CA1147839A - Method for switching in a three-phase high voltage circuit - Google Patents
Method for switching in a three-phase high voltage circuitInfo
- Publication number
- CA1147839A CA1147839A CA000319268A CA319268A CA1147839A CA 1147839 A CA1147839 A CA 1147839A CA 000319268 A CA000319268 A CA 000319268A CA 319268 A CA319268 A CA 319268A CA 1147839 A CA1147839 A CA 1147839A
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- Prior art keywords
- phase
- switch
- switching
- high voltage
- time
- Prior art date
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Abstract
ABSTRACT
A method for interrupting an inductive load in a three-phase, high voltage network by means of a switch having a quick dielectric recovery, in particular a vacuum switch, in which upon interruption two of the three switching paths, having a quick dielectric recovery, open at least 1/3 of a cycle of the network frequency later than the first switching path, augmented with the minimum arcing time in the first switching path, in order to present high over voltages, caused by virtual chopping.
A method for interrupting an inductive load in a three-phase, high voltage network by means of a switch having a quick dielectric recovery, in particular a vacuum switch, in which upon interruption two of the three switching paths, having a quick dielectric recovery, open at least 1/3 of a cycle of the network frequency later than the first switching path, augmented with the minimum arcing time in the first switching path, in order to present high over voltages, caused by virtual chopping.
Description
A msthod for Qwitching in a three-phase high voltage circuit.
The invention relates to a method for interrupting an inductive load in a three-phase high voltage network by means of a switch having a quick dielectric recover~.
It has been found that upon interruption of an induct-ive load in a three-phase high voltage networX, sometimes high overvoltages occur on the load to be interrupted.
Since these overvoltages may cause considerably damage to the network due to insulation breakdown and the like, several investigations have been made in order to discover the likely cau~es of these high overvoltages. ~rom these investigations it has become apparent that these high ovçr-voltages occur onl~ when in the pertaining circuit at least one of a number of conditions is fulfilled, the most import-ant ones of which being:
1. Switching should be performed by switches having a quick dielectric recovery; this condition being fulfilled by vacuum switches.
The invention relates to a method for interrupting an inductive load in a three-phase high voltage network by means of a switch having a quick dielectric recover~.
It has been found that upon interruption of an induct-ive load in a three-phase high voltage networX, sometimes high overvoltages occur on the load to be interrupted.
Since these overvoltages may cause considerably damage to the network due to insulation breakdown and the like, several investigations have been made in order to discover the likely cau~es of these high overvoltages. ~rom these investigations it has become apparent that these high ovçr-voltages occur onl~ when in the pertaining circuit at least one of a number of conditions is fulfilled, the most import-ant ones of which being:
1. Switching should be performed by switches having a quick dielectric recovery; this condition being fulfilled by vacuum switches.
2. The requirement of a predetermined network con-stellation; this implying among others the presence of a sufficient capacitance between the phases on both the source side and the load side of the switch.
3. ~he switching time should be such that upon separation of the contact members one pole of the switch is close to a zero current passage.
~, .
' 1~47839 U on interruption of a load under the above conditions, in the first phase interrupted at zero current passage an overvoltage will occur that may result in re-ignitions in this phase. Under the prevailing circumstances the current 5 resultin~ from these re-ignitions and having a very high frequency will be entirely or partially superi~posed on the network current in both the other phases which although alread~ being interrupted still carry current. When the rssultant of the superimposed current and the network curre~
10 in these pha~es becomes about zero both the other phases will also be interrupted. Since, however, at the re-ignition moment the network current in the first phase causing the re-ignitions is close to a zero current passage, the momentary current value in both the other phases is relativ-15 ely high, this resulting in a so-called high current chop-ping. In the literature this chopping of the relatively high current is generally called "virtual chopping". In view of the fact that at this "virtual chop?ing" the di/dt-value i9 high, very high overvoltages may occur in the 20 installation at "virtual chopping".
