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Glossary · Energy industry & energy transition

High Voltage Ride Through

High voltage ride through HVRT grid stability inverter renewable energies overvoltage grid connection

Definition and basic idea

High Voltage Ride Through, or HVRT for short, is often called OVRT (Over Voltage Ride Through) in German regulations. It refers to the ability of a generating plant, a storage unit or an inverter to withstand a brief overvoltage in the grid without disconnecting immediately. This does not mean that the plant can operate permanently at any arbitrarily high voltage. It is about a defined behaviour during a time-limited disturbance. The plant must remain connected within specified voltage-time limits and must not make the disturbance worse.

The decisive voltage is the voltage at the point of connection. Grid connection rules usually express it relative to a reference voltage, that is, as a multiple of the agreed supply voltage Uc or in per unit (pu). A value of 1.2 pu means 120 percent of the reference voltage. An HVRT requirement can be represented as a curve. The higher the overvoltage, the shorter the time the plant must withstand it. For very high values it often only has to ride through for about 100 milliseconds, whereas for moderate overvoltages it must do so for seconds or longer. Above the curve it may disconnect; within it, it must remain connected to the grid.

Place within the ride-through family

HVRT is part of the fault ride through requirements. They define how plants are to react to grid faults, switching operations or other disturbances. Low Voltage Ride Through concerns voltage dips, while HVRT concerns overvoltages. Both rest on the same idea: plants should not disconnect from the grid at every brief deviation. If many plants disconnect at the same time, a local disturbance can turn into a major stability problem.

Overvoltages have various causes. They occur when large loads are shed, through switching operations, immediately after a fault is cleared when the voltage returns and compensation equipment or plants injecting reactive current have not yet readjusted, and in the healthy phases during unbalanced faults. In the distribution grid, high feed-in from photovoltaics at low load can also raise the voltage. However, this is usually a slow, quasi-steady-state problem. HVRT mainly concerns short, dynamic events.

Distinction: voltage band, voltage control and protection

Three things should be kept apart. First, there is the quasi-steady-state voltage band within which a plant must be operated for minutes or permanently. EU Regulation 2016/631 (RfG) lays this down in tables for larger plants in the extra-high and high-voltage grid. In Continental Europe, for reference voltages below 300 kV, the following applies: unlimited operation between 0.90 and 1.118 pu. Between 1.118 and 1.15 pu, the transmission system operator sets a duration that must lie between 20 and 60 minutes. For 300 to 400 kV, a duration of 20 to 60 minutes likewise applies for 1.05 to 1.10 pu. These are limits for continuous operation, not HVRT curves for disturbances in the millisecond range.

Second, there is voltage control. It influences the voltage level continuously, for example through reactive power, tap changers on transformers or other equipment. HVRT, by contrast, only describes whether a plant stays connected to the grid during an overvoltage and which minimum requirements it meets in doing so. A plant can be HVRT-capable without solving a permanent voltage problem. Conversely, good voltage control does not prevent plants from disconnecting in an uncontrolled manner during brief overvoltages.

Third, there is overvoltage protection. HVRT does not make protection superfluous. Excessive voltages can damage equipment, overstress insulation or endanger people. The task is one of coordination: protection settings and the ride-through curve must fit together so that a plant disconnects neither too early nor dangerously late. For medium-voltage plants under VDE-AR-N 4110, the form for protection settings at the point of connection names, for example, an overvoltage protection U>> of 1.20 Uc with 300 ms and U> of 1.10 Uc with 180 s. At the generating unit on the low-voltage side of the machine transformer, U>> of 1.25 UNS with 100 ms is provided. These values are defaults given in the form. The grid operator may specify different values in individual cases, and they must not be read as a general HVRT curve.

Why HVRT is particularly important for power electronics

HVRT gained importance with the growing share of wind, photovoltaics and battery storage. These plants are coupled to the grid via power electronics. Synchronous generators react to disturbances mainly through their physical properties. With inverters, by contrast, hardware, protection concept, control algorithms and parameters determine the behaviour. If the thresholds are set too narrowly or identically everywhere, many inverters in an area can disconnect at the same time. Feed-in is then lost abruptly, even though each individual disconnection appears reasonable in itself. This aggregate effect is the core of the problem.

