CN102185281A - Method for compensating capacitance current in differential current of generator - Google Patents

Abstract

The invention discloses a method for compensating capacitance current in differential current of a generator. The winding capacity of a generator is equivalent to a generator terminal and a neutral point of the generator, but the winding capacity is not partitioned into two equal parts and the partitioning coefficient is calculated according to the structure of the generator. The method can be used to compensate the capacitance current in differential current so as to improve the protection reliability; meanwhile, the method is easy to operate and can prevent the protection false operation and failure action.

Description

The method that is used for the capacitance current of generator compensates for differential electric current

Technical field

The present invention relates to a kind of method of capacitance current of the fine compensation differential current that is used for generator.

Background technology

At the end of last century, a kind of high-voltage generator that utilizes high-tension cable coiling stator winding has been invented by ABB genco, thereby has realized the direct connection of generator unit and grid, and the generator of this novelty is exactly a high-voltage generator.The winding of high-voltage generator is to be made by the high pressure XLPE insulated cable that originally was used for transmission line, and cable earth capacitance can be thought and mainly formed by the charging and discharging between inner semiconductor layer and the outer semiconductor layer.Have the characteristics that are different from conventional generator on the high-voltage generator design of Windings, promptly the thickness of insulating barrier is also non-homogeneous, but increases gradually from neutral point toward the machine end.On the other hand, when conventional generator and high-voltage generator had identical rated capacity, every capacitance current relatively of high-voltage generator was 30 times of every capacitance current relatively of conventional generator.

Along with the growth and the The application of new technique of high-rating generator capacity, the differential protection of generator is faced with the affected danger of sensitivity that causes its differential protection because of the continuous growth of capacitance current.Therefore, the high-voltage generator capacitance current can not be ignored the influence of differential protection.

The method of having described capacitance current in the compensate for poor stream is arranged, but nearly all these documents all are the capacitance currents of paying close attention to the long line of compensation, and the capacitance current of documents generator is seldom arranged in existing a lot of documents.Because the direct-to-ground capacitance of conventional generator is less, the requirement of its precision has been satisfied in general difference stream protection.The document that for example has has been used for reference the compensation method of long line capacitance electric current, with machine end and the neutral point of generator windings capacitor equivalent to motor, respectively accounts for 50%.The winding insulation of conventional generator equates that its direct-to-ground capacitance is equally distributed, is similar to the situation of long line, and this equivalence this moment is rational.Yet, because the armature winding of high-voltage generator has adopted the structure of graded insulation, cable insulation at the neutral point place is thinner, cable insulation at machine end place is thicker, therefore the cable earth capacitance of high-voltage generator is not equally distributed, the unit length direct-to-ground capacitance reduces to the machine end gradually from neutral point, if still according to above-mentioned 50% equivalent dividing method, the capacitance current full remuneration in just difference can not being flowed be fallen.If the capacitance current in the difference stream can not be compensated, then can cause differential protection malfunction or tripping.

Therefore, prior art has yet to be improved and developed.

Summary of the invention

The object of the present invention is to provide a kind of method that is used for the capacitance current of generator compensates for differential electric current, be intended to solve the influence of capacitance current, prevent the problem of differential protection malfunction, tripping differential protection.

Technical scheme of the present invention is as follows:

A kind of method of capacitance current of the compensates for differential electric current that is used for generator wherein, may further comprise the steps:

A: motor windings electric capacity is pressed division coefficient ρ: (1-ρ) to neutral point and machine end two ends, makes that the winding total capacitance is C with lumped parameter equivalence _ω, the equivalent capacity that then is positioned at the machine end is ρ C _ω, and the equivalent capacity that is positioned at neutral point is (1-ρ) C _ω

B:, calculate division coefficient ρ according to the construction of cable and parameter;

Wherein, the computing formula of ρ is:

$\mathrm{\ρ}=\frac{1}{2}\frac{C_{01}{{\mathrm{\α}}_1}^2+C_{02}({{\mathrm{\α}}_2}^2-{{\mathrm{\α}}_1}^2)+...+C_{0N}({{\mathrm{\α}}_N}^2-{{\mathrm{\α}}_{N-1}}^2)}{C_{01}{\mathrm{\α}}_1+C_{02}({\mathrm{\α}}_2-{\mathrm{\α}}_1)+...+C_{0N}({\mathrm{\α}}_N-{\mathrm{\α}}_{N-1})}$

In the formula, ρ is a division coefficient; α ₁, α ₂... α _NIt is respectively the coefficient that first section, second section, N section conductor account for whole winding total length; C ₀₁, C ₀₂... C _0NIt is respectively the unit length direct-to-ground capacitance of first section, second section and N section conductor.

