WO2019059852A1 - Device and method for measuring electrical current - Google Patents
Device and method for measuring electrical current Download PDFInfo
- Publication number
- WO2019059852A1 WO2019059852A1 PCT/SI2017/000025 SI2017000025W WO2019059852A1 WO 2019059852 A1 WO2019059852 A1 WO 2019059852A1 SI 2017000025 W SI2017000025 W SI 2017000025W WO 2019059852 A1 WO2019059852 A1 WO 2019059852A1
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- current
- current transformer
- windings
- transformer
- winding
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Classifications
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/18—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
- G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
- G01R15/18—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers
- G01R15/183—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers using transformers with a magnetic core
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
- G01R19/0092—Arrangements for measuring currents or voltages or for indicating presence or sign thereof measuring current only
Definitions
- the present invention relates to the field of low and medium voltage conventional current measuring transformers.
- Present invention relates to all types of current transformers.
- only single phase and three phase current transformers are presented.
- Single phase and three phase current transformers are schematically illustrated in Figure 1 and Figure 4. Both figures are an external view of such a current transformer with transparent upper part of transformer.
- Reference 1 on a single phase current transformer and references la/l b/lc on a three phase current transformer represent aperture/apertures which is/are able to receive a cable or bus-bar. Cable or bus-bar is able to pass through transformer aperture/apertures and completely emerge on other side.
- Reference 2 on a single phase current transformer and references 2a/2b/2c on a three phase current transformer represent secondary current terminals to be connected further to protection circuit/auto detection/communication circuit - all protected inside current transformer housing (3 - transparent upper part of current transformer).
- Figure 2 and Figure 5 represent illustrated internal cross-section of the single phase and three phase current transformer.
- Reference 4 on a single phase current transformer (4a/4b/4c on a three phase current transformer) represents magnetic core which surrounds aperture 1 (la/lb/lc on a three phase current transformer).
- Magnetic core is surrounded by a secondary winding 5 (5a/5b/5c on a three phase current transformer).
- Primary cable or bus-bar passing through aperture/apertures, produces a magnetic field in the magnetic core/cores which then induces a proportionally smaller current in the secondary winding/windings.
- Secondary winding/windings is/are connected to secondary current terminals. Amount of inducted current, flowing in the secondary winding (connected to the secondary winding terminals) can then be measured using a separate measuring device.
- Inducted secondary current is proportional to the primary current. Described above are typical single phase and three phase current transformers which have several disadvantages in design: - To connect measuring device to current transformer typically 4 or more terminals (2 on current transformer side, 2 on measuring device side) have to be loosened (in case of three phase current transformer this number goes up to 12). Additionally corresponding amount of cable routing has to be done. Because of this high probability of wiring errors is present which can cause damage to the device or injury to a user. Another disadvantage of all the cable routing and terminals connecting is extensive labor cost.
- Device and method for measuring electrical current for measuring current in different types of current transformer devices (single phase solid core, single phase split core, three phase solid core, Rogowski coil, Hall, DC,...) solves above referenced technical problem by use of protection/auto detection/communication circuit, said protection/auto detection/communication circuit selected from group consisting of voltage divider, single- contact 1-wire EEPROM.
- Figure 3 and Figure 6 showing solution in accordance with this invention represents illustrated internal cross-section of the single phase and three phase current transformer.
- Reference 4 on a single phase current transformer represents magnetic core which surrounds aperture 1 (apertures la/lb/lc on a three phase current transformer).
- Magnetic core is surrounded by a secondary winding 5 (secondary windings 5a/5b/5c on a three phase current transformer).
- Primary cable or bus-bar passing through aperture/apertures, produces a magnetic field in the magnetic core/cores which then induces a proportionally smaller current in the secondary winding/windings.
- Secondary winding/windings is/are connected to at least two secondary current terminals 2 (terminals 2a/2b/2c on a three phase current transformer). Said secondary current terminals 2a (terminals 2a/2b/2c on a three phase current transformer) are connected to protection/auto detection/communication circuit 6. Depending on current transformer type, up to 6 connections 7 are made between protection/auto detection/communication circuit and RJ12 port 8. Everything is enclosed in current transformer housing.
- Present invention focuses on automatic detection of current transformer type and transformation rate. Eliminates the need for configuring measuring device.
- RJ12 port which assures plug and play compatibility with available measuring devices may in some cases present disadvantage due to easy disconnecting of RJ12 connector from RJ12 port. Access to RJ12 connector plugged into RJ12 port has to be protected in order for prevent disconnection by unauthorized personnel.
- Present inventions also relates to sealing protection of RJ12 port for billing certification.
- Present invention also provides for a method for for measuring electrical current, said method comprising the following steps:
- said current transformer either of a single phase or a three phase type, said current transformer further comprising magnetic field producing means selected from the group consisting of primary cable, bus-bar,
- the method according to this invention further comprises step of enclosing device for performing method according to claim 13 in current transfomer housing, and providing for sealing doors for tamper protection of RJ12.
- the method according to this invention further comprises the following steps:
- said first and second winding ends selected from the group consisting of windings ends (20, 21 ) on single phase current transformers, windings ends (20a, 21a, 20b, 21b, 20c,21c) on three phase current transformers,
- device and method for measuring electrical current for measuring current reduce labor costs that occur during physical installation of current transformer and software configuration of current transformer type and transformation rate (on measuring device side).
- Protection/auto detection/communication circuit in connection with RJ12 port on both current transformer and measuring device side zero out any potential damage to current transformer or injury to user, due to wiring error.
- Auto detection/communication circuit is implemented into each current transformer.
