What is a primary current _ what is a secondary current _ how is the calculation formula

Scientifically speaking, the amount of electricity passing through any cross section of a conductor per unit time is called current intensity, or simply current. Usually indicated by the letter I. The free charge in the conductor forms a current by making a regular directional motion under the action of the electric field force.

The electromotive force of the power source forms a voltage, which in turn generates an electric field force. Under the action of the electric field force, it is in electrical micro-ampere (μA) 1A = 1 000 mA = 1 000 000 μA, and it is electrically defined that the direction in which the positive charge is directed is the current direction. The microscopic expression of the current in the metal conductor is I=nesv, where n is the number of free electrons per unit volume, e is the charge of the electron, s is the cross-sectional area of ​​the conductor, and v is the charge velocity.

Nature has many kinds of carriers that carry charges, such as electrons that can move in an electric conductor, ions in an electrolyte, electrons and ions in a plasma, and quarks in a hadron. The movement of these carriers creates a current.

A constant electromotive force (electric field) is maintained in the circuit.

The circuit is connected, the switch is closed, and the circuit that is connected everywhere is called a path (also called a closed circuit).

1. There is an electric field. (In the circuit, the power source generates an electric field.)

2. There are charged particles that move freely. (In the circuit, it is also necessary to close the circuit.)

The current is divided into alternating current and direct current.

AC: Cyclical changes in both size and direction. In the life of the wall-mounted electrical appliances used is a civilian AC power supply.

DC: The direction does not change over time. The mobile external power supply used in life provides direct current.

AC power is widely used in family life and industrial production. The residential voltage 220V and the general industrial voltage 380V are dangerous voltages.

DC power is widely used in various types of small appliances such as flashlights (dry batteries) and mobile phones (lithium batteries). Dry batteries (1.5V), lithium batteries, batteries, etc. are called DC power supplies. Because these power supply voltages do not exceed 24V, they are safe power supplies.

Thermal effect

The conductor heats up when it is energized, and this phenomenon is called the current thermal effect. For example, the familiar Joule's law: is a law that quantifies the conduction current to convert electrical energy into heat. (Joule's Law)

Magnetic effect

The magnetic effect of the current (the electrokinetic energy produces magnetism): Oster found that any wire with current can generate a magnetic field around it, called the magnetic effect of the current. (Bio-Safar's Law)

Chemical effect

The chemical effect of electricity is mainly caused by the participation of charged particles (electrons or ions) in the current, which causes chemical changes in the substance. Electrolyzed water or electroplating in chemistry is a chemical effect of current. (Faraday's law of electrolysis)

Primary current: Generally refers to the current of the input side coil of the transformer. Secondary current: Generally refers to the current of the coil on the output side of the transformer.

1. Calculation formula of three-phase transformer current I=S/(root number 3*U), where:

U: is the line voltage of the transformer, KV;

S: is the apparent power (KVA) of the transformer.

2. Transformer current experience port algorithm:

Primary current I≈S*0.06

Secondary current I≈S*1.5

For example: a 500KVA transformer 10/0.4; calculate the primary current and secondary current as:

a. Use current formula I=S/(root number 3*U)

I=500/root number 3*10=500/17.32≈28.8A

I=500/root number 3*0.4=500/0.69=724.6A

b. Calculate the formula using the transformer current experience: I=500*0.06≈30A

I=500*1.5=750A

For example: a 800KVA10/0.4KV transformer, according to one, secondary current calculation, what is the various load current?

Solution: Primary current I=S*0.06=800*0.06=48A secondary current I=S*1.5=800*1.5=1200A

Low load: primary current I=48*15%=7.2A

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