Custom DC Power Supplies for Aluminum Smelters

Thursday, June 27th, 2019

Flexible, Custom Solutions – NEELTRAN makes a big difference by being one of the few transformer/rectifier manufacturers that can adopt a flexible design approach for every industrial power conversion project (designing reliable DC Power Supplies -- Rectifier Transformers and Rectifiers).  NEELTRAN has earned a reputation for supplying FLEXIBLE SOLUTIONS for reliable DC Power at reasonable cost, and ultimately, low Total Cost of Ownership (TCO).  Neeltran listens to customer needs.  Each DC Rectifier and Rectifier TraBooster Rectifier for Aluminum Smeltersnsformer is expertly customized to meet the specific needs of the customer. 
The Transformer and Rectifier design must consider pad size, location of inputs and output bus, dimensional restrictions, climate, special maintenance access, climate-controlled enclosures and features, hazardous environment customizations, future upgrade consideration, and accessory customization to mitigate risk.
NEELTRAN will work with you as a team to provide the best high current DC power supply solution possible, based on your needs, regardless of the market.  Whether it’s Electrolysis for the chemical industry, Electrowinning for metals, smelting, etc. we’ll make the DC Power Conversion system work – and perform reliably! 

This article focuses on Booster and Compensation Loop Units for the Aluminum Smelting Industry.

Aluminum Smelters often need to boost DC power to meet increasing demand as well as maximize revenue.  DC Power Supplies (Transformer and Rectifier) are placed in parallel to the existing Pot Line to accomplish this.  This increase means these Booster Rectifiers are just as important as the main Rectifier/Transformers that feed the pot-line – despite their smaller output.

The key for system longevity and performance is a robust design focusing on features to mitigate risk of possible shutdown of the DC Power Supply (either the Rectifier and/or Rectifier Transformer).
It is important to avoid production shutdown because unscheduled shutdowns result in reduced production, and lengthy shutdowns typically cost millions of dollars in lost revenue.

Power and Loss Requirements
The Initial Design Phase of the DC Power Conversion system begins with understanding - through mathematical analysis - the AC input available and the DC output required - to identify the power required and losses generated by the system.

Cooling System
Aluminum Smelters are found in diverse areas with very broad ambient conditions which are in either very cold or very hot extremes.  Cooling and safety of design are very important considerations when designing Power Conversion System solutions to meet these applications.
For the rectifier transformer some fundamental considerations are ONAN (oil natural, air natural), ONAF (oil natural, air forced), OFWF (oil forced, water forced).  Dry and water-cooled transformer options are available based on primary voltages. The most effective method will be selected through discussion and collaboration with the customer.
Rectifiers can be cooled with a deionized water to raw water heat exchanger or a deionized water to air heat exchanger. A design that allows a delta temperature of maximum 8 degrees (which is conservative), but it ensures the unit runs cool. For that reason, in extreme climate conditions we focus on the design of the heat exchanger.

Selection of appropriate components and accessories for the DC Power Supply are also critical to system performance, including filters, switches, taps, bus work, sensors, gauges, controls and their location.  In the Rectifier – items such as semiconductors – can be critical to the longevity and performance of the DC Power Supply, and this is accomplished using junction temperature analysis. 
In all cases, NEELTRAN involves the customer in the decision-making process in order to assist in a cost vs. benefit analysis.  Often, the customer will choose to mitigate risk up front rather than face possible future repairs and unplanned shutdowns of this important equipment.  For example, Aluminum Smelters often propose a Plasma boot or Ring as an optional to mitigate explosion effect on nearby components as a safety contingency.
Semiconductor selection for the rectifier also involves choosing between diodes (used on the Pot-Line Rectifier) or Thyristors which offer numerous benefits.  The decision is made jointly by educating the customer.

Free-Wheeling Circuit
For booster rectifiers, a free-wheeling circuit is needed to compensate for the possible effect of the huge electromagnetic field generated by the power conversion system.
These rectifiers require a Free-Wheeling diode to dissipate the inductive energy resulting from an instantaneous pot line shutdown.  Our qualified engineers will work with your team to provide a stable, robust power conversion system solution.

The enclosure for the rectifier is also an important consideration which requires flexibility.
The installation can be for a total outdoor unit or for a semi-outdoor/indoor unit.
For example - for total outdoor rectifier units snow load might need to be considered and so the structural integrity of the rectifier enclosure will be more robust. For a sun-load there may be a need to install a double roof to create a natural vent between the first and second roof. This is a very inexpensive but practical solution for locations such as a desert environment.
For semi outdoor rectifier units (in a lodge or under a cover) snow and sun load considerations are not necessary, and the cabinet can be designed as a standard unit with design consideration for temperature fluctuations which may be present.
For any type of installation, the enclosure needs to have explosion vents installed in the proper location to direct the energy to a safe area. Normally they are installed above man height (around 2000 mm) and are positioned in area of the cabinet where it is unlikely that a person will be present, typically on the back side between transformer and rectifier, or on the side where the doors are not present.
NEELTRAN can incorporate flexibility of design because of a strong emphasis on Engineering.  NEELTRAN’s engineering team include some of the best and brightest transformer and power conversion Engineers and designers available in the industry, many with 15 years or more experience in power electronics systems.  After an order is received, NEELTRAN’s unique Project Management approach allows you to team with NEELTRAN as a partner – not just a customer, from beginning to commissioning of the Power Conversion System.
“Customers want to do business with real people that will take care of their short and long-term needs.  By listening to our customers in the design process as well as the project management process, we’re able to accomplish that quite effectively.”  -- Antonio Capanna Jr., President/C.O.O.