GB2104739A

GB2104739A - Circuit arrangement for coupling and demagnetizing of electromagnets fed by direct current

Info

Publication number: GB2104739A
Application number: GB08223526A
Authority: GB
Inventors: Vaino Karjalainen
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-08-18
Filing date: 1982-08-16
Publication date: 1983-03-09
Also published as: GB2104739B; IT1206146B; NL8203232A; ZA825870B; ES8306284A1; SU1233817A3; NO158767C; ATA306282A; NO822795L; CH658743A5; FI812543L; JPS5842207A; DE3230254A1; SE8204728D0; BE894139A; FR2511806B1; FI66701B; ES515062A0; IT8248994A0; SE8204728L

Abstract

A circuit arrangement for enabling the magnetization and demagnetization of electromagnets operated by direct current utilising the self induction current produced in the coil of the electromagnet has two polarized capacitors (C1, C2) connected in parallel with the coil (L) of an electromagnet (M), the capacitors being series connected such that their like poles are connected to each other and a reverse direction diode (D1, D2) is connected in parallel with each capacitor (C1, C2). The magnetizing voltage charges one of the capacitors (C1) through diode (D1) so that it will not be damaged by the self induction voltage produced in the coil (L) of the electromagnet (M) after the magnetizing current has been cut off, the voltage being opposite to the polarity of the capacitor (C1). The electrical energy produced by self induction in the coil (L) of the electromagnet (M) after the magnetizing current has been cut off will become charged and levelled out into the capacitors (C1, C2), producing a low resistance to the self-induction voltage and thus causing strong demagnetizing current in the coil (L) of the electromagnet (M). In alternative circuits only one diode is used (Figs. 2, 3, not shown), and one or both of the capacitors may be a non-polarised capacitor. <IMAGE>

Description

SPECIFICATION Circuit arrangement for coupling and demagnetizing of electromagnets fed by direct current The present invention relates to a circuit arrangement for the energising of inductances, more especially electromagnets fed by direct current, especially high-power electromagnets, as weli as their de-energising (demagnetizing) by means of their own self-induction current.

From the US-Patent specification No 2,445,459 it is already known that an effective automatic and complete demagnetizing can be achieved by means of a capacitor connected in parallel with a coil of the electromagnet, upon switching off the magnetizing current to said coil.

However, the arrangement shown in said specification has a disadvantage in that unpolarized capacitors of high capacitance are needed, which are large, bulky and expensive, e.g.

when used for coupling arrangements of a highpowered electromagnets.

Therefore the purpose of the invention is to bring about a new and improved arrangement making possible the use of polarized capacitors of relatively small constructional size e.g. electrolytic capacitors as components in suitable circuits for magnetizing and demagnetizing electromagnets fed by direct current, particularly of high-powered electromagnets.

According to the present invention there is provided a circuit arrangement for enabling the coupling and demagnetization of inductances fed by direct current, utilising the current produced by self induction, wherein two capacitors in series with each other are connected in parallel with the inductance and a diode is provided, connected in parallel with one of said capacitors only and an operating switch is provided in the magnetizing circuit for the inductance.

Either polarized or non-polarized capacitors can be used. Where electrolytic capacitors are used, the preferred circuit arrangement is characterized in that the electrolytic capacitors coupled in parallel with the coils of the electromagnet are in series so that their like poles are connected together and a diode is connected in parallel with one or each of the electrolytic capacitors.

Where electrolytic capacitors are used the operation of the circuit arrangement is such that the above-mentioned diodes together with the charges in the electrolytic capacitors prevent the capacitors from becoming charged to a voltage opposite to their polarity under the influence of the excitation and self-induction voltages; consequently the demagnetization. current caused in the coil of the electromagnet by the selfinduction voltage merely increases the voltage in one electrolytic capacitor and cancels it in the other.

