Gjdanz2007
Member
- Location
- Pittsburgh Pa
Can someone please tell me how to find the current on the secondary side of a 277/480v step down transformer?? Thank you.
step down transformer
- Thread starter Gjdanz2007
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- Chapel Hill, NC
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- Retired Electrical Contractor
Again -- your posts have been okayed so please stop posting new threads
On the nameplate maybe?
Failing that, what kVA, and what secondary voltage?
gar
Senior Member
- Location
- Ann Arbor, Michigan
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- EE
140424-0930 EDT
Gjdanz2007:
The current will be what it will be. What this means is that within certain limits the current will be determined by the load impedance connected to the transformer secondary.
The circuit that you probably are considering is an ideal voltage source (meaning constant voltage, waveform shape, and frequency independent of load), an ideal step down transformer from the voltage source, a chunk of series impedance representing the equivalent series impedance of the real transformer, and then the load impedance.
For analysis this circuit boils down to a voltage source with some series internal impedance and a connected load impedance.
When the connected load impedance is zero (a short circuit), then the load or output current is defined by the ideal source voltage and the circuit internal impedance. This current is likely 20 times higher than the normal maximum allowed load current on the transformer secondary. This normal maximum current would be calculated from the VA rating of the transformer secondary under consideration and its output voltage.
When a transformer has multiple secondaries it is necessary to treat each secondary individually relative to its VA rating. Basically you are dealing with a thermal problem where some maximum internal temperature should not be exceeded.
Looking back at your original post another answer is: put a clamp-on current meter around an output lead from the transformer.
.
Gjdanz2007:
The current will be what it will be. What this means is that within certain limits the current will be determined by the load impedance connected to the transformer secondary.
The circuit that you probably are considering is an ideal voltage source (meaning constant voltage, waveform shape, and frequency independent of load), an ideal step down transformer from the voltage source, a chunk of series impedance representing the equivalent series impedance of the real transformer, and then the load impedance.
For analysis this circuit boils down to a voltage source with some series internal impedance and a connected load impedance.
When the connected load impedance is zero (a short circuit), then the load or output current is defined by the ideal source voltage and the circuit internal impedance. This current is likely 20 times higher than the normal maximum allowed load current on the transformer secondary. This normal maximum current would be calculated from the VA rating of the transformer secondary under consideration and its output voltage.
When a transformer has multiple secondaries it is necessary to treat each secondary individually relative to its VA rating. Basically you are dealing with a thermal problem where some maximum internal temperature should not be exceeded.
Looking back at your original post another answer is: put a clamp-on current meter around an output lead from the transformer.
.
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