WO2014162021A1

WO2014162021A1 - Method for calibrating the measurement error of instrument transformers

Info

Publication number: WO2014162021A1
Application number: PCT/ES2013/070216
Authority: WO
Inventors: Andoni GALLASTEGI URIARTE; Urko ZATICA LARRINAGA
Original assignee: Arteche Centro De Tecnología, A.I.E.
Priority date: 2013-04-02
Filing date: 2013-04-02
Publication date: 2014-10-09
Also published as: AR095714A1

Abstract

The invention relates to a method for calibrating a measurement error ε_ref of a first measuring transformer (10) connected to a phase (30) of a high-voltage line, said method comprising the following steps: a) establishing the first transformer as a reference transformer (20) and initially establishing that the measurement error ε_ref is zero; b) obtaining a measurement, at an instant of time, of a first voltage value V_ref of the reference transformer (20) for loading conditions; c) at the above-mentioned instant of time, measuring a second voltage value V_med of a second transformer (10) connected to the above-mentioned phase (30), said second transformer (10) operating under predetermined loading conditions; d) calculating a relative measurement error ε of the second transformer (10) in accordance with ε_med = (V_med- V_ref)/ V_ref; [1 ]; e) calculating the absolute measurement error ε of the second transformer (10) in accordance with ε = εmed + ε_ref[2]; f) repeating steps (b) - (e) for a plurality i of second transformers (10); g) assigning values to the measurement error ε_ref of the reference transformer (20) in order to minimise the difference between the absolute measurement error ε of each second transformer (10) and an expected error for each second transformer under its loading conditions.

Description

METHOD FOR CALIBRATING THE MEASUREMENT ERROR OF INSTRUMENT

TRANSFORMERS

TECHNICAL FIELD

The present invention has its application in capacitive voltage transformers (TTC) installed in high voltage substations, also being applicable to inductive voltage transformers.

BACKGROUND OF THE INVENTION

The capacitive voltage transformers (TTC) normally used in high-voltage lines serve to separate the high-voltage circuit measuring instruments, counters, relays, etc., reducing the voltages to manageable values and proportional to the original primary voltages with the possibility of transmitting high frequency signals through the high voltage lines.

Capacitive voltage transformers are essentially capacitive voltage dividers, that is, a series of capacitors arranged in series, so that if the voltage between the terminals of one of the capacitors is measured, the full voltage can be known.

With the passage of time, the capacitors may lose insulation, reaching perforation. This makes the rest of the capacitors withstand more voltage and can break down. This deterioration of the capacitors is manifested in a measurement error of the corresponding capacitive voltage transformer. Therefore, it is very important to know the status of the transformers before they break down. They could be taken to the laboratory to test them but logically they would have to be disconnected from the network, which is not feasible.

At present, what is done is to measure the accuracy of the equipment without disconnecting them. These transformers are precision measuring equipment (for example 0.2%), so that if an accuracy of 0.6% is measured, the degree of deterioration can be known.

The precision measurements are made at the operating voltage, using a high precision inductive voltage transformer (TTP) as the reference standard, placing the pattern as close to the equipment to be measured in order to avoid measurement errors.

According to the current procedure with TTP standard transformer, the actions to Perform to make the measurements are as follows:

Request disconnection from the work area.

Place the standard transformer under the connection point of the phase to be measured, respecting the distances indicated in the installation sketch.

- Connect the primary of the TTP to the phase and the secondary of the TTP and the TTC to the measuring bridge and install the precision loads.

Protect the TTP site by means of a safety fence (insulated mesh network).

Check the safety distances of the points in tension, between phases and earth.

Return the connection and request the test and test regime for the TTC transformers to be verified.

Measure the loads in service.

Carry out the measurements in each of the TTCs connected to the phase, as indicated below:

i) Angle ratio measurement for the service load on measurement windings.

ii) Disconnection of the measurement winding circuits and connection of the precision load.

iii) Measures of ratio and angle at 25% and 100% of the precision load. iv) Disconnection of the precision load and connection of the measuring circuits. v) Change the connection cables to another TTC of the same phase and another position and repeat the measurement sequence i) -iv).

