A starting resistor open circuit protection method and protection circuit for a flexible DC system

Abstract

The present invention discloses a method for protecting the starting resistor from an open circuit in a flexible direct current system and a protection circuit thereof. The instantaneous value of the current on the starting resistor is detected by a current transformer connected in series with the starting resistor; the current transformer needs to meet the minimum sampling frequency requirement; after continuously measuring at least two measuring points with zero current values, if the subsequent current change rate is greater than a preset value, it is determined that a starting resistor open circuit fault has occurred. When the starting resistor is open circuited, the uncontrolled charging process is stopped, and the starting resistor is checked; the starting resistor open circuit fault can be detected in time during the starting process, avoiding the resistor from being put into operation and starting next time after a partial open circuit, causing a more serious resistor fault and affecting the operation of the flexible direct current system.

Description

Technical Field

[0001] The present invention relates to the technical field of flexible direct current power transmission, and in particular to a starting resistor open circuit protection method and a protection circuit thereof for a flexible direct current system. Background Art

[0002] The starting resistor of the flexible DC system is an important device of the flexible DC system. The starting resistor is put into use when the flexible DC system is started. After the AC circuit breaker is closed, the AC power supply charges the flexible DC converter valve uncontrolled rectifier through the starting resistor. After the charging is completed, the bypass isolation switch in parallel with the starting resistor is closed to bypass the starting resistor.

[0003] After closing the AC circuit breaker, the voltage and current on the starting resistor rise rapidly to the maximum value, and then gradually decrease until the uncontrolled charging is completed. In this process, the internal components of the resistor may short-circuit and burn due to the quality problem of the resistor, and then form a local open circuit. Since the two ends of the starting resistor are subjected to a high voltage during the startup charging process, after the partial disconnection, the voltage will be applied to the break, which will cause the break to short-circuit and break down. The loop current continues, and the break is further burned, continuously expanding the short-circuit burning range and the exciting open circuit range. At this time, it is difficult to determine that an open circuit fault has occurred only from the current electrical quantity. In the later stage of uncontrolled rectifier charging, as the voltage across the break gradually decreases, when the voltage difference cannot maintain the arc burning of the break, the break may no longer break down and continue to flow for a transient period of time.

[0004] Moreover, after one phase of the starting resistor is open during one starting process, a very high voltage will be applied to the small gap at the beginning of the next start, and the air clearance at multiple parts of this resistor will not meet the requirements, causing severe short-circuit discharge in the gaps at multiple parts, resulting in more serious resistor ablation. Multiple starting processes will cause a cumulative effect of faults, causing serious damage to the starting resistor. Summary of the invention

[0005] An embodiment of the present invention provides a method for protecting a starting resistor from an open circuit in a flexible DC system, the method comprising:

[0006] When uncontrolled charging is performed through the starting resistor, the instantaneous value of the current on the starting resistor is detected through a current transformer connected in series with the starting resistor;

[0007] After continuously measuring at least two points with zero current values, if the subsequent current change rate is greater than a preset value, it is determined that an open circuit fault of the starting resistor has occurred, the uncontrolled charging process is stopped, and the starting resistor is checked.

[0008] Preferably, the minimum sampling frequency requirement of the current transformer is:

[0009] Among them, U1 is the preset gap breakdown voltage after the starting resistor is open-circuited, U M is the phase voltage peak value of the starting resistor.

[0010] As a preferred embodiment, the preset value of the current change rate is

[0011] Among them, f s is the working voltage frequency, and R is the single-phase starting resistance value.

[0012] Another embodiment of the present invention further provides a starting resistor open circuit protection circuit for a flexible DC system, the circuit comprising a current transformer, a starting resistor and a bypass switch;

[0013] The first end of the current transformer is connected to the first end of the bypass switch, the second end of the current transformer is connected to the first end of the starting resistor, the second end of the starting resistor is connected to the second end of the bypass switch, the first end of the bypass switch is also used to connect to the flexible DC transformer of the flexible DC system, and the second end of the bypass switch is also used to connect to the flexible DC converter of the flexible DC system.

[0014] Another embodiment of the present invention also provides a starting resistor open circuit protection circuit for a flexible DC system, the circuit comprising a current transformer, a starting resistor and a bypass switch; the first end of the current transformer is connected to the first end of the bypass switch, the second end of the current transformer is connected to the first end of the starting resistor, the second end of the starting resistor is connected to the second end of the bypass switch, the first end of the bypass switch is also used to connect to an AC power supply, and the second end of the bypass switch is also used to connect to the flexible DC transformer of the flexible DC system.

