GB1587652A - Safety device for rectifier plant - Google Patents

Safety device for rectifier plant Download PDF

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Publication number
GB1587652A
GB1587652A GB1413977A GB1413977A GB1587652A GB 1587652 A GB1587652 A GB 1587652A GB 1413977 A GB1413977 A GB 1413977A GB 1413977 A GB1413977 A GB 1413977A GB 1587652 A GB1587652 A GB 1587652A
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GB
United Kingdom
Prior art keywords
contactor
current
rectifier
welding
mains
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Expired
Application number
GB1413977A
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Individual
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Individual
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
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Publication date
Application filed by Individual filed Critical Individual
Priority to GB1413977A priority Critical patent/GB1587652A/en
Publication of GB1587652A publication Critical patent/GB1587652A/en
Expired legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H7/00—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions
    • H02H7/10—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers
    • H02H7/12—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers
    • H02H7/125—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for rectifiers
    • H02H7/1255—Emergency protective circuit arrangements specially adapted for specific types of electric machines or apparatus or for sectionalised protection of cable or line systems, and effecting automatic switching in the event of an undesired change from normal working conditions for converters; for rectifiers for static converters or rectifiers for rectifiers responsive to internal faults, e.g. by monitoring ripple in output voltage
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K9/00—Arc welding or cutting
    • B23K9/0061—Underwater arc welding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K9/00—Arc welding or cutting
    • B23K9/10—Other electric circuits therefor; Protective circuits; Remote controls
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
    • H02H3/00—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection
    • H02H3/50—Emergency protective circuit arrangements for automatic disconnection directly responsive to an undesired change from normal electric working condition with or without subsequent reconnection ; integrated protection responsive to the appearance of abnormal wave forms, e.g. ac in dc installations

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Plasma & Fusion (AREA)
  • Mechanical Engineering (AREA)
  • Arc Welding Control (AREA)

