CN103199495B - Method of preventing maloperation of generator power frequency zero sequence current protection - Google Patents

Abstract

The invention discloses a method of preventing maloperation of generator power frequency zero sequence current protection. An injection voltage element is adopted to carry out locking control on power frequency zero sequence current protection according to a characteristic that when an earth fault occurs to a high-voltage side of a booster transformer of a power plant, an injection type signal circuit remains unchanged, and the maloperation of the protection is prevented. A specific process as follows: in a running process of a generator, injection type voltage is monitored, if measured injection voltage is smaller than ULF0-act-max, the power frequency zero sequence current protection is opened, and otherwise, the power frequency zero sequence current protection is locked. The ULF0-act-max is the maximum value of the injection type voltage under the condition that all the stator earth fault currents are equal to safe currents. The method of preventing the maloperation of the generator power frequency zero sequence current protection can effectively prevent the maloperation of the power frequency zero sequence current protection caused by the transfer of overvoltage when the earth fault occurs to the high-voltage side of the booster transformer, and does not need to be matched with the earth protection of the high-voltage side of the booster transformer.

Description

A kind of method preventing maloperation of generator power frequency zero sequence current protection

Technical field

The present invention relates to a kind of method being prevented maloperation of generator power frequency zero sequence current protection by pouring-in voltage component, belong to Automation of Electric Systems control technology.

Background technology

The outer high-rating generator neutral point of Present Domestic mainly adopts the mode becoming ground connection through ground connection; grounding of stator winding protection adopts 20Hz injected type stator ground protection; this ground protection is protected by earth resistance and power frequency zero-sequence current protection forms; two kinds of protection ranges are overlapping without dead band, realize 100% stator ground fault protection.

In actual moving process; when boosting becomes high-pressure side generation earth fault; high-pressure side residual voltage is uprised by boosting, stray capacitance is coupled in generator unit stator winding loop between low-pressure side winding; generator neutral point voltage raises; this transferring over-voltage can cause the rising of power frequency zero-sequence current, very easily causes the misoperation of power frequency zero-sequence current protection.

Previously the used method of power frequency zero-sequence current protection malfunction that prevents has following two kinds:

1) method of power frequency zero-sequence current action threshold is raised

Introduce boosting and become high-pressure side residual voltage, judge that boosting becomes high-pressure side and whether has earth fault to occur, after confirming that earth fault occurs, raise power frequency zero-sequence current action threshold, prevent the misoperation of power frequency zero-sequence current protection.

The shortcoming of the method is: lifting ac threshold reduces protection range, reduces the sensitivity of protection, and the size of transferring over-voltage is not easily determined simultaneously, and power frequency zero-sequence current protection action threshold value is difficult to adjust.

2) power frequency zero-sequence current protection and boosting uprise the method that pressure side ground protection matches

Power frequency zero-sequence current protection and boosting uprise the ground zero-sequenceprotection of pressure side joint and coordinate, and adjustment action delay, escapes system earth side fault.

The shortcoming of the method is: when there is stator single-phase grounding fault fault, and protection excision is long for fault time.

Summary of the invention

Goal of the invention: in order to overcome the deficiencies in the prior art, the invention provides a kind of method effectively being prevented maloperation of generator power frequency zero sequence current protection by pouring-in voltage component, to improve power frequency zero-sequence current protection overall performance.

Technical scheme: for achieving the above object, the technical solution used in the present invention is:

A kind of method preventing maloperation of generator power frequency zero sequence current protection; when the method becomes high-pressure side generation earth fault generation transferring over-voltage according to power plant boosting; pouring-in signal circuit remains unchanged this feature; pouring-in voltage component is adopted to carry out locking control to power frequency zero-sequence current protection; prevent false protection; detailed process is as follows: in generator operation, to pouring-in voltage U _lF0monitor, if the pouring-in voltage U recorded _lF0be less than U _{lF0_act_max}, then open power frequency zero-sequence current protection, otherwise locking power frequency zero-sequence current protection; Wherein U _{lF0_act_max}for all stator ground-fault currents I of generator _eequal safe current I _safepouring-in voltage U under situation _lF0maximum.

