Switched on

Switchgears can be classified by voltage – low, medium or high-voltage, or by the type of insulation used to protect them.

Low-voltage switchgear is used to regulate electricity distribution in residential areas, for example in tower blocks; medium-voltage switchgear is employed in main substations; while high-voltage switchgear is used for transmission purposes.

Switchgears are mostly insulated by air or sulfur hexafluoride (SF6) gas. Their internal arc interrupting equipment is insulated with SF6 gas or vacuum technology in medium-voltage applications, while high voltage uses SF6 and air insulation is used for low voltage.

Relay race

As with most other power network components, there is strong demand at present for all types of switchgear in the Middle East, driven by booming development and population growth. And lead times are lengthening as a result.

“The lead time for low-voltage and medium-voltage switchgear is roughly 8-10 months,” says Mohsen Mubarak from Saudi-Arabia-based Wescosa.

“For manufacturers based here in the Middle East, delivery times have increased by one or two months as some of our raw materials are sourced from Europe and the US.”

Wescosa sells around 6 000 low and medium-voltage switchgear units and 2 000 transformers to customers across the region each year. The firm’s client list includes companies such as Saudi Electric Company, SABIC, Saudi Aramco and Dubai Electricity and Water Authority.

The company recently expanded its manufacturing plants and intends to extend its product offering to include 20 MVA power transformers in the near future.

Mubarak says sourcing relays is the main hold-up at present. “The relay manufacturers are overbooked,” he comments, adding, “Relays are not big devices but because these manufacturers are booked with orders from all over the world their lead time has doubled, so instead of 6-8 weeks lead times are now 12-14 weeks.”

More maintenance

With the switchgear supply-chain tightening, utility companies are understandably putting more emphasis on caring for and maintaining their existing assets.

Generally speaking, switchgear are exceedingly reliable and failures are rare. SF6 and vacuum-insulated equipment are described as low-maintenance.

But when malfunctions do occur the results can be catastrophic, causing structural damage, serious injury, or even death, and the financial losses from outages and repair work can run into several millions of dollars. So suppliers advise naturally against complacency.

This is especially important in the Middle East where power consumption is rampantly on the rise and electricity networks are constantly being put under immense strain, even though installations are reaching the end of their service life.

Systems here are regularly being stretched to the limit of their capacity and as equipment ages it becomes more prone to failure. In the case of switchgear, studies have shown that the majority of breakdowns occur at the moment when the equipment is called on to isolate and clear a fault current in the network, or shortly after.

The most frequent problem is a flashover voltage when electricity jumps from one conductor to another creating an arc.

If the breaker insulation fails to absorb this arc an explosion can occur. Therefore it is imperative to inspect, test and maintain all switchgear and other substation equipment on a regular basis.

“All equipment has a lifetime and we can see a lot of installations in the area are 20 or 25 even 30 years old and that is definitely the time to take action to avoid failures,” says Mubarak.

“After sometime you have to replace them with new equipment or to make a very major maintenance work, which includes looking into the busbar very closely, checking the insulation levels and the circuit breaker operation, the current transformers, the protection relays.

All this must be checked very thoroughly, before you decide yes you will continue using it or you need to replace some of those devices.”

“Our switchgear is almost maintenance-free,” says ABB’s Abdelwahab Yacoub. “Depending on the environment conditions (dust, humidity, aggressive gases) minor maintenance for circuit-breaker operating mechanism is needed and described in the operation manual.”

“Periodic maintenance is conducted maybe three times a year or every six months,” says Mubarak. The frequency depends on the type of switchgear, the interrupter technology, the age of the equipment and how often it has been called on to operate.

So it is crucial to keep detailed records of assets, including the number of fault clearance operations and previous test results. This allows operators to monitor changes in condition of the equipment between inspections and to adjust maintenance schedules accordingly.

Frequent testing and monitoring can help to detect deterioration in switchgear equipment before faults occur and prevent outages. Partial discharge (PD) monitoring is the main technique used to monitor the health of high-voltage switchgear.

