CN105911434A - Method for detecting high resistance ground faults of electric distribution network under interference of multiple harmonic sources - Google Patents

Abstract

The invention discloses a method for detecting high resistance ground faults of an electric distribution network under interference of multiple harmonic sources. The method comprises the steps of monitoring phase current and zero sequence current signals of a circuit in real time, calculating variations of various phase current power frequency amount amplitudes and phases, and when the various phase current power frequency amount amplitudes and the phases change suddenly and the triple-harmonic content of zero sequence current is detected to exceed a threshold and a phase value is within an action range, judging that the circuit has high resistance ground faults; and when each phase current signal changes suddenly but the triple-harmonic content of the zero sequence current does not exceed the threshold or the phase value is not within the action range, judging that the circuit does not have the high resistance ground faults and a harmonic source interference exist. According to the method disclosed by the invention, the characteristics of phase variations and amplitude variations of each phase current of a monitored circuit are fully excavated, so that reliable lockout of an algorithm for detecting the high resistance ground faults under the interference of multiple harmonic sources is ensured, the characteristics of the high resistance ground faults of the circuit are fully considered, the flexibility of the detection method is promoted to the maximum extent, and the method have both strong reliability and high flexibility for detection.

Description

Power distribution network high resistance earthing fault detection method under Multi-harmonic Sources interference

Technical field

The invention belongs to Power System Faults Detection field, the power distribution network high resistant under disturbing particularly to a kind of Multi-harmonic Sources Earth-fault detecting method.

Background technology

Along with the fast development of the regenerative resource such as wind-powered electricity generation, photovoltaic, distributed power source accounting in distribution is more and more higher, The fault form of power distribution network is the most only by major network power supply and trouble point type decided, in addition it is also necessary to consider that many distributed power sources access band The impact come.

Distributed power source is based primarily upon grid-connected inverters, has a feature that fault current fan-out capability is limited, therefore for The trouble point such as metallicity, low resistance grounding form, the fault signature accessing power distribution network containing many distributed power sources mainly depends on In major network power supply characteristic；Conventional failure detection method is substantially effective, is also only that sensitivity has declined even if impacted.But Another feature of distributed electrical source grid-connected inverter is that harmonic wave is relatively big, under multi-inverter acts on jointly, for distribution Net arc light high resistance earthing fault form, will appear from the situation of weak fault current superposition multiple-harmonic current so that tradition distribution high resistant The effectiveness of earth-fault detecting method is challenged.

For distribution arc light high resistance earthing fault is compared to low resistance grounding fault, exists near current zero-crossing point and put out Arc, the dynamic process restriked, result in containing higher triple-frequency harmonics in zero-sequence current, therefore tradition distribution high resistance earthing fault Detection is based primarily upon the content of triple-frequency harmonics in zero-sequence current and phase property is carried out.

Regrettably, triple-frequency harmonics is also the main component that inverter produces in harmonic content, directly affects existing joining The susceptiveness of net high resistive fault detection and reliability, be easily caused the error starting of fault detect.

Summary of the invention

In order to overcome the defect of above-mentioned prior art, it is an object of the invention to provide joining under the interference of a kind of Multi-harmonic Sources Electrical network high resistance earthing fault detection method, excavates faulted phase current power frequency amplitude and phase property further, utilizes phase current Phase and amplitude variable quantity, as auxiliary detection criteria, can prevent the malfunction of existing detection method under Multi-harmonic Sources interference, again Take into full account the feature of high resistance earthing fault, promoted the sensitivity of detection method to greatest extent, have by force may be used of detection concurrently By property and high sensitivity.

Power distribution network high resistance earthing fault detection method under Multi-harmonic Sources interference, specifically includes following steps:

Step (1), Real-time Collection distribution substation measure the current signal of circuit；Wherein φ is separate, comprises A Phase, B phase, C phase and zero sequence, if scene cannot measure zero-sequence current, calculate zero-sequence current i according to following formula₀(t):

i₀(t)=i_A(t)+i_B(t)+i_C(t)

Step (2), calculate and detect each phase current operating frequency phase

Wherein ω=2 π f=100 π, T=1/f=20ms, then calculates each phase current operating frequency phase in half cycle Variable quantity