- Auto detection/communication circuit is directly connected to RJ12 port which will assure plug and play compatibility with available measuring devices.
- Combination of auto detection/communication circuit, RJ12 port and compatible measuring device further reduce labor costs.
- Current transformer needs only to be connected to measuring device, using single cable with RJ12 connector, everything else is done by auto detection/communication circuit, which provides measuring device with current transformer transformation ratio and transformer type. No other configuration is needed on measuring device side when connecting current transformer.
- Auto detection/communication circuit also enables factory calibration of current transformers. Factory calibration on both current transformer and measuring device drastically improves system accuracy (accuracy of both current transformer and measuring device).
- Figure 9 schematically illustrates a current measurement system according to an embodiment of the present invention.
- FIG. 9 Three different types of current transformers 15/16/17 are shown in figure 9. Only three different types of current transformers are presented on figure 9., but note that present invention relates to all kinds of current transformers.
- Current transformers 15/16/17 connect to measuring device 18 via data cable 14 with RJ12 connectors 13.
- RJ12 ports on both current transformer and measuring device side ensure plug and play compatibility throw-out entire line of current transformers.
- Measuring device 18 auto detects type of current transformer and its transformation rate. Auto detection/communication is possible, due to auto detection/communication circuit in-bodied inside current transformers.
- Measuring device can have up to three RJ12 ports (current inputs). Connecting three phase current transformer to each of the three current inputs on measuring device, results in measurement of nine different primary currents.
- FIG 7 Present invention relates also to sealing protection of RJ12 port, and is schematically illustrated in figure 7. Invention is presented only on single phase current transformer, but relates to all types of current transformers.
- 9 represents single phase current transformer with implemented sealing protection for RJ 12 port. Data cable with RJ12 connector 13 plugs directly to RJ12 port 8.
- RJ12 port 8 is covered by sealing protection doors 12. Both current transformer housing 9 and sealing protection doors 12 have through holes 10/1 1 used for sealing with sealing wire.
- FIG. 7.1 Single phase current transformer 9, with opened sealing protection doors 12. Data cable with RJ12 connector 13 is disconnected from current transformer.
- FIG. 7.2 Single phase current transformer 9, with opened sealing protection doors 12. Data cable with RJ12 connector 13 plugged directly to RJ 12 port 8. RJ12 port 8 is covered by sealing protection doors 12.
- FIG. 7.3 Single phase current transformer 9, with closed sealing protection doors 12. Data cable with RJ 12 connector 13 plugged directly to RJ 12 port 8. RJ 12 port 8 is covered by sealing protection doors 12.
- Figure 8 Top/side/front view of single phase current transformer with opened/closed sealing protection door for RJ12 port is schematically illustrated in Figure 8.
- Auto detection communication circuit also enables factory calibration of current transformers. Factory calibration on both current transformer and measuring device drastically improves system accuracy (accuracy of both current transformer and measuring device)
- Figures 10, 1 1 , 12 and 13 schematically illustrate communication/auto detection circuitry 6 according to an embodiment of the invention.
- Figures 10 and 12 use voltage divider as a tool for obtaining referential voltage upon which transformer type and transformation ratio are determined.
- Figures 11 and 13 use single-contact 1 -wire EEPROM as a tool for obtaining data on transformer type and transformation ratio.
- Single-contact 1-wire EEPROM also provides additional features described in detail below. Each of the Figures is explained in detail below.
- FIG. 10 schematically illustrates communication/auto detection circuitry 6 according to an embodiment of the invention. Visible at the bottom of Figure 10 is the top portion of the magnetic core, with secondary windings 5.
- the winding 5 has ends 20 and 21 , which are connected to the communication/auto detection circuitry 6.
- 8 represents RJ12 connector port, connected to the circuit board 6.
- RJ12 connector port 8 is connected to various points of the communication/auto detection circuitry 6.
- the protection/auto detection/communication circuitry 6 comprises simple voltage divider (also known as potential divider).
- Winding end 20 is connected directly to current signal terminal Ti .
- Winding end 21 is connected directly to ground terminal TGnd- Winding ends 20 and 21 provide the amount of current being driven through the secondary winding 5, and thus the amount of current being driven through the corresponding primary cable or busbar.
- Voltage divider referenced to ground TGnd comprises two resistors 22 connected in series and voltage input connected to Ti unbe. Voltage input Tin applied across the resistor pair 22 results in output voltage Tout emerging from connection between them. Resistor voltage divider is used to create referential voltage on terminal Tout. Each type of transformer will have dedicated resistor pair providing specific footprint (referential voltage) used to determine transformer type and transformation ratio.
- Terminals Ti, TGnd, Tout and Tin are connected to RJ12 connector port 8.
- RJ12 connector port 8 therefore provides current signal, derived from secondary winding 5 at terminal Ti, as well as providing a grounded terminal TGnd, for connection and output to a measurement device.
- measuring device When first pairing measuring device and current transformer, measuring device will provide voltage input Tin to be applied across the resistor pair 22. Depending on the installed resistor pair, specific voltage output Tout is send back to the measuring device. Measuring device determines transformer type and transformation ratio based on voltage output Tout amplitude.
- FIG 11 schematically illustrates protection/auto detection/communication circuitry 6 according to an embodiment of the invention. Visible at the bottom of Figure 1 1 is the top portion of the magnetic core, with secondary windings 5. The winding 5 has ends 20 and 21, which are connected to the communication/auto detection circuitry 6. 8 represents RJ12 connector port, connected to the circuit board 6. RJ12 connector port 8 is connected to various points of the communication/auto detection circuitry 6.
