Section 75
00-02-0522
04-06-11 -
25 -
The low wye will read full output voltage (L-N) and half of the current (per phase). The high
wye will read half of the output voltage (L-N) and full current (per phase).
The CT
’
s have to be sized to read the current in the high wye configuration (The current
through a conductor is identical throughout the conductor) – A series connection adds voltage
but not current, and the low wye configuration.
A lot of confusion occurs because switching from windings in parallel to windings in series (and
vice versa) basically means that the measurement points always see exactly the same current
and voltage, but the
“
output
”
current and voltage differ.
The simplest way to keep track of this is to remember that in series – The output voltages add
but currents remain the same, while in parallel, output currents add but the voltages remain the
same.
For example, assume that we are in a high wye configuration. If we are loaded such that the
coil T7-T10, T8-T11, and T9-T12 are all producing 50A, the measurement points will read
nominal 240V and 50 A, but the output connections as measured at T1, T2, & T3 will read
480V but still be 50 A - In a high wye the voltages add but the series coil currents remain the
same.
Now assume a low wye - If we are loaded such that the coil T7-T10, T8-T11, and T9-T12 are
all producing 50A, the measurement points will read nominal 240V and 50 A, but the output
connections as measured at T1, T2, & T3 will read 240V and the output current will be 100 A -
In a parallel connection the voltages stay the same, but the currents add.
In either case, note that at the measurement point the voltage is always 240V, and the
measured current is always 50A.
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/ Discontinued
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