Buck-Boost Transformers

Question 1

Buck-Boost Transformers

Answer 1

-Typically used to make relatively small changes to a source voltage.
-Not used to boost voltage with a fluctuating load. = low load = very high voltage
-Common - boost 208 to 230, buck 240 to 208
-Typically have dual voltage primaries and secondaries. With primary and secondary wired in SERIES.
-USUALLY used for 5% - 25% changes, available up to 10kVA.

Question 2

Polarity of the voltage

Answer 2

The voltage that causes the current to flow from H1 to H2 in the primary results in current flow from X1 to X2 in the secondary.

Question 3

Fusing

Answer 3

NEC 450.4
Each buck boost autotransformers 600v, nominal or less shall be protected by an individual over-current device installed in series with each underground input conductor. The overcurrent protection device cannot be installed in series with the shared winding of the autotransformer.

Question 4

Grounding

Answer 4

NEC 450.5(A)
-3 phase, 4 wire circuits from 3 phase 3 wire systems
-Zigzag connected transformers are not permitted to be installed on the load side of any system grounding connection.

Question 5

Fluctuating Loads

Answer 5

When buck-boost transormers are installed for high load conditions, very high voltages may result during lightly loaded conditions.

Question 6

240V to 120V

Answer 6

SHOULD NOT BE DONE to create a 240V/120V single phase from a 208Y/120V 3 Phase, 4 wire source.
= Two neutrals would exist on the same circuit. Creating an unbalanced line to neutral voltages.