CN101777755B - High-voltage capacitor unbalance protection method for high-voltage direct-current transmission system - Google Patents

Abstract

The invention relates to a high-voltage capacitor unbalance protection method for a high-voltage direct-current power transmission system. The method comprises the following steps: 1) analyzing unbalanced current of a high-voltage capacitor of the high-voltage direct-current transmission system when a capacitive element breaks down in the fault development process; 2) judging the symmetric or asymmetric fault of a high-voltage capacitor of the high-voltage direct-current transmission system; 3) and aiming at symmetrical and asymmetrical faults, a corresponding setting principle and an action strategy are provided. The high-voltage capacitor unbalance protection method of the high-voltage direct-current power transmission system is simple to operate, convenient and practical.

Description

High-voltage capacitor imbalance protecting method for high-voltage DC transmission system

Technical field

The invention belongs to the HVDC transmission system technical field of relay protection, particularly high-voltage capacitor imbalance protecting method for high-voltage DC transmission system belongs to the innovative technology of high-voltage capacitor imbalance protecting method for high-voltage DC transmission system.

Background technology

In the investment of the AC/DC filter of HVDC transmission system (be called for short HVDC (High Voltage Direct Current) system), the investment of high-voltage capacitor has accounted for major part.The high-voltage capacitor of AC/DC filter has born the power frequency pressure drop of ac bus and the direct current pressure drop of DC line respectively; They have also born most of harmonic wave pressure drop in addition; When the element short circuit being arranged in the high-voltage capacitor or opens circuit; The voltage that other normal capacity cell bears raises, and causes the avalanche effect that capacity cell damages easily.Actual motion shows that high-voltage capacitor is the highest equipment of failure rate in the filter.Therefore the damage fault that in time detects the high-voltage capacitor inner member all is necessary to the safe and stable operation that ensures high-voltage capacitor and even HVDC system.

Because there is certain difficulty in the capacitance in capacitor run duration Measurement of capacitor, in order to detect the internal damage fault of capacitor, the high-voltage capacitor in the HVDC engineering adopts wiring of H shape or branch connection form usually.Because rated voltage, electric current and the capacity of single capacity cell are difficult to satisfy application requirements, 1 branch road capacitor need couple together a plurality of capacitor units with certain series-parallel system.Multiselect is used the inner fuse capacitor unit in the AC/DC filter at present.

The general fault that adopts the capacitor unbalance protection to detect the capacitor inner member.At present, the protection of HVDC system research mainly concentrates on commutation failure prediction protection, traveling-wave protection and 100Hz protection etc.Capacitor unbalance protection in the existing document focuses on the detection of research capacitor three-phase imbalance more, and the capacitor unbalance protection in the HVDC system need detect the imbalance between each branch road of single-phase electricity container.

In some HVDC engineerings, Unbalance Protection for High Voltage Capacitor is discerned the internal fault of capacitor through the effective value that detects unsymmetrical current.But unsymmetrical current receives the influence of ac and dc systems operational mode and frequency, and excursion is bigger.Under the situation of the identical damage of capacitor, adopting fixedly, the unbalance protection of threshold is difficult to meet the demands.The ratio that also has in some engineerings unsymmetrical current and the filter electric current of same frequency through calculating specific times harmonic, the internal fault of detection capacitor.Actual motion shows, based on capacitor unbalance protection tripping several times once under the situation that the inner few components of capacitor is damaged of this principle, has brought hidden danger for the safe and stable operation of high-voltage capacitor.

Summary of the invention

The objective of the invention is to consider the problems referred to above and a kind of high-voltage capacitor imbalance protecting method for high-voltage DC transmission system is provided.The present invention is convenient and practical.

Technical scheme of the present invention is: high-voltage capacitor imbalance protecting method for high-voltage DC transmission system of the present invention comprises the steps:

Unsymmetrical current when 1) analyzing the HVDC transmission system high-voltage capacitor capacity cell punctures in the fault progression process;

2) symmetry or the unbalanced fault of judgement HVDC transmission system high-voltage capacitor;

3), propose to adjust accordingly principle and action policy to symmetry and unbalanced fault.

Above-mentioned high-voltage capacitor includes the capacitor of H shape connection type and the capacitor of branch connection form.

The capacitor of above-mentioned H shape connection type for unbalanced fault, adopts the pulse detection method, promptly utilizes the variable quantity of unsymmetrical current and total current ratio to confirm the capacitor fault.

