Transformer Sizes Chart

Transformers are vital in numerous industries, including health care, manufacturing, electrical contracting, higher education, and corrections.

Large facilities and industrial processes need reliable transformers to convert power plant energy into energy for equipment and building utilities.

In what ways do transformers aid businesses and industries?

Transformers transform energy from a source to the load’s power. Businesses need to know how much power their transformers can deliver to successfully employ them. A transformer’s rating tells you this.

A transformer has two windings, a primary and a secondary. The primary winding receives power. Input leads from the secondary winding deliver power to the load. This is measured in kilovolt-amperes. (Read Microwave Sizes Chart)

Transformer Sizes

When an electrical device fails, the transformer is usually to blame. In that situation, you’ll need to replace your transformer and choose one with the appropriate kVA. If not, you risk frying your expensive equipment.

Choosing a transformer size Fortunately, transformer sizing is straightforward. It entails calculating your kVA requirements from your electrical load’s current and voltage. Here’s how to calculate the needed capacity kVA rating for a transformer.

What Are The Standard Sizes Of Transformers?

Standard dimensions for 3-phase transformers: 3, 5, 8, 10, 45, 75. Although it is better to know a bit more about such devices. When you begin talking about primary and secondary winding, it is handy to have a point of reference.

How Do Three-Phase Transformers Work?

A three-phase transformer functions similarly to a three-set iron core transformer.

Each set has its own primary and secondary windings, with three-phase AC providing the majority of the power.

A three-phase transformer is a self-contained, largely static device that operates in alternating current (AC).

A generator creates electricity by revolving three coils or windings within a magnetic field in power generation. You’ll discover that 3-phase transformers work the same way.

They have “Delta” or “Wye” connections, which have coils or windings spaced 120 degrees apart. Although, instead of generating power, a transformer doesn’t generate power; rather it converts voltage that passes through them.

Three coils or windings are present in every 3-phase system. When these coils are arranged in the correct order, voltages on desired ratings can be matched. (Read EMT Conduit Sizes Chart)

The transformer offers many advantages over a single-phase solution.

The following are the most notable:

  • It is less costly: Three single-phase transformers are more expensive than three of the same rating.
  • Lighter to maneuver.
  • More compact.
  • Easier to assemble and install.
  • Better efficiency and performance
  • You can convert from 3-phase to single phase

Sometimes a three-phase transformer isn’t suitable.

  • Maintenance and repair costs more.
  • If your three-phase transformers break in the middle of a load, all 3 coils shutdown.
  • A three-phase transformer’s faulty winding requires repair or replacement of all parts. In single-phase transformers, only the faulty part has to be changed.

To construct a three-phase transformer, three single-phase transformers are wound on a single core.

The components are subsequently placed in a dielectric oil-filled container by the manufacturers.

The oil in the system regulates the temperature. There are four well-known forms of three-phase connections:

  • Delta to Delta is a popular for industrial use.
  • Delta to Wye is popular for commercial and industrial use.
  • Wye to Delta is popular for high-voltage transmission line.
  • Wye to Wye is generally uncommon as harmonics and voltage regulation are useful.

Standard Sizes Of Transformers

What Size Of Transformer Do I Need?

The voltage of the transformer is calculated by multiplying the second-wave voltage by the needed amps. Divide transformer V by transformer secondary voltage to find transformer currents.

Making a Transformer Size Calculation?

To make a three-phase transformer calculation, you need to know the units involved.

  • VA represents Volts-amperes while kVA represents kilovolts-amperes.
  • These units are the sizing reference for every transformer and represent the apparent power of the device.
  • Apparent power differs from absolute power or real power represented by Watts.
  • Volts is the electromotive force present in a current, while Amperes represents the load current.

How To Calculate kVA?

  1. Look for the Load Voltage (Volts)
  2. Determine the load current (Amperes)
  3. Check line voltage
  4. Last, know which phase design you are using, whether single or three phases.

Use the formula here accordingly:

  • Single-Phase: Volts x Amps /1000 = kVA
  • Three-Phase: Volts x Amps x 1.732 /1000 = kVA

How To Use Three-Phase Transformer Calculation?

