CT refers to Current transformer and PT refers to Potential Transformer. They are used to measure current and voltage in high voltage circuits respectively where an ordinary ammeter and voltmeter cannot be used. Also they are used for protective purposes as input to relays in a power system..
Then, what are the functions of CT and PT in a substation?
Current transformer is an instrument transformer used in substation for measurement and protection purposes. CT used for the measurement of AC current by taking the samples of higher currents of the system. The reduced samples are in accurate proportion with the actual high current of the system.
Additionally, what is PT ratio? Potential Transformer ratio is the ratio of the primary rated voltage of the PT divided by the secondary rated voltage of the PT. Often, the primary rated voltage of the PT might be different from the system voltage at which the PT is applied.
Also to know, what is the difference between CT and PT?
CT is used for current measurement and PT is used for voltage measurement. While a PT has large number of turns on primary and fewer turns in secondary winding. e to get reduced voltage in secondary and V is proportional to Number of turns). And here primary winding is connected across the supply.
Where CT and PT are used?
CT & PT are called the instrument transformer, because those are used to assist the measuring instruments for the measurement of electrical parameters like current, voltage, frequency, power factor, active power(MW), reactive power(MVAR) etc. of high voltage system.
Related Question Answers
What is the function of PT?
Physical therapists (PTs) are health care professionals who diagnose and treat individuals of all ages, from newborns to the very oldest, who have medical problems or other health-related conditions that limit their abilities to move and perform functional activities in their daily lives.Why are transformers rated in KVA?
The transformer does not alter the power factor of its output power. Transformers are rated in kVA because the losses occurring in the transformers are independent of power factor. KVA is the unit of apparent power.What is the purpose of neutral CT?
A neutral current transformer is used as earth fault protection to measure any fault current flowing through the neutral line from the wye neutral point of a transformer.Why CT is connected in series?
The current transformer is designed to connect in series with the line to transform the line current to the standard 1/5 amperes suitable for the meter or relay,Current Transformers are used to measure large current which is flowing through a conductor.Why is CT used?
Current transformers are used for protection, measurement and control in high-voltage electrical substations and the electrical grid. A high-voltage current transformer may contain several cores, each with a secondary winding, for different purposes (such as metering circuits, control, or protection).What is CT and PT in transformer?
CT and PT stand for Current Transformer and Potential Transformer. Both are instrumentation transformers. CT measures current PT measures voltage. CTs are used in clamp meters. and in industries, CTs measure High Currents and PTs measure high voltages.How is CT PT ratio calculated?
Potential Transformer ratio is the ratio of the primary rated voltage of the PT divided by the secondary rated voltage of the PT. A 480:120V rated PT will have a PT ratio of 4.Why is PT open circuited?
Since, the power (P=VI) in a transformer (input and output) is same, the current rises to a very high level. Thus, a very high resistance is maintained at the secondary terminal to limit the current (which appears as open circuit) Short circuiting the secondary would burn out the windings.What is the use of CT?
A current transformer (CT) is a type of transformer that is used to reduce or multiply an alternating current (AC). It produces a current in its secondary which is proportional to the current in its primary. Current transformers, along with voltage or potential transformers, are instrument transformers.Why CT secondary is shorted?
Unless a burden (i.e. meters, relays, etc.) is connected to the CT, current transformers should always be shorted across the secondary terminals. The reason is very high voltages will be induced at the terminals. Think of the CT as a transformer, with a 1 turn primary and many turns on the secondary.Why secondary of PT is open?
Since, the power (P=VI) in a transformer (input and output) is same, the current rises to a very high level. Thus, a very high resistance is maintained at the secondary terminal to limit the current (which appears as open circuit) Short circuiting the secondary would burn out the windings.Why secondary of CT never left open?
The secondary side of a current transformer should never be kept in open condition because, when kept open, there is a very high voltage found across the secondary side. This high voltage causes a high magnetizing current to build up on the secondary side which inturn causes high flux and makes the core to saturate.What is meant voltage?
Voltage, also called electromotive force, is a quantitative expression of the potential difference in charge between two points in an electrical field. An example of direct voltage is the potential difference between the terminals of an electrochemical cell.Why Pt is used?
A potential transformer (PT) is a sensor devise which is used to measure high voltages on transmission lines and substations. Most indicating instruments like voltmeters or electronic circuits operate at low voltage range such as 0 to 5V. In PT the current flowing in secondary and primary is negligible.What is PT accuracy class?
Accuracy class in a voltage transformer is defined as the one if the voltage is guaranteed between 80% and 120% of the primary rated potential difference and for any type of load between 25% and 100% of the accurate rated power with a power factor having an inductive value of 0.8.How is PT voltage calculated?
You can determine the PT ratio by dividing the phase-to-phase voltage, which is 4,160V, by the voltmeter full-scale range, which is 150V. This simple calculation results in a value of 27.7, which you would interpret as an approximate 28:1 ratio.Why DC is not used in transformer?
When we use DC sources, the magnetic field produced by a DC current is uniform and does not change over time. Ultimately, a transformer cannot work on DC because, the primary coil will create a uniform and constant magnetic field, which will fail to induce EMF in the secondary coil. 