C: the lumped parameter equivalent electric circuit of setting up according to division coefficient ρ calculates capacitance current, to determine the condenser current compensation amount in the differential current.

The method of the capacitance current of the described compensates for differential electric current that is used for generator, wherein, the computing formula of described capacitance current is:

${\stackrel{\·}{I}}_{\mathrm{ca}}=\mathrm{j\ω}[(1-\mathrm{\ρ})C_{\mathrm{\ω}}{\stackrel{\·}{U}}_0+\mathrm{\ρ}{C}_{\mathrm{\ω}}{\stackrel{\·}{U}}_N],$

In the formula, Be capacitance current; ρ is a division coefficient; C _ωBe the winding total capacitance; Be neutral point voltage; Be set end voltage.

Beneficial effect of the present invention: the present invention is by with machine end and the neutral point of generator windings capacitor equivalent to motor, goes out division coefficient according to the Structure Calculation of motor.The capacitance current that adopts the present invention to can be used in the fine compensation differential current is protected reliability to improve, and possesses to implement simple and easy, as to prevent to protect misoperation and tripping work advantage.

Description of drawings

Fig. 1 is existing high-voltage generator cable cross-section schematic diagram;

Fig. 2 is a high-voltage generator cable capacitance equivalent circuit diagram;

Fig. 3 is a N section cable model schematic diagram;

Fig. 4 is a N section cable model generation external short circuit fault schematic diagram;

Fig. 5 is a high-voltage power computer capacitance current equivalent circuit diagram;

Fig. 6 is a N section cable model generation internal short circuit fault schematic diagram.

Fig. 7 is the method flow diagram of the capacitance current in the fine compensation differential current provided by the invention;

Embodiment

For making purpose of the present invention, technical scheme and advantage clearer, clear and definite, below develop simultaneously with reference to accompanying drawing that the present invention is described in more detail for embodiment.

The outer semiconductor layer of high-voltage generator cable is multipoint earthing at regular intervals, can think that the current potential of its outer semiconductor layer is identical with earth potential, the electric field that this means winding concentrates between the interior outer semiconductor layer of cable, the electric field that lets out seldom, can think there is not electrical couplings relation between the high-voltage generator cable that the situation of this and conventional generator is different.So, between the turn-to-turn that must consider during analytic routines generator windings capacitive earth current, winding and alternate coupling capacitance, and when analyzing the capacitance current of high-voltage generator, can ignore.

For the motor with the coaxial insulated cable coiling, because outer semiconductor layer is an earth potential, the electric field in the winding exists only between the inside and outside semiconductor layer, and its direct-to-ground capacitance is only formed by the charging and discharging between the inside and outside semiconductor layer.Be similar to the electric capacity computing formula of coaxial circles column jecket, the direct-to-ground capacitance C of this unit length ₀Size is:

C ₀=2 π ε ₀ε _r/ ln (r ₂/ r ₁) ... ... ... ... .. formula (1).

Wherein: absolute dielectric constant ε ₀Equal 8.854e-12F/m; Relative dielectric constant ε _rEqual 2～3; r ₁It is the outer radius of inner semiconductor layer; r ₂Be the inside radius of outer semiconductor layer, as shown in Figure 1.

Prior art has proposed a kind of circuit model that calculates the discrete lumped parameter of cable earth capacitance electric current, can prove after Taylor expansion: the direct-to-ground capacitance of certain section even distribution cable can replace with an electric capacity.Certainly, from formula (1) as can be known, along with the high-voltage generator cable insulation thickness increases to the machine end gradually from neutral point, the cable earth capacitance of unit length also is different.