The concrete grammar of above-mentioned pulse detection method is:

During according to single branch road capacitor fault; The unsymmetrical current that produces when damaging X internal capacitance element is provided with alarm section and deferred action section; The operation equation of protection is suc as formula shown in (1), and the maximum voltage stress that bears according to capacity cell confirms the operate time of protection, and the unsymmetrical current that produces during according to 1 row capacity cell short circuit is provided with the quick-action section; The operation equation of protection is suc as formula shown in (2)

$\left|\mathrm{\Δ}\frac{i_{\mathrm{unb}}}{i_s}\right|\≥K_{\mathrm{rel}}\frac{x}{4\mathrm{MN}-4\mathrm{Mx}+2x}---\left(1\right)$

$\left|\mathrm{\Δ}\frac{i_{\mathrm{unb}}}{i_s}\right|\≥\frac{K_{\mathrm{rel}}}{4M-2}---\left(2\right)$

In the formula: i _UnbI _sBe the ratio of unsymmetrical current and total current, K _RelBe safety factor; This parameter need be taken all factors into consideration measure error, the ratio correction of transformation coefficient of current transformer and measure the error of other link of loop; Be taken as 0.7～0.8, M is a series capacitance element line number in 1 branch road capacitor, and N is a shunt capacitor unit number in the 1 row capacity cell.

The capacitor of above-mentioned H shape connection type for symmetric fault, adopts off resonance degree detection method, and the off resonance degree that promptly passes through calculating filter is to judge fault.

The concrete grammar of above-mentioned off resonance degree detection method is:

Carrying out off resonance through the 12 subharmonic impedances of keeping watch on DC filter detects; Because DC filter is tuned in 12 subharmonic, therefore 12 subharmonic impedances are very little, when off resonance under the normal operation; 12 subharmonic impedances will obviously increase, and following off resonance detection criteria is promptly arranged:

$\frac{U_{12}}{I_{12}}>\frac{Z_{12}}{K_{\mathrm{rel}}}---\left(3\right)$

In the formula: U ₁₂And I ₁₂Be respectively the effective value of 12 subharmonic voltage harmonic electric currents of filter; Z ₁₂12 subharmonic impedances for this filter under the normal condition;

The operation characteristic of filter joint is provided with 2 sections, and the I section is used to prevent to cause owing to reasons such as sunshines the variation of filter parameter for the section of reporting to the police, and the II section is the quick-action section, is used to detect the symmetric fault of capacitor, surgical filtering device immediately after the protection action.

The capacitor of above-mentioned branch connection form, for unbalanced fault, adopting through detecting capacitor has capacity cell to be resected to 1 row capacity cell by fuse from 1 branch road to be discerned the capacitor fault by the pulse current in the short circuit process.

Above-mentioned employing has capacity cell to be resected to the concrete grammar that 1 row capacity cell discerned the capacitor fault by the pulse current in the short circuit process by fuse from 1 branch road to be through detecting capacitor:

Unbalance protection based on the pulse detection method adopts following operation equation:

$\left|\mathrm{\Δ}\frac{i_{\mathrm{unb}}}{i_s}\right|\≥K_{\mathrm{rel}}(\frac{K}{2\mathrm{MN}-2\mathrm{MK}+K}+\frac{1}{2M-1})---\left(4\right)$

In the formula: i _UnbI _sBe the ratio of unsymmetrical current and total current, K _RelBe safety factor; This parameter need be taken all factors into consideration measure error, the ratio correction of transformation coefficient of current transformer and measure the error of other link of loop; Can be taken as 0.7～0.8; M is a series capacitance element line number in 1 branch road capacitor, and N is a shunt capacitor unit number in the 1 row capacity cell, and K is by the capacitor unit number of fuse excision when 1 row capacity cell is by short circuit in 1 branch road;

When DC filter normally moved, filter impedance showed as capacitive, the impedance dominates of high-end capacity cell, and it is less to flow through the electric current of filter branches; When high-voltage capacitor was inner badly damaged, capacitance increased, and the electric current that flows through filter sharply increases, and therefore, adopts following action policy: work as i _sHour, the on high-tension side circuit breaker of tripping DC filter, otherwise locking converter and tripping AC circuit breaker.

The capacitor of above-mentioned branch connection form for unbalanced fault, adopts off resonance degree detection method, and the off resonance degree that promptly passes through calculating filter is to judge fault.