In a publication by M. Murano et al, "~hree-phase simultaneous interruption in int~rupting inductive current using vacuum switches", I.E.E.E. ~ran3ætions on Power Apparatus Systems, Jan./Febr. 1974, pages 272-280, concern-25 ing the phenomenon "virtual chopping" it has been proposedto include a resistance in series with a capacitance in parallel to the load between the phases and ground. This, however, entails the drawback that the resistance and capacitance values have to be adapted to the pertaining 30 circuit and the load to be interrupted, this solution more-over being rather expensive in case of high currents.
Another method referred to in the above publication employs a non-linear resistance the high cost of which is likewise of disadvantage.
A further method employs surge suppressors in order to restrict the detrimental results of "virtual chopping".
This method, however, also entails the drawback of relativ-ely high expenses accompagnied by the fact that the surge suppressors have to be installed as close as possible to the load.
~he abovementioned methods have furthermore in common that they are only operative under those network conditions for which they have been designed. Upon a change in these conditions one shall therefore have to adapt the method to this change. Furthermore the abovementioned methods have in c~mmon that they have not been directed to the prevention of "virtual chopping" but only to a protection against the result~ thereof.
A better method will therefore be complete prevention of "virtual chopping". ~his may be achieved by the provision of not fulfilling one of the abovementioned three conditjons for the occurrence of "virtual chopping".
If one wishes to profit by the specific advantages of a vacuum switch the first condition will ~et have to be met.
For eliminating the second condition the conductors connect-ed to both the source side and the load side of the switchhav~ to be completely shielded with respect to each other.
In practice, however, such appears to be a difficult and expen~ive task.
Finally the occurrence of condition 3 may be obviated by synchronizin~ the switching time with respect to the zero current passage in such a manner that the sep~ration of the contact members does not happen close to zero current passage. However, such likewise incurs the use of complicat-ed and expensive devices.
Now the object of the invention is to provide a switch-ing method for preventin the "virtual chopping" in a simple and consequently inexpensive manner irrespective of the net-work conditions. The invention therefore provides a switch-ing method of the above mentioned type having the character-istic that upon interruption two of the three switching paths hsving a quick dielectric recovery open at least 1/3 :
.
, ~147839 of a cycle of the network frequency later than the first switching path augmented with the minimum arcing time in the first switching path.
~ his switching me~hod guaranties that under no circum-stances "virtual chopping" is possible anymore.
~ he invention further~ore provides a switch machanism capable of preventing"virtual chopping". ~his switch mechanism is characterized by means whereby upon inter-ruption, the oprning of one switching path is initiated earlier than both the other switching paths in such a manner that between the time on which the first switching path i5 opened and the time on which both the other switch-ing paths are opened an interval is provided corresponding to at least 1/3 of a cyclè of the network frequency.
The invention will now be described in detail with referen¢e to the accompanying drawing.
Fig. 1 represents a simplified switching diagram for elucidating the switching method according to the invention;
Fig. 2 represents an oscillogram of the situation in which upon opening of one switching path or pole the current in the pertaining phase is interrupted at the next zero ¢urrent pa~sage;
Fig. 3 represents an oscillogram of the situation in which upon opening of a switching path or pole the current in the pertaining phase is not interrupted at the next zero current passage, In ~ig, 1 the switch and the load have been indicated by the reference letters K and L, respectivel~, the phases by R, S and ~ and the accessory switching paths of the switch by reference numerals 1, 2 and 3, re~pectively, It is now assumed that the switching path 1 of the phase R opens at an earlier time than the switching paths 2 and 3 of the phases S and ~, that is to say with an interval ~2 equa~ng or surpassing 1/3 of a cycle of the network frequency augmented with the minimum arcing time of the ~147839 switch at the current conduc~ive to "virtual chopping".
In ~ig. 2 a border-line case has been disclosed in which "virtual chopping" might occur, that is to say the situation in which the opening time t1 corresponding to the 5 opening of the switching path 1 has been selected such that between this point t1 and the next æero current passage at time t2 f the phase R the interval T1 is provided, said interval equaling the minimum arcing time of the switch.