Every section cable capacitance with same dielectric thickness is replaced with pi-network, when high-voltage generator has the cable of N section different insulative thickness, its equivalent capacity distributes as shown in Figure 2, the subscript of each electric parameters is represented the position at different hop counts place among the figure, and the hop count numbering increases to the machine end successively from neutral point.

Because the electromotive force in the stator winding is along the linear distribution of winding, and be directly proportional to umber of turn between the neutral point, so the voltage of the interior any point of winding all is neutral point voltage with this point

And set end voltage

Linear combination.Therefore, the voltage U of any point in the winding _iComputing formula can be defined as follows:

${\stackrel{\·}{U}}_i=k_{2i+1}{\stackrel{\·}{U}}_0+k_{2i+2}{\stackrel{\·}{U}}_N$ ... ... ... .... formula (2).

In the formula: k _2i+1, k _2i+2Be real number.

From Fig. 2 and formula (2) as can be known, a phase capacitance current

Can be by cable capacitance C _iWith both end voltage and

Calculate, so a phase capacitance current

Computing formula may be defined as:

${\stackrel{\·}{I}}_{\mathrm{ca}}=\mathrm{j\ω}\underset{i=0}{\overset{N}{\mathrm{\Σ}}}{C}_i{\stackrel{\·}{U}}_i=\mathrm{j\ω}\underset{i=0}{\overset{N}{\mathrm{\Σ}}}{C}_i(k_{2i+1}{\stackrel{\·}{U}}_0+k_{2i+2}{\stackrel{\·}{U}}_N)$

$({\stackrel{\·}{U}}_0+\underset{i=0}{\overset{N}{\mathrm{\Σ}}}{k}_{2i+1}{C}_i+{\stackrel{\·}{U}}_N\underset{i=0}{\overset{N}{\mathrm{\Σ}}}{k}_{2i+2}{C}_i)$ ... ... ... ... formula (3).

In the formula: C _iBeing to be positioned at an electric capacity at i place, also is whole a phase winding capacitor C _ωA part.

With the linear combination in the formula (3)

Write as ρ C _ω, be exactly C _ωA part, ρ is a division coefficient, it with the phase winding capacitance profile in machine end and neutral point capacitance current, 0≤ρ≤1 with the whole winding of Equivalent Calculation; And

Can be write as (1-ρ) C _ω, i.e. C _ωRemaining another part.

Then formula (3) can be rewritten as:

${\stackrel{\·}{I}}_{\mathrm{ca}}=\mathrm{j\ω}[(1-\mathrm{\ρ})C_{\mathrm{\ω}}{\stackrel{\·}{U}}_0+\mathrm{\ρ}{C}_{\mathrm{\ω}}{\stackrel{\·}{U}}_N]$ ... ... ... ... formula (4).

To prove above-mentioned conclusion by three kinds of typical running statuses (normal operation, external fault, internal fault) of analyzing high-voltage generator below.The cable that distributes with a N section insulation is an example, sets up the simplification cable model of high-voltage generator winding, as shown in Figure 3.Neutral point voltage and set end voltage use respectively and

Expression, C ₀₁, C ₀₂... C _0NBe respectively the unit length direct-to-ground capacitance of first section, second section and N section conductor, α ₁L, α ₂L... α _NL is respectively first section, second section, the length of N section conductor, wherein, and α ₁, α ₂... α _NBe respectively the coefficient that first section, second section, N section conductor account for whole winding total length, l is the winding total length, as shown in Figure 3.Thereby be not difficult to draw:

0≤α ₁≤α ₂≤…≤α _N-1≤1

α _N=1....................... formula (5).

And the computing formula of a phase winding field intensity may be defined as:

E _0aL=U _t-U _n... ... ... ... .. formula (6).

