The arc-suppression coil (ASC) in parallel low resistance (LR) multi-mode grounding is adopted in the mountain wind farm to cope with the phenomenon that is misoperation or refusal of zero-sequence protection in LR grounding wind farm. If the fault disappears before LR is put into the system, it is judged as an instantaneous fault; while the fault does not disappear after LR is put into the system, it is judged as a permanent fault; the single-phase grounding fault (SLG) protection criterion based on zero-sequence power variation is proposed to identify the instantaneous-permanent fault. Firstly, the distribution characteristic of zero-sequence voltage (ZSV) and zero-sequence current (ZSC) are analyzed after SLG fault occurs in multi-mode grounding. Then, according to the characteristics that zero-sequence power variation of non-fault collector line is small, while the zero-sequence power variation of fault collector line can reflect the active power component of fault resistance, the protection criterion based on zero-sequence power variation is constructed. The theoretical analysis and simulation results show that the protection criterion can distinguish the property of fault only by using the single terminal information, which has high reliability.
With the increase of the global environmental crisis and the reduction of traditional energy sources, wind power generation has attracted significant attention. Wind power generation has penetrated the power grid, which the internal fault may pose a threat to the operation of the power grid [
At present, the conventional three-section current protection is still applied to the collector line [
This paper analyzes the distribution of zero-sequence voltage (ZSV) and zero-sequence current (ZSC) after a single-phase grounding fault (SLG) appears in the collector line of multi-mode grounding mode. Based on the analysis of ZSV and ZSC, the zero-sequence power variation of non-fault collector line is small, while the zero-sequence power variation of fault collector line can reflect the active power component of fault resistance. The zero-sequence power of collector line is constructed as the characteristic quantity of SLG identification of wind farm. The protection principle is verified by simulation that can distinguish the property of fault only by using the single terminal information with voltage and current, which has high reliability.
The remaining of this paper is organized as follows:
Overhead line and cable are connected to mountain wind power. After a SLG occurs in the collector line, the overhead line always belongs to an instantaneous SLG, while the cable tends to appear permanent SLG accompanied by the higher capacitive current. The multi-mode grounding can weaken the recovery speed of fault phase voltage, which is the benefit to instantaneous SLG disappearance; LR is connected after a high-impedance fault or permanent SLG appears in the collector line, which can make ZSC increase and characteristics of fault obviously and that is conducive to improve the reliability of protection action. The following research will focus on the analysis of SLG that occurs in the collector lines of the mountain wind farm, the equivalent system diagram is shown in
As a SLG occurs in collector line
As ASC is connected, ZSV is defined as follows:
The fault current is
The ZSC is as follows:
If the zero-sequence power can still be detected after ASC is connected with a certain time delay, LR is put into and then the grounding mode is changed into the multi-mode grounding. The leakage resistance is higher than the resistance of neutral point
The fault current is
The ZSC is as follows:
From
To reduce the wind turbine off-grid caused by the fault, the multi-mode grounding is adopted in the mountain wind farm. ASC is connected to clear the instantaneous SLG; while LR is connected after a permanent SLG appears, it can increase the fault current and make the protection device operate reliably.
According to the characteristics of ZSV and ZSC, the zero-sequence power [
where
Due to ZSV and ZSC of the fault collector line contains the zero-sequence component generated by the fault resistance, which the zero-sequence power variation
From the analysis of
where
The protection device should avoid possible unbalance condition, and the threshold value of protection can be set with a certain margin. It is appropriate to set the threshold value to 7.5 kW with considering the reliability of the protection operation.
