Table of Contents
- How Do You Compare Servo Stabilizer Quotes? (Short Answer)
- First, Make Sure Every Quote Is for the Same Type
- Manufacturer, Dealer or Online Listing: Who Is Quoting?
- Step 1: Send Every Supplier the Same Brief
- Step 2: Check These 20 Points in Every Quote
- Why Does the Input Range Change the Price So Much?
- Step 3: Compare the Total Delivered Cost
- Step 4: Compare the Running Cost, Not Just the Price
- Step 5: Put the Quotes Side by Side
- What Should a Servo Stabilizer Test Report Show?
- 11 Red Flags in a Servo Stabilizer Quote
- 7 Claims You May Hear While Comparing Quotes
- 7 Lessons From Indian Buyer Forums
- Example: Two 25 kVA Quotes Compared
- Key Takeaways
- How We Quote at SG Power
- Frequently Asked Questions
- Related Reading
- Sources
How Do You Compare Servo Stabilizer Quotes? (Short Answer)
To compare servo stabilizer quotes fairly, first make the basics match. Then check output accuracy, correction speed, winding, protections, testing, warranty and service, and add GST, freight and installation to get the total delivered cost. Only then compare prices.
How to compare servo stabilizer quotes in 5 steps
Send every supplier the same brief: load list, supply, voltage readings and site.
Check the 20 specification points in every quote.
Add up the total delivered cost: GST, freight, installation and extras.
Compare the running cost: efficiency, maintenance and service.
Put the quotes side by side and question every gap.
Compare specifications, not brand names. Five things must match before you compare servo stabilizer prices:
Capacity (kVA) and phase: A 20 kVA quote is not comparable with a 25 kVA quote
Input voltage range: A wider range needs a larger transformer and costs more
Cooling (air or oil): Oil-cooled units (60–500 kVA) cost more than air-cooled units but suit dusty, hot or 24×7 sites
Balanced or unbalanced design: Unbalanced units correct each phase separately and cost more
What the price includes: GST, freight and installation are often left out
First, Make Sure Every Quote Is for the Same Type
Servo, relay and static stabilizers are often quoted under the same “voltage stabilizer” name, but they are different machines at very different prices. Check the type before you compare anything else.
| Servo Stabilizer | Relay Stabilizer | Static Stabilizer | |
|---|---|---|---|
| How it corrects | A servo motor moves a carbon brush along a variac, smoothly and steplessly | Relays switch between fixed transformer taps, in steps | Power electronics (IGBTs) correct the voltage with no moving parts |
| Output accuracy | High (SG Power: ±1%) | Lower; output changes in steps | High |
| Correction speed | Fast enough for almost all homes and industry | Fast but in steps | Fastest |
| Overload handling | Robust; handles motor starting well | Limited | Sensitive to overloads and short circuits |
| Best for | Whole buildings, CNC machines, motors, lifts, hospitals | Single basic appliances | Some highly sensitive lab or medical loads |
| Relative price | Medium | Lowest | Highest |
A relay quote will always look cheaper than a servo quote, and a static quote dearer. Compare servo with servo, and for three-phase sites, compare 3 phase servo stabilizers of the same design.
Manufacturer, Dealer or Online Listing: Who Is Quoting?
Quotes also differ because of who is selling. India has hundreds of servo stabilizer manufacturers, dealers and online sellers, and the same servo stabilizer supplier label can hide very different businesses. Check who actually builds the unit before you compare prices:
| Direct Manufacturer | Dealer or Distributor | Online Listing | |
|---|---|---|---|
| Who builds it | Their own factory | Another company | Often not stated |
| Custom input range or kVA | Yes | Depends on the factory behind it | Rarely |
| Test report | Can be supplied with each unit | Depends on the factory | Rarely |
| Price for the same build | Usually lowest (no middle margin) | Includes dealer margin | Low list price, vague specifications |
| After-sales service | Factory engineers or service partners | Dealer’s own team | Often left to the buyer |
| Best for | Industrial, commercial and custom loads | Small standard units | Very small home units |
For a deeper checklist, read our guide to choosing an automatic servo voltage stabilizer manufacturer in India.
