3 Phase Power

3ph overview.
2012 After having problems with UPS & Gen set failure due to Neutral failure, did some investigation.
- Failure of Switch-over box.
Features
- double conversion technology - separates the input ac power from the output power
  - Less desirable design is off-line, line-interactive or delta
Important factor
- input power factor of the UPS
- Efficiency at <50% especially important if dual UPS used in data-center.
Installation factors to consider.
- UPS installation design - space cabling etc.
- Redundant configuration n+1
- Downstream earthing system: TN-S if transformer is in ownership and TT if it is not
- Neutral section equal or double to phases
- Different protection to UPS grid connection and by-pass connection
- Over voltage protections downstream and upstream UPS
- Disconnecting switch at UPS output to easy replacement
- Air conditioning system
UPS with input filters (especially with 0-pulse UPS) to minimize voltage

waveform distortion.

A separate isolation transformer to serve the UPS (making the UPS a separately derived system) will be useful in avoiding operational problems with the UPS, providing better quality power to the load, and preventing ground fault sensing problems.
External Maintenance Bypass Switch If your load is critical to you, you should always install an External Maintenance Bypass Switch, even though the UPS already has internal bypass switches. The EMBS lets you perform any maintenance on the UPS, or even remove and replace the UPS, without ever dropping the load. If your load is very critical, the EMBS is very important!

Switch box's / commutation and power transfer issues

Switch from mains power to generator in case of failure or testing.
commutation between the grid connection and the generator
Important neutral schemes
four-pole breaker and therefore, the neutral wire is also sectioned.
- During neutral switching spikes can be experienced, as neutral floats until connected to generator.
- Sollution is to use transformer isolation downstream of UPS, generating new independent neutral.
  - adding a transformer in the by pass (static and dynamic)
Transfer switches can cause problems in the following areas:
- Oversized neutral requirements
- Ground fault sensing and UPS input sensing problems
- Nuisance UPS input breaker tripping. (Caused if transfer switch to fast <0.5s and still voltage on circuits)
- Facility designers should be aware that oversized neutral capacity in a transfer switch is not currently commercially available, so transfer switches must be derated for non-linear loads if a neutral of significantly greater capacity than the phase conductors is needed. This is less of an issue in 3-pole transfer switches, since there is a solid neutral connection between the sources.
Makes
- TELYS
- NEXYS

BACS - Battery Analyze & Care System
- Some can retrofit on current system, add unit to each battery.
Alternate
- Flywheel DC storage system.
  - Riello Fly Wheel 215KW - spinning at 36,000 RPM

Standby Rating, Prime Power, Continuous Rating.
Things to check
- Sizing and selection
- Electrical factors
- Cooling
- Ventilation
- Fuel storage
- Noise
- Exhaust
- Starting systems
Three phase RMS sensing circuits - prevents pulsing, accurate load following.
alternator capacity is relatively inexpensive, this is not a significant burden to the first cost of the facility.
- Class H insulation provides additional high temperature resistance over Class F insulation systems.
When powering UPS loads, fast response is not a prime concern. UPS equipment is very tolerant of voltage and frequency excursions, but very intolerant of fast changes in these parameters. So, setting up the generator set in a typical emergency/standby fashion may not result in best overall system performance, especially when the UPS is the major load on the emergency/standby system.

* care should be taken to be sure that the UPS could perform properly given the quality of power that can be provided by the generator set used.

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