WO2016019641A1

WO2016019641A1 - Main transformer neutral point overvoltage protection device

Info

Publication number: WO2016019641A1
Application number: PCT/CN2014/090169
Authority: WO
Inventors: 齐进
Original assignee: 齐进
Priority date: 2014-08-06
Filing date: 2014-11-03
Publication date: 2016-02-11
Also published as: CN104167723A

Abstract

A main transformer neutral point overvoltage protection device is characterized by comprising a base (5), a transient high-frequency overvoltage absorption protection unit (a) and a rod gap power frequency overvoltage protection unit (b), wherein the transient high-frequency overvoltage absorption protection unit and the rod gap power frequency overvoltage protection unit are installed on the base and are connected in parallel. In the transient high-frequency overvoltage absorption protection unit, a lightning arrester (6, 7) and a capacitor (2) are combined, the neutral point lightning arrester is divided into an upper segment and a lower segment that are connected in series, the lower segment of the lightning arrester (7) is connected with the capacitor in parallel, and due to the bypass absorption capacity of the capacitor for transient high-frequency overvoltage, the lightning and operation residual voltage is 40% lower than that of an existing commonly-used neutral point lightning arrester on the premise that the power frequency residual voltage of the lightning arrester is kept higher than the upper limit of the rod gap power frequency discharge voltage. Compared with an existing commonly-used neutral point protection product with a rod gap and a lightning arrester connected in parallel, the situation that because the rod gap discharges frequently when lightning invades, abnormal action occurs in relay protection and a main transformer is cut off can be remarkably improved.

Description

Main transformer neutral point overvoltage protection device

Technical field

The invention relates to a transformer protection device, in particular to a main transformer neutral point overvoltage protection device.

Background technique

110kV and 220kV are the main voltage levels of the power supply network. Due to the requirements of relay protection setting and prevention of communication interference, in order to limit the single-phase short-circuit current, some of the transformers adopt the neutral point ungrounding method. In this mode of operation, due to lightning strikes, single-phase grounding short-circuit faults, etc., which will cause neutral overvoltage, and the transformers are mostly graded insulation, the overvoltage poses a great threat to the insulation of the neutral point and must be protected. The device prevents accidents.

110kV, 220kV system is an effective grounding system during normal operation, some main transformers are not grounded, and the neutral point overvoltage is not high. If a single-phase ground fault occurs, if part of the main transformer consists of a partial system, it is not effectively grounded or even grounded. In the abnormal operating conditions of the system, dangerous overvoltages such as arc grounding and ferromagnetic resonance, which are common in ungrounded systems, may occur. The arrester of the neutral point of the main transformer cannot be tolerated. It is required to use rod clearance protection. To withstand short-circuit current, the discharge current of the rod gap must be delayed to start the relay to remove the lost ground transformer. The discharge voltage of the rod gap has statistical characteristics, large dispersion, cutoff overvoltage during discharge, and rod gap during discharge. The burning loss in the gap changes the discharge characteristics of the gap.

For the neutral point overvoltage protection of the graded insulation transformer, the arrangement of the arrester and the parallel bar gap is adopted. The cooperation principle of the two is: the lightning arrester bears the lightning overvoltage and the normal operation condition of the operation overvoltage protection, when the system occurs single phase During the ground fault and switch reclosing, the rod gap should not be discharged. The residual voltage of the arrester should be less than the lower limit of the impact voltage of the rod gap; only when the system loses ground and the system is not full-phase or resonant, The rod gap should be reliably operated to protect the neutral point insulation of the transformer and the insulation of the line end equipment to prevent the lightning arrester from exploding; the arrester cannot withstand the power frequency overvoltage exceeding its rated voltage, and the upper limit of the power frequency discharge voltage of the rod gap needs to be less than the rated value of the arrester. Voltage; the starting point of this protection principle is that the lightning arrester is the main protection for lightning and operating overvoltage under normal operating conditions, and the rod gap is used as backup protection. Once abnormal conditions occur, the rod gap discharge protects the arrester. However, the discharge voltage of the rod gap itself has statistical characteristics, and is greatly affected by the gap geometry and meteorological factors. The above ideal coordination is difficult, and poor coordination may cause the rod gap to discharge during the ground fault of normal operating conditions, especially Frequent discharge during lightning weather will lead to changes in the zero-sequence parameters of the system, which will bring uncertainties to the setting of relay protection, which may cause abnormal operation of relay protection; frequent discharge of rod gap will burn the rod head. Will change the discharge characteristics of the gap, need to replace the maintenance.

