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  2. Frontmatter - Electric Distribution Systems - Wiley Online Library
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This same technology is tried and proven which has already been operating flawlessly in a pilot substation in Sweden since The technology is also available as a disconnecting circuit breaker DCB , which means the disconnecting function is integrated with the breaker. This enables high equipment availability and reliability in a compact footprint. What are the risks, if any, in the shift to this level of transmission and distribution equipment and insulators?

Moreover, every product needs to go through a long-term testing and pilot installations before releasing it to the market. How do you see the potential market for high voltage direct current HVDC transmission in light of all the utility-scale wind and solar capacity growing?

Distributed Switchgear (IEE Power & Energy Series)

The offshore wind market is growing in most regions of the world, supporting the increasing generation mix change to renewables, including the NAM region. With the accelerated pace of retiring fossil fuel generation facilities — which historically were located near major load centers — and the rapid growth of utility-scale wind and solar capacity to replace such generation, the requirements on the existing transmission grid are about to change.

HVDC technology has the right characteristics to meet the new demands.

For example, some of the best wind resources in New England and New York are either far offshore or to the north, whereas the major population and load centers are in the south. Hence, to deliver reliable renewable energy from new resources to major population and load centers, new transmission line capacity will be needed. In addition, since the voltage control and reactive power needs at load centers were historically supported by local fossil-fuel based generators, new devices will be needed at the load centers for such support.

Where is this most visible? At this point, adding additional renewable generation capacity would result in increasingly smaller additions in the level of delivered renewable generation.

Frontmatter - Electric Distribution Systems - Wiley Online Library

Ltd for over 20 years. Table of Contents Chapter 1: Basics and general principles Chapter 2: Interruption techniques Chapter 3: Fault level calculations Chapter 4: Symmetrical and asymmetrical fault currents Chapter 5: Electromagnetic forces and contact design Chapter 6: Switching transients Chapter 7: Insulation Chapter 8: Operating mechanisms Chapter 9: Primary switchgear Chapter Cable connected secondary switchgear Chapter Overhead conductor connected secondary switchgear Chapter High-voltage fuse-links Chapter Switchgear type tests Chapter Product conformity, quality control and service problem resolution Chapter Cost of ownership Chapter The future Chapter Further reading Chapter National, International and customer Specifications Show More Customer Reviews Average Review.

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See All Customer Reviews. Shop Textbooks. Add to Wishlist. USD Buy Online, Pick up in Store is currently unavailable, but this item may be available for in-store purchase. A cross-section through a typical double-break oil circuit breaker is shown in Figure 2. The increase in breaking capacity achieved by employing two breaks in series per phase will not be twice that of a single break device, owing to the relative capacitance to earth giving unequal voltage sharing. This suggests that the voltage withstand of a gap between electrodes is proportional to both the electrode spacing and the gas pressure.

It is fortunate that this law is only true within finite limits, otherwise vacuum switchgear could not exist. However, at very low pressures, a remarkable Breakdown voltage kV. Further reductions in pressure result in the withstand voltage increasing see Figure 2. Since the first commercial introduction of vacuum interrupters in the s, continuous development has dramatically reduced the size and increased the short-circuit ratings available. The photograph in Figure 9. However, the realisation of the practical working interrupter must rank alongside many of the great achievements in engineering.

An arc cannot exist in a vacuum and requires metal vapour from the metal contacts to sustain itself, ideally until a natural current zero is reached. At this point, the metal vapour should condense back onto the contacts, denying conductivity so that current ceases to flow.

Therefore, the contact materials are all important to the interrupting process. In addition, the materials used for the contacts must have the right characteristics for the conduction of normal current and they must minimise the natural tendency of metals to cold weld when pressed together under high-vacuum conditions. Further, they must not release gas when interrupting current, as this would destroy the high-vacuum necessary for the whole process to be repeated many times over, during the life of the vacuum interrupter.

It follows that, as a voltage will be impressed across an interrupter following current interruption, insulating materials have to be included in the design of the vacuum interrupter envelope.

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These insulating materials must be protected from condensing metal vapour from the contacts which would otherwise destroy their insulating properties. In practice, this is achieved in several different ways. Protection for the internal surfaces of the insulating envelopes is provided by three metal shields, known as spatter shields, brazed to the centre band and end caps of the interrupter. An alternative method of protecting the insulating envelope is to have both the fixed and moving contacts arranged to have their contact faces located within a central 16 Distribution switchgear Figure 2.

