Two-steps start-up contactor

Limit the inrush current on starting up the system to 8 times the nominal input current (15 times as standard).

Addition of a two-steps start-up device to limit the inrush current due to the magnetisation of the transformer. The device uses a timing relay to firstly magnetise the input transformer through resistors. The contactor is then switched to close position to allow starting up the charger part of the UPS.

Black Start

Start-up of the UPS (inverter part only) to provide power to the load, even when the Main is not present on the input of the UPS.

This option is made of a key switch to force the battery circuit breaker Q5 to close. In this way, the battery circuit is powered, thus allowing the inverter to start thanks to the battery current.

Low Voltage disconnect contactor LDV

Protect the battery from deep discharges and thus enhance battery lifetime.

The LDV option includes an output contactor controlled by voltage relay in order to disconnect the load at the end of

battery autonomy period. Reconnection of the load is automatic at the charger restoration and upon the resumption of normal conditions.

MAKE BEFORE BREAK CHANGEOVER

Under normal operation switches A and C will be closed and switch B will be open.  The inverter will be feeding the load through its static switch at a phase and frequency which is synchronized with the bypass supply.

To initiate a manual transfer the inverter is first switched off after verification that the inverter is synchronized with the bypass.  This will force the static switch to affect an immediate no-break transfer to the bypass supply (can expand on this if required).  Now the manual bypass switch B can be safely closed consequently paralleling the bypass through 2 circuits: the manual bypass switch and the bypass static switch.  All that then remains is to isolate the UPS for maintenance by opening switches A and C.

Retransfer to inverter can by carried out by effectively reversing the above procedure.

2 x 50% BATTERY

 

Assume we have a110VDC installation of 2 x 50% batteries, previously sized at 82 x LBE600P (600Ah) per 50% battery. Both batteries are connected by a normally open DC bus-tie A. Should the need to arise to close the bus-tie, what would be the magnitude of the circulating current between a potentially fully charged 50% battery and a fully discharged 50% battery:

 

 

On the basis that the battery complies to DEP standards, i.e. 110VDC +10%/-15% without dropping diodes, the end cell voltage after a full discharge will be 1.14V per cell.  On closing the bus-tie A there will be a potential difference between the 2 battery halves of (82 x 1.2V) – (82 – 1.14V) = 4.92V.

Each LBE600P cell has an internal resistance of 0.3mOhm per cell when fully charged.  On discharging this will increase significantly so a fully discharged battery will have a significantly higher internal resistance.  For the purposes of this example we’ll assume the worst case which is the lowest resistance.  So the complete DC circuit comprises 82 cells x 2 batteries x 0.3 mOhm = 0.0492 Ohm

For a short period immediately after the bus-tie is closed a current will circulate from the fully charged half battery to the fully discharged half battery of 4.92V / 0.0492 Ohm = 100A.  This will very quickly diminish as the battery voltages become more equal.