After the verification of all the TTCs of the phase, the disconnection of the work area is requested again, the TTP is installed in another phase and the sequence is repeated. The same procedure is followed for the third phase.

That is, the TTP standard transformer must be taken to the substation where the TTC transformers to be tested are connected. By means of a measuring bridge (electronic comparator) that is connected to the TTP standard transformer and to each TTC transformer to be tested, as the accuracy of the TTP is known, the margin of error of the TTC transformer being tested is obtained. To connect the standard transformer, the voltage in the line to which it is to be connected must be removed and then reconnected. Once the measurement has been carried out in one phase, the same applies to the rest of the phases.

This procedure currently used has a number of problems: In the first place, there is little availability of standard transformers throughout Spain, and the standard transformer is very large (for voltages of 400 KV it has approximately 4m). In addition you have to take it to the substation, which are usually in places that are not easily accessible. The measuring bridge must also be taken in a van to the substation.

In addition, to handle the standard transformer it is necessary to have specialist technicians to decide where to place it in the substation. To measure with the standard transformer, you must disconnect the area where that standard transformer (discharge) is before and after its connection. When you finish measuring in one phase you have to move on to another, which requires a lot of time and specialized personnel, in addition to many security measures.

On the other hand, the measuring bridge is sensitive to electromagnetic waves, and there are many in the substation. The cables that go from the standard transformer and from the transformer to be tested to the measuring bridge are very long (eg 300 m). In order for the measurements to be correct, there should not be much voltage drop in the cable, and furthermore these measurements cannot be influenced by electromagnetic waves; Therefore, very thick and highly shielded cables are needed.

The result is that using the current procedure with a conventional measuring bridge and using the standard transformer in each substation it takes approximately one week to take the measurements. Taking into account that you can only work with the standard transformer for 2 to 3 months per year, with this procedure it is only possible to inspect about 7 substations per year, that is, 10% of the total substations.

DESCRIPTION OF THE INVENTION

The invention relates to a method for calibrating a measurement error of a measuring transformer according to claim 1; Preferred embodiments of the process are defined in the dependent claims.

By means of the procedure to calibrate the measurement error of the invention, it allows the measurements of the error to be carried out eliminating the need to use a standard transformer, using instead any voltage transformer of the substation as a reference transformer, thus avoiding having to perform line disconnections. Likewise, they are also preferably eliminated. the long cables through the substation since for the measurements a modular measuring bridge is used, in which the different elements of the same are divided and connected remotely to each other.

Thus, the present invention relates to a method for calibrating an erf measurement error of a first measurement transformer connected to a phase of a high voltage line. The procedure includes the following steps:

a) establish said first measurement transformer as a reference measurement transformer and initially establish that said measurement error £ _ref is zero; b) measure a first voltage value V _ref of said reference measurement transformer for load conditions at a given time;

c) at that same time measure a second voltage value V _med of a second measuring transformer connected to said same phase, this second measuring transformer being working according to certain load conditions;

d) calculate a relative measurement error ε of the second measurement transformer according to the following expression:

emed = (Vmed "V _ref ) / V _ref ; [1]

e) calculate the absolute measurement error ε of the second measurement transformer according to the following expression:

ε = £ _me d + _ref [2]

f) reiterate steps b) -e) for a plurality i of second measurement transformers;

g) giving values to said measurement error £ _ref of the reference measurement transformer (20) to minimize the difference between said absolute measurement error ε of each second measurement transformer and an expected error for each second measurement transformer in its conditions loading

According to a preferred embodiment, said expected error NC for each measuring transformer in its load conditions is calculated according to the following expression:

NC = x1 - (x1 -x2) ^* C1 - (x2-x3) ^* (C2 + C3) / (n ^e sec-1)

being:

- n ^e sec: number of secondary of the measuring transformer;

- x1: accuracy of the corresponding measurement transformer when working with its secondary in vacuum;

- x2: accuracy of the corresponding measurement transformer to work with its secondary of measurement to 100% of load and the rest of secondary in empty;

- x3: accuracy of the corresponding measurement transformer to work with all its secondary ones at 100% load; Y

- C1, C2 and C3: percentage of load of each secondary of the measuring transformer with respect to the maximum permissible load.

