Selecting an Uninterruptible Power Supply For Telecoms

Power protection technologies range from simple filters to solutions such as an Uninterruptible Power Supply. The Riello UPS range includes both line interactive and on-line systems, as well as a wide range of accessories including: battery extension packs, maintenance bypasses, remote monitoring software and interfaces.

PBX and Critical Voice over IP (VoIP) hardware – On-line UPS

An on-line UPS such as the Riello Dialog Plus or Dialog Dual is always recommended for the protection of a PBX. In an on-line UPS the inverter constantly powers the load. The inverter is powered when mains is present from a rectified mains supply. When the mains fails the inverter is kept running by the UPS battery.

As the inverter always powers the load the transfer to and from battery is without a break. The inverter is generating a pure sinewave supply that is clean and stable. It is free of any sags, brownouts, surges, spikes and transients and electrical noise that may be present on the incoming mains supply.

In addition an on-line UPS has a built-in automatic bypass. This features allows the UPS to transfer its load(s) to the mains supply should the UPS suffer an overload or component failure or other serious alarm condition.

The UPS is rated for continuous operation. It is therefore possible with an on-line UPS to increase the standard battery runtime from several minutes to over 7 hours using additional battery packs.

For added security, this type of UPS is normally installed with two additional accessories:

• An external maintenance bypass
• Remote UPS monitoring software

The maintenance bypass allows the UPS to be powered down for service without disruption to the load. The bypass has a manual switch (normally of the make-before-break – MBB – variety) that is used to transfer between the output of the UPS and the local mains supply. The Riello UPS MultiPass bypass also has an automatic transfer function. This is a further safety feature that protects the load if the UPS is accidentally disconnected.

19” rackmount versions of the MultiPass are available in addition a rackmount Dialog Plus-R range. The Dialog Dual is both floor standing and 19” rackmount depending on its orientation at installation.

KeyPhones – Line Interactive UPS

Line interactive systems such as the Dialog Active or Net Dialog comprise of a filter and/or Automatic Voltage Stabiliser (AVS). The filter cleans the incoming mains supply. It ‘clips' spikes and electrical noise down to preset levels, whilst the AVS boosts the mains voltage (sags and brownouts) or reduces it down (surges), to preset levels. The inverter is normally switched off and only powers up when the mains fails.

This type of UPS is therefore less sophisticated and has no automatic bypass. Failure can result in a crashed load. The UPS also has a small break (mS) in its output supply when the load is transferred between the inverter output and mains supply.

UPS manufacturers typically produce two types of inverter for their line interactive UPS – those that can supply a sinewave such as the Dialog Active and lower cost versions such as the Net Dialog that offer a square-wave supply. Some older switch mode power supplies and electronic processes may not be able to tolerate a square-wave supply and/or small break in electrical supply.

In addition the UPS does not regulate its output voltage and frequency because its inverter is normally switched off. In a line interactive UPS the output waveform tracks the input when mains is present and the AVS uses taps on its transformer to try to get its output voltage within around +10 to -15% of 230Vac. By comparison the output voltage of an on-line UPS will be within +/- 1%.

In terms of extended runtimes few line interactive UPS below 2kVA have the capability for external battery extension packs. The Dialog Active at 2kVA has a battery extension pack connector and can be used to support loads without over sizing up to several hours. The Net Dialog does not and must be oversized for the load if a longer runtime is required.

For 19” rackmount applications the Dialog Active-R range is available.

PC Based Voice Mail and Call Logging Applications – Line Interactive UPS

Where it is important to protect PC based applications and keep them running during a mains failure the options include:

• Power them using the same UPS powering the PBX – an on-line UPS.
• Power them using the same UPS powering the Keyphone – a line interactive UPS.
• Install a separate line interactive UPS to allow them to be safely powered down on mains failure.

The key point is to make a conscious decision whether you need these devices to be kept running for as long as you will power your PBX or keyphone system.

The Win Dialog Plus and Plug Dialog are two Riello UPS systems ideal for such applications where a short duration runtime is required in a compact desktop size box. Their size also means that they can sat on a shelf in a 19” rackmount cabinet.

Selecting an Uninterruptible Power Supply For Telecoms

PBX and Critical Voice over IP (VoIP) hardware – On-line UPS

KeyPhones – Line Interactive UPS

PC Based Voice Mail and Call Logging Applications – Line Interactive UPS

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