Online monitoring device and method for traction power supply cable based on circulation

Abstract

The invention discloses an online monitoring device and method for a traction power supply cable based on circulation. A 27.5 kV single-phase traction power supply cable is crucial to guarantee normal operation of a locomotive. The system comprises current sensors CT1 and CT2 and current acquisition devices IED1 and IED2, wherein the current sensors CT1 and CT2 are mounted at a traction power supply cable terminal; the method comprises the following steps: firstly, calculating current effective values I1 and I2 at current sensors CT1 and CT2 by using a DFT method; calculating the leakage current I0 of the traction power supply cable; calculating sheath current coefficients K1 and K2; and according to the values of the coefficients K1 and K2, corresponding judgment is made, and the collection, calculation and fault judgment of the circulation of the traction power supply cable are realized. According to the on-line monitoring method, the amplitude of the traction voltage does not need to be measured, communication between the IED1 and the IED2 is not needed, and synchronization between the IED1 and the IED2 is not needed.

Description

Technical Field

[0001] The present invention belongs to the technical field of traction power supply cable monitoring, and in particular relates to a circulating current-based online monitoring device and method for traction power supply cables. Background Art

[0002] 27.5kV single-phase traction power supply cable is crucial to ensure the normal operation of locomotives. During the long-term operation of the cable, there may be a variety of potential faults, mainly the following: 27.5kV single-phase traction power supply cable main insulation strength reduction; 27.5kV single-phase traction terminal direct grounding impedance abnormality; 27.5kV single-phase traction power supply cable sheath protector abnormality; There are three main insulation abnormality detection methods for 27.5kV single-phase traction power supply cables: offline detection, live detection, and online monitoring.

[0003] Offline detection mainly relies on various forms of insulation performance tests, and each method has different focuses. The live detection of 27.5kV single-phase traction power supply cables mainly includes temperature monitoring and partial discharge monitoring; temperature monitoring is not effective for 27.5kV single-phase traction power supply cables, and it is difficult to detect temperature anomalies; partial discharge accuracy is average.

[0004] Therefore, for the installed 27.5kV single-phase traction power supply cable lines, it is necessary to develop an effective cable online monitoring device. Summary of the invention

[0005] In order to make up for the deficiencies of the prior art, the present invention provides an online monitoring device and method for a traction power supply cable based on circulating current, which can judge various grounding faults and anomalies of a 27.5kV single-phase traction power supply cable.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] An online monitoring device for a traction power supply cable based on circulating current, characterized in that: it comprises current sensors CT1 and CT2 installed at the terminals of the traction power supply cable, for obtaining the power frequency current waveform at the cable terminals;

[0008] The current collection devices IED1 and IED2 are used to collect, calculate and identify faults of the circulating current of the traction power supply cable.

[0009] Furthermore, according to the needs on site, the current sensors CT1 and CT2 adopt closed-type or clamp-type power frequency CT.

[0010] Furthermore, the cable terminal is provided with a sheath protector.

[0011] A method for online monitoring of a traction power supply cable based on circulating current, characterized in that it comprises the following steps:

[0012] Step 1: The current acquisition devices IED1 and IED2 regularly acquire the current waveforms of the current sensors CT1 and CT2;

[0013] Step 2: Use the DFT method to calculate the effective current values ​​I1 and I2 at the current sensors CT1 and CT2;

[0014] Step 3: Calculate the leakage current I0 of the traction power supply cable;

[0015] Step 4: Calculate the sheath current coefficients K1 and K2;

[0016] Step 5: Make corresponding judgments based on the sizes of coefficients K1 and K2.

[0017] Furthermore, in step 1, the current acquisition devices IED1 and IED2 acquire two power frequency cycles at a time, and the sampling frequency is not less than 10K / s.

[0018] Furthermore, the traction power supply cable leakage current I0=ωCU0, ω is the grid angular frequency, and U0 is the system phase voltage.

[0019] Furthermore, K1 means the ratio of the current flowing through the left end of the cable to the cable leakage current, and K2 means the ratio of the current flowing through the right end of the cable to the cable leakage current:

[0020]

[0021] Furthermore, the grounding condition of the traction power supply cable sheath directly grounded side is determined according to the size of K1, and the grounding condition of the traction power supply cable sheath protector side is determined according to the size of K2.

