CN109980614B - Self-adaptive discrimination method for zero sequence protection direction of distribution line - Google Patents
Self-adaptive discrimination method for zero sequence protection direction of distribution line Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
- H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
- H02H7/26—Sectionalised protection of cable or line systems, e.g. for disconnecting a section on which a short-circuit, earth fault, or arc discharge has occured
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Abstract
The invention relates to the technical field of circuit protection, in particular to a self-adaptive judging method for the zero sequence protection direction of a distribution line, which comprises the steps of putting a CT polarity automatic detection function when the distribution line is put on a load in operation, comparing the phase difference between three-phase CT phase current Ip and phase voltage Up, comparing the phase difference with a manually set load current direction, judging the CT polarity, automatically reversing the three-phase CT polarity if the CT polarity is reversed, and quitting the CT polarity automatic detection function and the load current direction after the line is put in operation; when the line has a ground fault, the 3U is compared0And 3I0And phase difference and judging the zero sequence protection direction according to the phase difference. The invention can avoid the problem of insufficient zero sequence current measurement precision caused by too small secondary value of the self-produced zero sequence current, the zero sequence protection direction is judged by adopting the self-produced zero sequence current and the self-produced zero sequence voltage, and the polarity of the three-phase CT is verified when the three-phase CT is loaded, thereby effectively avoiding the risk of refusing action caused by polarity reversal of the zero sequence CT.
Description
Technical Field
The invention relates to the technical field of circuit protection, in particular to a self-adaptive judging method for zero sequence protection direction of a distribution line.
Background
The neutral point grounding mode of a 10 kV-66 kV power distribution system is closely related to power supply reliability, overvoltage and insulation coordination, relay protection and the like, and is an important condition for ensuring safe, reliable and stable operation of people, equipment and power systems. At present, the following neutral point grounding modes are widely adopted in power distribution systems: (1) neutral ungrounded mode; (2) the neutral point is grounded through an arc suppression coil; (3) the neutral point is grounded through a small resistor; (4) the neutral point is connected with a small resistor in parallel through an arc suppression coil in a combined grounding mode; (5) the fault phase is grounded through a small reactance. The most common way is to ground the neutral point via an arc suppression coil and a small resistor. The arc suppression coil grounding system has the main advantages that the fault operation can be carried out during single-phase fault, the power supply reliability is ensured, and meanwhile, the grounding line selection device is matched to provide technical support for operators to find out faults.
In most distribution network power supply systems, because the system only has one grounding point, zero sequence protection is not generally put into the direction, but in part of core city power supply areas, because full cables are adopted for power supply, the circuit capacitance current is larger, and particularly when 20kV voltage class power supply is adopted, the circuit capacitance current is more obvious and can reach 3A/kilometer; meanwhile, the power supply capacity and radius of the 20kV line are larger than those of the 10kV line, so that the situation that the constant value of the zero sequence protection II section cannot hide the capacitance current of the line often occurs, and the zero sequence protection direction must be judged. If the zero-sequence protection of the 10kV or 20kV distribution line adopts a self-generating zero-sequence Current Transformer (CT), the zero-sequence protection has a small fixed value secondary value due to a large phase current CT transformation ratio, and in addition, the self-generating zero-sequence CT is adopted, so that the zero-sequence protection misoperation of the zero-sequence protection can be caused when the single-phase CT is disconnected, and the zero-sequence protection of the 10kV or 20kV distribution line adopts an external zero-sequence CT; and the adoption of external zero sequence CT can cause the following problems: because the zero sequence current only appears when the ground fault occurs, the polarity of the zero sequence CT can not be verified to be correct through a normal load current actual measurement hexagonal graph during operation, and the directional zero sequence protection has the action refusing risk.
Disclosure of Invention
The invention aims to overcome the defects of the prior art, provides a self-adaptive judging method for the zero sequence protection direction of a distribution line, and solves the problem of the movement rejection risk caused by the polarity reversal of the external zero sequence CT of the distribution line.
