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The rated capacity of a transformer is the maximum continuous output capacity that can be achieved throughout its specified normal service life, such as 30 years. The actual output capacity is the product of the voltage under load (under inductive load, the voltage under load is less than the rated no-load voltage), the rated current, and the corresponding coefficient.

Conceptual explanation

Rated capacity refers to the customary value of apparent power under the main tap. The capacity specified on the transformer nameplate is the rated capacity, which refers to the tap changer located on the main tap, and is the product of the rated no-load voltage, rated current, and corresponding phase coefficient. For three-phase transformers, rated capacity=rated no-load line voltage x rated line current, and rated capacity is generally expressed in kVA or MVA. The rated capacity is the maximum continuous output capacity that can be achieved throughout the specified normal service life, such as 30 years. The actual output capacity is the product of the voltage under load (under inductive load, the voltage under load is less than the rated no-load voltage), the rated current, and the corresponding coefficient.

Error

For no-load tap changer transformers, the rated capacity can be output at -5% tap position, and the output capacity should be reduced below -5% tap position.

For on load voltage regulating transformers, manufacturers generally stipulate that the rated capacity can still be output at the -10% tap position, and the rated capacity can be reduced below the -10% tap position. The above are all for constant flux voltage regulating power transformers or distribution transformers. For variable flux voltage regulating furnace transformers or rectifier transformers, the rated capacity refers to the maximum output capacity, and the output capacity at most tap positions is less than the rated capacity.

Actual situation

In actual operation, the transformer also has a load capacity, and the additional burden of a fixed capacity is not the load capacity of the transformer. Load capacity refers to the actual capacity value that a transformer can output only within a confirmed time interval. This capacity value is determined by the operating conditions of the transformer within the recognized time interval, or by whether it damages its normal service life, increases its natural aging of insulation, and endangers the safe operation of the transformer. The load capacity can exceed the rated capacity, but there is an upper limit value for the load capacity, which is that the temperature of the winding hot spot cannot exceed 140 ℃. When the temperature exceeds 140 ℃, it will cause the oil near the winding hot spot to decompose into gas, affecting safe operation. Although the temperature of the winding hot spot does not exceed 140 ℃, when the oil temperature exceeds 120 ℃, due to the combined effect of heat and electricity, it will affect the field strength of the oil. When the temperature of the winding hot spot exceeds 98 ℃, it will affect the service life of the transformer.

Due to the need for emergency treatment, the actual load capacity of the transformer can exceed the rated capacity, but it is necessary to ensure that the hot spot temperature of the winding does not exceed 140 ℃. The sacrificial service life needs to be compensated with the increased life when operating below the rated capacity. When the emergency operation exceeds the capacity of the nameplate, the load loss is much higher than the rated load loss. The output voltage under load is much lower than the rated no-load voltage, and the efficiency is also poor.

The rated capacity of an autotransformer refers to the actual structural capacity that is much smaller than the rated capacity. Only a portion of the output capacity of an autotransformer belongs to the capacity of electromagnetic induction, while a portion of the output capacity is directly passed through.

The rated capacity of a three winding transformer is generally expressed as a percentage of the rated capacity of each winding. For example, 100%/100%/100% means that each winding can reach the rated capacity, and 100%/100%/60% means that the low-voltage winding can only reach 60% of the rated capacity.

The low-voltage winding of an autotransformer generally cannot reach its rated capacity. When expressed as 100%/100%/50%, the low-voltage winding can only reach 50% of its rated capacity.

Other

In addition, when a transformer has several cooling methods, the rated capacity refers to the maximum capacity, and when changing the cooling method, the output capacity needs to be changed.

When a transformer operates under three different cooling conditions, such as forced oil circulation air cooling, oil immersed air cooling, and oil immersed natural cooling, the rated capacity of each cooling method, expressed as a percentage, is 100%/80%/60%. When forced oil circulation air cooling is used, it can output 100% of the rated capacity. When the cooling pump is in operation, it can output 80% of the rated capacity under oil immersed air cooling. That is, when the pump is stopped, the output capacity needs to be reduced by 20%. When both the cooling pump and the cooling fan are stopped, not only can it output 60% of the rated capacity under oil immersed self cooling, but also when both the pump and fan are stopped, the output capacity needs to be reduced by 40% of the rated capacity.