Description

(54) SAFETY DEVICE FOR RECTIFIER PLANT Where priority as provided by subsection (2) or (3) of Section 5 is desired in respect of one or more provisional specifications, quote No. or Nos and date or dates.
(71) I, FRANZ HIRSCHMANN, of 93 High View Road, London, W.13, a British Subject, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The invention refers to solid state electric rectifier plant which is to be used under hazardous conditions involving a risk to the operator, if one or more of the components of the plant should fail. Such conditions occur with the use of solid state rectifiers for arc welding, in particular, when welding under water where the operator is positioned in an electric field produced by the voltage gradient between the workpiece and the lead carrying the current to the welding torch.
The measured resistance of a diving suit is reported to be in the order of 2000 ohms; it can usually not be avoided that a small current flows through the body of the operator who reports that he can feel as a slight shock any changes of the welding current, as for instance when striking the arc.
Object of the invention is a safety device which affords protection to the operator without introducing components which increase the risk in case of their failure.
The human body is more sensitive to alternating current than to direct current, because the alternating current can produce a cramp of the muscles at a level which is lower than that of a dangerous d.c. current.
Another object of the invention is a safety device which reduces the risk of a dangerous alternating current.
According to one aspect of the invention in an electric arc welding plant, in which the welding current is supplied by a static rectifier fed from an alternating current supply over a contactor, there is provided a device which monitors the a.c. components of the d.c. output voltage and trips the contactor if this component exceeds a set critical value.
It is known to provide on welding rectifiers the devices which disconnects the plant if asymmetric phase load indicates faulty diodes. Such devices which are intended to protect the still sound diodes against overloading will not prevent a plant from supplying a voltage with a large a.c. component, until they are loaded, and will therefore not give the operator the protection given according to the invention.
With a three-phase rectifier fitted with semi-conductor diodes the 6th harmonic of the output voltage is only about 4.2% of the d.c. voltage and therefore no more than a few volts. This a.c. component can increase if one or more diodes go open circuit, perhaps through thermal fatigue. The device, according to the invention, will take account of such a condition which although unlikely cannot be completely excluded.
With some welding processes, in particular, welding with a consumable electrode under a gas shield, the metal is transferred in drops which cause a temporary short circuit or at least a considerable reduction of the arc voltage, and the output voltage of a static welding rectifier used for such a process may include a certain superimposed a.c. voltage which itself may not mean a risk to the operator. The safety device according to the invention will then be fitted with means for changing the critical a.c.
voltage component according to the d.c.
load, e.g. by reducing the a.c. voltage which could result in tripping of the mains contactor, if that a.c. voltage is small compared to the d.c. voltage. A device according to the invention might be built up of a step up transformer with an earthed screen between the primary and secondary windings. The secondary winding, with a larger number of turns, is connected to a relay or an equivalent switching device, the normally closed contacts of which are connected in series with the operating coil of the mains contactor. This transformer would transfer hardly any voltage from its secondary winding connected to the relay, into the primary winding connected to the output of the welding rectifier, even if the secondary winding of the transformer, by some accident received an a.c. voltage.
The safety device according to the invention can be combined with one of those known devices which reduce the no-load voltage of the plant and pass the full output voltage of the rectifier only when the welding operation is started. To be used in connection with the invention such a device should, however, not introduce any asymmetry which could cause the safety device to trip. The additional equipment could consist of a second mains contactor connecting the static rectifier to the mains through symmetrical chokes, and a current relay in series with the output of the welding plant which causes the closing of the mains contactor if the operator touches the workpiece with the welding electrode, and makes a small current flow. The voltage which occurs on the output of the rectifier between the workpiece and electrode, when the auxiliary contactor is closed, but when the mains contactor is still open, should in the interest of safety be very small and it can therefore only produce a very small signal current, although the current relay must be able to take without damage a very high welding current. Such a relay could be connected over a so-called d.c. current transformer. This consists of a small reactor saturated by d.c. current, with the magnetising current of the reactor changing according to the d.c. saturation.
With an electric arc welding plant in which the welding current is supplied by a static rectifier fed from an alternating current 3 phase supply over a contactor and where there is provided a current relay closing the contactor when a low voltage auxiliary supply feeds the load, it is possible to achieve the aims of the invention in an alternative way by a differential relay, which compares the phase current of the 3 phase supply and prevents the closing of the contactor at an unbalance of the currents. Such a relay will still prevent the plant from supplying its normal output voltage, if that output voltage would contain a large a.c.
component.
The invention can be used for welding rectifiers which are installed above or below water level. With rectifiers installed above water level, e.g. on board ship, the voltage drop over long cables leading to the welding site may make it necessary to use welding plant with a high output voltage, thereby increasing the risk arising from an a.c. component of that voltage.
An example of the invention is shown in the drawing. The rectifier 1 which consists of the transformers 2 and the diodes 3 is connected to the three phase mains 4 by the contactor 5. The rectifier 1 is connected by cables 6 to the workpiece 7 and the welding electrode 8. A transformer 17 with a primary winding with a low number of turns, is connected to the output of the rectifier 3.
Its secondary feeds the relay 18, the normally closed contacts of which are connected in series with the operating coil 9 of the mains contactor 5 and the contacts of the differential delay 10. The differential relay is fed from current transformers 11 connected between the rectifier and its mains supply. An auxiliary contactor 12 connects the rectifier 1 to the mains 4 over chokes 13. When the electrode 8 touches the workpiece 7, a current relay 14 operates and completes the circuit for the coil 9 of the contactor 5, keeping the contactor 5 closed as long as the rectifier is loaded. If one of the diodes fails by going open circuit or by becoming conductive in both directions, one of the relays 18 and 10 or both, will cause the mains contactor to open immediately.
The auxiliary contactor 12 and the mains contactor 5 will be fitted with the usual control circuits for manual operation and with holding contacts, not shown in the drawing; these will prevent the mains contactor closing again on its own if it has been tripped. After the mains contactor has been tripped known circuitry may be used to trip the auxiliary contactor and block reconnection until special measures are taken by the operator. A warning light, not shown, may indicate the occurrence of a failure.
