Process and apparatus for the reduction of surges in switch-on current in the operation of a rotary current load

• US 5,642,025 A
• Filed: 03/01/1994
• Issued: 06/24/1997
• Est. Priority Date: 03/09/1993
• Status: Expired due to Fees

• Current Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Original Assignee: Fraunhofer Gesellschaft Zur Foerderung Der Angewandten Forsching E.V.
• Inventors: Freitag, Stefan, Konstanzer, Michael
• Primary Examiner(s): Sircus, Brian
• Application Number:
  US08/203,374
• Time in Patent Office: 1,211 Days
• Field of Search: 318/254, 318/138, 318/439, 318/778-784, 318/807-817, 323/321, 323/238
• US Class Current: 318/778
• CPC Class Codes: H02H 9/002 limiting inrush current on switching on of inductive loads subjected to remanence, e.g. transformers

Abstract

A method for reduction of switch-on surges while operating an inductive rry current load is described, having a magnetizable core and three windings arranged in different connection patterns to a rotary current alternating network. A phase angle control unit provides at least a temporary phase operation of the voltages between the lines of the windings. The arrangement includes core sectors allocated to a winding being brought to pre-determined state of magnetization, at least two of three voltages between the lines of the windings having unipolar voltage halfwaves reduces to at least half their voltage-time surface being connected successively to the rotary current load according to the present phase shift of the voltages between the lines. After at least the duration of a length of one period of the last applied voltage between the lines, one of the three voltages having an effective value raised to one desired value or up to the nominal value of the remain voltage remaining switched on and then the other two phases also having a raised effective value being switched on in sequence.

Claims

1. A method for reduction of switch-on surges while operating an inductive rotary current load having a magnetizable core having core sectors allocated to three windings arranged in different connections on a rotary current alternating network, with a phase angle control unit which provides at least a temporary phase operation of voltages between the lines of the windings, said method comprising the steps of:

bringing said core sectors to a predetermined state of magnetization, at least two of three voltages between the lines of the windings having unipolar voltage halfwaves reduced to at least half their voltage-time surface being connected successively to said rotary current load according to a present phase shift of said voltages between the lines, and after at least the duration of a length of one period of the last applied voltage between the lines, one of said three voltages having an effective value raised to one desired value or up to a nominal value of a main voltage remaining switched on and then the other two phases also having a raised effective value being switched on in sequence.

2. A method according to claim 1, wherein said unipolar voltage halfwaves reduced to at least half their voltage-time surface being reduced in one sector corresponding to a phase angle of approximately 135°

to approximately 90°

with approximately a sinusiodal main voltage.

3. A method according to claim 1, wherein said three core sectors being magnetized in a same-direction, respectively rectified, magnetic flux in at least two of said core sectors.

4. A method according to claim 1, wherein, said windings are delta-connected windings arranged side by side on an iron core, having current flowing through successively first the windings arranged on outer limbs of said core and then the winding arranged on a center limb.

5. A method according to claim 1, wherein effective voltages applied to the windings during the premagnetization phase being increased from a switch-on timepoint to an effective voltage corresponding to unipolar voltage halfwaves cut at approximately 90°

.

6. A method according to claim 1, wherein, said windings are delta-connected windings arranged side by side on an iron core, outer windings being successively applied with respective voltages between the lines having homopolar, unipolar voltage halfwaves reduced to half their voltage-time surface, and after the duration of at least a length of one period of the last applied voltage between the lines, one of the two voltages between the lines remaining switched on following one of these voltage halfwaves having a reduced effective value, respectively of a reduced current flow angle, and the other two voltages between the lines also having a reduced current flow angle, respectively, a reduced effective value being switched on successively.

7. A method according to claim 1, wherein, in the case of windings selectively delta-connected or star-connected on the primary side, all three voltages between the lines being connected successively and corresponding to a present phase shift unipolar and having a reduced effective value to their respective, allocated windings for premagnetization of the core, and subsequently, after a duration of at least the length of one period of the last applied voltage between the lines, one voltage between the lines remaining switched on following one of said voltage halfwaves having a reduced effective value, respectively of a reduced current flow angle, and the other two voltages between the lines being switched on successively also with a reduced current flow angle, respectively of a reduced effective value.

8. A method according to claim 1 wherein in the case of said winding connected on the primary side to form a star having a center point line, all three windings being connected successively to the respective strand voltage between a phase and said center point line for premagnetization of the core.

9. An apparatus for reduction of a switch-on current surge of an inductive rotary current load having a magnetizable core operated as a rotary current transformer, said apparatus comprising:

servo components comprising alternating current switches connected to a phase angle control in the phase branches for carrying out a method according to any one of claims 1 to 8, wherein said servo components being provided in at least two phase branches and said servo components being connected like said phase angle control to a sequence control for switching on and off said servo components during premagnetization of the core sectors to predetermined values as well as for subsequent consistent switching on said servo components and for triggering said phase angle control in the sense of changing of the phase angle from approximately 135°

to approximately 90°

during the premagnetization to smaller phase angles in the directly following phase of operation.

10. An apparatus according to claim 9, wherein said sequence control being designed with preferably a steadily increasing current flow angle, respectively a decreasing phase angle to a setable end value from approximately a 135°

to approximately 90°

phase angle for connecting said inductive rotary current load to the rotary current alternating network from a switch-on moment.

11. An apparatus according to claim 9, further comprising by a detection device having a sequence control for temporally staggered flowing of current during the individual phases in dependence of the allocation of the servo components to the respective windings and voltages between the lines.

12. An apparatus according to claim 9, wherein said servo components being provided with mechanical contacts as well as semiconductor switches which can be bridged by said contacts.