- the communication/auto detection circuitry 6 comprises single-contact 1 -wire EEPROM and pullup resistor. Winding end 20 is connected directly to current signal terminal Ti . Winding end 21 is connected directly to ground terminal TGnd. Winding ends 20 and 21 provide the amount of current being driven through the secondary winding 5, and thus the amount of current being driven through the corresponding primary cable or busbar.
- Single-contact 1-wire EEPROM 23 referenced to ground TGnd provides both communication and power between current transformer and measuring device on a single line connected to Tout. In some cases depending on the EEPROM operation, additional power is required. During these periods of increased power demand, it is important that the voltage on the 1-wire bus does not fall below the device's minimum operating pullup voltage.
- a pull-up resistor 24 is installed between EEPROM communication wire and voltage input Ti n . Communication (reading and writing) over single-conductor 1 -wire bus enables wide variety of operations over current transformers (in connection to measuring device):
- Terminals Ti , TGnd, Tout and Tin are connected to RJ12 connector port 8.
- RJ12 connector port 8 therefore provides current signal, derived from secondary winding 5 at terminal Ti , as well as providing a grounded terminal TGnd, for connection and output to a measurement device.
- measuring device reads data from EEPROM and determines transformer type and transformation ratio. Also based on the calibration data stored on EEPROM, measuring device will accommodate current measurements according to the calibration points.
- Figure 12 schematically illustrates protection/auto detection/communication 6 according to an embodiment of the invention. Visible at the bottom of Figure 12 are the top portions of the magnetic cores, with secondary windings 5a/5b/5c.
- the winding 5a has ends 20a and 21a, which are connected to the communication/auto detection circuitry 6.
- the winding 5b has ends 20b and 21b, which are connected to the communication/auto detection circuitry 6.
- the winding 5 c has ends 20c and 21c, which are connected to the communication/auto detection circuitry 6.
- 8 represents RJ12 connector port, connected to the circuit board 6.
- RJ12 connector port 8 is connected to various points of the communication/auto detection circuitry 6.
- the communication/auto detection circuitry 6 comprises simple voltage divider (also known as potential divider). Windings ends 20a/20b/20c are connected directly to current signal terminals Ti , T 2 , T 3 . Windings ends 21 a/21 b/21 c are all connected directly to ground terminal TGnd. Winding ends 20a and 21a provide the amount of current being driven through the secondary winding 5 a, and thus the amount of current being driven through the corresponding primary cable or busbar. Winding ends 20b and 21b provide the amount of current being driven through the secondary winding 5b, and thus the amount of current being driven through the corresponding primary cable or busbar.
- Winding ends 20c and 21c provide the amount of current being driven through the secondary winding 5c, and thus the amount of current being driven through the corresponding primary cable or busbar.
- Voltage divider referenced to ground TGnd comprises two resistors 22 connected in series and voltage input connected to Tin. Voltage input Tin applied across the resistor pair 22 results in output voltage Tout emerging from connection between them. Resistor voltage divider is used to create referential voltage on terminal Tout.
- Each type of transformer will have dedicated resistor pair providing specific footprint (referential voltage) used to determine transformer type and transformation ratio.
- Terminals Ti , T 2 , T 3 , TGnd, Tout and Ti n are connected to RJ12 connector port 8.
- RJ12 connector port 8 therefore provides current signals, derived from secondary windings 5a/5b/5c at terminals T1/T2/T3, as well as providing a grounded terminal TGnd, for connection and output to a measurement device.
- measuring device When first pairing measuring device and current transformer, measuring device will provide voltage input Tin to be applied across the resistor pair 22. Depending on the installed resistor pair, specific voltage output Tout is send back to the measuring device. Measuring device determines transformer type and transformation ratio based on voltage output Tout amplitude.
- FIG 13 schematically illustrates protection/auto detection/communication circuitry 6 according to an embodiment of the invention. Visible at the bottom of Figure 13 are the top portions of the magnetic cores, with windings 5a/5b/5c.
- the winding 5a has ends 20a and 21a, which are connected to the communication/auto detection circuitry 6.
- the winding 5b has ends 20b and 21b, which are connected to the communication/auto detection circuitry 6.
- the winding 5c has ends 20c and 21c, which are connected to the communication/auto detection circuitry 6.
- 8 represents RJ12 connector port, connected to the circuit board 6.
- RJ12 connector port 8 is connected to various points of the communication/auto detection circuitry 6.
- the communication/auto detection circuitry 6 comprises single-contact 1-wire EEPROM and pullu resistor. Windings ends 20a/20b/20c are connected directly to current signal terminals Ti , T 2 ; T 3 . Windings ends 21a/21b/21c are all connected directly to ground terminal TGnd. Winding ends 20a and 21a provide the amount of current being driven through the secondary winding 5a, and thus the amount of current being driven through the corresponding primary cable or busbar. Winding ends 20b and 21b provide the amount of current being driven through the secondary winding 5b, and thus the amount of current being driven through the corresponding primary cable or busbar.
- Winding ends 20c and 21c provide the amount of current being driven through the secondary winding 5 c, and thus the amount of current being driven through the corresponding primary cable or busbar.
- Single-contact 1 -wire EEPROM 23 referenced to ground TGnd provides both communication and power between current transformer and measuring device on a single line connected to Tout. In some cases depending on the EEPROM operation, additional power is required. During these periods of increased power demand, it is important that the voltage on the 1-Wire bus does not fall below the device's minimum operating pullup voltage. To prevent power shortage, a pull-up resistor 24 is installed between EEPROM communication wire and voltage input Tin.
