Facilities may find that taking proper preventative measures to deal with specific generator/UPS compatibility issues is usually more effective than searching for generator/UPS solutions.

Line Notches and Harmonic Current

The majority of UPSs produce line notches, which in turn adversely affect some types of generator controls. In addition, a distortion that forms when a generated current clashes with a sine wave known as total harmonic current (THD) could create overheating in the generator.

An effective way to prevent these types and many more disturbances is to use a shunt active filter. This one step can improve the quality of power being generated while compensating for the load power factor.

Power Load Variations

Sudden variations in frequency and voltage can occur from the instant load reaction as the generator turns on and the switch connecting it to the UPS closes. This scenario can be prevented if the UPS rectifier can control power flow (usually via thyristors) over a 10 to 20 second period to the generator.

Voltage Rise

If the generators dimensions are almost the same as the UPS, a surge in voltage can occur, such as in the case when the input filter is the only load on the generator. The best prevention to counter this effect is to use one that disconnects its filter when its charger is inactive.

Frequency Fluctuations

Generators and UPS chargers both have limitations in how they respond to fluctuations in voltage and frequency or to changing loads. They key to handling these performance challenges stems from effective control design from generator and UPS suppliers to reduce or to stop frequency fluctuations.

To ensure proper system function, the generator should have a responsive governor that is properly sized and adjusted. Moreover, the generator’s voltage regulator should not register at the same response level as the governor. The UPS should have a control responsive to swift frequency fluctuations and the charger should perform properly with a slew rate on input frequency fluctuations over 5 Hz per second. In order to preserve battery life, a double-conversion online UPS is capable of filtering frequency variations as part of its normal function.

Automatic Transfer Switches

A large number of generator/UPS installations are configured using automatic transfer switches. When this function happens too fast, it can be devastating for both the motors and the UPS. To prevent this problem a facility can use a rack transfer switch instead which outperforms standard automatic switches.

The demand for electricity continues to grow as facilities turn to generators as a popular source for backup power. However, generators that protect essential loads have potential to create unique power glitches with sensitive electronic equipment, which is why an uninterruptible power supply device (UPS) is often paired with a generator during extended power outages. The biggest hurdle of syncing generators with UPSs is performance compatibility.

Avoiding compatibility issues that inherently accompany generator/UPS power systems can be done by understanding function characteristics, load power interaction and control design of these devices to ensure power-supply protection.