Sometimes you need to size a single phase transformer or three-phase transformer, and the KVA rating is the only parameter.

With simple equations, you can determine the correct transformer size.

This equation is the basic transformer formula applied in sing-phase designs:

Volts x Amps / 1,000 = kVA

However, add an extra component when computing a three-phase transformer: the square root of 3 (√3) or 1.732.

This constant is required for three phases, as coils could not simultaneously produce a constant amount of power.

Here, it represents three phases of AC handled by the system, where each line is 120 degrees apart.

Volts x Amps x √3 / 1,000 = kVA

As an example, if you have a 120 voltage and 50 amps for a three-phase system.

120 x 50 x 1.732 / 1,000 = kVA

= 10.392 kVA ~ 11kVA

Rounding up gives you a whole number of 11kVA.

15kVa is of the standard and nearest option here.

Note: Although anything higher than a required kVA can handle lower loads, it pays to be practical in your calculations.

• You don’t want to overkill a load by using a transformer exceeding required ratings.
• In addition, you want to give enough leeway for further expansion.

The best advice is that all calculations are rounded up and you add 20% for a comfort threshold.

• 11kVA x .2 = 2.2
• 11kVA + 2.2 (spare threshold) = 13.2 kVA rounded up to 14 kVA

For our example you would possibly need a 15 kVA three-phase transformer.

Three Phase Transformer

How Many Amps Is A 37.5 kVA Transformer Good For?

To get the appropriate transformer rating for commercial and industrial applications, consider the adjoining requirements such as load and ampacity on our three-phase transformer sizing chart.

Use this Transformer Amperage Chart as a reference for the standard rating among different voltage levels and specifications.

KVA Transformer Size Chart


What Size Transformer Do I Need For A 200 Amp Service?

A 50 VDC transformer would be required if the system carried 200 amps, (50 / 25 = 202.23).

For single and three phase transformers, there are also the following methods for determining or obtaining the Required Capacity transformer kVA Rating or Amperage transformer Capacity:

To calculate kVA, you’ll need at least two pieces of data:

  • Line-to-line voltage of the load (V)
  • The highest current during the load phase (I)

kVA = (V * I) /1000 for single phase transformers

kVA = (V * I * 1.732) / 1000 for three-phase transformers

The square root of 3 has a simple numerical value of 1.732. (1.7320508.)

Then multiply by three to get the following standard 3ph kVA rating.

1. Single Phase Transformer Example:

V = 240, I = 175; Your kVA = (240 x 175) / 1000 = 42 kVA

This works out to 42 kVA thus it is safe to round up to a standard Single Phase size of 50kVA.

2. Three Phase Transformer Example:

V = 208, I = 175; Your kVA = (208 x 175 x 1.732) / 1000 = 63.05kVA
This works out to 63+ kVA thus you can safely round up to a standard Three Phase size 75kVA.

Note: This is a hypothetical kVA estimate that ignores any particular full load needs, such as those found with motors or some medical equipment or other specialty uses. (Learn How To Turn Off Hard-wired Smoke Alarm)

Similar techniques can be used to determine the required capacity KVA rating for an amperage.

3. Single Phase Example:

As a primary voltage starting point, a 50 KVA Single Phase Transformer was used. 50,000 VA is equal to 50KVA.
(K= 1,000) The full load value in VA, 50,000, is then divided by the Voltage 240V = 208 Amperes.

A Two-Step Division, technique such as VA / Voltage = Amperage.

4. Three Phase Example:

Using a 75 KVA Three-Phase systems and Transformer as to start, 75 KVA is equal to 75,000 VA.

(K= 1,000) The full value in VA, 75,000 divided by 1.732 = 43,302, is divided by the Voltage 208V = 208.2 Amperes.

This is a “Three-Step Division”, technique: VA / 1.732 / Voltage = Amperage.

Chart example: Using the figures from the previous Three Phase Transformer Example (V=208, I=175), create a chart. Use the “Three Phase Low Voltage Dry Type Transformers.”

Transformer Sizes Chart

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