GB2159673A - Alternator protection and control - Google Patents
Alternator protection and control Download PDFInfo
- Publication number
- GB2159673A GB2159673A GB08510697A GB8510697A GB2159673A GB 2159673 A GB2159673 A GB 2159673A GB 08510697 A GB08510697 A GB 08510697A GB 8510697 A GB8510697 A GB 8510697A GB 2159673 A GB2159673 A GB 2159673A
- Authority
- GB
- United Kingdom
- Prior art keywords
- voltage
- alternator
- difference
- reactive component
- grid
- 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.)
- Granted
Links
- 230000005611 electricity Effects 0.000 claims abstract description 17
- 230000005284 excitation Effects 0.000 claims abstract description 10
- 238000000034 method Methods 0.000 claims description 14
- 238000012544 monitoring process Methods 0.000 claims description 4
- 230000001419 dependent effect Effects 0.000 claims 1
- 238000002955 isolation Methods 0.000 description 4
- 230000008569 process Effects 0.000 description 3
- 230000008859 change Effects 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 230000004075 alteration Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 230000008676 import Effects 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
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
- H02H7/06—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 dynamo-electric generators; for synchronous capacitors
- H02H7/062—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 dynamo-electric generators; for synchronous capacitors for parallel connected generators
Landscapes
- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Control Of Eletrric Generators (AREA)
Abstract
To detect disconnection of a local alternator from the grid supply and, in that event, to isolate it, the excitation of the alternator is controlled to reduce any difference 26 between a monitored value of a reactive component 42 of the electricity supplied by the alternator and a predetermined value. The predetermined value is selected 14,20 to be a value which cannot occur naturally in the event of a disconnection of the grid supply from the alternator system. The difference signal from 26 controls the excitation of the alternator. If the difference, in a sense in which the actual value of the reactive component would move in the event of a disconnection of the grid supply from the alternator system, is not reduced to less than a predetermined difference within a predetermined time period as detected by timer 44, the alternator system is isolated from the grid by relay 46. <IMAGE>
Description
SPECIFICATION
Alternator control
The invention reiates to alternator control.
Alternators, driven by a steam turbine, a gas turbine or diesel engine and located on an industrial site for example, are often used to supply electricity in parallel with a relatively large electricity supply system such as the public supply system (usually termed "the grid") to reduce the amount of power taken from the grid. Under such circumstances, it is essential to detect a disconnection of the grid supply from the alternator system to avoid damage to the alternator and its drive equipment. The damage can arise from the out-ofphase synchronisation of the alternator system and the grid which is likely to occur upon indiscriminate reconnection of the grid supply to the alternator system by the manual or automatic operation of circuit breakers in the grid.
In alternator systems in which the alternator is relatively small and does not normally export power to the grid (i.e. it only reduces the amount of power imported from the grid), the disconnection of the grid from the alternator system can often be detected by detecting the export of power to the grid. Such detection can be used to isolate the alternator system from the grid before the indiscrimate reconnection of the grid supply to the alternator system can occur.
However, the detection of the disconnection of the grid supply from the alternator system in systems in which the alternator is of a size such that it normally exports power to the grid has become a more frequent requirement.
The frequency of the electricity in the grid slowly changes with time owing to changes in load on the grid. When an alternator system is connected in parallel with a grid, because the alternator system is in synchronism with the grid supply, the changes in frequency in the alternator system are dictated by the grid supply and are relatively slow. However, if the alternator system is not connected to the grid supply, i.e. the grid supply has been disconnected therefrom, such changes of frequency occur relatively rapidly because changes in load affect the smaller alternator system to a greater extent.
The relatively rapid changes in frequency can be used to effect isolation of the alternator system from the grid as is described and claimed in our co-pending application No. 85 10695 (Applicants' reference AP-AL 1 343A).
However, as mentioned therein, changes in frequency occur when the load changes but, under certain circumstances, a load external to the alternator system can result in an insufficient change of frequency occuring which would result in the alternator system not being isolated from the grid. Additionally, if the grid is relatively small, the frequency changes therein may be relatively rapid and cause spurious isolation of the alternator system from the grid.
