Uninterruptible Power Systems in the Data Centre: Static, Rotary, and Generators
Joaquin Rodriguez Antibon
CEO/ General Manager, Data Centers M. | MBA,Sales Business Development, Organizational Change, General Management . Secure power, Thermal Management, security, global services at Data Centers , telco and Mission Critical
Introduction
A data centre requires a continuous, secure and reliable power supply to ensure the uninterrupted operation of servers and other critical equipment. Uninterruptible Power Systems (UPS) are essential for protecting against power supply interruptions, which can cause significant data loss and downtime. There are three main types of UPS used in data centres: static, rotary, and generators. This article provides a technical comparison of these systems, their suitable applications, and their ability to work simultaneously in the event of a power grid failure.
Static UPS
Description and Operation
Static UPS utilise electronic components to convert alternating current (AC) to direct current (DC) and then back to AC. This process is carried out by a rectifier and an inverter. Static UPS include batteries that store energy and provide continuous output when a power interruption occurs.
Advantages
Fast transfer time: Static UPS can switch to battery mode within milliseconds.
Lower maintenance: With no moving parts, they require less maintenance.
High efficiency: Modern units can achieve efficiencies above 95%.
Disadvantages
Limited battery life: Batteries need to be replaced periodically, 5 or 10 years.
Limited overload capacity: They do not handle prolonged overloads well.
Applications
Static UPS are suitable for critical loads requiring extremely short transfer times and where space and maintenance are important considerations. Examples include servers, network equipment, and sensitive electronic devices.
Maximum Power
Static UPS power ratings range from a few kilowatts (kW) to several megawatts (MW). For example, the Eaton 9395 model can supply up to 1100 kW. The Vertiv Liebert® EXL S1 up to1250 kW
Rotary UPS
Description and Operation
Rotary UPS, also known as dynamic UPS, use a generator coupled to a motor to store kinetic energy in a flywheel. In the event of a power failure, the flywheel continues to spin, generating electricity until a diesel generator can start or power is restored.
Advantages
Higher overload capacity: They can handle overloads better than static UPS.
Long lifespan: The use of robust mechanical components provides a long service life.
Reduced battery dependence: They use fewer batteries, reducing replacement and maintenance costs.
Disadvantages
Higher maintenance: They require regular maintenance of moving parts.
Space and weight: They are larger and heavier than static UPS.
Longer transfer time: The transfer time can be slightly longer compared to static UPS.
Applications
They are ideal for industrial loads and large data centres where overload capacity and long-term durability are crucial. They are also suitable for installations where space is not a major constraint.
Maximum Power
Rotary UPS can handle very high power, with some models capable of providing more than 20 MW. An example is the Piller UNIBLOCK UBT+ model, which can supply up to 3000 kW per unit.
Diesel or Gas Generators
Description and Operation
Diesel or gas generators provide backup power by burning fuel to generate electricity. They are activated during prolonged power outages, providing continuous power until the main power supply is restored. Generators can be integrated with UPS systems to provide seamless transition.
Advantages
High run time: They can operate for long periods if sufficient fuel is available.
Large power capacity: They can provide large amounts of power, suitable for data centres of any size.
Reliability: They are very reliable for providing backup power during prolonged emergencies.
Disadvantages
Startup time: They need time to start (usually a few seconds).
Emissions: They produce emissions, although gas models tend to be cleaner than diesel.
Maintenance and fuel supply: They require regular maintenance and a constant fuel supply.
Applications
They are ideal for providing long-term backup power in data centres and other critical facilities where prolonged power interruptions can be expected.
Maximum Power
Diesel or gas generators can supply very high power, with units ranging from a few kW to several MW. For example, the Caterpillar C175-20 diesel generator can supply up to 4000 kW.
Technical Comparison
Transfer Time
Static UPS: Generally less than 10 ms.
Rotary UPS: Can be 10 to 50 ms, depending on the specific design.
Diesel/Gas Generators: Generally 10 to 30 seconds to reach full capacity.
Maintenance
Static UPS: Lower due to the lack of moving parts.
Rotary UPS: Higher due to the moving parts.
Diesel/Gas Generators: Require regular maintenance and fuel management.
Efficiency
Static UPS: Can achieve more than 95%.
Rotary UPS: Generally in the 90-95% range.
Diesel/Gas Generators: Less efficient in terms of energy conversion compared to UPS, but effective for long-term supply.
Overload Capacity
Static UPS: Limited.
Rotary UPS: High overload capacity.
Diesel/Gas Generators: High overload capacity and long-term sustainability.
Simultaneous Use in Power Outage
It is possible to use all three types of UPS systems simultaneously to provide redundancy and enhance the resilience of the data centre. In a typical configuration, a static UPS could handle sensitive and critical loads with extremely fast transfer times, a rotary UPS could support industrial and higher energy consumption loads, and diesel or gas generators would provide long-term backup power in the event of a significant power interruption. This combination allows for smooth transition and continuous support, mitigating risks and ensuring the operability of the data centre.
Conclusion
The choice between a static UPS, a rotary UPS, and diesel or gas generators depends on several factors, including load requirements, overload capacity, available space, and maintenance considerations. Each type of system has its own advantages and disadvantages and can be used in conjunction to optimise continuous power supply in a data centre. Proper planning and implementation of a hybrid system can provide a robust solution for the critical power needs of a data centre.
References
Eaton. (n.d.). 9395 High Performance UPS.
Piller. (n.d.). UNIBLOCK UBT+.
Schneider Electric. (2021). Comparing Static and Rotary UPS Systems for Data Centres.
Vertiv. (2020). UPS System Comparison: Static vs. Rotary
Caterpillar. (n.d.). C175-20 Diesel Generator Sets.
Joaquín Rodríguez Antibón