[0015] The present invention provides a starting resistor open circuit protection method and a protection circuit for a flexible direct current system. The instantaneous value of the current on the starting resistor is detected by a current transformer connected in series with the starting resistor. The current transformer meets the minimum sampling frequency requirement. After continuously measuring at least two measuring points with zero current values, if the subsequent current change rate is greater than a preset value, it is determined that a starting resistor open circuit fault has occurred, the uncontrolled charging process is stopped, and the starting resistor is checked. The starting resistor open circuit fault can be detected in time during the starting process, so as to avoid the resistor being partially open and then continuing to be put into operation and starting next time, causing a more serious resistor fault and affecting the operation of the flexible direct current system. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a flow chart of a method for protecting a starting resistor from an open circuit in a flexible DC system provided by an embodiment of the present invention;

[0017] Figure 2It is a structural schematic diagram of a starting resistor open circuit protection circuit of a flexible DC system provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0018] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0019] The embodiment of the present invention provides a method for protecting the starting resistor from an open circuit in a flexible DC system. Figure 1 , is a flow chart of a method for protecting a starting resistor from an open circuit in a flexible DC system provided by an embodiment of the present invention, the method comprising steps S1 to S2:

[0020] S1, when uncontrolled charging is performed through a starting resistor, the instantaneous value of the current on the starting resistor is detected through a current transformer connected in series with the starting resistor;

[0021] S2, after continuously measuring at least two measuring points with zero current value, if the subsequent current change rate is greater than a preset value, it is determined that a starting resistance open circuit fault has occurred, the uncontrolled charging process is stopped, and the starting resistance is checked.

[0022] In the specific implementation of this embodiment, after the AC circuit breaker is closed, uncontrolled rectification charging is started through the starting resistor, and the instantaneous value of the current of the starting resistor is detected by a high sampling rate current transformer connected in series with the starting resistor;

[0023] After continuously measuring at least two points where the current value is zero, if the subsequent current change rate is greater than a preset value, it is determined that an open circuit fault of the starting resistor has occurred, the uncontrolled charging process is stopped, and the starting resistor is checked; by detecting the current zero-crossing measurement point combined with the change rate detection, it is determined whether the starting resistor has a fault.

[0024] The embodiment of the present invention provides a method for protecting the starting resistor from an open circuit in a flexible DC system. When uncontrolled charging is performed through the starting resistor, the instantaneous value of the current on the starting resistor is detected by a high sampling current transformer connected in series with the starting resistor. After continuously measuring at least two measuring points with zero current values, if the subsequent current change rate is greater than a preset value, it is determined that a starting resistor open circuit fault has occurred, the uncontrolled charging process is stopped, and the starting resistor is checked. The starting resistor fault can be accurately detected, and the starting resistor open circuit fault can be detected in time during the starting process, so as to avoid the resistor being partially open and then being put into operation and started next time, causing a more serious resistor fault and affecting the operation of the flexible DC system.

[0025] In another embodiment provided by the present invention, the minimum sampling frequency requirement of the current transformer is:

[0026]

[0027] Among them, U1 is the preset gap breakdown voltage after the starting resistor is open-circuited, U M is the phase voltage peak value of the starting resistor.

[0028] When this embodiment is implemented, the sampling frequency of the current transformer needs to meet certain conditions to complete the measurement of the instantaneous value of the current of the starting resistor.

[0029] In another embodiment provided by the present invention, the preset value of the current change rate is

[0030] Among them, f s is the working voltage frequency, and R is the single-phase starting resistance value.

[0031] In the specific implementation of this embodiment, the preset value of the current change rate is calculated according to the frequency of the operating voltage and the resistance of the starting resistor. When the current change rate exceeds the preset value, a fault is determined.

[0032] The embodiment of the present invention also provides a startup resistor open circuit protection circuit for a flexible DC system, see Figure 2 , is a schematic diagram of the structure of a starting resistor open circuit protection circuit of a flexible DC system provided by an embodiment of the present invention, including: a current transformer, a starting resistor and a bypass switch;

[0033] The first end of the current transformer is connected to the first end of the bypass switch, the second end of the current transformer is connected to the first end of the starting resistor, the second end of the starting resistor is connected to the second end of the bypass switch, the first end of the bypass switch is also used to connect the flexible DC transformer of the flexible DC system, and the second end of the bypass switch is also used to connect the flexible DC converter of the flexible DC system.

