CN210693449U

CN210693449U - Adjustable neutral point grounding small resistance system

Info

Publication number: CN210693449U
Application number: CN201921752283.XU
Authority: CN
Inventors: 谭开平; 谢元龙; 陈旭; 张宏阳; 黄博勇; 陈永志
Original assignee: Qingyuan Electric Power Planning And Design Institute Co ltd
Current assignee: Qingyuan Electric Power Planning And Design Institute Co ltd
Priority date: 2019-10-17
Filing date: 2019-10-17
Publication date: 2020-06-05
Anticipated expiration: 2029-10-17

Abstract

The utility model discloses an adjustable type neutral point grounding small resistance system, include the grounding transformer who is connected with electric power system, still include resistance and the single-phase transformer who is connected with grounding transformer's neutral point, the side of single-phase transformer is connected with grounding transformer's neutral point and ground wire respectively, single-phase transformer's secondary side is provided with at least three taking a percentage, each take a percentage and provide different small resistance access equivalence respectively, the different fault type and the processing mode of corresponding electric power system. Through the utility model discloses can guarantee that the equivalent resistance value that inserts electric power system has low-high characteristic, through the electric current and the temperature sensing effect that start the small resistance self, adjust ground resistance and pass through the electric current, guarantee the earthing device safety.

Description

Adjustable neutral point grounding small resistance system

Technical Field

The utility model relates to a neutral point ground connection field especially relates to an adjustable type neutral point ground connection small resistance system.

Background

When the neutral point of the power grid is not grounded, even if the capacitance current of the system is not large, the potential of the healthy phase may rise to a level enough to destroy the insulation level of the healthy phase and even form an interphase short circuit because of the intermittent arc overvoltage generated when the single phase is grounded. If the neutral point is led out from the neutral point of the transformer or the grounded transformer and electromagnetic energy in intermittent arc overvoltage is released after the neutral point is connected with a resistor in series, the potential of the neutral point is reduced, and the rising speed of fault phase recovery voltage is also reduced, so that the possibility of electric arc restrike is reduced, the amplitude of power grid overvoltage is inhibited, and selective grounding protection is realized.

In the current small-resistance grounding system in China, the grounding resistors are all linear resistors. When a system has a non-metallic grounding fault, the grounding resistor may be burnt out due to long-time accumulated heat generation because of the reasons that the grounding current is small, the over-current protection cannot be operated or the zero-sequence protection is refused.

SUMMERY OF THE UTILITY MODEL

The utility model aims at providing an adjustable type neutral point ground connection small resistance system can reduce ground resistance and pass through the electric current, guarantees the earthing device safety.

In order to achieve the purpose, the adjustable neutral point grounding small-resistance system comprises a grounding transformer connected with a power system, a resistor and a single-phase transformer connected with the neutral point of the grounding transformer, wherein the primary side of the single-phase transformer is respectively connected with the neutral point and the ground wire of the grounding transformer, the secondary side of the single-phase transformer is provided with at least three taps, and each tap is respectively connected with the ground wire through a switching control box for detecting the real-time temperature and current magnitude of the resistor and controlling the tap to be communicated and switched, so that an adjustable protection structure for carrying out resistor and system protection through tap switching is formed.

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 sequentially smaller than the transformation ratio corresponding to the second tap and the transformation ratio corresponding to the third tap.

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

Preferably, a switch structure for controlling switching of each tap, a current detection device for detecting a circuit flowing through the resistor, and a controller in signal connection with the switch structure and the current detection device, respectively, are provided in the switching control box.

Preferably, the controller is further in signal connection with a temperature detection device for detecting the temperature of the resistor.

Preferably, the temperature detection device is a thermistor disposed on a resistor.

Preferably, the change-over switch structure comprises 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 in signal connection with the controller.

Compared with the prior art, the utility model, its beneficial effect lies in:

the utility model discloses a setting has the single-phase transformer access resistance of taking a percentage more, can control the switching of taking a percentage according to the electric current that flows through the resistance, can reduce ground resistance and pass through the electric current, guarantees the earthing device safety. The utility model discloses single phase transformer is through setting up three taking a percentage, can protect resistance step by step, has guaranteed that electric power system overvoltage level initial stage is reasonable throughout to stationary phase. The utility model discloses in control through the temperature and the electric current that self detected and make whole job stabilization. When the utility model works at the first tapping position, the grounding small resistor runs at full power, and conditions are provided for the correct action of the relay protection of the power system; when the power system works at the second tap position, the power system is in a relative protection state, and conditions are provided for the correct actions of monitoring programs of the power system except relay protection; when the device works at the third tap position, the relay protection and monitoring program of the power system is determined to be out of order, the self safety of the small resistor is protected as far as possible, and therefore the resistor is protected step by step.

Drawings

Fig. 1 is a schematic diagram of the circuit structure of the present invention;

fig. 2 is a block diagram of the control structure of the present invention.

Detailed Description

The present invention will be further described with reference to the following examples, which are not intended to limit the scope of the invention, but are intended to be within the scope of the claims.

As shown in fig. 1-2, the utility model provides an adjustable type neutral point grounding small resistance system, include the grounding transformer T1 who is connected with electric power system S, still include resistance R and the single-phase transformer T2 of being connected with grounding transformer T1 'S neutral point, single-phase transformer T2' S primary side is connected with grounding transformer T1 'S neutral point and ground wire respectively, single-phase transformer T2' S secondary side is provided with three at least taps, each tap respectively through the real-time temperature that is used for detecting resistance R and the current size control tap the switching control box U1 and resistance R and ground wire connection formation that carry out resistance and system protection through the tap switch adjustable type protection architecture of switching.