How to check: ask for the factory address and make sure the company name on the quote matches the one on the GST invoice. For a large order, visit the factory or ask for photos of winding, assembly and testing. A real manufacturer can show these; a trader usually can't. SG Power manufactures in-house, with details on our about page.
Step 1: Send Every Supplier the Same Brief
Most quote confusion starts here. If each supplier guesses your requirement, each one quotes a different machine. Send the same short brief to everyone:
Load list: the rating of each machine or appliance, and which ones run together
Supply: single phase or three phase, and whether a DG set also feeds the load
Voltage readings: the lowest and highest voltage on each phase over a few days, including peak hours
Load balance: whether the three phases carry similar loads or very different single-phase loads
Site: indoor or outdoor, dust, heat, moisture and the space available
Output: the output voltage you need (for example 380, 400 or 415V three phase) and where the unit will be installed
Whether you send a simple email or a formal request for quotation (RFQ), this brief is what makes quotes comparable. On a tender or the GeM portal, put these points into the technical specification so every bidder quotes the same thing.
If your machines list amps instead of kW (and your power factor is around 0.8): single-phase kVA = volts × amps ÷ 1,000; three-phase kVA = 1.732 × volts × amps ÷ 1,000. For example, a three-phase machine drawing 50 A at 415V needs about 35.9 kVA before the safety margin. Our guide on how to calculate servo stabilizer kVA walks through the full method.
Don't size from your transformer or sanctioned load alone. A 100 kVA supply transformer doesn't mean you need a 100 kVA stabilizer. Size it for the load it will actually protect, with a margin for motor starting and future loads.
Ask every supplier to reply with a written specification sheet, not just a price. If a supplier can't tell you the input range or output accuracy in writing, treat the quote with caution.
Step 2: Check These 20 Points in Every Quote
Use this servo stabilizer quotation checklist on every quote. The first five points decide whether two quotes are even comparable; the rest decide which one is better value.
| # | What to Check | What to Ask | Red Flag |
|---|---|---|---|
| 1 | Capacity and phase | Is the kVA sized for my running load plus about 25% margin? Single or three phase? | kVA quoted without seeing your load list |
| 2 | Servo or relay | Is it a servo (motor-driven variac) or a relay (tap-changing) stabilizer? | “Automatic stabilizer” with no type stated |
| 3 | Input voltage range | What is the range per phase and phase to phase? Does it cover my lowest reading? | Range not stated, or stated only as “wide range” |
| 4 | Output voltage and accuracy | What output is held, and within what accuracy (for example ±1%)? | No accuracy figure |
| 5 | Balanced or unbalanced | Does it correct all phases together, or each phase separately? | Not stated on a three-phase quote |
| 6 | Cooling | Air cooled or oil cooled? Is the first fill of transformer oil included? | Oil cooling quoted without oil quantity |
| 7 | Correction speed | How many volts per second does it correct? | Unknown or not stated |
| 8 | Efficiency | What is the full-load efficiency (for example above 98%)? | No efficiency figure |
| 9 | Winding and core | Copper or aluminium winding? CRGO core? Transformers made in-house? | “Best quality” with no material stated |
| 10 | Standards | Which standard is the unit built to (for example IS 9815 (Part 1):2025 for single phase)? | No standard named |
| 11 | Protections | Over/under voltage, overload, time delay, phase reversal and single phasing? | Only “high/low cut-off” |
| 12 | Display and controls | Does the display show voltage, current and frequency for each phase? Is there a bypass switch? | Analog meters only, no bypass |
| 13 | Testing and certificates | Is every unit tested before dispatch? Is there a test report or a lab-tested design? | No test report offered |
| 14 | Warranty and AMC | What does the warranty cover, for how long, and is an AMC available — in writing? | Warranty given only verbally |
| 15 | Service and spares | Who services it near my site? Are carbon brushes and control cards stocked locally? | Service only from another state |
| 16 | Buck-boost transformer rating | What is the buck-boost kVA per phase, and what temperature rise is it designed for? | Not disclosed |
| 17 | Variac contact | Carbon brush or roller contact? How often does it need replacing? | No replacement interval given |
| 18 | Control card | Digital with display, fault codes and settings, or analog? | Analog card on a large unit |
| 19 | Enclosure | Indoor or outdoor? Sheet thickness, finish and IP rating? | Indoor enclosure quoted for an outdoor or dusty site |
| 20 | Weight and size | What is the weight and footprint? (On oil-cooled units, also the oil quantity.) | Much lighter than other quotes for the same kVA and range |
For three-phase sites, point 5 matters more than most buyers expect. Read our guide to balanced vs unbalanced servo stabilizers before you decide.
