CN200976492Y

CN200976492Y - Ground transformer neutral point DC current suppression device

Info

Publication number: CN200976492Y
Application number: CN 200620157555
Authority: CN
Inventors: 毛承雄; 陆继明; 王升; 王丹
Original assignee: Huazhong University of Science and Technology
Current assignee: Huazhong University of Science and Technology
Priority date: 2006-11-24
Filing date: 2006-11-24
Publication date: 2007-11-14
Anticipated expiration: 2016-11-24

Abstract

The utility model relates to a DC current suppression device for a neutral point of a grounding transformer, belonging to a field of the electrical engineering technology. The device is characterized in that the device is composed of an isolation capacitor, a thyristor solid-state switch which is connected with the two ends of the isolation capacitor in parallel and a trigger unit, a current-limiting reactor and a bypass switch. The neutral point DC current of the transformer caused by HVDC transmission or geomagnetic storm can be effectively suppressed by the utility model, the problems of harmonic increase, noise increase, overheat and possible induced protection misoperation caused by the DC biasing of the transformer are avoided. The uncontrolled rectifier part can be neglected in the utility model, the structure is simplified, and the cost is reduced. The turn off structure of the reverse parallel connected thyristor is simple, and the external connection of the reverse voltage is needless.

Description

Grounding transformer neutral point direct current electric current restraining device

Technical field

The utility model belongs to the electrical engineering technical field, is specifically related to a kind of grounding transformer neutral point direct current electric current restraining device.

Background technology

Much more more and more high voltage direct current transmission (HVDC) is used in China, has played very positive effect in regional interconnection of power system, but has also brought some new problems simultaneously, such as, the transformer DC magnetic bias problem that the HVDC asymmetric operation causes.Therefore be necessary to develop a kind of device that can suppress direct current inflow transformer neutral point, thereby can avoid the D.C. magnetic biasing phenomenon of transformer effectively.

When HVDC operates in big earthed return of one pole or bipolar asymmetric operation mode, DC potential is arranged near the earth electrode, the size of current that this current potential and HVDC carry with the soil resistivity at this place relevant.The electric current that HVDC carries is big more, and the resistivity of soil is high more, and current potential is also just high more.Owing to exist the direct current potential difference, and the resistance value of AC system is less between the neutral point of the grounding transformer of diverse location, thereby makes direct current pass through the grounding transformer neutral point, has formed the loop in AC system.When the electric current that flows through the grounding transformer neutral point was excessive, D.C. magnetic biasing can take place in transformer, and then caused problems such as harmonic wave increases, noise increases, overheated, can cause the damage of transformer when serious, and may cause the malfunction of protection.It can cause that also 220kV, 500kV ac grid voltage resultant distortion rate significantly raise, and the significantly rising of harmonic wave also can produce considerable influence to other electric equipments, and these influences finally will injure the safe operation of electrical network.

Because neutral point flows into the D.C. magnetic biasing problem that direct current causes, increasing people begin one's study and suppress the measure and the device of transformer neutral point direct current for fear of grounding transformer.At present, several measures have been proposed: reverse injection current method, neutral point string electric-resistivity method and neutral point string capacitance method.

Wherein, oppositely the injection current method is to seal in a direct voltage source at transformer neutral point, according to detected DC current values, dynamically adjusts this voltage source setting, and reverse direct current is provided in real time.Though this method has certain flexibility, can dynamically select to inject different reverse currents at the DC current values that different neutral points flows into, but it can not be offset direct current fully and flow into from neutral point, and must outside transformer station, build the independent grounding utmost point, quantities is bigger, and maintenance cost is high.

Neutral point string electric-resistivity method is to seal in a resistance between neutral point and earth mat, can be so that the direct current that neutral point flows into obviously reduces.Though this method principle is simple, this method also has a lot of shortcomings: a, also can't suppress direct current fully flows into from neutral point; B, to calculate the resistance that different grounding transformer was connected in series in an electrical network very loaded down with trivial details, can not all count because comprise many influencing factors such as geological conditions, soil moisture content, mineral content, buried metal.And for some transformer, required resistance value may be very big, can not guarantee the transformer neutral point effective grounding; C, neutral point seal in resistance the system zero order parameter have been produced influence, and then also can have influence on adjusting of relaying protection; D, when system breaks down, also can cause a series of problems such as transformer neutral point overvoltage.E, when electric network composition changes (such as in network, increasing or reduce a grounding transformer), the earth resistance resistance need recomputate, series resistor needs to change.

