Sizing Transformer

[isa7667]

Hi there!

I need help to size a transformer that will be used in a supermarket.

According to my calculations, I get the following kVA:

To get these numbers I start measuring Amps for each item. The formulas are shown below:

kVA(1-Phase) = Volts * Amps / 1000
kVA(3-Phase) = Volts * Amps * sqrt(3) / 1000

where Volts: 220V (S. America)

The total Power is 552kVA. So I added an extra 20% and I get 663kVA.

What size of transformer do you recommend? Is it better to have 2 transformers with lower capacity or a big one? Will compressors in the system have to be considered for power correction? Thanks in advance for your support!

Details on Power Calculation:

Item	Qty	Power/unit	Power	1-Phase	3-Phase
Microwave	1	12A	12A	2.64kVA
Fan	1	0.5A	0.5A	0.11kVA
Ventilation	1	2A	2A	0.88kVA
Scale Type1	4	0.3A	1.2A	0.264kVA
Scale Type2	1	1.5A	1.5A	0.33kVA
Hydraulic Press	1	4A	4A	0.88kVA
PC	1	1A	1A	0.22kVA
Kitchen Cutter	1	3.5A	3.5A	0.77kVA
Scale Type3	1	0.3A	0.3A	0.066kVA
Packager	3	1.5A	4.5A	0.99kVA
Meat Grinder	1	2.5A	2.5A		0.953kVA
Meat Saw	1	1.7A	1.7A		0.648kVA
Vacuum Packager	1	7.5A	7.5A	1.65kVA
Checkouts	18	5A	90A	19.8kVA
Server	1	5A	5A	1.1kVA
Cooling Equipment	1	400A	400A		152.4kVA
Water Pump 1	1	4A	4A		1.52kVA
Water Pump 2	1	5A	5A		1.9kVA
Illumination	1	214.4A	214.4A	94.33kVA
AC Unit 360k BTU	5	51.4A	257A		97.93kVA
AC Unit 500k BTU	1	71.4A	71.4A		27.2kVA
AC Unit 18k BTU	1	9.1A	2A
Electrical Doors	2	0.8A	1.6A	0.35kVA
Kitchen Equip 1Ph	1	11.85A	11.85A	5.2KVA
Kitchen Equip 3Ph	1	362.7A	362.7A		138.2kVA
SUB TOTAL				131.74KVA	420.78kVA
TOTAL					552.5kVA

 

[kingpb]

I would split up the loads on different panels. You certainly don't want to have lighting, receps, computers, scales, etc on a panel with motors and HVAC equipment.

 

[augie47]

Can you provide a bit more detail such as the utility supply voltage.
You show 3 phase equipment so hopefully you have a 3 phase supply. Can the large equipment not operate off the 3 phase supply (380 ? ).
Whichequipment actually needs the transformer ?

In many SA countries the only time you would need a transformer would be when you encountered 120v equipment.

 

[kingpb]

Oh, and stay with standard sizes. If you choose to use only one, then use a 750KVA.

 

[isa7667]

I would split up the loads on different panels. You certainly don't want to have lighting, receps, computers, scales, etc on a panel with motors and HVAC equipment.

Thanks for the suggestion. I will take this into account.

 

[isa7667]

Oh, and stay with standard sizes. If you choose to use only one, then use a 750KVA.

Thanks for the suggestion. Do you know what are the advantages and disadvantages of using a big unit instead of 2 smaller ones?

 

[isa7667]

Can you provide a bit more detail such as the utility supply voltage.
You show 3 phase equipment so hopefully you have a 3 phase supply. Can the large equipment not operate off the 3 phase supply (380 ? ).
Whichequipment actually needs the transformer ?

In many SA countries the only time you would need a transformer would be when you encountered 120v equipment.

The incoming voltage is 23kV. The transformers steps this voltage to 3 lines of 220V at 50Hz. I have the option for 3 phase supply 380V and most of the larger equipments will be connected this way.



In terms of the calculation, when I use the formula kVA(3-phase) = V * A * sqrt (3) / 1000, do I use 380V as my Voltage?

For motors or compressors do I have to consider a special factor to adjust for startup?

Any other factors for equipment not running at the same time?

Thanks in advance!

 

[kingpb]

Thanks for the suggestion. Do you know what are the advantages and disadvantages of using a big unit instead of 2 smaller ones?

The advantage is that if you put lights on a panel with a bunch of 3-phase motors you could end up with light flicker. So in those terms you could put in two transformers; one at 380V 3ph, for your three phase loads, and another at 380Y/220V for everything else. Disadvantage is that you will pay more for initial installation with two transformers, and space could be a consideration.

My previous comment about 750kVA was based on std US sizes. Looks like your standard size in that range would be 630KVA. Take a look at your operating load diversity, the continuous load may be quite low in comparison to running load.