How to troubleshoot and maintain rectifier circuit faults? What is a rectifier transformer? What is the working principle of rectifier transformer?

　　How to troubleshoot and repair rectifier circuit faults?

　　Rectifier diodes are mainly used in rectifier circuits, so the fault mechanism of the rectifier circuit is related to the rectifier diode. A set of methods for detecting diodes can be used to troubleshoot the rectifier circuit.

　　1. Failure mechanism

　　Regarding the fault mechanism of the rectifier circuit, the following points are mainly explained:

　　1. There are two fundamental reasons for the failure of the rectifier circuit: first, the destructive influence of the external circuit on the rectifier diode, which is not a fault of the rectifier circuit itself; second, the quality problem of the rectifier diode itself, because the working current of the rectifier diode is relatively Large and prone to failure.

　　2. The rectifier diode has two hard faults: open circuit and breakdown. Its soft faults are increased forward resistance and reduced reverse resistance of the diode, poor working stability, etc.

　　3. After the forward resistance of the rectifier diode increases, the voltage drop across the rectifier diode increases, and the DC voltage added to the load resistor of the rectifier circuit decreases, reducing the DC output voltage of the power circuit. The greater the rectifier DC operating current, the greater the tube voltage drop on the rectifier diode, and the rectifier diode itself will also generate heat. In severe cases, the rectifier diode will be burned out.

　　4. After the reverse resistance of the rectifier diode is reduced, the one-way conductive performance of the diode deteriorates, causing part of the other half-cycle AC voltage to be added to the load resistor of the rectifier circuit through the rectifier diode. Because this is an AC voltage, it increases The ripple voltage in the DC operating voltage increases the burden on the filter circuit.

　　2. Key test points

　　Regarding the key test points of the rectifier circuit, the following points are mainly explained:

　　1. The key test point of the rectifier circuit is the output end of the rectifier diode. You can use the DC voltage of the multimeter to set the appropriate range to measure the DC voltage at the output end of the rectifier diode. When there is a DC voltage output, it can be a preliminary indication that the rectifier circuit is working normally. Otherwise, it means that the rectifier is working properly. The circuit may be faulty.

　　2. In the positive polarity rectifier circuit, the negative electrode of the rectifier diode is the output terminal of the rectifier circuit, and the positive polarity DC voltage is measured at this time; in the negative polarity rectifier circuit, the positive electrode of the rectifier diode is the output terminal of the rectifier circuit, and at this time What is measured is negative polarity DC voltage.

　　3. Effective detection methods

　　Regarding the effective detection methods of rectifier circuit faults, the following points are mainly explained:

　　1. After the power is cut off, measure the forward and reverse resistance of the rectifier diode on the circuit to determine whether the diode is open circuit or short circuit. When the on-circuit measurement result is uncertain, you can measure the rectifier diode after disconnecting it from the circuit. This way The test results are accurate.

　　2. Measure the DC voltage drop between the two pins of the rectifier diode when the power is on. Under normal circumstances, the silicon rectifier diode is 0.6V and the germanium rectifier diode is 0.2V. This characteristic is true for any rectifier circuit regardless of polarity.

　　3. For the soft fault of the diode, you can use the method of replacing a new rectifier diode to verify. After the replacement, the fault disappears, indicating that the judgment is correct, otherwise the possibility of the rectifier diode failure is also ruled out.

　　What is a rectifier transformer, its working principle and characteristics:

　　Rectifier transformer The rectifier transformer is the power transformer of the rectifier equipment. The characteristic of the rectifier device is that the primary side inputs current, and the secondary side outputs DC after passing through the rectifier. Variable current is a general term for the three working modes of rectification, countercurrent and frequency conversion, and rectification is the most widely used one. The transformer used as the power supply of the rectifier device is called a rectifier transformer. Most of the rectified DC power supplies used in industry are obtained from the AC power grid through rectifier transformers and rectifier equipment.

　　Function

　　1. It is to supply the appropriate voltage to the rectification system,

　　2. It is to reduce the pollution to the power grid caused by waveform distortion caused by the rectification system.

　　Introduction to main uses

　　Rectifier transformer is the power transformer of rectifier equipment. The characteristic of the rectifier equipment is that the primary side inputs AC, and the secondary side outputs DC after passing through the rectifier. Variable current is a general term for the three working modes of rectification, countercurrent and frequency conversion, and rectification is the most widely used one. The transformer used as the power supply of the rectifier device is called a rectifier transformer. Most of the rectified DC power supplies used in industry are obtained from the AC power grid through rectifier transformers and rectifier equipment.

　　Electrochemical industry

　　This is the industry that applies the most rectifier transformers. It electrolyzes non-ferrous metal compounds to produce aluminum, magnesium, copper and other metals; electrolyzes table salt to produce chlor-alkali; electrolyzes water to produce hydrogen and oxygen.

