1. What is the efficiency and loss level of the transformer?

- The efficiency and loss level of a transformer are key performance indicators that reflect how well
it converts input electrical power to output power with minimal waste. Here's a basic explanation of
both:

- 1. Transformer Efficiency

 Definition: Efficiency is the ratio of the output power to the input power.
 Formula:

Efficiency(%)=(Output PowerInput Power)×100\text{Efficiency} (\%) = \left( \frac{\

text{Output Power}}{\text{Input Power}} \right) \times
100Efficiency(%)=(Input PowerOutput Power)×100

 Typical Range:
o Distribution transformers: 98% – 99.5%

Power transformers: 99% – 99.75%

 Note: Efficiency is usually highest at around 50% to 75% of full load.

2. Transformer Loss Level

Transformer losses are broadly classified into:

a. No-load Loss (Core Loss):

 Occurs when the transformer is energized but not supplying any load.
 Includes:
o Hysteresis loss
o Eddy current loss
 Depends on core material, flux density, and voltage.
 Fixed losses (independent of load).

b. Load Loss (Copper Loss):

 Occurs due to resistance in the winding when current flows under load.
 Proportional to the square of the load current (I²R losses).
 Varies with load level.

 2.What is the load capacity and how future-proof is the transformer?

- Load capacity- refers to the maximum electrical load a transformer can handle
safely without Influenced By-
 Ambient temperature
  Load profile (constant or fluctuating)
 Harmonics (from non-linear loads like solar/wind inverters)
 Overload tolerance (short-term)

Overload Capacity:

Many transformers can handle short-term overloads:

 Typically 10–20% overload for 1–2 hours (as per IS/IEC standards)
 Depends on insulation class and cooling

Future-Proofing of a Transformer

Oversized Rating

Low Loss Design

Expandable Cooling System

Dual/Multiple Tapping Range

Standard Compliant:- IS/IEC/BEE Star Rated (Level 1 = Most Efficient)

3.Is the transformer oil-immersed or dry type? Which one suits

my application better?

Oil-Immersed- Windings and core are submerged in insulating mineral oil or ester oil.
-Air-cooled, with epoxy or resin-coated windings, no oil
Dry Type
involved.
Feature Oil-Immersed Dry Type
Limited, suitable for lower
Cooling Efficiency Better, especially for high ratings
ratings
kVA Capacity Range Up to 10,000 kVA or more Usually up to 2500 kVA
Voltage Level
Ideal for 11kV / 33kV Mostly up to 11kV
Suitability
Indoor use (schools, malls,
Location Suitability Outdoor or indoor (with precautions)
hospitals)
Fire Safety Risk of fire due to oil (needs protection) Safer—no oil involved
Maintenance Requires periodic oil testing Lower maintenance
Cost More cost-effective for higher capacity Higher for same rating
Environmental Risk Potential oil leak/spill Environmentally cleaner

4.What type of tapping system is used (OCTC, OLTC, etc.) and how reliable
is it in continuous operation?
OCTC -Off-Circuit Tap Changer Manual, offline For fixed or rarely changing voltages
On-Load Tap Automatic or remote,
OLTC- For variable voltages/load fluctuations
Changer online
Benefit Description
Allows tap changes while transformer is energized, avoiding
⚡ Live Voltage Regulation
shutdowns.
Works with AVR (Automatic Voltage Regulator) to maintain
🧠 Automatic Voltage Control
constant output voltage.
Crucial for solar/wind/grid transformers, compensates for
📈 Grid Stability
fluctuating input voltages.
Adapts to varying industrial loads to ensure equipment
🏭 Load Compensation
receives stable voltage.
Keeps voltage within acceptable limits, reducing overvoltage
💡 Improved Power Quality
or undervoltage risks.
No need to interrupt service for tap changes – saves
🕒 Operational Flexibility
downtime and manpower.
🔧 Wide Voltage Adjustment Offers multiple tap steps (e.g., ±10% or more) for fine-tuned
Range control.
Reduces voltage-related faults, maintenance costs, and
💰 Cost-Efficient in Long Run
equipment wear.

5.Tests

1. Routine Tests (As per IS/IEC standards)

These are conducted on every transformer before dispatch.

🔹 a. Insulation Resistance (IR) Test

 Measures resistance between windings and earth.

 Ensures insulation quality.

🔹 b. Winding Resistance Test

 Measures resistance of each winding using micro-ohmmeter.

 Ensures proper connection and winding health.

🔹 c. Turns Ratio Test (Voltage Ratio Test)

 Verifies the correct transformation ratio.

 Ensures proper winding configuration.

🔹 d. Vector Group Test

 Ensures correct phase displacement and connection type.

  Essential for parallel operation and system compatibility.

🔹 e. Polarity and Phase Relation Test

 Confirms the correct polarity and phase sequence of windings.