This kind of cooperation mode causes the rod gap to be discharged under the normal system grounding condition during lightning weather. The reason is: 1) the lightning arrester has high rated voltage and large residual voltage; 2) the rod gap is too close to the grounding body, and the impact discharge The voltage is greatly affected by the space capacitance, the impact discharge coefficient is low, and the discharge voltage of the positive polarity operation wave is particularly obvious. 3) The gap discharge of the rod gap is large, which is greatly affected by climatic factors, and the power frequency discharge voltage of the horizontal gap of the heavy rain is decreased. ~10%.

110,220 The kV system cannot be operated for a long time under abnormal conditions of ground loss. The power frequency discharge voltage of the rod gap of the neutral point of the 220kV transformer should be between 87kV and 121kV. Between the former, the highest short-time power-frequency over-voltage steady-state RMS value that may occur at the neutral point in the single-phase ground fault under normal operating conditions, and the latter is the 80% arrester power-frequency withstand capability at the line end. Corresponding neutral point voltage value; in order to avoid frequent gap discharge, generally adopt the method of increasing the gap distance, but the upper limit of the bar gap power frequency discharge voltage must be matched with the neutral point zero sequence overvoltage protection of the delay action, satisfying the line The terminal arrester cannot be aged. That is, when single-phase grounding occurs, the power-frequency overvoltage of the line-end arrester cannot exceed 1.1 times the rated voltage of the arrester, and the corresponding neutral point voltage is the upper limit of the bar gap.

Commonly used 220kV=Neutral point arrester Y1.5W144/320 type rated voltage 144kV is close to the neutral point maximum power frequency overvoltage steady state value (145kV) when the system loses ground, meets the insulation coordination requirements of the neutral point of the transformer, but the rated voltage High, high residual pressure, and the coordination with the rod gap is not ideal. At present, the 220kV neutral point bar gap in parallel with the arrester is generally recommended to be 290mm, and the power frequency discharge voltage range is 104~125kV. The upper limit exceeds the power frequency withstand limit of the 220kV line end arrester (220kV line end arrester is selected according to the 80% line voltage principle, the rated voltage is 200kV, the neutral point voltage is 121kV, the line end voltage is 220kV, which is the rated voltage of the arrester. 1.1 times), the gap value is already high. Even so, the lightning residual voltage of the arrester is still greater than the lightning impulse discharge voltage of the rod gap, 144 The 1.5kA residual voltage of the kV arrester is 320 The upper limit of the negative lightning impulse discharge voltage of kV, 290mm rod gap is about 250kV, the positive polarity is about 230kV, the operating impulse is lower than the positive discharge voltage, and the discharge of the gap under lightning arrester and operating residual voltage is a high probability event, which is currently running. The main reason for the frequent discharge of the neutral point bar gap of the 220kV transformer.

In order to avoid frequent discharge of the gap, some operating units adjust the gap distance too large, only considering the requirements of the main transformer neutral insulation, but neglect the requirements of the line end insulation. Once the ground fault occurs, the line arrester may age. Even damaged, the insulation fit is flawed. When the 220kV neutral point is used alone, the current general information is recommended to be 275mm, and the power frequency discharge voltage is 99~120kV, which meets the requirements of insulation coordination, but there is no lightning arrester. The lightning overvoltage wave will be totally reflected at the neutral point. The higher the value, the higher the discharge probability of the rod gap, so a parallel arrester is necessary.

Based on the above analysis, the ordinary lightning arrester can not be ideally matched with the gap, and the problem of frequent discharge of 220kV main transformer bar gap is also reflected in the fault report.

