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(Firewall) What’s Inside Uninterruptible Power Supplies

By Percy Kinney

 Rectifier : this part of the UPS converts the incoming alternating current (ac) supply to direct current (dc) and can provide charging current for the battery and also the supply requirements for the inverter.

Charger : in a number of UPS systems due to the nature of their design a separate battery charger is used, this is more common on sub 60kVA UPS systems and is very common on small sub 3kVA units.

Battery : this is the power storage section and is kept charged either by the rectifier or a separate charger. Its storage capacity is generally displayed, as AH (ampere hour), which is the number of amperes of current that the battery can supply for an hour. There will be a number of limiting factors depending upon the application, typically if the design calls for a short autonomy (length of time the battery will support its load for), the batteries can be discharged to a lower level, in the case of emergency lighting where there is a requirement for a long autonomy the battery will not be allowed to discharge so far. These conditions help to allow the maximum design life of the battery to be achieved.

Inverter : this section of the Uninterruptible power supply provides an ac output to the load which is in phase with the input mains supply. Due to the number of conversions (ac to dc to ac) and the filtering involved it can be termed as a ‘clean supply’.

Static Switch : this circuit can be as simple as a relay or more commonly using thyristors, its purpose is to switch the load between the inverter and the utility mains supply. As has been previously mentioned the output of the inverter is in phase with the utility mains supply so that any switching between the two will be virtually seamless. This arrangement ensures that if the inverter experiences an overload situation, due to its extremely fast over-current detection circuits it will transfer the load to the more resilient mains supply. A typical example would be when a server rack is switched on, the inrush current, depending upon the size of your uninterruptible power supplies , could cause the transfer to the utility mains supply, and once switched on the load will transfer back to the inverter providing the inverter has sufficient capacity to support the load. Also a fault on the inverter will cause the load to be transferred, again virtually seamlessly; it would be unusual for any loss of load to occur during these conditions.

Maintenance Bypass : more typically found in UPS systems with a capacity of 6kVA or greater. This arrangement allows the load to be transferred under controlled conditions to the utility mains and the UPS to be shut down without loss. Normally carried out for routine UPS maintenance or UPS repair.

External Maintenance Bypass : the installation of an external maintenance bypass can allow the UPS to be removed/replaced without interruption to the load, also, if the actual maintenance bypass is fed from a separate supply it can allow load testing in the case of a major UPS repair and/or checking of the autonomy under simulated load conditions while the site load is being supported by the external maintenance bypass circuit. This is often used when allowing the UPS System to be bypassed onto standby diesel generator power. Alternatively, when batteries are replaced and removed, it can only be done by placing the uniterruptible power supply into external bypass.

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Transmitting Voice over A T1 Connection

By Moses Holder

 T1 connections are basically high speed data and voice connections. When you subscribe for a T1 connection the service provider lays optic fiber cables at your premises and you get a dedicated connection to the server of the internet service provider.

A conventional telephone line converts the voice of the speaker into analog signals which are transported through copper wires and get reconverted into sound at the receiver’s end. This has been the only mode of voice communication through the years and by itself is still a reasonably efficient means of communication.

But with globalization and liberalization being the driving force of most of the economies of the world and with phenomenally improved transportation facilities, business has become a multinational phenomenon and physical distances are no longer an insurmountable barrier.

With the spread of the business being far and wide, the need for rapid, uninterrupted and noise free communication has become the order of the day. The volume of communication has increased manifold and so is the need for a hyper efficient and reliable medium through which such communication can be done.

T1 service is another way making your voice communication more reliable and hassle free. The digital circuitry uses channels to carry voice and data. The capacity of such channels is far more than the conventional phone lines. In one such channel twenty four separate calls can be made! That is to say, if you take one T1 connection, you are actually taking twenty four telephone lines.

Instead of converting your voice in to analog signals, it is converted into digital signals and then transmitted over optic fiber cables. This lends extreme clarity to the spoken words - the receiver can hear exactly what is spoken without the accompanying noise or hum which is common in conventional phone lines.

Since the optic fiber cables carry any sort of digitized data, a T1 connection can be used for both the purposes. So, popularly T1 connections are referred to either as voice T1 or data T1.

The beauty of T1 lies in its flexibility. In conventional phones, lines are assigned to users. But in this sort of voice communication it is not so. Suppose you are in desperate need of some business discussion on the phone. You find that your boss’s phone is free but you can’t go in his cabin and use that instrument since he is busy in a meeting. What do you do? Well, twiddle your thumbs and perspire in anxiety!

But if your office has a T1 connection, you can call from any phone within the office and if at least one channel is free at that point of time; you would be able to communicate.

This flexibility allows maximum and most efficient utilization of a T1 service. To put matters in perspective, a twenty four channel T1 connection can serve at least one hundred members of an office without difficulty. Since this connection can utilized in a much better way, it is advisable to give this option a serious thought.

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Sunday, May 30th, 2010 at 2:30 am and is filed under internet. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.