Control equipment for DC steelmaking furnaces

General characteristics

The set of equipment enables high-precision adjustment (approximately 5%) of melting power in DC arc furnace, contains controllers for a high-voltage switch, furnace slope and oscillation, roof lifting and lowering:

• metal weight for melting in furnace:
  • up to 50 tons;
• converter rated current:
  • from 2000 till 50000 A;
• rated voltage:
  • from 100 till 1000 V;
• types of power control:
  • manual (automated maintenance of arc current);
  • automatic (automated maintenance of arc current and voltage);
• possible modes of converter’s bridge connections:
  • series connection is used for metal smelting;
  • parallel connection is used for molten metal.
• electrode drive types:
  • DC drive;
• controlled parameters of smelting:
  • arc current;
  • arc voltage;
  • smelting power (active and reactive);
  • energy consumed during smelting process (active and reactive energy);
  • temperature of furnace and converter elements.
• furnace mechanisms controlling features:
  • furnace slope;
  • roof lifting and lowering;
  • furnace rolling out and roof retraction.
• network interfaces:
  • Profibus DP, Modbus RTU, Ethernet, CAN, etc.

Technical specifications

The set of equipment consists of the following main cabinets:

• DC furnace control panel

Is designed to control the smelting process and contains electrode control drive to ensure maintenance of a given arc voltage;

• DC furnace controle cabinet

Is designed to control smelting parameters and furnace elements state;

• Thyristor converter control cabinet

Is designed to maintain arc current value on a set level;

• Thyristor converter

Is designed to convert alternating three-phase voltage into a rectified voltage, which value is determined by control pulse position received from the thyristor converter control cabinet.

Engeneering information

Equipment parameters:

Operational conditions

Design

Constructive composition of the set of equipment:

• Typical equipment mix for a DC furnace power source:
  – Furnace control panel – for regulation of the smelting process (FCP);
  – Furnace control cabinet – for control of the melting parameters (FCC);
  – Steelmaker console – for furnace mechanisms control by the steelmaker;
  – Steelmaker remote control – for furnace mechanisms control during tapping;
  – Power rectifier;
  – Rectifier control cabinet (RCC);
  – Heat exchanger;
  – Power transformer (optional, it is possible to use customer’s transformer).
• Additional equipment for the DC furnace power source, which can supplied optionally:
  – Diagnostic console;
  – Oil pump station control cabinet;

Design features:

• For currents up to 10000А and parallel connection, the rectifier and the rectifier control cabinet are combined;
• The maintenance of all cabinets is on one side, protection rating is IP21, except for bus arrangement outputs, where protection rating is IP00 according to GOST 14254-96;
• It is possible to design the rectifier combined with the transformer;
• The cabinet doors are equipped with internal locks, which can be opened with a special key.

Scope of cabinets and equipment

Composition of the thyristor converter control cabinet (TCCC):

• auxiliary power supply system;
• control system:
  • controller with the following functions: control, current adjustment and rectifier protection;
  • analog and discrete input devices;
  • external network interface module.
• relay equipment;
• independent recorder;
• local controllers and alarm system on the door:
  • Arc current and voltage devices;
  • Current devices in each parallel bridge;
  • Console terminal (or inside the cabinet);
  • Lamps: “Ready”, “Warning”, “Accident”;
• cabinet heating device (optional, for the CC design to be used under sub-zero temperature conditions).

Composition of the furnace control cabinet (FCC):

• auxiliary power supply system;
• control system:
  • controller with the following functions: control, furnace and transformer protection;
  • analog and discrete input devices;
  • external network interface module.
• relay equipment;
• devices converting signals from thermocouples;
• local controllers and alarm system on the door:
  • Network voltage device;
  • State and protection lamps for the transformer, heat exchanger, oil system, rectifier, furnace cooling system (composition of indicators is determined upon customer’s request);
  • Console terminal (or inside the cabinet);
  • Digital indicators of active and reactive melting power, hearth-level electrode temperature, furnace cooling system status;
  • On / off buttons for heat exchanger, transformer cooling system, protection reset.
• cabinet heating device (optional, for the CC design to be used under sub-zero temperature conditions);