Concrete, described pouring-in voltage U _lF0be less than U _{lF0_act_max}formula of sentencing be specially U _lF0≤ kU _{lF0_act_max}, wherein k is safety factor.

Concrete, described pouring-in voltage U _lF0account form as follows:

${\stackrel{\·}{U}}_{\mathrm{LF}0}=(1-\frac{R_{\mathrm{in}}}{R_{\mathrm{in}}+Z_{\mathrm{paral}}})\·{\stackrel{\·}{U}}_{\mathrm{source}\_\mathrm{inject}}$

Wherein, R _infor pouring-in signal power source equivalent internal resistance, Z _para1for conversion to the machine end in the ground connection transition resistance in pouring-in equivalent circuit, conversion to pouring-in equivalent circuit over the ground distributed capacitance and neutral ground become the resistance value after secondary load resistor coupled in parallel, for pouring-in signal power source.

Beneficial effect: the method preventing maloperation of generator power frequency zero sequence current protection provided by the invention; during according to generation transferring over-voltage; the pouring-in voltage recorded in the pouring-in equivalent circuit of generator injected type stator ground protection does not change; the characteristic that during generator unit stator winding earth, pouring-in change in voltage is large; locking control is carried out to power frequency zero-sequence current protection, only need by pouring-in voltage U _lF0monitoring, just correctly can distinguish the power frequency zero sequence excess current that transferring over-voltage and generator stator ground fault cause and rise, pressure side joint ground protection cooperation need not be uprised with boosting; When can effectively prevent boosting from becoming high-pressure side generation earth fault, transferring over-voltage causes the malfunction of power frequency zero-sequence current protection.

Accompanying drawing explanation

Pouring-in equivalent circuit when Fig. 1 is stator single-phase grounding fault fault;

Power frequency zero sequence equivalent circuit when Fig. 2 is stator single-phase grounding fault fault;

Fig. 3 is the logic diagram of power frequency zero-sequence current protection.

Embodiment

Below in conjunction with accompanying drawing, the present invention is further described.

A kind of method preventing maloperation of generator power frequency zero sequence current protection; when the method becomes high-pressure side generation earth fault generation transferring over-voltage according to power plant boosting; pouring-in signal circuit remains unchanged this feature; adopt pouring-in voltage component to carry out locking control to power frequency zero-sequence current protection, prevent false protection.

Under pouring-in voltage component mode is injected at generator neutral point place, during stator single-phase grounding fault fault, pouring-in equivalent circuit is as shown in Figure 1, can be obtained by this equivalent circuit:

${\stackrel{\·}{U}}_{\mathrm{LF}0}=(1-\frac{R_{\mathrm{in}}}{R_{\mathrm{in}}+Z_{\mathrm{paral}}})\·{\stackrel{\·}{U}}_{\mathrm{source}\_\mathrm{inject}}---\left(1\right)$

Wherein, U _lF0for pouring-in voltage, R _infor pouring-in signal power source equivalent internal resistance, Z _para1for the ground connection transition resistance R in conversion to pouring-in equivalent circuit _g' (distinguish over not through the ground connection transition resistance R of conversion _g), conversion is to the machine end distributed capacitance-jX' over the ground in pouring-in equivalent circuit _{c_inject}secondary load resistance R is become with neutral ground _nresistance value after parallel connection, for pouring-in signal power source; Wherein, Z _para1for conversion is to the value of ground connection change secondary side, R _g'=R _g/ n ², R _gfor ground connection transition resistance, n is that neutral ground becomes no-load voltage ratio.

When generator normally runs, ground connection transition resistance R _gbe equivalent to infinity, the pouring-in voltage U of mensuration _lF0for maximum; During generator stator winding single-phase earthing, the pouring-in voltage U recorded _lF0to diminish; As ground connection transition resistance R _gwhen being 0 ohm and Single Phase Metal earth fault time, pouring-in voltage U _lF0for minimum value 0.

