How to calculate the capacity of a transformer Details 0 3

Formulas can be represented. The selection of transformer capacity and the type and characteristics of the load, the load rate, and the need.

rate, power factor, transformer active and reactive power loss, electricity price (including basic electricity price), infrastructure investment, (including transformer** and installation civil construction costs and power supply subsidies), service years.

limit, transformer depreciation, maintenance costs, and future plans.

1) Basic estimation of transformer capacity.

The basic estimation of transformer capacity mainly includes the following three aspects.

1. Estimate by calculating the load method.

Find the total calculated load to be supplied by the transformer, and then estimate it as follows.

Total transformer capacity = total calculated load + considering future capacity allowance.

2. Estimate by the most economical operation effect method.

The transformer selected has an optimal economic load equal to or close to the actual operating load, i.e.:

The transformer capacity is approximately equal to s betam, where s - actual operating load, kva;

Beta M – the load factor at the highest efficiency of the selected transformer.

The transformer selected according to the above formula tends to have a large capacity and a corresponding load rate beta according to the highest efficiency.

m The transformer chosen to operate at the highest efficiency does not necessarily lead to the best for the company.

Good economic benefits. This is due to the lack of comprehensive consideration of the various transformers that affect the economic choice of enterprises.

Kind of factor.

3. Select the transformer according to the method of minimum annual power loss.

This method is suitable for different enterprise nature and production shift and load curve occasions, it is the root.

According to the principle of minimum annual power loss, the transformer capacity is selected, therefore, from the perspective of energy saving.

More reasonable. The calculation results show that the transformer capacity should be at the service load and the maximum economic load.

to choose. For one-shift enterprises, the transformer capacity can be selected according to the load used, or it can be omitted.

margin; Enterprises with intermittent second shifts and intermittent third shifts can use one level higher and higher loads respectively in proportion.

The capacity of the second stage or so selects the transformer; Three-shift continuous system enterprises, the transformer can be selected according to the most economical load.

However, this method only considers the minimum annual power loss, and does not consider other factors, so it is still incomplete. According to the transformer's annual power loss is the smallest and the operating cost is the lowest, and the comprehensive examination.

It is economical and reasonable to consider the investment in transformer installation to determine the installed capacity of transformer.

Why is the capacity of the transformer we use calculated according to the multiplier?

The capacity of the transformer in kilovolt amperes (kva) = primary input voltage (kv) * primary current. KVA is the apparent power.

For example: Choose a 35 10kV transformer. Assuming that the maximum load is 3500kw, the power factor is, choose two transformers, capacity s=, you can choose a transformer of 3150kva, and the voltage ratio is 35kv. Then select the model number from the product catalog.

When the calculated load of the building is determined, the ** capacity of the distribution transformer is: s=pjs b cos 2(kva).

where pjs - the active calculated load of the building kw, cos 2 - the average power factor after compensation, not less than.

=s/se。

The formula for calculating the capacity of the transformer: =s SE where S: calculate the load capacity (KVA) and SE: the transformer capacity KVA. : load factor (usually 80 90).

The principle of reasonable transformer capacity should follow the following points:

1. The rated capacity of the transformer should be able to meet the needs of all loads, that is, to meet the needs of the total calculated load of all electrical equipment, so as to avoid the overload of the transformer during operation.

2. The capacity of the transformer should not be too large or too small: for the substation or distribution station with two or more transformers, it should be considered that when one of the transformers fails, the capacity of the remaining transformers should be satisfied.

The need for the full load of the first and second categories.

3. The capacity of the selected transformer should be as small as possible to achieve the purpose of flexible operation, convenient maintenance and reducing the number of standby transformers.

4. The normal load of the transformer should be greater than 60% of the rated capacity of the transformer.

The capacity of 10kV dry-type transformer is:

10kva、20kva、30kva、50kva、80kva、100kva、125kva、160kva、200kva、250kva、315kva、400kva、500kva、630kva、800kva、1000kva、1250kva、1600kva、2000kva、2500kva、3150kva。<>

Transformer capacity calculation formula:

1. Calculate the maximum power of each phase of the load.

Add the load power of phase A, phase B, and phase C respectively. For example, the total load power of phase A is 10kW, the total load power of phase B is 9kW, and the total load power of phase C is 11kW. Its maximum value is 11kw.

Note: The power of the single-phase equipment is calculated according to the maximum value on the nameplate. The power of a three-phase device divided by 3 equals the power of each phase of the device.

2. Calculate the total power of the transformer.

11kw 3-phase = 33kw transformer three-phase total power.

3. Calculate the total power of the transformer.

Three-phase total power, this is the most important step, more than 90% of the transformers currently sold on the market have only the power factor, so it needs to be divided by the power factor. Hu Ming.

Total power = 33kw.

4. Calculate the total capacity of the transformer.

The total power of the transformer, according to the "Power Engineering Design Manual", should be selected according to the calculated load of the transformer's capacity. For a single transformer with stable load power supply, its load factor is generally about 85%.

The power of the transformer to be purchased can be purchased with a 50kva transformer.

Some problems with transformer capacity calculations:

The rated capacity of the transformer, the maximum load power to ensure the normal operation of the transformer under the specified use conditions.

The power of the load is the output power of the transformer, that is, the power of the transformer with the maximum load.

When the transformer is rated for operation, the output power of the transformer is equal to the rated capacity.

When the transformer is rated for operation, the input power of the transformer is greater than the rated capacity.

Due to the high efficiency of the transformer, it is generally believed that when the transformer is rated for operation, the input power of the transformer is considered to be equal to the rated capacity, and the calculation results are basically accurate. <>

1. The calculation formula of the load rate of the transformer:

1) Load rate Average load in a certain period of time (e.g., one month, one week) Maximum load in that period;

2) Average load: System power in a certain period, number of hours of operation in that period.

2. Example: The capacity of the transformer is known to be 100kva, and the measured three-phase current is A=, B=, C=, respectively, to find the maximum load current and load rate of the transformer.

Solution: The known condition is that 100kva is the apparent power, which is directly calculated by the apparent power, and cannot be converted into active power.

The maximum load current is the current that can be operated for a long time and cannot be greater than the rated current of the transformer. i=100/；

The load factor is equal to the average current divided by the rated current. Transformer load rate = (108 + 103 + 73) 3 144 = 66%.