When motor normally moves, the capacitance current of a phase winding

Computing formula then be:

${\stackrel{\·}{I}}_{\mathrm{ca}}/\mathrm{j\ω}=\underset{0}{\overset{{\mathrm{\α}}_{1}l}{\∫}}({\stackrel{\·}{U}}_n+{\stackrel{\·}{E}}_{0a}x)C_{01}\mathrm{dx}+\underset{{\mathrm{\α}}_{1}l}{\overset{{\mathrm{\α}}_{2}l}{\∫}}({\stackrel{\·}{U}}_n+{\stackrel{\·}{E}}_{0a}x)C_{02}\mathrm{dx}+...$

$+\underset{{\mathrm{\α}}_{N-1}l}{\overset{l}{\∫}}({\stackrel{\·}{U}}_n+{\stackrel{\·}{E}}_{0a}x)C_{0N}\mathrm{dx}$ ... ... ... .. formula (7).

When high-voltage generator normally moves, neutral point voltage

So formula (6) becomes Substitution formula (7), abbreviation gets:

${\stackrel{\·}{I}}_{\mathrm{ca}}/\mathrm{j\ω}=\underset{0}{\overset{{\mathrm{\α}}_{1}l}{\∫}}{\stackrel{\·}{E}}_{0a}x{C}_{01}\mathrm{dx}+\underset{{\mathrm{\α}}_{1}l}{\overset{{\mathrm{\α}}_{2}l}{\∫}}{\stackrel{\·}{E}}_{0a}x{C}_{02}\mathrm{dx}+...+\underset{{\mathrm{\α}}_{N-1}l}{\overset{{\mathrm{\α}}_{N}l}{\∫}}{\stackrel{\·}{E}}_{0a}x{C}_{0N}\mathrm{dx}$

$=\frac{1}{2}{\stackrel{\·}{E}}_{0a}{l}^2[C_{01}{{\mathrm{\α}}_1}^2+C_{02}({{\mathrm{\α}}_2}^2-{{\mathrm{\α}}_1}^2)+...+C_{0N}({{\mathrm{\α}}_N}^2-{{\mathrm{\α}}_{N-1}}^2)]$

$=\frac{1}{2}{\stackrel{\·}{U}}_{t}l[C_{01}{{\mathrm{\α}}_1}^2+C_{02}({{\mathrm{\α}}_2}^2-{{\mathrm{\α}}_1}^2)+...+C_{0N}({{\mathrm{\α}}_N}^2-{{\mathrm{\α}}_{N-1}}^2)]$ ... ... ... formula (8).

Because the high-voltage generator winding is made up of the cable of N section different insulative thickness, then have following formula to set up:

C _ω=C ₀₁α ₁L+C ₀₂(α ₂-α ₁) l+ ... + C _0N(α _N-α _N-1) l................ formula (9).

Make division coefficient ρ be:

$\mathrm{\ρ}=\frac{1}{2}\frac{C_{01}{{\mathrm{\α}}_1}^2+C_{02}({{\mathrm{\α}}_2}^2-{{\mathrm{\α}}_1}^2)+...+C_{0N}({{\mathrm{\α}}_N}^2-{{\mathrm{\α}}_{N-1}}^2)}{C_{01}{\mathrm{\α}}_1+C_{02}({\mathrm{\α}}_2-{\mathrm{\α}}_1)+...+C_{0N}({\mathrm{\α}}_N-{\mathrm{\α}}_{N-1})}$ ... ... .... formula (10).

Then, formula (8) but abbreviation be

${\stackrel{\·}{I}}_{\mathrm{ca}}=\mathrm{j\ω\ρ}{\stackrel{\·}{U}}_t{C}_{\mathrm{\ω}}$ ... ... ... .... formula (11).

The capacitance current that formula when motor normally moves (11) draws is the difference stream that differential relay detects.

When the construction of cable and parameter were all known, division coefficient ρ can precompute.The lumped parameter equivalent electric circuit of setting up according to formula (11) as shown in Figure 5.Whether this method is suitable for the situation of high-voltage generator generation external fault and internal fault, will be discussed in detail below.

