ratio is the ratio of primary current input to secondary current output at full load. For example, a CT with a ratio of 300:5 is rated for 300 primary amps at full load and will produce 5 amps of secondary current when 300 amps flow through the primary.
Why is CT ratio 1 or 5?
CTs typically have a standard secondary output rating of 1 or 5 amps. A CT ratio is simply the primary and secondary currents being expressed as a ratio where the secondary is either 1 or 5 amps. A 100/5 ratio CT means that the primary current is 20 times greater than the secondary current.
What does it mean by CT ratio 400 5?
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. This relationship is constant and it is linear.
What is CT ratio and Pt ratio?
CT is used to measure current while PT is used to measure voltage. CT is connected in series while PT is connected in parallel. CT ratio range is from 1 to 5A while the PT range is from 110V. We connect the output parameter from CT to the ampere meter while we connect the PT output to the voltmeter.
How do you calculate CT ratio?
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 and its types?
There are three basic types of current transformers: wound, toroidal and bar. Wound Current Transformer – The transformers primary winding is physically connected in series with the conductor that carries the measured current flowing in the circuit.
What is difference between 1A and 5A CT?
Less number of turns also means that reduced core size. Hence, for a given CT ratio and burden, a CT with a 5A secondary will be cheaper, smaller and lighter. Thus, on the outlook, it definitely appears that CTs with 5A secondary current are far more superior to those with 1A secondary.
Why CT burden is important?
The resistance of the connected wire and the meter input impedance contributes to resistance in the CT secondary circuit. The resistance of the connecting lead wires is more if the distance between the CT and the meter/relay is more. That is why it is important to reduce the burden.
What is the class of CT?
Accuracy class of current transformer is the highest permissible percentage composite error at rated current. The standard accuracy classes of current transformer as per IS-2705 are 0.1, 0.2, 0.5, 1, 3 and 5 for metering CT.
How do you read a CT rating?
CT Ratio: 100/5-5 A
CT ratio means the currant transformation ratio, here the CT contains Single primary current and dual secondary current output. The ratio 100/5 means If the CT primary carries 100 Amps then the output of the CT secondary will be 5 Amps.
What is use of CT and PT?
CT and PT both are measuring devices used to measure currents and voltages. They are used where large quantities of currents and voltages are used. The role of CT and PT is to reduce high current and high voltage to a parameter.
What is the work of CT?
A computerized tomography (CT) scan combines a series of X-ray images taken from different angles around your body and uses computer processing to create cross-sectional images (slices) of the bones, blood vessels and soft tissues inside your body. CT scan images provide more-detailed information than plain X-rays do.
How does CT measure current?
A Current Transformer (CT) is used to measure the current of another circuit. CTs are used worldwide to monitor high-voltage lines across national power grids. A CT is designed to produce an alternating current in its secondary winding that is proportional to the current that it is measuring in its primary.
How do you change CT ratio?
Large changes in the CT ratio can be achieved by modifying the primary turns through the CT window. One primary turn is equal to one pass of the primary conductor. Adding additional loops through the CT window will result in the electrical ratio being modified.
How do you calculate CT ratio error?
6) Current Ratio Error: The error with a transformer introduces into the measurement of a current and which arises from the fact that actual transformation ratio is not equal to the rated transformer ratio. The current error expressed in percentage is given by the formula: Current error in % = (Ka(Is-Ip)) x 100 / Ip.
What is current transformation ratio?
The transformation ratio is the relationship between the primary rated current and the secondary rated current, and is cited on the rating plate as an unsimplified fraction. Most frequently, x / 5 A current transformers are used. The majority of measuring devices have the highest precision class at 5 A.
What is the accuracy class of CT?
Current error and phase displacement limits are determined by the accuracy class. Accuracy classes are: 0.1, 0.2, 0.5 and 1.
What are the errors in CT?
There are two types of errors in a current transformer. They are ratio error and phase angle error.
How do you size a CT?
CTs can measure lower currents than they were designed for by passing the conductor through the CT more than once. For example, to measure currents up to 1 amp with a 5 amp CT, loop the conductor through the CT five times. The CT is now effectively a 1 amp CT instead of a 5 amp CT.
Why is CT short circuited?
The secondary side of the current transformer is always kept short-circuited in order to avoid core saturation and high voltage induction so that the current transformer can be used to measure high values of currents.
