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Title:
FAST BYPASS DEVICE
Document Type and Number:
WIPO Patent Application WO/2012/171995
Kind Code:
A1
Abstract:
The present invention relates to a fast bypass device (1), comprising a pair of reverse-parallel-connected thyristors (T1, T2), a lightning arrester (SA) and a backup protection switch (BPS), wherein the pair of reverse-parallel-connected thyristors (T1, T2), the lightning arrester (SA) and the backup protection switch (BPS) are connected in parallel with each other. The advantages of the present invention are: 1) it does not require the additional provision of a pair of thyristors and complementary electronic drive circuit, thereby reducing costs; 2) it operates in a passive way, and is not restricted by whether or not the power supply is working normally; 3) since the backup protection switch is capable of closing within 1 millisecond of a fault occurring, and the load through the lightning arrester before closing is limited, faster and more reliable protection of the main capacitor can be realized; moreover, a lower load allows a smaller lightning arrester to be selected for use, saving space and further reducing costs.

Inventors:
PHILIPP ANDREAS (DE)
SONG YING HUA (CN)
WU XUE ZHI (CN)
YAO JI LONG (CN)
ZHAO YAN FENG (CN)
Application Number:
EP2012/061287
Publication Date:
December 20, 2012
Filing Date:
June 14, 2012
Export Citation:
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Assignee:
SIEMENS AG (DE)
PHILIPP ANDREAS (DE)
SONG YING HUA (CN)
WU XUE ZHI (CN)
YAO JI LONG (CN)
ZHAO YAN FENG (CN)
International Classes:
H02H9/04; H02M1/08
Foreign References:
DE102009043229A12011-03-31
US6075378A2000-06-13
Other References:
None
Attorney, Agent or Firm:
SIEMENS AKTIENGESELLSCHAFT (Postfach 22 16 34, München, 80506, DE)
Download PDF:
Claims:
Claims

1. A fast bypass device (1), comprising a pair of reverse- parallel-connected thyristors (Tl, T2), a lightning arrester (SA) and a backup protection switch (BPS) , wherein the pair of reverse-parallel-connected thyristors (Tl, T2), the light¬ ning arrester (SA) and the backup protection switch (BPS) are connected in parallel with each other. 2. The fast bypass device (1) as claimed in claim 1,

characterized in that

the backup protection switch (BPS) comprises a triggering circuit (2); the triggering circuit (2) comprises a single- phase bridge rectifier circuit (RC) , a second resistance (R2), a breakover diode (BOD), and a pulse transformer (PT) with a first winding (Wl) and a second winding (W2), wherein the second resistance (R2), the breakover diode (BOD) and the first winding (Wl) are connected in series with the output ends of the single-phase bridge rectifier circuit (RC) to form a loop, the input ends of the single-phase bridge recti¬ fier circuit (RC) are connected in parallel with the backup protection switch (BPS), and the second winding (W2) is connected to a triggering pole of the backup protection switch (BPS) .

3. The fast bypass device (1) as claimed in claim 2, charac¬ terized in that the output ends of the single-phase bridge rectifier circuit (RC) are connected in parallel with a ca¬ pacitor (C) .

4. The fast bypass device (1) as claimed in claim 2,

characterized in that

the input ends of the single-phase bridge rectifier circuit (RC) are connected in parallel with the backup protection switch (BPS) via a first resistance (Rl) .

5. The fast bypass device (1) as claimed in any one of claims 1 to 4, characterized in that

the thyristors (Tl, T2) are connected in parallel with a main capacitor (Cm) . 6. The fast bypass device (1) as claimed in claim 5,

characterized in that

the main capacitor (Cm) is one or more capacitances connected in series between the neutral point (PI) and grounding elec¬ trode (P2) of a transformer.

Description:
Description

Fast bypass device Technical field

The present invention relates to a fast bypass device, in particular to a fast bypass device for a direct current iso ¬ lation device.

Background art

When a High Voltage Direct Current (HVDC) power transmission system is in the ground return operating mode, direct current flows through the ground and causes a change in electric po ¬ tential in the vicinity of the grounding electrode of a transformer, so that a DC potential difference will arise be ¬ tween the neutral points of two neighboring transformers. Since AC systems have relatively low resistance values, the potential difference will also give rise to a direct current in an AC system with the help of the neutral points of the transformers. If the direct current is too high, it will lead to saturation of the transformer and the occurrence of DC magnetic bias therein, resulting in an excessively high tem- perature in the transformer, an increase in harmonics, and increased noise, and in serious cases may even damage the transformer .