According to another preferred embodiment said expected error for each measuring transformer in its load conditions is obtained from previously recorded information of each measuring transformer.

Said first and second voltage values V _ref , V _med can be obtained by means of a measuring bridge simultaneously connected to said first and second measuring transformers, respectively.

According to another preferred embodiment said first and second voltage values V _ref , V _med are obtained by means of a modular measuring bridge; This modular measuring bridge comprises a first element and a second element, physically separated from each other, and connected, respectively, to said first and second measurement transformers. These first and second voltage values V _ref , V _med are sent to an electronic comparator that is also part of the modular measuring bridge and that receives these values and voltage and performs step d).

In this case, the first and second elements and the electronic comparator are preferably connected via a wireless local network.

The load conditions of the measuring transformers are calculated using a current measuring element for each measuring transformer, such as, for example, using a clamp meter.

Said first reference measurement transformer may be a capacitive voltage transformer; or it can also be an inductive voltage transformer.

Other advantages and features of the invention will be apparent from the detailed description that follows and will be particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

To complement the description and in order to help a better understanding of the features of the invention, according to an example of practical realization thereof, it is accompanied as an integral part of the description, a set of figures in which the following has been represented by way of illustration and not limitation:

Figure 1 shows a simplified scheme of a modular measuring bridge used to carry out the process of the invention.

Figure 2 shows a graph with the limit values acquired by the NC load level.

DESCRIPTION OF AN EMBODIMENT OF THE INVENTION

A simplified scheme of a modular measuring bridge 100 preferably used for the process of the invention is shown in Figure 1.

This modular measuring bridge 100 is used to determine the measurement error of a capacitive voltage transformer 10, connected to a phase 30 of a high-voltage line of an electrical substation as indicated below.

The modular measuring bridge 100 comprises the following distributed elements:

Two systems of acquisition of measures 1 10, 120 of high precision, with capacity of wireless communication 140, in this case WiFi.

An electronic comparator 130 implemented in an error and load calculation software running on a laptop, with wireless connection capability 150.

In addition, the preferred embodiment includes:

A router to build a wireless data network in the substation. In this case a WiFi router was used.

- Directional antennas.

Preferably, an ammeter clamp is also used to calculate the secondary load of the voltage transformers.

The two 1 10, 120 measurement acquisition systems used are two National Instruments equipment, with 24-bit analog / digital converters, and with a maximum sampling rate of 50 KS / s. These devices have the ability to transmit data via WiFi.

Of the two measurement acquisition systems the first measurement acquisition system 1 10 is connected to a reference transformer 20 that is connected to the same phase 30 of the high voltage line to which the capacitive voltage transformer 10 is connected to test; and the second acquisition system of measurements 120 is connected to the capacitive voltage transformer 10.

Each measurement acquisition system 1 10, 120 is connected to the three secondary (one secondary measurement and two secondary protection) of the reference transformer 20 and the capacitive voltage transformer 10, respectively.

In order to connect directly to the secondary of said transformers 10, 20, a signal adaptation module is used which in turn provides galvanic isolation between the channels. Each module has four measurement inputs, three that are used to simultaneously measure the voltage of the three phase of each transformer, and a fourth that is used together with the clamp meter to measure the load in service of the secondary.

In relation to wireless network 140, in order to achieve greater adaptability of the WiFi network to the different topologies of the substations, two directional antennas that multiply the range of wireless links are incorporated into the system.