If a certain phase current operating frequency phase variable quantityIn the range of 90 °～180 °, and remaining biphase current power frequency phase Position variable quantity in the range of 0 °～90 °, then goes to step (4)；If three-phase current operating frequency phase variable quantityAll at 0 °～90 ° In the range of, then go to step (3)；Other situations then go to step (5)；

Step (3) calculates and detects each phase current power frequency amplitude

Then each phase current power frequency amplitude variable quantity in half cycle is calculated

If a certain phase current power frequency amplitude change rateExceed threshold value of adjusting, described threshold value value 10% of adjusting, and Remaining biphase current power frequency amplitude change rateNot less than threshold value of adjusting, then go to step (4), otherwise go to step (5)；

Step (4) calculates zero-sequence current triple-frequency harmonics relative to the difference in magnitude Δ A of first-harmonic and zero-sequence current triple-frequency harmonics phase Phase difference φ to first-harmonic:

$\mathrm{\Δ}A=\frac{\sqrt{{\left({\∫}_{t_0}^{t_0+\frac{T}{2}}{i}_0\right(t)\·cos(3\mathrm{\ω}t\left)dt\right)}^2+{\left({\∫}_{t_0}^{t_0+\frac{T}{2}}{i}_0\right(t)\·sin(3\mathrm{\ω}t\left)dt\right)}^2}}{\sqrt{{\left({\∫}_{t_0}^{t_0+\frac{T}{2}}{i}_0\right(t)\·cos(\mathrm{\ω}t\left)dt\right)}^2+{\left({\∫}_{t_0}^{t_0+\frac{T}{2}}{i}_0\right(t)\·sin(\mathrm{\ω}t\left)dt\right)}^2}}$

$\mathrm{\Δ}\mathrm{\φ}=\arctan \frac{{\∫}_{t_0}^{t_0+\frac{T}{2}}{i}_0\left(t\right)\·cos\left(\mathrm{\ω}t\right)dt}{{\∫}_{t_0}^{t_0+\frac{T}{2}}{i}_0\left(t\right)\·\sin \left(\mathrm{\ω}t\right)dt}-\arctan \frac{{\∫}_{t_0}^{t_0+\frac{T}{2}}{i}_0\left(t\right)\·cos\left(3\mathrm{\ω}t\right)dt}{{\∫}_{t_0}^{t_0+\frac{T}{2}}{i}_0\left(t\right)\·\sin \left(3\mathrm{\ω}t\right)dt}$

If zero-sequence current triple-frequency harmonics exceedes, relative to the difference in magnitude Δ A of first-harmonic, threshold value of adjusting, this threshold value of adjusting takes 10%, And zero-sequence current triple-frequency harmonics relative to phase difference φ of first-harmonic in the range of 120 °～240 °, then be judged as that circuit there occurs height Resistance earth fault, sends alarm signal；Otherwise go to step (5)；

Step (5) detection method is judged as that circuit does not occurs high resistance earthing fault, locking alarm signal.

The feature of the present invention and beneficial effect:

The present invention is directed to current conventional electrical distribution net high resistive fault detection method defect of easily misoperation under harmonic wave disturbs, fill Divide phase changing capacity and the amplitude variable quantity feature excavating each phase current of monitored circuit, it is proposed that zero-sequence current action auxiliary is sentenced According to, both can guarantee that the reliable locking of high resistance earthing fault detection algorithm under Multi-harmonic Sources disturbs, taken into full account again that circuit was high The feature of resistance earth fault, promotes the sensitivity of detection method to greatest extent, has had the strong reliability of detection concurrently with highly sensitive Degree.

Accompanying drawing explanation

Fig. 1 is the detection algorithm flow chart of the application present invention.

Detailed description of the invention

Power distribution network high resistance earthing fault detection method under the Multi-harmonic Sources interference that the present invention proposes, in conjunction with accompanying drawing and enforcement Example describes in detail as follows:

Embodiment chooses power distribution network in the wind energy turbine set comprising single time collection electric line, Neutral Point Through Low Resistance, blower fan, collection Electric line and wind farm grid-connected system voltage grade are respectively 0.69kV, 35kV, 220kV, current collection total track length 20km, circuit There is A phase single-phase high-impedance in midpoint 5.0s, trouble point uses Cassie Arc Modelling, and it is wind farm grid-connected that emulation obtains At substation exit, three-phase current signal illustrates as implementing sample, as shown in the table:

