WO2015070345A1

WO2015070345A1 - Simultaneous measurement technique for line current, geomagnetically induced currents (gic) and transient currents in power systems

Info

Publication number: WO2015070345A1
Application number: PCT/CA2014/051082
Authority: WO
Inventors: Udaya ANNAKKAGE; Chithra Kirthi Gamini PIYADASA; Aniruddha GOLE; Shaahin FILIZADEH; Athula RAJAPAKSE
Original assignee: University of Manitoba
Current assignee: University of Manitoba
Priority date: 2013-11-12
Filing date: 2014-11-10
Publication date: 2015-05-21
Anticipated expiration: 2016-05-12

Abstract

Characteristics of a line current of a power line in an electrical power system are measured using a current sensor having a core comprising an annular body receiving the power line therethrough and a secondary winding extending about a portion of the annular body in which the core has a high magnetic permeability and a low saturation level relative to the line current. While monitoring voltage induced in the secondary winding, a repeating peak magnitude of the induced voltage resulting from a reversal of magnetic flux in the core is identified and related to a primary alternating current in the power line. The ac current to be measured is thus not converted into another ac current, but instead the rate of change of flux is measured when the flux wave is crossing the zero.

Description

SIMULTANEOUS MEASUREMENT TECHNIQUE FOR LINE CURRENT, GEOMAGNETICALLY INDUCED CURRENTS (GIC) AND TRANSIENT CURRENTS IN POWER SYSTEMS FIELD OF THE INVENTION

The present invention relates to a method of measuring alternating line current, geomagnetically induced currents, or transient pulses in a power line of a power system.

BACKGROUND

Current transformers (CT) are used to measure alternative current (ac) in conventional electrical power systems. In a power system fault conditions occur in addition to the normal operation. During the fault condition, usual currents increase more than several hundred times to the normally operated currents. One of the problems in power systems is to measure both the load currents and the fault currents with sufficient accuracy. In most cases, to handle such large fault currents, considerably large, heavy transformer cores have to be used. The larger cores prevent magnetic saturation, and thus allow accurate measurements in currents.

In addition to that, Geomagnetically induced currents (GIC) in power networks can cause unexpected damages and disturbances in power systems costing millions of dollars. The GIC currents are slowly varying currents compared to the normal 60 or 50Hz load currents, and they appear as direct currents (dc) in the power system. This GIC problem is common in power systems in countries in northern hemisphere, close to magnetic pole in the earth. Even though the GIC currents are random events in line currents, the simultaneous measurements of both, (low frequency G!C and large AC fault currents) have not been achieved successfully so far.

In conventional measurement systems in high voltage power systems, current and voltage transformers are used for stepping down the current and voltage signals to a range suitable for instrumentation. The band width of conventional current and voltage transformers is limited and therefore, not suitable measurement of high frequency transients. There are some protection and fault location applications, such as travelling wave based distance protection and fault location, which depend on the measurement of transient signals superimposed on power frequency currents and voltages. However, lack of economical, high bandwidth sensors applicable at high voltage levels is a major obstacle to the deployment of transient based protection methods. Currently available techniques such as high voltage, high bandwidth, high capacity current shunts and voltage dividers are expensive and bulky. Other techniques such as Hall effect and optical sensors are either expensive and have limitations in high voltage applications.

SUMMARY OF THE INVENTION

The newly invented system can measure line currents, fault currents,

GIC and transient currents. Resolution of real-current (not software controlled) measurements are considerably high. Furthermore, the magnetic core required for the proposed system is small in size and weight compared to presently available commercial equipment. The power required for the operation of proposed system is minimal.

The newly proposed system can measure both current and voltage transients up to several MHz. This will lead to fast identification of fault location and in turn reducing the risk of damage to the power system enabling better protection systems to be employed. The proposed system can be incorporated into the proposed line current and GIC measurements in power systems.

It is known that when two coils are magnetically coupled, an ac current in one winding results in an induced ac current in the other winding. The proportionality of this current is maintained when the magnetic core that couples the windings does not saturate. Here, the ac current to be measured is converted to a scaled ac current.

