CN111371076A - Differential protection method and system suitable for direct-current power distribution network line - Google Patents

Abstract

The invention discloses a differential protection method and system suitable for direct current distribution network lines. The method comprises: collecting the instantaneous current values of the current side differential protection device and the opposite side differential protection device of the direct current distribution network line, Calculate the current variation of the differential protection on the same side of the DC distribution network line; determine the differential current of the current variation according to the current variation of the differential protection on both sides; match the differential protection operating characteristics according to the current variation , to control the differential protection action signal output. The present invention performs differential protection action control through the current variation, can perform reliable and fast action on the single-pole grounding fault with no obvious change in the fault current on the DC distribution network line, and greatly improves the differential protection of the DC distribution network line. Sensitivity of protection; it can also be sensitively judged and act reliably and quickly for bipolar short-circuit faults with drastic changes in electrical quantities on the DC distribution network lines.

Description

Differential protection method and system suitable for DC distribution network lines

technical field

The invention relates to a differential protection method and system suitable for DC distribution network lines, and belongs to the technical field of DC distribution network.

Background technique

The existing DC distribution network line differential protection mainly uses the real-time sampling values on both sides of the line to calculate the differential current and requires that the ratio braking equation is satisfied before it can act.

However, due to the fact that the load current of the pseudo-bipolar DC distribution network can still maintain its original characteristics and operate for a short time when the single-pole grounding fault occurs, the single-pole grounding fault current value of the line is only about tens of amps, which is smaller than the load current. Real-time sampling is adopted. Therefore, the differential protection method using real-time sampling value has the problem of insufficient sensitivity when a single-pole grounding fault occurs. . If a lower action value and a lower ratio braking coefficient are used in a targeted manner to improve the sensitivity of the differential protection against single-pole faults, there may be a problem of malfunction due to electrical disturbances; and by additionally increasing the action delay In order to avoid the malfunction caused by disturbance, it will make the action speed slower when the actual failure occurs.

When a bipolar short-circuit fault occurs in the DC distribution network line, the current on both sides of the line presents a characteristic of a sharp increase. The differential protection method of real-time sampling value will not have the problem of insufficient sensitivity. However, for the DC system, the fault needs to be removed as quickly as possible to protect the power electronic components, and the differential protection method using real-time sampling values requires additional delay to avoid malfunctions caused by abnormal conditions such as sampling errors. Therefore, for bipolar short-circuit faults, the existing differential protection method using real-time sampling values has the problem that reliability and rapidity cannot be taken into account.

Therefore, there is an urgent need to find a differential protection method that takes into account sensitivity, reliability and quickness.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the deficiencies in the prior art, and to provide a new differential protection method and system suitable for direct current distribution network lines.

To achieve the above object, the present invention adopts the following technical solutions to realize:

In a first aspect, the present invention provides a differential protection method suitable for a DC distribution network line, the method comprising the following steps:

Collect the instantaneous current values of the differential protection device on the side of the DC distribution network line and the differential protection device on the opposite side, and calculate the current variation of the differential protection on the same side of the DC distribution network line;

Determine the differential current of the current variation according to the current variation of the differential protection on both sides;

According to the differential current matching of the current variation, the differential protection action characteristic is adapted to carry out the differential protection action signal output control.

In combination with the first aspect, further, the current variation is calculated and obtained by using the following equation:

ΔI _(t) =I _(t) -I _(tT)

In the formula: ΔI _(t) represents the current variation of the differential protection on the same side of the DC distribution network line at time t relative to time tT; I _(t) represents the instantaneous current of the positive or negative pole of the differential protection of the DC distribution network line at time t value; I _(tT) represents the instantaneous current value of the positive or negative pole of the differential protection of the DC distribution network line at time tT; T represents the preset time interval.

With reference to the first aspect, further, the differential protection operating characteristic includes a high operating value characteristic and a low operating value characteristic.

In combination with the first aspect, further, the high action value characteristic means that there are n consecutive sampling points in the sampling sequence that satisfy the corresponding current variation differential protection action equation, then after a delay _TH , the output current variation differential Action signal for protection, n is greater than 4.

In combination with the first aspect, further, the low action value characteristic means that there are m consecutive sampling points in the sampling sequence that satisfy the corresponding current variation differential protection action equation, then after the delay _TL , the output current variation differential Action signal of protection, wherein: T _L >_TH; m is greater than 5 and m is greater than n.

