Industrial mining operations are heavily dependent on the strength of their motor protection strategy. In washing plants, conveyors feed crushers, which in turn feed screens and feeders. When mis-coordination between relays, earth-leakage (EL) devices, or PLC logic occurs, the result is damaged mining equipment, avoidable downtime, lost tonnage, and scrambled troubleshooting.
Unplanned downtime in mining is notoriously expensive; estimates place the average cost per incident at USD 180,000 (≈ R3–4 million depending on exchange rate). Globally, unplanned downtime is reported to cost mining operations in the tens of billions annually (e.g. $15 billion cited for the sector). The pressure is real: a single conveyor failure at Rio Tinto’s Kennecott copper mine in 1Q 2023 caused a 36 % drop in mined copper throughput.
Given those stakes, engineers and specifiers cannot afford to treat relay selection as an afterthought. This article helps you make application-driven decisions quickly, with logic tied to real commissioning conditions, and points you to the Mining Relay Comparison Matrix for deeper evaluation.
Conveyors, Essential Protection Under Long Runs & VFDs
Conveyors in mining are in continuous demand. Many systems run over kilometers, with multiple drives, long cable runs, and frequent speed changes via VFDs. Failure or nuisance trips in this link ripple out to multiple downstream units. In fact, failure rates for conveyor systems are among the highest of any asset class in mines.
Key Protection Requirements
- Start supervision & locked-rotor detection
Conveyor belt jam, sudden increase in mechanical load torque or misalignment must register before catastrophic damage. Locked-rotor detection helps catch these early. - Underload/jam detection
If material flow is lost (belt tearing, blockages, broken coupling, loss of load), the relay should detect that and alarm or trip appropriately. - Earth Leakage coordination with VFDs and cable runs
EL relays are notoriously sensitive when placed on VFD-fed motors and long cables. Without careful coordination, harmonics and leakage currents can cause nuisance trips. - EL zoning & delay calibration
Segment EL zones per conveyor group and apply indicative trip delays in line with mine safety philosophy. Always verify with commissioning documents (as we show in the micro-case below).
Crushers, Managing High Inertia, Thermal Stress & PQ Issues
Crusher motors represent some of the most demanding starts in a plant. The rotational inertia is high; the load changes are drastic. Misconfigured protection exacerbates risk to rotors, bearings, couplings, and downstream drive gearboxes.
What Protection Needs to Deliver
- Accurate thermal modelling
Unrealistic thermal curves will lead to either a premature trip or insufficient protection. The relay must match the motor datasheet parameters and site testing data. - Stall logic & indicative windows
Too narrow a stall timer and the relay will trip even on beginning starts; too broad, and damage might precede detection. The window must match observed start profiles, including ore hardness and feed conditions. - Phase loss and phase unbalance detection
A single-phase fault or unbalance can lead to localized heating, vibration, and inefficiency. - Power quality (PQ) monitoring/trending
Voltage sags, ripple, or supply anomalies can look like faults. A feeder-level PQ insight helps isolate supply issues rather than relay fault.
Recommended Products:
- MA Series – proven for high-demand motor protection, including start supervision, unbalance, and stall logic.
- KD Series – adds feeder PQ trending and diagnostics to dig into “mystery trips.”
- NewCode – appropriate where logic coordination between crushers and upstream conveyors or screens is complex and needs PLC-level interlocks.
Screens & Feeders, Handling Cyclic Loads & Logic Interlocks
Screens and feeders live in a world of constant change. Starts and stops are frequent, feed rates rise and fall, and wet or sticky material can cause short, uneven loading. If the relay treats every dip as a fault, you will see nuisance trips that look random but follow the load pattern.
Why this happens
- Cyclic loading makes current and power swing below normal levels for short periods.
- Transient conditions at start and stop can cross fixed underload thresholds.
- Rapid retries without rest time create heat and stress that trigger protection.
Protection Priorities
- Stable underload thresholds
Set thresholds that tolerate normal variation, while still catching belt tear or feed starvation. - Anti-cycling / start permissive logic
Prevent starting immediately after a stop; enforce minimum off/on timers and logic interlocks. - Interlock integration with PLC / upstream logic
Tie relay permissives to bin levels, upstream feed flows, or sensor inputs.
Recommended Products:
- NewCode – includes programmable logic, permissives, and networked control, ideal for cyclic feeders.
- NewFeed – lighter-duty relay for ancillary feeders/pumps needing straightforward protection.
- MA Series – an option if uniformity is desired across MCCs and loads are stable.
