By Dr. Brian Nel, CEO DBCon Global
There is a widespread misconception in the mining industry regarding Power Factor Correction (PFC). Most Financial Managers and even some Electrical Engineers believe that the only reason to install PFC equipment is to avoid the “Maximum Demand” penalty on the Eskom or utility bill.
While it is true that utilities charge penalties for poor power factor, this view overlooks the massive internal cost of running an inefficient network.
For remote mining operations (like the Bissa and Lefa sites we have analyzed), the external connection charge is often not the primary concern. The real problem is internal efficiency.
Low power factor is an invisible thief. It increases the current flowing through your internal network, overheats your switchgear, increases voltage drops, and forces you to install oversized transformers and cables just to keep the machinery running.
At DBCon Global, we look at the physics of the loss. If you are ignoring power factor because “we generate our own power” or “the penalty isn’t that high”, you are likely burning millions in diesel and replaced components.
The Physics of Loss: Why Amps Are Rising
To understand the cost, we must look at the relationship between Current, Power, and Voltage.
When your power factor is low, your system has to draw significantly more current to deliver the same amount of real working power (kW).
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This extra current does no useful work. It just shuttles back and forth between the generator and the inductive load. However, as it travels through your cables, it creates heat. These are known as I²R losses (Current squared times Resistance).
We analyzed the data for a typical mining installation to quantify this damage. The results are alarming.
The Multiplier Effect Consider a standard circuit designed for unity power factor (1.0). If the power factor drops to 0.6, the losses in that circuit do not just double. They nearly triple.
- At PF 1.0: The current is 100%. The losses are baseline.
- At PF 0.7: The current rises to 142%. The losses increase by 104%.
- At PF 0.6: The current rises to 166%. The losses increase by 177%.
This means that for every hour you run a machine at 0.6 PF, you are dumping nearly three times the amount of wasted energy into your cables compared to a healthy system.
Case Study: The “Overloaded” Rectifier
To make this practical, let us look at a specific case study we encountered involving three 24 kW rectifier units feeding rotating equipment.
The Symptom The mine reported that the circuit breakers feeding these units were overheating. There were signs of thermal stress on the busbars. The engineering team assumed the load had increased and were planning a capital project to upgrade the entire distribution board to handle the “new” load.
The Investigation We measured the circuit.
- Design Spec: The unit efficiency at full load was 85% with a power factor of 0.85. The expected phase current was 144 Amps.
- Actual Reading: The current was measured at 204 Amps.
This was a massive discrepancy. The current was 60 Amps higher than the nameplate rating. This 40% overload was cooking the switchgear.
The Root Cause Further investigation revealed that the Power Factor was sitting at 0.6. Why? Because the internal Power Factor Correction capacitors inside the units had been disconnected. The maintenance staff reported that capacitors had caught fire in the past (likely due to resonance or heat), so they simply disconnected them to “stop the problem”.
The Solution We did not upgrade the distribution board. We simply restored the capacitor banks (with a modification to prevent the original fire risk). The current dropped back to 144 Amps. The heat disappeared. The breaker stopped tripping.
This case proves a critical point: The board was not overloaded. The efficiency was just poor. The mine almost spent capital on a board upgrade they did not need.
The Double Penalty: Air Conditioning Load
There is a secondary cost to low power factor that almost every engineer misses: HVAC load.
All those I²R losses in the cables and transformers are dissipated as heat. If your substation or motor control centre (MCC) is inside an air-conditioned room, you are paying a double penalty.
- You pay for the electricity to generate the heat (losses).
- You pay for the electricity to run the air conditioner to remove that heat.
In our calculations, assuming an HVAC Coefficient of Performance (COP) of 2, a drop in power factor from 1.0 to 0.7 results in a significant increase in the total building load just to manage the temperature.
Strategic Decision: Centralised vs. Distributed PFC
Knowing you have a problem is step one. Step two is deciding where to fix it. There are two main strategies for placing Power Factor Correction (PFC) equipment.
1. Centralised PFC (At the Powerhouse or Main Sub) This involves installing large automatic capacitor banks at the point of supply.
- Pros: Good for sites with many different loads switching in and out (like Bissa and Lefa). The bank automatically steps in and out to maintain a target PF.
- Cons: It corrects the penalty from the utility, but it does not fix the I²R losses in the cables running down to the plant. The high current still travels all the way from the load to the powerhouse.
2. Distributed PFC (At the Load) This involves installing capacitors directly at the motor or MCC.
- Pros: This is the engineering solution. It reduces the current flowing through the entire length of the cable back to the source. It reduces voltage drop and cable heating.
- Cons: It can be more expensive to maintain many small units vs one big unit.
For installations with long cable runs (common in open-cast mining), Distributed PFC is often the only way to solve voltage regulation issues.
The Voltage Drop Danger
Referring back to our data tables, low power factor has a direct impact on voltage regulation. At 0.7 PF, the voltage drop in a cable increases by roughly 100% compared to unity.
If you have a motor at the end of a long cable run, this voltage drop is critical.
- Induction Motors: If the voltage drops, the motor draws more current to maintain torque. This heats up the motor windings and can lead to premature failure.
- Control Systems: Voltage dips can cause PLCs and relays to drop out, causing nuisance plant trips.
Conclusion: It Comes Down to Training
The rectifier case study highlights a massive gap in technical maturity. The maintenance team disconnected the capacitors because they viewed them as a “nuisance” rather than a critical component. They did not understand that disconnecting them would overload the main breaker.
This is why DBCon Global focuses on Technical Maturity Assessments. You can buy the best capacitors in the world, but if your electricians disconnect them the moment a fuse blows, you are wasting your money.
We help mines optimise their networks not just to save utility bills, but to save the infrastructure itself.
Is your switchgear running hot for no apparent reason? Contact DBCon Global for a full Power Factor and Harmonic Audit.
