US4149208A
Expired / Lapsed
US
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Method of and apparatus for ground fault protection of generators connected in parallel
Assignee: BBC Brown Boveri AG Switzerland
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Filing: 1978-02-06
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Granted: 1979-04-10
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Expires: 1998-02-06
Abstract
Abstract A method of, and apparatus for, protecting electrical devices, such as generators connected in parallel against ground faults or shorts, wherein when there arises a ground short at one of the parallely connected generators a ground or earth current (response signal) flows between the fault location and a ground location. The network is grounded at the ground location by means of a ground transformer and a ground resistance. In order to essentially completely detect the ground short the phase of an alternating signal is modulated to produce an alternating injection or test signal which is delivered to the network containing the parallely connected generators. A response signal corresponding to the injection signal and indicative of the ground short is derived from the electrical network. The modulated alternating signal may be at the network frequency and modulation of the phase thereof preferably encompasses continuously switching the phase of the alternating signal between two phase positions in the sense of a phase oscillation. The alternating signal is preferably in the form of an alternating voltage.
Inventors
- 👤 Michael Fiorentzis
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-10-28 18:14
CPC Classifications
H; H02; H02H; H02H7/00; H02H7/06; H02H7/062; H02H3/00; H02H3/16; H02H3/17
Claims Analysis
Total Claims: 26
Claim 1
Independent Claim
92 words
A method of detecting ground shorts in generators connected in parallel in an electrical network, wherein for detecting essentially completely a ground short at one of the parallely connected generators there are carried out the steps of: modulating the phase of an alternating signal to produce an alternating injection signal; delivering the alternating injection signal to the electrical network containing the parallely connected generators; and deriving from the electrical network a response signal corresponding to the alternating injection signal and indicative of the ground short at one of the parallely connected generators.
Claim 2
Independent Claim
92 words
A method of detecting ground shorts in generators connected in parallel in an electrical network, wherein for detecting essentially completely a ground short at one of the parallely connected generators there are carried out the steps of: modulating the phase of an alternating signal to produce an alternating injection signal; delivering the alternating injection signal to the electrical network containing the parallely connected generators; and deriving from the electrical network a response signal corresponding to the alternating injection signal and indicative of the ground short at one of the parallely connected generators.
Claim 3
Dependent Claim
20 words
The method as defined in claim 1, further including the steps of: utilizing as the alternating signal an alternating voltage.
Claim 4
Dependent Claim
31 words
The method as defined in claim 1, wherein the phase modulation comprises the steps of: continuously switching the phase of the alternating signal forming the injection signal between two phase positions.
Claim 5
Dependent Claim
31 words
The method as defined in claim 3, wherein: the phase of the alternating signal forming the injection signal is switched between two phase positions in the sense of a phase oscillation.
Claim 6
Dependent Claim
20 words
The method as defined in claim 1, wherein: the alternating signal which is phase modulated is at the network frequency.
Claim 7
Dependent Claim
31 words
The method as defined in claim 1, further including the steps of: biasing the entire electrical network towards ground by means of the injection signal which is at the network frequency.
Claim 8
Dependent Claim
38 words
The method as defined in claim 1, wherein the phase modulation comprises the steps of: switching the phase of the alternating signal forming the injection signal between two phase positions which are opposite in phase to one another.
Claim 9
Dependent Claim
26 words
The method as defined in claim 7, including the steps of: performing phase switching of the alternating signal during switching periods amounting to about 60 ms.
Claim 10
Dependent Claim
29 words
The method as defined in claim 8, wherein: each of the switching periods encompasses a triggering time of about 45 ms and a remaining time constituting a safety time.
Claim 11
Dependent Claim
32 words
The method as defined in claim 1, wherein: the alternating signal is an alternating voltage, and the amplitude of said alternating injection voltage amounts to about 2% of the network phase voltage.
Claim 12
Independent Claim
263 words
An apparatus for detecting ground shorts in generators connected in parallel in an electrical network comprising: a transformer having two primary windings and a secondary winding for supplying an alternating injection voltage; said secondary winding serving to apply the injection voltage to the electrical network containing the parallely connected generators; a source for producing the injection voltage; said source having a pair of terminals; said source being connected at one terminal with a junction point of both primary windings of the transformer; two electronic switch means having inputs and outputs; said source being connected at its other terminal in parallel with the inputs of said two electronic switch means; a respective output of each of said electronic switch means being connected with the other terminal of a respective one of said primary windings; an oscillator delivering an output signal for alternately opening said electronic switch means; an insulation transformer having a primary winding and a secondary winding; a working resistor connected in parallel with the primary winding of said insulation transformer; said secondary winding of said insulation transformer delivering a response voltage corresponding to the injection voltage and indicative of the ground short; a multiplier having a first input and a second input; said response voltage of the insulation transformer being delivered to the first input of said multiplier; means for applying a voltage constituting a reference signal to the second input of the multiplier; said multiplier having an output carrying an output signal; a filter for carrying out an integration operation; the output signal of the multiplier being delivered to the filter.
