Distribution Transformer Overvoltage

[saladhawks]

What is the likely overvoltage that would result during a primary neutral break to an overhead single-phase distribution transformer rated 2.4 kV Line-to-Neutral that provides 120/240V three-wire secondary service?

A secondary voltage of 156 V was measured on one of the secondary legs to ground.

 

[waross]

If I understand the situation, the voltage may rise as high as 2.4 kV It depends on the local practice for interconnection between the primary neutral, the secondary neutral and the local ground rod or grid.
The impedance of the ground connection will be important. It sounds as if your local ground is of so high an impedance to be relatively ineffective.

Bill
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"Why not the best?"
Jimmy Carter

 

[saladhawks]

I apologize for the lack of detail in my original post. Primary overhead system is 4-wire multi-grounded with a line-to-line voltage of 4.16 kV.

Secondary voltage of 156 V was recorded at customer service panel. Upon inspection, it was noticed that the primary neutral connection to the transformer serving this customer was broken and no longer connected to the transformer. Transformer at this point was undergrounded (i.e. only capacitively connected to ground). Primary neutral was repaired and customer voltage returned to normal.

I would not expect such a large voltage fluctuation on the secondary side of the service transformer due only to the broken primary neutral connection.

 

[HornTootinEE]

What was the other leg of 120/240 V reading? I know if you get a secondary neutral break, you'll see a high voltage on one leg, and a low voltage on the other leg, but you'll still see 240V between the X1 and X3 bushings (assuming X2 is grounded). I'd say on the Primary side you could see anywhere from 0 to 2.4 kV across the transformer, if connected Line to Ground with a open or very high impedance ground.