In the pursuit of optimizing electrical equipment, Process Industry operators (oil & gas, Petrochem, chemicals, mining, minerals and metals, water), along with Engineering, Procurement and Construction (EPC) contractors, are paying closer attention to the benefits of low voltage (LV) selection. One of the critical decisions is finding the optimal voltage level, which influences the cost, footprint, weight, efficiency, and carbon emissions of the equipment, extending its impact to the size and cost of substations or e-houses.
A lesser-known fact, but equally significant, is that voltage level choice also affects the power system’s efficiency and carbon footprint. This makes it vital to select the optimal voltage according to the application’s characteristics. One such strategic choice includes the consideration of a higher level such as 690V over the traditional 400V. This decision influences various aspects, from LV components like switchboards, circuit breakers, and contactors, to medium voltage (MV)/LV transformers and induction motors.
The transition from 400V to 690V voltage levels
For greenfield projects, the usage of 690V presents an opportunity to supply motors up to 350kW in LV, as opposed to having these motors supplied at MV, offering extensive savings not only for the motors but also for their Controlgear. Previously, the common practice involved managing motors below 200-250kW at 400V and employing MV for higher ratings. However, the advent of high-performance solutions based on Molded Case Circuit Breakers (MCCB) and contactor combinations have made it possible to manage power up to 335-350kW at 690V.
Interestingly, switching to 690V from 400V does not significantly impact the cost, but it allows for a reduction in the cross-section of cables and/or cable losses. This is particularly true for motors below 5.5kW where cables are sized based on let-through energy (I²t). Here, the savings will be primarily on power losses.
The role of circuit breakers and digitization in efficiency and sustainability
But it’s not just about voltage levels. The transition to breakers over fuses also holds advantages. Circuit breakers offer features such as health and status monitoring, power systems monitoring, advanced protection, and alarm response, enabling operators to employ smaller switchboards while ensuring superior protection levels.
Meanwhile, savings from MV motors supplied at 690V instead of MV (up to 350kW) will come from upstream MV switchgears requiring fewer feeders, resulting in a smaller footprint. These LV motors contribute less to MV short-circuit current than similar motors supplied directly at MV. LV switchboard size will slightly increase, but this is curtailed by the latest generation of Air Circuit Breakers (ACBs), MCCB, and 690V contactors for motor starters and feeders.
The switch to 690V also positively affects the project’s carbon footprint. During the construction phase, using 690V improves the efficiency of switchboards, motors, and cables. Distribution transformers might be larger when supplying large motors, but during operation, the superior efficiency of LV motors as compared to MV motors leads to an improved carbon emissions profile.
There’s also a broader trend toward digitization in process industry maintenance. Capabilities like accurate aging assessment of main devices and event logging, coupled with the use of ACBs with integrated control units, offer footprint and cost savings due to extended protection features and IEC 61850 capability. This ensures more efficient operation and maintenance, demonstrating how digital trends deliver tangible benefits.
The careful selection of low-voltage levels can yield sizeable benefits in cost, efficiency, and sustainability. Therefore, it is important to thoroughly study the impacts of shifting to 690V, including motors up to 350 kW supplied at LV for each project to find the optimal voltage level.
You can dive deeper into the voltage selection and the practice of moving motors from MV to LV through the white paper, “Best Practices for Designing Low-Voltage Switchgear to Reduce Size, Costs, and CO2 Footprint“.