- Terminals Ti, T 2 , T 3 , TGnd, Tout and Tin are connected to RJ12 connector port 8.
- RJ12 connector port 8 therefore provides current signals, derived from secondary windings 5a/5b/5c at terminal Ti/T 2 /T 3 as well as providing a grounded terminal TGnd, for connection and output to a measurement device.
- measuring device reads data from EEPROM and determines transformer type and transformation ratio. Also based on the calibration data stored on EEPROM, measuring device will accommodate current measurements according to the calibration points.
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Abstract
Device and method for measuring electrical current, for measuring current will drastically reduce labor costs that occur during physical installation of current transformer and software configuration of current transformer type and transformation rate (on measuring device side). Protection/auto detection/communication circuit in connection with RJ12 port on both current transformer and measuring device side will zero out any potential damage to current transformer or injury to user, due to wiring error. Auto detection/communication circuit will be implemented into each current transformer. Auto detection/communication circuit will be directly connected to RJ12 port which will assure plug and play compatibility with available measuring devices. Combination of auto detection/communication circuit, RJ12 port and compatible measuring device will drastically reduce labor costs. Current transformer needs only to be connected to measuring device, using single cable with RJ12 connector, everything else is done by auto detection/communication circuit, which will provide measuring device with current transformer transformation ratio and transformer type. No other configuration is needed on measuring device side when connecting current transformer. Auto detection/communication circuit also enables factory calibration of current transformers. Factory calibration on both current transformer and measuring device drastically improves system accuracy (accuracy of both current transformer and measuring device).
Description
Device and method for measuring electrical current
DESCRIPTION OF INVENTION
Field of technology
The present invention relates to the field of low and medium voltage conventional current measuring transformers.
State of the art
Current transformers reduce large primary currents to a much lower value and provide a convenient way of safely monitoring the actual electrical current flowing in a transmission line. Secondary current is proportional to the primary current. Secondary winding supplies a current output to protection/communication/auto detection circuit. Communication/auto detection circuit and sealing protection of current transformer are present inventions related to this document.
Present invention relates to all types of current transformers. In the example below, only single phase and three phase current transformers are presented.
Single phase and three phase current transformers are schematically illustrated in Figure 1 and Figure 4. Both figures are an external view of such a current transformer with transparent upper part of transformer. Reference 1 on a single phase current transformer and references la/l b/lc on a three phase current transformer represent aperture/apertures which is/are able to receive a cable or bus-bar. Cable or bus-bar is able to pass through transformer aperture/apertures and completely emerge on other side. Reference 2 on a single phase current transformer and references 2a/2b/2c on a three phase current transformer represent secondary current terminals to be connected further to protection circuit/auto detection/communication circuit - all protected inside current transformer housing (3 - transparent upper part of current transformer).
Figure 2 and Figure 5 represent illustrated internal cross-section of the single phase and three phase current transformer. Reference 4 on a single phase current transformer (4a/4b/4c on a three phase current transformer) represents magnetic core which surrounds aperture 1 (la/lb/lc on a three phase current transformer). Magnetic core is surrounded by a secondary winding 5 (5a/5b/5c on a three phase current transformer). Primary cable or bus-bar passing through aperture/apertures, produces a magnetic field in the magnetic core/cores which then induces a proportionally smaller current in the secondary winding/windings. Secondary winding/windings is/are connected to secondary current terminals. Amount of inducted current, flowing in the secondary winding (connected to the secondary winding terminals) can then be measured using a separate measuring device. Inducted secondary current is proportional to the primary current. Described above are typical single phase and three phase current transformers which have several disadvantages in design:
- To connect measuring device to current transformer typically 4 or more terminals (2 on current transformer side, 2 on measuring device side) have to be loosened (in case of three phase current transformer this number goes up to 12). Additionally corresponding amount of cable routing has to be done. Because of this high probability of wiring errors is present which can cause damage to the device or injury to a user. Another disadvantage of all the cable routing and terminals connecting is extensive labor cost.
- Additional labor costs due to wiring error or wrong phase sequence connection (three phase current transformer).
- It is necessary to short circuit current output on secondary side when current transformer is not connected to measuring device. Open circuit on secondary side can cause damage to current transformer or even injury to a user.
- Configuring measuring device for appropriate current transformer type and transformation ratio.
Description of the new solution
Device and method for measuring electrical current, for measuring current in different types of current transformer devices (single phase solid core, single phase split core, three phase solid core, Rogowski coil, Hall, DC,...) solves above referenced technical problem by use of protection/auto detection/communication circuit, said protection/auto detection/communication circuit selected from group consisting of voltage divider, single- contact 1-wire EEPROM.
Figure 3 and Figure 6 showing solution in accordance with this invention represents illustrated internal cross-section of the single phase and three phase current transformer. Reference 4 on a single phase current transformer (references 4a/4b/4c on a three phase current transformer) represents magnetic core which surrounds aperture 1 (apertures la/lb/lc on a three phase current transformer). Magnetic core is surrounded by a secondary winding 5 (secondary windings 5a/5b/5c on a three phase current transformer). Primary cable or bus-bar passing through aperture/apertures, produces a magnetic field in the magnetic core/cores which then induces a proportionally smaller current in the secondary winding/windings. Secondary winding/windings is/are connected to at least two secondary current terminals 2 (terminals 2a/2b/2c on a three phase current transformer). Said secondary current terminals 2a (terminals 2a/2b/2c on a three phase current transformer) are connected to protection/auto detection/communication circuit 6. Depending on current transformer type, up to 6 connections 7 are made between protection/auto detection/communication circuit and RJ12 port 8. Everything is enclosed in current transformer housing.
