TRANSFORMER RECTIFIER INSTALLATION FOR THE TANGIER MED PORT II PROJECT

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Dwayne Dalton
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1 Case Study No 1 TRANSFORMER RECTIFIER INSTALLATION FOR THE TANGIER MED PORT II PROJECT Cathodic Protection Co Ltd

INTRODUCTION Tangier Gateway to Europe The city of Tangier, the third largest in Morocco, is the gateway from Northern Africa to Europe and a major city of almost a million people.

2 INTRODUCTION Tangier Gateway to Europe The city of Tangier, the third largest in Morocco, is the gateway from Northern Africa to Europe and a major city of almost a million people. Its strategic location, on the Strait of Gibraltar and just 15km from the European Union, has been vital in its more recent development as a trading hub. As a result, the city s infrastructure has seen considerable investment in recent years, including a new airport terminal, high speed rail and road links with the country s two largest cities, Casablanca and Rabat, and the Tangier Med Port. Tangier Med Port Expansion The Tangier Med Port project has created the largest sea port in Africa. It is a strategic project by the Moroccan government for the economic and social development of the North Morocco region. The first phase of the project, Tangier Med I went into service in July 2007 with an initial capacity of 3.5 million shipment containers. The second phase of the project, Tangier Med II has added an additional two new container terminals and a jetty length of 2,800m. The new jetty is built on 105 reinforced concrete caissons, each one some 35 metres tall and weighing approximately 8,000 tonnes. The caissons are initially hollow so that they can be floated into position and then sunk and filled with rubble.

THE CATHODIC PROTECTION CHALLENGE Placing almost a million tonnes of reinforced concrete structure into a hot marine environment creates the perfect conditions for the occurrence of corrosion.

3 THE CATHODIC PROTECTION CHALLENGE Placing almost a million tonnes of reinforced concrete structure into a hot marine environment creates the perfect conditions for the occurrence of corrosion. The client recognised that a high specification cathodic protection system was needed to ensure that their design life for the caissons of 100 years would be achieved. An impressed current system was therefore specified, split into 947 separate zones. This was dictated by the number of caissons, and the varying environmental conditions experienced by different parts of each structure (i.e. immersed, atmospheric etc.). Monitoring of the cathodic protection system would be achieved by 2,145 reference electrodes located throughout the structures. To facilitate operation of the cathodic protection system, full remote control and monitoring capability was also specified. The bill of materials required for the project was determined as follows: Transformer Rectifiers with Remote Monitoring and Control 28 Remote Monitoring & Control System (RMCS) with customised software in French language 1 Type 100 Metal Oxide Ribbon Anode 400,000 metres Titanium conductor bar 8,000 metres Titanium wire 1,200 metres Ag/Ag/Cl reference electrodes with 6mm² PVDF/HMWPE cable tails 1,000+ MMO Decay electrodes with 6mm² PVDL/HMWPE cable tails 1,000+ Cable (PVDF/HMWPE, 6 & 10mm²) 500,000 metres+ Anode Ribbon spacers 500,000+ Cable Ties 3 million+ Fibre Optic cable for RMCS network 2,000 metres These materials were progressively supplied by Cathodic Protection Co Ltd¹ in line with the site construction schedule with the Transformer Rectifiers delivered in 2014.

4 Transformer Rectifiers The Transformer Rectifiers for Med II would be one of the largest projects ever undertaken by this company. The specification for the TR units included the following requirements: TR design life of 25 years Operation in marine environment at 40 0 C and 75% humidity Zoned outputs ranging between 19 & 62 outputs per cabinet Control via 2145 reference electrode inputs Installation split into two remote locations separated by water, system A having 25 cabinets & system B having 3 cabinets Remote monitoring & control Precise synchronisation of TRs for instant off and depolarisation tests 947 separate outputs 28 TR cabinets Nearly 1,000 individual transformer rectifier outputs would be delivered over a 6 month period. Last but not least, these units would need to be provided at a very competitive price. The particular challenges associated with this project can be summarised as follows Achieving 25 years design life Increasing production capacity to deliver 1,000 channels in 6 months Minimising production costs Maximising reliability Synchronised switching and data collection These items are discussed in more detail below. 25 Year Life To provide a 25 year operational life, oil cooled transformer rectifiers using thyristor regulation were selected. Air cooled units using switch mode technology would have been cheaper, but would not have achieved the design life. Thyristor transformer rectifiers have a record of high reliability and long service life, particularly when the power components are immersed in oil. Oil cooling maximises heat dissipation from the electrical components whilst minimising the potential for any hot spots. To ensure that the cabinets for the transformer rectifiers survived in good condition for a minimum of 25 years, 316L stainless steel enclosures with a high quality paint finish from Akzo Nobel² were specified. To demonstrate the longevity of the paint system, samples were prepared and sent to an independent test house for verification before the production equipment was manufactured.

Increasing Production Capacity The scale of the Med II project presented some significant logistical problems. Up to 4 TR units would be in build at any one time and with units up to 4m long and 1.