WHAT I CLAIM IS: 1. Electric arc welding plant, in which the welding current is supplied by a static rectifier fed from an alternating current supply over a contactor, wherein there is provided a device which monitors the a.c.
component of the d.c. output voltage and trips the contactor if this component exceeds a set critical value.
2. Electric arc welding plant according to claim 1, with means changing the critical value of the a.c. voltage component according to the d.c. load.
3. Electric arc welding plant according to claim 1 or 2, with a step-up transformer, the primary of which is connected across the rectifier output, and the secondary of which is connected to a relay.
4. Electric arc welding plant according to claim 1 to 3, with a current relay closing the contactor when a low voltage auxiliary supply feeds the load.
5. Electric arc welding plant, in which the welding current is supplied by a static rectifier fed from an alternating current 3 phase supply over a contactor, wherein there is provided a current relay closing the contactor when a low voltage auxiliary supply
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. primary winding connected to the output of the welding rectifier, even if the secondary winding of the transformer, by some accident received an a.c. voltage. The safety device according to the invention can be combined with one of those known devices which reduce the no-load voltage of the plant and pass the full output voltage of the rectifier only when the welding operation is started. To be used in connection with the invention such a device should, however, not introduce any asymmetry which could cause the safety device to trip. The additional equipment could consist of a second mains contactor connecting the static rectifier to the mains through symmetrical chokes, and a current relay in series with the output of the welding plant which causes the closing of the mains contactor if the operator touches the workpiece with the welding electrode, and makes a small current flow. The voltage which occurs on the output of the rectifier between the workpiece and electrode, when the auxiliary contactor is closed, but when the mains contactor is still open, should in the interest of safety be very small and it can therefore only produce a very small signal current, although the current relay must be able to take without damage a very high welding current. Such a relay could be connected over a so-called d.c. current transformer. This consists of a small reactor saturated by d.c. current, with the magnetising current of the reactor changing according to the d.c. saturation. With an electric arc welding plant in which the welding current is supplied by a static rectifier fed from an alternating current 3 phase supply over a contactor and where there is provided a current relay closing the contactor when a low voltage auxiliary supply feeds the load, it is possible to achieve the aims of the invention in an alternative way by a differential relay, which compares the phase current of the 3 phase supply and prevents the closing of the contactor at an unbalance of the currents. Such a relay will still prevent the plant from supplying its normal output voltage, if that output voltage would contain a large a.c. component. The invention can be used for welding rectifiers which are installed above or below water level. With rectifiers installed above water level, e.g. on board ship, the voltage drop over long cables leading to the welding site may make it necessary to use welding plant with a high output voltage, thereby increasing the risk arising from an a.c. component of that voltage. An example of the invention is shown in the drawing. The rectifier 1 which consists of the transformers 2 and the diodes 3 is connected to the three phase mains 4 by the contactor 5. The rectifier 1 is connected by cables 6 to the workpiece 7 and the welding electrode 8. A transformer 17 with a primary winding with a low number of turns, is connected to the output of the rectifier 3. Its secondary feeds the relay 18, the normally closed contacts of which are connected in series with the operating coil 9 of the mains contactor 5 and the contacts of the differential delay 10. The differential relay is fed from current transformers 11 connected between the rectifier and its mains supply. An auxiliary contactor 12 connects the rectifier 1 to the mains 4 over chokes 13. When the electrode 8 touches the workpiece 7, a current relay 14 operates and completes the circuit for the coil 9 of the contactor 5, keeping the contactor 5 closed as long as the rectifier is loaded. If one of the diodes fails by going open circuit or by becoming conductive in both directions, one of the relays 18 and 10 or both, will cause the mains contactor to open immediately. The auxiliary contactor 12 and the mains contactor 5 will be fitted with the usual control circuits for manual operation and with holding contacts, not shown in the drawing; these will prevent the mains contactor closing again on its own if it has been tripped. After the mains contactor has been tripped known circuitry may be used to trip the auxiliary contactor and block reconnection until special measures are taken by the operator. A warning light, not shown, may indicate the occurrence of a failure. WHAT I CLAIM IS:
1. Electric arc welding plant, in which the welding current is supplied by a static rectifier fed from an alternating current supply over a contactor, wherein there is provided a device which monitors the a.c.
component of the d.c. output voltage and trips the contactor if this component exceeds a set critical value.
2. Electric arc welding plant according to claim 1, with means changing the critical value of the a.c. voltage component according to the d.c. load.
3. Electric arc welding plant according to claim 1 or 2, with a step-up transformer, the primary of which is connected across the rectifier output, and the secondary of which is connected to a relay.
4. Electric arc welding plant according to claim 1 to 3, with a current relay closing the contactor when a low voltage auxiliary supply feeds the load.
5. Electric arc welding plant, in which the welding current is supplied by a static rectifier fed from an alternating current 3 phase supply over a contactor, wherein there is provided a current relay closing the contactor when a low voltage auxiliary supply
feeds the rectifier, and a differential relay comparing the phase currents of the 3 phase supply which prevents the closing of the contactor at an unbalance of the currents.
6. Electric arc welding plant according to claim 1 to 5, with means blocking the reclosure of the tripped contactor.
7. The use of the electric arc welding plant according to claim 1 to 6 for underwater welding.
GB1413977A 1978-05-30 1978-05-30 Safety device for rectifier plant Expired GB1587652A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB1413977A GB1587652A (en) 1978-05-30 1978-05-30 Safety device for rectifier plant

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB1413977A GB1587652A (en) 1978-05-30 1978-05-30 Safety device for rectifier plant

Publications (1)

Publication Number Publication Date
GB1587652A true GB1587652A (en) 1981-04-08

Family

ID=10035720

Family Applications (1)

Application Number Title Priority Date Filing Date
GB1413977A Expired GB1587652A (en) 1978-05-30 1978-05-30 Safety device for rectifier plant

Country Status (1)

Country Link
GB (1) GB1587652A (en)

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2539342A1 (en) * 1983-01-14 1984-07-20 Framatome Sa Arc welding rig control
EP0286951A1 (en) * 1987-04-11 1988-10-19 Alcatel SEL Aktiengesellschaft Monitoring circuit for polyphase convertor

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2539342A1 (en) * 1983-01-14 1984-07-20 Framatome Sa Arc welding rig control
EP0286951A1 (en) * 1987-04-11 1988-10-19 Alcatel SEL Aktiengesellschaft Monitoring circuit for polyphase convertor

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PS Patent sealed
PCNP Patent ceased through non-payment of renewal fee