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GUEST COLUMN | RUNWAY ELECTRIFICATION SYSTEMS


Choosing the right runway electrification system: Key factors to consider


Selecting the correct runway electrification system is essential to ensure safety, efficiency and reliability in industrial settings, says Richard Warriner, VP at Span-Guard. Overlooking critical factors like temperature, duty cycle, power feed location and load calculations can lead to costly failures.


temperature variations. According to NFPA 70 NEC Article 610, load calculations must consider the operating temperature along a 9m (~30ft) span. Ground-level temperatures are typically lower than those near the ceiling of a manufacturing or processing facility. Ignoring this difference can result in inaccurate calculations and potential system issues.


T


Duty cycle Conductors provide power to equipment with a variety of load spectrum and duty cycles. Very few cranes will utilise a runway conductor branch over a 60% duty cycle. Even cranes used in refuse, magnet or bucket service only use the principal energy load (hoisting up) at most 50% of the time. Unless the current load of the “second largest motor or group of motors” approaches the running current of the main hoist, there is little chance the load remains above 40% of demand otherwise. As with any other application, a close analysis of your actual configuration and environment will pay dividends in the end.


Power feed location and number Consideration of the location of the power feed is critical and can result in a massive voltage drop


Impact temperature and duty cycle have on determining the proper conductor system


Number of cranes or hoists


2 3 4 5 6 7


38


Demand Factor 0.95


0.91 0.87 0.84 0.81 0.78


Winter 2024 | ochmagazine.com


emperature matters. One common oversight in runway electrification selection is failing to account for ambient


 For a single crane operating on its own conductor system, use the nameplate full-load ampere rating of the largest motor or group of motors for any single crane function, plus 50% of the nameplate full-load ampere rating of the next largest motor or group of motors.


Miscalculations can be costly.


problem. Contact the factory for proper feed point count and locations to avoid such problems. Since aluminium and steel systems have voltage drop losses 40–460% higher than copper and are very often ‘applied’ from a catalogue rather than engineered, losses are often overlooked.


Determining load Calculation of motor loads can be found in NEC 610.14(E). Below are two examples of sizing the system to your crane loads:


250Amp System (80.8mm2 ) 159.5kCM


Temp (C°/F°) 20°C / 68°F 30°C / 86°F 40°C / 104°F 50°C / 122°F 60°C / 140°F


520Amp System Duty cycle (%) (206.5mm2 ) 407.5kCM


Temp (C°/F°) 20°C / 68°F 30°C / 86°F 40°C / 104°F 50°C / 122°F 60°C / 140°F


100% 740 660 520 475 390


80% 816 783 710 620 579


60% 925 888 805 703 657


40%


1010 970 879 768 717


20%


1090 1046 948 828 774


100% 395 364 330 288 269


 For multiple cranes operating on the same conductor system, use the same method for a single crane for each crane. Add the results and multiply by the appropriate demand factor from Table 610.14(E) to determine the load (L).


Summary It is critical to incorporate ‘load’, ‘operating ambient temperature’ at the crane elevation and ‘duty cycle’ when calculating the correct conductors for each application. Examples of key indicators of an undersized runway electrification system failure include burn spots on the conductor, melted or heat deformed splice covers, coil failures, buzzing or chattering relays and contactors, hot brake coils, for example. 


RES 0.211/1,000m IMP 0.225/1,000m Duty cycle (%) 60%


80% 440 422 383 334 312


498 478 433 378 354


40% 552 530 480 420 392


20% 602 578 524 458 427


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