Present invention will drastically reduce labor costs that occur during physical installation of current transformer and software configuration of current transformer type and transformation rate (on measuring device side). Protection/auto detection/communication circuit in connection with RJ12 port on both current transformer and measuring device side will zero out any potential damage to current transformer or injury to user, due to wiring error. Auto detection/communication circuit will be implemented into each current transformer. Auto
detection/communication circuit will be directly connected to RJ 12 port which will assure plug and play compatibility with Iskra measuring devices. Combination of auto detection/communication circuit, RJ12 port and compatible measuring device will drastically reduce labor costs. Current transformer needs only to be connected to measuring device, using single cable with RJ12 connector, everything else is done by auto detection/communication circuit, which will provide measuring device with current transformer transformation ratio and transformer type. No other configuration is needed on measuring device side when connecting current transformer. Auto detection/communication circuit also enables factory calibration of current transformers. Factory calibration on both current transformer and measuring device drastically improves system accuracy (accuracy of both current transformer and measuring device).
Present invention focuses on automatic detection of current transformer type and transformation rate. Eliminates the need for configuring measuring device.
Using RJ12 port instead of secondary current terminals also eliminates possibility of error due to wrong connection or open circuit on secondary side.
Only single data cable connection between measuring device and current transformer. Reduced labor costs.
RJ12 port which assures plug and play compatibility with available measuring devices may in some cases present disadvantage due to easy disconnecting of RJ12 connector from RJ12 port. Access to RJ12 connector plugged into RJ12 port has to be protected in order for prevent disconnection by unauthorized personnel.
Present inventions also relates to sealing protection of RJ12 port for billing certification.
Present invention also provides for a method for for measuring electrical current, said method comprising the following steps:
- providing current transformer comprising at least one primary and at least one
secondary winding, said current transformer either of a single phase or a three phase type, said current transformer further comprising magnetic field producing means selected from the group consisting of primary cable, bus-bar,
- passing of said magnetic field producing means through at least one aperture provided in said transformer,
- inducing current by said magnetic field producing means in said secondary winding or plurality thereof;
- connecting said secondary winding or plurality thereof to at least one pair of
secondary current terminals,
- connecting said secondary current terminals to protection/auto
detection/communication circuit, said protection/auto detection/communication circuit selected from group consisting of voltage divider, single-contact 1-wire EEPROM.
The method according to this invention further comprises step of enclosing device for performing method according to claim 13 in current transfomer housing, and providing for sealing doors for tamper protection of RJ12.
The method according to this invention further comprises the following steps:
- connecting first and second winding ends of said secondary winding to said
protection/auto detection/communication circuit, said first and second winding ends selected from the group consisting of windings ends (20, 21 ) on single phase current transformers, windings ends (20a, 21a, 20b, 21b, 20c,21c) on three phase current transformers,
- connecting said first winding end selected from the group consisting of windings end (20) on single phase current transformers, windings end (20a, 20b, 20c) on three phase current transformers, directly to current signal terminal Tl,
- connecting said second winding end selected from the group consisting of windings end (21) on single phase current transformers, windings end (21a,21b,21c) on three phase current transformers, directly to ground terminal TGnd,
- assessing amount of current being driven through the corresponding primary cable or bus-bar by providing amount of current being driven through said secondary winding.
In preferred embodiment, device and method for measuring electrical current, for measuring current reduce labor costs that occur during physical installation of current transformer and software configuration of current transformer type and transformation rate (on measuring device side). Protection/auto detection/communication circuit in connection with RJ12 port on both current transformer and measuring device side zero out any potential damage to current transformer or injury to user, due to wiring error. Auto detection/communication circuit is implemented into each current transformer. Auto detection/communication circuit is directly connected to RJ12 port which will assure plug and play compatibility with available measuring devices. Combination of auto detection/communication circuit, RJ12 port and compatible measuring device further reduce labor costs. Current transformer needs only to be connected to measuring device, using single cable with RJ12 connector, everything else is done by auto detection/communication circuit, which provides measuring device with current transformer transformation ratio and transformer type. No other configuration is needed on measuring device side when connecting current transformer. Auto detection/communication circuit also enables factory calibration of current transformers. Factory calibration on both current transformer and measuring device drastically improves system accuracy (accuracy of both current transformer and measuring device).
Figure 9 schematically illustrates a current measurement system according to an embodiment of the present invention.
Three different types of current transformers 15/16/17 are shown in figure 9. Only three different types of current transformers are presented on figure 9., but note that present invention relates to all kinds of current transformers. Current transformers 15/16/17 connect to measuring
device 18 via data cable 14 with RJ12 connectors 13. RJ12 ports on both current transformer and measuring device side, ensure plug and play compatibility throw-out entire line of current transformers. Measuring device 18 auto detects type of current transformer and its transformation rate. Auto detection/communication is possible, due to auto detection/communication circuit in-bodied inside current transformers. Measuring device can have up to three RJ12 ports (current inputs). Connecting three phase current transformer to each of the three current inputs on measuring device, results in measurement of nine different primary currents.
Figure 7: Present invention relates also to sealing protection of RJ12 port, and is schematically illustrated in figure 7. Invention is presented only on single phase current transformer, but relates to all types of current transformers. In the figure, 9 represents single phase current transformer with implemented sealing protection for RJ 12 port. Data cable with RJ12 connector 13 plugs directly to RJ12 port 8. RJ12 port 8 is covered by sealing protection doors 12. Both current transformer housing 9 and sealing protection doors 12 have through holes 10/1 1 used for sealing with sealing wire.
