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CT Saturation 2
- Thread starter THD
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Ceast-
That is a good paper, but this statement is horribly wrong on many levels:
"Higher ratio cts (3000:5) contribute a resistance of 0.0025 ohms per turn to the burden and lower
ratios (300:5) 0.005 ohms per turn. Consequently, applying a 600 turn (3000:5) ct contributes an
internal resistance of 1.5 ohms."
First, unless the CT is a bushing CT, you can't be sure how many turns are on the secondary. For example, a 230 kV CT with a 300:5A ratio likely has 4 primary turns and 240 turns on the secondary.
Second, there isn't really a good way to give a rule of thumb for ohms/turn based on the ratio. The secondary wire size used is typically a function of the rated secondary current and the rating factor. In other words, the secondary wire is typically the same for the 3000:5A and a 300:5A CT. If anything, lower ratio CTs can often times have larger cross-section cores, which means the lead distance per turn is higher. Also, the diameter of the CT plays a role in secondary resistance, since windings are often equally distributed about the core.
Note sure why such a good paper would be so sloppy with a fairly important parameter.
That is a good paper, but this statement is horribly wrong on many levels:
"Higher ratio cts (3000:5) contribute a resistance of 0.0025 ohms per turn to the burden and lower
ratios (300:5) 0.005 ohms per turn. Consequently, applying a 600 turn (3000:5) ct contributes an
internal resistance of 1.5 ohms."
First, unless the CT is a bushing CT, you can't be sure how many turns are on the secondary. For example, a 230 kV CT with a 300:5A ratio likely has 4 primary turns and 240 turns on the secondary.
Second, there isn't really a good way to give a rule of thumb for ohms/turn based on the ratio. The secondary wire size used is typically a function of the rated secondary current and the rating factor. In other words, the secondary wire is typically the same for the 3000:5A and a 300:5A CT. If anything, lower ratio CTs can often times have larger cross-section cores, which means the lead distance per turn is higher. Also, the diameter of the CT plays a role in secondary resistance, since windings are often equally distributed about the core.
Note sure why such a good paper would be so sloppy with a fairly important parameter.
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