What is a CT Meter? A CT meter is a device that measures amperage in one or more conductors using sensors called current transformers (CTs). ... Typically, these meters are used to monitor the power of individual circuits in an electrical distribution panel.
What is CT metering?
Metering Current Transformers (CTs) are used with the measuring instruments, such as ammeters, voltmeters, kilowatt-hour meters, etc to: Isolate the instruments from the power circuits, Standardise the instruments, usually at 5 amps or 1 amp.
How does a CT meter work?
A CT rated meter socket carries an induced current , reducing the amperage of the current running through the meter. This is done through the use of current transformers, or CTs, which measure alternating current and produce a secondary current in phase with its primary current in a predetermined ratio.
Do I need a CT meter?
Current Transformer (CT) Metering is a requirement for supplies with an anticipated load of over 100Amp/ 70kVA. Anyone installing or refurbishing power supplies rated >100Amp/ 70kVA will need to incorporate CT metering in their design.
Why CT is used in panel?
The replica current is used as an input to a protective relay , which automatically isolates part of the power circuit, when a fault occurs. In doing so, the protection current transformer allows the unaffected areas of the circuit to continue in operation.
What will happen if we interchange protection CT with metering CT?
Metering current transformers are designed to be within quite accurate values up to say two x rated current, and down to <0.01 x rated. Consequently a protection relay connected to a metering current transformer will get a heavily saturated waveform during fault conditions and it won’t work properly.
What is difference between metering CT and protection CT?
Protection Current Transformer (CT) and Metering CT are two different types of CT as per their requirement and hence design. Therefore, Protection class CT should not be used as Metering CT . Similarly, a Metering Current Transformer should not be used for protection purpose.
How do I choose a meter for CT?
As discussed above, the key in selecting the proper CT should be based upon the minimum and maximum load size, selecting the CT that will give you the highest amount of sensor resolution . Using a 100 Amp CT on a 100 Amp Load will give you a better sensor resolution when compared to a CT that is rated to 5000 Amps.
What is CT ratio in meters?
Every current transformer, or CT, has a ratio. A typical CT ratio might be 200:5 or 400:5 . What this means is that a CT will step down higher current levels to a level that the meter can safely handle. In the case of a 400:5 CT, 400 amps will be stepped down, or transformed, to 5 amps.
How is CT meter reading calculated?
When analog ammeters are installed, we can easily determine the CT ratio by observing the meter full scale value and then divide that value by 5 .
What is CT connection?
CT (Current Transformer) Meters are installed on any connections with a load greater than 100 Amps. Conventional meters cannot be used to measure current for these larger connections as they would simply have to be too large to be practicable.
How do you size a CT?
For best accuracy, the diameter of the conductor being monitored should be more than half the opening size of the CT . For example, a 4/0 AWG conductor is typically 0.64 inches in diameter and commonly carries 200 to 250 amps. This will fit in a 0.75 inch CT and largely fill the opening (best case for accuracy).
Why CT is required?
Why it’s done
Your doctor may recommend a CT scan to help: Diagnose muscle and bone disorders , such as bone tumors and fractures. Pinpoint the location of a tumor, infection or blood clot. Guide procedures such as surgery, biopsy and radiation therapy.
What is CT burden?
The burden of the CT is the resistive load used to create the voltage on the output . It varies with turns ratio, desired output and current rating of the primary.
How do I connect to CT?
- Install CTs on the phase conductor that corresponds to the voltage input phase.
- Install CTs with the arrow or label ‘This side toward source’ facing towards the breaker feeding the load.
- Connect the white and black CT leads to the corresponding CT input terminals with the white and black dots.
Why CT secondary is grounded?
If the secondary is not connected to a load, then it tries to maintain the counter magnetic field , and voltage levels may skyrocket. Levels can get so high, the air around the CT may start to break down and lose its insulating properties. This is why you should always make sure the secondary side of the CT is shorted.
