Output Paralleling And Hot Insertion; Figure 23 Paralleling And Hot Insertion - ABB 827E Product Manual

Output Paralleling and Hot Insertion

Critical AC loads can be powered from the existing telecom battery plant via an inverter system IF:
• The inverters do not endanger or degrade the battery plant in any way (e.g., voice band noise), and
• The inverter system output (Vbus) does not fail.
When paralleling inverters both phase and amplitude must be matched and, preferably, the load
shared equally. This is normally done in the industry with common synchronization and load share
signals, but this method compromises system integrity to a single fault in the common circuits. The
827e inverters are totally independent, connected only by the common AC bus. This design allows
inverters to hot plug, which is critical to no-break maintenance and upgrade.
HERE IS HOW IT WORKS:
Figure 23 shows Inverter One running in the shelf and powering the load. The Inverter One voltage is
shown on Ch1, and its current is on Ch4. Then Inverter Two is plugged into the shelf. The Inverter Two
output relay is open and stays open until the Inverter Two voltage phase synchronizes with the
Inverter One voltage phase. After they synchronize, they lock together and then the output relay of
Inverter Two closes. The current sharing and synchronization circuit starts working and Inverter Two
takes half of the load current as shown in the figure below. The Inverter Two current is on Ch3.
Current sharing and synchronization features are implemented within each inverter, without the use
of inter-inverter signaling. This avoids the single point of failure created when inter-inverter
signaling is used.
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Figure 23 Paralleling and Hot Insertion