What is a 25 kVA Transformer

A 25 kVA transformer handles a maximum apparent power of 25,000 volt-amperes (VA), the product of voltage and current in an AC circuit.

The “25” in 25 kVA refers to the transformer’s maximum capacity to handle apparent power, not its actual power output. To determine the actual power output, consider the power factor of the connected load. A 25 kVA transformer with a power factor of 0.8 has a real power output of 20 kilowatts (kW).

Typical input and output voltage ranges

Output voltages for 25 kVA transformers often include 208V, 240V, and 120V. The 208V and 240V outputs power larger equipment, such as motors, heavy machinery, and high-power appliances. The 120V output is suitable for smaller devices, lighting, and general office equipment.

Types of 25 kVA Transformers

Single Phase Transformers

Single phase transformers are commonly used for 25 kVA power applications. These transformers feature two windings: a primary and a secondary winding. They operate on a single alternating current (AC) phase, making them suitable for residential and light commercial electrical loads.

Three Phase Transformers

Three-phase 25 kVA transformers are widely used in industrial and commercial settings for high-power applications. They offer a more efficient and balanced power distribution compared to single-phase transformers, making them suitable for handling larger loads. These transformers feature three separate windings, with each phase positioned 120 degrees apart, ensuring a steady and continuous power supply.

Three-phase transformers provide several benefits over single-phase transformers. They allow for reduced conductor size, improved power factor, and better voltage regulation. Additionally, they minimize harmonic distortion, resulting in a more stable power supply for sensitive equipment.

Key Specifications and Features

Power handling capacity and load considerations

A 25 kVA transformer has a maximum apparent power capacity of 25,000 volt-amperes (VA). Apparent power is the product of voltage and current in an AC circuit. The actual power delivered to the load, known as real power (measured in watts), will be less than the apparent power due to the power factor of the connected devices.

Cooling methods (ONAN, ONAF) and noise levels

ONAN (Oil Natural Air Natural) and ONAF (Oil Natural Air Forced) are the two primary cooling methods for 25 kVA transformers. ONAN cooling relies on natural convection for oil circulation and heat dissipation, making it a silent option ideal for residential and noise-sensitive areas. However, ONAN has lower cooling efficiency compared to ONAF.

ONAF cooling uses fans to force air circulation around the transformer, enhancing heat dissipation and allowing for higher load capacity. While more efficient than ONAN, ONAF generates more noise due to the fans.

ONAN transformers typically have noise levels around 40-50 dB, while ONAF transformers can reach 60-70 dB.
Factors Affecting Noise Levels

Overcurrent protection devices and fusing options

Overcurrent protection devices, including circuit breakers, fuses, and thermal overload relays, safeguard 25 kVA transformers and connected equipment from excessive current caused by overloads, short circuits, or fault conditions.

• Circuit breakers offer adjustable trip settings and easy resetting after tripping. Fuses provide fast-acting protection but require replacement once blown.
• Thermal overload relays monitor transformer temperature and trip when preset limits are exceeded.
• Current-limiting fuses quickly interrupt fault currents, minimizing damage. Expulsion fuses use gas-evolving materials to extinguish arcs. Fuse ratings must be coordinated with the transformer’s rated current and short-circuit capacity for proper protection.

Insulation and weatherproofing

Insulation materials for 25 kVA transformers include epoxy resins, silicone rubbers, and polyurethanes. These materials offer high dielectric strength, resistance to moisture, chemicals, and extreme temperatures, as well as mechanical strength and durability.

Weatherproofing is crucial for outdoor transformer installations. Corrosion-resistant enclosures made from stainless steel or aluminum, along with gaskets and seals, prevent water and dust ingress. Adequate ventilation dissipates heat and prevents condensation. Additional protections for harsh environments include anti-corrosion coatings, UV-resistant finishes, and rodent screens.

Taps and adjustability for voltage regulation

Taps, connection points on transformer windings, allow voltage output adjustment in 25 kVA transformers. Multiple taps provide a range of voltages, typically ±5% or more, to match specific requirements and compensate for voltage drops.

No-load tap switches enable voltage setting changes without disconnecting the transformer from the power source. They simplify voltage adjustments and minimize downtime.

Winding material (aluminum vs. copper) and its implications

Copper windings offer superior electrical conductivity, resulting in lower losses and higher efficiency compared to aluminum. Copper’s resistance to corrosion and its mechanical strength contribute to the transformer’s longevity and reliability.

Aluminum windings, while less conductive than copper, provide several advantages in transformer design. Aluminum’s lighter weight reduces the overall weight of the transformer, simplifying handling and transportation. Its higher resistance to short-circuit forces enhances the transformer’s durability, making it less susceptible to damage from electrical faults.

Dimensions and weight

A 25 kVA transformer’s dimensions typically measure 24-30 inches in length, 18-24 inches in width, and 24-30 inches in height.

Weight ranges between 400-600 pounds, contingent on materials and additional components like cooling fins or mounting brackets.

FAQs

How Many Amps Can a 25kVA Transformer Handle

A 25kVA transformer can handle approximately 60 amps at 240 volts or 120 amps at 120 volts, assuming a single-phase system with a power factor of 0.8.

What is the load capacity of a 25 kVA transformer

The load capacity of a 25 kVA transformer is 25,000 volt-amperes or 20,000 watts, assuming a power factor of 0.8.

How many AC can run on 25 kVA transformer

The number of air conditioners that can run on a 25 kVA transformer depends on their individual power consumption. Typically, a 25 kVA transformer can support around 12-15 standard residential AC units, assuming each unit has a power rating of 1.5 to 2 tons.

How Many Houses Can a 25 kVA Transformer Handle

A 25 kVA transformer can typically handle 5-7 average-sized homes, depending on the total electrical load of each household.

How Much Does a 25 kVA Transformer Cost

The cost of a 25 kVA transformer can vary based on factors such as brand, quality, and market conditions. On average, prices range from $2,000 to $5,000.

How Much Oil Do You Need in a 25 kVA transformer

The oil quantity required for a 25 kVA transformer is approximately 80 to 100 liters, depending on the transformer’s design and cooling system.

What Is the Typical Efficiency of a 25 Kva Transformer

The efficiency of a 25 kVA transformer is usually between 95% and 98%, depending on the load factor and transformer design.