Relay na farko da dace
Relays da ake amfani da su a cikin zaɓi na tashar jiki suna da abubuwa daban-daban. Daga cikinsu, differential relay shine mafi yawan amfani da shi don zabi muhimman kayan aiki kamar transformers da generators daga hanyoyi masu ƙasa.
Differential relays suna da maɗaɗin hanyoyi da ke faru a cikin ƙasar da aka zabe amma suna da maɗaɗin hanyoyi mai biyu a kan hanyoyi da ke faru wajen baya ƙasar da aka zabe. Yawan relays sun yi aiki idan wani abu ya kawo karfi har zuwa ma'aici da aka zama saboda misali over current relay yana yi aiki idan tsari a gaba ta ya kawo karfi har zuwa ma'aici da aka zama. Amma rayuwar differential relay shine mafi inganci. Yana yi aiki idan akwai farkon da duka waɗannan abubuwa masu ƙarfi.
Takaitaccen Differential Relay
Differential relay shine mafi yawan amfani da shi don zabi muhimman kayan aiki kamar transformers da generators daga hanyoyi masu ƙasa. A cikin ƙasar zaɓi na differential relay, akwai fadada tsari ne da suka fito daga baka-baka ga takardun tsari. Waɗannan fadada tsari suna kara a matsayin wurare da aka sanya relay coil. Idan a yi amfani da Kirchhoff Current Law, tsari na resulta da ke faru a gaba relay coil ba ce kuɗi da tsari da suka fito daga baka-baka ga takardun tsari. Idan a tsara ma'ana da karfi na waɗannan fadada tsari don haka, phasor sum na waɗannan fadada tsari ya zama zero a lokacin ƙarin aiki. Saboda haka, baa ci gaba relay coil a lokacin ƙarin aiki. Amma idan an yi abin da ba daidai a cikin takarda, idan wannan balansu ya zama, ya ni cewa phasor sum na waɗannan fadada tsari ya zama zero kuma ya ci gaba non-zero tsari a gaba relay coil don haka relay yana yi aiki.
A cikin ƙasar zaɓi na current differential, akwai fadada current transformer da suka fito daga baka-baka ga kayan aiki da ake zabe da differential relay. Tsari na current transformers suna da mutane da suka zama da suka ci gaba tsari na current transformers da suka ci gaba a kan karfi.
Polarities na current transformers suna da ma'ana da suka ci gaba tsari na secondary current na CTs da suka ci gaba a kan karfi. Daga ƙasar ita, idan akwai farkon da suka ci gaba waɗannan fadada secondary currents, idan wannan farkon ya kawo karfi har zuwa ma'aici da aka zama, relay yana yi aiki don kula circuit breakers don in kula kayan aiki da aka zabe daga ƙasar. Relaying element da ake amfani da shi a cikin differential relay shine attracted armature type instantaneously relay saboda ƙasar zaɓi na differential ba da ma'aici sai don in kula hanyoyi da ke faru a cikin kayan aiki da aka zabe. Ya ni cewa differential relay yana kula hanyoyi na kayan aiki kawai, saboda haka, kayan aiki da aka zabe yana iya kula idan akwai hanyoyi da ke faru a cikin kayan aiki. Ba da kyau a yi ƙaramin lokaci don in taimaka da waɗanda suka biyo a cikin ƙasar.
Abubuwan Differential Relay
Akwai abubuwa biyu na differential relay da suka da ma'ana da suka ci gaba rayuwarsu.
Current Balance Differential Relay
Voltage Balance Differential Relay
A cikin current differential relay, akwai fadada current transformers da suka fito daga baka-baka ga kayan aiki da ake zabe. Circuits na secondary na CTs suna sanya a cikin series da suka ci gaba tsari na secondary CT a cikin yawan karfi.
Coil na operating na relaying element yana sanya a matsayin wurare da aka sanya circuits na secondary na CTs. A lokacin ƙarin aiki, kayan aiki (ko power transformer ko alternator) yana ci gaba tsari na ƙarin. A wannan lokacin, cewa tsari na secondary na CT1 shine I1 da kuma tsari na secondary na CT2 shine I2. Ita ce da aka fi sani a kan ƙasar, tsari na ci gaba relay coil ba ce kuɗi da I1-I2. Idan a tsara ma'ana da karfi na current transformers, I1 = I2, saboda haka, baa ci gaba tsari a gaba relay coil. Idan akwai hanyoyi da ke faru waje a cikin ƙasar da CTs suka zabe, faulty current yana ci gaba primary na waɗannan current transformers da kuma secondary currents na waɗannan current transformers suna ci gaba a lokacin ƙarin aiki. Saboda haka, a wannan lokacin, relay ba zai yi aiki. Amma idan akwai hanyoyi na ground fault da ke faru a cikin kayan aiki da aka zabe, waɗannan fadada secondary currents ba zan zama equal. A wannan lokacin, differential relay yana yi aiki don kula kayan aiki da aka zabe (transformer ko alternator) daga ƙasar.
Principally, wannan ƙasar zaɓi na relay systems suna da batun da suka haifar da su.
Yana da kyau a yi ƙaramin cable impedance daga CT secondary zuwa remote relay panel.
Capacitance na pilot cables yana haifar da relay a lokacin da akwai through fault mai yawa waje a cikin ƙasar.
Ba zan iya samun ƙaramin characteristics na current transformer, saboda haka, yana da kyau a yi spill current a gaba relay a lokacin ƙarin aiki.
