Mission Critical Facilities Newsletter

Improving Generator - UPS Compatibility Traditional Diesel Generator Design v.s. Piller Diesel Coupled Solution

Smarter Reliability examines Mission Critical operations through the lens of power quality monitoring to ensure reliability & profitability

Backup Generators for “mission critical” applications can provide a false sense of security. Hospitals, data centers, manufacturing, food storage/processing companies, among others depend on Backup Generators to provide “regulated” power in case of a utility outage. Harnessing power quality information through monitoring is critical to ensuring reliability. Most mission critical facilities incorporate Backup Generators in the “traditional manner”, which also includes Transfer Switches, Uninterruptable Power Supplies (UPS’s), Batteries, and Transformers. Piller’s Diesel Rotary UPS (DRUPS) solution on the other hand, integrates these components into one system.

Smarter Reliability by On Power Systems www.smarter-reliability.com www.onpower.com.

Traditional Diesel Generator Design The Traditional mission critical facility incorporates a properly sized Diesel Generator into the building’s electrical design via a “Transfer Switch”. The transfer switch will transition to Generator Power when there’s a Utility Outage event. This design further requires one or more UPS’s to provide continuous regulated power to the “Critical Switchboard”. The UPS’s condition the critical power supplied by the Electrical Utility or by the Backup Generator. The 10~15 second transition to generator power, due to the startup of the generators, during a utility outage event is conditioned via the UPS’s. The UPS’s maintain output power during the 10~15 sec transition by drawing from their external energy storage, typically a battery string(s). As discussed above, the Traditional design has four key components (Generator, Transfer Switch, UPS, Batteries), which need to work harmoniously for the system to operate as intended. Generator/UPS Compatibility Issues Event Details/Waveforms

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A-B V

16:43:12.225 10/02/2011 Thursday

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B-C V

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Event Details/Waveforms

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Transfer F rom Generator to Uti li ty

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Electrical Utili ty Power

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2) Another compatibility issue is the UPS inrush characteristic while on Generator power. Typically UPS’s will step in at timed stages to prevent any issues associated with the UPS startup. Therefore the Generator must also be sized for UPS startup.

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Start Of Transfer

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End Of Transfer

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Utility/Generator/Transfer Switch Synchronization Some mission critical facilities utilize a make-before-break (closed transition) transfer switch to try to minimize the impact when switching back to utility power. When the Transfer Switch is ready to transition back to utility power, it will wait until the generator voltage becomes in phase with the utility voltage. The voltage amplitude and voltage phase between the two sources must be comparable before the transition can occur (ideally they should be exactly the same). Any slight difference between the two sources during the transition can cause issues within the facility. Smarter Reliability by On Power Systems www.smarter-reliability.com www.onpower.com.

B-C Vrms (val)

C-A Vrms (val)

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0 Amps

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1) The Generator and UPS’s HAVE to be compatible! A static UPS utilizes a front end AC/DC converter. This converter draws non-linear current which will introducing current harmonics into the electrical system. The current harmonics will vary depending on the UPS manufacturer and the total number of UPS’s. The current harmonics are reflected back to the Generator (Source Power) which will in tern generator voltage harmonics. Depending on the severity of the voltage harmonics, the Generator may have issues regulating its output voltage. If the Generator can not regulate its output voltage the UPS will not synchronize to Generator and will operate on the batteries until depleted.

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Associated Current Inrush Due to Transfer

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400 300 200 100 0 A Irms (val) 00:17:38.20 18/04/2008 Friday

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B Ir ms (val)

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Piller Diesel Rotary UPS (DRUPS) “UBTD” & “UBTDE” The Piller “UBTD/E” direct diesel engine coupled solution incorporates everything required for a mission critical facility into one system. The core items that make up the Piller UBTDE are the Synchronous Motor/Generator (M/G), Diesel Engine, PowerBridge (Pb), and Coupling Choke. The Critical Switchboard is supplied continuous regulated power from the UPS Q6 output breaker. The M/G, Pb, and Coupling Choke provide continuous regulated power and effectively de-couple’s the critical load from the utility supply. Note – The critical supply is fed from the “generator” windings of the Synchronous Motor/Generator (M/G). Piller uses the PowerBridge (Pb) kinetic energy storage flywheel into the UBTDE design. The Pb provides the required ride-through in order for the diesel engine to start and mechanically connect to drive the M/G. It is important to note that the diesel engine is unloaded during startup. Therefore the diesel engine can reach its required speed faster then a traditional diesel generator. The Diesel Engine mechanically connects to the Synchronous M/G via a clutch. Thus, when there’s a utility outage event the Diesel Engine will start, unloaded, and connects to the spinning M/G via the clutch. Once the diesel engine is connected to the M/G via the clutch, the engine itself is mechanically driving the M/G to provide critical power through the generator windings of the M/G. As a secondary feature, the Diesel Engine can be oversized relatively to the M/G to provide “break” power to the “essential loads”. When the diesel engine is driving the M/G, the Motor windings of the M/G act as a generator. Therefore by over sizing the diesel engine, Piller is able to pull additional power from the motor windings for an essential feed, labeled Q17 output. Piller eliminates all possible compatibility issues that can occur between the generator and UPS by mechanically connecting the diesel engine to its M/G. The Harmonic and Inrush issues associated with the traditional design are not an issue with the Piller UBTD/E solution because the engine is mechanically connecting to an already spinning M/G. The Essential Switchboard is fed direct utility power under normal conditions. When there is a utility power failure, the essential switchboard will transition to the Q17 supply from the UBTDE. Piller’s integrated system reduces the overall component count compared to the Traditional design. Equally, Piller’s UBTD/E solution eliminates any compatibility issues as power’s constantly derived from the Synchronous M/G. Specifically, the Utility/Generator/Transfer Switch Synchronization issues that can occur with the traditional design are no longer an issue because the Piller UBTD/E design does not require a transfer switch because the diesel engine mechanically connects to the M/G. To view the interactive Piller UBTDE simulator please Click Here.

Smarter Reliability by On Power Systems www.smarter-reliability.com www.onpower.com.

Traditional Diesel Generator Design

Piller Diesel Rotary DRUPS Design

v.s.

Complete 100% Synchronization between Engine & M/G via the Steiber Clutch

Utility/Generator/Transfer Switch Synchronization Issues

Generator/UPS Compatibility Issues (Harmonic Interaction)

Smarter Reliability by On Power Systems www.smarter-reliability.com www.onpower.com.