Samlexpower Evolution EVO-4248SP, Owner'S Manual

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4.5.2.1 Synchronized Transfer of Power
4.5.2.1.1 General information
When the frequency and phase of output voltages of two AC power sources are the same ( in sync ), the two AC
sources are considered to be “synchronized”.
Critical AC loads require un-interruptible AC input power. It is, therefore, necessary that when the primary AC
input power is interrupted / fails, the load should be transferred to the backup AC source “
very quickly ” within the
“holdup time” of the load(s) .
When AC power feeding motors or inductive loads like transformers etc. is interrupted / fails, residual voltage
is induced in the load due to “generator effect” created by a rotating motor or by the stored energy released
from the inductive loads like transformer’s windings or core. The induced residual voltage in the load has the
same frequency and phase as the voltage of AC input power when it failed and, this voltage does not dissipate
immediately but within a few seconds. This induced residual voltage in the load can cause extremely high inrush
currents to occur when such loads are “
very quickly
” transferred to a “
non-synchronized
” source of backup AC
power (the loads are transferred to the “non-synchronized” backup source before the residual voltage in the load(s)
has dissipated) . The resulting effect, frequently described as “bumping” can initiate nuisance tripping of circuit
protective devices or in extreme cases, cause mechanical damage to motor shaft and couplings. To prevent this
abnormal operating condition when the load is transferred between the primary and backup AC sources “
very
quickly (normally within around 16 ms) ”, it is to be ensured that the voltage of the backup AC power source is
always kept “ synchronized ” with the voltage of the primary AC power source.
Synchronization control logic used in a backup AC source is required to be based on the frequency stability
characteristics of the primary AC source which can be Grid or Generator. The frequency of Grid voltage is very
stable. On the other hand, the frequency of Generator voltage
(except Inverter Generators) may vary considerably
depending upon the performance of its Speed Governor that compensates for the drop in RPM / frequency when
electrical load is switched on / increased or, rise in RPM / frequency when electrical load is decreased / switched off.
4.5.2.1.2 Synchronization Algorithm Options
When operating as an Inverter Charger, the EVO-4248SP is designed to accept external AC input power through
AC Input Terminals
(2,3,4 and 8A in Fig 2.3)
.
The frequency and phase of the internal backup Inverter Section are always kept synchronized with the AC input
source. This facilitates “extremely fast” transfer time of up to 18 ms.
Also, transfer from the Inverter Section to the
AC input source and vice versa takes place at zero crossing of the voltage waveform – this ensures (i) negligible arcing
/ erosion of Transfer Relay contacts and (ii) negligible Electromagnetic Interference (EMI) associated with arcing
.
Programming parameter “SYNCHRONIZATION” has been provided with two synchronization algorithm options:
(i) 0= Fine, or (ii) 1= Coarse. Option “0 =Fine” is recommended for AC input power source that has more stable
output frequency like Grid / Inverter Generator. Option “1= Coarse” is recommended for AC input power source
with less stable output frequency like Generator.
For more details on programming parameter "SYNCHRONIZATION",
please refer to Section 4.5.2.8 in the Owner's Manual for Remote Control Model EVO-RC-PLUS.
SECTION 4 | General Description & Principles of Operation