[0034] In the specific implementation of this embodiment, as a preferred implementation mode, the first end of the AC circuit breaker is used to connect to the AC bus AC, and the second end of the AC circuit breaker is used to connect to the first end of the flexible DC transformer;

[0035] The second end of the flexible DC transformer is used to connect to the first end of the bypass switch, the first end of the current transformer is connected to the first end of the bypass switch, the second end of the current transformer is connected to the first end of the starting resistor, and the second end of the starting resistor is connected to the second end of the bypass switch.

[0036] The second end of the bypass switch is used to connect to the input end of the flexible DC converter of the flexible DC system, and the output end of the flexible DC converter is used to connect to the DC cable;

[0037] Specifically, by closing the AC circuit breaker, the AC bus AC is transformed by the flexible DC transformer, and the flexible DC converter is uncontrolled charged through the starting resistor. During the charging process, the current value passing through the starting resistor is detected by the current transformer, and different methods are used to determine the open circuit of the starting resistor according to the accuracy of the current transformer, so as to protect the starting resistor.

[0038] An embodiment of the present invention provides a starting resistor open-circuit protection method for a flexible DC system. When uncontrolled charging is performed through the starting resistor, the instantaneous value of the current on the starting resistor is detected by a current transformer connected in series with the starting resistor; the current transformer has a minimum sampling frequency requirement; after continuously measuring at least two measuring points with zero current values, if the subsequent current change rate is greater than a preset value, it is determined that a starting resistor open-circuit fault has occurred, the uncontrolled charging process is stopped, and the starting resistor is checked; the starting resistor open-circuit fault can be detected in time during the startup process, to avoid the resistor being partially open and then continuing to start the operation next time, causing a more serious resistor fault and affecting the operation of the flexible DC system.

[0039] The above is a preferred embodiment of the present invention. It should be pointed out that a person skilled in the art can make several improvements and modifications without departing from the principle of the present invention. These improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for protecting a starting resistor from an open circuit in a flexible DC system, characterized in that: The method comprises: When uncontrolled charging is performed through the starting resistor, the instantaneous value of the current on the starting resistor is detected through a current transformer connected in series with the starting resistor; After continuously measuring at least two points with zero current value, if the subsequent current change rate is greater than a preset value, it is determined that a starting resistor open circuit fault has occurred, the uncontrolled charging process is stopped, and the starting resistor is checked; The current change rate is preset to Among them, f s is the working voltage frequency, R is the single-phase starting resistance value, U M is the phase voltage peak value of the starting resistor.

2. The method for protecting the starting resistor from an open circuit in a flexible DC system according to claim 1, wherein: The minimum sampling frequency requirement of the current transformer is: Among them, U1 is the preset gap breakdown voltage after the starting resistor is open-circuited, U M is the phase voltage peak value of the starting resistor.

3. A starting resistor open circuit protection circuit for a flexible DC system, characterized in that: The circuit includes a current transformer, a starting resistor and a bypass switch; The first end of the current transformer is connected to the first end of the bypass switch, the second end of the current transformer is connected to the first end of the starting resistor, the second end of the starting resistor is connected to the second end of the bypass switch, the first end of the bypass switch is also used to connect to the flexible DC transformer of the flexible DC system, and the second end of the bypass switch is also used to connect to the flexible DC converter of the flexible DC system; The circuit is used to implement the starting resistor open circuit protection method for a flexible DC system as described in claim 1.

4. A starting resistor open circuit protection circuit for a flexible DC system, characterized in that: The circuit includes a current transformer, a starting resistor and a bypass switch; the first end of the current transformer is connected to the first end of the bypass switch, the second end of the current transformer is connected to the first end of the starting resistor, the second end of the starting resistor is connected to the second end of the bypass switch, the first end of the bypass switch is also used to connect to an AC power source, and the second end of the bypass switch is also used to connect to a flexible DC transformer of the flexible DC system; The circuit is used to implement the starting resistor open circuit protection method for a flexible DC system as described in claim 1.

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