In order to solve the technical problems, the invention adopts the technical scheme that:
the method for adaptively judging the zero sequence protection direction of the distribution line is provided, a three-phase CT, an external zero sequence CT and a protection device with the functions of automatically detecting the polarity of the CT and setting the direction of a load current are configured on the line to be judged, and the method for judging the zero sequence protection direction of the distribution line comprises the following steps:
s10, collecting and recording the magnitude and phase of a phase current Ip and a phase voltage Up through a three-phase CT;
s20, when the distribution line is put into operation and carries a load, the three-phase CT polarity automatic detection function is put into operation, and the phase difference of the phase current Ip and the phase voltage Up is compared; manually setting the load current direction, automatically comparing the phase difference between the phase current Ip and the phase voltage Up by the protection device, calculating the sampling current direction of the three-phase CT, comparing the sampling current direction with the actual load current direction, if the sampling current direction is consistent with the actual load current direction, judging that the CT polarity is correct, if the sampling current direction is opposite to the actual load current direction, judging that the CT polarity is reversed, and automatically reversing the three-phase CT polarity;
s30, after the distribution line is put into operation, the CT polarity automatic detection function and the load current direction setting function are quitted, and misjudgment is avoided when the load current direction changes;
s40, when the distribution line has a ground fault, judging whether the external zero sequence CT sampling current is larger than a zero sequence protection action fixed value or not, and simultaneously comparing the self values of the protection devicesProduce zero sequence voltage 3U0And self-generated zero-sequence current 3I0And judging the direction of the zero-sequence current according to the phase difference, if the direction is the positive direction, allowing the zero-sequence protection action to trip, and otherwise, locking the zero-sequence protection action to trip.
According to the self-adaptive judging method for the zero sequence protection direction of the distribution line, the magnitude of the zero sequence protection current is judged by adopting the current through the external zero sequence CT, the zero sequence protection direction is judged by comparing the phases of the self-produced zero sequence current and the self-produced zero sequence voltage, the three-phase CT automatically judges and confirms that the polarity is correct when the line is put into operation with load, the problem that the polarity of the zero sequence CT of the distribution line cannot be checked in a normal operation state is solved, the risk of protection refusal caused by the polarity error of the zero sequence CT of the distribution line is avoided, meanwhile, the polarity of the three-phase CT can be automatically.
Preferably, the CT polarity automatic detection function is turned on or off by a control word: 1 is input and 0 is output. The switching is carried out by the control word, the control logic is simple, and the implementation is easy.
Preferably, the actual load current direction is manually set by a control word: 1 is bus flow direction line, 2 is line flow direction bus, 0 is exit. The control word is used for setting, the control logic is simple, and the implementation is easy.
Preferably, in step S20, if the three-phase CT sampling current direction matches the actual load current direction, it is determined that the CT polarity is correct; if the three-phase CT sampling current direction is opposite to the actual load current direction, the CT polarity is judged to be reversed, and the three-phase CT polarity is automatically reversed. The three-phase CT automatically judges and confirms that the polarity is correct when the line is put into operation with load, solves the problem that the zero sequence CT polarity of the distribution line can not be checked under the normal operation state, and avoids the risk of protection refusal caused by the zero sequence CT polarity error of the distribution line.
Preferably, in step S20, the phase difference comparison logic between phase current Ip and phase voltage Up is as follows:
when the actual load current flows from the bus to the line to be judged: if-90 degrees + delta is less than or equal to arg (Up/Ip) is less than or equal to 90-delta, then the CT polarity is confirmed to be correct; if-90 DEG + delta is less than or equal to arg (Ip/Up) is less than or equal to 90 DEG-delta, confirming that the polarity of the CT is reversed;
when the actual load current flows to the bus from the line to be judged: if-90 DEG + delta is less than or equal to arg (Ip/Up) is less than or equal to 90 DEG-delta, then the CT polarity is confirmed to be correct; if-90 ° + Δ ≦ arg (Up/Ip) ≦ 90 ° - Δ, then the CT polarity is confirmed to be reversed.
The three-phase CT automatically judges and confirms that the polarity is correct when the line is put into operation with load, solves the problem that the zero sequence CT polarity of the distribution line can not be checked in a normal operation state, avoids the risk of protection refusal caused by the zero sequence CT polarity error of the distribution line, and simultaneously automatically judges the three-phase CT polarity, thereby improving the working efficiency.
Preferably, in step S40, the zero sequence protection action logic of the power distribution line includes: if 0 ° + Δ ≦ arg (3I)0/3U0) If the zero-sequence protection is less than or equal to 180 degrees to delta, the positive direction of the zero-sequence protection acts, and the zero-sequence protection outlet is allowed to trip; otherwise, the zero sequence outlet is locked and tripped. The magnitude of the zero sequence current adopts external zero sequence CT sampling current, the direction of the zero sequence current is judged by phase comparison of self-produced zero sequence current and self-produced zero sequence voltage, and the problem that the polarity of the zero sequence CT cannot be verified under a normal state is solved.