5 Increasing Production Capacity The scale of the Med II project presented some significant logistical problems. Up to 4 TR units would be in build at any one time and with units up to 4m long and 1.5m high, space would be an issue. Man hours estimated for the project were over 15,000 and the number of TR outputs for the project was over twice the prior year s total output. Physically moving the large units around would be a problem due to their weight. One part of the solution was to increase the build area on the shop floor for transformer rectifiers by 70%. A new mezzanine floor was commissioned and dedicated to smaller sub assembly work for the Tangier project. A separate test facility was also created with new data logging hardware and software to speed up the time taken to test finished units. This work was completed within a 2 month time period. To be able to move the largetrunitsaroundthefacility,theywerebuiltonlargewheeledtrolleys. This allowed the units to be easily moved by two people without mechanical assistance. On completion of test the wheels were removed and the wooden base that was left was used for the base of the packing crate used to protect the TRs whilst in transit.

Design innovations were also incorporated in the units to reduce the labour content,andworkwaspackaged into pre production sub assemblies that allowed work to take place prior to and in parallel to

6 Design innovations were also incorporated in the units to reduce the labour content,andworkwaspackaged into pre production sub assemblies that allowed work to take place prior to and in parallel to the main build of the units. A small number of temporary staff were recruited who were allocated to the repetitive sub assembly work, allowing a relatively short training period without risk to product quality. The photo below shows some of the TRs following testing. Note that the units were built directly on to the base of the packing crate used to ship the units. Wheels were added to this base to aid the movement of the units around the workshop. Minimising Production Cost The largest opportunity to reduce cost on the project was by optimising design to minimise labour content. Traditional thyristor power supplies involve individual components such as transformers and chokes which are fitted on to back plates and wired in accordance with wiring diagrams by trained electricians. For the low power outputs needed on the Tangier project, the opportunity was taken to use PCB mounted components, fitted to custom designed power boards which could then be immersed in the oil tank. In this way up to 4 individual TR circuits could be built up on one large circuit board. This work eliminated a significant amount of labour and hence cost. The PCB mounted components also offered a cost saving. A test jig was also developed for the power boards so that these could be tested separately before installation into the Transformer Rectifier. This eliminated any problems with these boards during final testing of the TR. Reliability With nearly 1,000 TR channels operating simultaneously, a reliability level of 99.9% is clearly insufficient as one channel will be faulty at any one time! With the system accumulating 680k channel operating hours per month a mean time between failures of 1,000,000 hours means that something would fail every two months. This exposure to such a high number of channel operating hours on a single installation means that any reliability problem with either hardware or software will become all too apparent.

7 To address this potential issue it was imperative to use tried and trusted technology and hardware. The heart of the Thyristor Transformer Rectifier is the PCB which controls the firing of the thyristors and regulates the TR output. This has been in constant development for the last 10 years and is a proven device. The new power board presented a possible reliability risk as this was a new development for the company. However the circuitry was proven, and extensive testing proved the reliability of the PCB build and its performance. The net result has been a highly reliable product with only two component failures in over 8 million operating hours. These failures occurred on standard off the shelf components which were not specific to this project. Synchronised Switching and Data Collection One of the particular challenges of a large multi channel cathodic protection system is data synchronisation. Corrosion engineers may require simultaneous site wide switching of TRs in order to perform procedures such as instant offs. In this procedure the potential of the structure being protected is measured against a reference electrode a short time after the CP current is turned off, typically 100ms later. Synchronised switching ensures that interference from adjacent zones or cathodic protection systems is eliminated. The time at which the data from reference electrodes is recorded is important as the potential changes with time during the off cycle. Discrepancies in this time will lead to errors in the CP data which in turn could lead to incorrect conclusions about the effectiveness of the CP system. TRs are often connected in a daisy chain configuration. In this arrangement an instruction to interrupt outputs or collect reference electrode readings is passed from one TR to the next. The TR unit requires time to receive and pass on the instruction, and to record reference electrode data. This results in a slight delay between the operation of one TR and the next. On a small system with a few outputs this difference may be small and insignificant. However on a system of 1,000 channels, the cumulative error will be large unless steps are taken to eliminate it. As interruption of the TR output is usually cyclic (for example a repeated cycle of 1 second on and 0.25 second off), some CP systems use a technique where data collection is staggered not synchronised. In this technique the reference electrode data for one channel is recorded on one cycle, and then the data for the next channel is recorded perhaps three cycles later. This allows the RMCS system to ensure that the reference electrode data is always recorded at the appropriate time in the off cycle (i.e. 100ms), but the data is recorded at different times. For the Tangier project the consequence of using this approach would have been a 1 hour delay between the reading of the first reference electrode and the last. We did not feel that this approach was appropriate due to the significant time difference and the opportunity for environmental factors such as tide to affect the readings during this process. The solution adopted for the Tangier project was to use Network Time Protocol (NTP) to ensure true synchronisation. The TRs are instructed by the operating network of the RMCS system to interrupt and to collect reference electrode data at a specific time. Using this approach the TR switching is precisely synchronised, as is the recording of reference electrode data. This data is recorded locally for each TR channel and then collected by the RMCS system with the relevant time stamp. This method totally eliminates discrepancies between channels in switching or data recording and allows true site wide instant off data to be captured.

