# Measuring CT Saturation

Thread Starter

#### Mehboob

We have installed 800/1 measuring CT.
We have noted that on digital ammeter current goes to 1200A, should it not saturate at 800A?
Should it measure load higher than 800A

#### MWO

A CT saturation is more dependent on the amount of iron in the CT. You can have a a small 800/1 CT or a large 800/1. The CT develops the voltage to drive the current through a given load or "burden" . Saturation refers to the iron in the CT becoming saturated with flux where it can no longer increase its voltage and drive the required current through a given burden. In your case, your CT is hefty enough to supply the current through your meter without saturating. Hope this feeble explanation helps.

#### PhilCorso

Mehboob....
What is it's temperature ?
Regards, Phil Corso

#### bertus

Hello,

Do you have the datasheet of the Current Transformer?
That should give you information on the measurement range and saturation point.

Bertus

#### MWO

I keyed on the saturation of the CT without asking an obvious question. Why do you have an 800/1 CT on a circuit pulling 1200 amps. Is the digital meter calibrated correctly. The CT will output 1 amp with 800 amps flowing through it. Is your digital meter calibrated to display 800 amps when 1 amp is flowing through it?

#### oneye14

To me Mehboob has mixed up ratio for power rating.
As with MWO I have had 1amp meters giving in supply max of 800A. But also seen 5A meters which would give a theoretical max of 4,000A. Guessing Mehboob would notice by the size of terminals ! Or is it 100ma meter for a 80A scenario.

Assuming meter calibrated to display 800 amps when 1 amp is flowing through it, the transformer saturation would need considerable overload before saturation occured, how high depends on the transformer.

I recall laboratory practicals energy the CT with open circuit secondaries. The result was early saturation with dangerous spikes which damages insulation which is why never leave a CT with open circuit secondaries. Has Mehboob mixed this up with any of the above ?

Finally I'm assuming this CT is ancient as in pre-1990's. Nowadays we separate power cable from other cores and pass it through a calibrated 'ring' acting as secondary winding, passing the power cable through 1, 2 or 3 times as necessary. I haven't seen large CT's for a long time - that's not to state they are no longer available, as they still have their uses.

Thread Starter

#### Mehboob

Mehboob....
What is it's temperature ?
Regards, Phil Corso
Sir, temperature is not measured,

Thread Starter

#### Mehboob

I keyed on the saturation of the CT without asking an obvious question. Why do you have an 800/1 CT on a circuit pulling 1200 amps. Is the digital meter calibrated correctly. The CT will output 1 amp with 800 amps flowing through it. Is your digital meter calibrated to display 800 amps when 1 amp is flowing through it?

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Thread Starter

#### Mehboob

To me Mehboob has mixed up ratio for power rating.
As with MWO I have had 1amp meters giving in supply max of 800A. But also seen 5A meters which would give a theoretical max of 4,000A. Guessing Mehboob would notice by the size of terminals ! Or is it 100ma meter for a 80A scenario.

Assuming meter calibrated to display 800 amps when 1 amp is flowing through it, the transformer saturation would need considerable overload before saturation occured, how high depends on the transformer.

I recall laboratory practicals energy the CT with open circuit secondaries. The result was early saturation with dangerous spikes which damages insulation which is why never leave a CT with open circuit secondaries. Has Mehboob mixed this up with any of the above ?

Finally I'm assuming this CT is ancient as in pre-1990's. Nowadays we separate power cable from other cores and pass it through a calibrated 'ring' acting as secondary winding, passing the power cable through 1, 2 or 3 times as necessary. I haven't seen large CT's for a long time - that's not to state they are no longer available, as they still have their uses.

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Thread Starter

#### Mehboob

CT measuring core is
400, 800, 1200, 1600 & 2000

We using 800/1 A my question 8s what about danger if 1200A follow

#### PhilCorso

Mehboob...
Meter Photos are unreadable !
Phil Corso

#### PhilCorso

Mehboob...
Can you identify what each of the 6 meters are measuring?
Phil Corso

#### PhilCorso

Mehboob..
Are these meters connected to multi-ratio CT's?
Phil Corso

#### Curious_One

Always make your metering match your CT output. If your CT is measuring 800 amps is should provide 1 amp to metering. The metering will provide a 800 amp display at 1 amp input.

Therefore, I have no idea what you are trying to figure out.

#### Curious_One

Always make your metering match your CT output. If your CT is measuring 800 amps is should provide 1 amp to metering. The metering will provide a 800 amp display at 1 amp input.

Therefore, I have no idea what you are trying to figure out.
On that note, if one changes a CT and does not look at metering. A mistake is made.

Sometimes, one will double wrap the metering circuit to make the meter work properly.

#### MWO

Looking at the pictures the meters are all overloaded. My guess is that the CT is on the 400 amp tap instead of the 800 amp as you think. This would mean the actual current closer to 600 amps instead of 1200. Just a guess on my part.

#### MWO

Looking at the picture a little closer it would indicate 2 phases are pegged past 800 amps while the third phase shows 1114 amps, ~132 KV, MW pegged, and ~ 40 Mvars. This would be about 255MVA which would mean you would be flowing about 251 Mwatts which would explain the Mwatt meter being pegged. Is this reasonable? If I am correct about the CT being hooked up wrong (400/1 instead of 800/1) this would mean about 120 Mwatts are flowing. Is this more reasonable? I would be curious as to what you find.