　　DC power supply for traction

　　DC grid for mining or urban electric locomotives. Since the valve side is connected to overhead wires, there are many short-circuit faults, the DC load changes with a large amplitude, and the electric locomotive is often started, resulting in varying degrees of short-term overload. For this reason, the temperature rise limit and current density of this type of transformer are both low. The impedance is about 30% larger than the corresponding power transformer.

　　DC power supply for transmission

　　It is mainly used to power DC motors in electric transmission, such as the armature and excitation of steel rolling mills. (4) The voltage of this type of rectifier transformer used for DC transmission is generally above 110kV, and the capacity is tens of thousands of kilovolt-amperes. Special attention should be paid to the AC and DC superposition of ground insulation. In addition, there are DC power supplies for electroplating or electrical processing, DC power supplies for excitation, DC power supplies for charging and electrostatic precipitating, etc.

　　reason

　　In the chemical industry where rectifier transformers are most used, high-power rectifier devices also have low secondary voltage and large current. Therefore, they are similar to electric furnace transformers in many aspects. That is, the structural characteristics mentioned above are also possessed by rectifier transformers. The biggest feature of the rectifier transformer is that the secondary current is no longer a sinusoidal alternating current. Due to the unidirectional conduction characteristics of the subsequent rectifier components, each phase line no longer has a load current flowing at the same time but conducts soft current. The pulsating current in one direction is transformed by the filter device. For DC, the secondary voltage and current of the rectifier transformer are not only related to the capacity connection group, such as the commonly used three-phase bridge rectifier line, the double inverse rectifier line with balanced reactor, for the same DC output voltage and current required The secondary voltage and current of the rectifier transformer are different, so the parameter calculation of the rectifier transformer is based on the rectifier line. Generally, the parameter calculation is calculated from the secondary side to the primary side.

　　Since the rectifier winding current is non-sinusoidal and contains many high-order harmonics, in order to reduce harmonic pollution to the power grid and improve the power factor, the pulse number of the rectifier equipment must be increased, which can be solved by phase shifting. The purpose of phase shifting is to create a phase shift between the voltages at the same end of the secondary winding of the rectifier transformer.

　　The simplest method of phase shifting

　　The simplest phase shifting method is to use two windings connected in magnitude and angle on the secondary side, which can double the pulse number of the rectifier electric furnace.

　　For high-power rectification equipment, the 10kv dry-type rectifier transformer requires a large number of pulses. The number of pulses is 18, 24, 36, etc., which are increasingly used. This requires a phase-shifting winding on the primary side of the rectifier transformer for phase shifting. There are three ways to connect the phase-shifting winding and the main winding, namely zigzag line, hexagon and extended triangle.

　　The voltage regulating range of the rectifier transformer used in the electrochemical industry is much larger than that of the electric furnace transformer. For chemical salt electrolysis, the voltage regulating range of the rectifier transformer is usually 56%--105%. For aluminum electrolysis, the voltage regulating range is usually 5%--105%. Commonly used voltage regulation methods include variable flux voltage regulation, series transformer voltage regulation and auto-coupling voltage regulator, such as electric furnace transformers. In addition, due to the characteristics of the rectifier element, the phase angle of the silicon rectifier element conduction can be directly controlled on the valve side of the rectifier electric furnace, and the average value of the rectified voltage can be smoothly adjusted. This voltage regulation method is called phase-controlled voltage regulation. To achieve phase-controlled voltage regulation, one is to use a transistor, and the other is to use a self-saturation reactor. The self-saturation reactor is basically composed of an iron core and two windings. One is the working winding, which is connected in series to the rectifier transformer. The load current flows between the secondary winding and the rectifier; the other is the DC control winding, which is provided by another DC power supply. The main principle is to use the nonlinear changes of ferromagnetic materials to make the working winding reactance value very large. The change. By adjusting the DC control current, the phase control angle α can be adjusted, thereby adjusting the average value of the rectified voltage.

　　Applicable rectifier circuit

　　Commonly used rectifier circuits are single-phase half-wave, single-phase full-wave, three-phase half-wave, three-phase full-wave (Y or △) bridge type, three-phase zigzag type (Zo shape), six-phase Y shape (midpoint connection), Six-phase forked (also zigzag), six-phase Y-shaped parallel bridge type (with balanced reactor), six-phase △Y-shaped series bridge type, twelve-phase four-shape zigzag type with balanced reactor, six-phase Y-shaped or △ Form, six-phase (twelve or twenty-four phases) double reverse star with balanced reactor, or multiple sets of parallel bridge type, double reverse star circuits. The DC current can reach 25KA, and the DC voltage ranges from tens to hundreds of volts. The valve side often adopts the same-phase and anti-parallel connection method.

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