Percentage Differential Relay
Wannan ƙarfin relay yana da ma'ana da suka ci gaba differential current a kan fractional relation na tsari na ci gaba protected section. A cikin wannan ƙarfin relay, akwai restraining coils da suka sanya operating coil na relay. Restraining coils suna produce torque opposite to operating torque. A lokacin ƙarin aiki da kuma through fault, restraining torque yana da karfi da yake da operating torque. Saboda haka, relay yana ci gaba inactive. Idan akwai internal fault, operating force yana kawo karfi har zuwa bias force kuma relay yana yi aiki. Bias force yana iya canzawa da vary the number of turns on restraining coils. Kamar da aka fi sani a cikin ƙasar, idan I1 shine tsari na secondary na CT1 da kuma I2 shine tsari na secondary na CT2, tsari na operating coil yana iya zama I1 – I2 da kuma tsari na restraining coil yana iya zama (I1 + I2)/2. A lokacin ƙarin aiki da kuma through fault, torque produced by restraining coils due to current (I1+ I2)/2 yana da karfi da yake da torque produced by operating coil due to current I1– I2 amma a lokacin internal faulty condition, waɗannan yana zama opposite. Bias setting yana iya zama ratio of (I1– I2) to (I1+ I2)/2.
Ita ce da aka fi sani, yaɗa tsari na ci gaba restraining coils, yaɗa tsari na ci gaba operating coil don haka relay yana yi aiki. Relay yana zama percentage relay saboda operating current required to trip yana iya zama a percentage of through current.
CT Ratio and Connection for Differential Relay
Thumb rule shine mafi yawan amfani da shi don haka, current transformers da suka fito daga star winding yana da kyau a sanya da delta da kuma current transformers da suka fito daga delta winding yana da kyau a sanya da star. Wannan ƙarfi shine mafi yawan amfani don in kula zero sequence current a cikin relay circuit.
Idan CTs suka sanya da star, CT ratio yana iya zama In/1 ko 5 A
Idan CTs suka sanya da delta, CT ratio yana iya zama In/0.5775 ko 5×0.5775 A
Voltage Balance Differential Relay
A cikin wannan ƙarfin, current transformers suna fito daga baka-baka ga kayan aiki da suka sanya da ma'ana da suka ci gaba EMF induced in the secondary of both current transformers will oppose each other. Yana nufin cewa secondary na current transformers daga baka-baka ga kayan aiki suna sanya da series da polarity mai yawa. Coil na differential relay yana sanya somewhere in the loop created by series connection of secondary of current transformers as shown in the figure. A lokacin ƙarin aiki da kuma through fault, EMFs induced in both of the CT secondary suna ci gaba equal and opposite of each other, saboda haka, baa ci gaba tsari a gaba relay coil. Amma idan akwai internal fault a cikin kayan aiki da aka zabe, waɗannan EMFs ba zan ci gaba balanced, saboda haka, tsari yana faru a gaba relay coil don haka trips circuit breaker.
Akwai batun da suka haifar da voltage balance differential relay kamar multi tap transformer construction da suka da kyau a yi ƙaramin current transformer pairs. Ƙarfin yana da kyau don in zabe cables da take da ƙarin lokaci amma capacitance na pilot wires yana haifar da performance. A cables da take da ƙarin lokaci, charging current zai iya kula relay even if a perfect balance of current transformer achieved.
Waɗannan batun zai iya zama da Translay system/scheme da suka da ma'ana da suka ci gaba modified balance voltage differential relay system. Translay scheme yana da ma'ana da suka ci gaba differential protection of feeders.
A cikin wannan ƙarfin, akwai fadada current transformers da suka fito daga baka-baka ga feeder. Secondary na kowace current transformer yana sanya da individual double winding induction type relay. Secondary na kowace current transformer yana sanya da primary circuit na double winding induction type relay. Secondary circuit na kowace relay yana sanya da series don haka in forma closed loop by means of pilot wires. Sanya yana da ma'ana da suka ci gaba, induced voltage in secondary coil of one relay will oppose same of other. Compensating device neutralizes the effect of pilot wires capacitance currents and effect of inherent lack of balance between the two current transformers.
A lokacin ƙarin aiki da kuma through fault, tsari na baka-baka ga feeder yana ci gaba equal, saboda haka, tsari induced in the CT’s secondary yana ci gaba equal. Da waɗannan equal currents na CT’s secondary, primary na kowace relay yana induce same EMF. Consequently, EMF induced in the secondaries of the relay yana ci gaba equal amma coils yana sanya da ma'ana da suka ci gaba, waɗannan EMFs yana ci gaba opposite direction. Saboda haka, baa ci gaba tsari a gaba pilot loop and thereby no operating torque is produced either of the relays.
Amma idan akwai hanyoyi da ke faru a cikin feeder within the zone in between current transformers, tsari na ci gaba feeder yana zama different from the tsari na ci gaba feeder. Consequently, baa ci gaba equality between the currents in both CT secondaries. Unequal secondary CT currents yana produce unbalanced secondary induced voltage in both of the relays. Therefore, tsari yana faru a gaba pilot loop and hence torque is produced in both of the relays.
As the direction of secondary current is opposite into relays, therefore, the torque in one relay will tend to close the trip contacts and at the same time torque produced in other relay will tend to hold the movement of the trip contacts in normal un-operated position. The operating torque depends upon the position and nature of faults in the protected zone of feeder. The faulty portion of the feeder is separated from healthy portion when at least one element of either relay operates.
This can be noted that in translay protection scheme, a closed copper ring is fitted with the Central limb of primary core of the relay. These rings are utilised to neutralise the effect