The situation of N section cable model generation external short circuit fault as shown in Figure 4.With a is the fault signature phase mutually, makes the place, fault point that voltage is A relatively capacitance current is:

${\stackrel{\·}{I}}_{\mathrm{ca}}/\mathrm{j\ω}=\underset{0}{\overset{{\mathrm{\α}}_{1}l}{\∫}}({\stackrel{\·}{U}}_n+{\stackrel{\·}{E}}_{0a}x)C_{01}\mathrm{dx}+\underset{{\mathrm{\α}}_{1}l}{\overset{{\mathrm{\α}}_{2}l}{\∫}}({\stackrel{\·}{U}}_{n+}+{\stackrel{\·}{E}}_{0a}x)C_{02}\mathrm{dx}+$

$...+\underset{{\mathrm{\α}}_{N-1}l}{\overset{l}{\∫}}({\stackrel{\·}{U}}_{n+}+{\stackrel{\·}{E}}_{0a}x)C_{0N}\mathrm{dx}$

$={\stackrel{\·}{U}}_n[C_{01}{\mathrm{\α}}_1+C_{02}({\mathrm{\α}}_2-{\mathrm{\α}}_1)+...+C_{0N}(1-{\mathrm{\α}}_{N-1})]+$

$\frac{1}{2}{\stackrel{\·}{E}}_{0a}{l}^2[C_{01}{{\mathrm{\α}}_1}^2+C_{02}({{\mathrm{\α}}_2}^2-{{\mathrm{\α}}_1}^2)+...+C_{0N}(1-{{\mathrm{\α}}_{N-1}}^2)]$

... ... formula (12).

With formula (6) substitution formula (12), and by means of formula (9), (10), formula (12) abbreviation is:

${\stackrel{\·}{I}}_{\mathrm{ca}}/\mathrm{j\ω}={\stackrel{\·}{U}}_n{C}_{\mathrm{\ω}}+\frac{1}{2}({\stackrel{\·}{U}}_t-{\stackrel{\·}{U}}_n)\left[2\mathrm{\ρ}{C}_{\mathrm{\ω}}\right]$

$={\stackrel{\·}{U}}_n[C_{\mathrm{\ω}}-\mathrm{\ρ}{C}_{\mathrm{\ω}}]+{\stackrel{\·}{U}}_t\mathrm{\ρ}{C}_{\mathrm{\ω}}$

$=(1-\mathrm{\ρ}){\stackrel{\·}{U}}_n{C}_{\mathrm{\ω}}+\mathrm{\ρ}{\stackrel{\·}{U}}_t{C}_{\mathrm{\ω}}$ ... ... ... ... ... formula (13).

From formula (13) as can be seen, capacitance current can be simplified circuit with one and calculate, as shown in Figure 5.

In fact, the capacitance current when Fig. 5 can calculate high-voltage generator equally and normally moves only needs order

Get final product.And, when

Be that formula (13) also can calculate the capacitance current of b, c phase when perfecting phase b, c phase set end voltage.Therefore, the capacitance current of this two-phase also can calculate with the circuit of Fig. 5.

The situation of N section cable model generation internal short circuit fault as shown in Figure 6.Can described capacitance current still calculate with equivalent electric circuit shown in Figure 5.The case of internal fault occurs in the S section, is the fault signature phase mutually with a still, makes the place, fault point that voltage is

As previously mentioned, the electromotive force in the high-voltage generator stator winding is along the linear distribution of winding, and is directly proportional to umber of turn between the neutral point with this point.Therefore have a relatively capacitance current be:

${\stackrel{\·}{I}}_{\mathrm{ca}}/\mathrm{j\ω}=\underset{0}{\overset{{\mathrm{\α}}_{1}l}{\∫}}({\stackrel{\·}{U}}_n+{\stackrel{\·}{E}}_{0a}x)C_{01}\mathrm{dx}+\underset{{\mathrm{\α}}_{1}l}{\overset{{\mathrm{\α}}_{2}l}{\∫}}({\stackrel{\·}{U}}_n+{\stackrel{\·}{E}}_{0a}x)C_{02}\mathrm{dx}+$

$...+\underset{{\mathrm{\α}}_{N-1}l}{\overset{l}{\∫}}({\stackrel{\·}{U}}_n+{\stackrel{\·}{E}}_{0a}x)C_{0N}\mathrm{dx}$

$={\stackrel{\·}{U}}_n[C_{01}{\mathrm{\α}}_1+C_{02}({\mathrm{\α}}_2-{\mathrm{\α}}_1)+...+C_{0N}(1-{\mathrm{\α}}_{N-1})]+$

$\frac{1}{2}{\stackrel{\·}{E}}_{0a}{l}^2[C_{01}{{\mathrm{\α}}_1}^2+C_{02}({{\mathrm{\α}}_2}^2-{{\mathrm{\α}}_1}^2)+...+C_{0N}(1-{{\mathrm{\α}}_{N-1}}^2)]$ ... ... ... ... ... formula (14).

