Question 1

What is transformer sizing in electrical engineering?

Accepted Answer

Transformer sizing is the process of determining the appropriate power rating, voltage levels, current ratings, and other electrical parameters for a transformer to meet specific load requirements. It involves calculating power ratings, efficiency, impedance, voltage regulation, and losses to ensure proper operation and safety.

Question 2

How do you calculate transformer power rating?

Accepted Answer

Transformer power rating is calculated using P = V × I, where P is power in VA (or kVA), V is voltage, and I is current. For three-phase transformers, the formula becomes P = √3 × V × I. The power rating must be sufficient to handle the connected load plus any future expansion requirements.

Question 3

What is transformer efficiency and how is it calculated?

Accepted Answer

Transformer efficiency is the ratio of output power to input power, expressed as a percentage. It's calculated as η = (P_out/P_in) × 100%. Typical efficiencies range from 95-99% for distribution transformers and 97-99.5% for power transformers. Efficiency decreases with load and increases with transformer size.

Question 4

How do you determine transformer impedance?

Accepted Answer

Transformer impedance is typically expressed as a percentage and represents the voltage drop under full load conditions. It's calculated as Z = (V²/P) × 100%, where V is the rated voltage and P is the power rating. Standard impedances are 2-5% for distribution transformers and 5-15% for power transformers.

Question 5

What is voltage regulation in transformers?

Accepted Answer

Voltage regulation is the change in secondary voltage from no-load to full-load conditions, expressed as a percentage of the full-load voltage. It's calculated as VR = ((V_no_load - V_full_load)/V_full_load) × 100%. Good voltage regulation is typically less than 5% for distribution transformers.

Question 6

How do you calculate transformer losses?

Accepted Answer

Transformer losses consist of core losses (iron losses) and copper losses (winding losses). Core losses are constant and depend on the core material and flux density. Copper losses vary with the square of the load current. Total losses = Core losses + Copper losses = P × (100 - η)/100, where η is efficiency percentage.

Question 7

What factors affect transformer sizing?

Accepted Answer

Key factors include: 1) Load requirements (power, voltage, current), 2) Load type (continuous, intermittent, peak), 3) Ambient temperature and cooling requirements, 4) Voltage regulation requirements, 5) Efficiency requirements, 6) Future expansion plans, 7) Installation environment, 8) Cost considerations, and 9) Standards and regulations.

Question 8

How do you size a transformer for motor loads?

Accepted Answer

For motor loads, consider: 1) Motor starting current (typically 6-8 times full-load current), 2) Motor efficiency and power factor, 3) Multiple motor coordination, 4) Voltage drop during starting, 5) Transformer impedance effects. Size the transformer to handle starting current without excessive voltage drop (typically 5-10% of motor full-load current).

Question 9

What is transformer derating and when is it needed?

Accepted Answer

Transformer derating is reducing the transformer's rated capacity due to environmental conditions or operating factors. Common derating factors include: 1) High ambient temperature (above 40°C), 2) High altitude (above 3300 ft), 3) Non-linear loads (harmonics), 4) Poor ventilation, 5) Frequent overload conditions. Derating factors range from 0.8 to 0.95 depending on conditions.

Question 10

How do you select transformer cooling methods?

Accepted Answer

Transformer cooling methods include: 1) ONAN (Oil Natural Air Natural) - for small transformers, 2) ONAF (Oil Natural Air Forced) - for medium transformers, 3) OFAF (Oil Forced Air Forced) - for large transformers, 4) OFWF (Oil Forced Water Forced) - for very large transformers. Selection depends on power rating, ambient conditions, and installation requirements.

Transformer Sizing Calculator - Electrical Transformer Calculator & Power Rating Calculator

Electrical Parameters:

Losses:

Applications:

Common Examples

Practical Examples

Transformer Sizing Calculator Types & Methods

Quick Example Result

How Our Transformer Sizing Calculator Works

Transformer Sizing Principles

Electrical Engineering Foundation

Sources & References

Transformer Sizing Calculator Examples

Given Parameters:

Calculation Steps:

Efficiency Calculation Example

Impedance Calculation Example

Frequently Asked Questions

Found This Calculator Helpful?

Related Calculators