Why Transformer Rated In kVA, Not in KW?

Transformers are always rated in kVA instead of KW

As the name suggests, a transformer only transfers power from one circuit to another without changing the values ​​of power and frequency. In other words, It can only increase or decrease the value of current and voltage while the power and frequency remain the same. General date on printed transformer nameplate for more details, such as VA rating, single phase/three phase (power or distribution transformer), step up/down, connections, etc. , Simply put, Read: why evaluate transformers at kva two types of losses in transformers;

  • first. Copper loss
  • 2. Iron Loss or Core Loss or Insulation Loss

Copper loss (I²R) depends on current which passes through the transformer windings while Iron loss or core loss or insulation loss depends on Voltage. i.e. the sum of losses depending on voltage (V) and current (I) is expressed as Amp volts (VA) and no load power factor (PF). That’s why transformer rating can be expressed in VA or kVA, not in W or kW.

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Please delete rating of transformer In VA instead of W With a solved example. The transformers will stay the same as long as the amperage of the current/voltage is the same. No matter what the power factor of the load current/voltage is.

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Example:Assume for a single phase lift transformer

  • Transformer rating in kVA = 11kVA
  • Main voltage = 110V
  • Main current = 100 One
  • Secondary voltage = 220V
  • Secondary current = 50 A.
  • Equivalent resistance on the secondary = 5Ω
  • Iron loss = 30W
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In first scriptIf we connect a resistive load to the secondary of the transformer at unified power factor = 1Then the total loss of the transformer will be copper loss + iron lossIE:I²R + Iron LossOffer values: Read more: why can’t I find a girlfriend | Top Questions & Read More: Why is my cat grabbing my arm and biting me (502 x 5) + 30W = 12.53kWi.e. the losses on the primary and the secondary of the transfer remain equal. (See the example below for more on secondary losses) The output of the transformer will be:P = V x I x CosAgain, set the secondary word value (Similar value if we set the main word values) P = 220 x 50 x 1 = 11kW. Current rating of transformer: kVA = VA / 1000kVA = 220 x 50/1000 = 11kVA.

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Now, in second scenarioconnect one capacitive or inductive load arrive secondary of the transformer in power factor = 0.6Also, total transformer loss will be copper loss + iron loss, ie: I²R + Iron loss Set the values: Read more: why can’t I find a girlfriend | Top Questions & Read More: Why is my cat grabbing my arm and biting me (502 x 5) + 30W = 12.53kWIt is thus proved that the losses in both the primary and the secondary are the same, but the output of the transformer will be: P = V x I x Cos θ Still set the value from the secondary (Same value if they are equal). we set the values ​​from the elementary)P = 220 x 50 x 0.6 = 6.6kW.Now rating of transformer: kVA = VA / 1000kVA = 220 x 50/1000 = 11kVA.

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It means, 11kVA . transformer Rating which means it can handle 11kVA. It’s our turn to convert and use 11kVA as 11kW (we can do it by improving the power factor by 1 in case net resistive load) is unpredictable and even difficult to obtain in the case of inductive and capacitive loads where the power factor will have different values ​​From the above example it is clear that The rating of the transformer is the same (11kVA) but different output power (11kW and 6.6kW) because of different power factor values after connecting different types of loads that are unpredictable to transformer manufacturers, where same loss in both cases.So these are correct reason to rate transformer in kVA instead of kWA.

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Like transformers, Generators & Generators rating and capacity, Voltage Regulator, UPS, Power Transmission Line are also rated in VA instead of W while power plant capacity, AC (Condition air) and the motor is rated in W (watts) and not VA (Volt -Preview).Read more: Why are schools made of bricks

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Posts “Why Transformer Rated In kVA, Not in KW?” posted by on 2021-09-03 14:14:11. Thank you for reading the article at wallx.net

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