Figure 7.1: Single phase current transformer 9, with opened sealing protection doors 12. Data cable with RJ12 connector 13 is disconnected from current transformer.
Figure 7.2: Single phase current transformer 9, with opened sealing protection doors 12. Data cable with RJ12 connector 13 plugged directly to RJ 12 port 8. RJ12 port 8 is covered by sealing protection doors 12.
Figure 7.3: Single phase current transformer 9, with closed sealing protection doors 12. Data cable with RJ 12 connector 13 plugged directly to RJ 12 port 8. RJ 12 port 8 is covered by sealing protection doors 12.
Figure 8: Top/side/front view of single phase current transformer with opened/closed sealing protection door for RJ12 port is schematically illustrated in Figure 8.
Auto detection communication circuit also enables factory calibration of current transformers. Factory calibration on both current transformer and measuring device drastically improves system accuracy (accuracy of both current transformer and measuring device)
Description of the Fxample Embodiments
Figures 10, 1 1 , 12 and 13 schematically illustrate communication/auto detection circuitry 6 according to an embodiment of the invention. Figures 10 and 12 use voltage divider as a tool for obtaining referential voltage upon which transformer type and transformation ratio are determined. Figures 11 and 13 use single-contact 1 -wire EEPROM as a tool for obtaining data on transformer type and transformation ratio. Single-contact 1-wire EEPROM also provides additional features described in detail below. Each of the Figures is explained in detail below.
Figure 10 schematically illustrates communication/auto detection circuitry 6 according to an embodiment of the invention. Visible at the bottom of Figure 10 is the top portion of the magnetic core, with secondary windings 5. The winding 5 has ends 20 and 21 , which are connected to the communication/auto detection circuitry 6. 8 represents RJ12 connector port, connected to the circuit board 6. RJ12 connector port 8 is connected to various points of the communication/auto detection circuitry 6.
The protection/auto detection/communication circuitry 6 comprises simple voltage divider (also known as potential divider). Winding end 20 is connected directly to current signal terminal Ti . Winding end 21 is connected directly to ground terminal TGnd- Winding ends 20 and 21 provide the amount of current being driven through the secondary winding 5, and thus the amount of current being driven through the corresponding primary cable or busbar. Voltage divider referenced to ground TGnd comprises two resistors 22 connected in series and voltage input connected to Ti„. Voltage input Tin applied across the resistor pair 22 results in output voltage Tout emerging from connection between them. Resistor voltage divider is used to create referential voltage on terminal Tout. Each type of transformer will have dedicated resistor pair providing specific footprint (referential voltage) used to determine transformer type and transformation ratio.
Terminals Ti, TGnd, Tout and Tin are connected to RJ12 connector port 8. RJ12 connector port 8 therefore provides current signal, derived from secondary winding 5 at terminal Ti, as well as providing a grounded terminal TGnd, for connection and output to a measurement device. When first pairing measuring device and current transformer, measuring device will provide voltage input Tin to be applied across the resistor pair 22. Depending on the installed resistor pair, specific voltage output Tout is send back to the measuring device. Measuring device determines transformer type and transformation ratio based on voltage output Tout amplitude.
Figure 11 schematically illustrates protection/auto detection/communication circuitry 6 according to an embodiment of the invention. Visible at the bottom of Figure 1 1 is the top portion of the magnetic core, with secondary windings 5. The winding 5 has ends 20 and 21, which are connected to the communication/auto detection circuitry 6. 8 represents RJ12 connector port, connected to the circuit board 6. RJ12 connector port 8 is connected to various points of the communication/auto detection circuitry 6.
The communication/auto detection circuitry 6 comprises single-contact 1 -wire EEPROM and pullup resistor. Winding end 20 is connected directly to current signal terminal Ti . Winding end 21 is connected directly to ground terminal TGnd. Winding ends 20 and 21 provide the amount of current being driven through the secondary winding 5, and thus the amount of current being driven through the corresponding primary cable or busbar. Single-contact 1-wire EEPROM 23 referenced to ground TGnd, provides both communication and power between current transformer and measuring device on a single line connected to Tout. In some cases depending on the EEPROM operation, additional power is required. During these periods of increased power demand, it is important that the voltage on the 1-wire bus does not fall below the device's minimum operating pullup voltage. To prevent power shortage, a pull-up resistor 24 is installed between EEPROM communication wire and voltage input Tin.
Communication (reading and writing) over single-conductor 1 -wire bus enables wide variety of operations over current transformers (in connection to measuring device):
- auto detection of transformer type
- auto detection of transformation ratio
- calibration for different current ranges - increased accuracy
- calibration over wide range of frequencies
Terminals Ti , TGnd, Tout and Tin are connected to RJ12 connector port 8. RJ12 connector port 8 therefore provides current signal, derived from secondary winding 5 at terminal Ti , as well as providing a grounded terminal TGnd, for connection and output to a measurement device. When first pairing measuring device and current transformer, measuring device reads data from EEPROM and determines transformer type and transformation ratio. Also based on the calibration data stored on EEPROM, measuring device will accommodate current measurements according to the calibration points.
Figure 12 schematically illustrates protection/auto detection/communication 6 according to an embodiment of the invention. Visible at the bottom of Figure 12 are the top portions of the magnetic cores, with secondary windings 5a/5b/5c. The winding 5a has ends 20a and 21a, which are connected to the communication/auto detection circuitry 6. The winding 5b has ends 20b and 21b, which are connected to the communication/auto detection circuitry 6. The winding 5 c has ends 20c and 21c, which are connected to the communication/auto detection circuitry 6. 8 represents RJ12 connector port, connected to the circuit board 6. RJ12 connector port 8 is connected to various points of the communication/auto detection circuitry 6.