The corresponding output capacity under different cooling conditions is related to the structure of the cooling device. Some cooler structures can only operate under forced oil circulation and air cooling. When the pump is stopped, the output capacity must be reduced to zero in a short period of time. The capacity of three different cooling methods, 100%/80%/60%, refers to the combination of a radiator cooling device, a pump, and a fan.

Transformers operating under three different cooling conditions can have three rated capacities, but performance parameters are based on the maximum rated capacity. The rated capacity of each cooling method is based on a temperature rise not exceeding the specified limit.

Battery capacity is one of the important performance indicators for measuring battery performance. It represents the amount of electricity released by the battery under certain conditions (discharge rate, temperature, termination voltage, etc.) (JS-150D can be used for discharge testing), which is the capacity of the battery. It is usually measured in ampere hours (abbreviated as A · H, 1A · h=3600C).

The battery capacity is divided into actual capacity, theoretical capacity, and rated capacity according to different conditions. The calculation formula for battery capacity C is C=Δ t0It1dt (integrating current I within t0 to t1 time), and the battery is divided into positive and negative poles.

The battery capacity is divided into actual capacity, theoretical capacity, and rated capacity according to different conditions.

The minimum capacity required to discharge at 25 ℃ to the termination voltage at a certain discharge rate is the specified capacity of the battery during design and production, which is called the rated capacity of a certain discharge rate RH.

Square lithium-ion battery

Square lithium-ion battery

The battery capacity is generally calculated in AH (ampere hours), and another method is to calculate in watts (W) per cell. (W/CELL)

1. Ah (ampere hour) calculation, discharge current (constant current) I x discharge time (hour) T. For example, if the continuous discharge current of a 7AH battery is 0.35A, the time can be continuous for 20 hours.

2. The charging time is based on 15 hours, and the charging current is 1/10 of the battery capacity. Fast charging will reduce the battery life.

Battery capacity refers to the amount of electricity stored by the battery. The unit of battery capacity is "mAh", and the Chinese name is milliampere hour (for convenience when measuring large capacity batteries such as lead-acid batteries, "Ah" is generally used, and the Chinese name is ampere hour, with 1Ah=1000mAh). If the rated capacity of the battery is 1300mAh, that is, a current of 130mA is used to discharge the battery, then the battery can operate continuously for 10 hours (1300mAh/130mA=10h); If the discharge current is 1300mA, the power supply time is only about 1 hour (the actual working time may vary due to individual differences in the actual capacity of the battery). This is an ideal analysis. The actual current of a digital device during operation cannot always be constant at a certain value (taking a digital camera as an example, the working current will undergo significant changes due to the opening or closing of components such as LCD screens and flash lights). Therefore, the power supply time that a battery can provide to a certain device can only be an approximate value, and this value can only be estimated through practical operating experience.

Usually, we talk about battery capacity in ampere hours, which is based on a specific battery that has already been determined.

For example, what is the battery capacity of this mobile phone; The capacity of this electric vehicle battery is determined by different batteries. The battery voltage has been determined without considering the actual voltage, and simply stating ampere hours can represent the capacity of this battery.

However, for batteries with different voltages, we cannot simply use ampere hours to represent capacity. For example, a 12V20AH battery, a 15V20AH battery, even if they are both 20AH, can supply the same power load, and the equipment can work normally, but the duration is different. Therefore, the standard capacity should be measured in power.

For example, if a device can support both 12V and 24V, and is powered by a 12V (20AH) battery for one hour, then using two pieces in series will result in 24V (20AH). The ampere hour does not increase, but the duration will double. Therefore, the capacity should be considered based on the power capacity of the battery, rather than just ampere hours.

W (work)=P (power) * T (time)=I (current) * U (voltage) * T (time)

Discussing battery capacity in this way has practical significance and must be truthful. Otherwise, there may be a claim that a mobile phone battery has a larger capacity than a car battery, which is obviously unscientific.

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