Three Phase Air Cooled Servo Stabilizer

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Overview

Three Phase Air Cooled Servo Voltage Stabilizer

Maintain Consistent Power Across Your Operations

A three phase air cooled servo stabilizer monitors all three phases at the same time instead of just one, and ensures that all three phases hold a 415 V steady supply.

Your machines get the same correct voltage on all three phases R, Y and B at the same time, even when the grid does not give it. SERVOLINK builds them from 6 kVA to 100 kVA in our own manufacturing unit, with the output kept within a variation of ±1% of 415 V between phases (230 V between phase and neutral), and without a single drop of transformer oil inside.

In a three phase supply, the three phases rarely go up and down at the same time. One phase can be low while the other two are normal — in a factory when a big motor starts, or in a building where most of the single phase load sits on one phase. Our servo stabilizer observes each phase on its own, and a slight variation triggers the servo motor of that particular phase to adjust its carbon brush position in the variac, while the other two phases are left untouched.

SERVOLINK makes three phase air cooled servo stabilizers in 3/6, 10, 15, 20, 25, 30, 40, 50, 60 and 100 kVA ratings, covering wide to normal working input voltage ranges from 240-470 V, 300-470 V and 340-470 V. Each phase has its own 100% copper wound variac and buck-boost transformer, both wound in our own factory.

Designed and produced by Servolink, ensuring superior quality, unwavering reliability, and optimal efficiency.

Servolink three phase air cooled servo voltage stabilizer

The Problem

Why Three Phase Supply Needs Stabilization

In India, factories and commercial buildings get three phase supply, but the voltage on the three phases is rarely equal. The grid voltage keeps changing during the day, and the load on each phase is also different. If most of the ACs, lights and single phase machines in a building are on one phase, that phase drops while the others stay high — very common on summer afternoons in office buildings, and in industrial areas at shift change when many machines start together.

Unbalanced and unstable voltage is very harmful for three phase machines. For a three phase motor, a voltage difference of just 2% between phases can push the winding current up by 12 to 20%, so one winding keeps heating more than the other two. CNC drives and PLCs trip or show errors, lifts stop between floors, chiller compressors fail, and control cards get damaged. This leads to breakdowns, production loss and costly repairs.

Engineering

Features

Multi-Phase ProtectionEnsures consistent and reliable voltage across all three phases, safeguarding your equipment and optimizing performance in complex electrical systems.

Advanced Servo TechnologyPrecisely regulates voltage fluctuations in each phase, preventing imbalances that can damage sensitive equipment.

Robust ConstructionBuilt to withstand demanding industrial environments with durable materials and rigorous quality control.

Efficient Air CoolingNatural air and, on higher ratings, fans remove the heat, in a compact footprint with no oil tank.

Wide Input Voltage RangeAdapts to fluctuating power conditions, offering unwavering stabilization for a wider range of applications.

Customized SolutionsAt Servolink, we understand that every business has unique power requirements. That's why we offer tailored solutions to match your specific needs.

User-Friendly InterfaceEasy-to-read display and intuitive controls for effortless monitoring and operation, simplifying management of your three-phase power supply.

The Right Fit

Who Needs A Three Phase Servo Stabilizer?

If your building has a three phase supply, then a three phase servo stabilizer is what you need. Factories, workshops, hospitals, banks, offices, gyms, hotels, schools and big houses with a three phase connection all come in this category. Machines like CNC, lifts, chillers, central AC plants, printing machines, air compressors and lab equipment run on three phase, and they are very sensitive to voltage changes.

Why choose an air cooled model? The air cooled design is compact, easy to move and install, and does not need transformer oil. If your load is up to 100 kVA and the stabilizer is placed in a clean, covered electrical room with proper ventilation, the air cooled model is the right choice for you. There is no oil to check or change, and the unit can be placed close to the machine or the main panel.

Main USPs

Three Phase Air Cooled Variants

Each Phase Corrected SeparatelyEven if one phase is low and the other two are normal, all three phases come out stable.

Compact And LightweightFits easily in electrical rooms and machine shops where space is limited.

No Oil MaintenanceNo oil level check, no oil testing and no leakage problem.

Branded Switchgear InsideLauritz Knudsen (L&T) MCB and MNX contactors; heavy duty rotary bypass switch available on request to keep the load running during service.

100% Copper WoundVariacs and buck-boost transformers, wound in our own factory.

How It Works

Working Mechanism

R, Y and B each have their own variac, buck-boost transformer and servo motor. The control card reads the input and output of every phase, and runs that phase’s motor forward or in reverse to move its carbon brush along the variac. The buck-boost winding then adds or subtracts exactly the correction needed. Follow the numbers in the diagram below.

Tap the diagram to open it full size

Mains inputR, Y, B supply enters through the 3-pole MCB.
SensingThe control card reads the input and output of every phase.
Range checkIf any phase goes beyond the low or high cut, the contactor cuts off the output.
Motor driveThe card runs that phase’s servo motor forward or in reverse.
Brush movesThe motor turns the carbon brush on that phase’s variac.
Buck or boostThe variac feeds the BBT primary and input. The secondary-output winding adds or subtracts voltage in series.
Stable outputCorrected R, Y, B voltage passes through the contactor to the output terminals.