The switching paths 2 and 3 of the phases S and T are open-10 ed at time t3 between which points t3 and t1 the above-mentioned interval ~2 is provided.
~ow two situations are conceivable, i.e.:
a) ~he situation represented by Fig. 2 in which the current in the phase R is interrupted at the first zero currsnt passage after opening the switching path 1, that is to say at point t2.
b) ~he situation represented by Fig. 3 in which the current in the phase R is not interrupted at the first zero current passage after opening the switching path 1.
In the situation a) no "virtual chopping" can occur be¢ause at point t3 the other switching paths 2 and 3 of the pha~e~ S and ~, respectively, are yet closed, this implying accordingly, ~Jfulfilment of one of the conditions for the "virtual chopping", i.e. the simultaneous three-phase 25 switchin~. Upon opening of the switching path~ 2 and 3 on point t~ the currents in these phases will be interrupted simultaneously in the known manner, that is to sa~ at point t4. ~hus when the opening time t1 of the switching path 1 is moved to an earlier point, i.e. when the interval batween 30 t1 and t2 extends beyond the interval ~1' the current in the pha~e R will be certainly interrupted at the point t2, because the arcing time of the switching path 1 is longer than the minimum arcing time T1 of the switch so that also in these situations "virtual chopping" appears to be im-~5 possible.
If, however, as shown for situation b) the current inthe phase R is not interrupted at point t2 this current will only be interrupted at the next zero current passage, that is at the point t4 as indicated in ~ig. 3. The other switch-ing paths 2 and 3 will then be opened at time t3, suchimplying for the switching path 2 that the opening occurs ~ust upon a zero current passage of the pertaining phase S.
Consequentl~ the phases S and ~ will in the known way simultaneously o~ly be interrupted at point t5. If the i~terruption of the current in the phase R will occur at point t4 as de~cribed above, there will be no "virtual chopping" because at that point the opening between the contact members of the switching path 1 has become sufficiently large to prevent re-ignition. Now when retardi~
the opening time t1 f the switching path 1, i.e. the interval between t1 and t4 becoming smaller the switching path R will always be interrupted at point t4 until this intsrval doe~ become so short that in fact the course re-presented by situation a) occurs again. It i9 evident that in case of situation a) in similar manner, upon setting point t1 at an accruing earlier time this situation a) i8 transposed in situation b). Where the situations a) and b) delimit the borders of the area conduc-ive to "virtual chopping", it has been demonstrated above that the switching method according to the invention eliminates the "virtual chopping" phenomenon.
Summarizing it may be remarked that in all the above-mentioned situations the current in the switching path opened first is also interrupted first a a time at which either both the other switching paths are yet closed or the switching path opened first has already been opened so far that no "virtual chopping" is possible anymore. As a matter of fact of course the above described situations also apply when one of the two other switching paths is opene,d first 3~ whereas the result of the switching method is also ~epend-..
` 1147839 ent from the phase order of the three phase current network.
The method according to the invention thus provides a-switching method conducive to switching under various situa-tions without the occurrence of "virtual chopping" and without requiring special measures apart from the simple adaptation of the switch. In practice this switching method may be realized by modifying the switching mechanisms of the switch in such a manner that upon interruption one switching path opens earlier at the above indicated time than both the other switching paths. It is self-evident that the switching-on may he performed in the normal way simultaneously for each of the three switching paths.
In Figure 1, a control mechanism 4 is illustrated which controls the opening of the switches 1, 2 and 3 so as to open the switch 1 at a given time and to open the two remaining swltches 2 and 3 at a time subsequent to said given time equal to a greater than at least one-third of the period of the three-phase high voltage network frequency plus the minlmum arclng time of the switch 1. One mechanism well ~ulted for adaptation for use as the mechanism 4 has been descrl~ed ln Dutch patent application 76.06848 published December 15, 1977 and the corresponding United States patent no. 4,119,820 dated October 10, 1978. The mechanism needs only modification in such a manner that the cam disks con-trolling the switching-on and interruption actuate two switching paths simultaneously whereas the third switching path is separately actuated by a separate or displaced cam disk. This separate cam disk may have such a configuration that the pertaining switching path is interrupted by means thereof at the desired time before the interruption of the - other two switching paths. The switching-on can remain unchanged.
