Page 7 - Energize November 2021

COVER STORY

Strategic maintenance always comes with
associated start-up costs, and it is advisable to
implement maintenance strategies for a minimum
of two to three years to accurately monitor and
record the savings from start-up to current levels.
This is when the maintenance strategy delivers
the results being sought and thereby supports
the optimisation of networks, which in turn has
positive results on increasing production and
minimising downtime.
It is advisable to use the services of specialist
service providers, such as ArmCoil, to assist in
choosing the correct strategic maintenance plan
for the network. Specialist engineers and service
providers can accurately pinpoint the unique
requirements necessary for maximum output
production and service provisions from plant to plant.
Replacement strategies are not that complicated
once all the information required is gathered. The
return on investment enables strategic decisions Based on the inspection results, which can take up to two weeks to be made available, in
based on accurate information of the distribution the worst-case scenario the unit is found to have the following defects:
network equipment, which was derived from • Furan tests are below the minimum requirement (insulation levels indicate overloading)
the preventive maintenance plan that the overall Moisture content is above the acceptable levels
strategic maintenance plan had in turn supported. • Dielectric results are below the minimum requirement
• PCB content is high (this has no impact on the unit’s performance)
Examining a hypothetical ArmCoil OSCA • The unit’s oil level is very low
scenario • Tap-changer, breather, Buchholz relay, auxiliary equipment, radiators and gaskets are in
Assume a 2000 kVA, 33 kV – 415 V distribution need of replacement.
transformer, manufactured in 1960 and currently
in operation. Armed with the inspection report, over a period of one or two days, the corrective
Assume there are no past maintenance maintenance, as put forward by the experts, could include the following:
records or historical staff knowledge of the Instead of oil purification, the oil is replaced. This is done because the Furan results
equipment – a common occurrence as staff are are so poor, and the purification procedure could weaken the insulation and cause the
promoted, retire or resign, etc. embedded sludge to loosen up and settle on other areas, thereby possibly creating a
failure condition during energising.
Initially, from a visual inspection, the following is All recommended parts including gaskets are replaced except for the tap changer due
noticed: to shut down time restrictions. The tap changer is therefore temporarily short-circuited in
• Oil is leaking from the unit, which is evident from the attempt to halt the fluctuation of supplied voltage.
looking at the plinth Since thermal imagery shows blocked radiator fins and channels, it is decided to
• Heavily discoloured, there is no evidence of what remove them and have them ‘flushed out’ on-site only. Replacement of radiators is
colour the unit should be delayed due to shut down time constraints.
• Rust is evident on the radiators, skids, conservator, A follow-up inspection is scheduled to be conducted within a month to start the
fasteners and piping preventive maintenance strategy, to predict failure or replacement of the unit. The above
• There is a continuous ‘buzz’ sound which corrective maintenance strategy and documentation received places the unit’s owner
increases during peak loads in a proactive position to evaluate the unit in operation in terms of reaching its ‘end of
• When standing close to the unit, an ominous service’ criteria. It is advisable to consult internally or externally on the requirements for
odour is evident the replacement unit, as there are many variables to consider, which are unique to each
• The unit trips randomly due to high temperatures network’s specifications.
during operation Furthermore, before taking the route of rewinding transformers from 50 kVA to
• Staff report that the tap changer has not worked 3,5 MVA, time should be taken to compare repair costs with locally manufactured costs.
for the past few months. Also, compare the repair delivery period with the manufacturing delivery period: both
options have advantages and disadvantages for your network’s specifications. The cost
There is a concern that this unit is unsafe and could saving potential that can be achieved if the measures of maintenance strategies discussed
‘explode’ at any time. An inspection of the unit is herein are implemented is, in general, not quantifiable. It depends on company-specific
undertaken by a specialist to establish the corrective factors such as input to increase efficiency or production, current maintenance strategies
maintenance action required. The inspection covers in practice, technical design of equipment and design of plant, network structure,
the full range of oil sampling, thermal imagery of topographic conditions and legal framework. n
the unit and cable joints, and full visual inspection
of the unit whilst in operation – culminating in the Contact Morné Bosch, ArmCoil, Phone 011 763-2351, morneb@armcoil.co.za,
submission of a comprehensive inspection report. www.armcoil.co.za

energize | November/December 2021 | 5