Success is sweet for Sunshine Sugar

Sunshine Sugar manufactures raw sugar from sugarcane supplied at its mills in the Northern Rivers region of New South Wales and also operates the Manildra Harwood Sugar refinery (MHS) in a joint venture with Manildra Group. All of Sunshine Sugar’s raw sugar production is sold to MHS, which has the capacity to process all the raw sugar produced by the three mills.

The NSW Sugar Milling Co-operative was formed when cane growers purchased the three NSW sugar mills from CSR in 1978. The mills are located at Condong on the Tweed River, Broadwater on the Richmond River and Harwood on the Clarence River.

Sunshine Sugar’s centrifugal drive system was aging and in need of replacement, and after considering all the options, the company chose a Siemens AC drive-motor combination for the upgrade. The decision to replace the 298 kW DC centrifugal drive system with a 184 kW AC motor-drive combination was not an easy one, but Siemens was determined to prove the value of the solution. Plant manager Stephen King explained how Siemens supported the company in its decision making, which ultimately led to the upgrade of the centrifugal drive system on time and even under budget.

“Siemens drew on their 1200 worldwide reference sites with successful centrifuges operated by AC drives. They also provided detailed analysis of their success with reducing the size of motors and drives by controlling the switching rate of the insulated-gate bipolar transistor (IGBT). And they even sent out a global expert on drives from their Sugar Competence Center in Germany to reassure us that this was the right solution,” said King.

Brian Jackson, Sunshine Sugar’s senior electrical superintendent, was also impressed: “We were convinced by the 184 kW drive system when we learned about the Active Front End technology, which is a standard feature in Sinamics drive systems. This allows us to reduce the size of the motor and drive without losing power, achieve harmonics of less than 1%, and consequently reduce our energy costs significantly.”

AC drives are particularly well suited for centrifuges, as they can provide the performance required. The largest centrifuge available can handle 1200 kg of massecuite in a single charge. Variable-speed AC drive systems require very little maintenance. They are robust and durable, can operate continuously, and offer much better reliability than variable-speed DC drives.

The technology used as a standard feature in the converters of centrifugal drives also provides several important benefits.

The use of self-commutated converters with IGBTs, and a clean power filter in the input, means that sinusoidal currents and voltages are maintained, with no mains-typical harmonics and thus absolute minimum mains pollution on the line side. Compensation and filter circuits are no longer needed and an overall unity power factor is achieved.

There is also no conduction-through with fuse tripping in response to mains undervoltage or failure in generator mode, thanks to active tripping; this makes the solution especially suitable for weak or unstable systems. Compensation of mains undervoltages is achieved by a voltage step-up mode.

Sunshine Sugar installed the Sinamics AC drive and motor solution, and it was commissioned and optimised locally by Siemens. Siemens also provided an I/O device to interface to the existing Bailey distributed control system for bidirectional communication.

Since the commissioning of the new drive, Sunshine Sugar has achieved a substantial reduction in power consumption.

“Power recordings have confirmed a reduction from 1.7 to 1.0 kWh per ton of massecuite, despite the recording being made prior to optimising the drive. So we’re planning to undertake further analysis soon to determine the final savings,” says Jackson.

Due to the success of this solution, Sunshine Sugar has placed a second order with Siemens to upgrade the drive and motor of a second centrifuge.