Compared with the prior art, the invention has the beneficial effects that:
according to the self-adaptive judging method for the zero sequence protection direction of the distribution line, the current of the zero sequence protection is externally connected, so that the problem of insufficient sampling precision of the zero sequence current caused by too small secondary value of the self-produced zero sequence current is solved; the zero sequence protection direction is judged by self-production, and the polarity of the three-phase CT is verified when the three-phase CT is loaded, so that the risk of movement rejection caused by polarity reversal of the zero sequence CT is avoided; the three-phase CT polarity automatic judgment method can improve the working efficiency.
Drawings
FIG. 1 is a schematic flow chart of a zero sequence protection direction adaptive discrimination method for a distribution line according to the present invention;
FIG. 2 is a schematic diagram of a three-phase CT polarity determination operation area when a load current flows from a bus to a line to be determined;
FIG. 3 is a schematic diagram of a three-phase CT polarity determination operation area when a load current flows from a line to be determined to a bus;
fig. 4 is a schematic diagram of a zero sequence protection direction determination action region.
Detailed Description
The present invention will be further described with reference to the following embodiments. Wherein the showings are for the purpose of illustration only and are shown by way of illustration only and not in actual form, and are not to be construed as limiting the present patent; to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if there is an orientation or positional relationship indicated by the terms "upper", "lower", "left", "right", etc. based on the orientation or positional relationship shown in the drawings, it is only for convenience of describing the present invention and simplifying the description, but it is not intended to indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes and are not to be construed as limiting the present patent, and the specific meaning of the terms may be understood by those skilled in the art according to specific circumstances.
Examples
Fig. 1 shows an embodiment of the zero-sequence protection direction adaptive discrimination method for a distribution line according to the present invention, in which a three-phase CT, an external zero-sequence CT, and a protection device having an automatic CT polarity detection function and a load current direction setting function are configured on a line to be discriminated. The CT polarity automatic detection function is switched on and off by control words: 1 is input, and 0 is exit; the actual load current direction may be set by a control word: 1 is bus flow direction line, 2 is line flow direction bus, 0 is exit. The switching is carried out by the control word, the control logic is simple, and the implementation is easy.
The discrimination method comprises the following steps:
s10, collecting and recording the magnitude and phase of a phase current Ip and a phase voltage Up through a three-phase CT;
s20, when the distribution line is put into operation and carries a load, the three-phase CT polarity automatic detection function is put into operation, and the phase difference of the phase current Ip and the phase voltage Up is compared; and manually setting the actual load current direction, comparing the three-phase CT sampling current direction with the actual load current direction and judging the polarity of the three-phase CT, and if the polarity is reversed, automatically reversing the polarity of the three-phase CT.
The specific control logic of step S20 is as follows:
when the actual load current flows from the bus to the line to be judged: if-90 degrees + delta is less than or equal to arg (Up/Ip) is less than or equal to 90-delta, then the CT polarity is confirmed to be correct; if-90 degrees + delta is less than or equal to arg (Ip/Up) is less than or equal to 90-delta, then the CT polarity is determined to be reversed, and the three-phase CT polarity discriminating element action region is shown in FIG. 2;
when the actual load current flows to the bus from the line to be judged: if-90 DEG + delta is less than or equal to arg (Ip/Up) is less than or equal to 90 DEG-delta, then the CT polarity is confirmed to be correct; if-90 ° + Δ ≦ arg (Up/Ip) ≦ 90 ° - Δ, then the CT polarity is determined to be reversed, and the three-phase CT polarity determination element is operated as shown in FIG. 3.
S30, after the distribution line is put into operation, quitting the automatic polarity detection function and the load current direction setting function, and avoiding misjudgment when the actual load current direction changes;
s40, when the distribution line has a ground fault, judging whether the zero sequence CT sampling current is larger than a zero sequence protection action fixed value or not, and simultaneously comparing the zero sequence voltage 3U self-produced by the protection device0And self-generated zero-sequence current 3I0And judging the zero sequence protection direction according to the phase difference.
The specific control logic of step S40 is as follows:
if 0 ° + Δ ≦ arg (3I)0/3U0) If the zero-sequence protection is less than or equal to 180 degrees to delta, the positive direction of the zero-sequence protection acts, and the zero-sequence protection outlet is allowed to trip; otherwise, the zero sequence outlet is locked to trip; the zero sequence protection directional action region is shown in fig. 4.
