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Voltage calculation

Publish: 2021-03-22 03:22:15
1. In the electric power design manual of iron and steel enterprises Volume I, P260 formula (5-5):
the rated line voltage UN of the network is taken in engineering.
2. Phase voltage calculation is applied to single-phase load and line voltage calculation is applied to three-phase load; The 1.732 times the line voltage used in three-phase load calculation is to expand the voltage to three times of the phase voltage (660V) to divide the current of each phase or the total power of three phases equally.
3. 10000 x (1 + 7%) = 10700 V and
10000 x (1 - 7%) = 9300 V

voltage fluctuation range 9300 ~ 10700 V
4. The only device I know that can convert pressure into voltage is piezoelectric crystal. Different components of piezoelectric crystal have different conversion relations. Usually, the manual attached at the time of purchase will give the empirical formula or experimental data of piezoelectric conversion. You can also search the relevant piezoelectric conversion formula on the Internet according to the proct model, composition and other information.
5. Voltage drop UD = u1-u2= Δ U+j δ U (UD, U1, U2 are all vectors)
Δ U is the transverse component, δ U is the longitudinal component
6. Power transformer is a static electrical equipment, its biggest advantage is that the no-load loss value is very low, so how to calculate the rated voltage of power transformer
what is the rated voltage of the power transformer
the rated voltage of the primary winding of power transformer can be divided into two types according to different connection conditions: when the transformer is directly connected with the generator, the rated voltage of the primary winding is the same as that of the generator, that is, 5% higher than the rated voltage of the grid at the same level; When the transformer is directly connected to the power grid, the rated voltage of its primary winding is the same as that of the power grid, which is equal to the rated voltage of the power grid at the same level. Rated voltage of secondary winding of power transformer refers to no-load voltage of secondary winding under rated voltage of primary winding
when the transformer is fully loaded, the impedance of the primary and secondary windings of the transformer will cause the voltage drop of the transformer itself (about 5% of the rated voltage of the grid), so that the terminal voltage of the secondary winding is less than the no-load voltage. In order to make up for the voltage loss in the line, the rated voltage of the secondary winding of the transformer should be 5% higher than that of the grid, so the rated voltage of the secondary winding of the transformer should be 10% higher than that of the grid at the same level; If the transformer is close to the user and the power supply radius is small, the voltage loss of the line can be ignored e to the short line. At this time, the rated voltage of the secondary winding of the transformer should be 5% higher than the rated voltage of the grid to compensate the voltage loss of the transformer itself.
7. Most of the 66kV and below distribution systems in China adopt ungrounded neutral point and arc suppression coil grounding system, which is related to the national conditions and grid structure of China. This kind of grounding mode, when single-phase grounding, the balance of three-phase line voltage is not damaged, so the three-phase motor and other loads operate normally. This outstanding advantage makes the existing distribution network in China maintain a high level of safe operation even though the automation level is relatively low. When the grid capacitance current to the ground reaches a certain value, if it exceeds 10 A, the arc can not be extinguished by itself, so it is necessary to take compensation measures and install arc suppression coil. Due to the different three-phase capacitance to the ground of the grid, there is asymmetric voltage UBD at the neutral point. In general, the UBD of overhead line or hybrid network is about 1 ~ 1.5% of the phase voltage, but in some power grids, such as 35 ~ 66kV system, the UBD is about 3 ~ 4% e to the unequal capacitance of bus to ground or the unreasonable layout of carrier communication combined with capacitor. The arc suppression coil system belongs to resonant grounding system, when it is put into neutral point, it will amplify UBD, The formula is as follows:
uwy = UBD / (v-square + d-square) to the second power...... (1)
where uwy - the displacement voltage (V) at the neutral point amplified by the arc suppression coil
UBD - the asymmetric voltage of the neutral point to the ground in the distribution network
V - the detuning degree of the arc suppression coil v = (il-ic) / IC × 100%
d-damping rate. It is the ratio of active current and reactive current. The active current caused by the leakage of power grid is about 1 ~ 2%, and the loss of arc suppression coil itself also exists. The active current is about 1 ~ 1.5%. The combination of these two factors is called the natural damping rate of power grid
it can be seen from the above formula that the neutral point displacement voltage uwy is related to asymmetric voltage, detuning degree and damping rate of power grid. The displacement voltage of the power grid with high asymmetric voltage must be high. The detuning degree can not be taken casually, but it is required. If the detuning degree is large, the resial current is large, which is not concive to the arc suppression and function of the arc suppression coil. The damping ratio of power grid is generally small. Therefore, the displacement voltage of resonance point is uwy = UBD / D when the asymmetry voltage is high and the inherent damping rate is small. About 40 times the asymmetrical voltage.
8. Voltage loss is mainly the voltage difference between the head end and the tail end of the line, which is related to the cross-sectional area and size of the wire. Power loss = square of voltage loss (voltage difference) / resistance of wire = square of current through wire x resistance of wire. Power loss = power loss x time
9. The unit of voltage is volt (V), the unit of electric quantity is ampere hour (ah), and the proct of voltage and current is power, expressed in W. The voltage times the quantity of electricity is VAH, that is, wh, that is, electric energy, and then divided by 1000, that is, kwh, that is, how many kilowatts of electricity. In short, know the voltage and quantity of electricity, two phases multiply and divide by 1000, is how much electricity.
10. The voltage drop of AC circuit is usually a vector, which can be projected on the vertical coordinates. The voltage drop in phase with the current can be called "active component" (transverse component), and the voltage drop perpendicular to the current can be called "reactive component" (longitudinal component). The former is the voltage drop on the resistance, and the latter is the voltage drop on the reactance.
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