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Zhangjiagang plant, Eastern China

SVC Light® for grid code compliance of 220 kV steel plant connection

An SVC Light® rated at 35 kV, 0-164 Mvar (capacitive) has been installed in ZPSS (Zhangjiagang Pohang Stainless Steel Co.), a green-field steel plant in Eastern China, comprising a very large electric arc furnace (EAF) for scrap-based stainless steel production. The EAF is rated at 35 kV, 140 MVA and takes its power from the 220 kV public grid. Due to very strict flicker demands at the point of common coupling, the plant could neither be started nor operated without corrective measures to ensure that the grid code is fulfilled with the EAF in operation. What is of concern is maintaining proper power quality in the grid.

The EAF generates several kinds of disturbances, which, unless remedied, result in more or less severe deterioration of power quality. Large and stochastic variations in reactive power consumption give rise to large and rapid grid voltage fluctuations, which show up as illumination flicker, a particularly annoying sensation for people exposed to it.

Furthermore, the EAF is an asymmetrical load on the threephase feeding grid, giving rise to current and voltage unbalance in the grid. Normally, only very limited levels of grid asymmetry can be allowed without causing deterioration of the power quality for other consumers connected to the same grid. And last but not least, the EAF generates harmonics, odd and even, as well as interharmonics.

The primary task of the SVC Light is to suppress flicker to acceptable levels, but also to yield a high and constant power factor, as well as to limit harmonic distortion and negative phase sequence components generated by the EAF.

Initially, a traditional SVC, i.e. an SVC based on thyristor control of shunt reactive devices, was considered for the task. It was found, however, that the flicker-damping capability of an SVC was insufficient for the purpose, and an SVC Light, a device more potent for the purpose, was decided on instead.

With the SVC Light in operation, a flicker reduction factor > 5 is achieved.

Diagram

Main data

Furnace bus voltage: 35 kV
Rated EAF power: 140 MVA
SVC Light rating: 35 kV, 0-164 Mvar (capacitive)
VSC 82 MVA, three-level, neutral point clamping converter; IGBT based, pulse width modulated.
Control system: Open-loop, phase-wise dynamic var control, plus closed-loop power factor control.
Flicker reduction factor: > 5
Power factor at 220 kV PCC > 0.995