Halving 220V Output Voltage: Investigating the Problem

[sbsapre]

Dear All,

In our plant , we have an 20 KVA UPS with three phase , 440 Volts , 50 HZ input . The output is single phase 220 Volts outputted from Isolation transformer.
I find it strange though output voltage between two terminal of isolation transformer is 220 Volts , when measured with respect to ground , it is 110 Volts.
I want to understand how the output voltage is halved when measured with respect to ground.
Another problem whenever output voltage is connected to load which is normally fed by another 20 KVA UPS having 3 phase , 4 wire , 440 volts output , the single phase UPS fails.
We have taken precaution of connecting two terminals of 220 KVA single phase UPS to one phase and ground of the load terminals which are normally fed by UPS having three phase output.
I shall appreciate valuable inputs from members.
Regards,

S.B. SAPRE

 

[NoTime]

Dear All,

I find it strange though output voltage between two terminal of isolation transformer is 220 Volts , when measured with respect to ground , it is 110 Volts.
I want to understand how the output voltage is halved when measured with respect to ground.

Most likely it is a center tap transformer. With the tap connected to ground.