Combined with the merits of the multi-mode grounding, zero-sequence power variation as the characteristic quantity of protection criterion is applied to mountain wind farm that can accurately differentiate instantaneous-permanent fault. The procedure of the proposed protection method is as follows:
Step 1: ZSV and ZSC after fault are obtained, and the zero-sequence power variation of each collector line is calculated;
Step 2: If the zero-sequence power variation
Step 3: LR is connected after the zero-sequence power variation
The multi-mode grounding mountain wind farm simulation is established by PSCAD, as shown in
It is an ungrounded system by breaking S1; the neutral point is grounded
Line type | Impedance | Resistance |
Inductance |
Capacitance |
---|---|---|---|---|
Overhead line | Zero-sequence | 0.2671 | 0.0045 | |
Positive-sequence | 0.1215 | 0.0011 | ||
Cable | Zero-sequence | 1.5762 | 0.0052 | |
Positive-sequence | 0.4525 | 0.0018 |
Supposed a permanent SLG fault occurs on collector line
As ZSV is detected in the ungrounded system, the data of 20 ms after the fault is selected to calculate the zero-sequence power variation. The zero-sequence power variation is 845 kW that is higher than the threshold value of protection
Supposed an instantaneous fault occurs on collector line
As ZSV is detected in the ungrounded system, the data of 20 ms after the fault is selected to calculate the zero-sequence power variation. The zero-sequence power variation is 783 kW that is higher than the threshold value of protection
To test the validity of the based on zero-sequence power variation protection, SLG under different fault resistance, fault distance and fault inception angle are set in different collector lines of the mountain wind farm simulation model, which the zero-sequence power variation of each collector line can be obtained and is listed in
With the increase of fault resistance, zero-sequence power variation of non-fault collector line and fault collector line gradually decrease, however, zero-sequence power variation of fault collector line is still higher than that of non-fault collector line. It can be seen that the zero-sequence power variation of the fault collector line is greater than the protection setting value
In
Fault |
Zero-sequence power variation of each collector line and protection |
|||
---|---|---|---|---|
Collector line |
Collector line |
Collector line |
||
10 | Zero-sequence power variation | 727 | −5.3 | −6.1 |
Operation | ▲ | ▼ | ▼ | |
Zero-sequence power variation | −6.9 | −5.5 | −6.2 | |
Operation | □ | □ | □ | |
Protective device | ||||
Result | Instantaneous |
Non-fault |
Non-fault |
|
50 | Zero-sequence power variation | −5.8 | −5.5 | 525.6 |
Operation | ▼ | ▼ | ▲ | |
Zero-sequence power variation | −6.1 | −5.9 | 527.3 | |
Operation | □ | □ | ■ | |
Protective device | √ | |||
Result | Non-fault |
Non-fault |
Permanent |
|
100 | Zero-sequence power variation | −4.4 | 323.9 | −4.7 |
Operation | ▼ | ▲ | ▼ | |
Zero-sequence power variation | −4.9 | 325.3 | −5.1 | |
Operation | □ | ■ | □ | |
Protective device | √ | |||
Result | Non-fault |
Permanent |
Non-fault |
|
200 | Zero-sequence power variation | −2.1 | 134.1 | −2.4 |
Operation | ▼ | ▲ | ▼ | |
Zero-sequence power variation | −2.5 | −3.6 | −2.7 | |
Operation | □ | □ | □ | |
Protective device | ||||
Result | Non-fault |
Instantaneous |
Non-fault |
|
500 | Zero-sequence power variation | 46.9 | −1.3 | −1.1 |
Operation | ▲ | ▼ | ▼ | |
Zero-sequence power variation | 48.7 | −1.9 | −1.5 | |
Operation | ■ | □ | □ | |
Protective device | √ | |||
Result | Permanent |
Non-fault |
Non-fault |
|
800 | Zero-sequence power variation | −0.6 | −0.5 | 21.3 |
Operation | ▼ | ▼ | ▲ | |
Zero-sequence power variation | −1.0 | −0.8 | −1.7 | |
Operation | □ | □ | □ | |
Protective device | ||||
Result | Non-fault collector line | Non-fault collector line | Instantaneous fault | |
1000 | Zero-sequence power variation | −0.07 | 8.9 | −0.1 |
Operation | ▼ | ▲ | ▼ | |
Zero-sequence power variation | −0.3 | 9.1 | −0.4 | |
Operation | □ | ■ | □ | |
Protective device | √ | |||
Result | Non-fault collector line | Permanent fault | Non-fault collector line |
Collector line | Fault resistance |
Zero-sequence power variation of each collector line and protection operation | |||
---|---|---|---|---|---|
Collector line |
Collector line |
Collector line |
|||
4 | Zero-sequence power variation | 267 | −3.3 | −3.2 | |
Operation | ▲ | ▼ | ▼ | ||
Zero-sequence power variation | −4.5 | −3.8 | −3.7 | ||
Operation | □ | □ | □ | ||
Protective device | |||||
Result | Instantaneous fault | Non-fault collector line | Non-fault collector line | ||
10 | Zero-sequence power variation | 255.6 | −1.9 | −1.8 | |
