Low-harmonic UPSs target telco networks: Power company energy-saving efforts create problems for telcos

Driven by a desire to conserve energy, utility companies are using more non-linear equipment, which pulls current in sharp, irregular pulses. The downside of this approach is that as the non-linear load flows through a power plant's electrical system, it causes voltage distortion, or harmonics, which can lead to overheating or a malfunction.

Telcos using programmable microprocess controls and monitoring devices may be particularly susceptible to harmonic problems. But recently introduced uninterruptible power supplies (UPSs) with low harmonic distortion factors can help solve this growing problem, experts say.

"Twenty, twenty-five years ago, harmonics wasn't a problem," said Dick Reehl, an engineer with U S West who specializes in noise mitigation. "But now the electric utility customers are using equipment with non-linear loads, which causes [telephone carriers' networks] noise.' This noise can manifest itself as a "hum" on the telephone line, Reehl said.

The resulting complaints from phone consumers are a problem that local and long-distance carriers have in common, Reehl said. Generally, carriers can reduce the harmonic distortion if a few customers are affected. But if thousands complain, then the carrier and the nearest electric utility can argue about which company is responsible for spending the money to solve the problem, Reehl added.

"At one time the telcos and the utilities had an agreement that there would be a cooperative effort when it came to dealing with harmonics," Reehl said. "But that was back when we were all guaranteed a profit. And with increased competition out there, no one is guaranteed a profit anymore, so no one wants to spend any more money than they have to."

UPSs with low harmonic distortion may be one solution, Reehl said. Groupe SAEI of France offers a series of UPSs that helps cut harmonic feedback in power networks. The Tech System series is designed to ensure total protection in environments with severe interference from electrical noise, voltage/frequency variations and micro-power interruptions.

"All mission-critical applications and very sensitive loads need a perfect immunity from power supply network disturbances," said Simon Tran, managing assistant at Groupe SAEI. "The telecommunications industry is one of the most demanding of such protection because it is using very sensitive devices such as numeric control process."

Reehl agreed, saying such UPSs are used to backup generators at carrier computer centers that handle billing and other large operational databases.

However, the government needs to pass a law forcing the use of lower-harmonic power supply designs, according to Reehl. The United States does have a standard, known as IEEE 519, which limits both utility voltage and user current distortions, but regulations aren't in place to enforce the standard.

"Europe is way ahead of us on this," said Reehl. Groupe SAEI's UPSs are being used by France Telecom and tested by China Telecom engineers, according to officials.

"The U.S. needs to do something to limit utility customers putting harmonics out on the utility system or it's going to get so bad we'll have a lot of telephone plants with a lot of hum," Reehl said.

The 2000 A power bay and power distribution bay from Telecommunications Power Systems are designed for high-current -48 V telecommunications applications. An internal bus marries the power bay to the power distribution bay, so users don't need large cables to interconnect the units.

The power bay features hot-swappable switch mode modular rectifiers rated at -48 V at 65 A as well as hot-swappable rectifier shelves. In addition, users can configure the device for up to eight rectifier shelves to hold as many as 32 rectifiers. The 7 ft. cabinet is front-accessible.

The distribution bay features eight 600 A breakouts and circuit breaker panels that can accommodate 50 breakers from 1 to 100 A. The unit also contains a bus meter, an alarm panel and a system remote alarm panel.

Users can add more power bays and distribution bays via the internal bus at any time to create 4000 or 6000 A power systems.