A novel aspect of the present invention is the ac current to be measured is not converted into another ac current, but instead the rate of change of flux is measured when the flux wave is crossing the zero (or reversal of flux direction inside the magnetic core). This happens twice in each cycle when the core has come out of saturation. So, even if the core is saturated, it comes out of saturation and crosses zero twice in each cycle. Voltage pulses are produced at these instances as a result of time derivative of magnetic flux inside the core and we measure the strength of these voltage pulses to determine the primary current.

General features of the proposed system and method include:

1) Use of a magnetic core with high permeability and low saturation around the current carrying conductor;

2) Use of said magnetic core with secondary open (or is terminated with very high impedance of a voltage measuring system);

3) Use of a secondary coil wound on said magnetic core to detect induced voltage when the magnetic flux change from one direction to other

(differentiation of flux);

4) Measurements taken are independent of whether the magnetic core saturates or not;

5) Measurements are taken as time signature when magnetic flux reverses its direction in the core; and

6) Measurements are taken as time derivative of this reversal of magnetic flux in the core.

AC measurements

Voltage pulses that are produced at these instances of the reversal of magnetic field inside the magnetic core-are proportional to the magnitude of the AC current to be measured.

The peak amplitude of differential waveform (when the magnetic flux in the core reverses its direction) is used to measure the amplitude of the alternative current (AC).

GIC measurements

When there is a dc bias the occurrence of these pulses appear with an uneven time shift. We propose to measure this time shift and use a feedback circuit to inject an opposing dc level to neutralize the shift. When the effect is fully neutralized, the voltage pulses become evenly spread and, under this condition, the injected current is equal to the dc current (i.e. the GIC) in the transmission line. To measure the Induced geomagnetically induce direct current (GIC), measure time difference between two consecutive peaks (either positive or negative) caused by reversal of magnetic flux as in claim #6.

DC is injected into another winding around the magnetic core to eliminate the time difference between measured peaks.

The GIC is then determined from the injected current.

The magnetic core used to measure AC and/or DC can be in any current carrying section (live or neutral) of the electric circuit.

Transient measurements

It is known that when a magnetic core is saturated, the core acts like an air core with a linear B-H relationship given by the permeability of free space. However, depending on the type of the magnetic material B to H ratio can be quite high even after the knee point of the B-H characteristics. This property leads to providing a significant induced emf in the secondary even past the knee-point of saturation. We propose to measure this voltage signal to in order detect transient pulses in a power system.

The induced transient of the secondary of the said magnetic core is used, independent of the saturation of the magnetic core, to measure the transient occurring in the power lines.

Measurement of current transients indirectly allows detection of voltage transients as well.

The said magnetic core is thus used to simultaneously measure, line current, geomagnetically induced current, and transients occurring in any electrical system from its induced voltage in secondary coil wound with any number of turns in the said magnetic core.

In power systems, the line current is measured using a conventional CT. There are some indirect methods to measure the induced DC currents such as GIC in power systems, but no direct measuring system is available at present. This proposed system provides simultaneous measurements of both AC and DC under normal and fault conditions at very high resolutions. Furthermore, the materials are readily available inexpensive ferrite materials. The size and weight is also greatly reduced compared to the present CTs.

In power systems, conventional voltage and current transformers are essentially power frequency devices with limited or no capability to measure faster transient events. This proposed system provides simultaneous measurements of AC, DC and voltage and current transients under normal and fault conditions at very high resolutions. Furthermore, the materials are readily available inexpensive ferrite materials. The size and weight is also greatly reduced compared to the present CTs.

Present CTs are based on magnetically non-saturated condition. If the saturation occurs the equipment fails to produces desirable data. The proposed invention does not require this condition, work within the magnetically saturation region and the above limitations do not apply. Again the system measures both AC and DC at the same time which is not currently available in present systems.

Present CTs are based on magnetically non-saturated condition. If the saturation occurs the equipment fails to produces desirable data. The proposed invention work independent of the state of magnetic saturation and the above limitations do not apply. Again the system measures AC, DC and the impulse detection at the same time which is not currently available in present systems.