8 TR Manufacture & Installation

9 Details of Remote Monitoring & Control (RMCS) Because of the complexity of the Port Med site and numbers of reference cells involved, to facilitate the commissioning of the Cathodic Protection system our client needed a remote monitoring and control system that could automate all of the standard commissioning routines. The company therefore developed instant off and deplorarisation routines requiring: Synchronisation of DC switching across 946 outputs Synchronisation of on and instant off readings across the reference cells and depolarisation probes Organising info back into a user friendly database A system which allowed the selection of the delay period between 100 milliseconds and 6 seconds in 100 millisecond steps The Process of Capturing Instant Off Data Each Transformer Rectifier unit has a programmable logic controller (PLC) controlling up to 62 outputs and associated reference cells. All PLC clocks are synchronised by the server PC. On initiation of the instant off function by the server PC, each PLC in the 28 TR units activates a voltage signal which is used to commence instant off function. This voltage signal commands the thyristor control boards to switch the DC outputs off and commands the reference monitoring boards to log on and record instant off values. All communication between the PLC and control boards is on a RS485 network. Although RS485 has many advantages, it is limited by the speed by which it collects data. Instant off data from all reference cells must be collected at the exactly the same point in time hence RS485 alone is not sufficient. To achieve a true instant off reading across the site the company used the following routine on the reference control boards: On receipt of voltage instant off command from plc reference on readings are held in storage register then readings are recorded every 100 milliseconds for 6 seconds. On completion of instant off the voltage signal is removed but all reference readings are held in registers. The required data (on and instant off) can then be collected by the PLC over the RS485 network without time constraints. Thus data, synchronised to within 10 milliseconds, can be gathered from thousands of reference points on a single command. The Med II site is split into two groups, each with an independent RMCS, referred to as RMCS system A and B. System A incorporates TR units 1 25 System B incorporates TR units 26, 27 and DST 3 (28) Each system has a Server PC, each housed in a site control room and connected to the relevant group of TR units on a dedicated fibre Ethernet network. The Server PC is the heart of the RMCS, providing the user with full TR monitoring and control, scheduling and access to all logged data for reporting. The controller PC is connected to the site LAN which is in turn connected to the internet. The user can access the system in the following ways:

Locally at the TR unit via the HMI digital controller Limited to TR functionality only with no access to

LAN Full TR functionality and RMCS access Any remote PC with internet connection Full TR functionality and

These are customised to the Med II project and provided in the French language.

System Topology The topology of the system is best represented by the Remote Monitoring and Control System

10 Locally at the TR unit via the HMI digital controller Limited to TR functionality only with no access to the RMCS system Site control room via Controller PC Full TR functionality and RMCS access Any PC on Site LAN Full TR functionality and RMCS access Any remote PC with internet connection Full TR functionality and RMCS access provided Site LAN is connected to the internet Examples of RMCS screen shots are shown below. These are customised to the Med II project and provided in the French language. The company has provided this interface in a number of other languages for other projects. System Topology The topology of the system is best represented by the Remote Monitoring and Control System overview. There are two control rooms, each of which has access to a number of associated TRs. System A: Accesses TR1 to TR25 System B: Accesses TR26 to TR28

11 CONCLUSION The Tangier Med Port is a strategic investment by the government of Morocco which has been built to serve the country for the next 100 years. An impressed current cathodic protection system has been installed to prevent the corrosion of the reinforced concrete caissons supporting the nearly 3km long jetty at the heart of the new port. The company was selected to provide the cathodic protection materials for the caissons, including embedded anodes, reference electrodes and cables. 28 multi channel, oil cooled, transformer rectifiers were manufactured to a rigorous client specification featuring nearly 1,000 separate DC outputs and monitoring/control using over 2,000 reference electrode inputs. These TR units were equipped with full remote control and monitoring capability. The large scale and complexity of the project presented a number of unique challenges affecting both the design and manufacture of these units which were successfully overcome. Many innovations were necessary to ensure that the client s expectations in terms of reliability, cost and performance were achieved. This was the largest Transformer Rectifier project ever undertaken the company. It was completed on time and on budget and we believe that it is the largest thyristor transformer rectifier installation in the world.

Technical Seminar for Cathodic Protection to GOGC Design Unit Specialists. Dr. Nick Kioupis, Cathodic & Lightning Protection Section Head, DESFA

Technical Seminar for Cathodic Protection to GOGC Design Unit Specialists Dr. Nick Kioupis, Cathodic & Lightning Protection Section Head, DESFA Photo of a typical T/R cabinet Impressed current stations