🔹 f. No Load Loss & No Load Current Test

 Measures losses when the transformer is energized but not loaded.

 Related to core performance.

🔹 g. Load Loss and Impedance Voltage Test

 Conducted at rated current to determine copper loss and impedance.

🔹 h. Dielectric/Applied Voltage Test

 High voltage applied to check insulation between windings.

🔹 i. Induced Over Voltage Test

 Double voltage applied to check insulation under stress.

2. Type Tests (On one unit of each design)

Performed on prototype/first unit to validate design.

🔹 a. Temperature Rise Test

 Transformer is loaded to full load for hours to check thermal behavior.

🔹 b. Lightning Impulse Withstand Test

 Simulates lightning surge impact.

 Confirms insulation level against overvoltage.

3. Special Tests (On request or per agreement)

These may be required for specific applications or client requirements.

🔹 a. Partial Discharge Test

 Detects insulation defects.

🔹 b. Frequency Response Analysis (FRA)

 Identifies mechanical displacement of windings.

🔹 c. Noise Level Measurement

 Ensures noise levels are within acceptable limits.

🔹 d. Harmonic Analysis

 Identifies distortion due to non-linear loads.

🔹 e. Oil BDV (Breakdown Voltage) & DGA (Dissolved Gas Analysis)

 Ensures transformer oil quality and detects faults.

Test provided (Free)

 1. Turns Ratio Measurement
 Purpose:
To ensure the correct voltage transformation ratio between primary and secondary
windings.
 How it's done:
A voltage is applied to one side, and the output voltage on the other side is measured.
The actual ratio is compared to the designed value.
 Proves:
That the windings are correctly designed and connected, with no shorted or open
turns.


 2. DC Winding Resistance Measurement

 Purpose:
To check the electrical resistance of transformer windings for uniformity and
correctness.
 How it's done:
A low DC current is applied to the winding, and the voltage drop is measured using
Ohm’s Law (R = V/I).
 Proves:
Quality of winding joints and terminations, and identifies issues like loose
connections or conductor damage.


 3. Vector Group Measurement

 Purpose:
To verify the phase relationship (vector group) between the primary and secondary
windings.
 How it's done:
Measurements are taken using voltmeters to identify the vector phase displacement
and terminal configuration.
 Proves:
Correct phase alignment for parallel operation and system compatibility.


 4. Insulation Resistance Measurement (IR Test)

 Purpose:
To assess the insulation health between windings and between windings to ground.
 How it's done:
A megohmmeter (megger) is used to apply high DC voltage and measure resistance in
Megaohms.
 Proves:
Good insulation and absence of moisture or degradation.


 5. No Load Loss Measurement (Core Loss)

 Purpose:
To measure the losses when the transformer is energized with no load connected.
 How it's done:
Rated voltage is applied to the primary, and power loss (in watts) is measured.
 Proves:
Quality of the core material and assembly.


 6. Full Load Loss Measurement (Copper Loss)

 Purpose:
To measure power losses under full load conditions (mainly in the windings).
 How it's done:
Rated current is passed through the transformer (usually using short-circuit test setup),
and losses are measured.
 Proves:
Winding resistance and overall copper loss at operating conditions.


 7. Magnetizing Current Measurement

 Purpose:
To measure the current required to magnetize the transformer core (without load).
 How it's done:
Current is measured while rated voltage is applied to one winding (usually the HV
side).
 Proves:
Core condition and absence of issues like core saturation or shorted laminations.


 8. Short Circuit Current Measurement

 Purpose:
To measure the voltage required to circulate rated current when the secondary is
shorted.
 How it's done:
Secondary winding is shorted, and a gradually increasing voltage is applied to the
primary until rated current flows.
 Proves:
Impedance of the transformer and is useful for protection system settings.


 9. Induced Over Voltage Withstand Test

 Purpose:
To check insulation strength between turns and phase windings under high voltage.
 How it's done:
A voltage about 2× rated is applied at double frequency to the secondary winding,
while the primary is left open.
 Proves:
That internal insulation can withstand overvoltage conditions (e.g., lightning surges).


 10. Separate Source Voltage Withstand Test (Applied Voltage Test)

 Purpose:
To verify insulation between windings and earth or between HV and LV windings.
 How it's done:
High voltage (usually 2 kV to 5 kV depending on the transformer rating) is applied
for 60 seconds between windings and ground using a separate test source.
 Proves:
Dielectric strength of the insulation system.


 11. BDV Test of Oil (Breakdown Voltage Test)

 Purpose:
To evaluate the dielectric strength of transformer oil.
 How it's done:
Oil is placed in a test cell with electrodes, and voltage is increased until breakdown
occurs.
 Proves:
Whether oil is clean, dry, and capable of insulating under high voltage.