Live Tank Oil Sampling (LTOS)

Non-disruptive condition assessment of live oil-filled switchgear

Millions of pounds each year are being wasted on time-based maintenance of oil-filled 11kV switchgear

Conventional regimes, based on shutting down equipment regularly to inspect and maintain ring main units and extensible switches, can reduce reliability, increase health and safety risks, and cause unnecessary downtime and disruption.

EA Technology has clear evidence that the need for intrusive servicing can be reduced dramatically by moving from conventional time-based maintenance to maintenance based on assessing the actual condition of switchgear and oil.

Our research proves that, by applying effective condition assessment to switchgear, the vast majority of units will operate safely and reliably for many years, without additional maintenance. This is confirmed by several reliability centred maintenance (RCM) studies.

The Solution

EA Technology Analytical offers Live Tank Oil Sampling or LTOS, which is an innovative approach to obtaining an oil sample from Ring Main Units and extensible switches whilst part of the unit remains live which minimises the disruption to the network. The oil sample is then returned to the laboratory and analysed and the need for maintenance for each individual unit determined. The process has been used with great success for the past eight years.

The process involves access to the oil tank via the test probe access point with only feeder isolation and earthing necessary to open the test access. The sampling process involves both the use of specifically designed equipment and adherence to a detailed written procedure. The sampling procedure and equipment has been designed to minimize the risk to the operator, whilst ensuring a consistent and reliable sample is obtained.

The oil analysis is completed at our laboratories at EA Technology and based on the results a classification allocated;

• PASS: Satisfactory oil condition, which enables an extended maintenance interval to be adopted and the unit should be re-sampled in five years.
• RETEST: Evidence of some oil degradation, the unit should be retested in 30-36 months (half PF interval for oil degradation).
• MAINTAIN: Indicates very poor oil quality, unit should be maintained within 6months.
• ACTION: Extremely poor oil quality indicating the unit is prone to a catastrophic failure in the short term and the client will be advised accordingly.

Typical results

Typical results obtained for a variety of switchgear populations are:

• PASS: >90%
• RETEST: approximately 5 – 7%
• MAINTAIN: approximately 1%
• ACTION: <0.05%

Benifits

• Saves money by eliminating wasteful, time-based maintenance
• Oil condition accurately indicates whether invasive maintenance is required OR NOT
• Safely extends periods between maintenance interventions
• Warns of switchgear degradation problems BEFORE they lead to failures
• Increases asset reliability AND reduces costs
• Cost effective and safe proven method of retrieving an oil sample, causing minimal disruption to the network