When establishing the wireless network, it must be borne in mind that with three elements (two measurement acquisition systems and the WiFi router), physical arrangements can almost always be found that allow a correct communication between the equipment.

The introduction of directional antennas means that there are practically no distance limits within the substation to establish the WiFi wireless network.

Despite the substation being a seemingly open space, the massive presence of metal "obstacles" present a barrier to the establishment of WiFi links. Therefore, for the correct functioning of the WiFi network it is advisable to establish visual contact between the different equipment.

Therefore, for the establishment of communications it is necessary to find the location of the router that allows the visualization of both remote units of measurement at the same time.

In any case, the fact of being an environment with strong electromagnetic fields such as a 400kV substation has not been a problem for WiFi communications.

Once the different elements that constitute the modular measuring bridge have been installed according to what has been indicated in the above, measures can be taken.

Measurement error calculated £ _med capacitive voltage transformer 10 is determined as the relative difference voltage value V _med measured by capacitive voltage transformer 10 and voltage value V _ref measured by reference transformer 20:

£ med = (Vmed- V _re f) / V _re f [1]

In this case the modular measuring bridge is not using the measurement given by a standard transformer; therefore, that calculated measurement error 8 _me d does not correspond to the absolute measurement error ε of the capacitive voltage transformer, but is a relative error. The absolute measurement error ε of the capacitive voltage transformer 10 is calculated as:

ε = £ med + ^ ref

where 8 _re f is the measurement error of the reference transformer 20.

The absolute measurement error ε of the capacitive voltage transformer 10 is therefore referenced to the measurement error 8 _ref of the chosen reference transformer.

As the reference transformer, an inductive voltage transformer is preferably used, whose precision is not altered in its life; but in those substations that do not have inductive voltage transformers, one of the capacitive voltage transformers TTC is chosen as the reference transformer.

This measurement error 8 _re f of the reference transformer 20 can be calibrated by the method of the invention.

For this, the same reference transformer 20 is used to measure different capacitive voltage transformers 10. For each transformer (i) that is measured, a measurement error value is obtained e _me d (i) - As indicated before, the absolute measurement error ε of each capacitive voltage transformer 10 is calculated:

8 (Í) = 8med (¡) + 6ref. [2]

If you want to have greater precision on the measurements, the absolute ε measurement error is calculated:

ε (ί) = 8med (¡) + ε _ΓΘ ί + s _m ed (i) ^* e _re f / (6 _m ed (i) + e _re f) / 100, [3]

the last term being almost negligible compared to the other two addends.

During the measurement process it has been considered that the measurement error 8 _re f of the reference transformer 20 is zero in all cases.

To calibrate the real value of this measurement error ε _ΓΘ ί the following procedure is followed:

The current of each of the three is known by the current clamp Secondary capacitive voltage transformers: 11 (current in the secondary measurement), 12 (current in the first secondary protection) and 13 (current in the second secondary protection).

With these current values and knowing the transformer nominal values, the percentage of load of each secondary% C1,% C2 and% C3 is calculated with respect to the maximum permissible load.

With this information you can know a load level, NC, at which each transformer is working. This level of load, in the absence of data from the equipment manufacturing protocol, provides an indicative value of the expected error in the secondary measurement as a function of the simultaneous loads in the three secondary. The NC load level is calculated according to the following equation:

NC = x1 - (x1 -x2) ^* C1 - (x2-x3) ^* (C2 + C3) / (n ^e sec-1)

where:

- n ^e sec: number of secondary of the transformer;

- x1: precision recorded in the corresponding transformer protocol when working with the three secondary in vacuum (position Ό / 0 / O '). If the data is not available, the value 0.1 is assigned in this case (although this value 0.1 may be different, which will depend on the characteristics of the measuring transformers);

- x2: Accuracy recorded in the corresponding transformer protocol to work with the secondary of measurement at 100% load and the rest of secondary in empty (position Ί / 0 / O '). If it is not available, in this case the value is assigned the value 0.07 (although, as before, another value can be assigned depending on the characteristics of the measuring transformers);

- x3: precision recorded in the corresponding transformer protocol to work with all secondary ones at 100% load (position '1/1 / 1'). If the data is not available, the value -0.1 is assigned (another value can also be assigned, depending on the characteristics of the measuring transformers).

