In an effort to provide cellular tower operators and others requiring longer term backup power systems with a quiet, reliable alternative, Kohler Power Systems has developed two new trailer-mounted generator sets. The Kohler 40KRC and 60KRC industrial gen-sets were officially unveiled in March at the CTIA Wireless Show in New Orleans, and are the first of a planned family of trailer-mortared gen-sets that will cover a range of 40 to 180 kW.

"We already have orders coming in from some of the leading cellular providers for these units because of the flexibility they provide," said Mark Repp, vice president of marketing for Kohler Power Systems, Kohler, Wis. "What makes them unique is they can be at one location, providing the same amount of back-up power as a permanently installed unit until the utility power source has been restored. Then, within hours, they're disconnected and transported to another location that needs power. It's truly power on demand."

Both of the new units incorporate Deere PowerTech diesel engines that meet the U.S. EPA's Tier 2 emissions standards. The engine packages include Donaldson air cleaners and Young Touchstone radiators. Kohler is one of the largest users of Deere engines for power generation and according to Richard R. Koehl, director, engineering and quality for Kohler Power Systems, the new Tier 2 engines "have a profile that's especially good for towables."

The engines drive Kohler's new Fast Response III alternators. Building upon the foundation of the Fast Response alternator that debuted in the late 1970s, the new alternators incorporate a new excitation system that Kohler said is powerful and cost-effective. An auxiliary stator winding that is independent of the main output winding and dedicated solely for field excitation, is key to the new alternator technology, Kohler said. It results in a significant power boost to the field and provides strong recovery during load transients or 250% sustained short-circuit current support for 10 seconds to clear downstream circuit breakers, according to the company.

The Fast Response III alternator also features an eight-position terminal block with links for simple voltage reconnection. Load leads may be lugged and bolted directly to the terminal block, eliminating the need for spliced cable connections and providing a much quicker power connection method, Kohler said.

A new and improved voltage regulator with +0.25% average regulation is standard on the new alternator. The encapsulated regulator has over-excitation shutdown, standard VAR/pf control capability, an optional droop kit for paralleling, and onboard diagnostic LEDs. The voltage regulator meets IEC standards for EMI fast transient and surge immunity, and has passed rigorous vibration and harsh environment tests.

Both the 40KRC and 60KRC gen-sets feature a threeway voltage selector switch for operation at 277/480 V three-phase, 120/208 V three-phase or 120/240 V single-phase. A voltage selection switch allows for easy and rapid change depending on specific site requirements, the company said. The units come standard with readily accessible and safe main output lugs for quick connection in the field.

Kohler has also gone to great efforts to reduce noise emissions in the new gen-sets. Most significantly, the Nelson critical grade silencer is positioned within the enclosure rather than externally. "Some of the other things you'll see" said Koehl, "is that we totally insulated everything including the exhaust chamber to reduce rattle, as well as gasketed all doors.

"Another key feature is the snorkel within the door frame which takes air from the bottom and vents it up through the top. That creates an ultra-quiet flow, because you're basically circulating the air within the chamber itself.

"We've also insulated between the skid and the trailer, which has also made it quieter. Just about everything in the whole package was insulated or sealed to reduce noise." The result is noise emissions of approximately 65 d(B)A, according to the company.

The gen-sets also include a 200 gal. polymer fuel tank that provides 59 hours of full-load run time for the 40 kW unit and 40 hours for the 60 kW set. "It's a base tank that's actually a new process tank that's positioned in a metalized containment basin," noted Koehl. "That way, we can get light weight and make sure we don't drip any fluids."

As an available option, the fuel tank can be equipped with an indicator that can send a signal over an annunciator or remote dial-up connection, remotely alerting operators to low fuel conditions. The company also plans to offer a smaller tank as an option on future models, Koehl said.

"Another feature is that this is a single-point lift trailer," Koehl added. "You can take this trailer and lift it by that point and it will stay perfectly balanced, with or without a flail load of fuel. It was engineered to provide the proper center of gravity so that if you're on a long-term site and you just want to make sure that it's not touchable by anybody, you can just lift it up with a crane and not worry about it tipping."