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Product category: Electrical hardware
News Release from: ABB Power Technologies | Subject: Substation technology
Edited by the Engineeringtalk Editorial Team on 21 April 2008

From unreliability to ubiquity

Hans-Erik Olovsson and Sven-Anders Lejdeby of ABB Power Systems look at a century of evolving substation technology.

When the first electrical systems were built some 100 years ago the network was not particularly reliable, something that had to change if electricity was to be made as widely available as it has in the intervening years Substations were very complex, labour intensive and not very reliable

Much of the last century has been devoted to transforming the technology to the point where electrical supplies are among the most reliable services generally available.

Some landmarks in substation evolution include the invention of the disconnector switch, gas-insulated switchgear and new techniques for constructing substations and getting them into service quickly.

Another factor has been a significant reduction in maintenance needs, for some components the servicing interval could be as much as 15 years.

The disconnector switch has helped to increase the availability of electrical networks.

The initial single-line configuration used involved surrounding circuit breakers by many disconnector switches so that adjacent parts of the switchgear remained in service while maintenance was carried out on the breakers.

These ideas led on to double busbar and double plus transfer busbar schemes.

Today's breakers require less maintenance than their predecessors.

In fact, ABB's SF6 circuit breakers have a maintenance interval (where the primary components need to be taken out of service) of 15 years.

Open air disconnector switches on the other hand have a maintenance interval of about four to five years in areas where there is little or no pollution and a significantly shorter interval where there is natural or industrial pollution.

Even though disconnecting switches - or rather a disconnecting function - are needed, their maintenance requirements are simply not practical, let alone economical.

A number of innovative switchgear concepts for air insulated substations (AIS) have effectively made the traditional open-air disconnecting switch redundant.

The disconnecting function has either been built onto or integrated into the breaker.

This not only increases the availability of the substation, but it helps to reduce its footprint by about 50%.

A smaller footprint means lower costs for land and preparation, easier retrofitting of existing substations, and less environmental impact.

Instrument transformers that pass on information about the primary current and voltages to the secondary equipment (protection, control and metering) used to be large apparatuses composed of insulation materials, copper and iron.

They also supplied power to the electromechanical secondary equipment.

These days, digital secondary equipment gets its power from a separate supply (ie a battery).

Also, thanks to fibre-optic technology, the old large instrument transformers can be replaced by fibre-optic sensors that give information about primary currents and voltages.

This further reduces the switchgear footprint and costs, while providing secondary equipment that is more flexible and secure.

Not only has substation technology changed dramatically in the last 100 years, so too has their appearance.

Originally they were built on the outskirts of towns, so they way they looked did not matter greatly.

However, in recent years, many of them have been swallowed up by the urban expansion of the past few decades.

Many of their neighbours find both their appearance and the humming of power transformers, unpleasant.

Now, substations are being placed in buildings that are in harmony with those around them.

A smaller footprint - 40 to 50% reduction for indoor AIS solutions and 70 to 80% reduction for indoor GIS solutions - has greatly simplified this process.

Putting GIS substations underground makes them really invisible, such as in city centres around the world.

To tackle high land cost and health and safety needs in and around cities, as well as adapting to individual requirements, ABB has developed the Urban concept, for compact indoor substations up to 170kV.

Both air-insulated and SF6-insulated modules can be used, depending on the actual requirements of the specific installation Another important factor is the ability to prefabricate substations, shortening erection time and minimising disturbance.

At the same time advance preparation means that much of the installation can be pretested and prepared before arriving on site.

MALTE, a type of a distribution substation with a transformer size of up to 16MVA, is good example of prefabricated, factory tested unit.

Primary and secondary cabling between the modules is prepared in a way that allows for rapid connection.

On-site assembly and testing takes just a week, after which the substation is ready.

Its footprint, around 100 m2, is less than 30% of an outdoor AIS substation.

MALTE consists of three main modules: a power transformer module of the main power transformer with a prefabricated foundation that also acts as an oil-pit, walls and a roof; a high-voltage (HV) module equipped with a removable Compact 52.5kV circuit breaker.

This requires no foundations as it is hinged onto the side of the power transformer module; and a medium voltage (MV) module with indoor switchgear mounted in cubicles.

Here, relay, control and auxiliary AC/DC equipment for the entire substation is included.

It is also hinged onto the transformer module.

Compared with traditional solutions, MALTE offers: higher availability because the equipment is indoors; lower maintenance and running costs.

The whole thing, including its foundations, can be quickly dismantled and moved.

It is environmentally friendly; and personnel and third-party, safe.

Substation secondary systems have also changed a lot over the years.

For example, manual operations have been succeeded by more sophisticated information management.

The secondary system in a modern substation is used for: primary system protection and supervision; local and remote access to the power system apparatus; local manual and automatic functions; communication links and interfaces within the secondary system; communication links and interfacing to network management systems.

All these functions are carried out by a substation automation system (SAS), which contains programmable secondary devices, known as intelligent electronic devices (IEDs), for control, monitoring, protection and automation.

Typical characteristics of an IED include: used in one or more switchgear bays; independent protection functionality for each feeder; high-speed calculations in real time which will trigger a trip signal, if necessary; and operation as a combined protection and control device.

But it can just as well function as a separate control or protection unit and can communicate with all other IEDs.

Prefabrication and pretesting is fast becoming the norm for a modern substation.

It is delivered in sections containing all that is needed for the primary system, and these sections are then simply connected via an optical fibre.

Effective and fast communication between IEDs is essential in a substation automation system.

Digital communication has been used for many years in ABB substations and the more recent advent of the IEC61850 communication standard has aided communication between IEDs from different suppliers.

Modern substations are generally operated remotely and communication with the control centre is over a wide area network (WAN).

These days, new overhead lines or power cable connections are equipped with optical-fibre to enable protective system communication.

The last 100 years witnessed a move from the industrial age to the information age.

A host of fascinating ideas, in particular the worldwide web, have changed the way we live and work.

For example, the Internet makes customer contact easier and faster for companies like ABB.

Projects can be managed via a common database accessed by both parties.

In the future, substation power handling equipment will be yet more integrated and compact, while measuring functions and all of the secondary functions will be done using fibre optics.

We can look forward to substations delivered more quickly, made more compact, with less environmental impact and economic to run and maintain.

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