The communication/auto detection circuitry 6 comprises simple voltage divider (also known as potential divider). Windings ends 20a/20b/20c are connected directly to current signal terminals Ti , T2, T3. Windings ends 21 a/21 b/21 c are all connected directly to ground terminal TGnd. Winding ends 20a and 21a provide the amount of current being driven through the secondary winding 5 a, and thus the amount of current being driven through the corresponding primary cable or busbar. Winding ends 20b and 21b provide the amount of current being driven through the secondary winding 5b, and thus the amount of current being driven through the corresponding primary cable or busbar. Winding ends 20c and 21c provide the amount of current being driven through the secondary winding 5c, and thus the amount of current being driven through the corresponding primary cable or busbar. Voltage divider referenced to ground TGnd comprises two resistors 22 connected in series and voltage input connected to Tin. Voltage input Tin applied across the resistor pair 22 results in output voltage Tout emerging from connection between them. Resistor voltage divider is used to create referential voltage on terminal Tout. Each type of transformer will have dedicated resistor pair providing specific footprint (referential voltage) used to determine transformer type and transformation ratio.
Terminals Ti , T2, T3, TGnd, Tout and Tin are connected to RJ12 connector port 8. RJ12 connector port 8 therefore provides current signals, derived from secondary windings 5a/5b/5c at terminals T1/T2/T3, as well as providing a grounded terminal TGnd, for connection and output to a measurement device. When first pairing measuring device and current transformer,
measuring device will provide voltage input Tin to be applied across the resistor pair 22. Depending on the installed resistor pair, specific voltage output Tout is send back to the measuring device. Measuring device determines transformer type and transformation ratio based on voltage output Tout amplitude.
Figure 13 schematically illustrates protection/auto detection/communication circuitry 6 according to an embodiment of the invention. Visible at the bottom of Figure 13 are the top portions of the magnetic cores, with windings 5a/5b/5c. The winding 5a has ends 20a and 21a, which are connected to the communication/auto detection circuitry 6. The winding 5b has ends 20b and 21b, which are connected to the communication/auto detection circuitry 6. The winding 5c has ends 20c and 21c, which are connected to the communication/auto detection circuitry 6. 8 represents RJ12 connector port, connected to the circuit board 6. RJ12 connector port 8 is connected to various points of the communication/auto detection circuitry 6.
The communication/auto detection circuitry 6 comprises single-contact 1-wire EEPROM and pullu resistor. Windings ends 20a/20b/20c are connected directly to current signal terminals Ti , T2; T3. Windings ends 21a/21b/21c are all connected directly to ground terminal TGnd. Winding ends 20a and 21a provide the amount of current being driven through the secondary winding 5a, and thus the amount of current being driven through the corresponding primary cable or busbar. Winding ends 20b and 21b provide the amount of current being driven through the secondary winding 5b, and thus the amount of current being driven through the corresponding primary cable or busbar. Winding ends 20c and 21c provide the amount of current being driven through the secondary winding 5 c, and thus the amount of current being driven through the corresponding primary cable or busbar. Single-contact 1 -wire EEPROM 23 referenced to ground TGnd, provides both communication and power between current transformer and measuring device on a single line connected to Tout. In some cases depending on the EEPROM operation, additional power is required. During these periods of increased power demand, it is important that the voltage on the 1-Wire bus does not fall below the device's minimum operating pullup voltage. To prevent power shortage, a pull-up resistor 24 is installed between EEPROM communication wire and voltage input Tin.
Communication (reading and writing) over single-conductor 1 -wire bus enables wide variety of operations over current transformers (in connection to measuring device):
- auto detection of transformer type
- auto detection of transformation ratio
- calibration for different current ranges - increased accuracy
~ calibration over wide range of frequencies
Terminals Ti, T2, T3, TGnd, Tout and Tin are connected to RJ12 connector port 8. RJ12 connector port 8 therefore provides current signals, derived from secondary windings 5a/5b/5c at terminal Ti/T2/T3 as well as providing a grounded terminal TGnd, for connection and output to a measurement device. When first pairing measuring device and current transformer, measuring device reads data from EEPROM and determines transformer type and transformation ratio.
Also based on the calibration data stored on EEPROM, measuring device will accommodate current measurements according to the calibration points.
Claims
PATENT CLAIMS
1. Device for measuring electrical current, said device comprising current transformer, said current transformer comprising at least one primary and at least one secondary winding, said current transformer either of a single phase or a three phase type, said current transformer further comprising magnetic field producing means selected from the group consisting of primary cable, bus-bar, said magnetic field producing means passing through at least one aperture provided in said transformer, said magnetic field producing means inducing current in said secondary winding or plurality thereof, said secondary winding or plurality thereof connected to at least one pair of secondary current terminals, wherein said secondary current terminals are further connected to protection/auto detection/communication circuit, said protection/auto
detection/communication circuit selected from group consisting of voltage divider, single-contact 1 -wire EEPROM.
2. Device according to claim 1 wherein said device is fully enclosed in current
transformer housing.
3. Device according to any of the previous claims wherein said device can have up to three current inputs, preferably up to three RJ12 ports.
4. Device according to any of the previous claims wherein connecting said three phase current transformer to each of said three current inputs on measuring device results in measurements of nine different primary currents.
