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Any nonlinear load on a system generates harmonics. Exampes are the magnetic core of a transformer or equipment which uses rectifiers to produce direct current. The triplen harmonics are unpopular because they add on a three-phase system, so they produce current in the neutral, which a three-phase system in balance does not.
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Is a current relay same as potential relay?
current relay are using for over current low state & high state.but potential relay are related to voltage.
How do you calculate setting for over current earth fault relay setting?
An artificial neutral is crated in the CT of the line to be protected (for transmission lines) a CT is fixed in the neutral of the CT. if there is any imbalance in the 3 phase current then the relay will develop a difference in neutral.that can be sensed by the CT,then gives the trip command to relay
Why impedance relay is called as distance relay?
because the distance is propotional to the impedance of the line ,so the operation of the impedance relay comes into picture when the impedance seen by the relay is less than the pre-setting value.When a fault occurs ,the current increases to a high value and so the Impedence decreases and the relay actuates
What is Inverse Definite Minimum Time?
(I.D.M.T.) RELAYThe over load inverse time relay is shown in fig 26. It consists of an upper electromagnet that has been provided with two windings one primary and the other secondary. Primary is connected to a current transformer in the line which is under protection and is provided with eight tappings. These tappings are connected to a plug setting bridge by which the number of turns to be used can be adjusted in order to have the desired current setting. The second winding called secondary is energized by the induction effect and is wound over the central limb of the upper magnet as well as it is spread over the two limbs of the lower magnet. By this method, the leakage flux from the upper magnet entering the disc have been displaced in phase from the flux entering the disc from the lower magnet. The deflecting torque is produced on the disc in the fashion as already explained. The spindle of the disc carries a moving contact which bridges two fixed contacts after the disc has rotated through a certain angle which has been set before. Any setting for this angle is possible varying from 0 to 360°. The variation of this angle imparts to the relay, various time settings.The speed of rotation of the disc is dependent upon the torque which in turn is dependent on the current setting, when the load current increases from this setting it will increase the speed of rotation of the disc resulting into decrease of operation time. Thus the time current characteristics of the relay observe inverse-Square law. The definite minimum time characteristics of the relay are obtained by the use of a saturated upper magnet. This ensures that there is no further increase in f1ux when the current has reached a certain value and any further increase of current will not affect the relay operation. This results in a flattened current time characteristic and the relay obtains its name as Inverse definiteminimum time lag (I.D.M.T.) relayThe current time characteristics of the relay have been illustrated in Fig. 27. It represents the time required to close the trip contacts for different values of over current. Its horizontal scale is marked in terms of current-setting multipliers i.e. number of times the relay current is in excess of current setting
What is an impedance relay?
Impedance relays are used whenever over-current relays do not provide adequate protection. They function even if the short circuit current is relatively low. The speed of operation is independent of current magnitude. Impedance relays monitor the impedance between the relay location and the fault. If the impedance falls within the relay setting, the relay will operate. The basic construction for impedance relays on which the principle of operation is easily explained is the balanced beam.
What is plug setting multiplier of relay?
The plug setting multiplier of a relay is a ratio used to determine the pickup current of the relay based on the nominal current rating of the system it is protecting. It is calculated by dividing the full load current of the protected system by the maximum current that the relay can handle. This multiplier helps in setting the relay's pickup current level accurately for proper coordination and protection.
What is psm tsm for idmt relay?
PSM stands for Plug setting multiplier and can be found on the front of the relay module in the form of a scale . PSM = Actual or fault current in the relay / ( CT Secondary current X Amp setting in the relay) From the above value of PSM find the time in seconds from the front of relay panel scale i.e., PSM Vrs Time in seconds Miltiply the time in seconds with the TSM to find the tripping time for the relay for the specific value of fault current TSM = Time setting multiplier Relay Operating time = TSM x time in seconds <- as observed from the scale .
What is the difference between an earth fault relay and an over current relay?
earth fault relay is also a type of over current relay but the set value of current or relay sensing current is much less than the maximum load current.in over current relay relay sensing current ise than maximum load current mor
How do you calculate earth fault current value by knowing the setting in electromagnetic relay?