That is, knowing the load in each of the secondary ones, you can calculate the working point of each transformer and obtain the NC load level (i) of each measurement. This NC load level gives an estimate of the accuracy that corresponds to the transformer according to the simultaneous loads of its secondary.

Figure 2 shows a graph with the limit values acquired by the NC load level in case of a capacitive voltage transformer with a secondary measurement and two secondary protection, specified for loads 20, 75 and 75 VA simultaneous.

For each transformer, the difference Δ (ί) between the value of the measurement error ε (ί) of each of the capacitive voltage transformers 10 and the value of the NC load level (i) calculated in each case is calculated. The value of the measurement error ε (ί) can be calculated by equation [2] or by equation [3] if more precision is desired.

Another possibility is that this expected error for each measurement transformer in its load conditions is obtained from previously recorded information of each measurement transformer.

In any case, what is done is to give values to the measurement error £ _re f of the reference transformer 10 so that the difference Δ (ί) is less than a pre-established value (e.g., somewhat percent of the transformer class) in the largest possible number of cases. That is to say, it is about obtaining the value of the measurement error £ _re f that makes the measurement error ε (ί) calculated in the different transformers as close as possible to the last known value of its error in the greatest possible number of cases; This last known value of your error is given by the calculated value of the level of charge or data of a previous campaign, unless there is a perforated capacitor.

To perform the calibration of the measurement error 8 _re f of the reference transformer, the following are also taken into account:

The main deterioration of the capacitive transformers occurs in its upper part. Therefore, in most cases, the error of a TTC or is equal to what it had when it was manufactured, or equal to the error measured the last time it was measured, or has suffered a positive drift.

- The probability of having perforated capacitors is proportional to the longevity of the equipment.

The following describes a couple of examples of precision measurements taken in two substations with the modular measuring bridge, in a first substation and in a second substation in which the calibration procedure of the measurement error of the user transformer has been used as reference.

First, before going to the substation, with the identification of each of the transformers to be measured in that substation, a series of data is recorded on the capacitive voltage transformers TTCs to be measured. Specifically, note is taken of: position, manufacturer, model, serial number, year of manufacturing, primary voltage V _prim , secondary voltage V _sec , N ^e of secondary and secondary powers Pi.

In addition, the measurement errors that are registered in the protocols of each of the transformers are recorded (in case these protocols are accessible), with the variation of loads in the secondary ones to which said errors correspond.

Once in the substation, a voltage transformer is chosen as the reference voltage transformer 20 of the measurements.

For each capacitive voltage transformer 10 whose measurement error is to be determined, the modular measuring bridge 100 is connected as explained above.

The information provided by the modular measuring bridge 100 for each of phases 0, 4 and 8 is:

Voltage in each of the secondary of the reference transformer 20. - Voltage in the secondary of the capacitive voltage transformer 10.

Current in each of the secondary.

Power factor (cosine of phi) of the load of each of the secondary.

Measurement error calculated according to equation [1] of the three phase module.

The modular measuring bridge 100 also provides information on the oscillation of the measurements of the three phases.

In the first substation in which measurements have been made, all the voltage measurement transformers in the substation are TTC capacitive voltage transformers. There are 9 TTCs in line positions and 4 in bars, making a total of 13 TTCs.

