# What is the transformer capacity unit? Transformer capacity grade and calculation formula

What is the transformer capacity unit?Dongguan Juke transformer manufacturer transformer capacity grade and calculation formula

In a power system, the total capacity of the transformer far exceeds the capacity of the generator set and the motor. In the process of transferring electrical energy, the transformer consumes a part of active power and reactive power. Reasonable and accurate calculation of the optimal economic capacity of the transformer is one of the necessary means to reduce energy consumption. What is the unit of transformer capacity? What are the transformer capacity levels and calculation formulas?

What is the transformer capacity unit?

The power transformer capacity unit uses KVA, which is the apparent power. The power load is mostly an inductive load, and its apparent power is equal to the vector sum of active power and reactive power. Therefore, the apparent power of the inductive load is greater than the active power. If the active power is used to select the transformer, the apparent power of the inductive load is greater than the capacity of the power transformer, and the load current must exceed the allowable value of the transformer. Therefore, the inductive load must use the apparent power selection transformer.

If the load on the transformer is all a resistive load, its total power can be equal to the KVA value of the transformer.

KVA instead of KW? VA or KVA is the apparent power, used in AC lines, also known as capacity, which is the product of the effective value of voltage and current, but... it will affect the load design of the transformer, so it is more accurate to calculate with VA or KVA. And W or KW is the name we usually used to, written formal.

Transformer capacity rating

Transformers are generally divided into oil-immersed transformers and dry-type transformers. Their representatives are S11-M transformers and transformers such as SCB10. Since oil-immersed transformers use oil as an insulating medium, the capacity is often made larger. The capacity specifications of dry-type transformers are much smaller.

1. Immersion transformer capacity grade

(1) 6kv and 10kv systems: 10kva, 20kva, 30kva, 50kva, 80kva,100kva, 125kva, 160kva, 200kva, 250kva, 315kva,400kva, 500kva, 630kva, 800kva, 1000kva,1250kva, 1600kva, 2000kva, 2500kva, 3150kva, 4000kva, 5000kva;

(2) 35kv and 60kv systems:315kva, 400kva, 500kva, 630kva, 800kva, 1000kva,1250kva, 1600kva, 2000kva, 2500kva, 3150kva, 4000kva, 5000kva;

(3) 110kv and above systems: 3150kva, 4000kva, 5000kva, 6300kva,8000kva, 10000kva, 12500kva, 16000kva, 20000kva, etc.

2, dry transformer capacity level

(1) 6kv and 10kv systems: 10kva, 20kva, 30kva, 50kva,80kva, 100kva, 125kva, 160kva, 200kva, 250kva, 315kva,400kva, 500kva, 630kva,800kva, 1000kva, 1250kva, 1600kva, 2000kva, 2500kva, 3150kva, 4000kva, 5000kva;

(2) 35kv system: 30kva, 50kva, 80kva, 100kva, 125kva,160kva, 200kva, 250kva, 315kva, 400kva,500kva, 630kva, 800kva, 1000kva, 1250kva,1600kva, 2000kva, 2500kva, 3150kva, 4000kva, 5000kva;

(3) 60kv system: 315kva, 400kva, 500kva, 630kva,800kva, 1000kva, 1250kva, 1600kva,2000kva, 2500kva, 3150kva, 4000kva, 5000kva;

(4) 110kv and above systems: 3150kva, 4000kva, 5000kva, 6300kva, 8000kva, 10000kva.

Calculation formula of transformer capacity

The capacity of the transformer should be selected according to the load. For a single transformer with smooth load supply, the load rate is generally about 85%.

Namely: β=S/Se-------Formula (1)

Where: S is the calculated load capacity (kVA) Se is the transformer capacity (kVA); β is the load rate (usually 80% to 90%)

Transformer capacity selection method

Here we use a simple example to illustrate how to use the above formula to select the transformer.

A 110kV/6.3kV substation with a self-supplied generator set capacity of 25MW. The total electrical load of the device is 16 MVA. It is expected that our factory will not increase the load for a long time. Under normal operating conditions, cosφ = 0.9 (power factor) in the system. For a single main transformer with a smooth load and a load factor of 0.85, calculate according to formula (1)

Se=S/β=p/β.cosφ=20915KVA

According to the calculated load Se and the transformer capacity class, a 110kv oil-immersed transformer with a capacity of 25000kva is selected.

What is the unit of transformer capacity? After the introduction of the transformer capacity class and calculation formula, everyone should have an understanding of the transformer capacity unit. Power transformers are indispensable and widely used equipment in power supply and distribution systems. Correct and reasonable selection of transformers is a guarantee for the economic, safe and reliable operation of power systems, and is also of great significance in terms of energy conservation and consumption reduction.