The concrete grammar of above-mentioned off resonance degree detection method is:

Carrying out off resonance through the 12 subharmonic impedances of keeping watch on DC filter detects; Because DC filter is tuned in 12 subharmonic, therefore 12 subharmonic impedances are very little, when off resonance under the normal operation; 12 subharmonic impedances will obviously increase, and following off resonance detection criteria is promptly arranged:

$\frac{U_{12}}{I_{12}}>\frac{Z_{12}}{K_{\mathrm{rel}}}---\left(3\right)$

In the formula: U ₁₂And I ₁₂Be respectively the effective value of 12 subharmonic voltage harmonic electric currents of filter; Z ₁₂12 subharmonic impedances for this filter under the normal condition;

The operation characteristic of filter joint can be provided with 2 sections, and the I section is used to prevent to cause owing to reasons such as sunshines the variation of filter parameter for the section of reporting to the police, and the II section is the quick-action section, is used to detect the symmetric fault of capacitor, surgical filtering device immediately after the protection action.

The present invention is because the structure that adopts; Compared with prior art; The advantage that has is: traditional capacitor unbalance protection is discerned the internal fault of capacitor through the effective value that detects unsymmetrical current; And unsymmetrical current receives the influence of ac and dc systems operational mode and frequency, and excursion is bigger, adopts the fixedly unsymmetrical current guard method of threshold to be difficult to satisfy actual requirement; The present invention has proposed new Practical Criteria to the capacitor unbalance protection of the wiring of H shape and two kinds of connection types of branch shape wiring respectively; And inquired into to adjust accordingly and calculated principle and action policy; Through asking for the ratio that unsymmetrical current accounts for passing through property electric current; Can eliminate the influence of operational mode to the unsymmetrical current size; Strengthened the adaptability of capacitor unbalance protection, improved the reliability of capacitor unbalance protection action, distributing rationally and adjusting to calculate and have reference value HVDC system high pressure capacitor unbalance protection.The present invention is a kind of convenient and practical high-voltage capacitor imbalance protecting method for high-voltage DC transmission system.

Description of drawings

Fig. 1-1 is the structural representation of the capacitor of H shape connection type;

Fig. 1-2 is the structural representation of the capacitor of branch connection form;

Fig. 2 is the internal structure sketch map of inner fuse capacitor unit.

Embodiment

Embodiment:

High-voltage capacitor imbalance protecting method for high-voltage DC transmission system of the present invention comprises the steps:

Unsymmetrical current when 1) analyzing the HVDC transmission system high-voltage capacitor capacity cell punctures in the fault progression process;

2) symmetry or the unbalanced fault of judgement HVDC transmission system high-voltage capacitor;

3), propose to adjust accordingly principle and action policy to symmetry and unbalanced fault.

Above-mentioned high-voltage capacitor includes the capacitor of H shape connection type and the capacitor of branch connection form.The concrete wiring of capacitor of H shape connection type is shown in accompanying drawing 1-1, and C1-C4 is the capacitor branch road that is coupled together through certain series-parallel system by a plurality of capacity cells among the figure, TA _dFor measuring the current transformer of unsymmetrical current, TA _sFor measuring the current transformer of total current; The concrete wiring of the capacitor of branch connection form is shown in accompanying drawing 1-2, and C1 among the figure, C2 are the capacitor branch road that is coupled together through certain series-parallel system by a plurality of capacity cells, TA ₁, TA ₂Be two current transformers on the capacitor branch road.The capacitor of above-mentioned H shape connection type for unbalanced fault, adopts the pulse detection method, promptly utilizes the variable quantity of unsymmetrical current and total current ratio to confirm the capacitor fault.

In the present embodiment, the concrete grammar of above-mentioned pulse detection method is:

During according to single branch road capacitor fault; The unsymmetrical current that produces when damaging X internal capacitance element is provided with alarm section and deferred action section; The operation equation of protection is suc as formula shown in (1), and the maximum voltage stress that bears according to capacity cell confirms the operate time of protection, and the unsymmetrical current that produces during according to 1 row capacity cell short circuit is provided with the quick-action section; The operation equation of protection is suc as formula shown in (2)

$\left|\mathrm{\Δ}\frac{i_{\mathrm{unb}}}{i_s}\right|\≥K_{\mathrm{rel}}\frac{x}{4\mathrm{MN}-4\mathrm{Mx}+2x}---\left(1\right)$

$\left|\mathrm{\Δ}\frac{i_{\mathrm{unb}}}{i_s}\right|\≥\frac{K_{\mathrm{rel}}}{4M-2}---\left(2\right)$

In the formula: i _UnbI _sRatio for unsymmetrical current and total current; Krel is a safety factor; This parameter need be taken all factors into consideration measure error, the ratio correction of transformation coefficient of current transformer and measure the error of other link of loop; Be taken as 0.7～0.8, M is a series capacitance element line number in 1 branch road capacitor, and N is a shunt capacitor unit number in the 1 row capacity cell.

