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What Is a Low Voltage Ride through?

Geisha A. Legazpi
Geisha A. Legazpi

A low voltage ride through is the capability to respond to a major decrease in energy input for alternative energy sources like wind and solar plants. It is pre-defined so that loads may be disconnected or energized by alternative sources such as uninterruptible power supplies (UPS). A low voltage ride through design is also considered in many critical applications such as satellites and spacecrafts.

An electric device relies on a relatively steady supply voltage; most electronic equipment may be able to function between about 60 and 130 volts alternating current (VAC). The electric power being drained is about the same even if the voltage has dropped due to flexible power supply circuits. The switching power supply is able to alter the “on” time on its main switching device to produce the same average direct current (DC) voltage to its load. Electronic circuits implement low voltage ride through to a certain extent as much as the size of capacitor storage components will allow. Practical design may provide low voltage ride through up to about half a second.

Wind turbines are subject to low voltage dips due to decreased wind speed.
Wind turbines are subject to low voltage dips due to decreased wind speed.

Fault ride through is a more general feature that includes low voltage ride through and other faults like overspeed ride through in wind turbines. It is the ability of a power-generating device to maintain its output voltage given short-term power dips. A wind generator farm may undergo decreased wind speeds leading to a voltage dip. Meanwhile, the power grid may demand the same amount of power that may be momentarily provided by backup mechanism on the generating device.

Reactive devices are able to support low voltage ride through for short-term loss of power. The capacitor or condenser is able to provide electrical power taken from the electric field generated between conductive plates, while the inductor is able to produce current on its winding taken from the collapse of a magnetic field in its core. The magnetic core is able to store a strong magnetic field.

Another resource for low voltage ride through is inertial storage. In this form, the mechanical energy may be stored as the momentum of a rotating flywheel. For instance, using magnetic bearings, a heavy flywheel weighing at least 220.5 lb. (100 kg) may be suspended in a vacuum, and once suspended, the flywheel has a motor drive that uses extra electrical energy to build up its rotation speed. Without any resistance, the flywheel keeps rotating. During power outages, a generator engages the flywheel and converts rotational energy to electrical energy.

The battery bank is able to provide low voltage ride through for up to several hours. There are systems that use DC directly so there is no need to convert the electrical energy during power outage. In some systems, an in-line UPS generates alternating current (AC) in sync with the mains power. If power is not available for some reason, the UPS drives the load as if the mains power had not disappeared. When the mains power returns, the electronics of the UPS senses this and reverts to monitor only.

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    • Wind turbines are subject to low voltage dips due to decreased wind speed.
      By: Gianluca Rasile
      Wind turbines are subject to low voltage dips due to decreased wind speed.