March 2009
You are currently browsing the articles from circuitmaniac.com written in the month of March 2009.
This system is similar to voltage balance system except that here balance or opposition is between the voltages induced in the secondary windings wound on the relay magnet and not between the secondary voltages of the line current transformers. This permits to use current transformers of normal design and eliminates one of the most serious [...]
Written by John on March 25th, 2009 with 2 comments.
Read more articles on Feeder protection and Power System and Switchgear&Protection.
Figure shows the single line diagram of Merz Price voltage balance system for the protection of 3-phse line. Identical current transformers are placed in each phase at both ends of the line. The pair of CTs in each line is connected in series with a relay in such a way that under normal conditions, their [...]
Written by John on March 25th, 2009 with 2 comments.
Read more articles on Feeder protection and Power System and Switchgear&Protection.
The differential pilot-wire protection is based on the principle that under normal conditions, the current entering one end of a line is equal to that leaving the other end. As soon as a fault occurs between the two ends this condition no longer holds and the difference of incoming and outgoing currents is arranged to [...]
Written by John on March 25th, 2009 with 3 comments.
Read more articles on Feeder protection and Power System and Switchgear&Protection.
Ring main system – In this system, various power stations or sub-stations are interconnected alternate routes, thus forming a closed ring. In case of damage to any section of the ring, that section may be disconnected for repairs and power will be supplied from both ends of the ring, thereby maintaining continuity of supply Fig [...]
Written by John on March 24th, 2009 with 26 comments.
Read more articles on Feeder protection and Power System and Switchgear&Protection.
PARALLEL FEEDER – Where continuity of supply is particularly necessary, two parallel feeders may be installed. If a fault occurs on one feeder, it can be disconnected from the system and continuity of supply can be maintained from the other feeder. The parallel feeder cannot be protected by non directional relay over current relays only. [...]
Written by John on March 24th, 2009 with 7 comments.
Read more articles on Feeder protection and Power System and Switchgear&Protection.
In this type of protection time settings of relays is so graded that in the event of fault, the smallest possible part of the system is isolated. Following are the important cases. RADIAL FEEDER The main characteristics of this system is that power can flow only one direction, from generator or supply end to the [...]
Written by John on March 24th, 2009 with 1 comment.
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The directional power relay is not suitable under short circuit conditions because as short circuit occurs the system voltage falls to a low value resulting in insufficient torque to cause relay operations. This difficulty is overcome in the directional over current relay, which is independent of system voltage and power factor. Constructional details: – Figure [...]
Written by John on March 23rd, 2009 with 5 comments.
Read more articles on classification of relays and Power System and Relays and Switchgear&Protection.
The step of relay operates when the, power in the circuit flows, in a specific direction. A directional power relay is so designed that it obtains its operating torque by the interaction of magnetic field derived from both voltage and current source of the circuit it protects. The direction of torque depends upon the current [...]
Written by John on March 23rd, 2009 with 1 comment.
Read more articles on classification of relays and Power System and Relays and Switchgear&Protection.
In this type of protection, transmission lines are used to carry protective currents at carrier frequency (30 to 200 kc/s) or at an ultra high frequency (above 900 mega cycles). When the transmission lines carry protective currents at carrier frequency it is called carrier current-pilot protection and when it carries protective current at ultra high [...]
Written by John on March 22nd, 2009 with 2 comments.
Read more articles on Feeder protection and Power System and Switchgear&Protection.
The distance impedance relays are normally used for phase- to-phase faults as for such faults the loop impedance between the phase is obtained which remains constant, but in case of earth fault the loop impedance consists of impedance of one line and the impedance of the earth fault which is a variable factor. Practically it [...]
Written by John on March 22nd, 2009 with 2 comments.
Read more articles on Feeder protection and Power System and Switchgear&Protection.
When a generating station supplies to three sub-stations radially, it is desired to isolate all those sub-stations beyond the fault point. This can be achieved by the use of time delayed over current relay but the main disadvantage is that if the fault is near the power station it will take much longer time to [...]
Written by John on March 22nd, 2009 with no comments.
Read more articles on Feeder protection and Power System and Switchgear&Protection.
This relay operates at a constant time for all faults independent of the distance of occurrence of fault. For its application consider Fig 10 which represents a power station feeding transforming sub-station. The power transformer is protected independently by inverse-time over current relay. Let, it be required to provide a relay at the input side [...]
Written by John on March 22nd, 2009 with 2 comments.
Read more articles on Feeder protection and Power System and Switchgear&Protection.
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