5. Device according to any of the previous claims wherein said protection/auto
detection/communication circuit enables factory calibration of said current transformer.
6. Device according to any of the previous claims further comprising tool for obtaining referential voltage upon which transformer type and transformation ratio are determined wherein said tool for obtaining referential voltage is selected from group consisting of voltage divider, single-contact 1-wire EEPROM.
7. Device according to any of the previous claims wherein said secondary winding comprises first and second winding ends, said first and second winding ends selected from the group consisting of windings ends (20, 21) on single phase current transformers, windings ends (20a, 21a, 20b, 21b, 20c,21c) on three phase current transformers, said winding ends connected to said protection/auto
detection/communication circuitry (6), and further wherein said first winding end selected from the group consisting of windings end (20) on single phase current transformers, windings end (20a, 20b, 20c) on three phase current transformers, is
connected directly to current signal terminal Ti, and said second winding end selected from the group consisting of windings end (21) on single phase current transformers, windings end (21 a,21 b,21 c) on three phase current transformers, is connected directly to ground terminal TGnd,.said winding ends said first and second winding ends selected from the group consisting of windings ends (20, 21) on single phase current transformers, windings ends (20a, 21a, 20b, 21b, 20c,21c) on three phase current transformers, providing the amount of current being driven through the secondary winding, said secondary windings selected from the group consisting of secondary windings (5) on single phase current transformer, secondary windings (5a,5b,5c) on three phase current transformers, and thus assessing the amount of current being driven through the corresponding primary cable or bus-bar.
8. Device according to any of the previous claims wherein said protection/auto
detection/communication circuitry (6) is comprised of said voltage divider, and further wherein said voltage divider referenced to ground TGnd comprises two resistors
(22) connected in series and voltage input connected to Tin wherein voltage input Tin applied across the resistor pair (22) results in output voltage Tout emerging from connection between them thus forming resistor voltage divider, wherein said resistor voltage divider is used to create referential voltage on terminal Tout , wherein each type of transformer will have dedicated resistor pair providing specific referential voltage used to determine transformer type and transformation ratio.
9. Device according to any of the previous claims wherein said protection/auto
detection/communication circuitry (6) is comprised of said single-contact 1-wire EEPROM (23) and a pullup resistor (24) wherein said ingle-contact 1-wire EEPROM
(23) referenced to ground TGnd, provides both communication and power between current transformer and measuring device on a single line connected to Tout.
10. Device according to any of the previous claims wherein terminals Ti, TGnd, Tout and Tin are connected to RJ12 connector port (8) providing current signal, derived from said secondary windings, said secondary windings selected from the group consisting of secondary windings (5) on single phase current transformer, secondary windings (5a,5b,5c) on three phase current transformers, at said terminal Ti as well as providing a grounded terminal TGnd for connection and output to said measurement device, said measuring device reading data from EEPROM and determining transformer type and transformation ratio.
11. Device according to any of the previous claims wherein based on the calibration data stored on EEPROM said measuring device will accommodate current measurements according to the calibration points.
12. Device according to any of the previous claims further comprising sealing doors (12) for tamper protection of RJ 12.
13. Method for measuring electrical current, comprising the following steps:
- providing current transformer comprising at least one primary and at least one
secondary winding, said current transformer either of a single phase or a three phase type, said current transformer further comprising magnetic field producing means selected from the group consisting of primary cable, bus-bar,
- passing of said magnetic field producing means through at least one aperture provided in said transformer,
- inducing current by said magnetic field producing means in said secondary winding or plurality thereof;
- connecting said secondary winding or plurality thereof to at least one pair of
secondary current terminals,
- connecting said secondary current terminals to protection/auto
detection/communication circuit, said protection/auto detection/communication circuit selected from group consisting of voltage divider, single-contact 1 -wire EEPROM.
14. Method according to claim 13 further comprising step of enclosing device for
performing method according to claim 13 in current transfomer housing, and providing for sealing doors for tamper protection of RJ12.
15. Method accordig to claim 13 or 14 further comprising the following steps:
- connecting first and second winding ends of said secondary winding to said
protection/auto detection/communication circuit, said first and second winding ends selected from the group consisting of windings ends (20, 21) on single phase current transformers, windings ends (20a, 21a, 20b, 21b, 20c,21c) on three phase current transformers,
- connecting said first winding end selected from the group consisting of windings end (20) on single phase current transformers, windings end (20a, 20b, 20c) on three phase current transformers, directly to current signal terminal Tl,
- connecting said second winding end selected from the group consisting of windings end (21) on single phase current transformers, windings end (21a,21b,21c) on three phase current transformers, directly to ground terminal TGnd,
- assessing amount of current being driven through the corresponding primary cable or bus-bar by providing amount of current being driven through said secondary winding.
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/SI2017/000025 WO2019059852A1 (en) | 2017-09-20 | 2017-09-20 | Device and method for measuring electrical current |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/SI2017/000025 WO2019059852A1 (en) | 2017-09-20 | 2017-09-20 | Device and method for measuring electrical current |
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| WO2019059852A1 true WO2019059852A1 (en) | 2019-03-28 |
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| PCT/SI2017/000025 WO2019059852A1 (en) | 2017-09-20 | 2017-09-20 | Device and method for measuring electrical current |
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| CN110907875A (en) * | 2019-12-05 | 2020-03-24 | 北京东方计量测试研究所 | Hall current sensor calibration device and method |
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| CN114609572A (en) * | 2022-03-24 | 2022-06-10 | 国网四川省电力公司营销服务中心 | Current transformer transformation ratio accuracy evaluation method based on fluctuating line loss |
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