Measurement of any type of current waveforms is very useful for monitoring power systems. This will help to identify type fault conditions, interferences for protection of power systems. The measurements using the time tag at zero crossing when magnetic flux reversal in the magnetic core as in this invention with high magnetic permeability and low saturation shows promising results for possibility of measuring any kind of wave shape with integrated noise.

According to a first aspect of the present invention there is provided a method of measuring characteristics of an alternating line current of a power line in an electrical power system, the method comprising:

providing a current sensor having a core comprising an annular body receiving the power line therethrough and a secondary winding extending about a portion of the annular body in which the core has a high magnetic permeability and a low saturation level relative to the line current, and in which the secondary winding is either open or connected to a high impedance;

monitoring a voltage induced in the secondary winding by the line current in the power line;

identifying a repeating peak magnitude of the induced voltage resulting from a reversal of magnetic flux in the core; and

relating the repeating peak magnitude of the induced voltage to a primary alternating current in the power line.

In a preferred embodiment, the method further comprises: providing an auxiliary winding extending about a portion of the annular body of the core of the current sensor;

when no direct current is applied to the line current, identifying a first duration between a first initial peak magnitude of the induced voltage and a second initial peak magnitude of the induced voltage which is consecutive and opposing in relation to the first initial peak magnitude;

monitoring a second duration between a first observed peak magnitude of the induced voltage and a second observed peak magnitude of the induced voltage which is consecutive and opposing in relation to the first observed peak magnitude;

when the second duration is different than the first duration, applying an auxiliary direct current to the auxiliary winding such that the second duration equals the first duration; and

relating the auxiliary direct current to a direct current in the power line.

The method of the preferred embodiment further comprises: removing the repeating peak magnitudes from the monitored induced voltage; and

identifying any remaining peak magnitudes of the induced voltage as a transient pulse in the power line.

According to a second aspect of the present invention there is provided a method of measuring characteristics of a line current having a dc component superimposed on an alternating current in a power line in an electrical power system, the method comprising:

providing a current sensor having a core comprising an annular body receiving the power line therethrough, a secondary winding extending about a portion of the annular body, and an auxiliary winding extending about a portion of the annular body in which the core has high magnetic permeability and a low saturation level relative to the line current, and in which the secondary winding is either open or connected to a high impedance;

when no direct current is present in the line current, monitoring a voltage induced in the secondary winding by an alternating current in the power line by identifying a first duration between a first initial peak magnitude of the induced voltage and a second initial peak magnitude of the induced voltage which is consecutive and opposing in relation to the first initial peak magnitude;

subsequently monitoring a second duration between a first observed peak magnitude of the induced voltage and a second observed peak magnitude of the induced voltage which is consecutive and opposing in relation to the first observed peak magnitude;

relating the auxiliary direct current to a direct current in the power line.

According to a third aspect of the present invention there is provided a method of measuring characteristics of a direct current of a power line in an electrical power system, the method comprising:

providing a current sensor having a core comprising an annular body receiving the power line therethrough, a secondary winding extending about a portion of the annular body, and an auxiliary winding extending about a portion of the annular body in which the core has a high magnetic permeability and a low saturation level relative to the line current, and in which the secondary winding is either open or connected to a high impedance;

superimposing an alternating current on the direct current in the power line having a known first duration between a first initial peak magnitude and a second initial peak magnitude which is consecutive and opposing in relation to the first initial peak magnitude;

monitoring a voltage induced in the secondary winding by the direct current and the alternating current superimposed thereon in the power line by identifying a second duration between a first observed peak magnitude of the induced voltage and a second observed peak magnitude of the induced voltage which is consecutive and opposing in relation to the first observed peak magnitude;

applying an auxiliary direct current to the auxiliary winding such that the second duration equals the first duration; and

relating the auxiliary direct current to the direct current in the power line.