The capacitor of above-mentioned H shape connection type for symmetric fault, adopts off resonance degree detection method, and the off resonance degree that promptly passes through calculating filter is to judge fault.

In the present embodiment, the concrete grammar of above-mentioned off resonance degree detection method is:

Carrying out off resonance through the 12 subharmonic impedances of keeping watch on DC filter detects; Because DC filter is tuned in 12 subharmonic, therefore 12 subharmonic impedances are very little, when off resonance under the normal operation; 12 subharmonic impedances will obviously increase, and following off resonance detection criteria is promptly arranged:

$\frac{U_{12}}{I_{12}}>\frac{Z_{12}}{K_{\mathrm{rel}}}---\left(3\right)$

In the formula: U ₁₂And I ₁₂Be respectively the effective value of 12 subharmonic voltage harmonic electric currents of filter; Z ₁₂12 subharmonic impedances for this filter under the normal condition;

The operation characteristic of filter joint is provided with 2 sections, and the I section is used to prevent to cause owing to reasons such as sunshines the variation of filter parameter for the section of reporting to the police, and the II section is the quick-action section, is used to detect the symmetric fault of capacitor, surgical filtering device immediately after the protection action.

The capacitor of above-mentioned branch connection form, for unbalanced fault, adopting through detecting capacitor has capacity cell to be resected to 1 row capacity cell by fuse from 1 branch road to be discerned the capacitor fault by the pulse current in the short circuit process.

In the present embodiment, above-mentioned employing has capacity cell to be resected to the concrete grammar that 1 row capacity cell discerned the capacitor fault by the pulse current in the short circuit process by fuse from 1 branch road to be through detecting capacitor:

Unbalance protection based on the pulse detection method adopts following operation equation:

$\left|\mathrm{\Δ}\frac{i_{\mathrm{unb}}}{i_s}\right|\≥K_{\mathrm{rel}}(\frac{K}{2\mathrm{MN}-2\mathrm{MK}+K}+\frac{1}{2M-1})---\left(4\right)$

In the formula: i _UnbI _sRatio for unsymmetrical current and total current; Krel is a safety factor; This parameter need be taken all factors into consideration measure error, the ratio correction of transformation coefficient of current transformer and measure the error of other link of loop, can be taken as 0.7～0.8, and M is a series capacitance element line number in 1 branch road capacitor; N is a shunt capacitor unit number in the 1 row capacity cell, and K is by the capacitor unit number of fuse excision when 1 row capacity cell is by short circuit in 1 branch road;

When DC filter normally moved, filter impedance showed as capacitive, the impedance dominates of high-end capacity cell, and it is less to flow through the electric current of filter branches; When high-voltage capacitor was inner badly damaged, capacitance increased, and the electric current that flows through filter sharply increases, and therefore, adopts following action policy: work as i _sHour, the on high-tension side circuit breaker of tripping DC filter, otherwise locking converter and tripping AC circuit breaker.

The capacitor of above-mentioned branch connection form for unbalanced fault, adopts off resonance degree detection method, and the off resonance degree that promptly passes through calculating filter is to judge fault.

In the present embodiment, the concrete grammar of above-mentioned off resonance degree detection method is:

Carrying out off resonance through the 12 subharmonic impedances of keeping watch on DC filter detects; Because DC filter is tuned in 12 subharmonic, therefore 12 subharmonic impedances are very little, when off resonance under the normal operation; 12 subharmonic impedances will obviously increase, and following off resonance detection criteria is promptly arranged:

$\frac{U_{12}}{I_{12}}>\frac{Z_{12}}{K_{\mathrm{rel}}}---\left(3\right)$

In the formula: U ₁₂And I ₁₂Be respectively the effective value of 12 subharmonic voltage harmonic electric currents of filter; Z ₁₂12 subharmonic impedances for this filter under the normal condition;

The operation characteristic of filter joint can be provided with 2 sections, and the I section is used to prevent to cause owing to reasons such as sunshines the variation of filter parameter for the section of reporting to the police, and the II section is the quick-action section, is used to detect the symmetric fault of capacitor, surgical filtering device immediately after the protection action.

