Automatic voltage regulator: what an AVR does, and what it does not.
AVR meaning, the difference between generator AVR and mains AVR, servo vs contact regulation, and how to size an AVR for a factory, clinic, or building.
- Output accuracy
- ±1–2%
- Servo input window
- 160–456 VAC
- Range
- 0.5–2000 kVA
- Protections
- 28
An automatic voltage regulator (AVR) holds the output voltage within a set band while the input changes. In a mains application, it protects equipment from brownouts, swells, and phase imbalance. In a generator application, it controls the alternator excitation. The two are different products, and confusing them is one of the most common specification errors.
This page is about the mains AVR: the cabinet installed between the utility supply and the load. It explains the two main mechanisms, the input windows, and the questions that determine the right unit.
What does an automatic voltage regulator do?
The AVR samples the output voltage, compares it with a reference, and adjusts a transformer tap, a brush position, or an electronic switch to keep the output within the target band. It responds to slow changes (a brownout) and, depending on the mechanism, to faster changes (a motor start).
It does not store energy. During a complete outage, the output goes to zero. If the load must ride through an outage, add a UPS. If the load only needs stable voltage, the AVR is the right device.
Why is “AVR” confused with generator excitation?
A generator has an automatic voltage regulator that controls the field current of the alternator. That AVR is a small electronic module inside the generator, not a cabinet. When a buyer says “I need an AVR for my generator,” they may mean the excitation module, not a mains stabilizer.
Ask for the generator make, model, excitation type, and the fault symptom. If the generator voltage is unstable, the excitation AVR or the generator itself may be the issue. A mains stabilizer can protect the load downstream, but it will not repair the generator.
Servo AVR or contact AVR?
A servo AVR uses a motor-driven brush on a toroidal transformer. It has a wide input window and is available in three-phase models with independent phase regulation. It is the right choice for a weak grid, a factory, or a building with large voltage swings.
A contact AVR uses a disc autotransformer and a carbon brush. It gives ±1% precision, but the input window is narrower. It is the right choice for a laboratory, a clinic, or a small production line where the grid is reasonably stable and the load is sensitive.
Servo vs contact AVR
| Criterion | Servo AVR | Contact AVR |
|---|---|---|
| Input window | 160–260 / 304–456 VAC | 220 VAC ±20% |
| Output | ±2% | ±1% adjustable |
| Three-phase independent regulation | Yes | Single-phase only |
| Capacity | 0.5–100 kVA | 10–30 kVA |
| Typical use | Factory, building, weak grid | Lab, clinic, precision bench |
How do I size an AVR?
Add the kVA of the protected loads and add 20–30% margin. Confirm the load power factor and the largest motor starting current. A 30 kVA AVR at 0.8 PF delivers 24 kW; if the load is 24 kW with a 0.7 PF, the required kVA is higher.
Measure the input voltage at the worst time of day. If the low extreme is below the AVR’s input window, the AVR will trip to bypass or disconnect. Choose a unit with enough input range, or fix the upstream supply.
Which standards and documents are referenced on this page?
The table lists the model-specific standards and conformity documents a project buyer should ask for. Availability depends on the frame, the battery, and the destination market; request the document that names your model.
Voltage stabilizer and AVR standards
| Reference | What it covers |
|---|---|
| IEC 61558-1 | Safety of power transformers and supply units |
| IEC 61000-3-2 | Harmonic current emission limits |
| IEC 61000-3-3 | Voltage fluctuation and flicker limits |
| IEC 62040-3 | Interface performance when feeding a UPS input |
| JB/T 10089 | Contact-type AC voltage stabilizer standard |
| GB/T 12325 | Voltage deviation limits for supply systems |
| CE / RoHS | EU conformity and restricted-substance declaration |
| ISO 9001 | Manufacturing quality management system |
| RS485 / MODBUS-RTU | Remote monitoring interface |
| IP20 / IP21 | Enclosure protection for indoor installation |
Certificates are issued against the exact model and configuration. See the certifications page for how to confirm scope and revision, or send the model to request the current document.
Confirm the inputs and documents before quoting.
Project inputs to confirm
| Item | What to confirm | Why it matters |
|---|---|---|
| Load | Running kW, largest motor, load step | Sets kVA, overload and topology |
| Runtime | Minutes, generator availability, battery room | Sets battery bank and charger |
| Supply | Voltage, frequency, phase, input current | Sets model, breaker and cable |
| Site | Country, altitude, ambient temperature, dust | Sets derating, IP and documents |
| Battery | VRLA, LiFePO4, footprint, weight limit | Sets chemistry and room layout |
| Documentation | Conformity route, test report, language | Sets document package and lead time |
Match the page to a platform.
SVC Series · 0.5–100 kVA
Servo Voltage Stabilizer
±2% output from a 160–456 V input swing.
KPD Series · 10–30 kVA
Contact-Type Voltage Stabilizer
±1% precision from a carbon-brush autotransformer.
SVC-T Series · 10–100 kVA
Three-Phase Voltage Stabilizer
Independent phase regulation for unbalanced three-phase loads.
Questions from project buyers.
Project-specific answers. If your question is not here, send the load list and the site conditions.
Talk to an engineer What does AVR stand for?
Automatic voltage regulator. In a mains application, it is a stabilizer cabinet. In a generator, it is the excitation control module.
Can an AVR fix low voltage from the utility?
It can boost the voltage to the setpoint, provided the input is within the AVR’s correction range and the load current is within rating. If the input falls below the range, the AVR cannot hold the output.
Do I need an AVR if I have a UPS?
Not necessarily. An online UPS already regulates its input and output. An AVR is useful when the UPS input is outside its window, or when non-UPS loads also need stable voltage.
How accurate is an AVR?
Servo AVRs are typically ±2%; contact AVRs are ±1%. The actual accuracy depends on the control loop, the load, and the input variation.
Can an AVR run a motor load?
It can supply a motor within its rating, but motor starting current can be 5–7 times rated. Check the starting current and the AVR overload capability, or use a soft starter.
Send the load list. We will return the configuration.
Tell us the kW, the backup time, the phase, and the site country. You will get a capacity recommendation, a battery configuration, and the model sheet.
- Capacity and topology recommendation
- Battery bank and runtime estimate
- Model sheet and commercial offer
Request a configuration and quotation
Send the load list, backup time, and site conditions. We will return a capacity recommendation, battery configuration, and commercial offer.