During generator unit stator winding generation earth fault, power frequency zero sequence equivalent circuit as shown in Figure 2, can be obtained by this equivalent circuit:

$R_g=\mathrm{Re}[\frac{\mathrm{\α}{\stackrel{\·}{U}}_E}{{\stackrel{\·}{I}}_E}-Z_{\mathrm{para}2}]---\left(2\right)$

Wherein, to be earth fault position account for the percentage of stator winding total number of turns to the number of turn of neutral point to α, for generator phase voltage, Z _para2for the equivalent impedance n of neutral ground equipment ²r _nwith stator side total capacitive reactance-jX over the ground _cresistance value after parallel connection; Wherein, Z _para2for conversion is to the value of ground connection change primary side.As earth fault current I _ebe greater than safe current I _safetime, the action of power frequency zero-sequence current protection is tripped, by ground connection transition resistance R _gexpression formula known, when α is 1 and machine end place occur single phase ground fault time, ground connection transition resistance R _gobtain maximum R _{g_max}, as follows:

$R_{g\_\max }=\mathrm{Re}[\frac{{\stackrel{\·}{U}}_E}{{\stackrel{\·}{I}}_{\mathrm{safe}}}-Z_{\mathrm{para}2}]---\left(3\right)$

From formula (1), Z _para1along with R _gincrease and increase, U _lF0along with Z _para1increase and increase, namely U _lF0along with R _gincrease and increase.

From formula (2), when α is 1, when namely there is single phase ground fault in machine end place, R _gobtain maximum R _{g_max}, now U _lF0obtain maximum U _{lF0_act_max}.

U _{lF0_act_max}for all generator stator ground fault current I _eequal safe current I _safepouring-in voltage U under situation _lF0maximum.In generator operation, as long as the pouring-in voltage U recorded _lF0be less than U _{lF0_act_max}, just open power frequency zero-sequence current protection, otherwise locking power frequency zero-sequence current protection.

As shown in Figure 3, the formula of sentencing of pouring-in voltage component is U to the logic diagram of power frequency zero-sequence current protection _lF0≤ kU _{lF0_act_max}, wherein k is safety factor; In figure, I ₅₀for power frequency zero-sequence current value, T _gpglfor the operation time limit of power frequency zero-sequence current protection.

The above is only the preferred embodiment of the present invention; be noted that for those skilled in the art; under the premise without departing from the principles of the invention, can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (3)

1. one kind prevents the method for maloperation of generator power frequency zero sequence current protection; it is characterized in that: when becoming high-pressure side generation earth fault generation transferring over-voltage according to power plant boosting; pouring-in signal circuit remains unchanged this feature; pouring-in voltage component is adopted to carry out locking control to power frequency zero-sequence current protection; prevent false protection; detailed process is as follows: in generator operation, to pouring-in voltage U _lF0monitor, if the pouring-in voltage U recorded _lF0be less than U _{lF0_act_max}, then open power frequency zero-sequence current protection, otherwise locking power frequency zero-sequence current protection; Wherein U _{lF0_act_max}for all stator ground-fault currents I of generator _eequal safe current I _safepouring-in voltage U under situation _lF0maximum.

2. the method preventing maloperation of generator power frequency zero sequence current protection according to claim 1, is characterized in that: described pouring-in voltage U _lF0be less than U _{lF0_act_max}formula of sentencing be specially U _lF0≤ kU _{lF0_act_max}, wherein k is safety factor.

3. the method preventing maloperation of generator power frequency zero sequence current protection according to claim 1, is characterized in that: described pouring-in voltage U _lF0vector account form is as follows:

${\stackrel{\·}{U}}_{\mathrm{LF}0}=(1-\frac{R_{\mathrm{in}}}{R_{\mathrm{in}}+Z_{\mathrm{para}1}})\·{\stackrel{\·}{U}}_{\mathrm{source}\_\mathrm{inject}}$

Wherein, R _infor pouring-in signal power source equivalent internal resistance, Z _para1for conversion to the machine end in the ground connection transition resistance in pouring-in equivalent circuit, conversion to pouring-in equivalent circuit over the ground distributed capacitance and neutral ground become the resistance value after secondary load resistor coupled in parallel, for pouring-in signal power source.