[0022] Furthermore, if 0.9≤K1≥1.1, the grounding state of the 27.5kV single-phase traction power supply cable is normal; otherwise, it is judged to be abnormal;

[0023] If K1<0.02, it can be determined that the terminal ground wire is cracked or the contact resistance is abnormal;

[0024] If K1>1.2, multiple grounding points may occur in the traction power supply cable.

[0025] Furthermore, if K2 ≥ ε1, the sheath protector of the 27.5 kV single-phase traction power supply cable is abnormal;

[0026] If K2<ε2, the sheath protection of the 27.5kV single-phase traction power supply cable is broken;

[0027] ε1 and ε2 are relative thresholds set according to the cable sheath protector.

[0028] Beneficial effects of the present invention:

[0029] 1) The present invention can judge various grounding faults and abnormalities of the 27.5kV single-phase traction power supply cable by only using the current amplitudes at the two terminals of the 27.5kV single-phase traction power supply cable;

[0030] 2) The online monitoring method of the present invention does not need to measure the traction voltage amplitude, does not need communication between IED1 and IED2, and does not need synchronization between IED1 and IED2;

[0031] 3) The present invention has a flexible power supply mode and can be powered by batteries, solar energy or industrial frequency power supply. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the work flow chart of the present invention;

[0033] Figure 2 This is a topological diagram of a 27.5kV single-phase traction power supply cable of the present invention;

[0034] Figure 3 This is a schematic diagram of the 27.5kV single-phase traction power supply cable insulation online monitoring system of the present invention;

[0035] Figure 4 This is a diagram showing changes in sheath circulating current of a 27.5kV single-phase traction power supply cable with position under normal conditions of the present invention. DETAILED DESCRIPTION

[0036] The present invention is described in detail below in conjunction with specific implementation modes.

[0037] like Figure 2 , 3 As shown, the circulating current-based online monitoring device for traction power supply cables of the present invention comprises current sensors CT1 and CT2 installed at the terminals of the traction power supply cables, and used to obtain the power frequency current waveform of the cable terminals; according to the needs of the site, the current sensors CT1 and CT2 adopt closed-end or clamp-type power frequency CTs; the cable terminals are provided with sheath protectors;

[0038] The current collection devices IED1 and IED2 are used to collect, calculate and identify faults of the circulating current of the traction power supply cable.

[0039] like Figure 1 As shown, the online monitoring method of the traction power supply cable based on circulating current includes the following steps:

[0040] Step 1: The current acquisition devices IED1 and IED2 regularly acquire the current waveforms of the current sensors CT1 and CT2;

[0041] The current acquisition devices IED1 and IED2 collect data for two power frequency cycles at a time, which is about 20ms. They do not collect data every 20ms, and the sampling frequency is not less than 10K / s.

[0042] Step 2: Use the DFT method to calculate the effective current values ​​I1 and I2 at the current sensors CT1 and CT2; DFT is an algorithm for calculating the harmonic content of discrete signals. Its advantage is that it can calculate the amplitude and phase of any harmonic, has a fast calculation speed, and is easy to program;

[0043] Step 3: Calculate the leakage current I0 of the traction power supply cable;

[0044] Traction power cable leakage current I0 = ωCU0, ω is the grid angular frequency, U0 is the system phase voltage;

[0045] The grid angular frequency ω=2πf=2*3.14*50=314, the system phase voltage U0=25.0kV, when ω and U0 are constant, the leakage current is constant. Under normal circumstances, the sheath circulating current of 27.5kV single-phase traction power supply cable varies with position. Figure 4 Under normal circumstances, the current flowing through I1 is mainly leakage current.

