Arc on transformer bank

[baaman]

Meterman and ape. changed a 480 volt meter at a water well. It is a 3 Ø 240/480 center grounded delta on the low side. High side is 14,400. Lineman grounded the high side before opening the cutouts. My question is when they closed the fuses in, they closed the 2 outside fuses in first. The center transformer was the one that was grounded, x2. When they shoved the center in, they missed and the barrel was swinging drawing a 3 to 4ft. arc. No load on this, as breakers were off. Why such a big arc? Thank you, Bob

 

[waross]

Was the primary neutral floating or connected? Did the primary neutral have a temporary connection to avoid switching surges? (Four cutouts, A,B,C and N. Neutral cutout is closed first. After A,B, and C are closed, the neutral fuse holder is opened and removed.)

Bill
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"Why not the best?"
Jimmy Carter

 

[baaman]

Temp. connection. 2 hot line clamps on #6 copper wire. One clamp on the floating high side, other clamp on the copper for the tank grounds. Thank you, Bob

 

[waross]

The primary voltages were probably not equal. It is a characteristic of the four-wire-wye:delta that the transformer or transformer bank will try to balance unequal primary voltages and or phase angles. On long rural lines with single phase voltage regulators, there are often equal line to neutral voltages but a combination of unequal phase angles and unequal phase to phase voltages. These conditions will cause a circulating current in the delta and fairly large currents in the line conductors. Once the transformer bank is on-line the wye point or neutral jumper is removed, the circulating current and the associated heavy line currents will disappear. You will only have magnetizing current until you close the load breakers.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[baaman]

Thank you, waross. Bob