Spellman ST SERIES Instruction Manual Download

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ST/STR/STA MANUAL

118107-001 REV J

Chapter 4

Principles of Operation

he ST series of high voltage power supplies utilizes
sophisticated power conversion technology. A variety
of analog, digital and power conversion techniques

are employed. This Principles of Operation will introduce
the basic function blocks that comprise the ST power
supply. For details on a specific circuit, consult
Spellman’s Engineering Department.

The ST power supply is an AC to DC converter.  Within
the  power  supply,  conversions  of  AC  to  DC,  high
frequency  AC,  then  to  high  voltage  DC  take  place.    By
reviewing  functionality  of  the  subassemblies,  a  basic
understanding of the process can be gained.

WARNING

THE ENERGY LEVELS USED AND GENERATED BY

THE POWER SUPPLY CAN BE LETHAL! DO NOT

ATTEMPT TO OPERATE THE POWER SUPPLY

UNLESS THE USER HAS A SUFFICIENT KNOWLEDGE

OF THE DANGERS AND HAZARDS OF WORKING

WITH HIGH VOLTAGE. DO NOT ATTEMPT TO

APPROACH OR TOUCH ANY INTERNAL OR

EXTERNAL CIRCUITS OR COMPONENTS THAT ARE

CONNECTED OR HAVE BEEN CONNECTED TO THE

POWER SUPPLY. BE CERTAIN TO DISCHARGE ANY

STORED ENERGY THAT MAY BE PRESENT BEFORE

AND AFTER THE POWER SUPPLY IS USED.

CONSULT IEEE RECOMMENDED PRACTICES FOR

SAFETY IN HIGH VOLTAGE TESTING #510-1983.

4.1 Line Rectification and
Filtering

WARNING

LINE VOLTAGE IS PRESENT WHENEVER THE

POWER SUPPLY IS CONNECTED TO THE INPUT LINE

VOLTAGE. BE SURE TO DISCONNECT THE LINE

CORD BEFORE OPENING THE UNIT. ALLOW 5

MINUTES FOR INTERNAL CAPACITANCE TO

DISCHARGE BEFORE TOUCHING ANYTHING

CONNECTED TO LINE REFERENCED CIRCUITRY

Simple three phase rectification provides the DC buss
voltage for the high frequency inverter.

An  input  line  cord,  three  phase  circuit  breaker  (customer
provided on 400Vac Option units), EMI Filter Assembly,
contactor,  inrush  bridge  rectifier,  electrolytic  capacitors,
rail  inductor  and  rail  capacitor  comprise  the  basic
components required for input line rectification.

The  standard  line  input  voltage  for  the  ST  Series  is  180-
264Vac,  50/60Hz.  An  optional  360-528Vac,  50/60Hz
input  voltage  is  available  (400Vac  Option).    Optional
Single  Phase  input  is  available  on  the  STR  and  STA.    If
the  user  is  unsure  which  input  voltage  is  required,  check
the  serial  tag  on  the  rear  of  the  power  supply  or  consult
Spellman’s Sales Department

The customer provided AC power input is provided to the
unit  via  the  four  conductor  AC  line  cord.  Circuit
protection is provided by CB1, a fast acting magnetic trip
type circuit breaker.  The load side of CB1 is connected to
EMI  filter  A2.    The  output  of  the  EMI  filter  connects  to
K1,  a  three  phase  contactor.    K1  provides  fail-safe  type
disconnection  of  the  line  voltage  to  the  power  supply
rectification circuits.  K1’s coil is controlled by a variety
of  circuit  conditions,  which  will  be  described  later  on.
The  load  side  of  CB1  is  also  connected  to  low  voltage
power  supply  assembly  A9,  which  provides  various
voltages for housekeeping and control circuit power.

When  contactor  K1  is  energized,  voltage  is  applied  to
isolated bridge rectifier power module CR1, used for line
voltage  rectification.    The  output  of  CR1  is  connected  to
aluminum  electrolytic  capacitors  C1  and  C2  for  line
filtering  purposes.  Capacitors  C1  and  C2  are  initially
charged  through  inrush  limiting  charging  resistors  which
is located on POWER PWB – A6.

After an appropriate period of time to charge C1 and C2,
relays  on  POWER  PWB  –  A6  are  energized  to  short  out
the  inrush  limiting  resistors.  The  generated  DC  buss
voltage  is  supplied  to  the  inverter  circuitry  through  L2,
L3,  L6  and  L7.  The  inductors  provide  isolation  for  the
electrolytic  capacitors  C1  and  C2,  so  the  inverter’s  high
frequency  pulse  currents  are  drawn  from  the  metalized
film high frequency “rail capacitors” C3 and C12.

The  POWER  PWB  –  A6  provides  the  inrush  limiting
function via R1, R2, R3 and R4. Relays K1 and K2 short
out  the  limiting  resistors  once  the  initial  charging  of  C1
and C2 is complete. Resistors R7, R8, and R10, R11 form
two  feedback  divider  circuits  with  terminating  resistors
located  on  the  SYSTEM  CONTROL  PWB  –  A1.  These
impedance  limited,  low  voltage  +  and  –  rail  feedback
signals  are  monitored  and  if  any  abnormal  conditions
appear, circuitry will shutdown the power supply.