How 440/230V Isolated Transformer Ratings in VA / KVA deside in Control Panels ?

[Er. Nirav M. Madhvani]

Hello, I am Er. Nirav M. Madhvani Can you tell me ..How 440/230V Isolated Transformer Ratings in VA deside in Control Panels ? Means How 200 VA , 250 VA , 300 VA etc .. Select the ratings of transformer in Control Panels ???? I have attech the transformer photo shown in image file and tell me about How 440/230V Isolated Transformer Ratings in VA deside in Control Panels ?

[rajsiyer]

Dear Nirav, You have to go by loading of the transformer. Typically, in control panels there are contactors, SMPS devices, Indicator lamps and some relays. Sometimes, there is a space-heater. Calculate the total consumption by adding up the wattage of all components on 230V side. For this, for each contactor, there are 2 VA ratings.. -1- The 'inrush currents' of each contactor (For small -relays this is insignificant) & -2 - The VA rating of the contactor when it is latched(closed, or sealed as others may say) The required VA(inrush) will be the square root of the sum of these 2 VA ratings. required inrush VA for each contactor.. = SQRT(VAlatched2 + VAinrush2 ). Also see the inrush capacity of the transformer at 90% Voltage. Typically This figure will be about 300-400%. See example below.. See how a 70VA X'mer gets 250VA is good enough for 250VA inrush. Edited June 8, 2015 by rajsiyer

[Er. Nirav M. Madhvani]

Thanks sir... I will Apply your method.