According to a further aspect of the present invention there is provided a method of measuring transient pulses in a line current of a power line in an electrical power system, the method comprising:

identifying any repeating peak magnitudes of the induced voltage resulting from a reversal of magnetic flux in the core;

removing the repeating peak magnitudes from the monitored induced voltage; and

According to each of the aspect of the present invention noted above, the method may further include providing a current sensor in which the core is arranged to be in a region of magnetic saturation relative to the line current. More preferably, the current sensor may have a core which comprises ferrite.

Preferably the method in each instance further includes monitoring a voltage induced in the secondary winding by taking measurements as a time signature when magnetic flux reverses direction, or as a time derivative of a reversal of magnetic flux in the core.

Various embodiments of the invention will now be described in conjunction with the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic representation of a first embodiment of the current sensor shown with single ferrite core and an electromotive force sensing winding around the core.

Figure 2 is a graphical representation of the relationship between the magnetic fiux B and the magnetizing field H.

Figure 3 is a graphical representation of the variation of current /^' or magnetizing force H over time in curve 1 and the resultant magnetic flux in the core over time in curve 2.

Figure 4a is a graphical representation of the waveform of the input sinusoidal current and the voltage induced on the sensing coil.

Figure 4b is an enlarged view of the highlighted portion of one of the curves shown in Figure 4a.

Figure 5 is a graphical representation of the relationship between the peak of the sensing winding voltage and the primary current.

Figure 6a shows the sensing coil voltage, which is proportional to the time derivative of flux density B, for AC current without any super imposed DC component.

Figure 6b shows the same when there is a DC current superimposed on the AC current.

Figure 7 is a schematic representation of a second embodiment of the current sensor for geomagnetically induced current measurements.

Figure 8 is a schematic representation of a third embodiment of the current sensor for transient measurements.

Figure 9 shows a 60 Hz current waveform with two transients superimposed on it.

Figures 10a through 10c show the waveforms of four measurements for three different voltage/current pulse widths (1 s, 10 s, 100 με). More particularly, in each waveform, CH4 (green curve) is the exciting pulse, CH. 1 (yellow curve) is the voltage at the load, CH. 3 (purple curve) is the output obtained from a Rogowski coil that is conventionally used for the transient measurement, and CH.2 (blue curve) is the voltage induced on the sensing coil of the proposed sensor.

Figure 11 is a schematic representation of the circuit used for the measurements represented in Figure 10.

Figure 12 is a schematic representation of an embodiment of the present invention comprising an integrated sensor capable of measuring AC, DC, and transients.

In the drawings like characters of reference indicate corresponding parts in the different figures.

DETAILED DESCRIPTION

The current sensor consists of a single ferrite core and an electromotive force (EMF) sensing winding around the core as shown in Fig. 1 . Ferrite is used because of its high magnetic permeability and low saturation level. The EMF v is induced [ref 1] in terminals of the sensing winding when the current flows in the primary circuit passing through the ferrite core. In present measuring systems, CT is designed to operate in the magnetically non-saturated region. CTs are usually made of high permeability iron alloy and the size and the weight depend on the current capacity of the power system. However, in this proposed system, ferrtte is used as a medium which is comparatively light in weight to the iron and the operational region of the ferrite is by design kept in the region of the magnetic saturation [ref 2,3]. Therefore, the physical size and the weight of the core are greatly reduced compared to the conventionally used ion core CTs. When a sinusoidal current / flows in the conductor passing through the core, magnetizing field H (A/m) due to the current /, produces corresponding magnetic fluxes B inside the core as in the Eq. 1

Β = μΗ =^γ (1) where μ is the permeability of the ferrite material, n=1 in the number of turns and / is the mean length of the core.

Due to the residual magnetism and the magnetic saturation of the material the relationship between the flux B and the current is not always linear and the relevant details can be found in [ref 3].

The actual relationship of B and H, which are also known as magnetic hysteresis or well-known B-H curve [ref 3,4,5], is shown in Fig. 2.

