Reasons and inspection methods for damage of rectifier diodes

Reasons and inspection methods for damage of rectifier diodes

A rectifier diode is a semiconductor device that can convert alternating current energy into direct current energy. It has unidirectional conductivity and usually includes a PN junction with two terminals, positive and negative. Current can only flow in from the positive terminal and out from the negative terminal. Rectifiers are generally planar silicon diodes used in various power rectifier circuits. When selecting rectifier diodes, the main considerations should be their maximum rectification current, maximum reverse operating current, cutoff frequency, and reverse recovery time. This article mainly introduces the causes and inspection methods of damage to rectifier diodes.

(1) The lightning protection and overvoltage protection measures are inadequate. The rectifier device is not equipped with lightning protection and overvoltage protection devices. Even if lightning protection and overvoltage protection devices are installed, their operation is unreliable and the rectifier diode may be damaged due to lightning strikes or overvoltage.

(2) The operating conditions are harsh. Indirect transmission generator sets, due to incorrect calculation of the ratio of rotational speeds or the ratio of the diameters of the two pulleys not meeting the requirements of the ratio of rotational speeds, cause the generator to operate at high speeds for a long time, and the rectifier diodes also work at high voltages for a long time, which accelerates the aging of the rectifier diodes and causes premature breakdown and damage.

(3) Poor operational management. The on duty operators are irresponsible in their work, not familiar with changes in external loads (especially between midnight and 6am the next day), or when there is a load shedding fault, the operators do not take timely action, resulting in overvoltage and damage to the rectifier diode.

(4) The equipment installation or manufacturing quality is not up to standard. Due to the long-term operation of the generator set under significant vibration, the rectifier diodes are also subjected to external interference caused by this vibration; At the same time, due to the high and low speed of the generator set, the working voltage borne by the rectifier diode also fluctuates rapidly, which greatly accelerates the aging and damage of the rectifier diode.

(5) The specification and model of the rectifier diode do not match. When replacing a new rectifier diode, mistakenly replacing a diode with working parameters that do not meet the requirements or wiring errors can cause the rectifier diode to break down and be damaged.

(6) The safety margin of the rectifier diode is relatively small. The overvoltage and overcurrent safety margin of the rectifier diode is too small, which makes the rectifier diode unable to withstand the peak values of overvoltage or overcurrent transient processes that occur in the generator excitation circuit and cause damage. Inspection method for rectifier diodes

Firstly, remove all rectifier diodes from the rectifier and measure the two lead wires of the rectifier diode using the 100 × R or 1000 × R ohm range of a multimeter (test the head and tail of the rectifier diode once each). If there is a significant difference in resistance values between two measurements, such as the high resistance value reaching several hundred K Ω to infinity, while the low resistance value is only a few hundred Ω or even smaller, it indicates that the diode is good (except for diodes that have experienced soft breakdown). If the resistance values measured twice are almost equal and very small, it indicates that the diode has been broken down and cannot be used. If the resistance values measured twice are both infinite, it means that the diode has been internally disconnected and cannot be used.

Replacement of rectifier diodes

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

Usually, rectifier diodes with high voltage resistance (reverse voltage) can replace rectifier diodes with low voltage resistance, while rectifier diodes with low voltage resistance cannot replace rectifier diodes with high voltage resistance. A diode with a high rectified current value can replace a diode with a low rectified current value, while a diode with a low rectified current value cannot replace a diode with a high rectified current value