Tripping Current and Short Circuit Current of High Voltage Tester

Transcription

1 Tripping Current an Short Circuit Current of igh oltage Teter Xu hezhun Wang Keqin Abtract: Tripping current an hort circuit current are iportant technical pecification of high voltage teter, an frequently require to be verifie accoring to the tipulation of relevant tet tanar uring laboratory aeent. owever, it i in ifficulty to verify the hort circuit current by irect eaureent becaue of the exitence of overloa protection. A inirect calculation etho for hort circuit current i introuce in thi article Key wor:. igh voltage teter, Tripping current, Short circuit current, verification. Introuction Accoring to tanar IEC60335-:00 claue 3.3, the high-voltage ource ue for the tet i to be capable of upplying a hort circuit current I between the output terinal after the output voltage ha been ajute to the appropriate tet voltage. The overloa releae of the circuit i not to operate for any current below the tripping current I r. The value of I an I r are given in table 5 for variou high-voltage ource. Tet voltage a Table 5 Characteritic of high-voltage ource Miniu current A I I r < an < an NOTE The current are calculate on the bai of the hort circuit an releae energie of 800 A an 400 A repectively at the upper en of the voltage range a The eaureent uncertainty of the tet voltage i not to excee During laboratory aeent, it i frequently require to how the ocuentation that the high voltage ource ue for the tet ha the capability of upplying a hort circuit current I of 00A. Many laboratorie are puzzle about it, becaue there i ifficulty to eaure the hort circuit current irectly for the reaon that the overloa releae of the high voltage teter operate when the tripping current reache.

2 . Theoretic analyi. Typical contruction of high voltage teter Figure give the block iagra of a coon ue high voltage teter, oel TOS5050 (anufacture by KIKUSI, Japan). It coprie of 6 block: Relay, oltage regulator,.. tranforer, Output terinal, Current etector, an Control circuit. AC line Relay oltage regulator.. tranforer k Output terinal Control circuit Current etector Fig. Block iagra of TOS5050. Equivalent oel of high voltage ource The high voltage ource i generate by oltage regulator, an boote by.. tranforer. The equivalent circuit of.. tranforer i hown in figure, where an are terinal of low voltage an high voltage, an I are output voltage an current of high voltage terinal which have been converte to the low voltage terinal. The output power of the high voltage ource i given by the equivalent circuit a: P out = I = I () where, I are actual output voltage an current of high voltage terinal. Uner the cae of hort circuit of high voltage terinal, the output current i given a: I = () ( + ) + where, i the input voltage of the low voltage terinal of the.. tranforer, naely the output voltage of the oltage regulator. i the leakage ipeance of the priary wining of the.. tranforer, an i the leakage ipeance of the econary wining of the.. tranforer, which ha been converte to the priary wining. i the agnetic fiel exciting ipeance of the.. tranforer. an: = r jx = k + = r + jx = r + jx (3) k i the converting ratio of.. tranforer, of typical value /5 an /50. For the reaon that the leakage ipeance of the tranforer i extreely all in

3 coparion with the agnetic fiel exciting ipeance, <<, an a a reult: = k << the forula for the calculation of the hort circuit current can be iplifie a: I (4) + I = k (5) I Figure 3 give the iplifie equivalent circuit uner the conition of hort circuit of output terinal. r jx r' jx' ' I r I' I' ' ' jx Fig. Equivalent circuit of.. tranforer Fig. 3 Siplifie equivalent circuit.3 Tripping current I r an hort circuit current I Equation () how the output power of high voltage ource of output voltage an output current I P out i the prouct, the. For certain output voltage output current I i eterine by the output power of.. tranforer P out. Accoringly, uner the conition of et tet voltage, the tripping current of the high voltage ource lie on the axiu output power of the.. tranforer. For a high voltage teter with appropriate output tet voltage, the requireent for the tripping current i the tipulation for the capacity of the high voltage ource, e.g., a tripping current of 00A i tipulate for a high voltage teter with the highet tet voltage of 5k, the capacity of the.. tranforer of the teter houl be at leat 500A. It i itinct fro equation (4), for certain output voltage of oltage regulator, the hort circuit output current of high voltage terinal I i invere proportion to the value of the leakage ipeance of the priary an econary winging of the.. tranforer +. The larger value of ipeance +, the aller current I. Wherefore, the tipulation for the hort circuit output current I i the requireent for the leakage ipeance of the priary an econary wining of the.. tranforer. Suppoing the equivalent ipeance of the evice uner tet (DUT), which ha been converte to the priary wining, i, the output voltage between the high voltage terinal can be erive fro figure a: = + ( + ) + + (6)