The sensing winding induces an emf at its output terminals and connected to high impedance input terminals of a data acquisition system (DAQ). No secondary current exists in the winding and therefore no disturbances to the measuring parameter / in the line current. Saturation occurs with a very small line current through the core because there is no load connected to the secndary. Once the core is saturated, the magnetic flux B remains almost constant even when the current increases (regions beyond a and d in Fig. 2). The situation is depicted in Fig. 3. Curve 1 in Fig. 3 shows the variation of current or magnetizing force H, and the curve 2 shows the resultant magnetic fiux in the core. Even when the current increases, the magnetic flux remains nearly constant but at the zero crossing point the magnetic moment of the particles of the core medium reverses [6].

Induced voltage v in sensor winding is proportional to the rate of change of magnetic flux linkage, (ηεΒΑ) (Faraday's second law) [ref 1 ]. where n∑ is the number of turns of the sensor winding and A is the cross section area of the magnetic core. If the primary current is sinusoidal, the maximum change of the flux density B in cores occur when the flux curve cross the zero flux axis (Eq. 2 and Fig. 5).

v₌ dB ₌ d(_fm₂Ai/l) _{= k} d_{L = k} W-** S> = _{w (2)}

dt dt dt dt Where k is a constant equals to

When the core is subjected to magnetic saturation the variation of the flux density B is no longer sinusoidal, and has the shape illustrated in Fig. 3. When the primary current is around its peak, the core operates in the regions close to a or d in Fig.2, thus the variation of the flux density B is small. As a result, the induced voltage v, which is proportional to dB/dt, remains small. On the other hand, near the zero crossing of the primary current, the core operates around the regions b and e in Fig. 2. The magnetic flux density B in the core changes polarity within a short period of time. Thus the magnitude of the voltage induced on the sensing coil v is high. For a sinusoidal primary current, the voltage peak occurs when cot is equal to an integer multiple of π or cos(ax) = l in Eq. 2. At the peak, the value of the induced voltage v is proportional to i_max and can be used as a measurement of the magnitude of current /. when ox = 0_t ±π, 2π, v = kai^ = (^ ^-)^

The waveforms of the input sinusoidal current and the voltage induced on the sensing coil are shown in Fig. 4a. An enlarged view of the peak of the induced voltage is shown in Fig. 4b.

1) Alternating current (AC) measurements

If the sensing coil voltage v is measured using a real time data acquisition system, it is possible to relate the peak values of the measured voltages with the corresponding primary current in the conductor passing through the core, with the assistance of a calibration curve. The peak of the measured voltage v, and thereby the sensitivity of measurement can be easily controlled by the number of turns of the sensor winding. The number of turns can be increased to increase the sensitivity with negligible effect on the primary system because the current in the sensing winding is nearly zero. The relationship between the peak of sensing winding voltage and the primary current (rms) is shown in Fig. 5 for a particular ferrite core. The range of primary currents is from 100 A to 2000A.

2) Geomaqneticallv induced current (GIC) measurements In addition to the AC current measurements described above, a saturated core can also be used to measure a DC current, which is superimposed on the AC current. Fig. 6a shows the sensing coil voltage, which is proportional to the time derivative of flux density B, for AC current without any super imposed DC component. Fig. 6b shows the same when there is a DC current superimposed on the AC current. Such a situation can occur in a real power system when a geomagnetically induced current (GIC) flows in a power transmission line [ref 7]. When a DC component is present, the current waveform sifts upwards (assuming positive DC current in this case) and the zero crossing points of the AC current is shifted to the negative half cycle, causing the time difference between the adjacent positive and negative peaks in the induced voltage to become asymmetrical as in Fig. 6b. If ti is the time difference between negative and positive peaks (in that order) when there is no DC component, addition of a positive DC component into the current alters the time between the same peaks to fc.

Fig. 6a shows practical values of 40AAC through the ferrite core and 6b show DC 20A superposition on the AC.