PD activity manifests itself through internal or surface arcing and noise, and is a sign that the insulating medium is failing. Portable detectors that record ultrasonic noise and transient earth voltage effects can indicate whether assets are working satisfactorily or whether they require further tests or urgent investigation.

In addition, for gas-insulated installations regular pressure checks are vital to protect against leaks and a breakdown in the integrity of the insulation.

Checks on switchgear and substations should also include visual inspections for evidence of sooting and distortion on enclosures, the detection of smells and high temperatures, corrosion leaks and so on. The immediate environment also needs regular inspection such as external walls in case of water ingress and fences for signs of unauthorised access or interference.

Vacuum V SF6

There is a growing debate about the use of SF6 gas in the power industry. Its use as an insulation material for high-voltage and medium-voltage switchgear is not in question.

The advantages of gas-insulated switchgear over air-insulated installations are obvious in that using SF6 gas as an insulating medium reduces the clearance distance needed between active and non-active parts of a switchgear, meaning less space is required to house the substation. Manufacturers say these systems occupy just 5-20% of the space used by the air-insulated design.

On top of that, gas-insulated substations are less sensitive to air pollution and to interference from salt and sand particles than substations open to the elements. “Using gas-insulated switchgear gives the advantage of having a very compact design which reduces space requirements and building costs,” notes Yacoub.

But SF6 is a man-made gas and it has a global warming potential 24 000 times that of carbon dioxide (CO2). Furthermore, SF6 has an estimated atmospheric life of up to 3 200 years compared to 50-200 years for CO2.

It is possible to replace SF6 with vacuum technology when it comes to insulating the circuit-breakers in medium-voltage switchgear. And as environmental awareness grows in the region the vacuum option is expected to gain in popularity.

The use of vacuum technologies for arc interruption in circuit-breakers is not new: the technology has been around for several decades and over the years improvements in design have made the technology more practical. The size of a 15 kV vacuum interrupter bottle has shrunk from 180 mm to 50 mm diameter during the past 40 years.

Meanwhile, modern sealing techniques ensure that units retain their vacuum for more than 30 years and in the event of a problem the leaks are completely harmless to the environment. SF6 on the other hand is non-toxic and non-flammable on its own, but when used as a circuit-interrupting medium it can produce a number of dangerous and toxic decomposition products.

“I can see good potential for vacuum technology, replacing a lot of the existing gas-insulated switches, which are utilised heavily by utility companies,” says Mubarak. “If you go around any city you find them on every corner.

Those devices are actually full of SF6 gases. That can be avoided by using vacuum technology, which has been developed by some European manufacturers. If someone is interested in having an environment-friendly product then that is a good alternative and I think the cost difference is not that much.”

“If you see a switchgear, as in a gas-insulated switchgear, outdoor mounted in a utility network it would not be any different to a vacuum switchgear in the same place, there will be no advantage or disadvantage in terms of network performance,” he adds.

But some switchgear producers play down the negative aspects of SF6 and its potential threat to the environment, after all it has been the technology of choice for many years, and if used correctly with appropriate controls and safety measures it poses little immediate danger.

“Latest studies in the EU show that SF6 in switchgear is not harmful considering the small volume used in switchgears,” insists Yacoub. “SF6 gas is inert, but precautions must be taken in case of internal arc in the switchgear. SF6 gas is applied in much larger quantities in industry rather than in switchgear.”

Safe evolution

Safety and efficiency are at the forefront of all developments in the switchgear sector and like most industries suppliers are constantly working to improve control and protection by making best use of the latest technologies.

Smarter and more intelligent designs are just around the corner, as Yacoub concludes: “Switchgear design has improved a lot in recent years. We talk today about intelligent switchgear using bay control units for communication, control, protection and metering.

In the future we see more wireless communication solutions being integrated into this very traditional industry and product range.