In order to solve this problem, people have switched in a ca- pacitor between the neutral point and the grounding electrode of a transformer. A capacitor can block direct current while allowing the passage of alternating current. However, in view of the fact that the voltage which a capacitor is able to sustain is limited, there is a necessity to use a fast bypass device in parallel, to short-circuit the capacitor in the event of an electrical system fault or a power surge in the transformer, in order to prevent the voltage or current from exceeding the limit of the capacitor. Thyristors have been used in fast bypass devices on account of having good current control capability and a fast re ¬ sponse. Reverse-parallel-connected thyristors are widely em ¬ ployed as they can allow current to flow in both directions. An electronic drive circuit is generally used to actively in ¬ ject a certain current into the gate of a thyristor and thereby achieve triggering of the thyristor. In view of the fact that safety and reliability are of the utmost importance for a device which blocks direct current in an electrical system, it is necessary to additionally install a pair of thyristors and a complementary electronic drive circuit to serve as a backup protection device. In this case, the bypass function can be jointly borne by the two pairs of thyristors during normal operation. If one of the pairs develops a fault, the other pair can still achieve the bypass function alone. Such a solution has the following shortcomings: 1) a backup protection device requires a pair of thyristors and a complementary electronic drive circuit to be additionally provided, resulting in greatly increased costs; 2) the backup protection device must operate in an active way, i.e. trig ¬ gering may only be performed when the power source is working normally. If the power source should suffer paralysis as a result of a serious fault, triggering will be unable to be carried out. Another existing solution is to employ a me- chanical switch (for example a contactor) and a lightning arrester at the same time to serve as a backup protection de ¬ vice, but since the reaction time of a mechanical switch is long, generally several tens of milliseconds, it may be un ¬ able to meet the requirements for protecting the main capaci- tor, and also has a relatively high cost.

Content of the invention

The object of the present invention is to provide a fast by- pass device which is capable of protecting a main capacitor effectively and overcoming the above shortcomings in the prior art. This is achieved by way of the fast bypass device of the present invention; the fast bypass device comprises a pair of reverse-parallel-connected thyristors, a lightning arrester and a backup protection switch, wherein the pair of reverse-parallel-connected thyristors, the lightning arrester and the backup protection switch are connected in parallel with each other.

According to one aspect of the present invention, the backup protection switch comprises a triggering circuit. The triggering circuit comprises a single-phase bridge rectifier cir- cuit, a second resistance, a breakover diode, and a pulse transformer with a first winding and a second winding, wherein the second resistance, the breakover diode and the first winding are connected in series with the output ends of the single-phase bridge rectifier circuit to form a loop, the input ends of the single-phase bridge rectifier circuit are connected in parallel with the backup protection switch, and the second winding is connected to a triggering pole of the backup protection switch. According to another aspect of the present invention, the output ends of the single-phase bridge rectifier circuit are connected in parallel with a capacitor.

According to another aspect of the present invention, the thyristors are connected in parallel with a main capacitor.

According to another aspect of the present invention, the input ends of the single-phase bridge rectifier circuit are connected in parallel with the backup protection switch via a first resistance.

According to another aspect of the present invention, the main capacitor is one or more capacitances connected in se ¬ ries between the neutral point and grounding electrode of a transformer.

The advantages of the present invention are: 1) it avoids the additional provision of a pair of thyristors and complemen- tary electronic drive circuit, thereby reducing costs; 2) it operates in a passive way, and is not restricted by whether or not the power supply is working normally; 3) since the backup protection switch is capable of closing within 1 mil- lisecond of a fault occurring, and the load through the lightning arrester before closing is limited, faster and more reliable protection of the main capacitor can be realized; moreover, a lower load allows a smaller lightning arrester to be selected for use, saving space and further reducing costs.

Description of the accompanying drawings

The features and advantages of the present invention will be ¬ come clearer with reference to the following accompanying drawings, in which identical symbols indicate identical com ¬ ponents or devices:

Fig. 1 illustratively shows a fast bypass circuit 1 of the present invention connected in parallel with a main capacitor C m , in which electric potential points with the same labels are at the same potential;

Fig. 2 illustratively shows a triggering circuit 2 for a backup protection switch BPS.