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What is DTOC relay?
A definite time over-current relay operates like an instantaneous over-current relay coupled with a timer. Once current reaches the pick-up value, it initiates the timing circuit. As long as current stays above this pick-up value, the timer will continue to time. Once the definite time setting is reached, the relay gives trip signal to the circuit breaker.
Is a current relay same as potential relay?
current relay are using for over current low state & high state.but potential relay are related to voltage.
How do you calculate setting for over current earth fault relay setting?
An artificial neutral is crated in the CT of the line to be protected (for transmission lines) a CT is fixed in the neutral of the CT. if there is any imbalance in the 3 phase current then the relay will develop a difference in neutral.that can be sensed by the CT,then gives the trip command to relay
How do you test over current relay?
Normally the Over current relay is connected using a suitable CT (Current Transformer). Say the CT ratio is 100/5 Amps. (secondary is normally 5 or 1 amps). 100 Amps in the primary induces 5 amps in secondary which flows through over current relay circuit. Secondary current is proportional to the primary current. To test the OCR , inject the current into relay circuit ranging from 0 to 5 amps in steps (which represents upto full load current on primary). Relay will operate accordingly operate the trip contacts. These relays are normally with a time factor setting as well.
What is the theory behind a definite time overcurrent relay?
A definite time overcurrent relay operates like an instantaneous overcurrent relay coupled with a timer. once current reaches the pickup value, the relay overcurrent relay will trip, which initiates the timing circuit. as long as current stays above this pickup value, the timer will continue to time. Once the definite time setting is reached, the timer will close the relay tripping contacts.
Why impedance relay is called as distance relay?
because the distance is propotional to the impedance of the line ,so the operation of the impedance relay comes into picture when the impedance seen by the relay is less than the pre-setting value.When a fault occurs ,the current increases to a high value and so the Impedence decreases and the relay actuates
What is Inverse Definite Minimum Time?
(I.D.M.T.) RELAYThe over load inverse time relay is shown in fig 26. It consists of an upper electromagnet that has been provided with two windings one primary and the other secondary. Primary is connected to a current transformer in the line which is under protection and is provided with eight tappings. These tappings are connected to a plug setting bridge by which the number of turns to be used can be adjusted in order to have the desired current setting. The second winding called secondary is energized by the induction effect and is wound over the central limb of the upper magnet as well as it is spread over the two limbs of the lower magnet. By this method, the leakage flux from the upper magnet entering the disc have been displaced in phase from the flux entering the disc from the lower magnet. The deflecting torque is produced on the disc in the fashion as already explained. The spindle of the disc carries a moving contact which bridges two fixed contacts after the disc has rotated through a certain angle which has been set before. Any setting for this angle is possible varying from 0 to 360°. The variation of this angle imparts to the relay, various time settings.The speed of rotation of the disc is dependent upon the torque which in turn is dependent on the current setting, when the load current increases from this setting it will increase the speed of rotation of the disc resulting into decrease of operation time. Thus the time current characteristics of the relay observe inverse-Square law. The definite minimum time characteristics of the relay are obtained by the use of a saturated upper magnet. This ensures that there is no further increase in f1ux when the current has reached a certain value and any further increase of current will not affect the relay operation. This results in a flattened current time characteristic and the relay obtains its name as Inverse definiteminimum time lag (I.D.M.T.) relayThe current time characteristics of the relay have been illustrated in Fig. 27. It represents the time required to close the trip contacts for different values of over current. Its horizontal scale is marked in terms of current-setting multipliers i.e. number of times the relay current is in excess of current setting
What is an impedance relay?
Impedance relays are used whenever over-current relays do not provide adequate protection. They function even if the short circuit current is relatively low. The speed of operation is independent of current magnitude. Impedance relays monitor the impedance between the relay location and the fault. If the impedance falls within the relay setting, the relay will operate. The basic construction for impedance relays on which the principle of operation is easily explained is the balanced beam.
