Adjustable neutral point grounding low resistance system and control method thereof

Abstract

The present invention discloses an adjustable neutral point grounding small resistance system and a control method thereof. On the one hand, the present invention provides an adjustable neutral point grounding small resistance system, including a grounding transformer connected to a power system, and also including a resistor and a single-phase transformer connected to the neutral point of the grounding transformer, the primary side of the single-phase transformer is respectively connected to the neutral point and the ground wire of the grounding transformer, and the secondary side of the single-phase transformer is provided with at least three taps, each of which provides a different small resistance access equivalent value, corresponding to different fault types and processing methods of the power system. On the other hand, the present invention provides an adjustable neutral point grounding small resistance control method. The present invention can ensure that the equivalent resistance value connected to the power system has low-high characteristics, and by starting the current and temperature sensing function of the small resistor itself, the current passing through the grounding resistor is adjusted to ensure the safety of the grounding equipment.

Description

Technical Field

[0001] The invention relates to the field of neutral point grounding, in particular to an adjustable neutral point grounding small resistance system, and also to an adjustable neutral point grounding small resistance control method. Background Art

[0002] When the neutral point of the power grid is not grounded, even if the capacitive current of the system is not large, intermittent arc overvoltage will be generated when the single-phase is grounded, which may increase the potential of the healthy phase to a level sufficient to destroy its insulation level, or even form a phase-to-phase short circuit. If the neutral point of the transformer or the neutral point is drawn out by a grounding transformer, and a resistor is connected in series to discharge the electromagnetic energy in the intermittent arc overvoltage, the neutral point potential will be reduced, and the speed of voltage rise of the fault phase recovery will also be slowed down, thereby reducing the possibility of arc reignition, suppressing the amplitude of the power grid overvoltage, and enabling selective grounding protection.

[0003] In the current low-resistance grounding system in my country, grounding resistors are all linear resistors. When a non-metallic grounding fault occurs in the system, due to the small grounding current, the overcurrent protection will not work or the zero-sequence protection will not work, which may cause the grounding resistor to burn out due to long-term accumulated heat. Summary of the invention

[0004] The first object of the present invention is to provide an adjustable neutral point grounding low resistance system, which can reduce the current passing through the grounding resistance and ensure the safety of the grounding equipment.

[0005] A second objective of the present invention is to provide a control method for the system.

[0006] To achieve this purpose, an adjustable neutral point grounding small resistance system is provided, including a grounding transformer connected to the power system, and also including a resistor and a single-phase transformer connected to the neutral point of the grounding transformer, the primary side of the single-phase transformer is respectively connected to the neutral point and the ground wire of the grounding transformer, and the secondary side of the single-phase transformer is provided with at least three taps, each of the taps is respectively connected to the resistor and the ground wire through a switching control box for detecting the real-time temperature and current size of the resistor to control the tap connection switching to form an adjustable protection structure for resistor and system protection through tap switching.

[0007] Preferably, the secondary side of the single-phase transformer is provided with three taps, namely a first tap, a second tap and a third tap, and the transformation ratio corresponding to the first tap is respectively smaller than the transformation ratio corresponding to the second tap and the transformation ratio corresponding to the third tap.

[0008] Preferably, the transformation ratio corresponding to the first tap is N, and the transformation ratio corresponding to the third tap is 3N.

[0009] Preferably, the switching control box is provided with a switching switch structure for controlling the switching of each tap, a current detection device for detecting the current flowing through the resistor, and a controller respectively connected to the switching switch structure and the current detection device signal.

[0010] Preferably, the controller is also signal-connected to a temperature detection device for detecting the temperature of the resistor.

[0011] Preferably, the temperature detection device is a thermistor arranged on a resistor.

[0012] Preferably, the switching switch structure includes a first relay for controlling the connection or disconnection of the first tap, a second relay for controlling the connection or disconnection of the second tap, and a third relay for controlling the connection or disconnection of the third tap, and the first relay, the second relay and the third relay are respectively connected to the controller signal.

[0013] To achieve the second objective, an adjustable neutral point grounding small resistance control method is provided, the method comprising the following processing steps:

[0014] Step 1: Connect the resistor to the first tap of the single-phase transformer, perform normal operation, and detect the current flowing through the resistor in real time;

[0015] Step 2: When the current flowing through the resistor is greater than the set value, the resistor is switched to connect to the second tap to perform current limiting protection on the resistor and limit overvoltage. When the current flowing through the resistor is less than the safety set value, the resistor is switched to connect to the first tap;

[0016] Step 3: If the current flowing through the resistor is still greater than the set value after the resistor is connected to the second tap, the resistor is switched to connect to the third tap to protect the resistor while maintaining the power system grounding, waiting for the power system to be repaired.

[0017] Preferably, in step 3, after the power system is repaired, the resistor is controlled to be connected to the second tap first according to the current flowing through the resistor, and after the current flowing through the resistor is less than the safety set value, the resistor is switched to be connected to the first tap.

