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What factor cause spill current on external fault in case of transformer differential protection?
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What is differential transformer protection?
The current input (primary) to a transformer is proportional to the output (secondary) current. Differential protection relays monitor these via current transformers (CT). The percentage of difference between primary and secondary can be adjusted. If it is over the seting the relay will trip the primaryand secondary feeder breakers. Thus indicating an inbalance between internal phasewindings and or shorts to earth.
What is defrential protection relay?
I am going to assume that you are asking about a differential relay. It is basically just that- it compare two different sources and will trip at a set value value of the difference. These can be directional as well. A couple of examples are transformer protective relays and bus differential. A transformer relay will measure the amount of current coming into the transformer and the amount of current going out. If there is a disparity due to an internal fault the relay will trip the supply source and deenergize the transformer. Same for the Bus differential.
What is the reason for using a neutral current transformer on a transformer?
A current transformer is primarily used at the neutral point of a transformer for earth fault protection. A neutral current transformer will measure any ground fault current which will essentially flow from the star point of the transformer. A fault-detection device other devices is connected to the current transformer and, if the fault current exceeds a certain trigger value, the fault-detection device will give a trip command to an earth-fault relay to disconnect the supply of electricity to the transformer.
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.
Would you expect to find an alternating or direct current in the secondary coil of a transformer?
An Alternating Voltage is induced in the secondary winding. When connected to an external load, you will have an alternating current.
Why percentage differential protection is preferred over differential protectionfor internal faults?
if we are seeking for internal protection of transformer only, then if any external fault occurs then it will show the fault though it should not. what a percentage differential protection will do means, it will include a restraining coil which is excited by the current in the transformer itself. Also the percentage differential relay ha taps. So it is easy to avoid the external fault. for reference check 'theory and applications of transformer differential protection' by GEORGE W.McKENNA, AIEE transactions 1950,volume 69
What is differential transformer protection?
The current input (primary) to a transformer is proportional to the output (secondary) current. Differential protection relays monitor these via current transformers (CT). The percentage of difference between primary and secondary can be adjusted. If it is over the seting the relay will trip the primaryand secondary feeder breakers. Thus indicating an inbalance between internal phasewindings and or shorts to earth.
How differential protection work in a transformer?
Power flowing into a transformer must match the power flowing out (minus losses which are minimal). If this is not the case, there's something wrong. Differential protection monitors current only; Current flowing into one side of the transformer will be equal to current flowing out the other side scaled by the turns ratio of the transformer. Since the turns ratio is equivalent to the voltage ratio, this is easily set.
Dear all what direct consequences can be from Current transformer on generator with respect to differential protection relay?
CT's are used as inputs to the differential. If the CT is bad, or it is not wired to the differential correctly, it will cause differential current to be seen by the relay, resulting in a trip.
What is the definition of differential relay and how does it function?
In power transformer, a differential relay is a relay that verifies the balance of current between the primary and the secondary face of a transformer. It is also employed in other components of the power system like in protecting cables. Differential relay is also called a unit protection.
What is defrential protection relay?
I am going to assume that you are asking about a differential relay. It is basically just that- it compare two different sources and will trip at a set value value of the difference. These can be directional as well. A couple of examples are transformer protective relays and bus differential. A transformer relay will measure the amount of current coming into the transformer and the amount of current going out. If there is a disparity due to an internal fault the relay will trip the supply source and deenergize the transformer. Same for the Bus differential.
What is the type of generator protection to protect against unequal phase current?
differential protection
What is restricted earth fault protection and how is it provided?
A Restricted Earth Fault (REF) means an earth fault from a restricted/localized zone of a circuit. The term "REF protection method " means not to sense any earth faults outside this restricted zone. REF is a type of "unit protection" applied to transformers or generators and is more sensitive than the method known as differential protection. An REF relay works by measuring the actual current flowing to earth from the frame of the unit. If that current exceeds a certain preset maximum value of milliAmps (mA) then the relay will trip to cut off the power supply to the unit. Differential protection can also be used to protect the windings of a transformer by comparing the current in the power supply's neutral wire with the current in the phase wire: if the currents are equal then the differential protection relay will not operate; if there is a current imbalance then the differential protection relay operates. However, REF protection is also applied to transformers in order to detect ground faults on a given winding much more sensitively than differential protection can do.
How current transfomer is step up voltage transformer n step down current transformer?
Current transformers are not voltage transformers. Current transformer are used for metering or protection purposes, with single turn primary. Generally the secondary current is either 1Amps or 5Amps.
What is the reason for using a neutral current transformer on a transformer?
A current transformer is primarily used at the neutral point of a transformer for earth fault protection. A neutral current transformer will measure any ground fault current which will essentially flow from the star point of the transformer. A fault-detection device other devices is connected to the current transformer and, if the fault current exceeds a certain trigger value, the fault-detection device will give a trip command to an earth-fault relay to disconnect the supply of electricity to the transformer.
What is a transformer and its functions?
Voltage transformer or potential Transformers are used in conjunction with Current transformers for metering and protection purpose in HT and LT power system.
How relay used for protection purpose?
Relay are operated by small current /voltage connected to Secondary side of Current Transformer and /or Voltage Transformer. The signal stimulates the magnetic substance nearby with the attracting force. This closes or opens the circuit being used in protection purpose.
