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A Magnetically Controllable Transformer for low cost SVC application

IP.com Disclosure Number: IPCOM000222776D
Publication Date: 2012-Oct-23
Document File: 5 page(s) / 457K

Publishing Venue

The IP.com Prior Art Database

Related People

Xiaobo Yang: AUTHOR [+4]

Abstract

Traditional SVC consists of thyristor controlled reactor (TCR) and fix capacitor banks (FC). Although the advantage of using SVC is well known, it is still not applied widely at medium voltage (MV) level due to relatively high cost, in particular compared with mechanical switched capacity bank (MSC). This invention proposes a novel controllable transformer, which has both functions of power transition and reactive power regulation. With the combination of FC, a low cost SVC system is established. Besides, the same technology can be also applied for UHV level as an alternative solution of shunt reactor. In this document, the application for reactive power compensation as a low cost SVC is focused.

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Invention Title: A Magnetically Controllable Transformer for low cost SVC application

Principal Applications/Uses of the Invention

Low cost SVC: Traction substation, wind farm, distribution network.

Problem Overcome by the Invention

Traditional SVC consists of thyristor controlled reactor (TCR) and fix capacitor banks (FC). Although the advantage of using SVC is well known, it is still not applied widely at medium voltage (MV) level due to relatively high cost, in particular compared with mechanical switched capacity bank (MSC). However, MSC brings several disadvantages such as:

§  Low regulation speed

§  Low control precision due to discontinuous regulation;

§  High current stress on mechanical switches;

§  Potential resonant issue

It would be good to develop a novel SVC for low end application to eliminate or mitigate the disadvantages mentioned above. 

This invention proposes a novel controllable transformer, which has both functions of power transition and reactive power regulation. With the combination of FC, a low cost SVC system is established.

Besides, the same technology can be also applied for UHV level as an alternative solution of shunt reactor.

In this document, the application for reactive power compensation as a low cost SVC is focused.

Detailed Description of the Invention

The proposed controllable transformer has similar structure as a traditional AC transformer, except for the additional DC winding, which is embedded into the iron core. The electrical diagram of the controllable transformer is shown in Figure 1.

Figure 1 Electrical diagram of controllable transformer

   In Figure 1, besides primary windings 1, secondary windings 2 and iron core 3, an additional DC winding 4 are added to generate a transverse flux in the iron core to adjust the magnetic permeability μ of the iron core. Essentially, the proposed control transformer is a “magnetic permeability controllable transformer”. By increasing the DC current at the DC winding i.e. decreasing the permeability of iron core, the reactive power absorbed by the transformer will increase, which can be explained based on the equivalent circuit of the controllable transformer, as shown in Figure 2:

Figure 2 Equivalent circuit of controllable transformer

The reactive power absorbed by a transformer comprises two parts: 1) the inductive reactive power Q1 and Q2’ from leakage inductance x1 and x2’; 2) The inductive reactive power Qm from excitation inductance xm. The excitation inductance xm and the leakage inductance x1 and x2’ are changed by decreasing permeability μ:

§   Xm is decreased, which means higher Qm;

§  x1 and x2’ are increased,  decrease the secondary voltage of the transformer  Uac2

Eventually, the total reactive power at the PCC of the controllable transformer is changed.

Combine the proposed controllable transformer with fixed capacitor banks (FC), a new type of SVC is formed, as shown in Figure 3.

Figure 3 A SVC consists of controllable transfo...