question

bernhardhofbauer avatar image
bernhardhofbauer asked

MPII/5000 uninterrupted maintenance/bypass switch

Hello,

In the course of planning together with my electrician (who is very open minded, but only has basic knowledge of the MPII) we are at the point of designing the "bypass switch" or disconnecting the MPII in the event of maintenance (3-phase MPII network in Austria/Lower Austria network).

Normally, a 1-0-2 changeover switch (or 2 pieces) is used, but these are planned for emergencies when there is no grid and always go over 0 (with interruption).


Now to my question, which I am currently stuck with my electrician:

3 switch disconnectors (1xAC-In = C, 1xAC-Out1 = B, 1xBypass = A) to enable and activate the bypass in normal operation (and only then) without interruption

Initial state: A = open, B = closed, C = closed


Switching Normal->Bypass:

close A. grid is also connected to the synchronized and connected AC-Out1. Can something happen here? According to our understanding, the phase-synchronized potential is already there, since PassThrough.

open B. Disconnect AC-Out1 from the house network and from the grid potential.

open C Disconnect from AC-In


Switching Bypass->Normal:

close C. Connect AC-In to grid potential. MPII recognizes network and synchronizes.

close B. Switching through from the synchronized AC-Out1 to the home network

open A


As I said: will not be used for switching in the event of a power failure; only in the event of MPII maintenance. The entire house is connected to AC-Out1.

What can happen? What are we missing?


Thanks!

Bernhard

Multiplus-IIESS
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1 Answer
sharpener avatar image
sharpener answered ·

I have a (single phase) 5kVA MPII system supplying the whole house from AC-Out1.

The input to the inverter is from a 50amp circuit breaker and a rotary isolating switch.

The house is either connected to the inverter or directly to the grid supply by means of one of these changeover switches.

It works well, you can isolate the inverter for maintenance and there is no possibility of error. If you move the switch quickly the supply is continuous and computers etc stay running.

Your arrangement could be dangerous and I think you should not connect the input to the output of the inverter as you propose.

A refinement is to use a changeover contactor (relay) instead of the switch, with the coil connected to AC-Out1 (via a small circuit breaker to protect the wiring). Then if the inverter fails the house is connected automatically to the grid which will keep your freezer and alarms powered up if you are away when it happens.

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