Claim 13
Independent Claim
263 words
An apparatus for detecting ground shorts in generators connected in parallel in an electrical network comprising: a transformer having two primary windings and a secondary winding for supplying an alternating injection voltage; said secondary winding serving to apply the injection voltage to the electrical network containing the parallely connected generators; a source for producing the injection voltage; said source having a pair of terminals; said source being connected at one terminal with a junction point of both primary windings of the transformer; two electronic switch means having inputs and outputs; said source being connected at its other terminal in parallel with the inputs of said two electronic switch means; a respective output of each of said electronic switch means being connected with the other terminal of a respective one of said primary windings; an oscillator delivering an output signal for alternately opening said electronic switch means; an insulation transformer having a primary winding and a secondary winding; a working resistor connected in parallel with the primary winding of said insulation transformer; said secondary winding of said insulation transformer delivering a response voltage corresponding to the injection voltage and indicative of the ground short; a multiplier having a first input and a second input; said response voltage of the insulation transformer being delivered to the first input of said multiplier; means for applying a voltage constituting a reference signal to the second input of the multiplier; said multiplier having an output carrying an output signal; a filter for carrying out an integration operation; the output signal of the multiplier being delivered to the filter.
Claim 14
Dependent Claim
15 words
The apparatus as defined in claim 11, wherein: said source operates at the network frequency.
Claim 15
Dependent Claim
22 words
The apparatus as defined in claim 11, wherein: said voltage applying means delivers a reference voltage substantially equal to the network frequency.
Claim 16
Dependent Claim
27 words
The apparatus as defined in claim 11, wherein: said voltage applying means delivers said injection voltage as said reference voltage at the second input of the multiplier.
Claim 17
Dependent Claim
40 words
The apparatus as defined in claim 11, wherein: said voltage applying means supplies a separate signal which is generated essentially in synchronism with the injection voltage and which appears as said reference signal at the second input of the multiplier.
Claim 18
Dependent Claim
14 words
The apparatus as defined in claim 11, wherein: said electronic switch means comprise triacs.
Claim 19
Dependent Claim
23 words
The apparatus as defined in claim 16, wherein: the amplitude of said injection voltage amounts to about 2% of the network phase voltage.
Claim 20
Dependent Claim
18 words
The apparatus as defined in claim 17, wherein: the triacs have switching periods amounting to about 60 ms.
Claim 21
Dependent Claim
49 words
The apparatus as defined in claim 16, wherein: the triacs have switching periods amounting to about 60 ms; said triacs being fired for about 45 ms and the remainder of the time serving as a safety time in order to prevent simultaneous firing of both triacs by disturbance currents.
Claim 22
Dependent Claim
30 words
The apparatus as defined in claim 11, further including: directional relay means for measuring the useful current which flows in the presence of an insulation fault at the electrical network.
Claim 23
Independent Claim
96 words
A method of detecting ground shorts in electrical devices connected in parallel in an electrical network, wherein for detecting essentially completely a ground short at one of the parallely connected electrical devices there are carried out the steps of: modulating the phase of an alternating signal to produce an alternating injection signal; delivering the alternating injection signal to the electrical network containing the parallely connected electrical devices; and deriving from the electrical network a response signal corresponding to the alternating injection signal and indicative of the ground short at one of the parallely connected electrical devices.
Claim 24
Independent Claim
96 words
A method of detecting ground shorts in electrical devices connected in parallel in an electrical network, wherein for detecting essentially completely a ground short at one of the parallely connected electrical devices there are carried out the steps of: modulating the phase of an alternating signal to produce an alternating injection signal; delivering the alternating injection signal to the electrical network containing the parallely connected electrical devices; and deriving from the electrical network a response signal corresponding to the alternating injection signal and indicative of the ground short at one of the parallely connected electrical devices.
Claim 25
Independent Claim
109 words
A method of detecting ground shorts in electrical devices of an electrical network, especially parallely connected generators, wherein for detecting essentially completely a ground short at the electrical device there are carried out the steps of: modulating by means of a modulation function the phase of an alternating signal to produce an alternating injection signal; delivering the alternating injection signal to the electrical network containing the electrical devices at which there is to be detected any ground short; deriving from the electrical network a response signal corresponding to the alternating injection signal; demodulating the response signal to form a signal indicative of the ground short at the electrical device.
Claim 26
Independent Claim
109 words
A method of detecting ground shorts in electrical devices of an electrical network, especially parallely connected generators, wherein for detecting essentially completely a ground short at the electrical device there are carried out the steps of: modulating by means of a modulation function the phase of an alternating signal to produce an alternating injection signal; delivering the alternating injection signal to the electrical network containing the electrical devices at which there is to be detected any ground short; deriving from the electrical network a response signal corresponding to the alternating injection signal; demodulating the response signal to form a signal indicative of the ground short at the electrical device.
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CH446499A
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1982-04-09 | 1982-10-09 | 1983-04-10 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1986-04-09 | 1986-10-09 | 1987-04-10 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1990-04-09 | 1990-10-09 | 1991-04-10 | $7700.00 | Window Closed / Lapsed |