Why Does the Input Range Change the Price So Much?
The input range changes the price because the buck-boost transformer must be sized for the largest correction the stabilizer has to make. A wider range means a bigger transformer, more copper and steel, and a higher price for the same kVA.
The input voltage range is usually the biggest single reason two quotes for the same kVA differ. The buck-boost transformer has to make up the gap between the lowest input voltage and the output voltage, at full load current.
Example: 25 kVA three-phase stabilizer, 415V output
| Input Range (phase to phase) | Largest Correction Needed | Buck-Boost Capacity (before margin) |
|---|---|---|
| 340–460V | 75V boost (about 18% of 415V) | about 4.5 kVA |
| 295–465V | 120V boost (about 29% of 415V) | about 7.2 kVA (about 60% more) |
So a quote built for 340–460V can look much cheaper than one built for 295–465V, even though both say “25 kVA”. If your site voltage falls below 340V in the evenings, the cheaper unit can't protect your equipment. The most common reason for a “cheap” quote is a narrower input range than you asked for. Always check the range on every quote, and state it the same way: per phase or phase to phase (phase to phase is about 1.73 times the per-phase value).
Use weight as a sanity check. For the same kVA and input range, more copper and steel usually means a heavier unit. If one quote is much lighter than the others, ask why.
Step 3: Compare the Total Delivered Cost
Two quotes can look far apart until you add what each one leaves out. Ask each supplier to confirm, in writing, whether these are included:
GST servo stabilizers are generally billed at 18%
Input MCCB and bypass switch and whether they are standard or extra
Test reports and whether you can witness a test at the factory before dispatch
Freight and unloading to your site
Installation and commissioning including connection and first switch-on
Cables, lugs and glands between the stabilizer and the distribution board
Transformer oil (first fill) on oil-cooled units
Base frame or foundation for heavier units
Delivery time if downtime costs you money
Quote validity and payment terms so the price doesn’t change between quote and order
Then compare the total delivered and installed cost, not the ex-works price.
Step 4: Compare the Running Cost, Not Just the Price
The cheapest quote isn't always the cheapest stabilizer to own. Think in terms of total cost of ownership: the purchase price plus energy losses, maintenance and downtime.
A servo stabilizer runs every hour of every day for 10 years or more, so its losses matter. Ask each supplier for the full-load efficiency in writing.
Example: a 25 kVA stabilizer carrying a 16 kW load around the clock. Every 1% difference in efficiency is about 160 W, or roughly 1,400 kWh a year, wasted as heat. Over a ten-year life, a slightly more efficient unit can recover much of a small price difference.
Also count the cost of downtime and repairs. An undersized transformer, aluminium windings or missing protections often cost more in breakdowns and damaged machines than the money saved on day one.