For a constant frequency sinusoidal current, ti is a constant. Addition of DC current, laic to the AC current changes the time difference ti according to the polarity of the DC component. This change of ti can be recognized using a suitable software through the DAQ (Fig. 7) and devise a feedback controller to inject an appropriate reverse current iac/rev via a digitally programmable current source to neutralize the magnetic field caused by the ieic. The magnitude of the neutralizing current, ieic/rev is then proportional to the DC component in the primary current, hie. 3) Transient measurements

The bandwidth of conventional current and voltage transformers used in high voltage power systems is limited and therefore, they are not suitable for transient measurements required for applications such as travelling wave based transmission line protection and fault location. Such applications require detection of high frequency (>100 kHz) transient signals superimposed on power frequency currents and voltages. The new transient sensor uses the same arrangement as described in the previous sections and shown in Fig. 8. The core is designed to saturate under the normal AC current. The sensor uses the open circuit voltage induced in the sensing winding as the transient detection signal.

Fig. 9 shows a 60 Hz current waveform (yellow curve) with two transients super imposed on it. The sudden change of current / due to transient change the magnetic field H in the ferrite core. Even though the core is saturated, a small change in the magnetic flux density B occurs, as the B-H characteristics never become flat. Even though the change in B is small, the rate of change of B is high as the change is occurring in a short time. Therefore, a voltage pulse with a significant magnitude is induced on the sensing coil and that can be used to detect the occurrence of the transient. This induced voltage is shown by the light blue curve in Fig. 9. Note that the pulse due to transient is much sharper and larger than those occurring at the zero crossing of the 60 Hz current waveform.

Measurements made with different exciting pulses are shown in Fig 10.

The circuit used for measurements is shown in Fig. 11. in Fig, 10, CH4 (green curve) is the exciting pulse, CH. 1 (yellow curve) is the voltage at the load, CH. 3 (purple curve) is the output obtained from a Rogowski coil that is conventionally use for the transient measurement, and CH.2 (blue curve) is the voltage induced on the sensing coil of the proposed sensor. Fig. 10.1-3 shows the waveforms of above four measurements for three different voltage/current pulse widths (1 ps, 10 ps, 100 ps). The measurement bandwidth of the sensor will be limited by the self-inductance of the sensing coil that depend on the core material and the number of turns of the sensing coils.

The advantages in transient detection using a ferrite core are its wider frequency response compared to conventional iron cores and the higher output signal amplitudes compared to air core CTs such as Rogowski coils. Although CTs with ferrite cores are used as internal CTs in instrumentation, they are expected to operate in unsaturated region. However, the new sensor is expected to operate independent of magnetic saturation by design. The proposed sensor can be used to detect the transients in current signals. However, the high frequency transients in a power network are generated by events such as faults, switching actions, or lighting, and in most occasions, the current transient is associated with a corresponding voltage transient. Therefore, measurement of current transients indirectly allows detection of voltage transients as well.

The final arrangement of an integrated sensor capable of measuring AC, DC, and transients is shown in Fig. 12. In the transient measurement system, the detection voltage v is processed to remove repetitive voltage peaks at the zero crossings of the 60 Hz signal.

The following references have been referred to above by number and are herein incorporated by reference.

1. Branislav, M. N., Electromagnetics, Pearson Education New jersey, ISBN-13: 978-0-13-247364-4

2. Kuphaldt, T. Ft., Lessons in Electric Circuits 5^th Edition, Vol. 1Chap. 14

3. Aharoni, Amikam, Introduction to the Theory of Ferromagnetism.

Clarendon Press. (1996), ISBN 0-19-851791-2.

4. U. D. Annakkage, P. G. McLaren, E. Dirks, R. P. Jayasinghe, and A. D.

Parker, "A current transformer model based on the Jiles-Atherton theory of ferromagnetic hysteresis," IEEE Trans. Power Delivery, vol. 15, pp.

