THE NAVAL ENGINEER

A Close Shave?
By Paul Lloyd MBE FInstLM GCGI LCGI MCMI
Electric Propulsion Systems
Paul, aka Jeff, joined the Electric Propulsion Systems team in March 2009 following 33
years in the RN, attaining the rank of WO1WEA(ADC).
He joined the Navy as an Artificer Apprentice in 1975 at HMS Fisgard and was streamed
as an REA. Sea training was undertaken in HMS Brighton before returning to Collingwood
whereupon branch changes saw him complete the apprenticeship as a WEA (AD/CEW).
Interspersed with SFM Devonport, where there was the opportunity to work on a broad
range of WE equipment, two sea jobs as a section maintainer were undertaken in HMS
Phoebe, Seacat radar and guidance, and HMS Charybdis, Seawolf surveillance radar.
This was followed by loan service with the St Vincent and the Grenadines Coastguard with
responsibility for anything electrical or electronic fitted to their four patrol boats. On return to
the UK he undertook CCWEA QC and then at short notice
joined HMS Coventry. Then it was back to SFM where time
in the Seawolf Assistance Team was interrupted by a short
foreign trip to serve with the United Nations Transitional
Authority Cambodia. HMS Chatham followed and during this
draft he was made an MBE. Advanced to WO1 where jobs as
ASWEO F2, DCSA SO3 Customer Account Manager (Navy),
FOST WESRI – foreign ships lead, MTE co-ordinator and
finally back at SFM Devonport as FTSP Package Manager
followed. He was awarded the Meritorious Service Medal in
2007 just prior to leaving the RN in March 2008.
Introduction
In mid 2009 HMS Argyll reported
damage to one of her propulsion
motor commutators. This was
caused by brushes wearing
down beyond their minimum limit,
resulting in the copper tails scoring
the commutator segments. Both
commutators were profiled by ESG
staff to establish the shape and
truth of running and the results
showed that both were in a similar
condition. A PUMA was conducted
in HMS Lancaster and likewise
the commutators were noticed to
be visibly damaged. At this point it
was decided that all of the Type 23
commutators should be profiled
and the remaining commutators
were subsequently checked over a
12-month period and all displayed
varying levels of degradation.
The problem
The rough surface, seen in Figure 1,
causes increased brush wear that
consequently leads to an increased
production of carbon dust. This
conductive dust has subsequently
coated many components within
the motor; static field windings
and rotating armature windings,
busbars, brush
gear, insulators
and motor
internal casing.
There has been
19
a commensurate reduction of the
motor’s insulation resistance (IR)
and this could subsequently lead to
a flashover (now more commonly
referred to as “Arc Flash”) event
within a motor. The lowest
acceptable limit of IR in the motors
is 1 Mohm. Low IRs were reported in
several vessels and the lowest was
an armature at 0.45 Mohm, reported
by HMS Kent. She was emerging
from upkeep and was initially
directed to clean the brushgear
and retake measurements. The IR
increased marginally and, following
a system split by disconnecting
the motor’s busbar link plates, the
low IR was determined to be within
the motor’s armature windings/
commutator risers. Ship’s Staff were
subsequently directed to obtain
specialist assistance to carry out a
deep clean of the motor, to avoid the
possibility of a flashover – Figure 2 1 .
The main concern with a flashover
is whether or not personnel could
be injured by the event. A flashover
was increasingly likely to occur if
no action was taken to improve
the condition of commutators
and reduce the dust levels within
the motors. Following two safety
reviews, it was considered that the
most likely area that a flashover
would occur would be within the
brushgear and that this may or may
1. http://www.wmea.net/Technical%20
Papers/Technical%20Developments%20
in%20the%20Measurement%20of%20
Commutator%20Profiles%20-%20Nov%20
07.pdf, (accessed 18 December 2012).
Figure 1: HMS Argyll profile before repair
Figure 2: This is what we’re trying to avoid
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