Relay na Hagu da Kyau na Inganci

Takardarwa da Kiyaye na Amfaniyar Impedance Relay (Distance Relay)

Impedance relay, wanda ake kira distance relay, shine babban alama mai amfani da yake da cewa shi ne mafi amfani da ita don kawo sarrafa waɗannan hankali. Yadda ake amfani da shi yaɗuƙe da ɗalilin hankali (impedance) daga wurin hankalin zuwa wurin da ake gudanar da shi. Ana amfani da shi don ƙara impedance ta ƙasashe da ƙasashe da suka haifar da ƙwayoyin hankali.

Yadda Ake Amfani Da Shiko

• Ƙara da Koyarwa: An yi fice da tarihin jirgin ruwa (don ina iya karanta voltage) da tarihin kasuwanci (don ina iya karanta current) don ƙara impedance (Z = V/I).

• Yadda Ake Farko Da Hankali: Idan an ƙara da impedance mai kyau da takawa, wanda yana nuna cewa hankali ana faru a tsakiyar da aka sanya, za a yi ƙwace maɗaɓa kan circuit breaker. A lokacin da hukuma, impedance ya fi ƙarin (voltage >> current), wanda yana ba shi ba ake amfani da shi. Daga baya, idan hankali ana faru, current zai ƙare da voltage zai ƙare, wanda yana ƙare da impedance da kuma ya ƙare da shi ake amfani da shi.

Kiyaye Na Amfani

A lokacin da hukuma, ratio na voltage da current (impedance) take da ƙarin da takawa. Idan hankali ana faru (misali, F1 a kan abubuwan AB), impedance zai ƙare da takawa. Misali, idan an gudanar da relay don ƙara abubuwan AB da impedance mai hukuma Z, hankali zai ƙare da impedance, wanda yana ƙare da shi ake ƙwace maɗaɓa kan circuit breaker. Idan hankali ana faru a kan waje (misali, a waje AB), impedance zai da ƙarin, wanda yana ba shi ba ake amfani da shi.

Muhimman Tsarin Amfani

Relay na da muhimmin abubuwa biyu:

• Abubuwa Don Koyar Current: Yaɗuƙe da koyar torque mai ƙare da current.

• Abubuwa Don Koyar Voltage: Yaɗuƙe da koyar torque mai ƙare da voltage. Equation na koyar torque shine:k₁I² −k₂VIcos(θ−ϕ)=0 wanda yana nuna phase angle bayan voltage da current, da θ shine maximum torque angle. A diagram na impedance, tsarin amfani na relay yana ƙunshi da dutsen da ke da ƙasar da radius mai ƙarin da takawa. Wannan tsari na dutsen yana ba shi da ƙarin da ƙarin da koyar magnitude da kuma phase, wanda yana ba shi da amfani da shi don ƙwarewa da ƙwarewa da hankali a kan tsakiya da waje.

-K3 yana nuna spring effect na relay. A lokacin da hukuma, net torque = 0 don values na V da I.

Idan spring control effect ya ƙare, equation ya ƙare ne

Wannan figure yana nuna tsarin amfani na voltage da current; dashed line yana nuna constant line impedance.

Wannan figure tare da tsarin amfani na impedance relay. Region na ƙarin da tsarin amfani yana nuna positive torque, inda line impedance yana ƙare da impedance ta ƙasashe, wanda yana ƙare da shi ake amfani da shi. Daga baya, region na negative torque (waje da tsarin amfani) yana nuna cewa fault impedance yana ƙare da line impedance, wanda yana ba shi ba ake amfani da shi. Wannan distinction yana ba shi da ƙarin da ƙarin da ƙwarewa da ƙwarewa da hankali, wanda yana ba shi da amfani da shi don ƙwarewa da ƙwarewa da hankali a kan power systems.

Radius na dutsen yana nuna line impedance; X-R phase angle yana nuna vector position. Impedance < radius = positive torque (relay operates); impedance > radius = negative torque (relay inactive). Wannan visual distinction yana ba shi da ƙarin da ƙarin da ƙwarewa da ƙwarewa da hankali a kan power systems.

Wannan relay yana ƙunshi da high-speed relay.

Electromagnetic Induction Relay

Torque a wannan relay yana ƙunshi da electromagnetic interactions bayan voltage da current, wanda suka koyar don amfani. A cikin circuit, Solenoid B&mdash;powered by a potential transformer (PT)&mdash;yaɗuƙe da clockwise torque, wanda yana ƙare da plunger P2 downward. Spring on P2 yaɗuƙe da restraining force, wanda yana ƙare da clockwise mechanical torque.

