Enhancing reliability and energy efficiency in Indiana rolling mill

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In rolling mill applications, as metal slabs, blooms, or billets pass through the mill rolls, the electrical motors driving these rolls must generate higher torque. This increased torque demand also raises the need for reactive power due to the drives’ performance characteristics, causing a voltage drop at the load bus. Since motor torque is proportional to voltage, any voltage drop limits torque and reduces material throughput. By compensating for reactive power, voltage drops are eliminated, allowing for higher torque and greater productivity. Additionally, fluctuating voltage can lead to nuisance trips, disrupting operations, and poor power factor can result in reactive power penalties, impacting plant efficiency and costs.

Challenges at the customer’s factory

The customer’s aluminium factory has four different rolling mills: one hot mill that operates continuously, two cold mills and one reversing mill. The loads are fed with parallel transformers that can feed the loads individually or together. They suffered from voltage unbalance and low power factor caused by high reactive power demand of the rolling mills.

The high reactive power demand of the plant’s aluminium manufacturing process increases the electric power system losses, reduces the power transmission and distribution capability of the grid and maintains a voltage profile outside permissible limits. In addition, power quality disturbances like voltage sags could make the rolling mill motor drives disconnect, causing several economical and technical problems for the plant operator.

The mills can be in operation at the same time or different times, creating a mix of possible load scenarios. This means that the loads can fluctuate heavily within a day and the power quality of the plant must be ensured with a flexible solution. Traditional passive solutions are prone to resonances in transient conditions, which means that a dynamic compensation solution is needed.

Our Merus^® Solution

Merus Power was chosen to deliver two identical 16 MVAr Merus^® STATCOM systems to the site. Merus Power’s scope of delivery included a total of 16M2000 STATCOM modules (2 MVAr per module) and two stepdown transformers installed at 15 kV bus, 2 Control & Protection systems, cooling systems, two detuned capacitor banks, spare parts, and complete system engineering in a containerized solution.

The detuned capacitor banks were both rated at 22 MVAr, which means that the installed Merus® STATCOM solution can control reactive power seamlessly and in real-time between 12 MVAr (capacitive) and 74 MVAr (capacitive) for an undefined period. Merus^® STATCOM provides real-time reactive power compensation and active harmonic filtering in demanding applications. This minimizes voltage variations and mitigates flicker caused by heavy industrial loads.