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Transcript
SYNCHRONISM CHECK EQUIPMENT Introduction It is used to check whether or not two parts of the same system or two separate systems are in synchronism with each other. Synchronism check devices are basically permissive devices Synchronism check devices do not initiate reclosing. These devices require single-phase (line-to-line or line-to-neutral) potentials from the same phase(s) Classification There are two kinds of synchronism check equipment available. 1--->>IJS # Slow-speed device 2--->>GXS # High-speed device Operating principle of IJS The ijs relay is an induction disk device that receives single-phase voltages from the same phase(s) on both sides of the circuit breaker. Two electromagnets each has two coils. In the first operating electromagnet Coils are connected in such a way that they receive the vector sum of voltages (incoming Vi and running Vr). Top=kop(Vi -Vr) 2 ---------------------(1 ) two kop is a design constant. The second electromagnet is the restraining device. It receives the vector difference of the incoming & running voltages from the same phase(s) . Tr=kr(Vi+Vr) 2 ---------------------(2) kr is a design constant. contd. IN addition to electrical torques in the relay, there is also a mechanical restraint in the form of the control spring. So net torque operating in the relay is T = kop (Vi+Vr) 2 - kr (Vi -Vr) 2 - k s since ks is small as compare to electrical torques, so the 2 2 above eqn. becomes T= kop (Vi+Vr) - kr (Vi -Vr) -------------------->>(3) # It should be noted that with equal voltages on the running & incoming busses, (Vi + Vr) will be equal to (Vi - Vr) when Vi & Vr are 90 degrees apart. # As the two voltages approach each other in phase angle, (Vi+Vr) will become greater than (Vi - Vr) & vice versa. # Thus the net operating torque tends to increase as the two systems tends to be more in phase with each other. # Whether net torque is in the operating direction (T>0) or in the restraining direction (T<0) will also depend on the relative magnitudes of k op & kr In all ijs relays kr is designed to be greater than kop # So the net torque goes from restraining to operating at some angular separation that is smaller than 90 degrees. # This angle is called the closing angle. # Some ijs relays have fixed closing angle while others have closing angles that are adjustable. The operating time of the ijs is determined by two factors , 1Strength & position of the permanent drag magnet that the acts on the disk to slow its motion. 2- Rotary distance that the disk has to travel to close the contacts. //- Since kr > kop, if only one voltage is applied to the relay the T will be –ve &the relay contacts will be held open. //-This is apparent from eqn.3 //-With neither voltage applied, the net electrical T is Zero, but the spring will keep the contacts of the relay open. //-Thus , in order for the ijs relay to close its contacts, there must be voltage present on both sides of the circuit breaker, & the phase angle between these voltages must be within the closing angle setting the relay. //-This means that the synchronism check unit by itself will not permit picking up a dead line. -----Some models of the ijs include these dead line & dead bus aux. (Vi + Vr) iliry devices , while others do not. OPERATING CHARACTERISTIC OF IJS Internal connections for IJS There are several different model of ijs relays. IJS51A FEATURES & BENEFITS OF IJS Telephone type relay units available. Mechanical targets available. APPLICATION OF IJS RELAYS These relays find application wherever slow-speed synchronism check for automatic or manual closing of a line terminal is required. Synchronism time delay. Instantaneous bus & line undervoltage. OPERATING PRINCIPLES OF GXS // High speed device with a lock out feature. This relay is comprised of three units. 1- time delay (T) induction disk unit similar to that in the ijs relay 2- instantaneous (i) induction cup voltage unit. Provides the closing angle. 3- a dc-operated auxiliary lockout unit (x) for indicating to the circuit breaker. contd. Torque equn. is same as ijs relay T=kop(Vi +Vr)2-kr(Vi-Vr)2 The only diff. is in kop & kr These constants are such that the closing angle of the disk unit is appx. 85 degrees. Other diff. apparent from equn., is the strength of the drag magnet. # In GXS, the drag magnet is weak so that the unit operates quit a bit faster than the IJS. Instantaneous cup unit # like the disk unit # connected to receive both running (bus) & incoming (line) voltages. #Electrical torque developed Te=k vivr sin Ø where k =design constant vi=magnitude of incoming voltage vr=magnitude running voltage Ø =angle by which vr leads vi Suppose for a condition where vr leads vr by say 30 degrees , then Te=0.5 k vivr If vi leads vr by same degrees then, Te= - 0.5 k vivr Thus Te at rated voltage proportional to the sine of the angular separation of the two voltages, but the direction of the torque will depend on which voltage is leading. The contact assembly as shown in the next slide The cup shaft is fastened to the lever arm plate so that they rotate together. A spring with adjustable tension A spring with adjustable tension is provided so that Te is equal to mechanical torque of the spring (ks) Now equn.4 becomes ks = k vi vr sin Ø --------->>(5) This equn. Shows that the calibration of the instantaneous cup unit is dependent on the applied voltages. The GXS12A relay also includes a dc-operated auxiliary unit. This has a time delay pick-up of about six cycles, & it is incorporated in the relay to provide a lockout feature. This relays depend upon the fixed closing angle at which the relay is set & the cut-off-frequency diff. of the voltages applied to the relay. The max. slip for which the relay will permit closing may be approximated from the curves34 by taking the following steps: 1>read the operating time of the disk unit from the curve of phase angle diff. that is same as the closing angle 2>repeat 1 above for the zero phase angle curve. 3>calculate the avg. time from the results of 1 & 2 above. 4>divide twice the closing angle setting of the cup unit by 360 times the time calculated in 3 above. The result is max. slip cycles per second for which the relay could permit closing. Another important cha. Is that from fig.21 , The magnitudes of the applied voltages have a significant effect on the actual closing angle, & that the higher the closing angle setting, the greater is this effect. FETURES OF GXS 10 to 45 degree closing angle adjustment. 10 to 99 cycles time delay adjustment. APPLICATION OF GXS Used in high-speed automatic reclosing on transmission lines. Hydraulic turbine-driven generators. Internal combustion driven generators. Tie line or bus-tie circuits. CONCLUSION It is reliable & efficient. It is applicable to other fields such as hydraulics etc.. Cost is less & maintenance is also less. And always useful in power system. ….. REFERENCES www.GEindustrial.com/Multilin www.GEindustrial.com/pm