A ground protection detection device applied to a static frequency converter and a detection method thereof

Abstract

The application relates to the technical field of pumped storage control, in particular to a grounding protection detection device applied to a static frequency converter and a detection method thereof, which comprises an inverter cabinet and an AC reactor, an output transformer and an output transformer input switch S1 are arranged between the inverter cabinet and the AC reactor, the neutral point of the output transformer is short-circuited and grounded through a grounding resistor R; the output transformer short-circuiting comprises a grounding detection device for detecting the voltage between the two ends of the grounding resistor R; when the output transformer is put into use, the grounding resistor R is automatically put into use and detects the grounding fault through the grounding detection device, the safe and reliable operation of the SFC is ensured, and the situation that the grounding protection is misoperated due to two-point grounding during the operation of the SFC is avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of pumped storage control, and particularly relates to a grounding protection detection device applied to a static frequency converter and a detection method thereof. BACKGROUND

[0002] Generally, pumped storage units are provided with injection type stator grounding protection. In a static frequency converter (SFC) provided with an output transformer, the pumped storage unit needs to be dragged in two stages, i.e., a low-speed running stage and a high-speed running stage. Whether running in which stage, the body grounding fault may occur. At present, the grounding fault is detected in the following several ways.

[0003] 1) The SFC is not provided with a grounding protection device (as shown in FIG. 1): Figure 1 ):

[0004] If the SFC is not configured with an output transformer, the SFC device can not be provided with grounding protection, and the whole dragging process is detected by the 100% stator grounding protection of the unit. If the SFC is configured with an output transformer, the grounding fault can only be detected by the 100% stator grounding protection device of the unit in the low-speed stage. In the high-speed stage, the grounding fault occurs, the inverter output is isolated from the unit through the transformer, the 100% stator grounding protection of the unit cannot detect the grounding fault, and the grounding fault can only be found when the unit is dragged next time. Thus, the grounding fault cannot be found in time, which may cause the failure of the SFC dragging.

[0005] 2) The SFC body three-phase PT primary neutral point is short-circuited and grounded through a resistance, and the grounding fault is detected by detecting the grounding resistance voltage (as shown in FIG. 2): Figure 2 ):

[0006] Under normal circumstances, the voltage at the neutral point of the PT should be 0. If the grounding fault occurs, the voltage at the neutral point will change, so it can be judged whether there is grounding. In the low-speed running stage, the output side of the SFC is connected with the unit end. At this time, the 100% stator grounding protection of the unit and the SFC body grounding protection are put into operation at the same time, and there are two grounding points in the dragging loop at the same time, which is easy to cause the grounding protection to malfunction.

[0007] 3) A knife switch is installed between the SFC body PT neutral point and the grounding protection resistance (as shown in FIG. 3): Figure 3 ):

[0008] When the SFC drag unit operates in the low-speed stage, the knife gap is disconnected, and the ground fault is detected by the unit 100% stator ground protection; when operating in the high-speed stage, the knife gap is closed, and the SFC body ground protection device is put into operation, at this time, the SFC inverter output is isolated from the unit stator through the output transformer, and the situation that two-point grounding leads to protection misoperation does not occur; However, this method needs to add a ground protection knife gap, which increases the cost of equipment and needs to increase the switching logic lock of the ground protection knife gap, and there is a risk of switching failure of the ground protection knife gap. SUMMARY

[0009] In order to solve the above problems, the application provides a grounding protection detection device applied to a static frequency converter and a detection method thereof, which ensures safe and reliable operation of the SFC and avoids the situation that two-point grounding leads to grounding protection misoperation during SFC operation. The following technical solutions are adopted:

[0010] A grounding protection detection device applied to a static frequency converter, comprising an inverter cabinet and an AC reactor, an output transformer and an output transformer input switch S1 are arranged between the inverter cabinet and the AC reactor, and the neutral point of the output transformer is short-circuited and grounded through a grounding resistor R;

[0011] The output transformer short circuiting comprises a ground detection device for detecting the voltage across the grounding resistor R.

[0012] Optionally, the low-voltage side neutral point of the output transformer is short-circuited and grounded through a grounding resistor R, and the output transformer input switch S1 is provided with a bypass switch S2 in parallel.

[0013] The input end of the bypass switch S2 is connected to the input end of the switch S1, and the output end is connected to the output end of the output transformer.

[0014] Optionally, when the static frequency converter (SFC) operates in the low-speed stage, the bypass switch S2 is closed, and the ground fault is detected by the unit stator ground protection.

[0015] When the static frequency converter (SFC) operates in the high-speed stage, the output transformer input switch S1 is closed, and the ground fault is detected by the grounding resistor R ground protection.

[0016] A grounding protection detection method applied to a static frequency converter, comprising a static frequency converter (SFC) and a pumped storage unit electrically connected thereto; the static frequency converter (SFC) comprises an output transformer, a grounding resistor R and a ground detection device;

[0017] When the output transformer is in use, the grounding resistor R is automatically put into operation and the ground fault is detected by the ground detection device.

