As our dependency on electricity continues to grow, so does the need to design larger backup generator systems. When considering a medium voltage generator system, the transition from low voltage to medium voltage is influenced by a mix of economic and system design considerations including cabling distance, bus capacity, fault current capacity, switchgear cost, genset cost, and utility integration configurations.
In medium voltage system designs, the backup generator voltage is often configured to match the system voltage such as 4160V or 15kV, however, this may not always be the right solution to meet project goals and budgets. This topic discusses the potential benefits of using step-up transformers with low voltage generators as an effective alternative for medium voltage systems.
Generator equipment costs can be a key determining factor in the decision to transition to a medium voltage system. Within the market, transitioning a 480V 2MW (megawatt) generator to a 15kV unit will likely add $100,000 to the overall cost, while making the same transition to a 4160V generator will add $40,000.
Another area of significant cost is the medium voltage metal-clad switchgear necessary for paralleling medium voltage generators or creating transfer pairs with the serving utility. This equipment with its associated vacuum breakers, protective relays, and instrument transformers typically costs $50,000 to $60,000 per section. When comparing to low voltage solutions, the transfer and paralleling equipment for medium voltage is generally twice the cost.
Considering these added generator system costs, many system designers look at implementing a step-up transformer configuration to achieve cost savings. Some designs might benefit from a combination low voltage / high voltage strategy. Instead of using medium voltage alternators and paralleling with medium voltage gear, it may be possible to configure a system in which the paralleling occurs on the low voltage side of step-up transformers, thus allowing the use of low voltage paralleling. This configuration could be implemented with single or multiple transformer configurations.
An effective alternative for a medium voltage application below 2 MW is to implement on-generator low voltage paralleling functionality terminating at the low voltage side of a step-up transformer. For medium voltage applications below 6-8 MW, using multiple step-up transformers with the medium voltage sides terminated together at the gear also creates an effective alternative.
Equipment & Parts Availability
Low voltage generator systems are generally more common and manufactured in larger volume than medium voltage generator systems. As such, low voltage generators could have shorter lead times and parts are often more readily available.
Ease of Service
Compared to low voltage generator systems, a medium voltage generator can be more challenging to service. Be sure any technician that works on a medium voltage system is qualified to do so. Accessing the medium voltage bus can be dangerous and will require specialized equipment and knowledge. When using step-up transformers and low voltage generators, routine maintenance and repairs can be performed on the low voltage side without the concern of specialized equipment or medium voltage qualifications.
If you have questions about designing a medium voltage system with low voltage generators and step-up transformers, our power experts are here to help.
To review more on this topic, see the complete white paper from Generac Industrial Power: Medium Voltage On-Site Generation Overview.
Clifford Power Systems, Inc. provides dependable generator equipment, service, and rental. We are solely focused on power generation and offer professional consultation to meet all your project needs. For additional information, contact us at any of our locations in Oklahoma, Texas, Missouri, Kansas, or Arkansas.