UPS: It Has to Be a Tall Order

There may be disagreements among AC- and DC-based UPS designers, but the

telecom and IT professionals are sure that they need solutions that can address physical space

constraints, fast-track construction realities, long critical system lead times,

and bus scalability. Traditionally, DC-based UPS systems have been the mainstay

of telcos to support their telecom switches. The enterprises protect their IT

infrastructure using AC-based UPS systems.

TECHNOLOGY

n Telecom Power

Systems: Both power plant and battery technologies have made rapid advances in

the recent past. Switch Mode Power Systems (SMPS) have become the norm, as have

Valve Regulated Lead acid (VRLA) batteries. Both these technologies make for a

far more compact power plant design, modular approach, and low maintenance.

Power plants are made up of rectifier modules, controllers, input AC

distribution, load distribution, and battery connection modules.

DC versus AC: Telecom equipment works with DC power. The voltage levels are

generally 48V or in a few cases 24V. A typical rectifier converts the AC utility

power to 48 V DC, charging a bank of batteries usually designed for two to eight

hours of critical protection from power outage. Since a battery bank is floated

across the DC bus, to provide battery backup, the working voltage is in reality

the float voltage of the battery. For VRLA batteries, the float voltage is

typically 2.25V/cell or 54V for a 48V system and 27V for a 24V system. The

positive in a 48V system is grounded, whereas in a 24V system, the negative is

grounded. This difference is due to the practice adopted by the pioneering

telecom equipment manufacturers, which is continuing today. In contrast to AC

systems, DC systems do not require converting the source power from AC/DC and

DC/AC.

Basic DC Technology: Three basic technologies comprise large DC power plants:

silicon-controlled rectifier (SCR) phase, controlled ferroresonant rectifiers,

and high-frequency switch-mode rectifiers. The SCR phase control and controlled

ferroresonant technologies have been around for more than three decades and are

widely accepted. Single-phase switch-mode rectifiers have been around since the

Eighties and have not been a problem.

n New Look Power

Plants: Though the need for power is constant, the way telecom carriers obtain

it is not. New types of power plants, with the intelligence and with additional

features that support the increased demand on telco operations and supporting

the data transported, are coming up. The key here is remote management. Critical

features in today’s power systems automate routine tasks, allowing the plant

to monitor self-health and even notify the provider to perform preventive action

maintenance. Tasks such as load sharing, generator control, and data logging are

becoming standard issues in many of today’s premier power systems.

Load Sharing: Today, rectifiers still are used in power systems to change

standard AC power into a flat DC voltage, making power plants less dangerous. In

today’s systems, the current that delivers power to network equipment and the

backup battery charge current is measured at actual value and is evenly divided

across the rectifiers installed in the system. Further, rectifiers can

communicate directly with each other in the event that a control unit is removed

for maintenance or for a software feature upgrade.

Generator control: Power systems can monitor the AC main input, which is

particularly helpful during power outages. By integrating the monitor system

with an auto-transfer switch, batteries and a generator set, the power system

can control fuel usage during failures.

Data Logging: Data collection is a valuable tool for service providers. The

intelligence built into power plants to support data logging can be used by

technicians to pinpoint potential system failures and proactively plan for

maintenance. Data logs can help determine the source of potential power problems

within an equipment site.

n Power for Data

Communication: When it comes to data communication equipment, one has a choice

of AC or DC powered systems. AC powered systems are used because of the

availability of uninterrupted AC power source, but in application where

reliability is the paramount consideration, as in data centers, DC powered

equipment are preferred.

Single Conversion: Under normal operating conditions, AC power from the

utility passes straight through the UPS to the critical load. A charger or ‘4-quadrant

converter’ converts AC power to DC to charge the battery. The inverter is used

to convert the DC power from the battery to create AC power to support the load

when the utility fails. Normally, the inverter is operating in the standby mode,

keeping the batteries charged. Should the utility power go out of specification,

the inverter powers the load, drawing energy from the battery. At any point in

time, power is only being converted once (AC to DC, or DC to AC).