In combination with the first aspect, further, the current variation differential protection action equation is as follows:

Among them: ΔI _dΦ represents the current variation differential current, ΔI _dΦ = |ΔI _MΦ +ΔI _NΦ |; ΔI _rΦ represents the current variation current variation braking current, ΔI _rΦ = |ΔI _MΦ -ΔI _NΦ |; ΔI _MΦ represents The current variation of the differential protection device on the side of the DC distribution network line; ΔI _NΦ represents the current variation of the differential protection device on the opposite side of the DC distribution network line; k represents the ratio braking coefficient corresponding to the operating value characteristics; I _set Indicates the action value corresponding to the action value characteristic.

In combination with the first aspect, further, the high operating value characteristic is suitable for bipolar short-circuit faults, and the low operating value characteristic is suitable for single-pole grounding faults.

In a second aspect, the present invention provides a differential protection system suitable for a DC distribution network, the system comprising:

Sampling module: used to collect the instantaneous current value of the differential protection device on the local side and the differential protection device on the opposite side of the DC distribution network line;

Calculation module: used to calculate the current variation of the differential protection on the same side of the DC distribution network line;

Determination module: used to determine the differential current of the current variation according to the current variation of the differential protection on both sides;

Matching control module: It is used to match the differential protection action characteristics adapted to the differential current according to the current variation, so as to control the differential protection action signal output.

In a third aspect, the present invention also provides a differential protection system suitable for a DC distribution network, including a processor and a storage medium;

the storage medium is used for storing instructions;

The processor is configured to operate in accordance with the instructions to perform the steps of any of the preceding methods.

A fourth aspect. A computer-readable storage medium having a computer program stored thereon, the program implementing the steps of any of the foregoing methods when executed by a processor.

Compared with the prior art, the beneficial effects achieved by the differential protection method and system suitable for DC distribution network lines provided by the present invention at least include:

The differential protection action control is carried out by using the characteristic that the differential current of the current variation is only generated when the line is faulty, and the sampling error of the real-time sampling value does not need to be considered, which can significantly improve the line failure of the DC distribution network, especially the bipolar short-circuit fault. The reliability of the differential protection action when

According to the differential current matching the corresponding differential protection action characteristics according to the current variation, the corresponding action delays can be set for unipolar grounding faults and bipolar short-circuit faults, which helps to improve the sensitivity of unipolar grounding faults and the bipolar short-circuit fault. Fastness of short circuit fault removal.

Description of drawings

1 is a flowchart of a differential protection method suitable for a DC distribution network line provided according to an embodiment of the present invention;

2 is a current waveform diagram of differential protection on both sides of the line when a positive ground fault occurs in a DC distribution network line provided by an embodiment of the present invention;

Fig. 3 is the differential current waveform diagram of the positive current variation at the time of the positive ground fault obtained according to Fig. 2;

Fig. 4 is the braking current waveform diagram of the positive current variation at the time of the positive ground fault obtained according to Fig. 2;

5 is a current waveform diagram of differential protection on both sides of the line when a bipolar short-circuit fault occurs in a DC distribution network line provided by an embodiment of the present invention;

Fig. 6 is the differential current waveform diagram of positive current change amount obtained according to Fig. 5 at the moment of bipolar short-circuit fault;

FIG. 7 is a waveform diagram of the braking current of the positive current variation at the moment of the bipolar short-circuit fault obtained according to FIG. 5 .

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings. The following examples are only used to illustrate the technical solutions of the present invention more clearly, and cannot be used to limit the protection scope of the present invention.

In the DC distribution network line, the differential protection is installed on one side and the opposite side of a DC distribution network line as a pair, and the instantaneous current sampling is realized through the current acquisition modules installed at the switches on both sides of the DC distribution network line. The differential protection on both sides of the DC distribution network line exchanges information with each other through the optical fiber channel.

The differential protection method applicable to the DC distribution network line provided by the implementation of the present invention is realized based on the aforementioned structure of the DC distribution network line. As shown in FIG. 1 , the method includes the following steps:

Collect the instantaneous current values of the differential protection device on the side of the DC distribution network line and the differential protection device on the opposite side, and calculate the current variation of the differential protection on the same side of the DC distribution network line;

Calculate the differential current of the current variation according to the current variation of the differential protection on both sides;

According to the differential current matching of the current variation, the differential protection action characteristic is adapted to carry out the differential protection action signal output control.