List of reference symbols:

1 Fast bypass device; triggering circuit;

C capacitor; C m capacitor;

SA lightning arrester; backup protection switch; BOD breakover diode; pulse transformer;

Wl, W2 windings; Tl thyristors ;

Rl, R2 resistances;

RC single-phase bridge rectifier circuit;

PI, P2, P3, P4, P5, P6, P7, P8 electric potential points

Particular embodiments According to an embodiment of the present invention, the fast bypass device 1 as shown by the dashed line in Fig. 1 com ¬ prises a pair of reverse-parallel-connected thyristors Tl and T2, a lightning arrester SA and a backup protection switch BPS, wherein the reverse-parallel-connected thyristors Tl and T2, the lightning arrester SA and the backup protection switch BPS are connected in parallel with each other between the electric potential points P3 and P4. The backup protec ¬ tion switch BPS has a good capacity for sustaining strong currents, and is capable of closing within 1 millisecond of a fault occurring. The backup protection switch BPS may be obtained from amongst products such as the Siemens HVDC PLUS® and SVC PLUS®. If the pair of reverse-parallel-connected thy ¬ ristors Tl and T2 serving as a bypass circuit becomes unable to perform bypassing on account of a fault, the lightning arrester SA can be made to conduct within a few microseconds to short-circuit the main capacitor C m . Subsequently, the backup protection switch BPS closes within 1 millisecond of the oc ¬ currence of the fault, to short-circuit the main capacitor C m and at the same time remove the load on the lightning ar ¬ rester SA. Although the lightning arrester SA has a more rapid response, the backup protection switch BPS is capable of sustaining a far higher load than the lightning arrester SA; the present invention is able to protect the lightning arrester SA from damage caused by an excessive load by way of the backup protection switch BPS, while ensuring rapid short- circuiting of the main capacitor C m by way of the lightning arrester SA. According to another embodiment of the present invention, the backup protection switch BPS further comprises a triggering circuit 2 as shown in Fig. 2. The triggering circuit 2 comprises a single-phase bridge rectifier circuit RC, a resis ¬ tance R2 serving as a second resistance, a breakover diode BOD, and a pulse transformer PT with a winding Wl serving as a first winding and a winding W2 serving as a second winding, wherein the resistance R2, the breakover diode BOD and the winding Wl are connected in series with the output ends of the single-phase bridge rectifier circuit RC to form a loop, and the input ends of the single-phase bridge rectifier cir ¬ cuit RC are connected in parallel with the backup protection switch BPS at the electric potential points P3 and P4. The winding W2 is connected to a triggering pole (not shown) of the backup protection switch BPS at the electric potential points P5 and P6. When the electrical system develops a fault, the triggering circuit 2 will receive a fault signal through the electric potential points P3 and P4, which is rectified by way of the single-phase bridge rectifier circuit RC . If the rectified signal reaches the voltage level defined by the breakover diode BOD, a current will be produced in the winding Wl, so that a current is produced in the winding W2 of the pulse transformer PT to trigger the backup protection switch BPS; here, the second resistance serves to limit the current .

In another embodiment of the present invention, the output ends of the single-phase bridge rectifier circuit RC are con- nected in parallel with a capacitor C at the electric poten ¬ tial points P7 and P8, and/or the single-phase bridge recti ¬ fier circuit RC is connected in parallel with the backup pro ¬ tection switch BPS via a resistance Rl serving as a first re ¬ sistance, i.e. the resistance Rl is connected between the electric potential point P3 and an input end of the single- phase bridge rectifier circuit RC . Here, the capacitor C is used to suppress peaks while the first resistance is used to limit the current. According to another embodiment of the present invention, the fast bypass device 1 may be further connected in parallel with a main capacitor C m as shown in Fig. 1. In this case, the main capacitor C m connected between the neutral point PI and grounding electrode P2 of a transformer is connected in parallel with the reverse-parallel-connected thyristors Tl and T2 in the fast bypass circuit 1 at the electric potential points P3 and P4, wherein the main capacitor C m can be one or more capacitances connected in series between the neutral point PI and grounding electrode P2 of the transformer.

Although embodiments of the present invention are set forth above, these embodiments are not intended to set forth all possible forms of the present invention. Furthermore, the contents of this description are descriptive, not restric ¬ tive. Those skilled in the art could make various changes and amendments to the contents of this description without de- parting from the purport of the present invention and the scope of the claims.