Through the steps, the problem that the zero sequence CT polarity of the distribution line cannot be checked in a normal operation state is solved, the risk of protection refusal caused by the zero sequence CT polarity error of the distribution line is avoided, meanwhile, the three-phase CT polarity can be automatically judged, and the working efficiency is improved.
It should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.
Claims (5)
1. A distribution line zero sequence protection direction self-adaptive judging method is characterized in that a three-phase CT, an external zero sequence CT and a protection device with the functions of automatic detection of CT polarity and setting of load current direction are connected to a line to be judged, and the judging method comprises the following steps:
s10, collecting and recording the magnitude and phase of a phase current Ip and a phase voltage Up through a three-phase CT;
s20, when the distribution line is put into operation and carries a load, the protection device is put into a CT polarity automatic detection function, phase difference of phase current Ip and phase voltage Up is compared, a three-phase CT sampling current direction is calculated and compared with an actual load current direction: if the current direction is consistent with the actual load current direction, the CT polarity is judged to be correct; if the three-phase CT polarity is opposite, the CT polarity is judged to be opposite, and the three-phase CT polarity is automatically inverted;
s30, after the distribution line is put into operation, the protection device quits the CT polarity automatic detection function and the load current direction setting function, and misjudgment is avoided when the actual load current direction changes;
s40, when the distribution line has a ground fault, judging whether the external zero sequence CT sampling current is larger than a zero sequence protection action fixed value or not, and simultaneously comparing the self-produced zero sequence voltage 3U of the protection device0And self-generated zero-sequence current 3I0And determining the direction of the zero sequence current according to the phase difference.
2. The self-adaptive discrimination method for the zero-sequence protection direction of the distribution line according to claim 1, wherein the automatic CT polarity detection function is started or stopped by a control word: 1 is input and 0 is output.
3. The self-adaptive discrimination method for the zero-sequence protection direction of the distribution line according to claim 1, wherein the actual load current direction is manually set by a control word: 1 is bus flow direction line, 2 is line flow direction bus, 0 is exit.
4. The self-adaptive discrimination method for the zero-sequence protection direction of the distribution line according to claim 1, wherein in step S20, the phase difference comparison logic of the phase current Ip and the phase voltage Up is as follows:
when the load current flows from the bus to the line to be judged: if-90 degrees + delta is less than or equal to arg (Up/Ip) is less than or equal to 90-delta, then the CT polarity is confirmed to be correct; if-90 DEG + delta is less than or equal to arg (Ip/Up) is less than or equal to 90 DEG-delta, confirming that the polarity of the CT is reversed;
when the load current flows to the bus from the line to be judged: if-90 DEG + delta is less than or equal to arg (Ip/Up) is less than or equal to 90 DEG-delta, then the CT polarity is confirmed to be correct; if-90 ° + Δ ≦ arg (Up/Ip) ≦ 90 ° - Δ, then the CT polarity is confirmed to be reversed.
5. The self-adaptive distinguishing method for the zero-sequence protection direction of the power distribution line according to claim 1, wherein in step S40, the distinguishing logic for the zero-sequence protection direction of the power distribution line is as follows: if 0 ° + Δ ≦ arg (3I)0/3U0) If the zero-sequence protection is less than or equal to 180 degrees to delta, the positive direction of the zero-sequence protection acts, and the zero-sequence protection outlet is allowed to trip; otherwise, the zero sequence protection outlet is locked to trip.
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| CN110927631B (en) * | 2019-12-03 | 2022-01-11 | 陕西省地方电力（集团）有限公司宝鸡供电分公司 | Polarity judgment method for zero-sequence current transformer |
| CN111725778B (en) * | 2020-05-27 | 2022-03-11 | 湖南省湘电试验研究院有限公司 | Line protection CT disconnection locking method, system and medium under condition of reversed trend |
| CN112087048B (en) * | 2020-09-07 | 2022-06-14 | 西安热工研究院有限公司 | High-voltage plant branch zero-sequence protection configuration system and method |
| CN113872151B (en) * | 2021-09-08 | 2023-08-11 | 许继集团有限公司 | Protection method and protection device capable of automatically adapting to polarity and phase sequence of overhead line |
| CN114200354B (en) * | 2022-02-16 | 2022-04-19 | 广东电网有限责任公司肇庆供电局 | Zero sequence CT polarity online detection method, system and equipment |
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