[0018] Preferably, the temperature of the resistor is detected during the working process, and after the temperature of the resistor reaches the set temperature, the resistor is connected to the second tap to protect the resistor.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] The present invention, by setting a single-phase transformer with multiple taps to access the resistor, can control the switching of the taps according to the current flowing through the resistor, can reduce the current passing through the grounding resistor, and ensure the safety of the grounding equipment. In the present invention, the single-phase transformer can protect the resistor in steps by setting three taps, ensuring that the overvoltage level of the power system is always reasonable from the initial stage to the stable period. In the present invention, the temperature and current detected by itself are controlled to make the overall operation stable. In the present invention, when working in the first tap position, the small grounding resistor operates at full power, providing conditions for the correct operation of the relay protection of the power system; when working in the second tap position, it is a relative protection state, providing conditions for the correct operation of the monitoring program of the power system except the relay protection; when working in the third tap position, it is determined that the relay protection and monitoring program of the power system have failed, and the safety of the small resistor itself is protected as much as possible, thereby protecting the resistor in steps. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the circuit structure of the present invention;

[0022] Figure 2 This is a control structure block diagram of the present invention. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with the embodiments, but it does not constitute any limitation to the present invention. Any limited number of modifications made within the scope of the claims of the present invention are still within the scope of the claims of the present invention.

[0024] like Figure 1 to Figure 2 As shown, the present invention provides an adjustable neutral point grounding small resistance system, including a grounding transformer T1 connected to a power system S, and also including a resistor R and a single-phase transformer T2 connected to the neutral point of the grounding transformer T1, the primary side of the single-phase transformer T2 is respectively connected to the neutral point of the grounding transformer T1 and the ground wire, and the secondary side of the single-phase transformer T2 is provided with at least three taps, each tap is respectively connected to the resistor R and the ground wire through a switching control box U1 for detecting the real-time temperature and current size of the resistor R to control the tap connection switching to form an adjustable protection structure for resistor and system protection through tap switching.

[0025] The secondary side of the single-phase transformer T2 is provided with three taps, namely, the first tap a, the second tap b and the third tap c. The transformation ratio corresponding to the first tap a is greater than the transformation ratio corresponding to the second tap b and the transformation ratio corresponding to the third tap c. The transformation ratio corresponding to the first tap a is N, and the transformation ratio corresponding to the third tap c is 3N. In this embodiment, the transformation ratio corresponding to the second tap b can be set to 2N as needed. The access equivalent resistance value of the resistor R can be 36Ω.

[0026] The switching control box U1 is provided with a switching switch structure K for controlling the switching of each tap, a current detection device 1 for detecting the current flowing through the resistor R, and a controller 2 respectively connected to the switching switch structure K and the current detection device 1. The controller 2 is also connected to a temperature detection device 3 for detecting the temperature of the resistor R. The temperature detection device 3 is a thermistor arranged on the resistor R. In this embodiment, the controller 2 can be a PLC, and the current detection device 1 is a current transformer. The controller 2 can also be connected to a display to display individual data in real time, and an alarm device can be set to alarm when the current or temperature is too high, and can also be connected to the power system monitoring center in a wired or wireless manner.

[0027] The switching switch structure K includes a first relay for controlling the connection or disconnection of the first tap a, a second relay for controlling the connection or disconnection of the second tap b, and a third relay for controlling the connection or disconnection of the third tap c. The first relay, the second relay, and the third relay are respectively connected to the controller 2 by signal. In this embodiment, the first tap a is connected to the normally closed contact of the first relay, the second tap b is connected to the normally open contact of the second relay, and the third tap c is connected to the normally open contact of the third relay, so that the control is convenient and energy-saving.

[0028] The present invention also provides an adjustable neutral point grounding small resistance control method, the method comprising the following processing steps:

[0029] Step 1: Connect the resistor R to the first tap a of the single-phase transformer T2, perform normal operation, and detect the current flowing through the resistor R in real time;

[0030] Step 2: When the current flowing through the resistor R is greater than the set value, the resistor R is switched to be connected to the second tap b to perform current limiting protection on the resistor R and limit overvoltage. When the current flowing through the resistor R is less than the safety set value, the resistor R is switched to be connected to the first tap a;

[0031] Step 3: If the current flowing through the resistor R is still greater than the set value after the resistor R is connected to the second tap b, the resistor R is switched to be connected to the third tap c to protect the resistor R while maintaining the power system grounding, waiting for the power system to be repaired.

[0032] In step 3, after the power system is repaired, the resistor R is controlled to be connected to the second tap b first according to the current flowing through the resistor R. After the current flowing through the resistor R is less than the safety set value, the resistor R is switched to be connected to the first tap a.

[0033] During the working process, the temperature of the resistor R is detected at the same time. After the temperature of the resistor R reaches the set temperature, the resistor R is connected to the second tap b to protect the resistor R. The equivalent value of the resistor R connected to the system changes from a low value to a high value, ensuring that the overvoltage level of the power system is always reasonable from the initial stage to the stable period. At the same time, the control process of this system is controlled by the temperature and current detected by itself, so that it does not rely on external protection and improves the stability of the work.