The inside face of this canister acts in the same way as a spatter shield, in that condensing metal contact vapour is collected on its inner face, well away from the interrupter barrel insulating material. In this design of interrupter, the envelope is in the form of a barrel brazed to each end of the central canister.

If a vacuum interrupter is cut open after a large number of fault current interruptions, the spatter shield will be found to have a copper plated appearance on its inner face, and the insulating materials forming the body of the interrupter should be clean.

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  4. As the vacuum interrupter contacts have to open and close within a vacuum envelope, it follows that the mechanical drive to the moving contact has to be able to conduct movement into the vacuum envelope through a gas-tight seal. In practice, this is done by arranging for the moving contact to be attached to the end plate of the vacuum interrupter by metal bellows.

    These bellows are usually manufactured from stainless steel which is either hydroformed to form the convolutions, or they are manufactured by welding the edges of a number of belled annular stainless steel discs, such as is shown in Figure 2. Regardless of the method of manufacture, the integrity of the bellows is of paramount importance.

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    They must be able to maintain an internal vacuum over many years and many operating cycles. Therefore they must be tested over a very large number of operating cycles to ensure that they will not fail due to metal fatigue. When interrupting currents of less than about 10 kA peak, the arc that is drawn between the contacts of a vacuum interrupter will be in the form of a number of parallel arcs.

    This is known as a diffuse arc and high-speed photographs show this to be like an internally illuminated cloud with a large number of points of light dancing across the Interruption techniques 17 contact surface. In reality, this form of arc consists of a large number of small parallel arcs that are kept separated from each other by electromagnetic force.

    This is because each arc acts like a small magnet and the arc roots simulate the magnetic poles. The poles of these arcs will, therefore, exert a repelling force on each other maintaining the arc in a diffuse state. At currents of about 10 kA and above, the main body of each of the small arcs will exert sufficient attractive force to overcome the pole effect and tend to cause the small arcs to fuse together into one large arc.

    A large single arc will produce an extremely high temperature at the arc root, causing an excessive amount of contact material to be vapourised, and so limiting the short-circuit current interrupting capability of the vacuum interrupter. To minimise this effect and hence increase the short-circuit current rating, some manufacturers force the arc root to move over the contact face, preventing excessive temperatures and material vaporisation at one spot.

    They do this by employing what is known as contrate contacts. A contact of this type appears in Figure 2. The surface of a contrate contact is provided with a number of slots which, by electromagnetic force, will impose a self-generated rotational drive to the arc, increasing the short-circuit rating of the interrupter. In more recent times, it was realised that if each of the small arcs in a diffuse arc could have their magnetic polarity increased, they would continue to maintain the diffuse state by resisting the parallel current effect, and thus increase the short-circuit rating of the interrupter.

    There are several different ways in which this has been achieved by manufacturers.

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    The fixed and moving contacts in this interrupter are in the shape of a spiral, which causes the electromagnetic field of the short-circuit current, as it approaches the contact face, to produce a vector of magnetic field to reinforce the magnetic polarity of the small individual parallel arcs see Figure 2. This technique for arc control is known as an axial magnetic field.

    Toshiba introduced another very successful method of producing an axial magnetic field to maintain the arc in a diffuse state up to very high fault current levels. The construction of the contacts using this method is shown in Figure 2. This current then flows outwards along the four radial arms, as indicated by the arrows. The current paths in Interruption techniques 19 the outgoing contact mirror those of the incoming contact and it is these paths which provide the strong axial magnetic field that maintains the arc in a diffuse state up to very high levels of fault current.

    In order to be competitive, the manufacture of vacuum interrupters must be carried out in significant quantities. The manufacturing equipment is very specialised and, therefore, expensive. For example, consider how specialised the vacuum furnace which is used in the manufacture must be. The brazed joints, both metal to metal, and metal to insulating material, have to be carried out in such a furnace at the same time in the presence of a very high-vacuum.

    As heat convection cannot be used, the heat necessary for brazing can only be radiated and conducted to the joints, without causing overheating of some of the joints and subsequent loss of brazing material. Such an arrangement requires very careful design and is expensive to implement. In addition, the manufacturing conditions have to be such that no measurable contamination can be allowed on the internal components after full cleaning. This means that a clean room with positive internal pressure has to be provided.