The differential protection method provided by the embodiment of the present invention uses the characteristic that the differential current of the current variation is only generated when the line is faulty to perform differential protection action control, without considering the sampling error of the real-time sampling value, and can significantly improve the DC power distribution. The reliability of the differential protection action when the network line is faulty, especially the bipolar short circuit fault; according to the current variation, the differential current matches the corresponding differential protection action characteristics, and the phase can be set separately for the single-pole grounding fault and the double-pole short-circuit fault. The adaptive action delay helps to improve the sensitivity of single-pole ground fault and the rapidity of double-pole short-circuit fault removal.

Wherein, the instantaneous current value may be the instantaneous current value of the positive pole of the differential protection, or may be the instantaneous current value of the negative pole. However, it should be noted that the sampling time of the instantaneous current value of the differential protection on both sides should be synchronized, so as to ensure that the current variation of the differential protection on both sides is also calculated at the same time. Taking time t as an example, the current variation in the embodiment of the present invention is calculated and obtained by using the following equation:

ΔI _(t) = I _{(t) -} I _(tT) (1)

In the formula: ΔI _(t) represents the current variation of the differential protection on the same side of the DC distribution network line at time t relative to time tT; I _(t) represents the instantaneous current of the positive or negative pole of the differential protection of the DC distribution network line at time t value; I _(tT) represents the instantaneous current value of the positive or negative pole of the differential protection of the DC distribution network line at time tT; T represents the preset time interval, considering that T should be greater than the current distortion duration when the DC distribution network fails, In this embodiment of the present invention, T may be 5 milliseconds.

In order to realize not only differential protection for single-pole grounding faults, but also differential protection for double-pole short-circuit faults, the embodiment of the present invention sets a high action value characteristic for double-pole short-circuit faults, and sets a high-action value characteristic for single-pole grounding faults. Low action value feature. The so-called high action value characteristic means that there are n consecutive sampling points in the sampling sequence that satisfy the corresponding current variation differential protection action equation, then the action signal of the current variation differential protection is output after a delay _TH , where: n greater than 4. The so-called low action value characteristic means that there are m consecutive sampling points in the sampling sequence that satisfy the corresponding current variation differential protection action equation, then the action signal of the current variation differential protection is output after the delay _TL , where: m is greater than 5 and m is greater than n. The action delay _TH when the high action value characteristic is satisfied is smaller than the action delay _TL when the low _action value characteristic is satisfied _.

Whether it is a high action value characteristic or a low action value characteristic, the following current variation differential protection action equation is adopted:

Among them: ΔI _dΦ represents the current variation differential current, ΔI _dΦ = |ΔI _MΦ +ΔI _NΦ |; ΔI _rΦ represents the current variation braking current, ΔI _rΦ = |ΔI _MΦ -ΔI _NΦ |; ΔI _MΦ represents the DC power distribution The current variation of the differential protection device on the local side of the grid line; ΔI _NΦ represents the current variation of the differential protection device on the opposite side of the DC distribution network line; k represents the ratio braking coefficient corresponding to the operating value characteristics, with k _H representing high The ratio braking coefficient of the action value characteristic, and k _L represents the ratio braking _coefficient of the low action value characteristic. In the embodiment of the present invention, the value of k _H can be 0.3, and the value of k _L is 0.1; For the corresponding action value, I _setH represents the action value corresponding to the high action value characteristic, I _setL represents the action value corresponding to the low action value characteristic, the value of I _setH can be 1.2 times I _N , and the value of I _setL can be 0.12 times I _N , I _N is the primary value of the rated current of the DC distribution network. The values of _IsetH and _kH are used to sensitively reflect the occurrence of bipolar short-circuit faults on the lines of the DC distribution network. The values of _IsetL and _kL are used to sensitively reflect the single-pole grounding fault with insignificant changes in electrical quantities on the DC distribution network lines.