In addition, the volt-second characteristic of the rod gap is mainly affected by the geometry of the gap, that is, the electric field distribution. The electric field distribution has a great influence on the operating impulse discharge voltage. The grounding body close to the discharge gap will significantly reduce its positive breakdown voltage, and there is a significant "proximity effect". And "polar effects." Increasing the gap-to-ground distance can improve the geometric symmetry of the gap to the space and improve the impact discharge voltage of the positive polarity operation. It is common to report the abnormal movement of the 220kV main transformer bar gap from the fault report. The current mainstream manufacturers ignore the vertical ground body pair. The effect of the discharge characteristics of the rod gap is to shorten the length of the device, and the length of the rod pole is short. The voltage equalization effect of the charged body and the grounding body on the gap electric field reduces the impact coefficient of the rod gap, and the lower limit of the positive operating wave discharge voltage is even Below the lower limit of the power frequency discharge voltage peak, it may cause the discharge under the operating overvoltage. In some lightning-free mechanical grounding faults, the rod gap discharge also occurs. This proves that the operating overvoltage is generally accompanied by grounding. Therefore, the grounding of the lightning is also accompanied by the operation of the overvoltage, which makes the probability of the positive operating overvoltage of the low impact discharge coefficient high. The lightning overvoltage is generally 85% negative-polarity wave, but the lightning current becomes a high-frequency oscillation wave when the transformer winding reaches the neutral point, and its positive half-peak value may be much larger than the amplitude of the operating over-voltage, and the negative-voltage lightning impulse The lightning discharge voltage of the coefficient calculation bar gap also has certain problems. In order to avoid frequent discharge of the rod gap, it is necessary to reduce the lightning and operating residual voltage of the arrester as much as possible while improving the discharge characteristics of the rod gap. Increasing the pole length can improve the discharge characteristics of the rod gap, but at the same time, the volume of the equipment is greatly increased. The vertical rod gap can effectively utilize the support height of the neutral point arrester to meet the gap-to-ground distance without increasing the length of the base. The cost of manufacturing, packaging, transportation, and installation, but the vertical rod gap is easily shorted by the dirty rain column and is less used.

In operation, the abnormal operation of relay protection caused by the frequent movement of the rod gap occurs in lightning weather. Therefore, how to improve the characteristics of the main transformer neutral point overvoltage protection device and improve the power supply reliability of the main transformer is very issue concerned. After searching the relevant literature, there are some reports about the main transformer neutral point overvoltage protection device, but no technical solutions similar or identical to this patent have been found.

Summary of the invention

The technical problem to be solved by the present invention is to provide a neutral point overvoltage absorbing protection device for a main transformer capable of avoiding frequent discharge of a 220 kV main transformer bar gap in a lightning weather.

In order to solve the above technical problem, the technical solution of the present invention is: a main transformer neutral point over-voltage protection device, which is innovative: comprising a base, and a transient high-frequency over-voltage absorption protection unit and a rod mounted on the base The gap power frequency overvoltage protection unit, the transient high frequency overvoltage absorption protection unit and the rod gap power frequency overvoltage protection unit are arranged in parallel.

Preferably, the transient high frequency overvoltage absorption protection unit comprises an upper node arrester and a lower node arrester connected in series, and a capacitor connected in parallel with the lower node arrester; the bar gap power frequency overvoltage protection unit includes a relative setting a pole pole, a second pole pole, and a current transformer mounted on the base, the P1 terminal of the current transformer is electrically connected to the second pole pole, the P2 terminal of the current transformer is grounded; and the rod gap power frequency overvoltage protection unit The upper limit of the power frequency discharge voltage is less than 1.1 times the sum of the rated voltages of the upper node arrester and the lower node arrester.

Preferably, the lower lightning arrester is mounted on the base, the upper lightning arrester is mounted on the upper terminal of the lower lightning arrester, one terminal of the capacitor is connected to the upper terminal of the lower lightning arrester, and the other terminal of the capacitor is connected to the counter; The second rod and the first rod are arranged opposite each other on a vertical line to form a vertical gap, and the first rod is provided with a silicone rubber shed.

Preferably, the upper and lower lightning arresters are metal oxide surge arresters, and the rated voltage of the upper lightning arrester is 84 kV. The residual voltage of 1.5kA is less than 180kV; the rated voltage of the lower arrester is 30kV, the residual voltage of 1.5kA is less than 62kV; the capacity of the capacitor is 1.0μF.

Preferably, the first rod pole and the second rod pair have a vertical rod gap power frequency 50% discharge voltage effective value of 110 kV, a first rod length of 500 mm, and a second rod length of 750 mm.