Neutral point string capacitance method is at present in popular a kind of scheme aspect the inhibition transformer neutral point direct current: seal in capacitor between neutral point and earth mat, because electric capacity has the effect of handing over every straight-through, behind the main transformer neutral point installing electric capacity, can eliminate the direct current that flows through transformer neutral point effectively, and not influence alternating current and flow through neutral point.Under some improper situations, such as AC system short trouble, thunderbolt etc., the main transformer neutral point can flow through very big electric current, and produces the very high transient voltage of amplitude, might damage capacitor like this.Current bypass device in parallel at the capacitor two ends; after capacitor voltage at both ends surpasses setting; electric current flows through by the current bypass protective device; thereby with capacitive bypass; limit the transient voltage amplitude of neutral point capacitor, so then do not needed the very big capacitor of installed capacity to bear fault current, saved installing space; reduced cost, guaranteed that transformer and capacitor safe move reliably.Behind failure removal, the current bypass protective device automatically returns to the preceding state of action, and capacitor drops into the neutral ground operation again.

In sum, compare with reverse injection current method, neutral point string electric-resistivity method, neutral point string capacitance method is more effective, can suppress direct current inflow transformer neutral point up hill and dale.After sealing in block capacitor between neutral point and the earth mat, effective, an economic current bypass device (promptly suppressing transformer neutral point direct current device) is the assurance of block capacitor reliability service.

At present, utilizing the neutral point crosstalk to hold the technical scheme that suppresses the transformer neutral point direct current has two kinds: a kind of alternating voltage with the electric capacity two ends adopts diode rectification, connects the thyristor solid-state switch at DC side parallel then; Another kind is direct bidirectional thyristor solid-state switch in parallel at the electric capacity two ends.The common drawback of these two kinds of schemes is: all disposed baroque thyristor breaking circuit, and scheme one makes structure more complicated because of there being diode rectifier bridge.

Summary of the invention

The purpose of this utility model is to provide a kind of grounding transformer neutral point direct current electric current restraining device; this device can suppress the transformer neutral point direct current that caused by high voltage direct current transmission or earth magnetism storm effectively, avoided transformer because the harmonic wave that D.C. magnetic biasing causes increases, noise increases, overheated and may cause the problem of protection malfunction.

The grounding transformer neutral point direct current electric current restraining device that the utility model provides, it is characterized in that: it comprise capacitor C1, K switch 2, K3, circuits for triggering and n group bidirectional thyristor solid-state switch S1, S2 in parallel ..., Sn, wherein n is a bidirectional thyristor solid-state switch number in parallel, n 〉=1; Capacitor C1 is connected in parallel on K switch 2 two ends; K switch 2 is connected in parallel on transformer neutral point ground connection disconnecting link K1 two ends; K switch 3 is connected in parallel on the bidirectional thyristor two ends, is used to turn-off the bidirectional thyristor solid-state switch; Circuits for triggering are used to control the open-minded of n group bidirectional thyristor solid-state switch, when capacitor C1 overvoltage or overcurrent, continue to open the bidirectional thyristor solid-state switch.

The utility model device adopts the bidirectional thyristor solid-state switch directly in parallel with capacitor, does not control rectifying part thereby save, and makes designs simplification, and volume reduces, the cost reduction; The triggering link of bidirectional thyristor solid-state switch triggers the loop parallel connection by two-way and constitutes, thereby improves reliability; The bypass of direct metal switch short circuit is adopted in the shutoff of bidirectional thyristor solid-state switch, compares with the complicated circuit that common external reverse voltage turn-offs, and turn-offs reliable, simple in structure.

Description of drawings

Fig. 1 is the topology diagram of the utility model grounding transformer neutral point direct current electric current restraining device.

Embodiment

Below in conjunction with accompanying drawing and example the utility model is described in further detail.

As shown in Figure 1, the utility model electric current restraining device 1 comprise capacitor C1, K switch 2, K3, circuits for triggering 2 and n group bidirectional thyristor solid-state switch S1, S2 in parallel ..., Sn, wherein n is a bidirectional thyristor solid-state switch number in parallel, n 〉=1.T is a transformer among the figure, and K switch 1 is the direct ground connection disconnecting link of transformer neutral point.

