STA SERIES THYRISTOR STACKS DATA SHEET EXTRACT

Data Sheet Extract	Caledon
STA SERIES	THYRISTOR STACKS FOR BURST FIRE CONTROL OF TRANSFORMER COUPLED LOADS

FEATURES


	Versions for single or 3-phase loads
	Current rating from 80A to 1000A air cooled
	Operation without derating up to 50^oC ambient
	Low cost 2-line control of 3-phase load
	Minimum radio frequency emissions
	Minimum waveform distortion
	No power factor degradation
	Simple installation, commissioning and maintenance
	Microprocessor controlled
	Long life ball-bearing fans
	Compact size, only 290mm deep

GENERAL DESCRIPTION

This is a range of thyristor stacks, specifically designed for burst fire control of the primary of transformer coupled loads in heating applications. A typical application example is in high temperature furnaces with low resistance graphite heating elements. These stacks switch on near the peak of the voltage waveform, thus minimising transient flux and transformer inrush without recourse to phase angle operation. This technique enables the control of a 3-phase transformer load by switching only two lines, and causes the minimum possible line disturbance, waveform distortion and radio frequency emissions. Special drive techniques ensure the minimum possible rfi associated with zero crossing commutation of the thyristors, enabling the units to be used with confidence in emc compliant systems. The driver control circuit is microprocessor controlled, and accepts either analogue (1-5V, 4-20mA) or logic input signals. A separate enable input is provided, which can be used in conjunction with system interlocks, current overload monitor etc. A logic output is provided for synchronising other thyristors if required. Semiconductor fuses and power supplies are electronically monitored, and an alarm relay is provided for system integration.These units do not have a current limit facility, and are not suitable for use with loads which have a low cold resistance requiring current limiting.