strengthening a critical part of the treated water
infrastructure to provide reliable supplies to customers in the
mid/south Essex supply zones
by Kevin Packard BSc CEng MIET
Pumping Station - Courtesy of NWG
Northumbrian Water Group (NWG) provides water services to 1.5
million customers across a large part of Essex and east London,
where it operates as Essex and Suffolk Water. As a vital part of
Northumbrian Water’s treated water network, demand up to 55Ml/d
is pumped from the Langham WTW on the Essex/Suffolk borders and
forward boosted at Tiptree Pumping Station into the Layer to
Danbury Aqueduct to the west. Both pumping stations were
constructed in the 1930s and although they have provided
reliable service for some 80 years, it had become increasingly
difficult to maintain pumps, drives, diesel sets and associated
equipment along with safety issues on both LV and HV electrical
switchboards. Obsolescence and non-availability of spares were
the critical drivers to necessitate significant investment to
ensure a resilient water supply to customers.
The Essex region is
broadly supplied from four water treatment works; Chigwell to
the west, Hanningfied centrally, Layer-de-la-Haye to the east
and Langham to the north-east. Langham and Tiptree pumping
stations are linked such that total failure of either one will
result in the loss of all water produced from Langham WTW as the
pressure in the main is too low to overcome the pressure in the
aqueduct into which the water needs to be fed. The Layer WTW
some 10 miles south can provide some short term back up but
there would be a major impact on deployable output. The network
would thus be very vulnerable to any issues at Layer WTW
especially if its raw water supply from Abberton Reservoir is
experiencing variable water quality.
challenges and issues
Since their original
construction, the pumping stations have evolved from coal-fired
to diesel to electric powered pumps, both low voltage and high
voltage, and combinations of these still remained. Common
challenges faced at both sites include age and condition of main
assets, in particular with pumps, motors, and drives, plus the
requirement of frequent and costly reactive maintenance of what
is essentially obsolete equipment. The scheme offered low
resilience; the sites often ran without standby pumps available
due to maintenance difficulties.
Electric pumps and old MCC at Tiptree PS
Courtesy of NWG
PS diesel pumps
Courtesy of NWG
Electrical equipment was
non-compliant and the company’s network pumping optimisation
tool Aquadapt was severely hampered by drives and pumps not
running well together and with ineffective priming systems.
Particular issues were:
2 (No.) HV electric
pumps, motors require regular refurbishment.
Drives are obsolete DC
types, no spare parts available.
Existing back up
generator is LV hence cannot support electric pumps.
On mains failure, manual
operation of diesel pump required, also second non-compliant
between pumps means a gap in flow rates between 35 and 42Ml/d.
3 (No.) LV electric
pumps: 1 failed beyond repair, 2 requiring regular maintenance.
Drives are obsolete DC
types, no spare parts available.
Safety and reliability
issues with both HV and LV switchboards.
auto-changeover panel regularly fails.
Investigate and define
Critical to the
performance of both pumping stations, the correct choice of
pumps was the principal factor in the new design. NWG engaged
their long term pump performance specialists Integrated Water
Services Ltd (IWS) as principal contractor to bring the
necessary expertise to the project.
For both pumping
stations, the historical approach would be to have 3 (No.) pumps
in duty/assist/standby arrangement to achieve the required flow
rates and resilience. IWS evaluated several pump manufacturers’
proposals and it soon became clear that a two pump duty/standby
regime would be capable of providing the required flow of 55Ml/d
with a minimum of 40Ml/d if only one pump available. Under usual
running conditions, one pump would be sufficient to meet the
majority of planned operations.
Original Harland 1931 pumpsets
Courtesy of NWG
Courtesy of IWS
Controlling the pumps by
variable speed drives would also give further flexibility to
provide the required flows under varying network head
conditions. In addition, the proposed pumps indicated a
significant OPEX efficiency saving over the old machines as well
as the CAPEX saving by installing just two pumps. This approach
was reviewed and agreed technically with NWG Operations and
Prior to the project, NWG
was investigating the use of 3D laser scanning and modelling
techniques and internal/external scans of the pumping stations
were undertaken. The resulting site models were incorporated
into IWS’s 3D Solidworks design package giving an instant view
of the stations’ topographies and saving many hours of manual
measurements and transcriptions of 1930s drawings.
The proposed solution
included (per site):
2 (No.) new horizontal
split case pumps, associated pipework and manifolds.
ABB AC800 series variable
A new HV transformer.
New motor control centre
New LV generator and
controls at Langham and new controls for existing generator at
New HV switchgear.
As well as a significant
increase in reliability and safety, the proposed system will
eliminate the need for operations staff to attend site to ensure
correct pump starting (no priming issues) or to start/stop the
generator during mains failures.
As strong synergies exist
between the sites, both procurement and delivery advantages
could be gained. The use of the same suppliers for MCC, pumps
and generator controls, common contractors and equipment
consistent with other NWG sites, means that benefits are gained both in
maintenance requirements and familiarity of equipment for
A major factor governing
construction activities was that treated water output to the
distribution network had to be maintained throughout the project
lifecycle. Agreement was reached to run at around 35Ml/d, the
historic 5 year average, with other treatment works in the
network making up additional water as required. This meant
effectively that a single pump at each station could provide the
required output, allowing a planned staged installation with
unforeseen and unusual combination of below average rainfall and
high algal blooms meant that for much of the project, required
flows were much higher than predicted. Combinations of old and
new pumps had to be run together often by a mix of temporary
software and manual control.
