0
This can be done, but is usually not done because a metering CT is made to be very accurate at expected load current levels. A protection CT is made to be accurate At Fault current levels (which is often significantly above load current). If the CT is too small, and has too small of a ratio, the CT will likely saturate, which will skew the results the protective device expects to get.
An example: a metering CT may have a ratio of 100:5 (made for 100A load current, which will produce 5 amps secondary current). Fault current levels may be ~10,000A. You'd expect the secondary output of a perfectly linear CT to be 500A. One way resistance of the cable connecting the protective device to the CT may be on the order of .5 - 2 ohms. Ignoring the resistance of the CT and connected devices, secondary voltages would reach 250 - 1,000 volts for a phase fault, and 500 - 2,000 volts for a ground fault. The biggest CTs may be rated for 800 volts output below the knee point, so this 100:5 CT would clearly saturate. The real output current would likely be on the order of 150A at the most.
...And the above is ignoring any DC offset, which would cause the CT to saturate at unpredictable AC current levels.
Wiki User
∙ 13y ago
Wiki User
∙ 11y agoIf the production CT is used for metering, the production CT will not give the accurate current at the secondary. Because of it's constructed to give the abnormal condition to the productive devices.
Add your answer:
Earn +20 pts
How does a transformer protect an appliance?
Normally current transformers are used for two things . For measuring and protection. Whenever the CT is a protection CT it will be connected with the protection relays and there will be setting in the relays based on our requirement. when the current pass through the relays are more than the setting range then relay will send the tripping signal to the breaker available in the system to isolate the fault section. Finally the CT is not protecting the system. it will transfer the high primary current from the system to relay as small secondary current.
What is class PS in current Transformer?
PS is a special class of protection transformer used in differential protection schemes. The CT is specified by what is known as the knee point (that is the point at which the CT saturates). Because they are specified using the knee point, two separate CTs will have the same characteristics. These matched CTs won't introduce measurement error during through faults on differential protection schemes.
When shall you use class x CT?
in substation protection To be connected to unit protection relays (i.e. differential, REF, Dist., etc.)
Why is burden not used in protection ct?
Generally accuracy at low current values isn't important for protective functions. The burden is taken into account when looking at the saturation curve and available short circuit current to insure the CT doesn't saturate during fault conditions.
What is the advantage of 1 amps current transformer than that of the old type 5 amps current transformer?
If the protection relay and CT installed for away, then it is advised to install 1A CT rather than 5A CT. Because of lower amps it will reduce the losses on the cable. p = i^2.R
Where is 5P20 CT used and where is Class PS CT used?
5P20 CT give more accuracy than PS class CT. 5P20 cant be used in unit protection. Class PS CT is a protection class ct. It is used for differtial proction,distance (UNIT)proction.
How does a transformer protect an appliance?
Normally current transformers are used for two things . For measuring and protection. Whenever the CT is a protection CT it will be connected with the protection relays and there will be setting in the relays based on our requirement. when the current pass through the relays are more than the setting range then relay will send the tripping signal to the breaker available in the system to isolate the fault section. Finally the CT is not protecting the system. it will transfer the high primary current from the system to relay as small secondary current.
What is the ISO protection class for Windsor Locks CT 06096?
What is the ISO protection class for Windsor Locks CT
Class px ct?
Class PX is the definition in IEC 60044-1 for the quasi-transient CT formerly covered by Class X of BS-3938, commonly used with unit protection schemes. These are Protection CTs used for Earth fault protection. Knee point voltage is an important parameter for these type of CTs. Shaikh
Why you use current transformer and rogowski coil both?
if you want to measure a wide range of current, example 1mA to 200A (if the device is intended for the metering and protection), normally CT and rocoil is used together, it is difficult to make rocoil sensitive in range of 1mA, but you can do the task with the CT, but the same CT gets saturated above 5A, in that case rocoil start measuring, since rocoil is air core it wont saturate.
Will REF protect the outgoing cables when the Ct's are fitted at the transformer?
REF protection, when installed and set correctly, will protect everything within the CT's. If the CTs are on breakers, then yes, the cables from the transformer to the breakers will be in the zone of protection. If the CTs used are in the bushings of the transformer, then no.
What is CT burden in electrical engineering?
CT (current transformer) Burden is the maximum load that the CT secondary can drive (e.g. meters or protection relays) Why do you care about burden when ordering current transformers? The burden is the termination impedance of the measuring instrument. The measuring instrument can be an analog or digital energy meter, a data logger or a recorder. All instruments that use a current transformer to measure line current must terminate the CT with a resistance (impedance in same case which means there is some inductance involved). A CT supplier should be given the burden when ordering. Technically, the total burden for a CT is the internal winding resistance, the connecting lead resistance and the measuring instrument input resistance. Some Ct's are installed a long distance from the measuring instrument and the connecting leads can have a resistance as much as 0.002 ohms per foot (both ways because the current makes a complete round trip). This resistance will cause an error if not taken into account.
When did CT Special Forces happen?
CT Special Forces happened in 2001.
Wts the use of CT in Grid station?
ct is currrent transformer are use is protection instromentAnswerA current transformer is an instrument transformer. It allows the current flowing through high-voltage (h.v.) circuits to be monitored safely by (1) reducing the size of that current to a safe level, and (2) electrically isolating its secondary winding from the high-voltage system.A CT provides a safe means of (1) measuring the h.v. circuit's current, as well as (2) providing an input to the high-voltage system's protection relays.
Are there tornadoes in CT?
They are relatively rare, but they do happen.
What is The operation of Current Transformer?
CT together with a ammeter is used to measure the current in high current or high voltage circuit, where a normal ammeter can not be connected in series in such high voltage or high current circuits. It is a secondary winding (like in transformer) wound on a single core primary wire and relative secondary current reperesnets the primary current. CT are also used protection purposes. Basic principle of CT i same either for metring or protection.
What is the difference between CT and PT?
A ct is a step up transformer where as a pt is a step down transformer because both are used for measurement and protection purpose . current is stepped down if the secondary windings are more so we can obviously say thar ct is step up transformer
