Common causes of damage to rectifier diodes and inspection methods

(1) Inadequate lightning protection and overvoltage protection measures. The rectifier device is not equipped with lightning protection and over-voltage protection devices. Even if it is equipped with lightning protection and over-voltage protection devices, its work is unreliable and the rectifier tube is damaged due to lightning strikes or over-voltage.

(2) Bad operating conditions. Indirect drive generator set, due to incorrect calculation of the speed ratio or the ratio of the diameters of the two belt pulleys does not meet the requirements of the speed ratio, so that the generator runs at a high speed for a long time, and the rectifier tube is also at a higher voltage for a long time. Under work, the rectifier tube accelerates aging and is damaged by premature breakdown.

(3) Poor operation management. Operators on duty are irresponsible and do not understand the changes in external load (especially between midnight and 6 am the next day), or when a load dump failure occurs in the outside world, the operators do not perform corresponding operations in time Deal with it, generate overvoltage and break down and damage the rectifier.

(4) The quality of equipment installation or manufacturing is not good enough. Because the generator set has been operating under large vibration for a long time, the rectifier tube is also under the interference of the external force of this vibration; at the same time, because the generator set speed is high and low, the working voltage of the rectifier tube also increases and fluctuates. Low ground changes greatly accelerate the aging and damage of the rectifier tube.

(5) The specifications and models of the rectifier tube do not match. When replacing a new rectifier tube, wrongly replace the tube whose working parameters do not meet the requirements or the wiring is wrong, causing the rectifier tube to breakdown and damage.

(6) The safety margin of the rectifier tube is too small. The overvoltage and overcurrent safety margin of the rectifier tube is too small, so that the rectifier tube cannot withstand the overvoltage or the peak value of the overcurrent transient process that occurs in the generator excitation circuit and is damaged.

After the rectifier diode is damaged, it can be replaced with a rectifier diode of the same model or another model with the same parameters.

Generally, rectifier diodes with high withstand voltage (reverse voltage) can be substituted for rectifier diodes with low withstand voltage, while rectifier diodes with low withstand voltage cannot be replaced with rectifier diodes with high withstand voltage. A diode with a high rectification current value can be substituted for a diode with a low rectification current value, while a diode with a low rectification current value cannot be substituted for a diode with a high rectification current value.

First remove all the rectifier diodes in the rectifier, use the 100×R or 1000×R ohm file of a multimeter to measure the two lead wires of the rectifier diode (the head and the tail are adjusted once each). If the resistance value measured twice is very different, for example, the resistance value is as high as a few hundred KΩ to infinity, and the resistance value is only a few hundred Ω or less, indicating that the diode is good (soft breakdown has occurred) Except for diodes). If the resistance value measured twice is almost the same and the resistance value is very small, it means that the diode has been broken down and cannot be used. If the resistance value measured twice is infinite, it means that the diode has been internally disconnected and cannot be used.

The composition of the diode

A diode is an electronic device made of semiconductor materials (silicon, selenium, germanium, etc.). It has unidirectional conductivity, that is, when a forward voltage is applied to the anode and cathode of the diode, the diode is turned on. When a reverse voltage is applied to the anode and cathode, the diode is turned off. Therefore, the turn-on and turn-off of the diode is equivalent to the turn-on and turn-off of the switch.

The diode is one of the earliest semiconductor devices, and its application is very wide. Especially in various electronic circuits, diodes and resistors, capacitors, inductors and other components are used to make reasonable connections to form circuits with different functions, which can realize AC rectification, modulation signal detection, amplitude limiting and clamping, and power supply Various functions such as voltage stabilization. Whether in common radio circuits or other household appliances or industrial control circuits, you can find traces of diodes

The diode is encapsulated by a PN junction plus the corresponding electrode leads and the case.  

Using different doping processes, through diffusion, the P-type semiconductor and the N-type semiconductor are fabricated on the same semiconductor (usually silicon or germanium) substrate, and a space charge area called PN junction is formed at their interface

The electrode drawn from the P zone is called the anode, and the electrode drawn from the N zone is called the cathode. Because of the unidirectional conductivity of the PN junction, the current direction when the diode is turned on is from the anode to the cathode through the inside of the tube.

The circuit symbol of the diode is shown as in Fig. 1. The diode has two electrodes. The electrode drawn from the P area is the positive electrode, also called the anode; the electrode drawn from the N area is the negative electrode, also called the cathode. The direction of the triangle arrow indicates the direction of the forward current, and the text symbol of the diode is indicated by VD.