The data of the transformers of this first substation are the following:

Position ANO Vprim Vsec N ^g Sec P1 P2 P3

A0 2006 396000 / R3 1 10 / R3 3 20 75 75

A4 2006 396000 / R3 1 10 / R3 3 20 75 75

A8 2007 396000 / R3 1 10 / R3 3 20 75 75

B8 2007 396000 / R3 1 10 / R3 3 20 75 75

C0 2000 396000 / R3 1 10 / R3 3 50 100 100

C4 2000 396000 / R3 1 10 / R3 3 50 100 100

C8 2000 396000 / R3 1 10 / R3 3 50 100 100

OJ 1999 396000 / R3 1 10 / R3 3 50 100 100 D4 1999 396000 / R3 1 10 / R3 3 50 100 100

D8 1990 396000 / R3 1 10 / R3 3 50 100 100

EO 2006 396000 / R3 1 10 / R3 2 20 75 75

E4 2006 396000 / R3 1 10 / R3 3 20 75 75

E8 2006 396000 / R3 1 10 / R3 3 20 75 75

In this substation line E was chosen as the reference position.

The measurements are made in the measurement centralization box, located near the capacitive voltage transformers of each line position. The choice of this measuring point, the closest accessible point to the capacitive transformers, makes it possible to eliminate almost entirely the contribution to the error of the secondary connection cables.

The measured data and the calculated values of the load percentages of each secondary% C1,% C2 and% C3 and the NC load level are as follows:

Position 0/0/0 1/0/0 1/1/1 11% C1 12% C2 13% C3 NC Smed

A0 0.03 0.01 -0.03 0 0% 0 0% 0 0% 0.03 0.000

A4 0.03 0.01 -0.04 0 0% 0 0% 0 0% 0.03 0.012

A8 0.07 0.06 -0.012 0.006 2% 0 0% 0 0% 0.07 0.010

B8 0.1 0.08 -0.14 0.007 2% 0.058 5% 0.001 0% 0.09 0.023

C0 0.1 0.05 -0.1 0.055 7% 0.06 4% 0.001 0% 0.09 0.074

C4 0.1 1 0.05 -0.1 0.05 6% 0.07 4% 0.005 0% 0.10 0.1 10

C8 0.1 0.05 -0.1 1 0.004 1% 0.07 4% 0.004 0% 0.10 0.084

OD 0.13 0.05 -0.13 0.008 1% 0.024 2% 0 0% 0.13 0.280

D4 0.1 0.04 -0.1 1 0.01 1% 0 0% 0 0% 0.10 0.278

D8 0.1 0.03 -0.1 1 0.001 0% 0.024 2% 0 0% 0.10 0.090

E0 0.07 0.02 -0.05 0.01 3% 0.022 2% 0.001 0% 0.07 0.000

E4 0.04 0.02 -0.06 0.009 3% 0.001 0% 0.001 0% 0.04 0.000

E8 0.05 0.02 -0.03 0.001 0% 0.024 2% 0.001 0% 0.05 0.000

With these values, the absolute error ε of each capacitive voltage transformer of the substation referred to the measurement error £ _re f of the reference transformer E0, E4, E8 is also calculated. Is obtained:

Position Year NC Ref £ _mec i ε

A0 2006 0.03 E 0.000 0.05 A4 2006 0.03 E 0.012 0.052

A8 2007 0.07 E 0.010 0.06

B8 2007 0.09 E 0.023 0.073

CO 2000 0.09 E 0.074 0.124

C4 2000 0.10 E 0.1 10 0.15

C8 2000 0.10 E 0.084 0.134

OJ 1999 0.13 E 0.280 0.33

D4 1999 0.10 E 0.278 0.318

D8 1990 0.10 E 0.090 0.14

EO 2006 0.07 E 0.000 0.05

E4 2006 0.04 E 0.000 0.04

E8 2006 0.05 E 0.000 0.05

With these measurements and following the procedure indicated above, values are given to the measurement error 8 _re f of the reference transformers E0 _, E4 and E8 (one for each phase) to make the largest number of transformers their calculated measurement error be as close as possible to the calculated load level.