The present invention will be described further, by way of example, with reference to the accompanying drawings, in which: Fig. 1 illustrates a circuit, including two diodes, operating in accordance with the method of the present invention; Fig. 1 a illustrates an equivalent circuit to that of Fig. 1; Fig. 2 illustrates a circuit, including one diode, operating in accordance with the method of the present invention; Fig. 2a illustrates an equivalent circuit to that of Fig. 2, and Figs. 3, 4 and 5 voltage/time diagrams relating to the circuit of Fig. 1.

When circuit 1, shown in Fig. 1, is closed by means of switch K, the voltage of current source VL is applied across the poles of coil L of electromagnet M (Fig. 3, T1-T2), and the current going through coil L magnetizes electromagnet M, electrolytic capacitor C, becomes charged through diode D, to a voltage higher than that of current source VL (Fig. 4, T1-T2) and electrolytic capacitor C2 becomes charged under the influence of pulsating direct current through diode D2 to a voltage lower than that of current source VL (Fig. 5, T1-T2). When circuit 1 is switched off by opening Switch K, the energy of electromagnetic field is discharged creating in the coil L of electromagnet M a self induction voltage of opposite polarity to the voltage of current source VL (Fig. 3, T2-T3), which raises the charge in the electrolytic capacitor C2 through diode D2 and electrolytic capacitor C, (Fig. 4, T2-T3) and in the coil L of electromagnet M causes a current opposite to the magnetizing current i.e.

demagnetizing current.

Owing to its resistance in conducting direction, diode D2 is not able to prevent the effect of the demagnetizing current on the charge in the electrolytic capacitor C1, but the charge will be partly cancelled by it (Fig. 4, T2-T3). When demagnetization has taken place similar charges remain in the electrolytic capacitors C, and C2 (Fig. 4 and 5, T3-T4). In cases where the charge in electrolytic capacitor C, is sufficiently high, the same operation can be achieved even without diode D2 (Fig. 2). Depending on the intended use, the electrolytic capacitors C1 and C2, one or both, in circuits according to the present coupling method (Fig. 1, 1 a, 2, 2a), can be replaced by non-polarized capacitors. The switch K of the circuit can be a contact switch, transistor, thyristor or another type of switch.

The present coupling method is suitable for the coupling and demagnetizing of various inductances, more especially electromagnets fed by direct current.

Claims

1. A circuit arrangement for enabling the coupling and demagnetization of inductances fed by direct current, utilising the current produced by self induction, wherein two capacitors in series with each other are connected in parallel with the inductance and a diode is provided, connected in parallel with one of said capacitors only and an