It goes without saying that the switch according to the invention is not restricted to the said switch.
D
~, .
' 1~47839 U on interruption of a load under the above conditions, in the first phase interrupted at zero current passage an overvoltage will occur that may result in re-ignitions in this phase. Under the prevailing circumstances the current 5 resultin~ from these re-ignitions and having a very high frequency will be entirely or partially superi~posed on the network current in both the other phases which although alread~ being interrupted still carry current. When the rssultant of the superimposed current and the network curre~
10 in these pha~es becomes about zero both the other phases will also be interrupted. Since, however, at the re-ignition moment the network current in the first phase causing the re-ignitions is close to a zero current passage, the momentary current value in both the other phases is relativ-15 ely high, this resulting in a so-called high current chop-ping. In the literature this chopping of the relatively high current is generally called "virtual chopping". In view of the fact that at this "virtual chop?ing" the di/dt-value i9 high, very high overvoltages may occur in the 20 installation at "virtual chopping".
In a publication by M. Murano et al, "~hree-phase simultaneous interruption in int~rupting inductive current using vacuum switches", I.E.E.E. ~ran3ætions on Power Apparatus Systems, Jan./Febr. 1974, pages 272-280, concern-25 ing the phenomenon "virtual chopping" it has been proposedto include a resistance in series with a capacitance in parallel to the load between the phases and ground. This, however, entails the drawback that the resistance and capacitance values have to be adapted to the pertaining 30 circuit and the load to be interrupted, this solution more-over being rather expensive in case of high currents.
Another method referred to in the above publication employs a non-linear resistance the high cost of which is likewise of disadvantage.
A further method employs surge suppressors in order to restrict the detrimental results of "virtual chopping".
This method, however, also entails the drawback of relativ-ely high expenses accompagnied by the fact that the surge suppressors have to be installed as close as possible to the load.
~he abovementioned methods have furthermore in common that they are only operative under those network conditions for which they have been designed. Upon a change in these conditions one shall therefore have to adapt the method to this change. Furthermore the abovementioned methods have in c~mmon that they have not been directed to the prevention of "virtual chopping" but only to a protection against the result~ thereof.
A better method will therefore be complete prevention of "virtual chopping". ~his may be achieved by the provision of not fulfilling one of the abovementioned three conditjons for the occurrence of "virtual chopping".
If one wishes to profit by the specific advantages of a vacuum switch the first condition will ~et have to be met.
For eliminating the second condition the conductors connect-ed to both the source side and the load side of the switchhav~ to be completely shielded with respect to each other.
In practice, however, such appears to be a difficult and expen~ive task.
Finally the occurrence of condition 3 may be obviated by synchronizin~ the switching time with respect to the zero current passage in such a manner that the sep~ration of the contact members does not happen close to zero current passage. However, such likewise incurs the use of complicat-ed and expensive devices.
Now the object of the invention is to provide a switch-ing method for preventin the "virtual chopping" in a simple and consequently inexpensive manner irrespective of the net-work conditions. The invention therefore provides a switch-ing method of the above mentioned type having the character-istic that upon interruption two of the three switching paths hsving a quick dielectric recovery open at least 1/3 :
.
, ~147839 of a cycle of the network frequency later than the first switching path augmented with the minimum arcing time in the first switching path.
~ his switching me~hod guaranties that under no circum-stances "virtual chopping" is possible anymore.
~ he invention further~ore provides a switch machanism capable of preventing"virtual chopping". ~his switch mechanism is characterized by means whereby upon inter-ruption, the oprning of one switching path is initiated earlier than both the other switching paths in such a manner that between the time on which the first switching path i5 opened and the time on which both the other switch-ing paths are opened an interval is provided corresponding to at least 1/3 of a cyclè of the network frequency.