Age and evolving
technology also created problems. Originally being coal then
diesel then electric driven, the stations, particularly Langham,
contained a network of diesel pipes below floor level. Langham
had an operational diesel pump, redundant diesel pump and
operational diesel generator all situated within the main pump
hall amongst the current electric pumps hence creating risk of
fire and cross contamination.
The existing pumps were
sited at pump hall ground level, allowing minimal positive
suction pressures relative to the external chlorine contact
tanks. The pumps had auto priming systems which were notoriously
unreliable and often required operative call-outs in order to
get pumps started. The solution proposed was to fit the new
pumps at some 4m lower in the basement area to provide a
positive suction head to eliminate the need for any priming
To gain the necessary
space, several large areas and several tonnes of concrete floor
support had to be removed by diamond wire cutting. This had the
potential to create a large amount of dust but was managed by
tenting of work areas and forced air ventilation.
new 40Ml/d pumps - Courtesy of NWG
Pumpsets and drives
The existing electrical
pumpsets at both sites were the original 1931 units manufactured
by Harland. The new units chosen are Flowserve LNNV single stage
horizontal split case types, selected to provide a maximum
single pump capacity of 40Ml/d at 47mHead (Tiptree) and 78mHead
(Langham). The pump motors are 315kW WEG high efficiency IE4
types at Tiptree with larger 500kW units to cope with the
increased head requirement at Langham.
The existing pumps were
driven by 12-pulse DC drives at 480VDC. The drives had become
obsolete with no source of spare parts and with no technical
expertise remaining within the UK. Frequent breakdowns and
maintenance intervention was required.
The new drives are ABB
ACS800 series types, consistent with many other drives across
NWG and hence fall under the ABB service & maintenance agreement
already in place within Essex. A further advantage of common
systems is the ability to ‘borrow’ parts between sites in the
event of an emergency. At Langham, the drives are run
super-synchronous in order to achieve the required output at the
higher network heads.
All pumpsets are fitted
with pressure/flow/bearing protection and monitoring. Dual axis
vibration monitoring is fitted to each pump and motor which is
monitored remotely via the Ethernet enabled communications
Electrical power supplies
Both sites are supplied
by twin 11kV REC incoming supplies. The existing NWG substations
were equipped with ancient switchgear which was both unreliable
and difficult to maintain. These have been replaced with
Schneider Premset vacuum breaker units.
At Langham, the supply
was onwardly distributed via 3 (No.) ring main units (RMUs) to 3
(No.) external transformers, one to the remote ozone plant and
one each to either end of the main power distribution board. The
refurbishment work has simplified this to provide a new single
2000kVA transformer-fed supply to the new MCC whilst maintaining
the separate ozone supply.
At Tiptree, the situation
was somewhat worse with two internal 11kV transformers mounted
within the same power distribution board as the LV pump
controls. A new external 800kVA transformer has now been fitted
which supplies the new MCC.
Arrangement of new pumps at Tiptree - Courtesy of NWG
New motor control centres
have been fitted at both stations. Manufactured by TES they are
of Form 4 Type 2 construction built to NWG’s engineering
standards. The MCCs are symmetrically fed each end by mains
incomer and generator incomer respectively with a central bus
coupler to allow isolation for maintenance purposes.
The existing control
software has been extensively re-written and is accessed from
local HMI screen or remotely via the company’s SCADA system.
At Langham, standby power
was supplied by an LV Blackstone generator which could only
provide general site services power as the pumps were HV types.
In the event of a mains power failure, manual intervention was
required to start one of the two Blackstone diesel pumps which,
lacking comms feedback, required manned supervision until power
was restored. All old diesels have now been removed and the
generator replaced with a JCB 1736kVA prime rated generating set
in its own remote soundproofed room.
standby generator at Langham PS
The set is fully
automated to provide automatic start and load take-up in the
event of mains failure plus a G59 synchronised no-break return
to mains power on restoration of mains supply.
At Tiptree, the existing
800kVA generator is retained but has been fitted with the same
automated control system features as the Langham set to provide
full automatic operation. At both stations, the standby design
capacity allows single pump operation to provide flows of up to
The project provides an
excellent example of a collaborative approach between project
team, framework partners and tier 2 suppliers to provide two
modern and efficient pumping stations to meet NWG’s future needs
and maintain a continuous reliable supply for our customers. The
construction programme kept to plan despite unforeseen flow
demand which called for some radical solutions to maintain the
Lessons learnt and good
practice will be taken forward to a third pumping station in
2018 whereby Essex’s primary raw water pumping station at
Stratford St. Mary will undergo a similar upgrade.
and publishers would like to thank Kevin Packard, Project
Engineer with Asset Delivery, Essex and Suffolk Water, part
of the Northumbrian Water Group, for providing the above
article for publication.