UPS Bypass Synchronising

[micksouth]

Hi All,
We have 3 x EDP90 UPS(200KVA each) and it is set up as a distributed parallel system.
All of the handles on the maintenance bypass (QS3), on each module have been removed for some reason!
As a result, each module can only be maintained once the input power has been removed.
It looks like the intention was to prevent the bypass being used.
I can only assume there was some concern over supplying the load by raw mains and UPS power simultaneously, due to synchronising worries.
Any suggestions welcomed.

 

[rbulsara]

What is the question? I do not understand the relationship between removing the handle for MBP and ensuring removal of the normal power! It is never advisable to remove normal power, until after the system is in a bypass mode (either static or maintenance).

Firstly, a UPS should not be placed in a location where non-authorized people can access it. There should be a well written procedure for placing the UPS in maintenance bypass and putting it back to normal, pasted at the UPS.

People not able to understand it, should not go near it. Because while there are industry accepted interlocks and procedures, those are not idiot-proof and one can still drop the critical load or cause an accident.








Rafiq Bulsara

http://www.srengineersct.com

 

[EmergencyPowered]

In my experience, if the breaker handle is removed it may indicate that the CB is controlled by a control switch with has various electrical interlocks. Are you sure the CB does not have an electrical close spring release?

 

[sibeen]

It wouldn't surprise me if the handles were missing from the time of installation. For these units to be installed all the switch handles needed to be removed so that the cover plate can be taken off, giving access to the cable entry points. Many of the commissioning techs wouldn't bother putting the maintenance bypass handle back on and would leave it lying on the door jam, so it a tech did ever require it it was a minute operation to screw it back on.

Leaving it off also stopped people who didn't know what they were doing from mucking around with it. In this case I suspect this was highly warranted!

In a distributed UPS system you CANNOT place one unit into bypass and have the other units running the load. What you can do, depending upon the load on the system, is take one unit completely off line to do the maintenance whilst the other two, in this case, support the load. Luckily the design engineers for these units did take into account clients, or others, not knowing what they were doing and installed a microswitch in the maintenance bypass switch. If the maintenance bypass switch is closed a signal will be sent from the microswitch forcing all the units in the distributed system to bypass.

You CANNOT parallel the mains and the inverters on these UPS units.