According to the invention, a method of operating an alternator system which is connected in parallel with a grid comprises monitoring the system to determine a reactive component of the electricity supplied by the alternator of the system, comparing the monitored value of the reactive component with a predetermined value of the reactive component to determine any difference therebetween, said predetermined value being selected to be a value which cannot occur naturally in the event of a disconnection of the grid supply from the system, controlling the excitation of the alternator to reduce any such difference and if any such difference, in a sense in which the actual value would move in the event of a disconnection of the grid supply from the system, is not reduced to less than a predetermined difference within a predetermined time period, isolating the system from the grid.
Preferably, the method comprises isolating the system only if the system is substantially not importing power from the grid.
Preferably, the method comprises monitoring the link between the system and the grid to determine the reactive component of the electricity supplied by the alternator.
According to another aspect of the invention, an alternator system which is connected in parallel with a grid comprises apparatus for determining whether there is any difference between a monitored actual value and a predetermined value of a reactive component of the electricity supplied by the alternator of the system, said predetermined value being selected to be a value which cannot occur naturally in the event of a disconnection of the grid supply from the system and for providing a signal proportional to any such difference to a controller which controls the excitation of the alternator and for providing a signal to operate timer means if any such difference, in a sense in which the actual value would move in the event of a disconnection of the grid supply from the system, is greater than a predetermined difference and means operable to isolate the alternator system from the grid if the timer means operates for a predetermined time period.
According to a further aspect of the invention, apparatus as defined in the preceding paragraph.
Apparatus will now be described to illustrate the invention by way of example only with reference to the accompanying drawing which is a schematic circuit diagram of apparatus in accordance with the invention.
The apparatus has a processor means 10 for generating DC outputs proportional to the true power (KW) and the reactive voltamperes (kVAr) supplied by the alternator of an alternator system which is connected in parallel to a grid; two potentiometers 12, 14; two summing amplifiers 16, 18, three potentiometers 20, 22, 24 for presetting DC voltages; three comparators 26, 28, 30; and an AND gate 32.
A voltage transformer 34 and current transformers 36 connected to the phases of the electricity supply 38 from the alternator provides inputs for the processor means 10. The processor means 10 electronically simulates the twowattmeter method of determining power. The means 10 processes the inputs to give a DC voltage at an output 40, the voltage at the output 40 being proportional to kW and processes the inputs, including phase shifting the voltage signals by 90o, to give a
DC voltage at an output 42, the voltage at the output 42 being proportional to kVAr.
The output 40 is connected directly to one side on each of the potentiometers 12, 14 and, via a unity gain inverterl3 , to the opposite side of the potentiometers 12, 14.
The output 40 is also connected to an input of the comparator 30.
The output 42 is connected to inputs of the comparators 26, 28, respectively.
The outputs of the potentiometers 12, 14 are connected to inputs of the summing amplifiers 16, 18, respectively. The other inputs of the amplifiers 16, 1 8 are connected to the potentiometers 20, 22, respectively, and the outputs of the amplifiers 16, 18 are connected to the other inputs of the comparators 26, 28, respectively.
The other input of the comparator 30 is connected to the potentiometer 24.
The output of the comparator 26 is connected to a controller (not shown) for controlling the excitation of the alternator.
The outputs of the comparators 28 and 30 are connected to respective inputs of the gate 32. The output of the gate 32 is connected to a presetable timer 44 which can operate a relay 46 which in turn operates circuit-breakers to isolate the alternator system from the grid.
In operation, the potentiometers 14 and 20 are set to values which will result in the kVAr of the electricity supplied by the alternator being at a predetermined level which cannot occur naturally if the grid supply is disconnected from the system. The potentiometers 14 and 20 can be set to give a constant kVAr, or to represent a constant power factor, or a variable power factor.
The potentiometers 12 and 22 are set to values which will result in a signal from the summing amplifier 18 which is a predetermined difference from the signal from the summing amplifier 1 6 in a sense in which the
DC voltage from the output 42 will move if the grid supply is disconnected from the alternator.
The use of potentiometers 20, 22 ensures that the predetermined value of kVAr is not set on the zero lines, i.e. no export or import of power to or from the system, since that is a permitted condition. The potentiometer 24 is set to ensure that the system has to be positively importing power from the grid to prevent isolation of the system from the grid.
For example, the predetermined value of kVAr could be 50 kVAr leading and the predetermined difference could be 25 kVAr.
Accordingly, the signal from the summing amplifier 1 8 will be equivalent to a kVAr value of 25 kVAr leading since, upon a disconnection of the grid from the alternator, the actual value of kVAr will try to go lagging.