Technically, an inverter must be designed for this. Semiconductors, DC link and protection circuits must withstand the brief overvoltage. The DC link voltage must not rise to an impermissible level, the current control must remain stable, and the plant must detect whether the voltage is still within the ride-through range. A contribution to lowering the voltage, for example through under-excited reactive current, is often additionally required. How strong this contribution must be is governed by the respective set of rules.

Legal framework: Europe, Germany, North America

Europe: The RfG currently in force, from 2016, expressly regulates fault ride-through only via a voltage-time profile for voltage dips. It contains no harmonised curve for brief overvoltages. For overvoltages it mainly contains the voltage bands for continuous operation mentioned above. HVRT has therefore so far been regulated nationally. According to an IRENA overview from 2022, HVRT was not yet widespread in grid connection rules worldwide, but is likely to become more common with more fluctuating generation. The revision of the RfG (RfG 2.0) is intended to change this. ACER submitted its recommendation in December 2023. In 2026, the European Commission put its own amended draft out for consultation. According to a statement by the French industry association UFE of August 2026, this draft provides for a fixed HVRT requirement even for small type A plants: 1.3 pu for 100 ms and 1.2 pu for one minute. UFE criticises these values as potentially incompatible with protection in low- and medium-voltage grids. The content applies only once the regulation has been adopted and the transitional periods have expired.

Germany: The technical connection rules of VDE FNN specify the requirements for each voltage level. VDE-AR-N 4105 applies to low voltage, 4110 to medium voltage, 4120 to high voltage and 4130 to extra-high voltage. With the 2018 versions, requirements for riding through overvoltages were introduced for medium and high voltage in addition to the curves for voltage dips. Which curve applies in an individual case depends on the voltage level, plant type, version of the rule and the technical connection conditions of the grid operator. Proof is provided through unit and plant certificates, that is, through grid code compliance.

North America: There, the regulatory authority FERC approved the reliability standard NERC PRC-029-1 in 2025. It contains requirements for riding through frequency and voltage disturbances, expressly including high voltage, for inverter-based resources in the interconnected grid. According to NERC, the trigger was several events in which such plants failed to ride through disturbances.

Common misunderstandings

  • "Overvoltage-proof" as a blanket statement: HVRT is always tied to a specific curve, voltage level, measuring point and version of a set of rules. A certificate under one set of rules does not automatically apply to another.

  • HVRT equals voltage maintenance: The plant stays connected to the grid. However, this does not by itself resolve permanently excessive voltages in a grid area.

  • HVRT as flexibility: HVRT is a minimum technical capability for safe operation, not flexibility in the market sense. A plant can be flexible in the market and still have weak properties during disturbances, and vice versa.

  • Renewables as an inherent risk: Renewable generation does not automatically destabilise the grid. What matters is that its behaviour during disturbances is clearly regulated, correctly set and verifiable.

Economic and operational significance

The costs of HVRT rarely appear as a separate item on an invoice. They are embedded in the design of the inverters, type tests, certificates, simulation models, parameterisation and commissioning. Grid operators need reliable information about the behaviour of many plants in order to align their protection concept and grid operation accordingly. Requirements that are too weak can later cause problems in the grid. Requirements that are too strict, without regard to devices and protection systems, make plants more expensive or come into conflict with personal and equipment protection. This trade-off shapes the current discussion on RfG 2.0.

HVRT contributes to grid stability but describes only a narrow segment: the behaviour of connected plants during brief overvoltages. Security of supply also encompasses sufficient generation, grid capacity, reserves, system operation and crisis preparedness. The concept nevertheless shows clearly that the stability of an electricity system depends heavily on the controlled reactions of many individual plants in brief exceptional moments.

Sources

Related glossary entries

Edited by eCMS on 12.11.2026 05:06

© 2026 Erik Schmidt. All rights reserved. Quotations with a link to the source are welcome.