CN110618341A - Microgrid ground fault discrimination method based on combination of traditional ground current, unbalanced current and action delay - Google Patents
Microgrid ground fault discrimination method based on combination of traditional ground current, unbalanced current and action delay Download PDFInfo
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- CN110618341A CN110618341A CN201910680393.8A CN201910680393A CN110618341A CN 110618341 A CN110618341 A CN 110618341A CN 201910680393 A CN201910680393 A CN 201910680393A CN 110618341 A CN110618341 A CN 110618341A
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- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
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Abstract
The invention provides a microgrid ground fault discrimination method based on combination of traditional ground current, unbalanced current and action delay. When a ground fault occurs in the microgrid, a judging method based on the traditional ground current is adopted according to the characteristics of the single-phase ground fault, and the main power supply side protection firstly acts on the switch of the main power supply side; meanwhile, when a single-phase earth fault occurs in the microgrid, the distributed power supply can provide fault current for a fault point when the earth fault occurs, the fault current forms a loop through the ground, and the three-phase voltage is unbalanced, so that the sum of the three-phase current output by the distributed power supply is not zero; therefore, as long as the fixed value is set to be larger than the maximum unbalanced current when the system is in asymmetric operation, in order to ensure the selectivity of the protection action, the switch on each distributed power supply side is selected to be tripped by adding time delay.
Description
Technical Field
The invention belongs to the field of relay protection of power systems, and particularly relates to a microgrid ground fault judgment method based on combination of traditional ground current, unbalanced current and action delay.
Background
In recent years, with the rapid development of distributed power generation and microgrid technology, various types of distributed power sources (most of which are inverter-type distributed power sources) are connected to a power distribution system or constitute a microgrid. The micro-grid contains a distributed power supply and can provide fault current for a fault point when a ground fault occurs, and the grounding mode of the system influences the distribution of current in the ground, so that the grounding protection (grounding current protection) is disabled under certain conditions. The ground fault often has a ground transition resistance, and the resistance of the earth also limits the current characteristics of the ground fault, so that the general overcurrent protection can not normally judge the fault and operate. Ground faults also cause system imbalance, resulting in an increase in the neutral line voltage, which in turn causes the neutral point voltages of all distributed power supplies in the area of the ground fault to deviate, affecting the normal operation of the consumer.
Currently, research on microgrid earth fault protection is mainly focused on communication-based or non-communication-based protection schemes, but all have their own disadvantages. The traditional protection principle only using local information is easily influenced by the characteristics of the distributed power supply to cause protection misoperation, so that the reliable operation of the system is influenced. The communication-based protection scheme needs the support of a communication network, so that the hardware investment is inevitably increased, and the complexity of the system is greatly improved. Therefore, the research on the new protection principle based on the local electrical quantity information has important practical significance for realizing the application of the microgrid technology.
Disclosure of Invention
The invention aims to: the defects of the prior art are overcome, and a microgrid ground fault distinguishing method based on combination of traditional ground current, unbalanced current and action delay is provided.
In order to achieve the purpose, the invention is realized by the following technical scheme: a microgrid ground fault discrimination method based on combination of traditional ground current, unbalanced current and action delay comprises the following steps:
step 101: when a ground fault occurs in the microgrid, according to the characteristics of a single-phase ground fault, a traditional ground current-based judgment method is adopted, and the main power supply side protection firstly acts on the switch of the main power supply side;
step 102: meanwhile, the distributed power supply can provide fault current for a fault point when a ground fault occurs, the fault current forms a loop through the ground, and the three-phase voltage is unbalanced, so that the sum of the three-phase current output by the distributed power supply is not zero; therefore, the fixed value of the protection criterion is only set to be larger than the maximum unbalanced current when the system runs asymmetrically;
step 103: in order to ensure the selectivity of the protection action, the switches on the distributed power supply sides are selected to be tripped by adding time delay.
In step 101, when a single-phase ground fault occurs in the microgrid, the single-phase ground fault is characterized in that:
a, B, C phase current and neutral line N current, when single-phase earth fault occurs to C phase, imbalance exists in three-phase current, so
Since the fault current flows back through the earth, the current flowing through the earthAt the moment satisfy
Thus is provided with
By utilizing the fault characteristic and adopting a judging method based on the traditional grounding current, the main power supply side protection acts on the main power supply side switch in a tripping mode.
