SIEMENS
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Siemens KT 10.1 · 2016
15
Technical information and configuration
Parallel connection
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Overview
Parallel connection for redundant operation
Two SITOP power supplies of the same type can be connected
in parallel through diodes for a redundant configuration. 100%
redundancy only exists for two power supplies when the total
load current is no higher than that which one power supply can
supply alone and when the supply for the primary side is also im-
plemented redundantly (i.e. a short-circuit on the primary side
will not trigger a shared fuse which would disconnect both
power supplies from the mains).
Parallel connection with decoupling diodes for redundant oper-
ation is permitted for all SITOP power supplies. The diodes V1
and V2 are used for decoupling. They must have a blocking volt-
age of at least 40 V (when decoupling from 24 V power supplies)
and it must be possible to load them with a current equal to or
greater than the maximum output current of the respective
SITOP power supply. For diode dimensioning, see the following
note "General information on selection of diodes".
The ready-to-use add-on "SITOP PSE202U modular redundancy
modules" are available as a simple alternative to diode dimen-
sioning (Article number: 6EP1962-2BA00, 6EP1964-2BA00,
6EP1961-3BA21) for redundant connection of two power
supplies.
Parallel connection of two SITOP power supplies for redundant operation
General information on selection of diodes:
The diodes must be dimensioned for the maximum dynamic
current. This can be the dynamic current during power-up in the
short-circuit case, or the dynamic current during a short-circuit
in operation (the larger of the two values should be taken from
the relevant technical specifications).
To dissipate the significant power loss of the decoupling diodes
(sustained short-circuit current x diode conductive-state volt-
age), the diodes must be equipped with suitably dimensioned
heat sinks.
An additional safety margin is recommended, because the
output capacitor integral to the power supply generates an
additional peak current in the short-circuit case. This additional
current flows only for a few milliseconds so it is within the period
in which diodes are permitted to be loaded with a multiple of the
rated current (8.3 ms, known as the permissible surge current for
diodes).
Example
Two 1-phase SITOP modular power supplies with 10 A rated out-
put current (Article number: 6EP1334-3BA10) are connected in
parallel. The dynamic current in the event of a short-circuit
during operation is approx. 30 A for 25 ms.
The diodes should therefore have a loading capability of 40 A to
be safe, the common heat sink for both diodes must be dimen-
sioned for the maximum possible current of approximately 24 A
(sustained short-circuit current) x diode conductive-state volt-
age.
Parallel connection for performance enhancement
To enhance performance, identical types of most SITOP power
supplies can be connected in parallel galvanically (the same
principle as parallel connection for redundant operation, but
without decoupling diodes):
The types permitted for direct galvanic parallel connection are
listed in the relevant technical specifications under "Output,
parallel connection for performance enhancement".
Requirement:
•
The output cables connected to terminals "+" and "-" of every
power supply should be installed with an identical length and
cross-section (or the same impedance) to the common
external linking point.
•
The power supplies connected in parallel must be switched
simultaneously using a common switch in the mains supply
line (e.g. using the main switch available in control cabinets).
•
The output voltages of the power supplies must be measured
under no-load operation before they are connected in parallel
and are permitted to differ by up to 50 mV. This usually corre-
sponds to the factory default setting. If the output voltage is
changed in case of variable power supplies, the "-" terminals
should first be connected and then the voltage difference
between the "+" output terminals measured under no-load
conditions before they are connected. The voltage difference
must not exceed 50 mV.
Note
With a direct galvanic connection in parallel of more than two
SITOP power supplies, further circuit measures may be neces-
sary for short-circuit and overload protection!
SITOP
+
-
SITOP
+
-
V1
V2
Load
G_KT01_EN_00017
© Siemens AG 2016