Turn Relays into Reliability: Start Your Selection
In mining, choosing motor protection relays by general spec rather than application is a shortcut to trouble. The relay itself rarely bears the cost of a relay-caused shutdown, but rather by lost production, cascading trips, and time-consuming root cause investigations. With proper application alignment:
- Conveyors gain dependable start supervision and EL coordination
- Crushers get thermal and stall protection matched to real load curves
- Screens and feeders benefit from logic blocking, anti-cycling, and forgiving thresholds
Start your decision process using the Mining Relay Comparison Guide. Use the Relay Selector Tool to narrow options based on application, MCC space, and network integration. Then drill into the MA Relay Deep Dive (or equivalent product datasheets) to confirm settings and intricacies.
Case Study, Coal Mine Washing Plant (Mpumalanga)
Context:
A new washing plant was recently commissioned at a coal operation in Mpumalanga. The plant demanded consistent, reliable motor protection and the ability to integrate into the existing SCADA/PLC infrastructure across several MCCs.
Challenges:
- Harsh environment (dust, temperature, humidity)
- Multiple conveyors, crushers, screens, and feeders
- High expectation for resilient communications and minimal nuisance trips
- Frequent load variability requires dynamic interlock logic
Solution:
The plant operator specified the NewCode Dual Ethernet Motor Protection Relay across all main lines, for these reasons:
- Dual Ethernet paths provided redundant, resilient communication linking local MCCs and the plant PLC.
- Built-in configurable logic blocks for anti-cycling, start permissions, permissive interlocks, and failover behavior.
- Straightforward parameter configuration and stability post-commissioning, per feedback from the MCC panel builder.
Outcome:
- Predictable, repeatable protection logic across multiple motor lines
- Clean integration with PLC, reducing custom logic work in SCADA
- Fewer “false trips” or relay-related mystery faults
- Improved uptime consistency across the wash circuit
Quote:
“The NewCode Dual Ethernet relay delivered reliable protection and easy PLC integration; the mine was satisfied with performance and uptime.”
MCC Panel Builder, Mpumalanga
Frequently Asked Questions (FAQs)
How much does a single minute or hour of downtime cost in mining?
Mining industry studies estimate that the cost of unplanned downtime averages USD 180,000 per incident (many incidents last hours). One report suggests mining, metals, and heavy industry lose 23 hours per month to equipment downtime, at rates up to $187,500/hour. In practice, a mis-trip or miscoordination that forces a line shutdown by even 15 minutes can jeopardize multiple downstream processes and cost tens of thousands in lost revenue and disruption.
Why do conveyor systems have among the highest failure or trip rates in mines?
Long cable runs, exposure to harsh environments, alignment issues, multiple drives, and heavy throughput stress all conspire. Conveyor failures are “among the highest of any asset type used in the industry,” and even a single conveyor fault can cause 30–40 % throughput loss downstream (as happened at Kennecott). Research into conveyor reliability shows that even when individual sections are statistically reliable, the serial nature of many belt segments compounds system failure probability.
How often do mines experience cyclic or nuisance trips on screens/feeders because of relay logic?
Cyclic loads inherently risk false trips; if protection logic has no hysteresis, minimum off/on timers, or interlocks, you’ll see chattering trips, especially in wet feed conditions. Because many plant control philosophies require logic blocking (e.g., “don’t start unless upstream belt is running”), relays that offer built-in permissives and logic (like NewCode) reduce complexity and improve stability over trying to replicate via PLC ladder logic.
What role does power quality (PQ) play in apparently “relay failures”?
PQ anomalies, voltage sags, harmonics, and phase unbalance can mimic overload or fault conditions. A relay trips, the motor protection is blamed, and yet the root cause is a supply disturbance. The addition of KD Series devices provides feeder-level PQ trending to help you differentiate between supply and motor/relay issues, and can reduce unnecessary replacements or misconfiguration.
What are typical retrofit constraints to watch for before selecting relays for plant upgrades?
- CT/VT ratio compatibility, many existing MCCs may have fixed CTs with limited ratio flexibility.
- Space and form factor, some relays are larger or require additional wiring/terminals.
- Network and comms capability, if PLC, SCADA, or redundant Ethernet is required, choosing relays with built-in dual paths or modular comms is essential (e.g., NewCode).
- Wiring/cable layout, ensure your cable paths and shielding support the selected EL and PQ devices without cross-coupling or induced leakage.
- Commissioning support availability, mis-set delays, or logic can nullify even robust relay hardware.
