RESPONSIBLE FOR KUWAIT'S POWER NETWORK, THE MINISTRY OF ELECTRICITY AND WATER used to be able to manage and fulfill, by way of its own resources, the full range of preventive-maintenance practices on the transmission system. However, for the past decade, due to a lack of skilled workers, the ministry has been successfully outsourcing its preventive-maintenance work on transmission lines, transformers and substations. In 2000, the ministry extended the outsourcing to include routine maintenance on its underground-cable transmission system.

With a route length of some 5000 km (3107 miles), underground cables comprise 49% of Kuwait's transmission network; the remainder of the network consists of overhead transmission lines. Almost 96% of the underground feeders are fluid-filled, or oil-filled, cable. Currently, the transmission system operates with voltages of 300 kV (4.5%), 132 kV (69%) and 33 kV (26.5%). With the network aging, the ministry acknowledges the urgent need to review its policy on fluid-filled cable.

Although the transmission network's maintenance staff is quite experienced, issues such as resource availability, difficulty in hiring new skilled staff, weather conditions and a general lack of system security limited the quality and quantity of preventive maintenance the ministry could perform. For these reasons, in 2000, the ministry decided to outsource fluid-filled cables for preventive maintenance on a regular basis using clearly defined and structured contracts.

PILOT CONTRACTS

CIGRÉ's recommendation for high-voltage cables and accessories specifies that preventive maintenance can be external or internal, with the former being linked to damage by external forces (for example, third-party civil works). The Ministry of Electricity and Water limited its pilot contracts to focus on the prevention of damage due to internal causes, requiring the use of various tests to assess the overall condition of the cables and their vulnerability to failure. The contracts defined the tests required on circuits selected by utility staff.

National legislation only allows companies pre-approved and registered by the Central Tenders Committee to bid; it is normal practice in Kuwait to accept the lowest bid, provided it satisfies the technical specifications.

The first outsourced preventive-maintenance work on a fluid-filled power cable was through direct contracts with various international cable manufacturers to perform maintenance work on two feeders originally manufactured and installed by them. The companies were ABB (Zurich, Switzerland), J-Power Systems (Tokyo, Japan), Brugg Cables (Brugg, Switzerland) and Pirelli, now Prysmian Cables and Systems (Milan, Italy).

In 2001, three additional contracts were awarded to companies irrespective of the cable's manufacturer, and these contracts included 12 to 15 feeders. Various tests were performed on each feeder, ranging from simple visual inspections to oil diagnostic tests. The result of the three additional contracts formed the basis of the current three-year 50-feeder contracts.

The experience and benefits obtained from the pilot contracts can be summarized as follows:

• Exclusion of the outer sheath test, as it proved to be time-consuming, expensive and not very effective on aging lead-sheathed fluid-filled cables

• FORMAT OF THE CURRENT CONTRACT

  Inclusion of oil flushing and treatment, as many of the cables failed the test and required the injection of new or treated oil

• Provision of computerized data, where the contractor is required to make data collected available in a software format for easy analysis by the ministry's engineers, thereby helping to assess the quality and effectiveness of preventive measures

• Inclusion of clearly labeled and dated digital photos to report any aging defects (for example, cracked manhole walls, rust and broken gauges), as digital photos help in assessing the effectiveness of visual inspections, and they may serve as a lucid representation to help justify visual inspection costs; before and after photos also must be included in reporting any clearing out of dust and debris

• TECHNICAL BENEFITS AND DISADVANTAGES

  The 33-kV fluid-filled feeders also were excluded, because this network is almost fully loaded, making it difficult to arrange circuit outages for maintenance. Also, the 33-kV network is being redesigned and replaced, and failure costs are considerably less than those for the 132-kV network. Therefore, the cost of preventive maintenance on 33 kV was not justified.

The current maintenance contract can be considered in two parts: preventive and conditional.

Preventive maintenance, or diagnostics, includes a visual inspection of the entire exposed hydraulic and electrical system for signs of damage, wear and oil leaks, reported with recommended action on any such signs. This inspection is done separately for every oil section of the feeder. The contractors are required to check the joint pits and oil tank pits for accumulated dust or rubbish, and to remove such accumulation. Part of this task includes reporting any needed civil repairs and tightening all loose fittings on earth bolts and oil feeding connections. The contractors also must check and calibrate oil-pressure gauges for correct readings, and test the integrity and operation of the low-oil-pressure alarm system. Oil tests performed on the oil system include a residual gas-pressure test to check the gas content in pressure tanks and cable sealing ends (the gas content should be less than 20 torr) and an impregnation test to check the impregnation coefficient for every oil section.

