Whole-Line Voltage Sag Protection

WS-DVR Dynamic Voltage Restorer

Protect critical industrial feeders and mixed sensitive loads from voltage sags with fast, controlled series voltage injection.

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Protection boundary: Critical AC feeder
Typical load mix: VFDs, PLCs, servo systems and controls
Energy support: Sized from the measured disturbance and load

Short answer

What Is a Dynamic Voltage Restorer?

A Dynamic Voltage Restorer (DVR) is a power-electronic system installed in series with a critical AC feeder. When the incoming voltage falls during a voltage sag, the DVR detects the disturbance and injects the missing voltage so the protected load sees a substantially more stable supply.

Unlike drive-level DC-bus support, a DVR protects the AC supply seen by the downstream load. This makes it useful when a production line contains a mixture of VFDs, PLCs, contactors, servo systems, controls and other voltage-sensitive equipment that must remain energized together.

Load-layered application boundary

AC-Side Voltage Restoration for Loads That Require It

WS-DVR is recommended when critical loads genuinely require AC-bus voltage restoration, including large non-VFD motors or production architectures where DC-side ride-through is not practical.

For VFD-dominant lines, evaluate the Wilson Load-Layered Architecture before sizing a full-line DVR.

Compare protection boundaries with the Wilson architecture →

Series voltage injection

How WS-DVR Protects a Critical Feeder

Utility / Plant BusSeries Injection StageProtected AC FeederCritical Production Loads

Optional High-Power Energy SupportDC LinkConverterSeries Injection Stage

Simplified protection architecture

WS-DVR continuously observes the incoming supply and compares it with the required load-side voltage. During a voltage sag, the converter generates a compensating voltage and injects it in series with the feeder.

The amount of real energy required depends on sag depth, sag duration, load power and compensation strategy. Shallow voltage sags may require relatively little active energy. Deep sags and near-zero-voltage events require substantially more real energy and may require dedicated short-duration energy storage.

Protection boundary

When Whole-Line Protection Makes More Sense

Protecting each machine individually is not always practical. A production line may trip because several different devices respond to the same voltage sag: the VFD, PLC, contactor, servo controller or auxiliary control power supply.

WS-DVR moves the protection boundary upstream. Instead of modifying every individual load, it protects the critical feeder supplying the group of loads.

Mixed sensitive loads on one feeder
Multiple VFDs plus PLC and control systems
Production lines where DC-bus access is unavailable
Retrofit projects where machine-by-machine modification is undesirable
Processes where several devices must ride through the same disturbance together

Architecture comparison

WS-DVR or VFD DC-Bus Support?

Engineering question	WS-DVR	VFD DC-Bus Support
Protection boundary	Critical AC feeder	VFD DC link
Typical load mix	VFD + PLC + servo + controls + other sensitive loads	Primarily VFD-driven loads
Requires VFD DC-bus access	No	Yes
Protects non-VFD control loads	Yes, if connected downstream and within the engineered protection boundary	Normally no
Main advantage	Protects a group of mixed loads together	Directly supports the drive where the sag causes the trip
System rating	Based on feeder/load and required compensation	Can avoid protecting unrelated AC loads
Best fit	Whole-line / feeder-level protection	Drive-heavy applications with accessible DC buses

Neither architecture is universally better. The correct choice depends on the failure point, load mix, electrical access, sag depth, sag duration and the amount of equipment that must remain operating.

Compare VFD DC-Bus Support →

Energy requirement

Why Deep Voltage Sags Need Real Energy

A DVR does not create energy. During compensation, the required load-side active power must come from the remaining grid voltage, the DC link, an auxiliary source, or a combination of these.

As the residual grid voltage becomes lower, the energy contribution required from the support system increases. For very deep voltage sags or momentary interruptions approaching zero voltage, short-duration energy storage becomes increasingly important.