K switch 2 is connected in parallel on transformer T neutral ground disconnecting link K1 two ends, is the fling-cut switch that suppresses transformer neutral point direct current device;

Capacitor C1 is for being connected in parallel on K switch 2 two ends, under the device normal operating conditions, it plays and stops direct current to flow to transformer neutral point or flow to the earth from transformer neutral point from the earth, and inoperative to the alternating current of the transformer neutral point of flowing through, and briefly is exactly " handing over every straight-through ".

Be connected in parallel on capacitor C1 two ends n group bidirectional thyristor solid-state switch S1, S2 ..., Sn, when being used under abnormal conditions capacitor C1 overcurrent or overvoltage, C1 provides bypass branch for capacitor; Each bidirectional thyristor solid-state switch constitutes by thyristor SCR1, SCR2 and the reactor L polyphone of two reverse parallel connections.Wherein reactor L is used to limit the current changing rate of thyristor, is used for the current-sharing between bidirectional thyristor solid-state switch parallel branch simultaneously.

K switch 3 is connected in parallel on the bidirectional thyristor two ends, is used to turn-off the bidirectional thyristor solid-state switch.

Circuits for triggering 2 are controlled the open-minded of n group bidirectional thyristor solid-state switch simultaneously, when capacitor C1 overvoltage or overcurrent, continue to open the bidirectional thyristor solid-state switch.

The circuits for triggering 2 of thyristor belong to existing topological structure.

Under the normal operating condition of ac and dc systems, the magnitude of voltage at capacitor two ends is within allowed band, and bidirectional thyristor bypass solid-state switch is failure to actuate.In case capacitor C1 overcurrent or overpressure situation occur, two kinds of action schemes arranged:

Action scheme 1: trigger the bidirectional thyristor solid-state switch, connect the capacitor bypass branch, make fault current can pass through the thyristor by-pass, thereby capacitor for voltage protection can not damage to the earth.The certain hour of delaying time again after the pending fault current vanishes K3 that closes a switch, at this moment, the bidirectional thyristor solid-state switch automatically shuts down after by the K3 short circuit, and then time-delay certain hour cut-off switch K3, and capacitor drops into again.

Action scheme 2: send K switch 3 switching signals in the time of triggering and conducting bidirectional thyristor solid-state switch, because K switch 3 feed motions are slower than thyristor conducting, so fault current can pass through the thyristor by-pass earlier to the earth, thereby capacitor for voltage protection can not damage, fault current will be transferred to K switch 3 by-passes to the earth by the thyristor bypass after K switch 3 is closed, and thyristor begins to turn to shutoff by conducting simultaneously; The certain hour tripping K switch 3 of delaying time again after the pending fault current vanishes, capacitor drops into again.

Action scheme 1 is compared with action scheme 2, the amount of capacity of the length of through-flow time of thyristor and K switch 3 when mainly being the fault current bypass.During the fault current bypass of action scheme 1, the through-flow time of thyristor is long, and certain caloric value is arranged, and K switch 3 is only as cutoff thyristor usefulness, and contact capacity can be very little.Action scheme 2, during the fault current bypass the through-flow time of thyristor very short, be the K3 closing time only, caloric value is less, but the amplitude of passing through fault current of K switch 3 is big and the time is longer, so require the capacity of K switch 3 bigger.

If block capacitor damages or the current bypass protective device breaks down; then pass through diagnostic loop; closed by-pass switch K1 in parallel with it is with its bypass; make main transformer neutral-point solid ground; and then the isolating switch K2 at device for opening two ends; itself and system are isolated, can keep in repair capacitor or current bypass protective device.

Claims

1, a kind of grounding transformer neutral point direct current electric current restraining device, it is characterized in that: it comprise capacitor C1, K switch 2, K3, circuits for triggering (2) and n group bidirectional thyristor solid-state switch S1, S2 in parallel ..., Sn, wherein n is a bidirectional thyristor solid-state switch number in parallel, n 〉=1;

Capacitor C1 is connected in parallel on K switch 2 two ends;

K switch 2 is connected in parallel on transformer neutral point ground connection disconnecting link K1 two ends;

K switch 3 is connected in parallel on the bidirectional thyristor two ends, is used to turn-off the bidirectional thyristor solid-state switch;

Circuits for triggering (2) are used to control the open-minded of n group bidirectional thyristor solid-state switch, when capacitor C1 overvoltage or overcurrent, continue to open the bidirectional thyristor solid-state switch.