Operation | ▲ | ▼ | ▼ | ||
Zero-sequence power variation | 258.3 | −2.7 | −2.4 | ||
Operation | ■ | □ | □ | ||
Protective device | √ | ||||
Result | Permanent fault | Non-fault collector line | Non-fault collector line | ||
3 | Zero-sequence power variation | −2.6 | 243.9 | −2.8 | |
Operation | ▼ | ▲ | ▼ | ||
Zero-sequence power variation | −3.3 | 247.5 | −4.1 | ||
Operation | □ | ■ | □ | ||
Protective device | √ | ||||
Result | Non-fault collector line | Permanent fault | Non-fault collector line | ||
7 | Zero-sequence power variation | −1.9 | 134.1 | −2.1 | |
Operation | ▼ | ▲ | ▼ | ||
Zero-sequence power variation | −2.4 | −3.5 | −2.8 | ||
Operation | □ | □ | □ | ||
Protective device | |||||
Result | Non-fault collector line | Instantaneous fault | Non-fault collector line | ||
2 | Zero-sequence power variation | −2.6 | −2.9 | 26.9 | |
Operation | ▼ | ▼ | ▲ | ||
Zero-sequence power variation | −3.1 | −3.7 | 28.5 | ||
Operation | □ | □ | ■ | ||
Protective device | √ | ||||
Result | Non-fault collector line | Non-fault collector line | Permanent fault | ||
5 | Zero-sequence power variation | −0.8 | −0.5 | 21.3 | |
Operation | ▼ | ▼ | ▲ | ||
Zero-sequence power variation | −0.9 | −0.6 | −1.7 | ||
Operation | □ | □ | □ | ||
Protective device | |||||
Result | Non-fault collector line | Non-fault collector line | Instantaneous fault | ||
11 | Zero-sequence power variation | −0.5 | −0.3 | 16.9 | |
Operation | ▼ | ▼ | ▲ | ||
Zero-sequence power variation | −0.7 | −0.4 | 17.5 | ||
Operation | □ | □ | ■ | ||
Protective device | √ | ||||
Result | Non-fault collector line | Non-fault collector line | Permanent fault |
Fault inception angle |
Zero-sequence power variation of each collector line and protection operation | |||
---|---|---|---|---|
Collector line |
Collector line |
Collector line |
||
5 | Zero-sequence power variation | 287 | −2.6 | −2.1 |
Operation | ▲ | ▼ | ▼ | |
Zero-sequence power variation | −4.1 | −3.4 | −2.8 | |
Operation | □ | □ | □ | |
Protective device | ||||
Result | Instantaneous fault | Non-fault collector line | Non-fault collector line | |
30 | Zero-sequence power variation | −4.8 | −5.1 | 282.6 |
Operation | ▼ | ▼ | ▲ | |
Zero-sequence power variation | −5.3 | −5.9 | 287.3 | |
Operation | □ | □ | ■ | |
Protective device | √ | |||
Result | Non-fault collector line | Non-fault collector line | Permanent fault | |
60 | Zero-sequence power variation | −4.6 | 276.9 | −4.8 |
Operation | ▼ | ▲ | ▼ | |
Zero-sequence power variation | −5.7 | 279.4 | −5.5 | |
Operation | □ | ■ | □ | |
Protective device | √ | |||
Result | Non-fault collector line | Permanent fault | Non-fault collector line | |
90 | Zero-sequence power variation | −3.1 | 281.1 | −2.5 |
Operation | ▼ | ▲ | ▼ | |
Zero-sequence power variation | −4.5 | −4.8 | −3.7 | |
Operation | □ | □ | □ | |
Protective device | ||||
Result | Non-fault collector line | Instantaneous fault | Non-fault collector line |
Through the analysis of ZSV and ZSC after SLG occurs in mountain wind farm based on multi-mode grounding, a zero-sequence power variation protection method is proposed that is applicable to the collector line of the mountain wind farm. The effectiveness of zero-sequence power variation protection is verified by simulation, the following conclusions are obtained.
The protection criterion is constructed and based on the fact that the zero-sequence power variation of non-fault collector line is small, while the zero-sequence power variation of fault collector line can reflect the active power component of fault resistance. The multi-mode grounding in the mountain wind farm is conducive to the disappearance of the instantaneous fault so that the protection will not mal-operation; when high impedance grounding fault occurs, the protection will not refuse to operate; it can improve the reliability of protection. The proposed protection criterion only needs ZSV and ZSC of each collector lines before and after the fault, which is easy to realize in the multi-mode grounding of the mountain wind farm. Based on zero-sequence power variation protection is verified by the simulation results, which can efficiently differentiate fault property and reliably protect the fault collector line and that is not affected by operating conditions such as fault resistant, fault distance, and inception time.
Single-phase grounding fault
Zero-sequence current
Low voltage ride through
Low resistance
Zero-sequence voltage
Doubly-fed induction generator
Arc-suppression coil
The authors gratefully acknowledge the National Natural Science Foundation of China (51667010 and 51807085), and the support of the Major Science and Technology Projects in Yunnan Province (202002AF080001).