Step 5: Put the Quotes Side by Side
Copy this table into a spreadsheet and fill one column per supplier. Any blank cell is a question to send back before you decide.
| Item | Quote A | Quote B | Quote C |
|---|---|---|---|
| Capacity and phase | |||
| Servo or relay | |||
| Input range (per phase / phase to phase) | |||
| Output voltage and accuracy | |||
| Balanced or unbalanced | |||
| Cooling (and oil quantity) | |||
| Correction speed (V/s) | |||
| Buck-boost kVA per phase | |||
| Variac contact (brush / roller) | |||
| Control card (digital / analog) | |||
| Enclosure and IP rating | |||
| Weight | |||
| Efficiency | |||
| Winding and core | |||
| Protections included | |||
| MCCB and bypass included? | |||
| Testing / test report | |||
| Warranty and AMC | |||
| Nearest service centre | |||
| GST, freight, installation included? | |||
| Total delivered and installed cost | |||
| Delivery time |
Stuck between two quotes? Send them to us. Our engineers will point out what each one leaves out, free and with no obligation to buy. Ask for a second opinion.
What Should a Servo Stabilizer Test Report Show?
“We test every unit” means little without a report. Ask for a sample report before you order, and check that it includes:
Insulation resistance and a high voltage (dielectric) test
Output voltage at no load and full load, across the input range
Correction rate in volts per second
Temperature rise after a load run
Protection checks: high and low voltage cut-off, overload, single phasing and phase reversal
Serial number and date, matching the unit you receive
Indian standard: the Bureau of Indian Standards has replaced IS 9815 (Part 1):1994 with IS 9815 (Part 1):2025, which covers single-phase servo stabilizers. It requires the output to stay within ±1% of rated voltage, and a correction rate of at least 6 V/s between phase and neutral. Use these as the minimum. For three-phase units, ask for the same checks on each phase. For large orders, ask to witness the load test at the factory.
11 Red Flags in a Servo Stabilizer Quote
A servo stabilizer quote is a red flag when key specifications are missing, the price is far below the rest, or the supplier can't show testing and service details. Watch for these 11 warning signs:
A price with no written specification sheet
An input range that doesn’t cover your lowest recorded voltage
No output accuracy or efficiency figure
A three-phase quote that doesn’t say balanced or unbalanced
Protections limited to “high/low cut-off” on a three-phase unit
An unusually low price with no mention of winding material or transformer core
No named service contact in your city
Token or placeholder prices on marketplaces that change once you ask for a firm quote
A unit much lighter than other quotes for the same kVA and input range
Single phasing protection, bypass or MCCB listed as “optional” on a three-phase unit
A relay or static stabilizer quoted when you asked for a servo stabilizer
7 Claims You May Hear While Comparing Quotes
While you collect quotes, a salesperson or an online answer may tell you that you don't need a servo stabilizer at all, or that a different product is better. Some of these claims are partly true. Here is how to judge them:
“Servo stabilizers are too slow.” A servo stabilizer corrects by moving a motor, so it is slower than a static (electronic) stabilizer. Older units were slow. What to do: Ask for the correction rate in volts per second, in writing, and compare it across quotes; it should be well above the 6 V/s minimum in IS 9815.
“It lets spikes and surges through.” Correct. A servo stabilizer corrects slow rises and falls in voltage; it doesn’t block fast surges or lightning spikes. What to do: If your site has surges, add a surge protection device. Check whether a quote includes surge protection or lists it as extra.
“There is no isolation.” Correct. A standard servo stabilizer is an auto-transformer, so input and output are not isolated. What to do: If you need isolation from line noise or a poor neutral (for example, for medical or lab equipment), ask for a stabilizer with a built-in or separate isolation transformer.
“UPS and inverters have replaced stabilizers.” A UPS is the right choice for computers and servers that need backup power. What to do: For whole buildings, motors, ACs, lifts and CNC machines, a UPS of the same kVA costs far more and isn’t designed for motor starting. Servo stabilizers remain the standard choice for voltage correction at 10 kVA and above.
“Modern devices with SMPS don’t need a stabilizer.” Many phones, laptops and LED drivers use switch-mode power supplies that accept a wide input range. What to do: Motors, compressors, ACs, pumps, lifts and machine tools don’t. They draw more current and run hotter when the voltage is low or high. Size the stabilizer for these loads.
“Output within ±3V is good enough.” Older home stabilizers held about ±3V. What to do: Industrial servo stabilizers, including SG Power’s, hold ±1%. Ask each supplier for output accuracy as a percentage.