The effectiveness of the differential protection method provided by the embodiment of the present invention is described below by using a positive ground fault and a bipolar short circuit fault respectively:

As shown in Figure 2, after the positive ground fault occurs on the DC distribution network line, the differential protection on both sides can reflect the fault characteristics through the positive current, and the positive current of the differential protection device on the side and the positive pole of the differential protection device on the opposite side can be reflected. The current is increased, and the value of the change is about 60A. Based on the well-known circuit superposition principle, it can be inferred that the change in the positive current of the differential protection device on the local side and the positive current of the differential protection device on the opposite side is the fault current generated by the positive ground fault. Use formula (1) to calculate and calculate the positive current variation differential current and braking current of the differential protection on both sides, and then substitute it into the differential protection equation shown in formula (2) to calculate, the obtained positive current variation differential current and braking current are shown in Figure 3 and Figure 4, respectively. It can be found that the differential current of the positive current variation increases rapidly after a fault occurs, and its value is continuously greater than the set low operating value I _setL = 60A (the horizontal dotted line in Fig. 3 represents the low operating value 60A), and due to the positive The value of the braking current of the current variation is small, and the ratio braking coefficient also satisfies the equation when the differential current is greater than the low action value. Therefore, after a delay of _TL =5ms, the differential protection action signal of the current variation is output, and the differential protection action signal may be a switch signal used to control the corresponding circuit breaker to perform the tripping action.

The analysis of bipolar short-circuit faults on DC distribution network lines is similar to that of positive-to-ground faults. The differential protection on both sides reflects the fault characteristics at the positive current sampling, as shown in Figure 5. Both the positive current on the side and the positive current on the opposite side both increased significantly. Use formula (1) to calculate the differential current and braking current of the positive current change on both sides, and then substitute it into the differential protection equation of formula (2) for calculation. The obtained positive current variation differential current and braking current are shown in Figure 6 and Figure 7, respectively. It can be found that the positive change differential current increases rapidly after a fault occurs, and its value is continuously greater than the set high operating value _IsetH= 600A (the horizontal dotted line in Fig. 6 represents the high operating value 600A), and due to the positive current The value of the variation braking current is small, so the ratio braking coefficient also satisfies the equation after the differential current is greater than the high action value, which conforms to the condition that among the consecutive N sampling sequences, there are consecutive n sampling points that satisfy the equation. After the delay of _TH= 1ms, the differential protection action signal of the current variation is output. Similarly, the differential protection action signal can also be a switch signal used to control the corresponding circuit breaker to perform the tripping action.

The embodiment of the present invention also provides a differential protection system suitable for a DC distribution network, the system comprising:

Sampling module: used to collect the instantaneous current value of the differential protection device on the local side and the differential protection device on the opposite side of the DC distribution network line;

Calculation module: used to calculate the current variation of the differential protection on the same side of the DC distribution network line;

Determination module: used to determine the differential current of the current variation according to the current variation of the differential protection on both sides;

Matching control module: It is used to match the differential protection action characteristics adapted to the differential current according to the current variation, so as to control the differential protection action signal output.

The differential protection system provided in the embodiment of the present invention can be used to implement the aforementioned differential protection method. For example, the calculation module can be configured to calculate the current variation by using the following equation:

ΔI _(t) =I _(t) -I _(tT)

In the formula: ΔI _(t) represents the current variation of the differential protection on the same side of the DC distribution network line at time t relative to time tT; I _(t) represents the instantaneous current of the positive or negative pole of the differential protection of the DC distribution network line at time t value; I _(tT) represents the instantaneous current value of the positive or negative pole of the differential protection of the DC distribution network line at time tT; T represents the preset time interval.

The embodiment of the present invention also provides a differential protection system suitable for a DC distribution network, which can also be used for the aforementioned differential protection method, including a processor and a storage medium;

the storage medium is used for storing instructions;

The processor is configured to operate in accordance with the instructions to perform the steps of any of the preceding methods.

Embodiments of the present invention further provide a computer-readable storage medium, on which a computer program is stored, and when the program is executed by a processor, implements the steps of any of the foregoing methods.

To sum up, the differential protection system and the computer-readable storage medium provided by the embodiments of the present invention can perform differential protection action control through the amount of current change when executing the aforementioned differential protection method, and can control the operation of the differential protection on the lines of the DC distribution network. Reliable and fast action for single-pole grounding faults with insignificant changes in fault current, greatly improving the sensitivity of differential protection of DC distribution network lines; Faults can also be judged sensitively and act reliably and quickly.

As will be appreciated by those skilled in the art, the embodiments of the present application may be provided as a method, a system, or a computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) having computer-usable program code embodied therein.

The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present application. It will be understood that each flow and/or block in the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to the processor of a general purpose computer, special purpose computer, embedded processor or other programmable data processing device to produce a machine such that the instructions executed by the processor of the computer or other programmable data processing device produce A system for implementing the functions specified in one or more of the flowcharts and/or one or more blocks of the block diagrams.

