How to bypass UPS?

How to perform automatic and manual UPS bypass?

2 min read

UPS (Uninterruptible Power Supply) is an electrical device that provides power to the consumer in case the grid power supply, either ashore or on the vessel, fails to deliver power supply of a certain standard. This instances include blackout, undervoltage, overvoltage or a power surge.

UPS’ work principles can easily be found and understood online.

When talking about UPSs larger than few kW, it is important to periodically perform maintenance such as battery replacement, capacitors renewal or rectifier/inverter service check etc.

In order to perform the maintenance, it is necessary to isolate the power from these components prior to commencing any work.

To safely isolate power from these components AND maintain uninterrupted power supply to the consumers, a manual bypass feature is used.

To explain how to set the UPS in a manual bypass, I will use the UPS installed on the yacht I work on – GE Sitepro S8.

Inverter is to be disconnected by pressing Inverter 0 red button. This puts UPS in automatic bypass, which means the power is not following the standard route Input-Rectifier-Inverter-Output anymore but is now being transferred from the input through the static switch to the output.

Manual bypass switch Q2 to be closed. Consumers are now being supplied through the automatic and manual bypass.
Output switch Q1 to be opened. Consumers are now being supplied only through the manual bypass.
Input rectifier switch Q4 to be opened. Power supply to the rectifier is now isolated.

Battery fuses to be removed.
Now, the UPS is in manual bypass mode and rectifier, inverter and batteries are isolated.
The only part of the UPS that is still powered on is the control part of the UPS.
To isolate this part, it is necessary to use external manual bypass switch which in this case is an outside rotary type of switch.
Please note that even in the case of the external manual bypass, there is still battery DC power present inside the UPS, so one should always be super careful when performing a UPS maintenance.