4 It inicate, for certain output voltage of oltage regulator, the output tet voltage between the high voltage terinal i relate to the equivalent ipeance of the DUT, the agnetic fiel exciting ipeance, an the leakage ipeance of the priary an econary wining of the.. tranforer an. For ieal tranforer, =, becaue of = = 0. It ean the output tet voltage which ha been converte to the priary wining i equal to the output voltage of the oltage regulator. owever, for general tranforer, the output tet voltage which ha been converte to the priary wining iffer fro the output voltage of the oltage regular accoring to the paraeter,,, an. Figure 4 give the curve of varying veru (uppoe = = % ). '/ /' Fig. 4. Output tet voltage varying v. leakage ipeance of.. tranforer The curve how that ecreae when increae. In the conition that output voltage of the oltage regulator an the equivalent ipeance of the DUT are eterine, the output tet voltage ecreae a leakage ipeance an increae. Two calculation exaple are given fro the curve: -- =0. 90 a 0 05 =., when the leakage ipeance of the wining of the tranforer reache the 5 percent the ipeance of the DUT, the output tet voltage which ha converte to the priary winging rop to the 90 percent of the output voltage of oltage regulator. -- In the tet conition that the require output tet voltage i 5k, an the output current pa through the DUT i 00A, to enure the output tet voltage rop within the liit of 3%, the leakage ipeance of the priary an econary wining of the.. tranforer, which ha been converte to priary wining, hall not excee 0.8Ω, for the typical converting ratio of.. tranforer k = :5. 3. erification of hort circuit current Coonly ue high voltage teter ha the function of overloa current protection. The overloa releae of the circuit operate when the output current reach

5 the tripping current I r. In orer to carry out the irect eaureent of the hort circuit output current, the protective circuit nee to be renere inoperative, which ay reult in aage to the intruent. So, it i in ifficulty to eaure the hort circuit current of the teter irectly. A ubtitute, a ort of inirect eaureent etho of hort circuit current i introuce here. It can be erive fro equation (6): I = + ( + ) + + Equation (7) how, for a given ipeance of DUT, the hort circuit current I i epene on the output voltage of oltage regulator, an the ipeance paraeter of the tranforer. A a general rule,. Uner the conition of a eterine value of, if two eaureent value of output current I with ifferent known DUT ipeance are obtaine, the hort circuit current which ha been converte to the priary wining I S can be eaily calculate with the conition =0. In practice, i electe a the iniu require output tet voltage, for exaple 500. If the tipulate hort circuit current can be outputte uner thi tet voltage, the high voltage teter i capable of upplying require hort circuit current uner any other higher tet voltage. An ajutable reitance with appropriate value an aequate rate power, for exaple one with ax. value not le than 0 kω an with in. power of 00W for 00A current eaureent, i electe a loa ipeance. Two eaureent of current I i carrie out with appropriate reitance of. The converting ratio k of the.. tranforer can be referre to the Uer Manual of the intruent. By following converion: = k ( i the open circuit value) I = I k = k the hort circuit current which ha been converte to the priary wining I S can be calculate, an the actual hort circuit current i given a: I = k S I S Exaple: Table give five group of eaureent ata uner ifferent loa ipeance carrie out on high voltage teter oel TOS505, of which the converting ratio of.. tranforer i k = /5. Two of the five group of the ata are electe for the calculation of equation (7), an the reult are: = =. 89Ω = 88. Ω When = 0, the calculate reult i I S = 36 A. The eaureent an calculation reult how the intruent checke output a hort circuit current of 36A uner the iniu tet voltage of 500. If 00A hort circuit current i (7)

6 require, the iniu output tet voltage hall be not le than 734. Table Output current of high voltage teter oel TOS505 with ifferent loa / (oae) / (Open circuit) I /A oa ipeance /kω / I /A /Ω Concluion Tripping current an hort circuit current are two of the iportant technical pecification of high voltage teter, an relevant tet tanar give appropriate tipulation. Tripping current epen on the capacity of.. tranforer of the high voltage teter, an hort circuit current eterine by the tet voltage an the ipeance paraeter of the.. tranforer. For a high voltage teter incorporating a.. tranforer of 500A, if the range of output tet voltage i 0~5k, the ax. output current i 00A. Tripping current, or the capacity of the.. tranforer can be referre to the technical pecification of the high voltage teter, otherwie, it can be verifie by irect eaureent. owever, becaue of exitence of the function of overloa protection of coonly ue teter, it i in ifficulty to verify the hort circuit current by irect eaureent. A ubtitute, inirect calculation etho can be ue for the verification of hort circuit current.