What is ring type CT?
A range of ring type tape wrapped current transformers suitable for primary currents from 1A – 10000A with 1A or 5A secondary output. This standard range of measuring and protective CTs is available in tape wrapped style.
Which is better 5P10 or 5P20?
Its application which differetiate the use of 5P10 and 5P20. If the breaker is used for backup protection say incommer etc you can use 5P20, but if it is say an incommer ACB/ MCCBof PMCC, you should use 5P10 only.
What is base kVA?
This common kVA which is taken as an arbitrary one is known as the base kVA of the system. ADVERTISEMENTS: A base kVA may be chosen in the following manner: (i) Equal to the kVA rating of the largest unit connected in the network. (ii) Equal to the sum of the kVA ratings of all the units connected in the network.
Why Pt burden is more than CT?
The higher CT burden cause error in the measurement and in a long run may fail the CT. That is why PT burden is high Compared to CT burden.
What is difference between CT and PT?
The current transformer and potential transformer (also called voltage transformer) are both measuring devices. A CT lowers the current signals for measurement purposes, while a PT lowers high voltage values into lower ones. The transformers are designed to measure whether power systems are both accurate and safe.
What is accuracy limit factor of CT?
CT accuracy class is 5. It means if 20 times of the rated primary current(4000 amperes) flows in the primary at the time of fault, the CT reads the current with 5 % accuracy. This factor (In x 20)20 is called the accuracy limit factor(ALF).
What is ratio error?
Error ratio is generally calculated by the ratio of the number of error occurrences divided by the number of trials in HIP task. Error ratio is measured as one of the indices of the performance, mental workload, and fatigue in the task.
What is RCT in CT?
Indoor current transformer. The RCT indoor current transformer is used for metering and relaying applications in medium voltage (5 – 15 kV) switchgear.
What is a Class 1 CT?
The class designation is an approximate measure of the CT’s accuracy. The ratio (primary to secondary current) error of a Class 1 CT is 1% at rated current; the ratio error of a Class 0.5 CT is 0.5% or less. Errors in phase are also important, especially in power measuring circuits.
What does 5P10 for a CT of 100 5 mean?
If you see the specification or name plate of a protection class CT, you will find that it is given like 5P10. This CT can be interpreted as a protection class CT having an accuracy of 5% over a current range of 10 times of normal primary current rating.
What is protection class CT?
The protection class CT is designed to take care of fault current. To ensure this, the Protection CT requires an Accuracy Limit Factor (ALF). Accuracy Limit Factor (ALF) is the multiple of rated current up to which CT will operate, complying with accuracy class requirement. According to IEEE C57.
What is Burden of PT?
The burden is the total external volt-amp load on the secondary at rated secondary voltage. The rated burden of a PT is a VA burden which must not be exceeded if the transformer is to operate with its rated accuracy. The rated burden is indicated on the nameplate.
How many types of CT and PT are there?
Such specially constructed transformers with accurate turns ratio are called as Instrument transformers. These instruments transformers are of two types – (i) Current Transformers (CT) and (ii) Potential Transformers (PT).
Why do we use PT?
A prothrombin time (PT) test uses blood samples to measure how quickly your blood forms a clot. Healthcare providers often do this test to monitor your prothrombin levels if you’re taking the blood thinner warfarin. This test is also used to investigate potential blood disorders.
Why kVA rating is used in transformer?
The first reason is the power loss in the transformer.
Thus, the total losses in a transformer depend upon volt-ampere (VA) only and not on the power factor of the load. That is why the transformer rating is given in kVA and not in kW.
Why is CT polarity important?
A subtractive turn runs the opposite direction (from the side with the polarity mark). Observing CT polarity is important when adding or subtracting secondary turns. CTs are manufactured to produce a secondary current that is in phase with the primary current when installed with the correct orientation.
Is CT output is AC or DC?
Current transformers can only measure AC current and output signal is AC 5A or AC1A, external power supply isn’t needed. Common current transformer can only measure AC current.
Why CT is used in energy meter?
A current transformer (CT) is used to measure the current electric flow, or total power being consumed.
What is P1 & P2 in CT?
P1 indicates the side on which the current source is located, whilst P2 indicates the load side.
What are the types of current transformer?
The three types of current transformers in general use are the window, bar, and wound.