The Line-Interactive UPS: It resembles the offline product, but inserts a

transformer or inductor in series between the utility power source and the load.

This inline inductor enables the UPS inverter to ‘interact’ with incoming

power and provide a measure of power conditioning to the load. This ‘buck-and-boost’

circuitry helps with high and low input voltage conditions.

Delta Conversion Topology: Delta conversion UPS consists of input stage

called the delta conversion stage or active filter made of delta inverter and

delta transformer. The delta transformer not only bucks or boost input voltage,

but also has many other functions such as input current control to reduce

harmonics, improvement of power factor, and control input power flow using power

transformation method. On the output side of Delta conversion UPS is a main

inverter which is similar to any inverter used in double conversion stage which

continuously monitors the output voltage and keeps it regulated to +/- 1 percent

of nominal voltage setting (380V/400V/415V). In case of the mains’ failure, it

supplies the 100 percent power to the load from battery without any break in the

output voltage waveform. The UPS has input mains’ static switch used to

isolate the UPS from mains under the battery operation to avoid any floating

voltage to appear at main. The UPS also has the internal bypass static switch to

transfer the load to mains in case of overload above specified limit or inverter

failure like any other double conversion UPS.

Double Conversion Topology: As the name indicates, this technology uses two

conversion stages–the rectifier at input and the inverter at out put. In

double conversion topology, input AC power is first converted to DC power using

a rectifier. This DC power is then converted to AC power using an inverter to

supply the load. This topology has been in use since last two decades by the

manufacturers. The double conversion online topology is believed to give 100

percent protection against the typical power problems.

DC POWER BUYING TIPS

DC POWER BUYING TIPS

Service Providers



n Reliability:

Look for reliability of the power system including batteries. Irrespective of

the technology, if the power system is not engineered correctly or lacks a high

degree of reliability, the telecom network can fail.

n Other

parameters: In addition to the important electrical parameters like efficiency,

power factor, input current harmonics, input voltage window, and EMI

specifications, the following characteristics need to be looked at.

High power density leading to compact footprint. Higher the footprint,

greater is the money spent on floor space for equipment rooms or shelters.

There are two sets of arguments. One, integrated input and output

distribution allows for ease of maintenance and also keeps the footprint low.

Two, having input and output distribution separate form UPS helps in

maintenance. Because during repair or maintenance of UPS, it is normally

transferred to manual bypass to keep the continuity to the critical load and

hence it is advisable to isolate UPS completely from any electrical circuit

during this repair or maintenance to ensure human safety as well as load safety.

n Buy as You

Grow: Easy expandability of modules, shelves, distribution and frames in live

condition help to keep the costs commensurate with the stage of growth of the

network.

n Digital

Controls: Look for digitally controlled modules with digital user interface.

This eliminates the need of manual adjustments by trial and error.

n Remote

monitoring and remote control: Centralized and remote monitoring systems help in

lowering the cost of operation and maintenance or those systems which have that

option, so that it is possible to upgrade when the need arises.

UPS buying tips

Enterprise



n Load: When

choosing a large UPS system, understand the need of electrical load and its

dynamic response. This has to be matched to the capacity of UPS. UPS vendors

specify VA (volts * amperes) and watts ratings to indicate the maximum amount of

power that it can supply to the loads. The wattage ratings listed on an

equipment like computer does not accurately represent the amount of power it

consumes. One should either measure actual power drawn for buying a compatible

UPS capacity or select a UPS with a VA rating that significantly exceeds

(approx. double) the wattage rating on the equipment.

However with the advent of new technology, there has been significant

improvement in power characteristics of most of servers in computer room. These

servers are equipped with Power Factor Corrected Switch Mode Power Supply (PFC

SMPS) which draw sine wave current with almost unity power factor.

n Hardware/Software:

Look at the optional hardware and software or other features that the vendor

provides before buying.