Formula (14) is consistent with formula (12) form, so formula (14) also can become formula (13) by abbreviation.As seen, no matter which kind of running status high-voltage generator is under, capacitance current can calculate with equivalent electric circuit shown in Figure 5, and and the location independent of fault point, therefore, the equivalent electric circuit of capacitance current is not only applicable to the analysis of high-voltage generator capacitance current when normal operation, the computing of capacitance current when equally yet being adapted to high-voltage generator generation external fault, internal fault.

The winding builtin voltage of high-voltage generator progressively raises to the machine end from central point, so the insulating barrier of its XLPE cable constantly increases, and promptly r2 constantly increases, and interior semi-conductive radius r 1 remains unchanged, and therefore should have following relational expression:

C ₀₁＞C ₀₂＞...＞C _0N... ... ... ... formula (15).

Based on formula (5), (15), provable division coefficient ρ＜0.5 proves as follows:

$\mathrm{\&rho;}=\frac{1}{2}\frac{C_{01}{{\mathrm{\&alpha;}}_1}^2+C_{02}({{\mathrm{\&alpha;}}_2}^2-{{\mathrm{\&alpha;}}_1}^2)+...+C_{0N}(1-{{\mathrm{\&alpha;}}_{N-1}}^2)}{C_{01}{\mathrm{\&alpha;}}_1+C_{02}({\mathrm{\&alpha;}}_2-{\mathrm{\&alpha;}}_1)+...+C_{0N}(1-{\mathrm{\&alpha;}}_{N-1})}<0.5$

$\&DoubleLeftRightArrow;C_{01}{{\mathrm{\&alpha;}}_1}^2+C_{02}({{\mathrm{\&alpha;}}_2}^2-{{\mathrm{\&alpha;}}_1}^2)+...+C_{0N}(1-{{\mathrm{\&alpha;}}_{N-1}}^2)<$

$C_{01}{\mathrm{\&alpha;}}_1+C_{02}({\mathrm{\&alpha;}}_2-{\mathrm{\&alpha;}}_1)+...+C_{0N}(1-{\mathrm{\&alpha;}}_{N-1})$

$\&DoubleLeftRightArrow;{{\mathrm{\&alpha;}}_1}^2(C_{01}-C_{02})+{{\mathrm{\&alpha;}}_2}^2(C_{02}-C_{03})+...+{{\mathrm{\&alpha;}}_{N-1}}^2(C_{0N-1}-C_{0N})+C_{0N}<$

${\mathrm{\&alpha;}}_1(C_{01}-C_{02})+{\mathrm{\&alpha;}}_2(C_{02}-C_{03})+...+{\mathrm{\&alpha;}}_{N-1}(C_{0N-1}-C_{0N})+C_{0N}$

$\&DoubleLeftRightArrow;{\mathrm{\&alpha;}}_1(C_{01}-C_{02})({\mathrm{\&alpha;}}_1-1)+{\mathrm{\&alpha;}}_2(C_{02}-C_{03})({\mathrm{\&alpha;}}_2-1)$

$+...+{\mathrm{\&alpha;}}_{N-1}(C_{0N-1}-C_{0N})({\mathrm{\&alpha;}}_{N-1}-1)<0$

Referring to Fig. 7, by foregoing description, the method for the capacitance current in the fine compensation differential current provided by the invention specifically may further comprise the steps:

Steps A: motor windings electric capacity is pressed division coefficient ρ: (1-ρ) to neutral point and machine end two ends, makes that the winding total capacitance is C with lumped parameter equivalence _ω, the equivalent capacity that then is positioned at the machine end is ρ C _ω, and the equivalent capacity that is positioned at neutral point is (1-ρ) C _ω

