Summation CT

Mr vaghela,

Have you used ICT any time? Think how this can be used for summation CT.

No,

In current summation all CT's must have the same transformation ratio.

If your current reading equipment is analog, change it or add digital, and than do a digital summation. there are several companies making this type of a calculator.

Wangito.

You are wrong!! using Intermediate CT different ratio CT can be summationed. Think over.

I don't think I am,

Suppose we have a three phase system where all phases have same current which is 100Amp. Case 1, where CT's have all different transformation ratios:

1. CT #1 is 100/5 will read 5Amp
2. CT #2 is 200/5 will read 2.5Amp
3. CT #3 is 400/5 will read 1.25Amp.

Total instrument reading 8.75Amp.

Case 2, where all CT's are same transformation ratio:

1. CT #1 is 100/5 will red 5Amp.
2. CT #2 is 100/5 ditto
3. CT #3 is 100/5 ditto

Total instrument reading 15.0Amp.

Wangito.

wanqito good example make all CT's 600/5

Bhuuuuu!!! Well let me explain.

CT 600/5, 500/5, 300/5 in three different feeders.

ICT of ratio 5/4.17 for 500/5 is required

ICT of ratio 5/2.5 for 300/5 is required

No ICT for 600/5.

600+500+300 = 1400 corresponds to 4.17+2.5+5 = 11.67 A

summation CT ratio 11.67/1 A. That is 11.67 = 1400A

Now if 600/5 feeder is off, and other two feeders are fully loaded the total primary current is 500+300=800 corresponds to 4.17+ 2.5 = 6.67

Means (1400/11.67)*6.67 = 800 A

Did you get?

Regards to all !

Take example from the question:

600/5, 300/5, 200/5, 100/5, 400/5 Amps

Following pionts be kept in mind

1. Most of the CTs in power-distributin have */5A with a specified "Dump" in VA which should be maitained in all cases.

2. Phase displacements in different feeders must be considered. otherwise NO result accuracy or even approximation be thought of.

3. Out-put of CTs to Meters be considered how it is being fed;

without rectification [AC-Ammetre] or rectified [DC-Ammeter].

My view:

a. All CTs [for AC Ammeters] can only be summed only if phase is also same in addition to the same Ratio, Dump values.

Note:

In some cases where the construction of CT allows:

600/5, 300/5 CTs can be combined by making 600/5 can be modified to 300/5 by passing 2 turns through CT & 400/5 to 200/5 by the same way.

b. All CTs [for DC Ammeters] should only have the same Ratio & Dump values.

<< If all feeder contain same CT ratio, its cool >>

I think that the phase displacement is the most important in Power measurements, which must be considered primarily.