Table 1 high resistive fault circuit three-phase current signal sampled value

(1) Real-time Collection transformer station in wind farm side measures the current signal of circuitWherein φ is separate, bag Containing A phase, B phase and C phase, then it is calculated zero-sequence current i according to following formula₀(t):

i₀(t)=i_A(t)+i_B(t)+i_C(t)

(2) t is calculated₀Each phase current operating frequency phase during=5s

ω=2 π f=100 π, T=1/f=0.02s

Then each phase current operating frequency phase variable quantity in half cycle is calculated

Δθ_a=| θ_a(t₀=5.01)-θ_a(t₀=5) |=0.52 °

Δθ_b=| θ_b(t₀=5.01)-θ_b(t₀=5) |=1.5 °

Δθ_c=| θ_c(t₀=5.01)-θ_c(t₀=5) |=1.16 °

Three-phase current operating frequency phase variable quantityAll in the range of 0 °～90 °, it should go to step 3)；(3) each phase electricity is calculated Stream power frequency amplitude

$I_a(t_0=5)=2\·\sqrt{{\left({\∫}_{4.99}^5{i}_a\right(t)\·cos(100\mathrm{\π}t\left)dt\right)}^2+{\left({\∫}_{4.99}^5{i}_a\right(t)\·sin(100\mathrm{\π}t\left)dt\right)}^2}=1.0808$

$I_b(t_0=5)=2\·\sqrt{{\left({\∫}_{4.99}^5{i}_b\right(t)\·cos(100\mathrm{\π}t\left)dt\right)}^2+{\left({\∫}_{4.99}^5{i}_b\right(t)\·sin(100\mathrm{\π}t\left)dt\right)}^2}=1.0772$

$I_c(t_0=5)=2\·\sqrt{{\left({\∫}_{4.99}^5{i}_c\right(t)\·cos(100\mathrm{\π}t\left)dt\right)}^2+{\left({\∫}_{4.99}^5{i}_c\right(t)\·sin(100\mathrm{\π}t\left)dt\right)}^2}=1.0830$

$I_a(t_0=5.01)=2\·\sqrt{{\left({\∫}_5^{5.01}{i}_a\right(t)\·cos(100\mathrm{\π}t\left)dt\right)}^2+{\left({\∫}_5^{5.01}{i}_a\right(t)\·sin(100\mathrm{\π}t\left)dt\right)}^2}=0.6145$

$I_b(t_0=5.01)=2\·\sqrt{{\left({\∫}_5^{5.01}{i}_b\right(t)\·cos(100\mathrm{\π}t\left)dt\right)}^2+{\left({\∫}_5^{5.01}{i}_b\right(t)\·sin(100\mathrm{\π}t\left)dt\right)}^2}=1.0759$

$I_c(t_0=5.01)=2\·\sqrt{{\left({\∫}_5^{5.01}{i}_c\right(t)\·cos(100\mathrm{\π}t\left)dt\right)}^2+{\left({\∫}_5^{5.01}{i}_c\right(t)\·sin(100\mathrm{\π}t\left)dt\right)}^2}=1.0869$

Then each phase current power frequency amplitude variable quantity in half cycle is calculated

${\mathrm{\ΔI}}_a=2\·\left|\frac{I_a(t_0=5.01)-I_a(t_0=5)}{I_a(t_0=5.01)+I_a(t_0=5)}\right|=55.01\%$

${\mathrm{\ΔI}}_b=2\·\left|\frac{I_b(t_0=5.01)-I_b(t_0=5)}{I_b(t_0=5.01)+I_b(t_0=5)}\right|=0.12\%$

${\mathrm{\ΔI}}_c=2\·\left|\frac{I_c(t_0=5.01)-I_c(t_0=5)}{I_c(t_0=5.01)+I_c(t_0=5)}\right|=0.36\%$

A phase current power frequency amplitude change rateMore than 10%, and remaining biphase current power frequency amplitude change rateDo not surpass Cross 10%, it should go to step 4)；

(4) t is calculated₀During=5s, zero-sequence current triple-frequency harmonics is relative to the difference in magnitude Δ A of first-harmonic and phase difference φ:

