Dingxin Group has invested in Indonesia to explore the local nickel ore resources and produce nickel alloy on Sulawesi Island.

In project phase-I, 3pc*11MVA ore furnaces had been used to melt ores and produce nickel alloy. Ore furnaces operate with a load similar to those of electric arc furnaces but more smoothly. However, the situation during its boring stage is still challenging to the system with high three-phase unbalances and voltage fluctuations. Things can become worse in weak grids.

The nickel alloy plant was powered by its own power generation plant of merely 2*65MW. As it’s such a small grid with no inter-link with the outside world, the network is very weak and could easily fial when powering such impacting loads.

Before the SVC was introduced into this system, “the power generators tripped 4～5 times every day due to its unbalance protection, which proved annoying and caused significant losses”, said by the plant operation engineers. Sometimes the furnaces can hardly operate. This became an incredible headache for workers at the plant.

It is noticed that unbalance is the most key problem in this case. Static var compensators can be one of the possible measures to mitigate the unbalance of the ore furnaces.

• Generators: 2pcs • 35kV/65MW
• Ore furnaces: 3pcs • 11 MVA+20% overload

After a careful system examination and simulation, it shows that a 75Mvar SVC at 35kV busbar can solve the problem.

The SVC was rated as -25Mvar (inductive) to +50Mvar (capacitive) with a total dynamic reactive power range of 75Mvar. The SVC branches were connected at the 35kV busbar, same with the ore furnaces.

In order to mitigate the three-phase unbalance, a control strategy with combined close-loop and open-loop controls are adopted. The open-loop control mainly focuses on three phase balancing and voltage fluctuation, while the close-loop control will take care of the power factor compensation. Below is a comparison of unbalance mitigation with/without SVC.

From this comparison we see that the SVC detects the loads’ real-time currents, and then compensates a certain amount of unbalanced currents to successfully mitigate the three-phase unbalance. This finally resulted in the ore furnaces operating with "balance loads".

The Sulawesi nickel plant SVC was delivered in the year 2015. It had successfully solved the unbalance problem of the loads. The plant's power generators had operated smoothly with no more trips again after the SVC was put into operation. The customer is so happy that they had purchased another two of RXPE SVCs for their project phase-II in the same year.