These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable memory result in an article of manufacture comprising a system of instructions, the instructions The system implements the functions specified in the flow or flow of the flowcharts and/or the block or blocks of the block diagrams.

These computer program instructions can also be loaded on a computer or other programmable data processing device to cause a series of operational steps to be performed on the computer or other programmable device to produce a computer-implemented process such that The instructions provide steps for implementing the functions specified in the flow or blocks of the flowcharts and/or the block or blocks of the block diagrams.

The above are only the preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, without departing from the technical principle of the present invention, several improvements and modifications can also be made. These improvements and modifications It should also be regarded as the protection scope of the present invention.

Claims (10)

1. A differential protection method suitable for a direct current distribution network line is characterized by comprising the following steps:

acquiring instantaneous current values of a differential protection device at the same side and a differential protection device at the opposite side of a direct current distribution network line, and calculating current variation of differential protection at the same side of the direct current distribution network line;

determining current variation differential current according to the current variation of the differential protection at two sides;

and matching the adaptive differential protection action characteristic according to the current variation differential current so as to output and control the differential protection action signal.

2. The differential protection method for the direct-current distribution network line according to claim 1, wherein the current variation is obtained by calculating according to the following equation:

ΔI_(t)＝I_(t)-I_(t-T)

in the formula: delta I_(t)The current variation quantity of differential protection at the same side of a direct current distribution network line at the T moment relative to the T-T moment is represented; i is_(t)The instantaneous current value of the positive pole or the negative pole of the differential protection at the moment t of the direct-current power distribution network line is represented; i is_(t-T)The instantaneous current value of the positive electrode or the negative electrode of the differential protection at the T-T moment of the direct-current distribution network line is represented; t represents a preset time interval.

3. The differential protection method for the direct-current distribution network line according to claim 1, wherein the differential protection operation characteristic includes a high operation value characteristic and a low operation value characteristic.

4. The differential protection method suitable for the direct-current power distribution network line according to claim 3, wherein the high action value characteristic means that if n continuous sampling points in a sampling sequence meet a corresponding current variation differential protection action equation, a delay T is passed_HOutputting an action signal of current variation differential protection, wherein: n is greater than 4.

5. The differential protection method suitable for the direct-current power distribution network line according to claim 4, wherein the characteristic of the low action value means that if m continuous sampling points in a sampling sequence meet a corresponding current variation differential protection action equation, a delay T is passed_LOutputting an action signal of current variation differential protection, wherein: t is_L＞T_HM is greater than 5 and m is greater than n.

6. The differential protection method suitable for the direct current distribution network line according to claim 4 or 5, wherein the current variation differential protection action equation is as follows:

wherein: delta I_dΦIndicating the differential current, Δ I, of the amount of current change_dΦ＝|ΔI_MΦ+ΔI_NΦ|；ΔI_rΦRepresenting the amount of current change, braking current, Δ I_rΦ＝|ΔI_MΦ-ΔI_NΦ|；ΔI_MΦThe current variation of the differential protection device at the current side of the direct-current distribution network line is represented; delta I_NΦThe current variation of the differential protection device on the opposite side of the direct-current distribution network line is represented; k represents a rate brake coefficient corresponding to the action value characteristic; i is_setRepresents an operation value corresponding to the operation value characteristic.

7. The differential protection method for the direct-current distribution network line according to claim 3, wherein the high-action-value characteristic is suitable for a double-pole short-circuit fault, and the low-action-value characteristic is suitable for a single-pole ground fault.

8. A differential protection system for a dc power distribution network, the system comprising:

a sampling module: the device is used for acquiring instantaneous current values of a local side differential protection device and an opposite side differential protection device of a direct-current power distribution network circuit;

a calculation module: the current variable quantity is used for calculating the current variable quantity of differential protection on the same side of the direct current distribution network circuit;

a determination module: the current variation differential current is determined according to the current variation of the differential protection at two sides;

a matching control module: the differential protection circuit is used for matching adaptive differential protection action characteristics according to the current variation differential current so as to output and control differential protection action signals.

9. A differential protection system suitable for a direct current distribution network is characterized by comprising a processor and a storage medium;

the storage medium is used for storing instructions;

the processor is configured to operate in accordance with the instructions to perform the steps of the method according to any one of claims 1 to 7.

10. Computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the steps of the method according to any one of claims 1 to 7.

Images