e-mosty June 2017: Osman Gazi B. US Suspension. Hålogaland B. e-mosty June 2017: Suspension Bridges | Page 60

3.7 System Commissioning and Operation
The system commissioning process included the
evaluation of the mechanical, electrical and controls
system in the field. Extensive checklists were used to
evaluate the system and its performance. The process
also included soapy water testing of the cable wrap
and sealants to identify air leaks, as well as air flow
trials to further evaluate system performance.
The Westbound Bridge dehumidification system was
commissioned and operational in early 2014 while the
Eastbound Bridge system was commissioned and
operational by late 2015. The systems have remained
in general operation since.
Figure 25: Sensors in NEMA 4X sensor box
The NEMA enclosure standards are defined in North
America by the National Electrical Manufacturers
Association (NEMA). For this application, the contract
required an enclosure rating of 4X setting a standard
for both corrosion protection, commonly used near
salt water, and water tightness.
Flow, temperature, and humidity are monitored at
injection and exhaust points, in addition to pressure at
injection points. The injection pressure is both
recorded and directly fed back to the
dehumidification plant controllers to allow active
control of the fan speed for a consistent injection
pressure. A weather station is also installed to record
weather data and the system feeds this data back to
the plant room as well.
The system is accessed by either an operator interface
terminal (OIT) in the plant rooms or remotely through
the SCADA computer located in the MDTA
administration building. The system is also accessible
through a secure web-enabled interface.
Data collected and analyzed from the SCADA systems
on both bridges illustrate the systems are performing
as intended. The graphs in Figure 26 demonstrate the
efficacy of the Westbound System in two ways. The
left graph plots the relative humidity over time for the
first two years of operation to evaluate the cable
drying process.
As can be seen, the relative humidity starts out quite
high indicating the prevalence of moisture in the
cable. However, within approximately the first nine
months, the relative humidity has dropped and then
sustained below 40% RH.
The graph on the right plots the cumulative water
removed over time, which is not directly measured
but calculated from the relative humidity and
temperature data collected.
As can be seen again in the first two years,
approximately 1,200 equivalent liters of water have
been removed from the North Cable. Similar results
have been observed for the South Cable and for the
Eastbound Bridge.
Figure 26: Westbound data – relative humidity over time (left); cumulative water removed over time (right)
2/2017