In the case of the measurements made in this substation, the values of the measurement error that meet this condition are (indicated in bold in the table above):

E0 -> £ _re f = 0.05

E4 -> £ _ref = 0.04

E8 -> £ _ref = 0.05

By means of the indicated procedure, once the measurement error £ _re f of the reference transformer has been determined, the absolute measurement errors of the voltage transformers measured precisely enough to apply predictive maintenance to said transformers are determined, since You can determine which transformers are a certain number of times (4xCI or 7xCI, for example) out of accuracy class.

In this case, none of the voltage transformers measured has an error greater than 0.8 (4xCI), so predictive maintenance of all transformers of this substation not less than 4-5 years could be recommended.

In the case of the second substation, all voltage transformers in the substation are capacitive voltage transformers TTC. In this substation the lines dedicated to the AVE are biphasic. There are 18 TTCs in three-phase line positions, 4 in two-phase lines and 6 in bars, making a total of 28 TTCs.

In the case of this second substation it was not possible to have the data of the manufacturing protocols. The available data of the transformers of this substation are the following:

Position ANO Vprim Vsec N ^g Sec P1 P2 P3

A0 1991 220000 / R3 1 10 / R3 3 50 100 100

A4 1991 220000 / R3 1 10 / R3 3 50 100 100

A8 2008 220000 / R3 1 10 / R3 3 20 75 75

BO 1991 220000 / R3 1 10 / R3 3 50 100 50

B4 1991 220000 / R3 1 10 / R3 3 50 100 50

B8 1991 220000 / R3 1 10 / R3 3 50 100 100

CO 1990 220000 / R3 1 10 / R3 3 50 100 50

C8 1990 220000 / R3 1 10 / R3 3 50 100 50

D20 2009 220000 / R3 1 10 / R3 3 20 75 75

D28 2009 220000 / R3 1 10 / R3 3 20 75 75

EO 1991 220000 / R3 1 10 / R3 3 50 100 50

E4 1991 220000 / R3 1 10 / R3 3 50 100 50

E8 1991 220000 / R3 1 10 / R3 3 50 100 50

FO 2009 220000 / R3 1 10 / R3 3 20 75 75

F4 2009 220000 / R3 1 10 / R3 3 20 75 75

F8 2009 220000 / R3 1 10 / R3 3 20 75 75

GO 2009 220000 / R3 1 10 / R3 3 20 75 75

G4 2009 220000 / R3 1 10 / R3 3 20 75 75

G8 2009 220000 / R3 1 10 / R3 3 20 75 75

HO 2005 220000 / R3 1 10 / R3 3 50 100 50

H4 2005 220000 / R3 1 10 / R3 3 50 100 50

H8 2005 220000 / R3 1 10 / R3 3 50 100 50

JO 1991 220000 / R3 1 10 / R3 3 50 100 50

J4 1991 220000 / R3 1 10 / R3 3 50 100 50

J8 1991 220000 / R3 1 10 / R3 3 50 100 50

KO 1991 220000 / R3 1 10 / R3 3 50 100 50

K4 1991 220000 / R3 1 10 / R3 3 50 100 50

K8 1991 220000 / R3 1 10 / R3 3 50 100 50 In this substation line H was chosen as the reference position.

