To get started let’s define low voltage (LV) and medium voltage (MV). LV would be anything up to 1000 V. MV would be above 1000V up to a certain point (typically at the utility). In industry, LV is usually considered defined as anything up to 600 V and this is what you are most likely used to. In industry, MV is usually broken down into 1000-5000 and 5000-15,000. Standard voltages in the industry are 4160, 12,000 and 13,000 ranges.
Costs that should be considered during the evaluation phase are:
- Length of distribution runs should be considered
- Longer the cable the more copper and the more costs associated with the cable run
- At lower voltages, longer runs create problems such as voltage drop
- A 2% voltage drop at low voltage can be significant on the equipment.
Distribution equipment can vary greatly when it comes to costs. When moving to MV equipment the costs associated can be significantly higher. MV equipment also takes more physical room the overall weight is typically more. Sometimes lead times for equipment can also be impacted although that could be impacted on both LV and MV.
The physical area should be considered when looking at the selection of a system. Voltage drop could be significant in LV systems and could have a negative impact on motor loads in an industrial environment.
Loads are the second major consideration when looking at LV versus MV. Considering a 500 HP motor the overall load varies greatly from an LV to an MV system. On a 480V motor, the current draw would be around 550-600 amps versus a 4160V motor at the same rating would be in the 60-70-amp rating. That is significant and should go into the consideration of your upgrade or greenfield solution. Especially if you have to consider where the motor is located physically in relation to the distribution equipment that is supplying power.
Personnel knowledge of power distribution systems is important to consider. If MV knowledge is lacking, a solid place to begin training is NFPA70E. The risk factors are covered and could greatly improve the foundation of the teams involved in engaging with this equipment. The OEM’s are another great resource for training and can be very applicable as it is specific to the equipment that personnel is working on directly.
Considering the different aspects of costs, driven loads and overall knowledge of the personnel that will be supporting the distribution system should be vetted thoroughly when trying to design a distribution system. Many times, this is already established but for certain projects and applications going back to these fundamentals could help challenge your thinking and ultimately deliver the best system possible for your facility.