LVRT/OVRT

The current position: Home - Customer Support

A voltage dip is a very short drop in voltage in an electrical transmission or distribution system, with a normal duration in the range of milliseconds. These sudden voltage drops (or increases in the case of over-voltages) may be caused by several problems, as may be a blockage of a high power motor in a nearby manufacturing plant or a short circuit between two or three cables in an electrical supply circuit.

These faults may cause in turn, before the protection of the motor or line switch off and separate the fault from the grid, an abrupt reduction of the voltage level, which propagates through the electrical distribution or even transmission system. Such voltage faults may be balanced (three-phase) or unbalanced (two-phase or one phase to ground).

When a wind turbine or solar inverter face this fault, its protections would typically disconnect it from the grid, in order to protect the generation equipment, causing a sudden discontinuity in power generation, thus making the grid more unstable, and starting a chain effect that normally affects more wind turbines, up to the whole generation plant, and nearby or even distant wind farms in the same electrical system, causing a huge production loss in the whole system.

Low Voltage Ride Through (LVRT) is an electrical feature, required today for any generation equipment, that prevents the disconnection of the generator from the electrical system when a voltage dip occurs by withstanding the severe arising mechanical and electrical consequences.

The increased penetration of renewable energy sourced power generation in the grid, especially that of wind and solar energy, have also posed a growing threat to grid stability due to the lack of older equipment of LVRT capabilities. This has also the negative side effect of limiting the new capacity that can be connected to the grid, and therefore expanded plans of renewable energy power penetration make LVRT capabilities of wind turbines and solar inverters a top priority. As can be seen below, several grid operators and regulation Authorities have issued stringent mandatory requirements in this sense enacted in several countries, with several profiles (depth and duration) of the voltage dip where the generation equipment is required to stay connected to the grid.

Moreover, several grid codes have also other requirements for system support, especially regarding reactive power injection during the voltage dip to support fault recovery.