57-61 , Jan. 2000

5. Giorgio Bertotti, Hysteresis in Magnetism: For Physicists, Materials Scientists, and Engineers (Electromagnetism), Academic Press Inc, CA ISBN: 0-12-093270-9

6. Hysteresis Simulation:

http://demonstrations.woifram.com/MaaneticHvsteresis/

7. W. Chandrasena, P. G. McLaren, Fellow, U. D. Annakkage, Member, and R. P. Jayasinghe, Member, An Improved Low-Frequency Transformer Model for Use in GIC Studies, IEEE Trans Power Delivery, vol. 19, Apr. 2004 8. Paulo Fernando Ribeiro (Editor), Time-Varying Waveform Distortions in Power Systems, August 2009, Wiley-IEEE Press, ISBN: 978-0-470- 71402-7

9. http://en.wikipedia.org/wiki/Magnetic_domain

10. Cullity; C. D. Graham (2008). Introduction to Magnetic Materials. 2nd e . New York: Wiley-IEEE. p. 116. ISBN 0-471 -47741 -9..

Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.

Claims

CLAIMS:

1. A method of measuring characteristics of a line current of a power line in an electrical power system, the method comprising:

2. The method according to Claim 1 further comprising: providing an auxiliary winding extending about a portion of the annular body of the core of the current sensor;

relating the auxiliary direct current to a direct current in the power line.

3. The method according to either one of Claims 1 or 2 further comprising: removing the repeating peak magnitudes from the monitored induced voltage; and

4. The method according to any one of Claims 1 through 3 including providing a current sensor in which the core is arranged to be in a region of magnetic saturation relative to the line current.

5. The method according to any one of Claims 1 through 4 including providing a current sensor in which the core comprises ferrite.

6. The method according to any one of Claims 1 through 5 including monitoring a voltage induced in the secondary winding by taking measurements as a time signature when magnetic flux reverses direction.

7. The method according to any one of Claims 1 through 6 including monitoring a voltage induced in the secondary winding by taking measurements as a time derivative of a reversal of magnetic flux in the core.

8. A method of measuring characteristics of a line current of a power line in an electrical power system, the method comprising:

when no direct current is applied to the line current, monitoring a voltage induced in the secondary winding by an alternating current in the power line by identifying a first duration between a first initial peak magnitude of the induced voltage and a second initial peak magnitude of the induced voltage which is consecutive and opposing in relation to the first initial peak magnitude;

relating the auxiliary direct current to a direct current in the power line.

9. The method according to Claim 8 including providing a current sensor in which the core is arranged to be in a region of magnetic saturation relative to the line current.

10. The method according to either one of Claims 8 or 9 including providing a current sensor in which the core comprises ferrite.

1 . The method according to any one of Claims 8 through 10 including monitoring a voltage induced in the secondary winding by taking measurements as a time signature when magnetic flux reverses direction.

12. The method according to any one of Claims 8 through 11 including monitoring a voltage induced in the secondary winding by taking measurements as a time derivative of a reversal of magnetic flux in the core.

13. A method of measuring characteristics of a direct current of a power line in an electrical power system, the method comprising:

relating the auxiliary direct current to the direct current in the power line.

14. The method according to Claim 13 including providing a current sensor in which the core is arranged to be in a region of magnetic saturation relative to the line current.

15. The method according to either one of Claims 13 or 14 including providing a current sensor in which the core comprises ferrite.

16. The method according to any one of Claims 13 through 15 including monitoring a voltage induced in the secondary winding by taking measurements as a time signature when magnetic flux reverses direction.

17. The method according to any one of Claims 13 through 16 including monitoring a voltage induced in the secondary winding by taking measurements as a time derivative of a reversal of magnetic flux in the core.

18. A method of measuring characteristics of a line current of a power line in an electrical power system, the method comprising:

removing the repeating peak magnitudes from the monitored induced voltage; and

19. The method according to Claim 18 including providing a current sensor in which the core is arranged to be in a region of magnetic saturation relative to the line current.

20. The method according to either one of Claims 18 or 19 including providing a current sensor in which the core comprises ferrite.

21. The method according to any one of Claims 18 through 20 including monitoring a voltage induced in the secondary winding by taking measurements as a time signature when magnetic flux reverses direction.

22. The method according to any one of Claims 18 through 21 including monitoring a voltage induced in the secondary winding by taking measurements as a time derivative of a reversal of magnetic flux in the core.