The inputs of the comparator 28 has links 48 so that they can be reversed if the value of the predetermined difference of kVAr is in the opposite sense, for example the actual kVAr would increase from the predetermined value.
The timer 44 ensures that the alternator system is not isolated from the grid owing to transitory excursions of the value of the actual kVAr to values which would result in isolation.
Such transitory excursions can occur through grid voltage variations or factory load changes, for example. The delay can be of the order of several seconds, for example seven seconds, so that the alternator system can correct the actual kVAr value back to within the predetermined difference from the predetermined value of kVAr.
The voltage and current transformers 34, 36 are preferably located on the link between the system and the grid as is shown in the drawing. It is possible to locate them elsewhere in the system. However, because of local load fluctuations such alternative locations are not desirable and may require that a less favourable predetermined value of the reactive component be used. Additionally, it would not be possible to determine whether the system is importing electricity from the grid in the manner described above and alternative ways of deriving a signal equivalent to the signal from the comparator 30 would have to be used. For example, a comparison could be made of the amount of power generated by the alternator and the amount of power consumed by the site load to determine whether power is being imported to the system.
In a modification (not shown), the apparatus could be arranged to isolate the system from the grid whether or not the system is importing power from the grid. In that instance, the apparatus described above would be modified by the omission of potentiometer 24, comparator 30 and AND gate 32, the comparator 28 being connected directly to the timer 44.
Although the apparatus derives control signals based on kW and kVAr, the alteration of the excitation of the alternator results in a change in the reactive current of the system since the alternator voltage is fixed. It would be possible within the scope of the invention to derive control signals using inphase current and reactive current by using a processing means 10 adapted to process the inputs thereto in an appropriate manner.
Claims (14)
1. A method of operating an alternator system which is connected in parallel with a grid comprising monitoring the system to determine a reactive component of the electricity supplied by the alternator of the system, comparing the monitored value of the reactive component with a predetermined value of the reactive component to determine any difference therebetween, said predetermined value being selected to be a value which cannot occur naturally in the event of a disconnection of the grid supply from the system, controlling the excitation of the alternator to reduce any such difference and if any such difference, in a sense in which the actual value would move in the event of a disconnection of the grid supply from the system, is not reduced to less than a predetermined difference within a predetermined time period, isolating the system from the grid.
2. A method according to claim 1, which comprises isolating the system only if the system is substantially not importing power.
3. A method according to claim 1 or claim 2, which comprises monitoring the link between the system and the grid to determine the reactive component of the electricity supplied by the alternator.
4. A method according to claim 1, which comprises:
(a) determining a true power component and the corresponding reactive component of the electricity supplied by the alternator;
(b) deriving first and second DC voltages proportional to the true power and the reactive component, respectively;
(c) (i) summing a proportion of the first voltage with a first preset DC voltage to obtain a third voltage representing said predetermined value of the reactive component;,
(ii) comparing the third voltage with the second voltage to determine any difference therebetween; and
(iii) using the resultant voltage representing said difference in said step of controlling the excitation of the alternator;
(d) (i) summing a proportion of the first voltage with a second preset DC voltage to obtain a fourth voltage representing a value of reactive component, the difference between the third and fourth voltages representing said predetermined difference; and
(ii) comparing the second voltage with the fourth voltage to determine whether the difference between the actual and the predetermined reactive component is greater than said predetermined difference and, if it is, obtaining a signal; and
(e) if said signal is obtained, operating timer means which, if operated for said predetermined time period, initiates said isolating step.
5. A method according to claim 2 or claim 3 as dependent on claim 2, which comprises:
(a) determining a true power component and the corresponding reactive component of the electricity supplied by the alternator;
(b) deriving first and second DC voltages proportional to the true power component and the reactive component, respectively;
(c) (i) summing a proportion of the first voltage with a first preset DC voltage to obtain a third voltage representing said predetermined value of the reactive component;
(ii) comparing the third voltage with the second voltage to determine any difference therebetween; and
(iii) using the resultant voltage representing said difference in said step of controlling the excitation of the alternator;
(d) (i) summing a proportion of the first voltage with a second preset DC voltage to obtain a fourth voltage representing a value of reactive component, the difference between the third and the fourth voltages representing said predetermined difference; and
(ii) comparing the second voltage with the fourth voltage to determine whether the difference between the actual and the predetermined reactive component is greater than said predetermined difference and, if it is, obtaing a first signal;
(e) comparing the first voltage with a third preset DC voltage to determine whether the system is substantially not importing power from the grid and, if it is not, obtaining a second signal; and
(f) if both of said first and second signals are obtained together, operating timer means which, if operated for said predetermined time period, initiates said isolating step.