[0018] Optionally, the static frequency converter (SFC) further comprises switches S1 and S2, and the detection method is as follows:

[0019] (1) The static frequency converter (SFC) sends a switch S2 closing order to enter the rotor position measurement mode;

[0020] (2) The static frequency converter (SFC) sends a low-speed operation signal;

[0021] (3) The pumped storage unit feedbacks a high-speed operation signal, and the static frequency converter (SFC) sends a switch S1 closing order and a switch S2 opening order.

[0022] Optionally, in the step (2), when the static frequency converter (SFC) operates in the low-speed stage, the ground fault is detected through the unit stator ground protection.

[0023] Optionally, in the step (3), when the static frequency converter (SFC) operates in the high-speed stage, the output transformer is put into operation, and the ground fault is detected through the ground resistance R ground protection.

[0024] A ground protection detection method applied to a static frequency converter (SFC), the static frequency converter (SFC) comprising an output transformer and a ground detection device;

[0025] The neutral point of the output transformer is short-circuited and connected to the ground detection device;

[0026] The ground detection device is used to detect the voltage change of the neutral point.

[0027] Optionally, when the static frequency converter (SFC) operates in the low-speed stage, the ground fault is detected through the unit stator ground protection;

[0028] When the static frequency converter (SFC) operates in the high-speed stage, the ground fault is detected through the ground detection device.

[0029] In summary, the present application has the following beneficial effects:

[0030] 1. When the SFC is configured with an output transformer, the SFC device sets the body ground protection, and when the ground fault occurs when the SFC operates in the high-speed stage, the ground fault can be detected through the neutral point short-circuiting and the ground detection device connected to the output transformer, so that the SFC drag failure caused by the failure to discover the ground fault in time is avoided.

[0031] 2. The SFC body ground protection detection device adopts to short-circuit the output variable low-voltage side neutral point and ground through a resistance, judges the ground fault through detecting the ground resistance voltage, when the SFC runs in the low-speed stage, can detect the ground fault through the 100% stator ground protection of the unit, when the SFC runs in the high-speed stage, the output transformer is put into use, the ground resistance R is automatically put into and detects the ground fault through the ground detection device, no matter which stage is run, the 100% stator ground protection of the unit and the SFC body ground protection cannot be put into at the same time, avoids the situation that the two grounding points exist in the drag circuit at the same time, causes the misoperation of the ground protection.

[0032] 3. The application makes the SFC obtain the ground protection in the whole running process, the SFC body ground protection is automatically put into, reduces the equipment cost and does not need to lock through increasing the switching logic of the ground protection knife switch, improves the reliability of the SFC running, avoids the situation that the switching of the ground protection knife switch fails in the running process of the SFC, thus causes the misoperation of the ground protection. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 It is a single-line diagram of the SFC system without ground detection;

[0034] Figure 2 It is a single-line diagram of the SFC system PT neutral point ground protection detection;

[0035] Figure 3 It is a single-line diagram of the SFC system PT neutral point ground protection detection plus the knife switch;

[0036] Figure 4 It is a single-line diagram of the SFC system output transformer low-voltage side neutral point ground protection detection. DETAILED DESCRIPTION

[0037] The following will be combined with the drawings Figure 4 The application is further explained.

[0038] The embodiment of the application discloses a ground protection detection device applied to a static frequency converter and a detection method thereof, the detection device comprises an inverter cabinet and an alternating current reactor, the inverter cabinet and the alternating current reactor are connected in parallel with a switch S1 and a switch S2, the switch S1 is connected with an output transformer, the switch S1 is used as an output transformer switching switch, an input end of the switch S2 is connected with an input end of the switch S1, and an output end of the switch S2 is connected with an output end of the output transformer to form a bypass, and the switch S2 is used as a bypass switch.

[0039] The pumped storage unit is provided with 100% stator ground protection (injection type stator ground protection) as the main protection of stator winding and its lead wire ground fault, which detects the change of resistance between stator winding and ground by adding 20Hz external power supply between the stator loop of the unit and the ground to determine the stator ground fault, and realizes 100% full area ground protection of the stator winding of the unit in any state.

[0040] As shown in Figure 4 When the output transformer is configured in the static frequency converter (SFC), the static frequency converter (SFC) is provided with a body ground protection detection device, the static frequency converter (SFC) body ground protection detection device adopts the neutral point short circuit of the output transformer and is grounded through a grounding resistor R, the short circuit is located at the low voltage side of the output transformer, that is, the neutral point of the low voltage side of the output transformer is short-circuited and grounded through the resistor, and the neutral point of the output transformer is also connected to a ground detection device for detecting the voltage across the grounding resistor R, and the ground detection device determines whether a ground fault occurs by detecting the voltage change of the neutral point of the output transformer.

