Power system voltage levels: making the right choices

Unsuitable voltage levels could:

• cause system operation constraints.
• have significant financial consequences on the project.
• limit future development of an industrial or mining site.
• affect the safety of operations personnel.

Choosing the optimal voltage level for the main power system, as well as the secondary and tertiary systems, needs to be based on a comprehensive view of the site’s electrical installations and must reflect both technical and financial aspects. The following should be considered:

• the quantity and type of loads to feed
• the site layout and load location
• expansion needs and new load additions
• voltage levels standardized in the industry and in the region where the system is located
• availability, space requirements and cost of electrical equipment

The basic principle

For the same power, a higher voltage level reduces a system’s rated current and fault current levels. By lowering the rated current, it is possible to reduce the size or number of cables, thereby reducing costs. However, higher voltage levels require equipment with greater insulation levels, which may also affect purchase costs and size (footprint).

When a significant amount of power needs to be transmitted over a long distance, higher voltage levels are selected, which is usually the case for the main power system of an industrial site or a utility’s transmission system.

Performance issue

Voltage levels must be well suited to system use. For example, service loads like lighting, heating and small motor loads are typically powered by voltages below 1,000 volts, while large motors are normally connected to 4,160 V, 7,200 V or 13,800 V systems.

Optimal voltage selection ensures good voltage regulation in both steady state and transient, especially when starting a motor. Powering a sizable load block far from the main substation or power plant requires special care. This is especially true if the load block is supplied by an overhead line, because it has a higher impedance than a power cable, which negatively impacts voltage regulation performance.

Selecting standard equipment

Power systems must be designed based on voltage, current rating and fault current values according to recognized industry standards and major equipment manufacturers. Using non-standard equipment leads to higher costs and longer delivery times. In the event of a failure, it will be more difficult to correct the issue quickly, thereby affecting site production.

Energy efficiency

System losses usually decrease with higher voltage levels, directly impacting the site’s energy efficiency. However, multiple transformation levels should be avoided, as they have a negative impact on a system’s energy efficiency and performance and incur additional investments. As a result, choosing higher voltages is not always the best solution.

Ensuring personnel and equipment safety

To promote adequate performance while maintaining safety, the fault level must be well suited to the system’s voltage level. Often enough, compromises must be made on system performance to increase personnel safety. Lowering the fault current generally reduces the incident energy, thereby improving personnel safety and minimizing equipment damage. However, fault levels that are too low can cause voltage regulation issues. They may also affect the operating performance and speed of overcurrent protection elements.

The level of incident energy from an arc is directly related to the value of the fault current and the approach distance. Therefore, installations at 1,000 volts or less are generally more hazardous than those at medium voltage in terms of arc flash hazards.

Rely on BBA’s expertise

For over 40 years, BBA experts have been designing industrial and mining power systems to the most rigorous standards, taking into account all applicable standards and incorporating the latest technology.