Conditional maintenance, or oil flushing and treatment, is decided based on the result of oil tests performed during preventive maintenance. If either of the oil tests are below standard, the oil in the hydraulic section is flushed out and taken to a treatment unit for degasification to improve its breakdown voltage. In some 85% of these cases, the oil is treatable, but when untreatable, it is replaced by new oil.

FEEDER SELECTION FOR MAINTENANCE

There are four main benefits of outsourcing this maintenance activity:

• Outsourcing improved maintenance organization through specified timetables, contract structure and progress requirements.

• DATA ANALYSIS OF CONTRACT RESULTS

  Outsourcing preventive maintenance improved data recording and data presentation.

• Fewer in-house staff, engineers and technicians are required.

• FUTURE CONTRACTS

  Outsourcing helped create a competitive market, which is always good for the national economy. This has contributed to a decrease in the contract price (Fig. 1).

The ministry, however, also has experienced some disadvantages and shortcomings as a result of outsourcing preventive maintenance.

• The contracts and contractors create more work associated with contract management.

• There is a fear of losing in-house skills because of the work being done by contractors, although this has not been a problem for the ministry because flushing work, oil treatment and oil tests are still being carried out by in-house repair teams on feeders being repaired after faults.

• It is not always easy to supervise and ensure contractor work is being done properly.

• It can be difficult to identify where such maintenance needs to be performed. This, of course, must be decided early, before issuing a contract.

The criteria used to select cables for outsourced maintenance contracts is a demanding challenge for the ministry's utility staff as they aim to optimize the return on the contract investment. The selection process depends on technical aspects like the circuit's failure history, average load and age of the cable.

Non-technical considerations include circuit accessibility and control center consent because of circuit loadings. In Kuwait, there is a summer peak demand, and control center consent is difficult during this period. A decision on these factors must be made well in advance as the contracts are for a period of three years.

The significance of the oil tests undertaken on completed contracts are shown in Fig. 2, which plots the number of feeders tested and the percentage that have failed the oil tests. A feeder is considered faulty if at least one section or one tank requires oil treatment. Fig. 3 divides the number of feeders tested and found faulty in the past four contracts by the number of oil sections (or phases) found in need of oil treatment. It was observed that the majority of feeders have all three phases in critical condition.

As some 79% of all feeders tested were found in critical condition, this highlights the significance of the ministry's preventive maintenance contracts. The results confirmed that tests are not being performed unnecessarily.

The constant evaluation of the completed contracts provides a scope for possible improvement of all future contracts. A change in the specification of future contracts will likely include doubling the number of cable sections to be tested, while keeping the current three-year time period. Hence, participating contractors will be expected to submit offers with double the staff and equipment compared to those used on previous contracts. Currently, consideration is being given to the retesting of cables with flushed or treated oil sections within six months or a year to verify eradication of the problem. If the gas content has increased above the critical level, the section will be referred to the fault repair teams for further investigation.

Salem Alshibani (salem28@qualitynet.net) graduated in 1999 from the University of Hartford (Hartford, Connecticut, U.S.) as an electrical engineer and then joined Kuwait's Ministry of Electricity and Water as a cable maintenance engineer. On study leave, in 2005, he was awarded a master's degree in advanced technologies in electronics by the University of the West of England (Bristol, U.K.). Alshibani is a lecturer at Kuwait's College of Technological Studies.

Ahmad Sharaf (ahmed_sharaf57@yahoo.com) graduated as an electrical engineer from Hilwan University (Egypt) in 1976, and in 1980, he joined the maintenance team for the 300-kV, 132-kV and 33-kV transmission system in Kuwait's Ministry of Electricity and Water. In 1991, Sharaf was appointed head of the cable maintenance section, for which he is responsible for directing the preventive and corrective maintenance of the nationwide underground transmission system. Currently, Sharaf is a senior consultant operations engineer.