Claims (4)

1. a high-voltage capacitor imbalance protecting method for high-voltage DC transmission system is characterized in that comprising the steps:

Unsymmetrical current when 1) analyzing the HVDC transmission system high-voltage capacitor capacity cell punctures in the fault progression process;

2) symmetry or the unbalanced fault of judgement HVDC transmission system high-voltage capacitor;

3), propose to adjust accordingly principle and action policy to symmetry and unbalanced fault;

Above-mentioned high-voltage capacitor includes the capacitor of H shape connection type and the capacitor of branch connection form;

The capacitor of above-mentioned H shape connection type for unbalanced fault, adopts the pulse detection method, promptly utilizes the variable quantity of unsymmetrical current and total current ratio to confirm the capacitor fault;

The capacitor of above-mentioned H shape connection type for symmetric fault, adopts off resonance degree detection method, and the off resonance degree that promptly passes through calculating filter is to judge fault;

The capacitor of above-mentioned branch connection form, for unbalanced fault, adopting through detecting capacitor has capacity cell to be resected to 1 row capacity cell by fuse from 1 branch road to be discerned the capacitor fault by the pulse current in the short circuit process;

The capacitor of above-mentioned branch connection form for symmetric fault, adopts off resonance degree detection method, and the off resonance degree that promptly passes through calculating filter is to judge fault.

2. high-voltage capacitor imbalance protecting method for high-voltage DC transmission system according to claim 1 is characterized in that the concrete grammar of above-mentioned pulse detection method is:

During according to single branch road capacitor fault; The unsymmetrical current that produces when damaging X internal capacitance element is provided with alarm section and deferred action section; The operation equation of protection is suc as formula shown in (1), and the maximum voltage stress that bears according to capacity cell confirms the operate time of protection, and the unsymmetrical current that produces during according to 1 row capacity cell short circuit is provided with the quick-action section; The operation equation of protection is suc as formula shown in (2)

In the formula: i _UnbI _sBe the ratio of unsymmetrical current and total current, K _RelBe safety factor; This parameter need be taken all factors into consideration measure error, the ratio correction of transformation coefficient of current transformer and measure the error of other link of loop; Be taken as 0.7～0.8, M is a series capacitance element line number in 1 branch road capacitor, and N is a shunt capacitor unit number in the 1 row capacity cell.

3. high-voltage capacitor imbalance protecting method for high-voltage DC transmission system according to claim 1 is characterized in that the concrete grammar of above-mentioned off resonance degree detection method is:

Carrying out off resonance through the 12 subharmonic impedances of keeping watch on DC filter detects; Because DC filter is tuned in 12 subharmonic, therefore 12 subharmonic impedances are very little, when off resonance under the normal operation; 12 subharmonic impedances will obviously increase, and following off resonance detection criteria is promptly arranged:

In the formula: U ₁₂And I ₁₂Be respectively the effective value of 12 subharmonic voltage harmonic electric currents of filter; Z ₁₂12 subharmonic impedances for this filter under the normal condition;

The operation characteristic of filter joint is provided with 2 sections, and the I section is used to prevent to cause owing to reasons such as sunshines the variation of filter parameter for the section of reporting to the police, and the II section is the quick-action section, is used to detect the symmetric fault of capacitor, surgical filtering device immediately after the protection action.

4. high-voltage capacitor imbalance protecting method for high-voltage DC transmission system according to claim 1 is characterized in that above-mentioned employing has capacity cell to be resected to the concrete grammar that 1 row capacity cell discerned the capacitor fault by the pulse current in the short circuit process by fuse to be through detecting capacitor from 1 branch road:

Unbalance protection based on the pulse detection method adopts following operation equation:

In the formula: i _UnbI _sBe the ratio of unsymmetrical current and total current, K _RelBe safety factor; This parameter need be taken all factors into consideration measure error, the ratio correction of transformation coefficient of current transformer and measure the error of other link of loop; Can be taken as 0.7～0.8; M is a series capacitance element line number in 1 branch road capacitor, and N is a shunt capacitor unit number in the 1 row capacity cell, and K is by the capacitor unit number of fuse excision when 1 row capacity cell is by short circuit in 1 branch road;

When DC filter normally moved, filter impedance showed as capacitive, the impedance dominates of high-end capacity cell, and it is less to flow through the electric current of filter branches; When high-voltage capacitor was inner badly damaged, capacitance increased, and the electric current that flows through filter sharply increases, and therefore, adopts following action policy: work as i _SHour, the on high-tension side circuit breaker of tripping DC filter, otherwise locking converter and tripping AC circuit breaker.

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