UPS - Unintreruptible Power Sources

In telecom applications UPS covers the outage start moment until power is restored via diesel generator back-up or commercial power. The first class UPS also protects the equipment versus all mains variations, distorsions and transients.
Classification of UPS Performance by IEC 62040-3
FIRST, SECOND and THIRD CLASS UPS
VFI: the UPS ouput is Voltage and Frequency Independent of commercial power variations
VI: the UPS output is Dependent on supply frequency variations, but supply Voltage variations are Independent of commercial power;
VFD: the UPS output is Voltage and Frequency Dependent on supply commercial power variations

FIRST CLASS UPS – ON LINE DOUBLE CONVERSION VFI TECHNOLOGY

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APC Silcon Series (Delta)
The Ideal Green UPS
Online vs Delta
APC Silcon 60-80kW 400V UPS - User Guide
Chloride - 70-NET (from 10 to 60 kVA)
Chloride - 90-NET (from 60 to 800 kVA)
Chloride - Active Power Rack
Chloride - Power Lan Plus
Detailed information on: APC Equipment
Detailed information on: Sunlight Equipment