion, the negative-sequence current cannot reach the start-up value (I ₂ ＝758.5A, less than 10% of the normal current (10189A)) can not operate.

Through the above qualitative analysis, it is recognized that the fault shown in Fig. 8 is not only the action dead zone of the fault component negative-sequence impedance direction protection proposed by the present invention, but also the action dead zone of the existing various protections (including complete longitudinal differential protection) of the turbo-generator. Action dead zone. Through more careful statistics, Figure 9 and Figure 10 can be used to briefly illustrate the number and size comparison and inclusion relationship of internal inter-turn short-circuit faults and inter-phase short-circuit faults for which various protections of the turbogenerator can reliably operate. Superior performance of component negative sequence impedance directional protection.

Claims (2)

1. the negative sequence impedance direction protection method of Stator Coil internal fault is characterized in that described method is carried out successively according to the following steps in computer:

Step 1. is sampled to three-phase voltage and three-phase current at generator machine end, and poor by between the neighbouring sample point, obtains the fault component instantaneous value of three-phase voltage and three-phase current, is expressed as: Δ u _a(k)=u _a(k+1)-u _a(k), Δ u _b(k)=u _b(k+1)-u _b(k), Δ u _c(k)=u _c(k+1)-u _c(k), Δ i _a(k)=i _a(k+1)-i _a(k), Δ i _b(k)=i _b(k+1)-i _b(k), Δ i _c(k)=i _c(k+1)-i _c(k), u wherein _a(k), u _b(k), u _c(k) be the k time sampled instantaneous value of a phase, b phase, c phase voltage, i _a(k), i _b(k), i _c(k) be the k time sampled instantaneous value of a phase, b phase, c phase current;

Step 2. utilizes the Fourier filtering algorithm to calculate the fundamental phasors of the fault component of three-phase voltage and three-phase current according to the sampled instantaneous value of above-mentioned three-phase voltage and three-phase current fault component

And the first-harmonic negative phase-sequence phasor of leaching false voltage

First-harmonic negative phase-sequence phasor with fault current

Δ U wherein _aWith Be the first-harmonic effective value and the phase angle of a phase voltage fault component, Δ U _bWith

Be the first-harmonic effective value and the phase angle of b phase voltage fault component, Δ U _cWith

Be the first-harmonic effective value and the phase angle of c phase voltage fault component, Δ I _aWith

Be the first-harmonic effective value and the phase angle of a phase current fault component, Δ I _bWith Be the first-harmonic effective value and the phase angle of b phase current fault component, Δ I _cWith First-harmonic effective value and phase angle for c phase current fault component;

Step 3. is according to fault current first-harmonic negative phase-sequence phasor effective value Δ I ₂Size judge whether to start fault component negative sequence impedance direction protection: if Δ I ₂Greater than 10% of normal operation fundamental current, go to step 4, start fault component negative sequence impedance direction protection; Otherwise, go to step 1 and continue sampling;

Step 4. is by the first-harmonic negative phase-sequence phasor of false voltage

First-harmonic negative phase-sequence phasor with fault current Calculate the negative sequence impedance of fault component

Step 5. is based on the fault component negative sequence impedance Symbol and the criterion expression-form described of size be:

If satisfy above-mentioned criterion, then be judged as the inner unbalanced fault of generator unit stator winding.

2. the negative sequence impedance direction protection method of Stator Coil internal fault according to claim 1 is characterized in that: described sampled point is no less than 12 points in a power frequency period.

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