In step 102, when a single-phase ground fault occurs in the microgrid, the fault characteristics at this time are as follows:
the distributed power supply can provide fault current for a fault point when a ground fault occurs, the fault current forms a loop through the ground, and the three-phase voltage is unbalanced, so that the sum of the three-phase current output by the distributed power supply is not zero
The phase currents of three phases of the distributed power supply A, B, C in the microgrid are respectively
Therefore, by using this fault characteristic, the distributed power source side protection operation trips the distributed power source side switch by using the determination method based on the unbalanced current.
In step 103, to ensure the selectivity of the protection action, the switches on the distributed power supplies are selectively tripped by adding a delay, that is, the following conditions are satisfied:
t1＝t2+Δt (5)
in the formula (5), t1Protecting the action time for the 1 st distributed power supply; t is t2Protecting the action time for the 2 nd distributed power supply; Δ t is the delay interval.
Compared with the prior art, the invention has the following beneficial effects: when a ground fault occurs in the microgrid, according to the characteristics of a single-phase ground fault, a traditional ground current-based judgment method is adopted, and the main power supply side protection firstly acts on the switch of the main power supply side; meanwhile, when a single-phase earth fault occurs in the microgrid, the distributed power supply can provide fault current for a fault point when the earth fault occurs, the fault current forms a loop through the ground, and the three-phase voltage is unbalanced, so that the sum of the three-phase current output by the distributed power supply is not zero; therefore, as long as the fixed value is set to be larger than the maximum unbalanced current when the system is in asymmetric operation, in order to ensure the selectivity of the protection action, the switch on each distributed power supply side is selected to be tripped by adding time delay.
Drawings
FIG. 1 is a schematic diagram of a microgrid configuration including distributed power sources;
fig. 2 is a schematic flow chart of a microgrid ground fault discrimination method based on the combination of conventional ground current, unbalanced current and action delay;
Detailed Description
The present invention is further illustrated by the following description in conjunction with the accompanying drawings and the specific embodiments, it is to be understood that these examples are given solely for the purpose of illustration and are not intended as a definition of the limits of the invention, since various equivalent modifications will occur to those skilled in the art upon reading the present invention and fall within the limits of the appended claims.
Fig. 1 is a schematic diagram of a microgrid structure including a distributed power supply, and the microgrid structure includes a main power supply and the distributed power supply, and the main power supply protection and the distributed power supply protection are respectively disposed on a main power supply output side and a distributed power supply output side. Fig. 2 is a schematic flow chart of a microgrid ground fault determination method based on the combination of conventional ground current, unbalanced current and action delay.
The invention comprises the following steps:
step 101: when a ground fault occurs in the microgrid, according to the characteristics of a single-phase ground fault, a traditional ground current-based judgment method is adopted, and the main power supply side protection firstly acts on the switch of the main power supply side;
step 102: meanwhile, the distributed power supply can provide fault current for a fault point when a ground fault occurs, the fault current forms a loop through the ground, and the three-phase voltage is unbalanced, so that the sum of the three-phase current output by the distributed power supply is not zero; therefore, the fixed value of the protection criterion is only set to be larger than the maximum unbalanced current when the system runs asymmetrically;
step 103: in order to ensure the selectivity of the protection action, the switches on the distributed power supply sides are selected to be tripped by adding time delay.
In step 101, when a single-phase ground fault occurs in the microgrid, the single-phase ground fault is characterized in that:
a, B, C phase current and neutral line N current, when single-phase earth fault occurs to C phase, imbalance exists in three-phase current, so
Since the fault current flows back through the earth, the current flowing through the earthAt the moment satisfy
Thus is provided with
Therefore, by using this fault characteristic, the main power source side protection is first operated to trip the main power source side switch using a conventional ground current based determination method.
In step 102, when a single-phase ground fault occurs in the microgrid, the fault characteristics at this time are as follows:
the distributed power supply can provide fault current for a fault point when a ground fault occurs, the fault current forms a loop through the ground, the three-phase voltage is unbalanced, the sum of the three-phase current output by the distributed power supply is not zero,
the phase currents of three phases of the distributed power supply A, B, C in the microgrid are respectively
Therefore, by using this fault characteristic, the distributed power source side protection operation trips the distributed power source side switch by using the determination method based on the unbalanced current.
