Title: Method for soft sensing of power source changeover.

Technical field: The present invention relates a method for soft sensing of power source changeover which includes measurement and characterization of various electrical parameters to determine the type of source as typically they resemble very closely for any distinction.

Background and prior art: Power outages are a frequent problem with which both customers and electric utilities must contend. The interruption of power at a customer's premises whether residential, industrial or business, can occur for any number of reasons. Interruption may be for example, lasting for several hours caused by a power line being disconnected by a collapsed tree. For the residential customer, the long term outage of power can represent anything from a mere inconvenience to an extreme health or safety risk. The owner of a factory or business may experience loss of sales and productivity due to the interruption in the supply of electric power. Conversely the outage may be momentary, such as caused by a breaker at a substation that trips due to a surge of electricity generated during a storm.

Consequently, generator sets have become a necessity in areas where power outages take place very often. With the continuous rise in generator fuel, and to have a clear distinction in unit pricing between the two, makes it vital to bill them separately. Thus it is important for the customer to realize the source of power to regulate his usage. In this manner, the customer can reduce his bill amount. One of the existing methods is wiring a generator sense cable to all the meters. However, the solution is not feasible as it becomes tedious and confusing when a panel has multiple energy meters. Therefore, there exists a need to identify the power source and cost allocation i.e. utility of generator. Another existing solution involves wiring the generator such that it sends signals to a remote computer regarding usage. But it involves additional wires, requires additional efforts for wiring and poses a safety hazard to the operator and associated equipment. Yet another existing solution requires that signals indicating usage are sent using communication modules such as PLCs. However such signals are not reliable due to the typically noisy environment.

Therefore, the present invention endeavors to provide for a robust solution which overcomes the disadvantages associated with the prior art.

Summary of the invention; The present invention relates to a method for identifying the power source based on set of electrical parameters which form the source signature. This method aids in accurate measurement without the need of dedicated links/contactors for switchover.

Detailed description of drawings: A full understanding of the invention can be gained from the following description of the preferred embodiments when read in conjunction with the accompanying drawings in which:
Figure 1 is the flowchart for determining the switchover from utility to generator
Figure 2 is the flowchart for determining the switchover from generator to utility.
Figure 3 is the graphical representation of variation in frequency in the power supply from utility
supply line monitored.
Figure 4 is the graphical representation of the variation in frequency in the generator power
supply monitored.
Figure 5 is an overview of the device employing the method of the present invention

Detailed description of the invention: The present invention provides for a method for soft sensing of power source changeover having a power line connected to first power source and at least one back-up second power source. The method comprises steps of sensing at least one electrical parameter of the power line connected to first power source or any one of back-up second power source. The method further comprises of comparing the sensed values of the said electrical parameters of the said power line connected to first power source or any one of backup second power source to source signature of said power source. Thereafter, the method comprises delivering an indication to the user whether the power line is connected to first power source of any one of the back-up second power sources.

The source signature for a power source supplying power to a power line can be determined by obtaining values for at least one electrical parameter of the said power including

first power source and at least one back-up second power source. The values so obtained for each electrical parameter are stored as a signature specific for that parameter and power source.
The first power source is utility whereas the second back-up power source may be selected from generator, wind, solar, hydel, thermal. For the purpose of explanation, the invention is described using two sources: utility and generator. The sensing step of the method of present invention comprises sensing of at least one electrical parameter including time to changeover i.e. cold start or warm start; power factor; VAR (Reactive power); frequency, changeover characteristics; voltage harmonics.

In a situation, when the source changeover takes place from utility to generator, the method comprises method steps of: a. Detection of a cold start (SI); b. Determination of power factor (S2); c. Determination of VAR (reactive power) (S3); d. Checking for frequency fluctuations (S4); e. Determination of voltage harmonics (S5); f. Confirming switchover to generator (S6) (Refer Figure 1)

The sequence of steps enlisted are performed by the microcontroller. Subsequently the power factor of the incoming power supply can be checked. For example, if the power factor for generator supply is 0.8 then this is used as a base. But since there is no capacitor bank connected to the generator, power factor varies as and when the loads are switched on and off. Because of this variation, the VAR (reactive power) also varies significantly. In the present embodiment, the power supply frequency from a generator is maintained at close to 50Hz. It is noticed that voltage harmonics is usually higher on generator power supply since the supply is limited to a confined area. Combination of these effects will distinguish generator supply from utility or other sources.

As mentioned hereinabove, there is a visible difference in certain parameters when the load is connected to different sources which can be captured and used as a signature to identify these sources. As depicted in graphs of figs. 3 and 4, the variation in frequency in utility power supply and generator supply monitored over one day. It is evident from the graphs that generator has a more stable frequency supply whereas the frequency on utility supply varies across the day.

Further, in case of switchover from generator to utility as seen in Figure 2, the method for soft sensing of power source changeover as provided by the present invention comprises method steps of: a. Detection of a warm start (Rl); b. Determination of power factor (R2); c. Determination of VAR (reactive power) (R3); d. Checking for frequency fluctuations (R4); e. Determination of voltage harmonics (R5); f. Detection of switching line transients (R6); g. Confirming switchover to generator (R7). Here, it is noticed that due to presence of capacitor banks attached to utility supply, fluctuations with switching loads in power factor and consequently in VAR (reactive power) are minimal. However, here the frequency of the power supply varies due to switching of heavy machinery in remote location across the grid whereas the voltage harmonics is lower on utility supply line due to spread of power across the grid. There is also the presence of line switchover transients which the meter can record to confirm switchover to utility.

