Polished ABS Lift Contact
Polished ABS Lift Contact Before selecting a varistor, you should first understand the following related technical parameters: The nominal voltage refers to the voltage across the varistor at the specified temperature and DC current. Leakage current is the value of the current flowing through...
Polished ABS Lift Contact
Before selecting a varistor, you should first understand the following related technical parameters: The nominal voltage refers to the voltage across the varistor at the specified temperature and DC current. Leakage current is the value of the current flowing through the varistor when a maximum continuous DC voltage is applied at 25 °C. The gradation voltage is the voltage peak that is present across the varistor at the ends of the 8/20 grading current pulse. The flow rate is a peak current when a predetermined pulse current (8/20 μs) waveform is applied. Surge environmental parameters include maximum inrush current Ipm (or maximum surge voltage Vpm and surge source impedance Zo), surge pulse width Tt, minimum time interval Tm between adjacent surges, and pre-determination at the varistor The total number of surge pulses is N during the working life.
Generally speaking, varistors are often used in parallel with protected devices or devices. Under normal conditions, the DC or AC voltage across the varistor should be lower than the nominal voltage, even in the worst case of power fluctuations. It should not be higher than the maximum continuous working voltage selected in the rated value. The nominal voltage value corresponding to the maximum continuous working voltage value is the selected value. For overvoltage protection applications, the varistor voltage should be greater than the actual circuit voltage. Generally, the following equation should be used: VmA=av/bc:
a is the circuit voltage fluctuation coefficient; v is the circuit DC working voltage (effective value when AC); b is the varistor voltage error; c is the aging coefficient of the component; the calculated VmA actual value is 1.5 times the DC working voltage In the AC state, the peak value should also be considered, so the calculation result should be expanded by 1.414 times.
In addition, you must also pay attention to the selection:
(1) It must be ensured that when the voltage fluctuation is maximum, the continuous working voltage will not exceed the maximum allowable value, otherwise the service life of the varistor will be shortened;
(2) When a varistor is used between the power supply line and the ground, the voltage between the line and the ground may rise due to poor grounding. Therefore, a varistor having a higher nominal voltage than that used between the line and the line is usually used.
The surge current absorbed by the varistor should be less than the maximum flux of the product.