The advantages of the invention are:

The arrester and the capacitor are combined, and the neutral point arrester is divided into two series in series, the lower node arrester is connected in parallel with the capacitor, and the bypass absorption capacity of the high frequency transient high frequency overvoltage is utilized, and the residual voltage of the arrester is maintained. Under the premise of the upper limit of the power-frequency discharge voltage of the rod gap, the lightning and operating residual voltage are 40% lower than the commonly used neutral point arrester Y1.5W144/320, which can meet the requirements of the volt-second characteristics of the rod gap; capacitors and arresters The combined structural design and parameter selection and the structural design of the rod gap make the impact residual voltage of the arrester lower than the lower limit of the impact discharge voltage of the rod gap, and the power frequency residual voltage is higher than the upper limit of the working voltage of the rod gap, and is effectively grounded at the normal neutral point. The lightning clearance and the stick clearance during operation are not operated under system conditions. Compared with the neutral point protection products that are commonly used in parallel with the lightning arrester, the rod gap is frequently discharged during the lightning intrusion, and the relay protection abnormal operation will be significantly improved.

The principle is as follows: the arrester is divided into upper and lower sections, and the capacitor is connected in parallel with the lower section arrester. Because the voltage distribution of the two arresters is extremely uneven, the upper section of the arrester is first turned on under the action of overvoltage, and the transformer windings are distributed according to the lightning and operation. Considering the parameters, the wave impedance is much larger than the short-circuit impedance at the power frequency. At this point, a neutral current is seen from the neutral point. This current source charges the capacitor through the on-resistance of the upper-arc arrester (very negligible). The lightning and operating wave head energy is very small, the charging voltage of the capacitor is very low, and the appropriate capacitance is selected. The charging voltage of the capacitor can be controlled within 5% of the residual voltage of the upper arrester, and the voltage acting on both ends of the rod gap is approximately the upper section. The residual pressure of the arrester. For the neutral point power frequency overvoltage, the impedance seen from the neutral point is very small, the equivalent value is a voltage source, the power of the power frequency half wave is much larger than the lightning and operation, and the charging voltage of the capacitor rises to the rated value of the next node arrester. At the current stage, the arrester starts to conduct, and the residual voltage of the upper and lower arresters is superimposed on both ends of the rod gap to discharge the rod gap. The upper limit of the power frequency discharge voltage of the rod gap is less than 1.1 times the sum of the rated voltages of the upper and lower node arresters, and the short-term power frequency of the arrester is satisfied. The tolerance characteristics are matched with the neutral point zero sequence overvoltage protection delay.

Related literature shows that the discharge voltage of the horizontal bar gap drops by 5~8% in heavy rain, and the utility model adopts the vertical rod gap and installs a silicone rubber shed above the gap to avoid the gap of the rain short rod and reduce the gap. The probability of the stick gap in the thunderstorm weather, while reducing the impact of raindrops on the gap discharge voltage. The vertical rod gap can effectively utilize the support height of the arrester, increase the ground distance of the gap, reduce the "proximity effect" of the grounding body on the discharge voltage, and improve the impact discharge coefficient of the rod gap, but does not increase the installation footprint of the equipment. Due to the large gap distance of the 220kV neutral point bar gap, the same impact coefficient is required to require a greater distance from the pole to the ground. This is especially important for the 220kV neutral point complete set, achieving the same clearance to ground distance, using vertical bars. The gap of the device base with a gap smaller than the horizontal bar gap is shortened by about 1000 mm.

DRAWINGS

FIG. 1 is a schematic structural view of a neutral point overvoltage protection device of a main transformer according to the present invention.

detailed description

As shown in FIG. 1, the base 5 includes a transient high-frequency over-voltage absorption protection unit a and a bar gap power frequency over-voltage protection unit b mounted on the base 5, and a transient high-frequency over-voltage absorption protection unit a and a rod The gap power frequency overvoltage protection unit b is arranged in parallel.

The transient high frequency overvoltage absorption protection unit comprises an upper node arrester 6 and a lower node arrester 7 connected in series, and a capacitor 2 connected in parallel with the lower node arrester 7. The bar gap power frequency overvoltage protection unit comprises a first rod 10 and a second rod 9 disposed opposite to each other, and a current transformer 1 mounted on the base, and the P1 terminal of the current transformer 1 is electrically connected to the second rod 9 The P2 terminal of the current transformer 1 is grounded; and the upper limit of the discharge voltage of the bar gap power frequency overvoltage protection unit is less than 1.1 times the sum of the rated voltages of the upper node arrester and the lower node arrester.