[0034] In this embodiment, whether the resistor R is connected to the first tap a, the second tap b, or the third tap c, the grounding of the power system can be ensured, so that the stability of the system operation is improved while the resistor R is protected. After the resistor R is switched to be connected to the third tap c, the operating power is as low as 1 / 9 of the normal power when the resistor R is connected to the first tap a, so the resistor R can be effectively protected; this state is an absolute protection state. If it is determined to be a serious accident, it can only protect the safety of the resistor R to the maximum extent, while retaining the grounding mode of the power system to buy time to wait for the accident to be handled. If the resistor R is connected to the second tap b, it is a relative protection state. It is determined that there is danger when the resistor R is connected to the first tap a normally, and a large current flows, but it is not sure whether it is caused by the failure of the protection device or the non-metallic grounding. If it is the latter, the connection of the second tap b can play a role in protecting the small resistor and limit the overvoltage level at the same time.

[0035] The above are only preferred embodiments of the present invention. It should be pointed out that for those skilled in the art, several modifications and improvements can be made without departing from the structure of the present invention, which will not affect the effect of the implementation of the present invention and the practicality of the patent.

Claims

1. An adjustable neutral point grounding small resistance control method, characterized by: The method involves an adjustable neutral point grounding low resistance system; The adjustable neutral point grounding small resistance system comprises a grounding transformer (T1) connected to a power system (S), a resistor (R) and a single-phase transformer (T2) connected to the neutral point of the grounding transformer (T1), the primary side of the single-phase transformer (T2) being respectively connected to the neutral point of the grounding transformer (T1) and the ground wire, the secondary side of the single-phase transformer (T2) being provided with at least three taps, each of the taps being respectively connected to the ground wire through a switching control box (U1) for detecting the real-time temperature and current magnitude of the resistor (R) and the resistor (R) for controlling tap connection switching to form an adjustable protection structure for performing resistor and system protection through tap switching; the secondary side of the single-phase transformer (T2) being provided with three taps, namely a first tap (a), a second tap (b) and a third tap (c), the transformation ratio corresponding to the first tap (a) being smaller than the transformation ratio corresponding to the second tap (b) and the transformation ratio corresponding to the third tap (c); The method comprises the following processing steps; Step 1: Connect the resistor (R) to the first tap (a) of the single-phase transformer (T2), perform normal operation, and detect the current flowing through the resistor (R) in real time; Step 2: When the current flowing through the resistor (R) is greater than the set value, the resistor (R) is switched to be connected to the second tap (b) to perform current limiting protection on the resistor (R) and limit overvoltage. When the current flowing through the resistor (R) is less than the safety set value, the resistor (R) is switched to be connected to the first tap (a); Step 3: If the current flowing through the resistor (R) is still greater than the set value after the resistor (R) is connected to the second tap (b), the resistor (R) is switched to be connected to the third tap (c) so as to safely protect the resistor (R) while maintaining the grounding of the power system, waiting for the power system to be repaired.

2. The adjustable neutral point grounding small resistance control method according to claim 1 is characterized in that: The transformation ratio corresponding to the first tap (a) is N, and the transformation ratio corresponding to the third tap (c) is 3N.

3. The adjustable neutral point grounding small resistance control method according to claim 1 is characterized in that: The switching control box (U1) is provided with a switching switch structure (K) for controlling the switching of each tap, a current detection device (1) for detecting a current flowing through a resistor (R), and a controller (2) respectively connected to the switching switch structure (K) and the current detection device (1) by signals.

4. The adjustable neutral point grounding small resistance control method according to claim 3 is characterized in that: The controller (2) is also signal-connected to a temperature detection device (3) for detecting the temperature of the resistor (R).

5. The adjustable neutral point grounding small resistance control method according to claim 4 is characterized in that: The temperature detection device (3) is a thermistor arranged on the resistor (R).

6. The adjustable neutral point grounding small resistance control method according to claim 3 is characterized in that: The switching switch structure (K) comprises a first relay for controlling the connection or disconnection of the first tap (a), a second relay for controlling the connection or disconnection of the second tap (b), and a third relay for controlling the connection or disconnection of the third tap (c), wherein the first relay, the second relay and the third relay are respectively connected to the controller (2) by signal.

7. The adjustable neutral point grounding small resistance control method according to claim 1 is characterized in that: In step 3, after the power system is repaired, the resistor (R) is controlled to be connected to the second tap (b) first according to the current flowing through the resistor (R). After the current flowing through the resistor (R) is less than the safety setting value, the resistor (R) is switched to be connected to the first tap (a).

8. The adjustable neutral point grounding small resistance control method according to claim 1 or 7, characterized in that: During the working process, the temperature of the resistor (R) is detected at the same time. After the temperature of the resistor (R) reaches the set temperature, the resistor (R) is connected to the second tap (b) to protect the resistor (R).

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