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# UPS uninterrupted power system

UPS uninterruptible power supply basic electrical principle

1. Conductors, insulators and semiconductors

Whether the electrons in the substance are easily moved between atoms (ie, conductivity), the material is divided into conductors, insulators, semiconductors.

(1) Conductor: Conductive good objects, such as silver, copper, aluminum, iron and so on.

(2) insulator: not easy to conduct charge objects, such as glass, plastic and other substances.

(3) Semiconductor: Conductivity between the conductor and the insulator and under certain conditions, its internal carrier concentration increases, such as germanium, silicon, arsenic, silicon and so on.

2. Current and voltage

(1) The current is defined as the amount of charge per unit time (t) through the cross-sectional area of the conductor, ie I = Q / t, Q: charge (C)

I: current (A), t: time (s).

(2) the voltage is defined as a coulomb charge, moving from one end of the element to the other, the work done, ie U = W / Q,

U: voltage (V), W: electric power (J), Q: charge (C).

3. resistance

Resistance to current through the resistance is called resistance. Ie R: ohm (Ω).

4. Ohm's Law

Ohm's Law: The current in the circuit is proportional to the voltage of the circuit and inversely proportional to the total resistance.

Ie I = U / R, I: current (A), U: voltage (V), R resistance (Ω).

5. Direct current

Amplitude and direction does not change over time with the voltage (or current).

6. Alternating current

(1) The magnitude and direction of the alternating current, ie voltage or current, vary with time.

(2) periodic changes in the AC according to its waveform can be divided into two categories:

Sine wave: its waveform changes sinusoidal curve over time.

Non-sine wave: non-sine wave changes in the waveform, are non-sine wave, such as triangular wave, square wave, sawtooth wave and so on.

(3) frequency and period

Frequency: The number of cycles per second amplitude and direction change, ie f: Hz (Hz).

Period: The time and direction required to complete a cycle, ie T: seconds (s).

The frequency and period are reciprocal: T = 1 / f.

(4) RMS and average

RMS: rms value, also known as rms value, we usually refer to the AC voltage is the effective AC

Value, which is equal to the same value of the DC voltage applied to the same load generated by the heat is equal.

Rms value = 0.707Vm, Vm is the peak of alternating current.

The mean value is the value of the total number of cycles divided by the number of cycles.

Average = total area / number of cycles, the total area can be calculated by the mathematical integration method.

7. Skin effect

When the alternating current passes through the conductor, the current density value is greater at the vicinity of the conductor surface than the conductor center.

8. Apparent power, active power, power factor

Apparent power: the product of the voltage across the circuit and the current rms that it flows, that is, S = UI,

S: W (W), U: voltage across the load, I: current flowing through the load.

Active power: the net power actually consumed by the load in the circuit, ie P = Scosφ, P: W (W), φ: the phase difference between the voltage U at both ends of the load and the current I flowing through it.

Power factor: the ratio of active power to apparent power, ie cosφ = P / S.

9. transformer

(1) Transformer: is to rely on electromagnetic induction to a certain voltage from one voltage into another frequency, can also be used to change the current, change the impedance, change the phase.

(2) ideal transformer

It is called "ideal transformer" if the following conditions are met.

a. Winding coil wire resistance is zero, no power consumption.

b. The two windings are fully coupled and have no magnetic leakage.

c. No magnetic core (core) loss.

d. magnetic flux in the magnetic circuit is proportional to the excitation current.

e. The distributed capacitance of the winding can be ignored.