[0046] Step 4: Calculate the sheath current coefficients K1 and K2;

[0047] K1 means the ratio of the current flowing through the left end of the cable to the cable leakage current, and K2 means the ratio of the current flowing through the right end of the cable to the cable leakage current:

[0048]

[0049] Step 5: Make corresponding judgments based on the size of coefficients K1 and K2;

[0050] 1) According to the size of K1, the grounding condition of the direct grounding side of the traction power supply cable sheath is judged as follows:

[0051] If 0.9≤K1≥1.1 (considering the fluctuation range of the traction grid voltage), the grounding state of the 27.5kV single-phase traction power supply cable is normal; otherwise, it is judged to be abnormal;

[0052] If K1<0.02, it can be determined that the terminal ground wire is cracked or the contact resistance is abnormal;

[0053] If K1>1.2, there may be multiple grounding points in the traction power supply cable;

[0054] 2) According to the size of K2, the grounding status of the traction power supply cable sheath protector side is judged as follows:

[0055] If K2 ≥ ε1, the sheath protector of the 27.5 kV single-phase traction power supply cable is abnormal;

[0056] If K2<ε2, the sheath protection of the 27.5kV single-phase traction power supply cable is broken;

[0057] ε1 and ε2 are relative thresholds set according to the cable sheath protector;

[0058] ε1 can be selected according to the site conditions, generally 0.05; ε2 can be selected according to the parameters of the sheath protector, generally 2.0.

[0059] In the description of the present invention, unless otherwise clearly specified and limited, the terms "set", "install", "connect", "connect", and "fix" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, it can be the internal connection of two elements or the interaction relationship between two elements. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0060] The content of the present invention is not limited to the embodiments listed, and any equivalent changes made to the technical solution of the present invention by ordinary technicians in this field after reading the description of the present invention are covered by the claims of the present invention.

Claims

1. A circulating current-based online monitoring device for traction power supply cables, characterized in that: It includes current sensors CT1 and CT2 installed at the traction power supply cable terminal, which are used to obtain the power frequency current waveform at the cable terminal; The current collection devices IED1 and IED2 are used to collect, calculate and identify faults of the circulating current of the traction power supply cable.

2. The online monitoring device for traction power supply cable based on circulating current according to claim 1 is characterized in that: According to the needs on site, the current sensors CT1 and CT2 adopt closed-type or clamp-type power frequency CT.

3. The online monitoring device for traction power supply cable based on circulating current according to claim 1 is characterized in that: The cable terminal is provided with a sheath protector.

4. A method for online monitoring of traction power supply cables based on circulating current, characterized in that: The steps include: Step 1: The current acquisition devices IED1 and IED2 regularly acquire the current waveforms of the current sensors CT1 and CT2; Step 2: Use the DFT method to calculate the effective current values ​​I1 and I2 at the current sensors CT1 and CT2; Step 3: Calculate the leakage current I0 of the traction power supply cable; Step 4: Calculate the sheath current coefficients K1 and K2; Step 5: Make corresponding judgments based on the sizes of coefficients K1 and K2.

5. The method for online monitoring of traction power supply cables based on circulating current according to claim 4 is characterized in that: In step 1, the current acquisition devices IED1 and IED2 collect two power frequency cycles at a time, and the sampling frequency is not less than 10K / s.

6. The method for online monitoring of traction power supply cables based on circulating current according to claim 4 is characterized in that: The traction power supply cable leakage current I0=ωCU0, ω is the grid angular frequency, and U0 is the system phase voltage.

7. The method for online monitoring of traction power supply cables based on circulating current according to claim 4 is characterized in that: K1 means the ratio of the current flowing through the left end of the cable to the cable leakage current, and K2 means the ratio of the current flowing through the right end of the cable to the cable leakage current:

8. The method for online monitoring of traction power supply cables based on circulating current according to claim 4 is characterized in that: According to the size of K1, the grounding condition of the direct grounding side of the traction power supply cable sheath is judged, and according to the size of K2, the grounding condition of the traction power supply cable sheath protector side is judged.

9. The method for online monitoring of traction power supply cables based on circulating current according to claim 8, characterized in that: If 0.9≤K1≥1.1, the grounding status of the 27.5kV single-phase traction power supply cable is normal; otherwise, it is judged to be abnormal; If K1<0.02, it can be determined that the terminal ground wire is cracked or the contact resistance is abnormal; If K1>1.2, multiple grounding points may occur in the traction power supply cable.

10. The method for online monitoring of traction power supply cables based on circulating current according to claim 8, characterized in that: If K2 ≥ ε1, the sheath protector of the 27.5 kV single-phase traction power supply cable is abnormal; If K2<ε2, the sheath protection of the 27.5kV single-phase traction power supply cable is broken; ε1 and ε2 are relative thresholds set according to the cable sheath protector.

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