วิธีระบุ UPS สำหรับโรงงานที่ใช้เครื่องกำเนิดไฟฟ้าสำรอง

"The building has a generator" is not enough information to select a UPS. The generator may start and the transfer switch may close, yet the UPS can still reject the new source or return to battery when another load starts. A useful specification tells the generator, ATS and UPS suppliers what must work together, under which load, and how the site will prove it.

This is a specification checklist for an online UPS with generator compatibility. Our UPS and generator handover guide covers the battery bridge time; here the focus is the equipment data and tests needed for generator-backed operation.

Mark the utility, generator, ATS, UPS input, UPS bypass input, battery and protected load on one drawing. Show any other loads the generator must carry, especially motors or air conditioning that may start near the UPS transfer. If the rectifier and bypass have separate supplies, show both. The accompanying diagram is conceptual; confirm the actual feeds on the site's one-line drawing. A phrase such as “generator feeds UPS" hides too much.

The outage duty needs a plain answer. One site may only need the UPS to hold controls while other plant loads restart; another may need the full protected load running throughout generator operation. State which duty applies, and what should happen if the generator fails or its output becomes unacceptable. Record measured running kW and kVA, short peaks, and planned growth. Our guide to rated, actual and peak UPS load power explains why these figures should not be collapsed into one kVA number.

The ATS decides when to connect the alternate source. The UPS makes a separate decision about its input. The submittal should compare the UPS model's permitted voltage and frequency ranges with the generator's steady and transient performance at the UPS terminals. It should also say when the rectifier returns from battery and how its input current ramps up.

Check bypass separately. A double conversion UPS system may keep the inverter supplying the load after its rectifier accepts generator power, while its static bypass remains out of tolerance or out of synchronization. That matters if the UPS must transfer to bypass during an overload or fault. State whether bypass must remain available on generator. If it must, ask the UPS supplier for that model's voltage, frequency and synchronization limits.

Some UPS models have a generator input or sensitivity setting; others do not. Record the proposed setting and its effect on input acceptance, battery use and bypass behavior. Do not make the acceptance window wider merely to clear an alarm without checking the protected equipment and the UPS manufacturer's limits.

The generator does not see only the protected output load. It sees UPS conversion losses, the rectifier's input behavior and, after a discharge, battery charging. Other equipment on the same generator adds its own running demand and load steps. Cummins' generator application manual specifically treats UPS input characteristics, charging and harmonic effects as part of generator sizing; a universal generator-to-UPS kVA ratio cannot replace a model-based review.

Ask the UPS supplier for input kW and kVA, power factor and current distortion at the planned load. Also record maximum input current, charger demand and rectifier walk-in—the rate at which input current returns after transfer. Ask whether charging current can be limited on generator, and what that does to recovery before a second outage. A large external battery bank can lengthen runtime while also increasing the energy that needs to be replaced; our guide to UPS battery charging modes and recharge time covers that question.

The generator supplier can then study the whole facility: alternator and engine ratings, expected voltage and frequency excursions, nonlinear loads, and the order in which loads connect. Harmonic filters and power-factor behavior also need attention when the chosen UPS has them. These are design inputs, not reasons to add an arbitrary margin to the generator nameplate.

One troublesome sequence starts after a successful ATS transfer. The rectifier ramps in and charging resumes; then an air-conditioning compressor starts on the same generator. If voltage or frequency moves outside the UPS input window, the battery may discharge again even though the generator never stopped. This is the kind of sequence a specification should expose before purchase.

The sequence matters most when loads reconnect together. List the largest coincident steps and whether they can be staggered. State what the UPS should do on a rejected generator source, a second ATS transfer, a low-frequency alarm and a return to utility. The guide to sizing UPS battery runtime from a real load can then be used for the agreed battery duty, including any additional reserve the project requires.

For an industrial online UPS project, have the generator and UPS suppliers review the same drawing and load schedule. “100 kVA UPS on a 200 kVA generator" is a pair of catalogue ratings. It does not describe the load steps, the charger's input demand or the UPS's response to the generator waveform.

At commissioning, test with the intended protected load and the planned generator load sequence. Record the ATS position and generator voltage and frequency during each transfer. Put the UPS mode, rectifier input, bypass availability, battery current and alarms on the same timeline. Compare the results with the agreed acceptance criteria. That record is more useful than a no-load demonstration that merely shows the generator can start.

Cummins, Liquid-Cooled Generator Set Application Manual T-030, sections 2.3 and 3.3.3.4 — one-line diagrams and UPS loads in generator sizing.

Eaton, Six considerations to achieving generator-UPS harmony — input windows, generator sizing and UPS topology.

Use the checklist to request a model-specific design review. Final settings, protection and test procedures must follow the approved site design and the equipment manufacturers' documents.