The complete set of equipment is mainly composed of rectifier power transformers, bus bars, low-voltage isolation switch cabinets, single-supply intermediate frequency power supplies, power control boxes, 3 ton electric furnace bodies, hydraulic pump stations, tilting furnace operation tables, water-cooled cables, cooling water distributors, crucible molds, and water cooling. System, etc.

The IF power supply should have the following functions:

1.Rectifier circuit

The intermediate frequency power supply uses a 12-pulse thyristor bridge rectifier circuit. At least 11 harmonics; the power factor on the grid side is always greater than 0.95; the rectifier transformer of the intermediate frequency power supply uses D / Y-11 and d0 wiring. The secondary of the transformer has two sets of three-phase outputs, and the line voltages of these two sets of output are equal , Both are 660V, but the phase difference is 30 °. The two sets of outputs are connected to I and II rectifier bridges, respectively.

The rectifier part of the thyristor uses a stacked radiator component; the radiator component has a scale for reference when tightening to ensure the correct pressing force between the thyristor and the radiator.

2.Inverter circuit

A half-bridge series inverter is used. Whether the electric furnace is cold, hot, half-charged or full-charged, the half-bridge series inverter can output rated power. The half-bridge series inverter adopts the method of changing the operating frequency to adjust the output power.

3.Control system

The intermediate frequency power supply uses an advanced all-digital control system based on a high-performance microcontroller.

(1) Digital inverter control

   The digital inverter controller is integrated inside the CPU. Adopt three closed-loop control algorithms of power, voltage and current. During normal operation, voltage, current and power are sent to the CPU through the respective converters. The control software detects these parameters and adjusts the operating frequency to ensure that the output power is always equal to the rated power.

When there are situations such as empty furnace power transmission (too much impedance) or freezing furnace power transmission (too small impedance), the control software can automatically call the voltage or current limiting algorithm to limit the output voltage or current not exceeding the allowable.

The control software has a variety of parameter limiting functions, including: full high power limit, thyristor current output limit, electric furnace voltage limit, capacitor voltage limit, full high and low operating frequency limits

The parameters of the control algorithm can be set by the keyboard, and they are stored in the EEPROM of the control board. The parameters are easy to change, making the half-bridge series inverter suitable for melting different metals, such as cast iron, copper, aluminum, etc.

The thyristor is a controlled shutdown device, and the startup of the inverter is completely controlled by the trigger pulse, so the inverter can start 100% in any furnace condition.

 (2) Multi-point temperature monitoring

The control system has a digital multi-point temperature monitoring function. Each control board can detect the temperature of up to 70 points at the same time. The upper limit alarm temperature of each point can be set independently. When the temperature at a certain point exceeds the set alarm temperature, the control system will automatically give a prompt. After the alarm signal lasts for a certain period of time (usually 10S), the IF power will be automatically turned off.

 (3) Comprehensive protection functions

The protective measures of the control system include:

High grid voltage, low grid voltage, high DC voltage, over thyristor current, high capacitor voltage, high furnace voltage, high operating frequency, high cooling water temperature, low cooling water pressure, low cooling water flow, and electric furnace leakage

 (4) Automatic restart function

When over-current, over-voltage, and high inverter frequency protection occurs (the presence of these protections does not indicate equipment failure, it is often caused by sudden charging, collapse of furnace charge, rapid fluctuations in grid voltage, etc.). Automatic restart in seconds to resume normal working conditions.

 (5) Delay protection function.

When there is protection from high grid voltage, low grid voltage, high water temperature, low water pressure, etc., the intermediate frequency power supply does not stop immediately, but first indicates a protection signal. If the protection signal still exists after 10 seconds, the shutdown enters the protection state. Because the above phenomenon will not cause any damage to the equipment within 10 seconds. On the contrary, the delayed protection can filter out some false protections. For example, when a large electrical appliance near the equipment suddenly closes or opens, it will cause an instantaneous fluctuation of the grid voltage. It usually returns to normal after a few seconds. In this case, the IF power supply will continue to work normally.

 (6) With LCD graphic display

The control system has a dedicated LCD graphic display. The display is installed on the operation panel of the intermediate frequency power supply. When the intermediate frequency power supply works normally, it dynamically displays the operating parameters, working status and multi-point temperature monitoring results of the intermediate frequency power supply. If there is an abnormality in the IF power supply, it will display the cause of the fault or protection, and automatically remember the trip source, so that maintenance personnel can quickly troubleshoot according to the prompts.

 (7) Fiber isolated pulse output

In the control system, the trigger pulses are optically isolated from the control board to the control pole of the thyristor using optical fiber isolation technology.

 (8) With computer communication interface

    The control system has a computer communication interface, which can be connected to the melting management computer to achieve the centralized monitoring of the parameters of multiple IF power supplies. The communication interface uses optical fiber as the communication medium, which can ensure the reliability of long-distance data transmission.

 (9) Leakage protection and ground alarm trip function

The control system has a dedicated furnace lining thickness detector. The alarm current of the furnace lining thickness detector can be adjusted.

(10) Computer melting control management system

Computer system for data sampling and control based on industrial control computer. It is used for automatic control and data recording of melting or process. Its main functions are:

Basic monitoring: continuous monitoring and display of meter readings, power, furnace current,

Furnace voltage, frequency, capacitor voltage, ground leakage current, total kilowatt hours, system alarm display, capacitor damage or cabinet door opening, overvoltage protection, internal cooling water temperature is too high, internal cooling water pressure is too low, external cooling water temperature Too high, external cooling water pressure is too low, furnace selection / isolation switch error, AC interruption, ground / leak detector alarm, display system operating status, inverter operation, full power operation, inverter current limit, voltage limit, frequency Limit, furnace voltage limit, AC current limit, real-time monitoring and display of electric furnace working parameters, remote centralized control of multiple electric furnaces

Automatically record equipment work and alarm parameters, generate various reports, and automatically analyze parameters,

Predicted failure:

Predict the working temperature of electric furnace, programmable automatic operation, including:

---- Furnace lining preheating procedure

---- Automatic sintering process of furnace lining

---- Automatic melting and holding procedure

3 ton series induction melting furnace main technical parameter configuration