The invention will now be described in detail with referen¢e to the accompanying drawing.
Fig. 1 represents a simplified switching diagram for elucidating the switching method according to the invention;
Fig. 2 represents an oscillogram of the situation in which upon opening of one switching path or pole the current in the pertaining phase is interrupted at the next zero ¢urrent pa~sage;
Fig. 3 represents an oscillogram of the situation in which upon opening of a switching path or pole the current in the pertaining phase is not interrupted at the next zero current passage, In ~ig, 1 the switch and the load have been indicated by the reference letters K and L, respectivel~, the phases by R, S and ~ and the accessory switching paths of the switch by reference numerals 1, 2 and 3, re~pectively, It is now assumed that the switching path 1 of the phase R opens at an earlier time than the switching paths 2 and 3 of the phases S and ~, that is to say with an interval ~2 equa~ng or surpassing 1/3 of a cycle of the network frequency augmented with the minimum arcing time of the ~147839 switch at the current conduc~ive to "virtual chopping".
In ~ig. 2 a border-line case has been disclosed in which "virtual chopping" might occur, that is to say the situation in which the opening time t1 corresponding to the 5 opening of the switching path 1 has been selected such that between this point t1 and the next æero current passage at time t2 f the phase R the interval T1 is provided, said interval equaling the minimum arcing time of the switch.
The switching paths 2 and 3 of the phases S and T are open-10 ed at time t3 between which points t3 and t1 the above-mentioned interval ~2 is provided.
~ow two situations are conceivable, i.e.:
a) ~he situation represented by Fig. 2 in which the current in the phase R is interrupted at the first zero currsnt passage after opening the switching path 1, that is to say at point t2.
b) ~he situation represented by Fig. 3 in which the current in the phase R is not interrupted at the first zero current passage after opening the switching path 1.
In the situation a) no "virtual chopping" can occur be¢ause at point t3 the other switching paths 2 and 3 of the pha~e~ S and ~, respectively, are yet closed, this implying accordingly, ~Jfulfilment of one of the conditions for the "virtual chopping", i.e. the simultaneous three-phase 25 switchin~. Upon opening of the switching path~ 2 and 3 on point t~ the currents in these phases will be interrupted simultaneously in the known manner, that is to sa~ at point t4. ~hus when the opening time t1 of the switching path 1 is moved to an earlier point, i.e. when the interval batween 30 t1 and t2 extends beyond the interval ~1' the current in the pha~e R will be certainly interrupted at the point t2, because the arcing time of the switching path 1 is longer than the minimum arcing time T1 of the switch so that also in these situations "virtual chopping" appears to be im-~5 possible.
If, however, as shown for situation b) the current inthe phase R is not interrupted at point t2 this current will only be interrupted at the next zero current passage, that is at the point t4 as indicated in ~ig. 3. The other switch-ing paths 2 and 3 will then be opened at time t3, suchimplying for the switching path 2 that the opening occurs ~ust upon a zero current passage of the pertaining phase S.
Consequentl~ the phases S and ~ will in the known way simultaneously o~ly be interrupted at point t5. If the i~terruption of the current in the phase R will occur at point t4 as de~cribed above, there will be no "virtual chopping" because at that point the opening between the contact members of the switching path 1 has become sufficiently large to prevent re-ignition. Now when retardi~
the opening time t1 f the switching path 1, i.e. the interval between t1 and t4 becoming smaller the switching path R will always be interrupted at point t4 until this intsrval doe~ become so short that in fact the course re-presented by situation a) occurs again. It i9 evident that in case of situation a) in similar manner, upon setting point t1 at an accruing earlier time this situation a) i8 transposed in situation b). Where the situations a) and b) delimit the borders of the area conduc-ive to "virtual chopping", it has been demonstrated above that the switching method according to the invention eliminates the "virtual chopping" phenomenon.
