When a harsh winter caused the loss of electricity supply in several provinces in China earlier this year, a struggle ensued to repair transmission lines and pylons to get power back to those regions as quickly as possible. But the freak seasonal snow storms also raised questions about why equipment made to international standards failed to stand up to the severe weather.

John Goss, Ceejay International, Hong Kong, PR China

The winter storms that ravaged many parts of China in January and February of this year were more severe than the country had experienced for decades. Deep snow and solid ice built up to damaging levels that affected infrastructure and caused damage and chaos. Worse still, they coincided with Chinese New Year, the season when millions of migrant workers leave the big cities to spend time with their families.

Mid-January saw the beginning of the worst of the weather, which continued into the first weeks of February. Overnight temperatures across many provinces in China dropped to well below freezing. Heavy snow started to block roads and railways, and ice began to form on transmission lines. But what made these storms unusual was that they were relentless.

Pylons collapsed under the weight of the ice during the recent winter storms
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The storms caused severe damage to the transmission grids, with ten of China’s eastern and central provinces suffering extensive damage. Much of the serious damage was to exposed transmission and distribution equipment. For example, pylons collapsed, transmission lines were severed, and the thick layers of ice coating all transmission and transformer equipment constantly threatened the security of electricity supplies.

According to the State Electricity Regulatory Commission, 36 056 power lines and 1933 transformer substations were badly damaged by mid-February and suspended from regular operation across many parts of the country. The heavy damage to power supply systems resulted in large-scale blackouts in over 170 cities and many provinces. Early cost estimates put the direct losses to the provinces and regions at 10.5 billion Yuan ($1.5 billion).

Disaster relief

With the situation in so many regions serious, the two largest Chinese power grid companies, the State Grid Corporation, which supplies 26 provinces and regions, and the China Southern Grid Corporation swiftly began to organize emergency repairs to get transmission grids and their ancillary equipment functioning effectively as soon as possible. The primary objective of the management of these organizations was the security of the main grids so that reliable power supplies could be restored.

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On 21 January, the Southern Grid Corporation set up an emergency command centre and agreed an emergency response plan to guarantee five things: the security of the main grid, the power supply to major cities, the power supply to key departments, residential electricity and the power demand of key end users.

While a week later, the State Grid Corporation held an urgent videophone conference to delegate the tasks required to meet the ten key measures of the disaster relief strategy.

China’s government also put emergency pre-planning into immediate action. It established a Power Grid Repairing Command Structure to organize and manage means and personnel to repair the damaged power grids so that power supplies would resume. Prime Minister Wen Jiabao arrived twice, in person, to direct the disaster relief in Hunan province, where the snow and ice had caused the worst damage. The State Grid Corporation immediately transferred technical experts from non-disaster regions to form a power supply grid repair team to arrange support in both materials and logistics. At the same time, operators started to dispatch electricity from unaffected provinces to the worst hit areas to ensure the safe operation of the main grids.

As an example of the massive resources that were mobilized to provide the fastest relief possible, Henan Province provided 600 personnel to repair the grid in Hunan province as well as transferring 816 million kWh of power to the Hunan, Hubei and Jiangxi provinces and others, even though its own power supply is not sufficient to meet its own needs.

By 14 February, about 165 000 electrical staff from the State Grid Corporation and 90 000 from the Southern Grid Corporation were busy repairing the damaged power grids in the storm hit regions. Additionally, the army provided over 10 000 soldiers to work with local electrical engineering crews.

Engineering and support staff from power supply enterprises worked day and night in the most difficult conditions, and 11 of these lost their lives. Power employees were getting up at five in the morning to use wooden sticks to hammer at and break the ice that coated towers, insulators and conductors. They would stop at ten o’clock in the evening.

The storms hit China immediately before the Spring Festival, the country’s biggest, which added pressure to rapidly resume power supply. Power staff, local authorities and the army restored electricity in 170 cities, in counties and in most countryside areas by 6 February, the eve of the Spring Festival. While most Chinese people had power for domestic needs such as heating over that festive season, a vast army of power employees and the army were still hard at work. Having already sacrificed their holiday, they were now trying to ensure the safe operation of power lines below 220 kV.

According to statistics from the Power Grid Repairing Command, by 5 pm on 14 February, out of the 34 543 power lines in China suspended because of the storms, 26 573 were operating again, 76.9 per cent of the total, as were 1752 of the 2002 suspended transformer substations, or 87.5 per cent. The 8146 pylons operating at 110-550 kV that had collapsed are still being replaced.

On 8 March, State Grid Corporation of China announced that it had successfully completed the extensive campaign to restore power across the nation, well ahead of schedules and estimates, and that 266 000 engineers and soldiers had been deployed in the repairs.

The Power Grid Repairing Command Structure says that by five o’clock pm on 12 March, 34 763 power transmission lines out of the 36 740 that were suspended, 94.62 per cent of the total, were supplying power again. At the same time, 2003 transformer substations out of the 2018 that had been badly damaged across the country, 99.3 per cent of the total, had started operating again.