In step 103, to ensure the selectivity of the protection action, the switches on the distributed power supplies are selectively tripped by adding a delay, that is, the following conditions are satisfied:
t1＝t2+Δt (5)
in the formula (5), t1Protecting the action time for the 1 st distributed power supply; t is t2Protecting the action time for the 2 nd distributed power supply; Δ t is the delay interval.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.
Claims (4)
1. A microgrid ground fault discrimination method based on combination of traditional ground current, unbalanced current and action delay is characterized in that: it comprises the following steps:
step 101: when a ground fault occurs in the microgrid, according to the characteristics of a single-phase ground fault, a traditional ground current-based judgment method is adopted, and the main power supply side protection firstly acts on the switch of the main power supply side;
step 102: meanwhile, the distributed power supply can provide fault current for a fault point when a ground fault occurs, the fault current forms a loop through the ground, and the three-phase voltage is unbalanced, so that the sum of the three-phase current output by the distributed power supply is not zero; therefore, the fixed value of the protection criterion is only set to be larger than the maximum unbalanced current when the system runs asymmetrically;
step 103: in order to ensure the selectivity of the protection action, the switches on the distributed power supply sides are selected to be tripped by adding time delay.
2. The microgrid ground fault discrimination method based on combination of traditional ground current, unbalanced current and action delay of claim 1 is characterized in that: in step 101, when a single-phase ground fault occurs in the microgrid, the single-phase ground fault is characterized in that:
a, B, C phase current and neutral line N current, when single-phase earth fault occurs to C phase, imbalance exists in three-phase current, so
Since the fault current flows back through the earth, the current flowing through the earthAt the moment satisfy
Thus is provided with
Therefore, by using this fault characteristic, the main power source side protection is first operated to trip the main power source side switch using a conventional ground current based determination method.
3. The microgrid ground fault discrimination method based on combination of traditional ground current, unbalanced current and action delay of claim 1 is characterized in that: in step 102, when a single-phase ground fault occurs in the microgrid, the fault characteristics at this time are as follows: the distributed power supply can provide fault current for a fault point when a ground fault occurs, the fault current forms a loop through the ground, and the three-phase voltage is unbalanced, so that the sum of the three-phase current output by the distributed power supply is not zeroThe phase currents of three phases of the distributed power supply A, B, C in the microgrid are respectively
Therefore, by using this fault characteristic, the distributed power source side protection operation trips the distributed power source side switch by using the determination method based on the unbalanced current.
4. The microgrid ground fault discrimination method based on combination of traditional ground current, unbalanced current and action delay of claim 1 is characterized in that: in step 103, to ensure the selectivity of the protection action, the switches on the distributed power supplies are selectively tripped by adding a delay, that is, the following conditions are satisfied:
t1＝t2+Δt (5)
in the formula (5), t1Protecting the action time for the 1 st distributed power supply; t is t2Protecting the action time for the 2 nd distributed power supply; Δ t is the delay interval.
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Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN2760563Y (en) * | 2004-12-28 | 2006-02-22 | 上海电器股份有限公司人民电器厂 | Sampling circuit for detecting triphase or quadri-phase unbalance current and grounding current |
| CN101478154A (en) * | 2008-01-06 | 2009-07-08 | 卢贺成 | Measure for solving AC, DC earthing and short circuit and novel design of DC system |
| CN101562333A (en) * | 2009-05-27 | 2009-10-21 | 天津大学 | Fast current protection method for distribution network containing distributed power |
| CN104267313A (en) * | 2014-09-25 | 2015-01-07 | 广东易事特电源股份有限公司 | Micro grid system feeder line fault type distinguishing and fault point positioning method |
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Patent Citations (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN2760563Y (en) * | 2004-12-28 | 2006-02-22 | 上海电器股份有限公司人民电器厂 | Sampling circuit for detecting triphase or quadri-phase unbalance current and grounding current |
| CN101478154A (en) * | 2008-01-06 | 2009-07-08 | 卢贺成 | Measure for solving AC, DC earthing and short circuit and novel design of DC system |
| CN101562333A (en) * | 2009-05-27 | 2009-10-21 | 天津大学 | Fast current protection method for distribution network containing distributed power |
| CN104267313A (en) * | 2014-09-25 | 2015-01-07 | 广东易事特电源股份有限公司 | Micro grid system feeder line fault type distinguishing and fault point positioning method |
Non-Patent Citations (1)
| Title |
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| 金强: "分布式电源故障特性分析及微电网保护原理的研究", 《中国博士学位论文全文数据库工程科技Ⅱ辑》 * |
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