Solenoid A, excited by a current transformer (CT), yaɗuƙe da clockwise deflecting (pick-up) torque wanda yana ƙare da plunger P1 downward. A lokacin da hukuma, relay contacts suna da ƙwarewa. Idan hankali ana faru a kan tsakiyar da aka sanya, current na system zai ƙare da torque na Solenoid A da kuma zai ƙare da restoring torque na Solenoid B. Wannan imbalance zai ƙare da balance arms na relay, wanda zai ƙare da contacts don ƙwace maɗaɓa. Wannan design yana ba shi da ƙarin da ƙarin da ƙwarewa da ƙwarewa da hankali don ƙoyar torque bayan electromagnetic da mechanical forces.

Force na solenoid A (current element) yana ƙunshi da I², while that from solenoid B (voltage element) yana ƙunshi da V2. Saboda haka, relay zai ƙare da shi idan force na current zai ƙare da force na voltage.

Constants k1 and k2 yana ƙunshi da ampere-turns na biyu solenoids da ratios na instrument transformers. Settings na relay zai iya canzawa via tappings on the coils.

A cikin characteristic curve, y-axis yana nuna operating time na relay, idan x-axis yana nuna impedance. Notably, operating time na relay yana da ƙarin (indicating instantaneous action) don impedances a kan preset protection zone. A kan predetermined distance (corresponding to the set impedance), voltage and current values stabilize; beyond this point, measured impedance theoretically becomes infinite, meaning relay remains inactive for faults outside its protective scope. This linear relationship between impedance and operating time ensures reliable, rapid fault detection within the defined zone.

Induction Type Impedance Relay

Circuit diagram na induction-type impedance relay yana ƙunshi da biyu elements: current da voltage, featuring aluminium disc wanda yake ƙare da electromagnets.

Upper electromagnet na biyu windings: primary winding connected to the secondary coil of a current transformer (CT), while the secondary winding is linked to a potential transformer (PT). Setting na current na primary winding zai iya canzawa via plug bridge positioned beneath the relay, allowing for precise calibration of the relay's sensitivity. Voltage element, energized by the PT, generates a magnetic field that interacts with the current-derived field from the CT.

This interaction induces eddy currents in the aluminium disc, producing a torque that drives its rotation. Under normal operating conditions, the disc remains stationary due to balanced torques; during a fault, the current surge unbalances the torques, causing the disc to rotate and trigger the relay contacts. This design ensures reliable impedance-based fault detection in power systems.

Electromagnets na relay suna ƙunshi da series, with their induced fluxes generating rotational torque that drives the aluminium disc. Permanent magnet provides both controlling and braking torque to stabilize the disc's motion.

Under normal operation, the force on the armature exceeds the torque from the induction element, keeping the trip contacts open. When a system fault occurs, the current through the electromagnets surges, causing the aluminium disc to rotate. The disc's rotational speed is directly proportional to the fault current, winding a spring as it turns. This rotational motion gradually overcomes the restraining torque from the permanent magnet.

Once the disc's rotation reaches a critical threshold (corresponding to the preset impedance), the trip contacts close, initiating the protective response. This design ensures that the relay reacts swiftly to faults while maintaining stability during normal operation, with the permanent magnet providing essential control over the disc's acceleration and braking to prevent false tripping.

The rotation angle of the relay's disc relies on the armature force, which is directly proportional to the applied voltage. Hence, voltage dictates the rotation angle.

Time-Characteristic of High-Speed Impedance Relay

The figure depicts that the relay remains inactive for values exceeding 100% of the pickup threshold. Curve 1 represents the actual operational characteristic, while Curve 2 offers a simplified model of Curve 1. This design ensures rapid response to faults within the preset range while maintaining stability under normal conditions. The relay's high-speed operation is critical for minimizing damage in power systems, with the simplified curve facilitating easier implementation and analysis in protective relay settings.

Drawbacks of Plain Impedance Relay

The following are the key disadvantages of impedance relays:

• Lack of Directional Discrimination
  The relay responds to impedance changes on both sides of the current transformer (CT) and potential transformer (PT). This makes it difficult for circuit breakers to distinguish between internal faults (within the protected zone) and external faults (outside the zone), potentially leading to unnecessary tripping or delayed isolation of faults.

• Sensitivity to Arc Resistance
  The relay's operation is significantly influenced by arc resistance during faults. Arc resistance introduces additional impedance, which can mask the true fault impedance and cause the relay to either under-react (fail to trip for internal faults) or over-react (falsely trip for external faults).

• Vulnerability to Power Swings
  Impedance relays are highly sensitive to power swings—periodic oscillations in voltage and current caused by system disturbances (e.g., sudden load changes or generator instability). Power swings can mimic fault conditions by altering the measured impedance, leading to false tripping or delayed operation.

• Non-Directional Operation
  The relay trips whenever the measured impedance falls below the preset threshold, regardless of the fault direction. This means it cannot differentiate between forward faults (within the protected line) and backward faults (toward the power source), limiting its applicability in complex, multi-source power systems.