Restoration of the grid

After power supply had resumed in many of the affected regions, the main concern of the State Power Grid Repairing Command from 13 February onwards was the widespread reconstruction it now faced. The most crucial part of this massive task was to accelerate all stages of the reconstruction and refurbishment of the grid network in the many hard-hit regions so that reliable power supplies would be resumed throughout China.

A power employee hammers at the ice covering a pylon, insulators and conductors
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The State Grid Corporation decided to run its many reconstruction projects in parallel to ensure that they were completed in the least possible time. Among the organization’s first priorities were the resumption of power supply to the Beijing to Guangzhou railway before 21 February, repairing and making operable the damaged key power facilities of the main power grids in Hunan, Jiangxi and Zhejiang provinces by 10 March, and repair of the power grids in the other regions before the end of February. The whole of the country’s power grid was to be repaired and put into operation before the end of March.

The Southern Grid Corporation decided that its all-inclusive power reconstruction and full resumption schedule of the 220 kV and 110 kV grids would be completed before 5 March. This would mean that power supplies would be mainly resumed in most of the disaster areas. The repair schedule meant that the 500 kV power grids would be repaired before the end of March. The agreed programme of repairs and reconstruction aimed at officially resuming power supplies completely by the end of March.

On 8 March, China Southern Power Grid also announced that all its power networks destroyed during the disaster had been fully restored. The company is now conducting research on upgrading the design standards of its power grids.

Line breakages

Whilst all efforts were being focused on the full resumption of reliable power supplies in the shortest time possible, teams of engineers were analyzing the causes of the breaking of transmission lines and the collapse of pylons. Gu Junyuan, the chief engineer of the State Electricity Regulatory Commission, reported that the main cause in the southern provinces were that the heavy snow and deep ice had far exceeded the equipment’s design standard, which was in line with international design parameters.

The army provided over 10 000 soldiers to help local electrical engineering crews carry out repairs
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The State Electricity Regulatory Commission’s response to the disaster saw You Quan, Chairman, call on all organizations involved in supplying power in China to improve the structure of the power grid to enhance its resistance to extreme weather. Meanwhile, the State Grid Corporation compiled a report entitled ‘Key Technologies Research and Development Programme of Grid De-icing’, which looked at major aspects of the power supply disaster, such as grid deicing equipment, ice storm forecasting and supervision system, emergency disaster relief processes and grid resumption and reconstruction. It comprised 40 technical projects in eight categories that covered procedures from power transmission grid planning and construction, grid operation and maintenance, electricity dispatching, customer service and emergency response.

The quality of power transmission construction and equipment in China has met international operating and safety standards. A large amount of China’s power supply equipment is sourced and provided by international transmission and distribution equipment companies. High voltage power lines and their ancillary equipment are rarely subjected to extremes of snow and ice. Even when they are, it can be in a 30-50 year cycle if at all. But the winter storms China this year were unique in their severity, and their duration had serious cumulative effects. Ice on conductors reached a thickness of 30-60 mm. This depth and its weight far exceeded normal de-icing standards. Any country would face the same problems if it experienced similar weather.

With this potential for future disasters in mind, Chief Engineer Gu suggests that international design standards for de-icing be improved. He explains that raising the standard for de-icing protection to 30 mm would increase the amount of materials needed to build a tower by 3.4 times. Tower costs would be 2.6 times greater initially, but the towers would be more cost effective in the long term. Power supply enterprises around the world should consider carefully whether it is necessary to upgrade their design standards in areas that frequently suffer winter storms.

Questions need to asked to prevent repetition

Experts have asked whether preferable technologies to resist grid disruption are available that can withstand such storms in the future. Chinese electrical engineering experts explain that today power lines of 220 kV and below could self-induce a short circuit for de-icing with logical adjustment when a partial regulation occurs. However, if a large-scale line disruption occurs, these lines would not be able to solve the problem by short circuiting as they would bear too high a current. Today’s 500 kV transmission lines are limited by technological constraints and a lack of long-term operating experience. They can only be de-iced slowly and manually.

There are many research and development specialists in China and around the world working on the problem of developing a system that provides short-circuit de-icing solutions for the new 500 kV lines, but this is still an unsolved problem internationally when it comes to heavy icing.

Meanwhile, to guarantee the stable and safe operation of China’s main power grid and continuous power supply to key end users under serious natural disaster, State Grid Corporation released its Guidance for Differentiation of Grid Plan.

It has also upgraded its grid design standards to instruct companies about grid reconstruction in future reconstructions that follows storms. From now on, design standards for China’s 35 – 330 kV grids will have a 30-year cycle rather than a 15-year one. For 500 kV grids, the cycle is now 50 years rather than 30 years, and the UHV grid, currently under construction, will be designed to withstand an icing-based disaster in a 100-year cycle. In 2008, State Grid Corporation will invest 253.2 billion Yuan ($36.2 billion) in the construction of power grids.