In order to reduce the volume of the entire protection device, as a more specific embodiment of the present invention:

The upper lightning arrester 6 and the lower lightning arrester 7 are arranged vertically: the lower lightning arrester 7 is mounted on the base 5, the upper lightning arrester 6 is mounted on the upper terminal of the lower lightning arrester 7, and one terminal of the capacitor 2 is passed through the flexible strand 3 and the lower The upper terminal of the surge arrester 7 is connected, the other terminal of the capacitor 2 is connected to the counter 4, and the other end of the counter 4 is grounded.

The first rod 10 and the second rod 9 are arranged in a vertical arrangement: the first rod 10 is electrically connected to the upper lightning arrester 6 through the conductive bracket 8 and suspended directly above the second rod 9, and the second rod 9 is The first rod 10 is oppositely arranged on a vertical line to form a vertical gap, and the first rod 10 is provided with a silicone rubber shed 11 to avoid the gap of the rain short rod and reduce the influence of the raindrop on the gap discharge voltage. , reducing the probability of discharge of the rod gap in thunderstorms.

As a preferred embodiment of the present invention, in the present embodiment, the first rod pole 10 and the second rod pole 9 are paired with a vertical rod gap power frequency 50% discharge voltage effective value is 110kV, and the first rod pole 10 length is 500mm, The two poles 9 are 750mm in length.

In this embodiment, the upper and lower lightning arresters are metal oxide surge arresters, and the rated voltage of the upper lightning arrester 6 is 84 kV. The residual voltage of 1.5kA is less than 180kV; the rated voltage of the 7th arrester is 30kV, The 1.5kA residual voltage is less than 62kV; the capacitor capacity is 1.0μF. Those skilled in the art will appreciate that the description herein is merely exemplary and not limiting.

The basic principles and main features of the present invention and the advantages of the present invention are shown and described above. It should be understood by those skilled in the art that the present invention is not limited by the foregoing embodiments, and that the present invention is only described in the foregoing description and the description of the present invention, without departing from the spirit and scope of the invention. Various changes and modifications are intended to be included within the scope of the invention as claimed. The scope of the invention is defined by the appended claims and their equivalents.

Claims

A main transformer neutral point overvoltage protection device, comprising: a base, and a transient high frequency overvoltage absorption protection unit and a rod gap power frequency overvoltage protection unit mounted on the base, the transient high frequency The overvoltage absorption protection unit and the rod gap power frequency overvoltage protection unit are arranged in parallel.
The main transformer neutral point overvoltage protection device according to claim 1, wherein:

The transient high frequency overvoltage absorption protection unit comprises an upper node arrester and a lower node arrester connected in series, and a capacitor connected in parallel with the lower node arrester;

The rod gap power frequency overvoltage protection unit comprises a first pole pole, a second pole pole and a current transformer mounted on the base, and the P1 terminal of the current transformer is electrically connected with the second pole pole, and the current mutual inductance Ground the P2 terminal of the device;

The upper limit of the power frequency discharge voltage of the bar gap power frequency overvoltage protection unit is less than 1.1 times the sum of the rated voltages of the upper node arrester and the lower node arrester.
The neutral transformer neutral overvoltage protection device according to claim 2, wherein the lower lightning arrester is mounted on the base, and the upper lightning arrester is mounted on the upper terminal of the lower lightning arrester, one terminal and the lower section of the capacitor The upper terminal of the arrester is connected, and the other terminal of the capacitor is connected with the counter; the second rod and the first rod are arranged opposite each other on a vertical line to form a vertical gap, and the first rod is provided with a silicone rubber umbrella skirt.
The neutral transformer overvoltage protection device of the main transformer according to claim 2 or 3, wherein the upper and lower lightning arresters are metal oxide surge arresters, and the rated voltage of the upper lightning arrester is 84 kV. The residual voltage of 1.5kA is less than 180kV; the rated voltage of the lower arrester is 30kV, the residual voltage of 1.5kA is less than 62kV; the capacity of the capacitor is 1.0μF.
The main transformer neutral point overvoltage protection device according to claim 2 or 3, characterized in that: the first rod pole and the second rod pair are formed by a vertical rod gap power frequency 50% discharge voltage effective value is 110 kV. The first rod has a length of 500 mm and the second rod has a length of 750 mm.