Voltage, also called the potential difference or potential difference, is a physical quantity that measures the difference in energy produced by the unit charge in the electrostatic field due to the difference in potential. The size is equal to the work done by the unit positive charge moving from point A to point B due to the electric field force, and the direction of the voltage is defined as the direction from the high potential to the low potential. The international unit of voltage is volt (V, volt for short), and commonly used units are millivolts (mV), microvolts (μV), kilovolts (kV), and etc.
Classification
Classified by size
The voltage can be divided into high voltage, low voltage and safe voltage.
The difference between high and low voltage is based on the voltage value of the electrical equipment to the ground. The voltage to ground is higher than or equal to 1000 volts. The low voltage to ground voltage less than 1000 volts.
The safety voltage refers to the voltage that the human body contacts for a long time without risk of electric shock. According to the national standard "GB3805-83" safety voltage, a voltage series that is used to prevent electric shock accidents and is powered by a specific power source. China has specified the following five levels for power frequency safety voltages, namely 42V, 36V, 24V, 12V and 6V.
Classified by function
1. Impedance voltage
Definition: A winding in a two-winding transformer is short-circuited with a voltage of a rated frequency applied to the other winding and the applied voltage value at which the rated current flows. For a multi-winding transformer, except for the pair of windings tested, the remaining windings are open and the applied voltage value is passed through the rated current corresponding to the winding of the pair of windings having a smaller rated capacity. The impedance voltage of each pair of windings is the value at the corresponding reference temperature and is expressed as a percentage of the rated voltage value of the applied voltage winding.
Impedance voltage calculation method: When the secondary winding of the transformer is short-circuited (steady state), the voltage applied by the primary winding to circulate the rated current is called the impedance voltage Uz. Usually Uz is expressed as a percentage of the rated voltage, ie uz = (Uz / U1n) × 100% 匝 potential: u = 4.44 × f × B × At, V where: B - magnetic density in the core, T At - core effective intercept Area, square meter can be converted into a common formula for transformer design calculation:
When f=50Hz: u=B×At/450×105,V
When f=60Hz: u=B×At/375×105,V
If the phase voltage and the number of turns are known, the zeta potential is equal to the phase voltage divided by the number of turns.
2. Medical voltage
The voltage referred to in the electrocardiogram refers to the distance between two horizontal lines on the ECG drawing. Often used to measure the amplitude of the ECG. Units are usually expressed in mm or mV. The value of the voltage is related to the adjustment of the *regular voltage. If a standard voltage of 1 mV is input to shift the baseline by 10 mm, the distance between the two thin horizontal lines is 1 mm and the voltage is 0.1 mV. When measuring the amplitude of an electrocardiogram, the voltage calibration side makes sense.