Step B:, calculate division coefficient ρ according to the construction of cable and parameter;

Wherein, the computing formula of ρ is:

$\mathrm{\&rho;}=\frac{1}{2}\frac{C_{01}{{\mathrm{\&alpha;}}_1}^2+C_{02}({{\mathrm{\&alpha;}}_2}^2-{{\mathrm{\&alpha;}}_1}^2)+...+C_{0N}({{\mathrm{\&alpha;}}_N}^2-{{\mathrm{\&alpha;}}_{N-1}}^2)}{C_{01}{\mathrm{\&alpha;}}_1+C_{02}({\mathrm{\&alpha;}}_2-{\mathrm{\&alpha;}}_1)+...+C_{0N}({\mathrm{\&alpha;}}_N-{\mathrm{\&alpha;}}_{N-1})}$

In the formula, ρ is a division coefficient; α ₁, α ₂... α _NIt is respectively the coefficient that first section, second section, N section conductor account for whole winding total length; C ₀₁, C ₀₂... C _0NIt is respectively the unit length direct-to-ground capacitance of first section, second section and N section conductor.

Step C: the lumped parameter equivalent electric circuit of setting up according to division coefficient ρ calculates capacitance current, to determine the condenser current compensation amount in the differential current.

The present invention is by with machine end and the neutral point of generator windings capacitor equivalent to motor, goes out division coefficient according to the Structure Calculation of motor.The capacitance current that adopts the present invention to can be used in the fine compensation differential current is protected reliability to improve, and possesses to implement simple and easy, as to prevent to protect misoperation and tripping work advantage.

Should be understood that application of the present invention is not limited to above-mentioned giving an example, for those of ordinary skills, can be improved according to the above description or conversion that all these improvement and conversion all should belong to the protection range of claims of the present invention.

Claims (2)

1. a method that is used for the capacitance current of generator compensates for differential electric current is characterized in that, may further comprise the steps:

A: motor windings electric capacity is pressed division coefficient ρ: (1-ρ) to neutral point and machine end two ends, makes that the winding total capacitance is C with lumped parameter equivalence _ω, the equivalent capacity that then is positioned at the machine end is ρ C _ω, and the equivalent capacity that is positioned at neutral point is (1-ρ) C _ω

B:, calculate division coefficient ρ according to the construction of cable and parameter;

Wherein, the computing formula of ρ is:

$\mathrm{\&rho;}=\frac{1}{2}\frac{C_{01}{{\mathrm{\&alpha;}}_1}^2+C_{02}({{\mathrm{\&alpha;}}_2}^2-{{\mathrm{\&alpha;}}_1}^2)+...+C_{0N}({{\mathrm{\&alpha;}}_N}^2-{{\mathrm{\&alpha;}}_{N-1}}^2)}{C_{01}{\mathrm{\&alpha;}}_1+C_{02}({\mathrm{\&alpha;}}_2-{\mathrm{\&alpha;}}_1)+...+C_{0N}({\mathrm{\&alpha;}}_N-{\mathrm{\&alpha;}}_{N-1})}$

In the formula, ρ is a division coefficient; α ₁, α ₂... α _NIt is respectively the coefficient that first section, second section, N section conductor account for whole winding total length; C ₀₁, C ₀₂... C _0NIt is respectively the unit length direct-to-ground capacitance of first section, second section and N section conductor;

C: the lumped parameter equivalent electric circuit of setting up according to division coefficient ρ calculates capacitance current, to determine the condenser current compensation amount in the differential current.

2. the method that is used for the capacitance current of generator compensates for differential electric current according to claim 1 is characterized in that the computing formula of described capacitance current is:

${\stackrel{\&CenterDot;}{I}}_{\mathrm{ca}}=\mathrm{j\&omega;}[(1-\mathrm{\&rho;})C_{\mathrm{\&omega;}}{\stackrel{\&CenterDot;}{U}}_0+\mathrm{\&rho;}{C}_{\mathrm{\&omega;}}{\stackrel{\&CenterDot;}{U}}_N],$

In the formula, Be capacitance current; ρ is a division coefficient; C _ωBe the winding total capacitance;

Be neutral point voltage;

Be set end voltage.

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