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So tell me about static phase converters and phase diagrams?

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In a static converter the 240 Vrms input (phase to neutral, L-N) is first passed through a transformer to raise it to 415 V (let us assume this becomes phases L1 and L3). Then one 415 V connection is exposed to a capacitor bank which yields an L2 where L2-L3 is also of 415 V but which is at almost exactly the same phase angle as the first, i.e. L1-L2 is almost zero when at rest. When this is connected to a three-phase motor the inductance of the motor is added in to the circuit and once the motor is up to speed the 'back emf' generates the voltage L2-L3.

Most manufacturers use what are called autotransformers in order to reduce the cost (at Boost we produce the smaller rotary converters with more expensive isolating transformers that create the same phase diagram as the electricity company - we think we are the only manufacturer in the world to offer these as a standard). With an autotransformer, only L3-N will be 240 V whilst L1-N will be 175V and L2-N will be 360 V. This is important because some three-phase machinery uses 'phase to neutral' as a 240 V supply to drive lighting and/or control circuits. If so, all these have to be supplied from L3 rather than randomly choosing a phase. Fortunately in most such machinery the manufacturers place all the single-phase loads on one phase as typically there is a step down transformer in the design and this means the manufacturer only needed to buy one transformer - you can imagine the problems of rewiring a machine where a manufacturer has carefully balanced all the single-phase loads across each of the three phases. Similarly - and especially with static phase converters - it is best to make sure that all the control circuits that use 415 V are fed from L1-L3 which is the maintained phase and does not vary at all.

It is worth explaining all of the problems that can occur with static converters and then discussing rotary converters and how far they overcome the problems.