Compensation equipment for large drives, arc furnaces for the steel industry or electrolysis rectifiers

We analyse the condition of your grid regarding line perturbances by large loads, serve as consultant for ultimate consumers and supply complete compensation plants. For equipment already in operation, we offer concepts for optimization and furnish modern, digital TCR controls. Our services include planning, design, commissioning and maintenance. For the steel industry we make use of mathematical models for the electric arc furnace (AC or DC) and we are in a position to inform about the disturbances to be expected. With the help of computer-based simulations, the layout of the components of a compensation system can be determined.

 

 

During the operation of arc furnaces, outputs of up to 100 MW are being drawn from the grid. The right hand graph shows the operation cycle of approx. one hour. In order to fathom the line disturbances, the dynamic current requirement within the range of milliseconds has to be analysed. A schematic graph of the active power is shown in the left picture:

 

Active power

Typical effect of the reactive power

The dynamic alterations of the reactive power will produce large alterations (fluctuations) of the voltage and subsequent flicker on the grid.

 

This graph shows, how according to the operation of the furnace even small changes in the active power may produce large changes in the reactive power.

Flickers lead to mayor disturbances in the grid. A compensation plant must control the reactive power.

 

 

Due to non-sinusoidal furnace currents, the line is disturbed by higher harmonic currents, which have to be reduced by filter circuits. Here we show the higher harmonic currents of AC - EAF - plants in relation to the basic waves:

 

 

Grid disturbances by EAF can be summarized as follows:

 

 

An executed SVC plant for an AC EAF which compensates all three of the described disturbances.

The left part of the circuit diagram shows the EAF switch gears. We project and deliver these solution including RC damping circuits.

 

 

 

Outdoor arrangement of the filter circuits consisting of reactors and capacitor banks.

 

Complete turnkey plants of arc furnaces for the production of steel together with a bar mill for rolling steel for armouring concrete will be offered together with our cooperation partners.

 

 

TCR Products

We can offer thyristor controlled reactors (TCR) for reactive power control with digital controls in order to optimize the reactive power flow into the feeder. The according AEG products are called Semivar and Megasemi. For TCR equipment in operation we can supply new digital controls, consisting of an electronic card within the high voltage power rack and a control cubicle. The connection between the power rack of the TCR and the control cubicle is effected by light transmissions which fully insulate the control.

Thyristor Power Rack for 33 kV

Thyristor Power Rack for 33 kV

TCR cubicle

TCR cubicle

 

Line Compensation

AEG has delivered several plants for dynamic power factor compensation in high voltage grids, e. g. eleven units for the South African Republic and another one to Nampower, formerly SWAWEK, in Namibia. A technical description of this plant is available here.

 

Line Measurements

In connection with new installations or in case of grid disturbances of existing plants, we can execute line measurements. Our report will include the causes of the disturbance and suggest changes and compensation measures. Typical points of measurement of an EAF plant are shown in the following graph:

 

 

Further information about EAF compensation:

> Dynamic reactive power compensation for an EAF at MEGASA steel plant, Spain (pdf)
> Essay on a reference project (pdf)
> Static VAR-Compensators for stabilizing traction and transmission systems in South Africa (pdf)