Challenges

The rain and lightning were particularly troublesome, especially in the area of the coal-fed generation plant. The reason: When coal gets wet, it has a higher likelihood of jamming the pulverizer. This would not only cause a fault near the generation plant, it also created considerable down time since employees would have to manually clear the pulverizer before it could be restarted to restore power to full capacity.

In addition to faults near the generation plant, the organization also had issues with faults along the transmission line. These came from a rather unusual source: Indonesia’s large population of geckos. Normally, these lizard-like creatures are completely harmless. But problems began arising during nighttime operations when the lights illuminating the power transmission lines would attract insects, an irresistible lure for the nocturnal geckos. Subsequently, the geckos would gather to feed on the insects.

Because the ore extracted from the open pit mine had to be transported to a port several kilometers away, PT Newmont Nusa Tenggara constructed an overland conveyor system that was nearly 7km long, requiring transmission lines up to 15km in length. When you consider that geckos have specialized toe pads that allow them to climb smooth vertical surfaces, you can see how a simple gecko can breach power transmission poles and trip a load. This load variation causes instability in the generators when operating at maximum load.

Compounding the problem was the difficulty in determining how much load had to be shed because the load variations were not consistent. Had this information been easier to obtain, power engineers would have been able to shut down lower priority power usage and maintain power to the three constant loads, which ran two mills and the overland conveyor. When there was a trip on one of the three constant loads, the company would lose process time costing upwards of US$300,000 per incident.

Solution: ETAP ILS

PT Newmont Nusa Tenggara needed a solution that would not only determine how much load needed to be shed, but would also make recommendations on the loads to be shed based on user-defined priorities. The answer for PT Newmont Nusa Tenggara was ETAP ILS (Intelligent Load Shedding).

ETAP ILS uses advanced monitoring and load trending to provide optimal load shedding for demand-side management and response, mechanical disturbances, and electrical faults. ETAP ILS provides much faster execution of load shedding, unlike conventional systems, even further reducing load relief requirements.

For example, the backbone of the entire process is the facility’s SAG mills, which require as much as 12,000 HP to operate. If these machines are shed, it typically takes 24 hours to bring them back into operation. ETAP ILS monitors the entire system collectively and knows the status of every individual load and the amount of loading. ETAP ILS uses this knowledge to reprioritize the load shedding list dynamically, ensuring that all critical loads are being preserved.

Another reason PT Newmont Nusa Tenggara selected ETAP ILS was its ability to scan the system for signs of potential disturbances. For example, if there was a trip on the pulverizer that crushes the coal for the steam generator, the coal feed into the combustion chamber would be reduced, resulting in a drop of electrical output. ETAP ILS does not wait for the system to reach that stage and instantaneously knows how much load shedding is required to prevent mechanical stress on generators and the rest of the system.

The ETAP ILS system was put to the test in April 2006 when an event triggered the shutdown of several of the operation’s turbines. The shutdown amounted to 35 MW of generation dropped. Prior to the installation of ETAP ILS, the same circumstances would have prompted the system to shed over 50 MW of power, which would have brought the operation to a temporary stop. But ETAP ILS recognized the problem and shed 39 MW based on the current customer preferences, and operations remained stable, much to the satisfaction of PT Newmont senior executives.

Benefits

In the first year of operation, PT Newmont Nusa Tenggara realized such benefits as:

Optimized load preservation – The mine’s power engineers can now reprioritize the load shedding list dynamically ensuring that all critical loads are preserved under both foreseen or unforeseen circumstances, with an estimated savings in the hundreds of thousands of dollars.

Elimination of unnecessary load shedding – ETAP ILS determines exactly how much load needs to be shed and what combination of loads would help it maintain system stability, resulting in load shedding less than 80ms after the initiation of the disturbance.

Reduction of spinning reserve requirements – With conventional systems, the speed and amount of load being shed can’t be controlled, requiring a spinning reserve. With ETAP ILS, the demand for a spinning reserve is reduced tremendously, resulting in extensive cost reductions in maintenance and fuel. In fact, the savings in the first year alone exceeded the cost of purchasing ETAP ILS.

Operator alerts for marginal operating conditions – If an overload condition coincides with peak demand, ETAP ILS Alerter notifies power engineers about potential peak charges. If the condition is not acknowledged and corrected within a defined time period, ETAP ILS initiates load shedding automatically.

Offline test and validation of load shedding response – Applying ETAP ILS gave PT Newmont Nusa Tenggara the flexibility to test various scenarios beforehand, exploring many possible disturbances as the program developed and selected the optimal load shedding configuration for their situation.