The present invention also provides for a system (10) employing the method of the present invention. Referring to figure 5, first power source (11) and a second back-up power source (12) are connected to the changeover switch (13). The changeover switch is in turn connected to the measurement device (14) which is integrated with the method of soft sensing of power source changeover of the present invention. The measurement device refers to any known measurement system including power meter, circuit monitor or any interface used for identifying the source and recording the various measurement parameters associated with that source. The measurement device thus provides accurate information regarding source of the power supply supplied to any residential, commercial or industrial establishment (15) to which it is connected.

The method of soft sensing of power source changeover as provided by the present invention is advantageous over prior art that it does not require any additional signatures or wiring and are not affected by power line noises or distortions. The method measures the basic electrical parameter measurements with display interface and includes the key idea of soft sensing features for capturing start-up behavior, to include cold and warm start sequences, reactive power variations with load, power factor and voltage harmonics for accurate determination of source behaviors.

Advantageously, the simplified wiring scheme eliminates the need for a dedicated DC source signaling for various measurement installations, typically utility to generator switchover and vice versa as in an industrial electrical distribution network. It is this soft sensing mechanism for the measurement products; wherein the internal parameter registers of the measurement equipment are defined as separate blocks in memory and are automatically swapped between sources after soft sensing; which in turn eliminates the dedicated sensing of the DC source internally on the measurement product whenever there is a changeover. This scheme efficiently eliminates the complex wiring sequence as typical applicable for all measurement products.

Furthermore, this method for soft sensing provides early information of the load degradation over time and monitoring this behavior provides early indicators for quality, product efficiency, operating life.

Yet another advantage of the present invention is that the method aids in accurate measurement without the need of dedicated links/contactors for switchover. This method clearly defines an intelligent & efficient measurement sequence for identifying the type of Source in the measurement system based on sequence of measurement sequence and switching over to defined source registers based on type of source.

The foregoing description has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed and obviously many modifications and variations are possible in the light of the above teachings as would normally occur to one skilled in the art to which the invention relates. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated.

We Claim:
1. A method for soft sensing of power source changeover having a power line connected to
first power source and at least one back-up second power source said method comprising
a. sensing at least one electrical parameter of the power line connected to any one of
first power source or any one of back-up second power source
b. comparing the sensed values of the electrical parameters of the power line connected
to any one of first power source or any one of back-up second power source to source
signature of said power source
c. delivering an indication to the user whether the power line is connected to a first
power source or the back-up second power source

2. The method for soft sensing of power source changeover as claimed in claim 1 wherein
the source signature is procured by,
a. obtaining values for at least one electrical parameter of each power source including
each back-up power source
b. storing the values for electrical parameter in memory which in turn is recorded as a
patter or signature for each of the power sources.

3. The method for soft sensing of power source changeover as claimed in claims 1 or 2 wherein the first power source is utility

4. The method for soft sensing of power source changeover as claimed in claims 1 or 2 wherein the back-up second power source is generator, wind, solar, hydel, thermal source.

5. The method for soft sensing of power source changeover as claimed in any of the preceding claims, wherein sensing step includes sensing of at least one electrical parameters including cold start or warm start; power factor; VAR (Reactive power); frequency, changeover characteristics; voltage harmonics.

6. The method for soft sensing of power source changeover as claimed in any of the
preceding claims wherein sensing the source changeover from utility to generator
comprises method steps of:
a. Detection of a cold start (SI)
b. Determination of power factor (S2)
c. Determination of VAR (reactive power) (S3)
d. Checking for frequency fluctuations (S4)
e. Determination of voltage harmonics (S5)
f. Confirming switchover to generator (S6)

7. The method for soft sensing of power source changeover as claimed in claim 6 wherein in due to the absence of capacitor bank being connected to generator, the power factor varies when the loads are switched on or off.

8. The method for soft sensing of power source changeover as claimed in claim 7, wherein the variation in power factor leads to variation in VAR (reactive power).

9. The method for soft sensing of power source changeover as claimed in claim 8, wherein the voltage harmonics is higher in generator power source supply as the supply is limited to a confined area.

10. The method for soft sensing of power source changeover as claimed in claim 5 wherein sensing the source changeover from generator to utility comprises method steps of:
a. Detection of a warm start (Rl)
b. Determination of power factor (R2)
c. Determination of VAR (reactive power) (R3)
d. Checking for frequency fluctuations (R4)
e. Determination of voltage harmonics (R5)
f. Detection of switching line transients (R6)
g. Confirming switchover to generator (R7)

11. The method for soft sensing of power source changeover as claimed in claim 10, wherein
due to presence of capacitor banks attached to utility supply, fluctuations in power factor
and in VAR (reactive power) are minimal.

12. The method for soft sensing of power source changeover as claimed in claim 10 wherein voltage harmonics is lower on utility supply line due to spread of power across the grid.

13. The method for soft sensing of power source changeover as claimed in claim 10 wherein there is fluctuation in frequency of power supply due to movement of heavy machinery in remote location across the grid.

14. The method for soft sensing of power source changeover as claimed in any of the preceding claims wherein the wiring for the first power supply source and back-up second power supply source is simple eliminating the need for dedicated DC source signaling for various measurement installation in an electrical distribution network.

15. The method for soft sensing of power source changeover as claimed in any of the preceding claims wherein the soft sensing optionally provides information of load degradation over time providing early indicators for quality, product efficiency and operating life.

16. A system (10) for soft sensing of power source changeover comprising a measurement device integrated with the method for soft sensing of power source changeover as claimed in any of the preceding claims.

17. The system (10) for soft sensing of power source changeover wherein the system comprises of first power source (11) and at least one second back-up power source (12) coupled to the measurement device (14) via changeover switch (13) for providing accurate information of source of power supplied to an establishment (15).