$\mathrm{\Δ}A=\frac{\sqrt{{\left({\∫}_5^{5.01}{i}_0\right(t)\·cos(300\mathrm{\π}t\left)dt\right)}^2+{\left({\∫}_5^{5.01}{i}_0\right(t)\·sin(300\mathrm{\π}t\left)dt\right)}^2}}{\sqrt{{\left({\∫}_5^{5.01}{i}_0\right(t)\·cos(100\mathrm{\π}t\left)dt\right)}^2+{\left({\∫}_5^{5.01}{i}_0\right(t)\·sin(100\mathrm{\π}t\left)dt\right)}^2}}=23.15\%$

Zero-sequence current triple-frequency harmonics is relative to fundamental voltage amplitude Δ A more than 10%, and triple-frequency harmonics is relative to fundamental phase poor Δ φ In the range of 120 °～240 °, it is judged that there occurs high resistance earthing fault for circuit, send alarm signal.

Claims (1)

1. the power distribution network high resistance earthing fault detection method under a Multi-harmonic Sources interference, it is characterised in that specifically include following Step:

Step (1), Real-time Collection distribution substation measure the current signal of circuitWherein φ is separate, comprises A phase, B Phase, C phase and zero sequence, if scene cannot measure zero-sequence current, calculate zero-sequence current i according to following formula₀(t):

i₀(t)=i_A(t)+i_B(t)+i_C(t)

Step (2), calculate and detect each phase current operating frequency phase

Wherein ω=2 π f=100 π, T=1/f=20ms, then calculates the change in half cycle of each phase current operating frequency phase Amount

If a certain phase current operating frequency phase variable quantityIn the range of 90 °～180 °, and remaining biphase current operating frequency phase becomes Change amount in the range of 0 °～90 °, then goes to step (4)；If three-phase current operating frequency phase variable quantityAll 0 °～90 ° of scopes In, then go to step (3)；Other situations then go to step (5)；

Step (3) calculates and detects each phase current power frequency amplitude

Then each phase current power frequency amplitude variable quantity in half cycle is calculated

If a certain phase current power frequency amplitude change rateExceed threshold value of adjusting, described threshold value value 10% of adjusting, and remaining Biphase current power frequency amplitude change rateNot less than threshold value of adjusting, then go to step (4), otherwise go to step (5)；

Step (4) calculates zero-sequence current triple-frequency harmonics relative to the difference in magnitude Δ A of first-harmonic and zero-sequence current triple-frequency harmonics relative to base The phase contrast of ripple

$\mathrm{\Δ}A=\frac{\sqrt{{\left({\∫}_{t_0}^{t_0+\frac{T}{2}}{i}_0\right(t)\·cos(3\mathrm{\ω}t\left)dt\right)}^2+{\left({\∫}_{t_0}^{t_0+\frac{T}{2}}{i}_0\right(t)\·sin(3\mathrm{\ω}t\left)dt\right)}^2}}{\sqrt{{\left({\∫}_{t_0}^{t_0+\frac{T}{2}}{i}_0\right(t)\·cos(\mathrm{\ω}t\left)dt\right)}^2+{\left({\∫}_{t_0}^{t_0+\frac{T}{2}}{i}_0\right(t)\·sin(\mathrm{\ω}t\left)dt\right)}^2}}$

$\mathrm{\Δ}\mathrm{\φ}=\arctan \frac{{\∫}_{t_0}^{t_0+\frac{T}{2}}{i}_0\left(t\right)\·cos\left(\mathrm{\ω}t\right)dt}{{\∫}_{t_0}^{t_0+\frac{T}{2}}{i}_0\left(t\right)\·\sin \left(\mathrm{\ω}t\right)dt}-\arctan \frac{{\∫}_{t_0}^{t_0+\frac{T}{2}}{i}_0\left(t\right)\·cos\left(3\mathrm{\ω}t\right)dt}{{\∫}_{t_0}^{t_0+\frac{T}{2}}{i}_0\left(t\right)\·\sin \left(3\mathrm{\ω}t\right)dt}$

If zero-sequence current triple-frequency harmonics exceedes, relative to the difference in magnitude Δ A of first-harmonic, threshold value of adjusting, this threshold value of adjusting takes 10%), and Zero-sequence current triple-frequency harmonics in the range of 120 °～240 °, is then judged as that circuit there occurs high resistant relative to phase difference φ of first-harmonic Earth fault, sends alarm signal；Otherwise go to step (5)；

Step (5) detection method is judged as that circuit does not occurs high resistance earthing fault, locking alarm signal.