Electrical Machinery, Electric Machines, 3-phase transformers
If by 3-phase bank you mean an array of two or three separate single-phase transformers, wired to handle 3-phase voltage changes, the 3-phase transformer will require less iron and copper to handle the same power.
Advantages Of Transformers
The advantage of a three phase transformer over a three phase bank are: It is easier to install and the unit occupies lesser space. The transformer unit can't pe pilferred easily because of its heavy weight. The disadvantages are: Cost of investment is high because a smaller capacity might have been used instead of a bigger unit.In a bank transformer, 2 units connected in delta may accomodate a given load for a given period. A third transformer may be installed later when load has increased requiring a third unit.
Generally if you see three single phase transformers all mounted on one pole( not sure what a hydro pole is?), they are connected to supply three phase service to the customer. Not usually three single phase services, at least in the USA. The three single phase transformers may supply 208Y/120 volt 4 wire three phase, 120/240 volt 4 wire three phase (usually one of the transformers in this configuration is larger than the other two), 240 volt three wire delta or 480 volt delta, or a 480/277 volt 4 wire service., And on and on. This is determined by the voltage ratios of the transformers used and what the local utility supplies as a normal service voltage. Hope this helps, Newton1Law
A cluster mounted bank of three 1? transformers has several advantages. - Reduced inventory levels since 1? transformers used for residential customers can be cluster mounted for 3? applications. - The standard 1? transformer in the US has 120/240 V secondary. The secondary windings can be connected to allow the cluster mounted bank to provide 120/240 V 3?, 4-wire or 120/208V 3?, 4-wire. Most 3? transformers only offer one secondary voltage. - If a 1? transformer fails, you can replace just that one, not scrap the whole bank. - Each of the 1? transformers weight substantially less than the corresponding 3? transformer. This allows a line truck to hang transformers where a 3? transformer might need a crane. - Cluster mounted transformers provide better loading on a single pole. Some utilities will cluster mount three 500 kVA 1? transformers on a single pole. Try hanging a 1500 kVA 3? transformer on one pole. - For smaller loads, or in rural locations, only 2? primary is needed to furnish 3?, 4-wire service using two 1? transformers connected with open-wye primary and open-delta secondary. - For 120/240 V 3?, 4-wire service, the lighter and power transformers can be selected to optimize the kVA of each transformer depending on the amount of 1? load being served. -------------------------------------- The advantages of a 3-phase transformers are: - Reduced labor to install since you do not have to wire the secondary connections. - Installation requires less skill since the crew does not have to understand additive and subtractive polarities, how to wire head-to-tail, etc.