“The variac wears out.” The carbon brush is a wear part and needs periodic checks. What to do: Ask how often the brush needs replacing, whether spares are in stock, and whether the warranty treats it as a consumable.
7 Lessons From Indian Buyer Forums
Buyers on Team-BHP, TechEnclave and HiFiVision share what went right and wrong after buying servo stabilizers. Here's what they learned the hard way, and what to check in your own quote:
A home was quoted a 30 kVA three-phase unit, far more than its load needed. Check the sanctioned load on your electricity bill and your real running load. A stabilizer far above both costs more without adding protection. A servo stabilizer for home use is usually a 10 kVA or 15 kVA single-phase unit.
Servo stabilizers are built to order, so the engineer you deal with matters most. Ask who sized the unit and how. A supplier who asks for your load list and voltage readings is a good sign.
One buyer returned a mainline stabilizer because after-sales support was poor. Get the service contact, response time and AMC terms in writing. A failed whole-house unit leaves every appliance unprotected.
Units failed after lightning or an HT line fault. Ask whether surge protection is included, and whether the warranty covers lightning damage (it usually doesn't). Budget for a surge protection device.
A three-phase unit cost far more than a single-phase unit of the same kVA. Compare like with like. For a home without three-phase loads, ask for both options before you decide.
The whole house went dark when one phase failed. Ask how the unit behaves on single phasing, and whether a bypass or changeover switch is included.
Owners asked whether the stabilizer maker pays if a failure damages appliances. Most warranties cover the stabilizer only. Make sure the quote lists output high and low voltage cut-off, which disconnects the load if the unit misbehaves.
Need help sizing a home unit? Our guide on how to calculate servo stabilizer kVA covers homes, offices and factories.
Example: Two 25 kVA Quotes Compared
A workshop with a CNC lathe, a compressor and lighting asked two suppliers for a 25 kVA three-phase servo stabilizer. Quote A was noticeably cheaper. Side by side, the difference was clear:
| Item | Quote A (lower price) | Quote B (higher price) |
|---|---|---|
| Input range | Narrow; did not cover the site’s evening low | Covered the lowest recorded voltage |
| Design | Balanced only | Balanced, matched to the three-phase motor load |
| Protections | High/low cut-off only | Over/under voltage, overload, time delay, phase reversal, single phasing |
| Testing | Not stated | Every unit tested; test report supplied |
| Included | Ex-works, GST extra | GST, freight and installation included |
| Service | From another state | Local service centre |
Once GST, freight and installation were added to Quote A, the gap narrowed sharply, and Quote A would not have protected the machines on the site's lowest evenings. Quote B was the better value.
Key Takeaways
Compare servo with servo and make sure every quote is for the same kVA, phase, input range, cooling and design.
Send every supplier the same brief, with your load list and real voltage readings, and ask for a written specification sheet.
The input range is the biggest hidden price driver; check it per phase.
Compare the total delivered and installed cost, then the running cost, not the headline price.
Ask for a sample test report, warranty terms and a named service contact before you order.
Treat a price far below the rest as a red flag, not a bargain.
How We Quote at SG Power
We're a servo stabilizer manufacturer, so we see both sides of this. When you ask us for a quote, you get a one-page specification for the exact model, with the input range, output accuracy, protections, testing and what the price includes written down. That makes it easy to put our quote next to anyone else's.
Our range runs from 10 kVA to 500 kVA (air cooled 10–50 kVA, oil cooled 60–500 kVA). Every unit holds the output within ±1% and is tested through 173 checkpoints before dispatch. See the servo voltage stabilizer range and price list.
Want a like-for-like quote? Send your load list and voltage readings, and we'll reply with a written quote you can compare line by line.
Frequently Asked Questions
* Prices are indicative. For the latest price, contact SG Power.
Sources
SG Power Products Pvt. Ltd., servo stabilizer catalogue (February 2026): models, input ranges, protections and testing
Indian buyer discussions on servo stabilizers: Team-BHP, TechEnclave, HiFiVision and Quora (read November 2026)