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Circuit arrangement for coupling and demagnetizing of electromagnets fed by direct current The present invention relates to a circuit arrangement for the energising of inductances, more especially electromagnets fed by direct current, especially high-power electromagnets, as weli as their de-energising (demagnetizing) by means of their own self-induction current. From the US-Patent specification No 2,445,459 it is already known that an effective automatic and complete demagnetizing can be achieved by means of a capacitor connected in parallel with a coil of the electromagnet, upon switching off the magnetizing current to said coil. However, the arrangement shown in said specification has a disadvantage in that unpolarized capacitors of high capacitance are needed, which are large, bulky and expensive, e.g. when used for coupling arrangements of a highpowered electromagnets. Therefore the purpose of the invention is to bring about a new and improved arrangement making possible the use of polarized capacitors of relatively small constructional size e.g. electrolytic capacitors as components in suitable circuits for magnetizing and demagnetizing electromagnets fed by direct current, particularly of high-powered electromagnets. According to the present invention there is provided a circuit arrangement for enabling the coupling and demagnetization of inductances fed by direct current, utilising the current produced by self induction, wherein two capacitors in series with each other are connected in parallel with the inductance and a diode is provided, connected in parallel with one of said capacitors only and an operating switch is provided in the magnetizing circuit for the inductance. Either polarized or non-polarized capacitors can be used. Where electrolytic capacitors are used, the preferred circuit arrangement is characterized in that the electrolytic capacitors coupled in parallel with the coils of the electromagnet are in series so that their like poles are connected together and a diode is connected in parallel with one or each of the electrolytic capacitors. Where electrolytic capacitors are used the operation of the circuit arrangement is such that the above-mentioned diodes together with the charges in the electrolytic capacitors prevent the capacitors from becoming charged to a voltage opposite to their polarity under the influence of the excitation and self-induction voltages; consequently the demagnetization. current caused in the coil of the electromagnet by the selfinduction voltage merely increases the voltage in one electrolytic capacitor and cancels it in the other. The present invention will be described further, by way of example, with reference to the accompanying drawings, in which: Fig. 1 illustrates a circuit, including two diodes, operating in accordance with the method of the present invention; Fig. 1 a illustrates an equivalent circuit to that of Fig. 1; Fig. 2 illustrates a circuit, including one diode, operating in accordance with the method of the present invention; Fig. 2a illustrates an equivalent circuit to that of Fig. 2, and Figs. 3, 4 and 5 voltage/time diagrams relating to the circuit of Fig. 1. When circuit 1, shown in Fig. 1, is closed by means of switch K, the voltage of current source VL is applied across the poles of coil L of electromagnet M (Fig. 3, T1-T2), and the current going through coil L magnetizes electromagnet M, electrolytic capacitor C, becomes charged through diode D, to a voltage higher than that of current source VL (Fig. 4, T1-T2) and electrolytic capacitor C2 becomes charged under the influence of pulsating direct current through diode D2 to a voltage lower than that of current source VL (Fig. 5, T1-T2). When circuit 1 is switched off by opening Switch K, the energy of electromagnetic field is discharged creating in the coil L of electromagnet M a self induction voltage of opposite polarity to the voltage of current source VL (Fig. 3, T2-T3), which raises the charge in the electrolytic capacitor C2 through diode D2 and electrolytic capacitor C, (Fig. 4, T2-T3) and in the coil L of electromagnet M causes a current opposite to the magnetizing current i.e. demagnetizing current. Owing to its resistance in conducting direction, diode D2 is not able to prevent the effect of the demagnetizing current on the charge in the electrolytic capacitor C1, but the charge will be partly cancelled by it (Fig. 4, T2-T3). When demagnetization has taken place similar charges remain in the electrolytic capacitors C, and C2 (Fig. 4 and 5, T3-T4). In cases where the charge in electrolytic capacitor C, is sufficiently high, the same operation can be achieved even without diode D2 (Fig. 2). Depending on the intended use, the electrolytic capacitors C1 and C2, one or both, in circuits according to the present coupling method (Fig. 1, 1 a, 2, 2a), can be replaced by non-polarized capacitors. The switch K of the circuit can be a contact switch, transistor, thyristor or another type of switch. The present coupling method is suitable for the coupling and demagnetizing of various inductances, more especially electromagnets fed by direct current. Claims

1. A circuit arrangement for enabling the coupling and demagnetization of inductances fed by direct current, utilising the current produced by self induction, wherein two capacitors in series with each other are connected in parallel with the inductance and a diode is provided, connected in parallel with one of said capacitors only and an operating switch is provided in the magnetizing circuit for the inductance.

2. A circuit arrangement as claimed in claim 1, in which a second diode is provided connected in parallel with the other of said capacitors.

3. A circuit arrangement as claimed in claim 1, in which the capacitors are polarized capacitors, connected in series so that their like poles are connected to each other and a reverse direction diode is connected in parallel with one of said capacitors.

4. A circuit arrangement as claimed in claim 3, in which a reverse direction diode is coupled in parallel with each of said capacitors.

5. A circuit arrangement as claimed in claim 1 or 2, in which both capacitors are non-polarized.

6. A circuit arrangement as claimed in claim 1, in which one of the capacitors is polarized and the other capacitor is non-polarized.

7. A circuit arrangement as claimed in any preceding claim, in which the switch is a contact switch, transistor, thyristor or other suitable type of switch.

8. A circuit arrangement as claimed in any preceding claim wherein said inductance is an electromagnet.

9. A circuit arrangement substantially as herein described with reference to and as illustrated in the accompanying drawings.