Summarizing it may be remarked that in all the above-mentioned situations the current in the switching path opened first is also interrupted first a a time at which either both the other switching paths are yet closed or the switching path opened first has already been opened so far that no "virtual chopping" is possible anymore. As a matter of fact of course the above described situations also apply when one of the two other switching paths is opene,d first 3~ whereas the result of the switching method is also ~epend-..
` 1147839 ent from the phase order of the three phase current network.
The method according to the invention thus provides a-switching method conducive to switching under various situa-tions without the occurrence of "virtual chopping" and without requiring special measures apart from the simple adaptation of the switch. In practice this switching method may be realized by modifying the switching mechanisms of the switch in such a manner that upon interruption one switching path opens earlier at the above indicated time than both the other switching paths. It is self-evident that the switching-on may he performed in the normal way simultaneously for each of the three switching paths.
In Figure 1, a control mechanism 4 is illustrated which controls the opening of the switches 1, 2 and 3 so as to open the switch 1 at a given time and to open the two remaining swltches 2 and 3 at a time subsequent to said given time equal to a greater than at least one-third of the period of the three-phase high voltage network frequency plus the minlmum arclng time of the switch 1. One mechanism well ~ulted for adaptation for use as the mechanism 4 has been descrl~ed ln Dutch patent application 76.06848 published December 15, 1977 and the corresponding United States patent no. 4,119,820 dated October 10, 1978. The mechanism needs only modification in such a manner that the cam disks con-trolling the switching-on and interruption actuate two switching paths simultaneously whereas the third switching path is separately actuated by a separate or displaced cam disk. This separate cam disk may have such a configuration that the pertaining switching path is interrupted by means thereof at the desired time before the interruption of the - other two switching paths. The switching-on can remain unchanged.
It goes without saying that the switch according to the invention is not restricted to the said switch.
D
Claims (3)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method for interrupting power to an inductive load sup-plied from a three-phase high voltage network using a vacuum switch having quick dielectric recovery characteristics in each phase of the high voltage network, comprising the steps of:
opening the vacuum switch in a first phase at a given time; and opening the two remaining vacuum switches at a time sub-sequent to said given time equal to or greater than at least one-third of the period of the three-phase high voltage network frequency plus the minimum arcing time of the vacuum switch in the first switch path.
opening the vacuum switch in a first phase at a given time; and opening the two remaining vacuum switches at a time sub-sequent to said given time equal to or greater than at least one-third of the period of the three-phase high voltage network frequency plus the minimum arcing time of the vacuum switch in the first switch path.
2. A method as claimed in claim 1, wherein said two remaining vacuum switches are opened substantially with one another.
3. A switch mechanism for interrupting power to an inductive load, supplied from a three-phase high voltage network com-prising vacuum switches having quick dielectric recovery characteristics in each phase of the high voltage network, characterized by a control mechanism which opens one of the vacuum switches in a first phase at a given time and opens the two remaining vacuum switches at a time subsequent to said given time equal to or greater than at least one-third of the period of the three-phase high voltage network frequency plus the minimum arcing time of the vacuum switch in the first switch path.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000319268A CA1147839A (en) | 1979-01-08 | 1979-01-08 | Method for switching in a three-phase high voltage circuit |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000319268A CA1147839A (en) | 1979-01-08 | 1979-01-08 | Method for switching in a three-phase high voltage circuit |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1147839A true CA1147839A (en) | 1983-06-07 |
Family
ID=4113264
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000319268A Expired CA1147839A (en) | 1979-01-08 | 1979-01-08 | Method for switching in a three-phase high voltage circuit |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1147839A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5119260A (en) * | 1989-02-22 | 1992-06-02 | Siemens Aktiengesellschaft | Method for operating a circuit-breaker |
-
1979
- 1979-01-08 CA CA000319268A patent/CA1147839A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5119260A (en) * | 1989-02-22 | 1992-06-02 | Siemens Aktiengesellschaft | Method for operating a circuit-breaker |
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