Composition of the furnace control panel (FCP):

• electrode control drive;
• auxiliary power supply system;
• control system:
  • controller with the following functions: electrode control and smelting process control;
  • analog and discrete input devices;
  • external network interface module.
• local controllers and alarm system on the door;

Functional characteristics

Power circuit:

• specific aspects of power circuit operation:
  • functionally, the power circuit is presented on the following figure:

• the power circuit comprises a connection of two rectifier bridges which supply transformer windings are opposite-connected;
• in series mode, control pulses are fed to the thyristors of switching half-bridge, one side of the first bridge and one side of the second bridge. Such a connection of bridges allows to obtain the required melting power due to increased voltage;
• in parallel mode of bridge connection, control pulses are fed to both power bridges. Such a connection of bridges allows to obtain the required melting power due to increased current.

Automatic power controller:

Controller functions:
– type: digital;
– control mechanism: precise PI-controller of current + P-controller of voltage;

Controller functions:
– arc current control via changing the power bridge thyristors on-state time, allowing to maintain the arc current with an accuracy of ± 1%;
– arc voltage control via changing the arc length by electrode positioning;
– automatic arcing after arc break;
– limitation of the rectifier output voltage upon arc break, which allows to reduce short-circuit currents during arcing;

Protection system:

– maximum rectifier current protection;
– power fuse failure protection;
– cooling liquid channel failure protection;
– rectifier elements overheating protection;
– furnace elements overheating protection;
– heart electrode overheating protection;
– oil overheating in the transformer;
– protection against malfunction of the converter cooling system;
– power voltage outage protection;
– protection against loss of conductivity on parallel thyristors in the arms.

Network interfaces:

– ProfibusDP;
– ModBusRTU;
– Ethernet;
– CAN etc.
Note: type of the protocol is agreed between the parties during engineering stage.

Recording and diagnostics tools:

– a recorder built into controller of Thyristor Converter Control Cabinet (TCCC):
– analog channels – 1 … 24;
– discrete channels – 1 … 32;
– measuring resolution – 3.3 … 100 msec;
– recording fragment length – 0.5 … 50 sec;
– data storing for emergency shutdowns – 90 fragments;
– a recorder separated from the TCCC controller for independent control of operation:
– 32 channels of analog sensor signals, discrete input and output signals;
– measuring resolution – 250 µs;
– recording fragment length – 0.5 … 50 sec;
– data storing for emergency shutdowns – 10 fragments;

The advantage of the built-in recorder lies in the possibility to register internal parameters (parameters of control and protection systems, etc.).
The advantage of an independent recorder lies in a high measuring resolution.

– event logging built into controller of TCCC, FCC, FCP:
– input control signals;
– output alarming and tripping signals;
– change of excitation system’s operation modes;
– exceeding and lowering by analog signals of specified limiting values;
– messages of control, regulation and protection systems displayed on the excitation system console terminal;
– software for a diagnostic console and a laptop enabling graphical visualization of data from recorders and text visualization of logged data.

Internet access:

• The remote access to the equipment via Internet is designed to allow equipment operation monitoring by experts of the manufacturer;
• Access to the manufacturer experts can be provided whether with engagement of the station maintenance staff (using a password) or without;
• Access is provided via Internet through the diagnostics panel (next figure) by using:
  – 3G radio modem included into the diagnostic panel package;
  – Wired or Wi-Fi Internet provided by the Customer – in this case, the quality of communication (speed and uninterrupted operation) and the number of available monitoring functions significantly increase;
•  The remote access ensures:
  – prompt response to malfunctions and failures in the furnace operation:
  – files downloading from “technological” and “emergency” recorders, reviewing technological log and event log for pre-accident and equipment failure analysis and subsequent recommendations as to elimination thereof;
  – monitoring of current smelting, furnace and converter parameters;
  – access to data management with the ability to review, edit and save values ​​of the converter’s required parameters;
  – exchange of files, voice and video messages with the station maintenance staff to provide, when necessary, prompt remote assistance and advice on emerging issues when servicing our equipment.
  – diagnostics system software update;
  – data receipt/transfer, remote restart of operation programs on the diagnostic system computer, as well as remote reboot.

