bazzer1962
Industrial
For efficient three phase metering in a substation,what is the minimum number of ct and pt required.
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Substation Metering
- Thread starter bazzer1962
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You must have entered the contest for the most badly worded question of the week. You might even win, although this week there have been some other strong contenders. ![[smile]](/data/assets/smilies/smile.gif "[smile] [smile]")
You give us virtually no information, so the only sensible answer you'll get is 'it depends'.
What quantities are you trying to meter?
Are there any single phase loads?
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If we learn from our mistakes I'm getting a great education!
You give us virtually no information, so the only sensible answer you'll get is 'it depends'.What quantities are you trying to meter?
Are there any single phase loads?
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If we learn from our mistakes I'm getting a great education!
chadwiseman
Electrical
Assume there are some single phase loads from the 3 phase substation. I seem to recall that two (2) CT's can be used, however I cannot find a reference to suppport this. Also, I cannot get any inidication on how many PT's are required. Any ideas?
I believe that ScottyUK is right when he says "it depends." You really need to consider Blondel's theorem & it's errors to determine the answer.
Blondel's theorem states that "If energy is supplied to any system of conductors through N wires, the total power in the system is given by the algebraic sum of the readings of N wattmeters, so arranged that each of the N wires contains one current coil (transformer), the corresponding voltage coil being connected between that wire and some common point. If this common point is on one of the N wires, the maeasurement may be made by the use of N-1 wattmeters."
So if you research, you will find 2-element, 2-1/2 element, & 3 element meters. The element is the number of PTs & CTs where for example, a 2-1/2 element is 2 voltages & 3 currents.
The 2-element & 2-1/2 element will introduce errors if the system is not symmetrical/balanced but it depends on your reason for metering & if you can live with these errors.
There are numerous manaufacturers of industrial grade meters. I personally like the SEL-734 for the cost & features.
Blondel's theorem states that "If energy is supplied to any system of conductors through N wires, the total power in the system is given by the algebraic sum of the readings of N wattmeters, so arranged that each of the N wires contains one current coil (transformer), the corresponding voltage coil being connected between that wire and some common point. If this common point is on one of the N wires, the maeasurement may be made by the use of N-1 wattmeters."
So if you research, you will find 2-element, 2-1/2 element, & 3 element meters. The element is the number of PTs & CTs where for example, a 2-1/2 element is 2 voltages & 3 currents.
The 2-element & 2-1/2 element will introduce errors if the system is not symmetrical/balanced but it depends on your reason for metering & if you can live with these errors.
There are numerous manaufacturers of industrial grade meters. I personally like the SEL-734 for the cost & features.
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