Technical Data

Specification

Brand	SERVOLINK
Product Type	Three Phase Air-Cooled Servo Voltage Stabilizer
Capacity	3/6, 10, 15, 20, 25, 30, 40, 50, 60 & 100 kVA; other ratings on request
Supply System	Three phase, 4 wire (R, Y, B + neutral), with protective earth
Input Voltage Range	240-470 V / 300-470 V / 340-470 V (phase to phase), as per selected model
Output Voltage	415 V ±1% phase to phase (230 V ±1% phase to neutral)
Frequency	50 Hz
Control Type	Independent phase control (unbalanced type), each phase corrected separately
Mode of Operation	Automatic, servo-controlled
Duty Cycle	Continuous operation within rated conditions
Efficiency	More than 98%
Variac	100% copper wound, made in-house
Cooling	Air-cooled (natural air, fan on higher ratings)
Installation	Indoor
Ambient Operating Temperature	Up to 50°C
Display	LCD display panel on all models
Voltage Protection	High/low voltage cut-off on all models
Phase Protection	Single phasing and phase reversal protection
Overload / Short-Circuit Protection	As per selected model
Restart Delay	Provided on all models
Switchgear	Lauritz Knudsen (L&T) MCB and MNX contactors
Bypass	Heavy duty rotary cam bypass switch (on request)
Mobility	Iron wheels provided
Standard	Built as per IS 9815 (Part 1):1994, IS 5142, IS 302 (Part 1)

Questions

Frequently Asked Questions

What is the output voltage of a three phase servo stabilizer?

415 V (±1%) between any two phases, and 230 V (±1%) between any phase and neutral. Both are the same supply, just measured in two ways. Your three phase machines use 415 V, and the single phase appliances in the building use 230 V.

What is the difference between a balanced and an unbalanced three phase servo stabilizer?

A balanced type has one motor driving all three variacs together, so it corrects all three phases by the same amount. It works only if all three phases go up and down together. An unbalanced type has a separate variac, motor and control card for each phase, so each phase is corrected on its own. In India the supply is mostly unbalanced, so the unbalanced type is the safer choice — SERVOLINK three phase stabilizers are unbalanced type.

My building has three phase supply but mostly single phase appliances. Do I need a three phase stabilizer?

Yes. One three phase servo stabilizer on the main incoming supply protects all three phases of the building, so every room and every appliance gets stable voltage. A single phase stabilizer on one phase protects only that one phase.

Should I use one three phase stabilizer or three single phase stabilizers?

One three phase stabilizer is better for most buildings. It is one unit with one bypass and less wiring, and it can run three phase machines like lifts, pumps and chillers. Three single phase stabilizers can only feed single phase loads, and they cannot run a three phase motor properly.

What happens if one phase fails (single phasing)?

A three phase motor running on only two phases gets overheated within minutes and can burn. Our single phasing protection disconnects the output as soon as any phase fails, and reconnects automatically when all three phases come back.

What happens if the neutral wire becomes loose or breaks?

This is called neutral failure, and it is very dangerous for single phase appliances. The voltage on the lightly loaded phase can shoot up towards 415 V, and appliances on that phase can burn. The high voltage cut-off disconnects the output to protect your equipment. Always keep the neutral connection tight, and get it checked if lights suddenly start glowing very bright or very dim.

How do I choose the right kVA for my machines?

Add the kW of all three phase and single phase loads that can run together, and divide it by the power factor (take 0.8 if you don’t know it) to get kVA. Then choose a rating so that this running load stays around 60–70% of the stabilizer rating. For example, a 24 kW load is 30 kVA, and at 60–70% loading it needs a 50 kVA stabilizer. This margin takes care of motor starting and keeps the stabilizer cool. Share your load list with us, or use our kVA calculator, and we will suggest the right kVA.

What does an input range like 340-470 V mean?

It means the stabilizer gives a stable 415 V output as long as the phase to phase input stays between 340 V and 470 V. If the input goes outside this range, the cut-off disconnects the output. For areas with very low voltage (end of a long line, rural areas or crowded industrial areas), choose a wider range like 240-470 V. A wider range needs a bigger buck-boost transformer, so select the range that matches your site.

Can I connect a CNC machine, lift or chiller to it?

Yes. These are the machines that need stable voltage the most. Tell us the kW rating and the starting current of the machine, because lifts and chillers draw a high current at start, and the stabilizer must be sized for it.

What is the bypass switch used for?

The bypass switch lets you run the load directly from the mains when the stabilizer needs service or has a fault, so your work does not stop. Operate it only as shown in the user manual, and switch the stabilizer back in once the service is done, because in bypass your equipment gets the raw grid voltage.

Why does the display show a different voltage on each phase?

The input side shows the actual grid voltage of each phase, and that is normally different on each phase. The output side should show nearly the same voltage on all three phases. If the output voltages are very different from each other, the stabilizer needs service.

Can a three phase servo stabilizer work with a DG set?

Yes. Connect it after the changeover switch, so it gets both the grid supply and the DG supply. DG voltage also changes with load, and the stabilizer keeps it steady. The restart delay gives the DG time to settle before the output switches on.

When should I choose a three phase oil cooled model instead?

Choose oil cooled if your load is above 100 kVA, if the load runs near full rating all day, or if the site is hot, dusty or outdoor. We make three phase oil cooled servo stabilizers up to 2000 kVA.

We have been making stabilizers since 1980. Every part of our servo is made in-house at our 16,000 sq ft factory in Ghaziabad — variac winding, variac motorization, buck-boost winding, enclosure fabrication, assembly and testing, each in its own workstation. Our variacs are 100% copper wound, our servos are built as per IS 9815, and every unit is tested in our own testing section before dispatch.

The Difference