The secondary side of the single-phase transformer T2 is provided with three taps which are respectively a first tap a, a second tap b and a third tap c, and the transformation ratio corresponding to the first tap a is sequentially larger than the transformation ratio corresponding to the second tap b and the transformation ratio corresponding to the third tap c. The first tap a corresponds to a transformation ratio of N and the third tap c corresponds to a transformation ratio of 3N. In this embodiment, the transformation ratio corresponding to the second tap b may be set to 2N as needed. The switch-in equivalent resistance of the resistor R may be 36 Ω.

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

The change-over 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 in signal connection with the controller 2. In this embodiment, the first tap a is connected with the normally closed contact of the first relay, the second tap b is connected with the normally open contact of the second relay, and the third tap c is connected with the normally open contact of the third relay, so that the control is convenient and energy-saving.

The utility model also provides an adjustable neutral point grounding small resistance control method, which comprises the following processing steps;

step 1: the resistor R is communicated with a first tap a of a single-phase transformer T2 to carry out normal operation, and the current flowing through the resistor R by the resistor R is detected in real time;

step 2: when the current flowing through the resistor R is larger than a set value, the resistor R is switched to be communicated with the second tap b to carry out current limiting protection on the resistor R and limit overvoltage, and when the current flowing through the resistor R is smaller than a safety set value, the resistor R is switched to be communicated with the first tap a;

and step 3: and if the current flowing through the resistor R is still larger than the set value after the resistor R is communicated with the second tap b, switching the resistor R to be communicated with the third tap c so as to carry out safety protection on the resistor R and simultaneously maintain the grounding of the power system, and waiting for the maintenance of the power system.

In step 3, after the power system is maintained, the resistor R is controlled to be communicated with the second tap b according to the current flowing through the resistor R, and after the current flowing through the resistor R after the connection is smaller than a safety set value, the resistor R is switched to be communicated with the first tap a.

And the temperature of the resistor R is detected simultaneously in the working process, and after the temperature of the resistor R reaches the set temperature, the resistor R is communicated with the second tap b to protect the resistor R. The equivalent value of the resistor R of the access system is changed from a low value to a high value, so that the overvoltage level of the power system is guaranteed to be reasonable from the initial stage to the stable stage. Meanwhile, the control process of the system is controlled by the temperature and the current detected by the system, so that the system does not depend on external protection and improves the working stability.

In this embodiment, the resistor R can be connected to the first tap a, the second tap b, or the third tap c to ensure the grounding of the power system, so that the resistor R is protected and the stability of the system operation is improved. The running power of the resistor R is reduced to 1/9 when the resistor R is normally communicated with the first tap a after the resistor R is communicated with the third tap c, so that the resistor R can be effectively protected; the state is an absolute protection state, is judged as a serious accident, can only protect the self safety of the resistor R to the maximum extent, and simultaneously reserves the grounding mode of the power system to strive for time to wait for accident treatment. The resistor R is communicated with the second tap b, so that the protection state is relative, when the resistor R is normally communicated with the first tap a, danger exists, larger current flows, but the protection device is uncertain to be caused by failure or non-metal grounding, if the reason is the latter reason, the communication of the second tap b can play a role in protecting a small resistor, and the overvoltage level is limited.

The above is only a preferred embodiment of the present invention, and it should be noted that for those skilled in the art, without departing from the structure of the present invention, several modifications and improvements can be made, which will not affect the utility of the invention and the utility of the patent.

Claims

1. An adjustable neutral grounding small resistance system comprising a grounding transformer (T1) connected to an electrical power system (S), characterized in that: the protection circuit further comprises a resistor (R) and a single-phase transformer (T2) connected with a neutral point of a grounding transformer (T1), a primary side of the single-phase transformer (T2) is respectively connected with the neutral point of the grounding transformer (T1) and a ground wire, at least three taps are arranged on a secondary side of the single-phase transformer (T2), and each tap is respectively communicated and switched through a switching control box (U1) used for detecting real-time temperature and current of the resistor (R) and controlling the tap and is connected with the ground wire through the resistor (R) to form an adjustable protection structure for carrying out resistor and system protection through tap switching.

2. The adjustable neutral grounding small resistance system of claim 1, wherein: the secondary side of the single-phase transformer (T2) is provided with three taps, namely a first tap (a), a second tap (b) and a third tap (c), and the transformation ratio corresponding to the first tap (a) is smaller than that corresponding to the second tap (b) and that corresponding to the third tap (c) in sequence.

3. The adjustable neutral grounding small resistance system according to claim 2, wherein: the first tap (a) corresponds to a transformation ratio of N, and the third tap (c) corresponds to a transformation ratio of 3N.

4. An adjustable neutral grounding small resistance system according to claim 1 or 2, wherein: and a switching switch structure (K) for controlling the switching of each tap, a current detection device (1) for detecting a circuit flowing through the resistor (R) and a controller (2) which is respectively in signal connection with the switching switch structure (K) and the current detection device (1) are arranged in the switching control box (U1).

5. The adjustable neutral grounding small resistance system according to claim 4, wherein: the controller (2) is also in signal connection with a temperature detection device (3) for detecting the temperature of the resistor (R).

6. The adjustable neutral grounding small resistance system according to claim 5, wherein: the temperature detection device (3) is a thermistor arranged on the resistor (R).

7. The adjustable neutral grounding small resistance system according to claim 4, wherein: the 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), and the first relay, the second relay and the third relay are respectively in signal connection with the controller (2).