Voltage

Voltage, also called potential difference or potential difference, is a physical quantity that measures the energy difference of a unit charge in an electrostatic field due to the difference in potential. This concept is similar to the "water pressure" caused by high and low water levels. Voltage is what drives the directional movement of charges to form current. The reason why current can flow in the wire is also because there is a difference between a high potential and a low potential in the current. This difference is called potential difference, also called voltage. In other words, in the circuit, the potential difference between any two points is called the voltage of these two points. The letter U is usually used to represent voltage. The unit is volt (V), abbreviated as volt, and the symbol V represents 1kV=1000V;

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, and the electric charge in the circuit is subjected to the action of the electric field force to produce directional movement, thereby forming the current in the circuit.

Usually expressed by the letter I, the unit is A (ampere), there are A (ampere), kA (kiloampere), mA (milliampere); 1kA=1000A, 1A=1000mA.

Note: In the unit kA, mA, k and m are lowercase and A is uppercase

Power

Physically, the amount of electricity indicates how much charge an object carries. Here we mean the amount of electrical energy used by electrical equipment or users, also known as electrical energy or electrical work, which is the cumulative value of power in a certain period of time.

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

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

Direct current

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

Alternating current

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

power

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

Unit: W (uppercase English letter W)

kW (k is lowercase, W is uppercase)

MW (all 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, light energy, thermal energy); or the power consumed by the pure resistance part of the circuit, in W. (For example: a 5.5-kilowatt motor converts 5.5-kilowatt electrical energy into mechanical energy, which drives a water pump to pump water or thresher threshing; various lighting equipment convert electrical energy into light energy for people’s life and work lighting. The symbol for active power is represented by P .

Unit: Watt (W), Kilowatt (kW), Megawatt (MW). )

Note: The unit is W (uppercase), kW (lower case k, uppercase W), MW (M and W are all uppercase)

Reactive power

When alternating current passes through pure resistance, electrical energy is converted into heat and consumes active power. When it passes through purely capacitive or purely inductive loads, it does not perform work and consumes reactive power. Reactive power is the electric power used to exchange the electric field and magnetic field in the circuit and to establish and maintain the magnetic field in electrical equipment. It does not work externally, but transforms into other forms of energy. All electrical equipment with electromagnetic coils consumes reactive power to build a magnetic field. (For example: a 40-watt fluorescent lamp requires more than 40 watts of active power (the ballast also consumes part of the active power) to emit light, but also requires about 80 kW of reactive power for the coil of the ballast to establish an alternating magnetic field. .Because it does not do external work, it is called "reactive power." The symbol of reactive power is represented by Q, and the unit is var or kvar.) Reactive power is by no means useless power. Very useful. The rotor magnetic field of the motor is established by obtaining useless power from the power source. The transformer also needs reactive power to make the primary coil of the transformer generate a magnetic field and induce a voltage in the secondary coil. Therefore, without reactive power, the motor will not rotate, the transformer cannot transform, and the AC contactor will not pull in. In order to illustrate the problem vividly, here is an example: the construction of water conservancy in rural areas requires digging and transporting soil. When transporting the soil, bamboo baskets are used to fill the soil. The soil picked up is like active power, and the empty bamboo basket is like reactive power. The baskets are not useless. How can the soil be transported to the embankment without the bamboo baskets?

Note: The unit var (v, a, r are all lowercase), kvar (k lowercase, v lowercase, a lowercase, r lowercase).

inspecting power

In the power network, the product of voltage and current is called apparent power, denoted by S, and S=UI. When the loads in the network are all pure resistances, the apparent power is equal to the active power. Usually, due to the presence of inductive or capacitive loads in the power grid, the apparent power is greater than the active power. To show the difference, the apparent power is not in watts (W), but in volt-amperes (VA) or kilovolt-amperes (kVA). In the power system, the apparent power reflects the capacity of the equipment, and the product of the rated voltage and the rated current of the electrical equipment is the capacity of the equipment.

Note: Apparent power unit VA (V, A are all uppercase), kVA (k lowercase, V, A uppercase)