6. A method according to any preceding claim, in which the reactive component is the reactive volt-amperes.
7. An alternator system which is connected in parallel with a grid comprising apparatus for determining whether there is any difference between a monitored actual value and a predetermined value of a reactive component of the electricity supplied by the alternator of the system, said predetermined value being selected to be a value which cannot occur naturally in the event of a disconnection of the grid supply from the system and for providing a signal proportional to any such difference to a controller which controls the excitation of the alternator and for providing a signal to operate timer means if any such difference, in a sense in which the actual value would move in the event of a disconnection of the grid supply from the system, is greater than a predetermined difference and means operable to isolate the alternator system from the grid if the timer operates for a predetermined time period.
8. An alternator system according to claim 7, in which said apparatus comprises means for generating first and second DC voltages at first and second outputs, respectively, proportional to a true power component and a reactive component of the electricity supplied by the alternator, respectively, first and second proportioning means, first and second summing means, first and second presetable
DC voltage supply means and first and second comparator means, said first and second proportioning means being connected between said first output of the generating means and first inputs of said first and second summing means, said first and second summing means having second inputs connected to said first and second DC voltage supply means and outputs connected to first inputs of said first and second comparator means, respectively, said first and second comparator means having second inputs connected to said second output of the generating means and outputs connected to said controller and to said timer means, respectively.
9. An alternator system according to claim 7, in which said apparatus comprises means for generating first and second DC voltages at first and second outputs, respectively, proportional to a true power component and a reactive component of the electricity supplied by the alternator respectively first and second proportioning means first and second summing means, first, second and third comparator means and an AND gate means, said first and second proportioning means being connected between said first output of the generating means and first inputs of said first and second summing means, said first and second summing means having second inputs connected to said first and second DC voltage supply means and outputs connected to first inputs of said first and seoond comparator means, respectively, said first and second comparator means having second inputs connected to said second output of the generating means and outputs connected to said controller and to a first input of said gate means, respectively, said third comparator having a first and second inputs connected to said first output of said generating means and to said third DC voltage supply means, respectively, for determining whether the system is substantially not importing power, said third comparator having an output connected to a second input of said gate means, the output from which is connected to said timer means.
10. Apparatus as claimed in claim 8.
11. Apparatus as claimed in claim 9.
12. A method accordinq to claim 1 substantially as hereinbefore described with reference to the accompanying drawing.
1 3. An alternator system according to claim 7 substantially as hereinbefore described with reference to the accompanying drawing.
14. Apparatus according to claim 10 substantially as hereinbefore described with reference to the accompanying drawing.
1 5. Apparatus according to claim 11 substantially as hereinbefore described with reference to the accompanying drawing.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB848412857A GB8412857D0 (en) | 1984-05-19 | 1984-05-19 | Alternator control |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB8510697D0 GB8510697D0 (en) | 1985-06-05 |
| GB2159673A true GB2159673A (en) | 1985-12-04 |
| GB2159673B GB2159673B (en) | 1988-03-09 |
Family
ID=10561221
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB848412857A Pending GB8412857D0 (en) | 1984-05-19 | 1984-05-19 | Alternator control |
| GB08510697A Expired GB2159673B (en) | 1984-05-19 | 1985-04-26 | Alternator protection and control |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB848412857A Pending GB8412857D0 (en) | 1984-05-19 | 1984-05-19 | Alternator control |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB8412857D0 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2317759A (en) * | 1996-09-13 | 1998-04-01 | Univ Belfast | Identifying loss of mains in electricity distribution system |
-
1984
- 1984-05-19 GB GB848412857A patent/GB8412857D0/en active Pending
-
1985
- 1985-04-26 GB GB08510697A patent/GB2159673B/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2317759A (en) * | 1996-09-13 | 1998-04-01 | Univ Belfast | Identifying loss of mains in electricity distribution system |
| GB2317759B (en) * | 1996-09-13 | 2000-06-14 | Univ Belfast | Loss of mains protection relay |
Also Published As
| Publication number | Publication date |
|---|---|
| GB8510697D0 (en) | 1985-06-05 |
| GB2159673B (en) | 1988-03-09 |
| GB8412857D0 (en) | 1984-06-27 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 19980426 |