For example, if the UPS is supporting a group of servers, a communication

software with ability to close applications running on each server and to ensure

its safe shut down might be an essential feature.

n Standards’

Compliance: Look for standard compliance. To meet these standards defined by IEC,

UPSs are typically subjected to various tests.

n Compare Basic

Specs: There are five basic specifications. Compare this for different models.

• Maximum output load inrush current capacity (expressed in amps and time
  
  duration–more the better)
• Transient voltage surge suppression capability (expressed in joules–more
  
  the better)
• Output voltage tolerance and battery recharge time (faster is better). The
  
  output voltage tolerance is important than the response or recovery time,
  
  because the IT equipment have wide voltage range and till the time voltage
  
  is within the band of +/-5%, the recovery time does not matter
• Number of AC outlets/sockets (more is better).

n Battery Life:

Compare battery backup times at specified watts output (how long the UPS will

keep running following the mains power failure while supplying the rated watts

output).

n Efficiency:

When the UPS is operating from battery, the efficiency of the inverter

determines the battery backup. When the UPS is operating from the mains, power

is lost as heat inside the UPS.

n Cost: Besides

the cost of the product, implementation cost, room cost, operational cost

(electricity charges), and generator backup for prolonged power cuts, where

batteries cannot be stretched, need to be taken into account. Also look at the

cost of support and AMC.

n Vendor

Selection: Ask about the vendor’s warranty terms and conditions and on-site

service options. Battery replacement is quite expensive in comparison to the UPS

purchase cost. Opting for on-site service options provided by the UPS vendor

will free the IT staff.

UPS MARKET

With errant power supply system in the country and along with newer

technologies available in the UPS space, it is only natural that the future for

the UPS market is bright. It is now seen as an important IT investment status.

n Hot Sectors:

The telecom, banking and finance, and manufacturing are the key buyers of the

UPS systems. Large enterprises have been going in typically for the 5 kVA online

UPS. Telecom services segment is highly lucrative. Reliability is the catchword.

The exchanges of networks, the server farms of Internet Data Centers (IDCs), the

hubs of satellite service providers, the gateways of international long distance

operators, modem pools of ISPs … all need redundant and efficient power

supply.

n Size: In fiscal

2001-02, DC power systems, used mainly in telecom switches, generated sales of

Rs 450 crore. That is growing even more rapidly. BSNL has the biggest buyer,

contributing roughly 70 percent of sales. The private sector service providers,

which contribute the rest, are however expected to contribute to future growth

as a number of players roll-out their basic, cellular, and long distance

networks. Reliance, Tatas, and the fourth cellular operators have made

significant investments in 2002.

n Movers:

Traditionally, telecom power systems was the domain of big vendors like Lucent,

Ericsson, and Nortel. They used to either manufacture their own brands or bundle

others products with their mainline telecom equipment. However, things are

changing. Telecom equipment providers are concentrating only on core areas and

getting out of the rest. Lucent has sold its power division to Tyco; Ericsson,

Nortel, and Huawei to Emerson. Even the bundling practice is slowly going out of

practice as customers start preferring independent vendors for not only cutting

out the margin taken by the switch vendors but also for their focused expertise

in power systems.

International companies are now directly getting involved in the Indian

market, by buying out their Indian JV partners or expanding their small

operations into full-fledged ones. Tata Liebert is now Emerson; Invensys has

come out of its CG days; APC is spreading its wings into the telecom space.

n Service:

Another important trend coming to the forefront has been services. Players like

Tyco and Emerson are building services division not only to design and implement

the solutions, but also to maintain and mange them. There are discussions that

they would look at the entire power life cycles.

EXPERTS PANEL SS Bapat, vice-president, solutions, Emerson Network Power (India). Sambhaji Wagh, applications engineering manager (Asia), Singapore, APC.