20 | SAMLEX AMERICA INC.
of loads and this load is required to be transferred to the Backup AC Source. When contacts of Transfer
Switch open, current flow in the inductive components of the load will be interrupted creating back EMF
voltage at the same frequency as the Primary AC Source. For faster load transfer to the Backup AC Source
(before the above back EMF is dissipated), it is desirable that the frequency and phase of the Backup
AC Source are kept synchronized with the frequency and phase of the Primary AC Source at all times. If
faster transfer takes place from the Primary AC Source to the Backup AC Source that is NOT synchronized
in frequency and in phase with the Primary AC Source, AC motor driven loads such as fans, pumps,
compressors etc. will experience mechanical stresses and can produce large inrush currents resulting in
malfunction of the motor and the motor driven load and unintended tripping of upstream circuit breakers.
All Switch Mode Power Supplies (SMPS) or equipment that have SMPS in their front end experience no
difficulties when their primary / backup AC input power sources are switched, regardless of whether the
sources are synchronized or not because the entire SMPS / equipment load is supplied at DC (Direct Current).
5.6.3 Programmable Parameter “Output FREQ”
The output frequency of the Inverter can be programmed through parameter called “Output FREQ”.
Programmable range is 45.0 to 65.0 Hz. Default value is 60Hz. For programming details, refer to Fig 10.1
/ Table 10.1 under Main Menu Parameter Group 3 – "Output Setup" / Sub Menu for Parameter Group 3,
Parameter (b) – "OUTPUT FREQ" (Section 10.2.3.2).
5.6.4 Programmable Parameter “Sync FREQ” for Determining Synchronizable Frequency Window
As described in Section 5.6.2 above, for safer and faster transfer of load between 2 AC sources, it is
desirable that the frequency and phase of the Backup Power Source i.e. the Inverter in this unit be kept
synchronized with the AC GRID input at all time. This unit has been designed to provide “synchronized
transfer” in the default condition.
Synchronized transfer is possible as long as the frequency of the AC GRID input is within programmable
“Synchronizable Frequency Window”. This window is determined by programmable parameter called
“Sync FREQ” with a range of 0.1 to 7 Hz (Default value is 5 Hz). For programming details, refer to Fig 10.1
/ Table 10.1 under Main Menu Parameter Group 3 – "Output Setup" / Sub Menu for Parameter Group 3,
Parameter (c) – "SYNC FREQ" (Section 10.2.3.3).
“Synchronizable Frequency Window” = Programmed value of “Output FREQ” of the In/-
Programmed value of the “Sync FREQ”. For example, if the
“Output Frequency” of the Inverter Section is set at 60 Hz (Default)
and “Sync. FREQ” is set at 5 Hz (Default), the “Synchronizable
Frequency Window” will be 60Hz ± 5Hz or “55Hz to 65Hz”.
As long as the AC GRID input frequency is within the “Synchronizable Frequency Window”, the frequency
and phase of the Inverter’s output voltage will be kept synchronized with the frequency and phase of the
AC GRID input.
5.6.5 Synchronized Type of Transfer
5.6.5.1 Synchronized Type of Transfer in Off-Line Mode: Under this condition, AC GRID input is the Primary
Source and the Inverter is the Backup Source. Please refer to information in Table 5.1 below related to
this condition:
SECTION 5 |
Description & Principles of Operation