High-Power Short-Duration Support

Wilson PowerTech can integrate high-power short-duration energy support when the protected process requires more than voltage correction alone. Flywheel energy storage is particularly relevant where the requirement is high power, short duration and frequent cycling.

A DVR is designed around voltage-disturbance compensation and feeder protection. A UPS is designed to carry the load from an independent energy source when the normal supply is inadequate or lost. The right architecture depends on disturbance depth, duration and required backup time.

Long-duration backup is normally a different engineering problem and may be better served by UPS or battery energy storage.

Review the flywheel technology fit →

Industrial applications

Where WS-DVR Fits

Textile Production

Protect production lines where multiple drives and control systems can trip during the same voltage sag.

Review the application →

Coating and Continuous Web Processes

Maintain critical controls, drives and auxiliaries through short-duration voltage disturbances where an unplanned stop can disrupt the process.

Semiconductor and Precision Manufacturing

Protect voltage-sensitive production equipment and controls where short electrical disturbances can interrupt high-value processes.

Chemical and Pharmaceutical Processes

Support critical continuous-process loads where nuisance trips can lead to restart delays and process losses.

Compressors, Pumps and Industrial Auxiliaries

Evaluate feeder-level DVR protection when several motors, VFDs and control systems must remain available together.

Review the application →

Evidence boundary

Field Evidence Matters More Than Product Claims

Voltage-sag protection should be engineered from the actual disturbance and the actual trip mechanism. Wilson Technology uses field measurements, verified ride-through records and production-line analysis to determine where protection should be applied and how much short-duration support is required.

View Verified Voltage-Sag Protection Cases →Fujian textile case →Hangzhou textile case →Textile application →

Start the assessment

What We Need to Size a WS-DVR

A complete power-quality study is helpful, but it is not required to start an engineering discussion.

Nominal system voltage
Protected load kW / kVA
One-line diagram, if available
Critical feeder current
Equipment that trips
VFD / PLC / servo / control-load mix
Measured residual voltage during a sag, if available
Sag duration, if available
Whether complete or near-zero-voltage interruptions must also be survived
Restart cost or production loss caused by a trip

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Engineering FAQ

Dynamic Voltage Restorer Questions

What does a Dynamic Voltage Restorer do?

A Dynamic Voltage Restorer detects a voltage sag on the incoming AC supply and injects a compensating voltage in series with the protected feeder. Its purpose is to keep the load-side voltage within the engineered ride-through range during short-duration voltage disturbances.

Can one DVR protect multiple VFDs?

Yes, a feeder-level DVR can protect multiple VFDs when they are supplied downstream of the protected feeder and the system is sized for the combined load and required voltage compensation. Whether this is more economical than direct VFD DC-bus support depends on the load mix and protection boundary.

Does a DVR require energy storage?

Not every voltage sag requires the same amount of stored energy. The required active-energy contribution depends on residual grid voltage, sag duration, load power and compensation strategy. Deep sags and near-zero-voltage interruptions require more real energy and are more likely to require dedicated short-duration storage.

What is the difference between a DVR and VFD DC-bus ride-through?

A DVR protects the AC feeder supplying the load, while VFD DC-bus support injects energy directly into the drive DC link. DVR protection is often better suited to mixed sensitive loads; DC-bus support can be more efficient when the critical risk is concentrated in accessible VFDs.

Can a DVR protect against a complete power interruption?

A DVR can support very deep voltage events only if the system has sufficient converter capacity and a suitable source of real energy. Protection against near-zero or zero-voltage interruptions therefore requires a different energy assessment from compensation of an ordinary voltage sag.

Preliminary diagnosis

Tell Us What Happened

Not sure whether whole-line protection is necessary? Tell us what stopped and what you observed.

No waveform or power-quality record is required. Just tell us what stopped and what you observed.

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Engineering review

Tell Us What Happened

You don’t need complete electrical data to start. Share the protected load, system voltage, trip mechanism and any sag record already available.

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