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Common Problems and Solutions of High Current Rectifier
May 24, 2017

The rectifying device is an electronic product, a technology-intensive product integrating electric power (strong current), electronics (weak current) and control technology and the critical equipment in the electrolytic system, so it must be operated in strict accordance with the operation rules. Its running status and operating parameters shall be regularly checked and recorded according to the requirements and the device shall be maintained according to the prescribed period. The parts not meeting the requirements (or failure during operation, such as damage of elements and parts) as discovered in the detection and maintenance shall be immediately replaced to ensure device operation in good conditions.

In case of failure for various reasons, the device debugged and put into operation, shall be checked step by step according to the failure phenomenon and analyzed according to the working principle in normal work. The common failure of the electrolyzer is mainly the electrical failure.

1. The cooling water pipe, if damaged or blocked in maintenance, shall be timely replaced.

Technical requirements for replacement of water pipe (scope of application: this regulation applies to the water pipe assembly of the rectifying device)

Tools: monkey wrench and pliers;

Auxiliary materials: cutting knife, cotton cloth and gloves;

Prepare the PVC water pipe, compressed spring, gland nut and other necessary materials for water pipe assembly;

Replacement method:

1.1 Measure the length of each PVC water pipe for short-circuiting the watercourse and make statistics of the quantity;

1.2 Uniformly prepare the materials according to the length and quantity subject to statistics in last step;

1.3 Install the cut short-circuit water pipe in the corresponding position and tighten the copper gland nut to prevent water leakage and seepage;

1.4 Check whether the short-circuit water pipe is seriously distorted or bent and immediately replace if any to prevent watercourse blockage;

2. Precautions for replacement of water nozzle

2.1 Place the O rubber ring in the notch at the water nozzle thread end, wrap with raw tape anticlockwise for 8-10 rounds and then fasten the nozzle end wrapped with the tape in the copper bar or radiator.

2.2 Place the other end of the water nozzle (tower type end) in the water pipe and place the compressed spring and gland nut in the water pipe with the thread towards the water nozzle.

2.3 Push the compressed spring to the end of the tower type end along the water pipe and then push the gland nut to the thread of the water nozzle tower type end for fastening.

3. Replacement steps and matters of components on site

Element damage means that the rectifying element loses the rectifying ability. The main reason for damage to the rectifier diode is reverse breakdown and excessive junction temperature due to poor overload or heat dissipation conditions, resulting in PN junction damage. The reverse breakdown is mainly caused by overvoltage.

Parallel elements lose the rectifying ability due to excessive forward voltage drop. Increase in the forward voltage drop is mainly caused by increase in bulk resistance and contact resistance.

The thyristor also has out-of-control (no forward blocking ability) and trigger impassability in addition to above damage phenomena and damage reasons. The reason for out-of-control is also caused by PN junction damage and trigger impassability (internal disconnection of control electrode). The rectifying element damage is generally permanent and cannot be repaired, so only the new element can be use.

      The factory has marked the number of threads exposed after the nut screening on the nut after test compliance of each element before product delivery.

3.1 See clearly the number of the threads exposed in the gland nut before removing the damaged element and make a mark (or record) on the corresponding screw of the replaced element to reduce the element replacement error;

3.2 Wipe clean the new element, press-fitting copper bar table board and radiator table board with the cotton cloth dipped with acetone (alcohol), ensure the conductive table board is not contaminated, and immediately replace the element;

3.3 Gently place the element anode (cathode) on the press-fitting copper bar table board and position with a locating pin. Do not drag the element on the press-fitting copper bar table board to avoid serious scratch of the table board;

3.4 Gently place the radiator on the element anode (cathode) face and place the radiator pin in the location hole of the element center;

3.5 Place an insulation briquette on the radiator and place the insulation briquette pin in the location hole of the radiator center;

3.6 Cover two steel spring pates on the insulation briquette and ensure that the semicircular convex ball of the insulation briquette falls in the semicircular concave ball of the steel spring plate;

3.7 Cover the nut on the bolt exposing the steel spring plate, tighten the nut with a wrench, basically ensure consistent height on both sides of the steel spring plate and make the elements fastening and the radiator current-carrying plate orderly;

3.8 Tighten two nuts alternately by 1/4 round each time, measure the height on both sides of the steel spring plate after tightening by a round (i.e. four times for each side) and try to ensure consistent height on both ends until the number of the threads exposed is consistent with the mark (or record) on the screw.

3.9 Enter next process after inspection without error.

4. Technical requirements for fast acting fuse assembly (scope of application: this regulation applies to the fast acting fuse assembly of the rectifying device)

Generally, one or two fast acting fuses are damaged occasionally mainly because of the damage of rectifying elements. Damage of a lot of fast acting fuses refers to most or full damage of a rectifier arm mainly because of vicious circle caused by poor current sharing and poor cooling conditions caused by low hydraulic pressure or unsmooth water pipe. The fast fuse of the whole arm in the thyristor device is damaged due to sudden closing and delivery of power to the main circuit under full-open pulse phase, which is mainly related to the phase and circuit parameters in closing.

Tools and auxiliary materials:

A: Tools: ruler and torque spanner;

B. Auxiliary materials: acetone, cotton cloth and gloves;

Precautions and preparation

 Determine the quantity and installation direction of the fast fuses according to the schematic diagram;

 Check whether the copper busbar table board is seriously scratched and timely treat if any;

 Prepare the fasteners required for acetone and cotton cloth;

 Wipe clean the copper busbar table board with the cotton cloth dipped with acetone, ensure that the table board is no longer contaminated and complete assembly within 1h;

 Finally gently place the fast fuse on the copper busbar table board, join with screws, adjust to align the fast fuse with the copper busbar and tighten the screw to the torque in (Table-1) according to the screw size;

Torque N·M