Do you know why the voltage kV should be in lowercase?

The unit of measurement in international standards is generally in figures. Only the units named by names, such as Volt V, Ampere A, Kelvin K, Watt W, are used in capital to show respect for the predecessors of scientists, and other units not named by human names are generally used in lower case. This explains why V is capital.

Secondly, for quantifiers, the initial magnitude is generally in lowercase. If the letters are the same, the uppercase and lowercase often distinguish different orders of magnitude, such as m Ω, M Ω, and lowercase m represents 1 × 10^-3； The capital M represents 1 × 10^6。 So k here represents 1 × 10 ^ 3, should be in lowercase. (Perhaps this lowercase k is still used to distinguish it from K (Kelvin)) To sum up, we can find that kV should be lowercase k and uppercase V.

In fact, even if it is all capitalized, people can understand it. Academically, we should write according to the national standards.

Volts V

Alessandro Volt, an Italian physicist, invented the "voltaic stack" in 1800. On March 5, 1827, Volt died at the age of 82. In memory of him, people named the electromotive force unit Volt.

Ampere A

Andre Marie Ampere, French physicist, chemist and mathematician. In 1820~1827, Ampere made outstanding achievements in the study of electromagnetic effects, and was known as "Newton in electricity". In memory of him, the international unit of current was named after his surname.

Kelvin K

Kelvin, formerly known as William Thomson, a British physicist, was awarded the title of Lord Kelvin by the Queen of England for his scientific achievements and contributions to the Atlantic cable project, so later generations changed his name to Kelvin. He established the temperature scale and reset the melting point of water to 273.7 degrees; The boiling point is 373.7 degrees. To commemorate his contribution, the unit of temperature is named after Kelvin (K).

Watt W

James Watt, a British inventor and an important figure in the sub-industrial revolution. The steam engine with practical value was produced in 1776. After a series of major improvements, it became the "prime mover" and was widely used in industry. He opened up a new era of energy utilization for mankind and brought mankind into the "steam age". In order to commemorate the great inventor, later generations set the unit of power as "watt" (abbreviated as "watt", symbol W).

Voltage, also known as potential difference or potential difference, is a physical quantity that measures the energy difference of unit charge in the electrostatic field due to the difference of potential. This concept is similar to the "water pressure" caused by high and low water level. Voltage is the reason that drives the directional movement of charge to form current. The reason why the current can flow in the wire is also because there is a difference between high potential and low potential in the current. This difference is called potential difference, also called voltage.

In other words, in a circuit, the potential difference between any two points is called the voltage of these two points. The letter U is usually used for voltage. The unit is Volt (V), which is abbreviated as Volt. 1kV=1000V is represented by the symbol V;

Note: Voltage unit: kV (k in figures, V in words)

electric current

The amount of charge passing through the cross section in unit time is called current. Because of the existence of voltage (potential difference), the electric field strength is generated, which makes the charge in the circuit move directionally under the action of the electric field force, thus forming the current in the circuit.

It is usually expressed with the letter I, and the unit is A (ampere), including A (ampere), kA (kiloampere) and mA (milliampere); 1kA=1000A，1A=1000mA。

Note: in kA and mA, k and m are in lower case and A is in upper case

Power

Physically, the quantity of electricity represents the amount of charge carried by an object. Here we refer to the quantity of electric energy used by electric equipment or users, also known as electric energy or electric work, which is the cumulative value of power in a certain time.

Unit: kilowatt-hour kW · h, megawatt-hour MW · h.

Note: unit kWh (k in lowercase, W in uppercase, h in lowercase), MWh (M in uppercase, W in uppercase, h in lowercase)

DC

Direct Current (DC for short) refers to the current that does not change periodically in direction and time, but the current size may not be fixed, resulting in waveform. Also known as constant current. Generally, the current in the dry battery is DC.

alternating current

Alternating current refers to a current whose size and direction change periodically with time. Most of the power generation, transformation, distribution and marketing links in the power system are AC power.

power

Power refers to the work done by an object in unit time, that is, power is a physical quantity describing the speed of work done. With a certain amount of work, the shorter the time, the greater the power value. The formula for calculating power is power=work/time.

Unit: W (capital English letter W)

KW (k in figures, W in words)

MW (all in capital letters)

1MW=1000kW

1kW=1000W。

Active power

It refers to the electrical power required to maintain the normal operation of electrical equipment, that is, the electrical power that converts electrical energy into other forms of energy (mechanical energy, optical energy, thermal energy); Or the power consumed by the pure resistance part of the circuit, in W. (For example, a 5.5 kW motor converts 5.5 kW electric energy into mechanical energy to drive the pump to pump water or thresher to thresh; various lighting devices convert electric energy into light energy for people's life and work lighting. The symbol of active power is indicated by P.

Unit: watt (W), kilowatt (kW), megawatt (MW).)

Note: Unit W (in words), kW (k in words, W in words), MW (M, W are in words)

Reactive power

When alternating current passes through a pure resistance, the electric energy is converted into heat energy and consumes active power. When it passes through a pure capacitive or purely inductive load, it does not work, and the consumed power is reactive power.

Reactive power is the electrical power used to exchange electric field and magnetic field in the circuit, and to establish and maintain magnetic field in the electrical equipment. It does not work externally, but transforms into other forms of energy.

All electrical equipment with electromagnetic coils must consume reactive power to establish magnetic field. (For example, a 40-watt fluorescent lamp needs more than 40 watts of active power (the ballast also needs to consume some active power) to emit light, and about 80 watts of reactive power for the coil of the ballast to establish an alternating magnetic field.

Because it does not work externally, it is called "reactive". The symbol of reactive power is expressed in Q, and the unit is var or kvar.)

Reactive power is not useless power, it is very useful. The rotor magnetic field of the motor is established by obtaining useless power from the power supply.

The transformer also needs reactive power to make the transformer coil produce magnetic field and induce voltage in the secondary coil. Therefore, without reactive power, the motor will not rotate, the transformer will not change voltage, and the AC contactor will not pull in.

In order to illustrate the problem visually, let's take an example: rural water conservancy construction needs to excavate earth and carry soil. When carrying soil, use bamboo baskets to fill it with soil. The picked soil is like active power, and the empty bamboo basket is like reactive power. The bamboo basket is not useless. How can the soil be transported to the embankment without bamboo baskets?

Note: unit var (v, a, r are all in lower case), kvar (k in lower case, v in lower case, a in lower case, r in lower case).

Apparent power

In power network, the product of voltage and current is called apparent power, expressed by S, and S=UI. When the loads in the network are all pure resistors, the apparent power is equal to the active power. Generally, the apparent power is greater than the active power because of the inductive or capacitive load in the network.

To show the difference, the apparent power is not in watts (W), but in VA or kVA. In the power system, the apparent power reflects the capacity of the equipment, and the product of the rated voltage and rated current of the electrical equipment is the capacity of the equipment.

Note: Apparent power unit VA (V, A are in words), kVA (k is in words, V, A is in words)