Note: implementation of the remote access via Internet, as well as its use by the manufacturer, can only be provided upon agreement with the Customer.

Diagram of Remote Access to the Converter

Setup and diagnostic complex

The setup and diagnostic complex is implemented on the basis of a portable computer and intended for:

• graphical visualization of data from the built-in recorder;
• reports storing by set-points;
• controller reprogramming;

The programmable setup complex consists of:

• a portable computer (it is possible to use the Customer’s own portable computer);
• adapter to connect a portable computer to the controller;
• software package.

Note: the setup and diagnostic complex software is free and is available on the manufacturer’s website: pcomplex.ua

Software content:

• Utility “Link” provides for:
  – console terminal mode;
  – dual-channel oscilloscope mode with display of any control and protection system parameters from the available parameters list;
  – work with the built-in program recorder in the converter:
  – start / stop the recorder;
  – data download after manual or emergency stop of the recorder;
  – download of data restored from NOVRAM, previous emergency shutdowns;
  – data save to a disk and upload of recorded data from disk;
  – display of recorded data in form of tables and graphically;
  – display of emergency, warning and service messages list from the control system at the time of shutdown, as well as the time of recorder shutdown.
• Utility “Code ReadWriter” ensures:
  – download (archive) from the controller to computer hard drive of NOVRAM copy as a .bin file;
  – upload from computer hard drive to the controller a previously saved NOVRAM copy as a .bin file;
  – importing to a file in the text form for the subsequent report on current values ​​of set-points;
  – copy, for the purposes of archiving, of the controller’s program in the form of a .bin file;
  – reprogramming the controller.

Note: the controller can be reprogrammed using a file previously stored in the archive, or received from the manufacturer, for example, via the Internet, in order to supplement the furnace control system with any specific functions as per agreed Terms of Reference.

Scope of delivery

The main equipment set consists of:

• power converter transformer – 1 pc.
• thyristor rectifier – 1 pc.
• thyristor converter control cabinet – 1 pc.
• furnace control cabinet – 1 pc.
• furnace control panel – 1 pc.
• heat exchanger – 1 pc.
• steelmaker’s panel – 1 pc.
• steelmaker’s remote control panel – 1 pc.
• spare parts kit – 1 pc.
• set of maintenance documentation on paper and electronic media – 1 pc.

Additional and supplementary equipment:

• Full set of redundancy boards for the furnace control system – 1 pc;
• Setup and diagnostic complex: – 1 pc:
  – Portable computer;
  – Adapter to connect a portable computer to the ES;
  – Software package.
• Diagnostic panel (RC) on the basis of personal computer – 1 pc.

Safety requirements

• The design and electrical diagrams of furnace control system are implemented in accordance with requirements of the Electrical Installations Rules (EIR);
• The furnace control complies with the safety requirements of GOST 12.2.007.0 and GOST 12.2.007.1, as well as the requirements of Regulations for Operation of Consumer Electrical Installations;
• The excitation system cabinet doors, which give access to conducting parts, have locks and can be opened with special keys;
• The cabinet external surface heating temperature in the most heated, hardly accessible point (except for the power converter transformer) does not exceed 70 ° C under normal operating conditions;
• The design of the furnace control system ensures fire safety due to:
  – use of non-combustible and low-combustible materials;
  – keeping necessary distances between differently potential conducting parts, as well as between conducting parts and the frame, use of insulating non-combustible partitions in necessary cases;
  – use of safety facilities to ensure rapid de-energization of current-carrying parts;
• Noise characteristics and permissible sound pressure levels correspond to GOST 12.1.003-83 “SSBT NOISE General requirements” and do not exceed 80 dB.