Review of substation busbar component reliability

In the distant past utility focus was the technical attributes of these components, but in the last few years the focus changed from quality to achieving the lowest purchase cost. The quality of substation busbar system components is being affected due to increasing pressure among component manufacturers who are competing in a world market with even smaller cost margins. It is even more surprising, that due to cost pressure, there are no sufficient regulations or standards in place to ensure the desired longevity, keeping in mind that without these components, no air insulated substation can be energized.

As a result, utilities have allowed one of the most critical parts to be cost optimized even below technical quality limits to optimize their own margins and leading a huge cost fight between the suppliers at the expense of quality. The drive for savings will inevitably continue to push the limits of both connectors and conductors and a change in priority in engineering of connectors and reduced reliability and eventually more outages.

CIGRE Working Group B3.49 gathered suppliers, utilities, testing lab and other experts in one group. The guideline is addressing basic topics for newcomers as well as high level studies for experts.

It also includes a survey and its analysis on the importance of connectors for the participants.

Some central aspects of the brochure are:

• Reliability
• Testing
• Installation

The reliability of each connector is influenced by several loading and ageing phenomena which cause different stresses, that the connector must withstand during the expected complete lifetime. Corona and radio interference effects on electrical connectors due to partial discharges or intermittent contact points must be avoided by appropriate design and careful installation as well as limiting the heating and resulting power losses on connectors. Busbar components should have an initial long and stable life expectancy.

Assessing the quality of connections in operation and estimating their remaining service life can be part of the maintenance strategy. This makes it possible to significantly improve the reliability of the overall system, particularly for highly loaded switchgear. Diagnosis with suitable infrared cameras (IR) has proven effective for this purpose.

To prove the reliability of connectors, type tests are mandatory at the outset, but to be able to fulfil testing requirements, a modular design is considered necessary. This means that each side of a connector is considered one module. Testing of a connector is done on connectors that have one module (one side of a connector) to be tested. The two tests would comprise a test package for the new connector. Two or more tests may be required on different module arrangements to prove the connector is fully tested.

Installation has also a very important role in the reliability of connectors. During assembly, it is essential to clean the contact surfaces carefully (thoroughly remove foreign layers) and to adhere to the specified screw tightening torque or compression force. In any case it is vital that the guidelines given in the supplier brochure should be followed to eliminate on site risks during installation. It is very important to install correctly to limit the initial temperature increase on the contact as much as possible, as the higher the temperature at...