[0041] The detection method is as follows:

[0042] (1) When the static frequency converter (SFC) is running, the static frequency converter (SFC) sends a closing order of switch S2, closes the bypass switch S2, and enters the rotor position measurement mode;

[0043] (2) The static frequency converter (SFC) sends a low-speed running signal, and the SFC drags the unit to run in the low-speed stage, at this time the output transformer input switch S1 is in the open state, at this time the output transformer and the SFC body ground protection connected are not put into use, and the whole dragging process is detected by the 100% stator ground protection of the unit.

[0044] (3) The pumped storage unit feedback high-speed running signal, the static frequency converter (SFC) sends a closing order of switch S1 and an opening order of switch S2 when the SFC drags the unit to run in the high-speed stage, closes the output transformer input switch S1 and opens the bypass switch S2, at this time the output transformer is put into use, the body ground protection detection device is automatically put into use, and at this time the whole dragging process is detected by the body ground protection.

[0045] When the static frequency converter (SFC) drags the unit to run in the low-speed stage, the static frequency converter (SFC) device can not be provided with ground protection, and the whole dragging process is detected by the 100% stator ground protection of the unit, and when the static frequency converter (SFC) drags the unit to run in the high-speed stage, the static frequency converter (SFC) enters the locked pulse into the output transformer for voltage regulation and speed reduction, because the inverter output and the unit are isolated by the transformer, the 100% stator ground protection of the unit cannot detect the ground fault, and the static frequency converter (SFC) device needs to be provided with ground protection for timely detection of ground fault.

[0046] The application adopts output variable low-voltage side neutral point short circuit and grounding through resistance, judges grounding fault by detecting grounding resistance voltage, when SFC runs in high speed stage, static frequency converter (SFC) enters closed pulse access output transformer, SFC body grounding protection detection device is automatically put into use, without setting grounding protection, also needs to set knife switch, and uses knife switch switching logic.

[0047] Moreover, the application adopts output variable low-voltage side neutral point short circuit and grounding through resistance, when static frequency converter (SFC) drag unit runs in low speed stage, output transformer is in off state, SFC body grounding protection detection device will not be put into use, so that in low speed running stage, unit 100% stator grounding protection and SFC body grounding protection will not be put into use at the same time, avoids two grounding points existing in drag circuit at the same time, and makes grounding protection misoperation.

[0048] The above are preferred embodiments of the application, which do not limit the protection scope of the application, so: equivalent changes made according to the structure, shape, principle of the application should be covered in the protection scope of the application.

Claims

1. A grounding protection detection device for a static frequency converter, comprising an inverter cabinet and an AC reactor, characterized in that: An output transformer and an output transformer connection switch S1 are provided between the inverter cabinet and the AC reactor. The neutral point of the output transformer is short-circuited and grounded through a grounding resistor R. The short-circuit of the output transformer includes a grounding detection device for detecting the voltage across the grounding resistor R. The neutral point of the low-voltage side of the output transformer is short-circuited and grounded through a grounding resistor R. A bypass switch S2 is connected in parallel with the output transformer connection switch S1. The input terminal of the bypass switch S2 is connected to the input terminal of the switch S1, and its output terminal is connected to the output terminal of the output transformer. When the static frequency converter (SFC) is operating at low speed, the bypass switch S2 is closed, and a grounding fault is detected through the stator grounding protection of the unit. When the static frequency converter (SFC) is operating at high speed, the output transformer connection switch S1 is closed, and a grounding fault is detected through the grounding protection of the grounding resistor R.

2. A grounding protection detection method applied to static frequency converters, characterized in that: It includes a static frequency converter (SFC) and a pumped storage unit electrically connected thereto, and the grounding protection detection device as described in claim 1; the static frequency converter (SFC) includes an output transformer, a grounding resistor R, and a grounding detection device; when the output transformer is put into use, the grounding resistor R is automatically connected and the grounding detection device detects grounding faults.

3. The grounding protection detection method for a static frequency converter according to claim 2, characterized in that: The static frequency converter (SFC) also includes switches S1 and S2, and the detection method is as follows: (1) The static frequency converter (SFC) issues a closing command for switch S2 and enters the rotor position measurement mode; (2) The static frequency converter (SFC) issues a low-speed operation signal; (3) The pumped storage unit feeds back a high-speed operation signal, and the static frequency converter (SFC) issues a closing command for switch S1 and a closing command for switch S2.

4. The grounding protection detection method for static frequency converters according to claim 3, characterized in that: In step (2), when the static frequency converter (SFC) is operating at low speed, the grounding fault is detected by the stator grounding protection of the unit.

5. The grounding protection detection method for a static frequency converter according to claim 3, characterized in that: In step (3), when the static frequency converter (SFC) is operating at high speed, the output transformer is engaged, and the grounding protection detects grounding faults through the grounding resistance R.

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