Position 0/0/0 1/0/0 1/1/1 11% C1 12% C2 13% C3 NC Emed

A0 0.1 0.07 -0.1 0 0% 0.024 2% 0 0% 0.10 0.840

A4 0.1 0.07 -0.1 0 0% 0 0% 0 0% 0.10 1, 290

A8 0.1 0.07 -0.1 0 0% 0.023 2% 0 0% 0.10 0.230

BO 0.1 0.07 -0.1 0 0% 0 0% 0.17 22% 0.08 0.690

B4 0.1 0.07 -0.1 0 0% 0 0% 0.22 28% 0.08 0.035

B8 0.1 0.07 -0.1 0.012 2% 0 0% 0.78 50% 0.06 0.084

CO 0.1 0.07 -0.1 0.01 1% 0.14 9% 0.12 15% 0.08 0.710

C8 0.1 0.07 -0.1 0 0% 0.14 9% 0.8 102% 0.01 0.740

OD 0.1 0.07 -0.1 0.012 4% 0.14 12% 0.125 1 1% 0.08 -0.070

D8 0.1 0.07 -0.1 0 0% 0.14 12% 0.83 70% 0.03 0.080

EO 0.1 0.07 -0.1 0 0% 0.024 2% 0 0% 0.10 0.060

E4 0.1 0.07 -0.1 0 0% 0 0% 0 0% 0.10 1, 260

E8 0.1 0.07 -0.1 0 0% 0.024 2% 0 0% 0.10 0.814

FO 0.1 0.07 -0.1 0.021 7% 0 0% 0 0% 0.10 0.042

F4 0.1 0.07 -0.1 0.021 7% 0 0% 0 0% 0.10 -0.075

F8 0.1 0.07 -0.1 0 0% 1, 1 93% 0 0% 0.02 -0.021

GO 0.1 0.07 -0.1 0.024 8% 0 0% 0 0% 0.10 0.256

G4 0.1 0.07 -0.1 0.01 1 3% 0.022 2% 0 0% 0.10 0.021

G8 0.1 0.07 -0.1 0 0% 0.83 70% 0 0% 0.04 0.067

HO 0.1 0.07 -0.1 0 0% 0.023 1% 0 0% 0.10 0.000

H4 0.1 0.07 -0.1 0 0% 0 0% 0 0% 0.10 0.000

H8 0.1 0.07 -0.1 0 0% 0.025 2% 0 0% 0.10 0.000

JO 0.1 0.07 -0.1 0 0% 0.1 6% 0.08 10% 0.09 1, 460

J4 0.1 0.07 -0.1 0.01 1% 0.1 6% 0.12 15% 0.08 1, 410

J8 0.1 0.07 -0.1 0.01 1% 0.1 6% 0.7 89% 0.02 0.740 κο 0.1 0.07 -0.1 0.07 9% 0.1 6% 0.08 10% 0.08 0.670

K4 0.1 0.07 -0.1 0.03 4% 0.1 6% 0.12 15% 0.08 0.060

0,18 0.1 0.07 -0.1 0.07 9% 0.1 6% 0.7 89% 0.02 0.800

With these values, the absolute error ε of each capacitive voltage transformer of the substation referred to the measurement error £ _re f of the reference transformer H0, H4, H8 is also calculated. Is obtained:

Position Year NC Ref £ med ε

A0 1991 0.10 H 0.840 0.94

A4 1991 0.10 H 1, 290 1, 39

A8 2008 0.10 H 0.230 0.28

B0 1991 0.08 H 0.690 0.79

B4 1991 0.08 H 0.035 0.14

B8 1991 0.06 H 0.084 0.13

C0 1990 0.08 H 0.710 0.81

C8 1990 0.01 H 0.740 0.79

OD 2009 0.08 H -0.070 0.03

D8 2009 0.03 H 0.080 0.13

E0 1991 0.10 H 0.060 0.16

E4 1991 0.10 H 1, 260 1.36

E8 1991 0.10 H 0.814 0.86

F0 2009 0.10 H 0.042 0.14

F4 2009 0.10 H -0.075 0.02

F8 2009 0.02 H -0.021 0.03

G0 2009 0.10 H 0.256 0.36

G4 2009 0.10 H 0.021 0.12

G8 2009 0.04 H 0.067 0.12

H0 2005 0.10 H 0.000 0.10

H4 2005 0.10 H 0.000 0.10

H8 2005 0.10 H 0.000 0.05

JO 1991 0.09 H 1, 460 1, 56

J4 1991 0.08 H 1, 410 1.51

J8 1991 0.02 H 0.740 0.79

KO 1991 0.08 H 0.670 0.77 K4 1991 0.08 H 0.060 0.16

K8 1991 0.02 H 0.800 0.85

With these measurements and following the procedure indicated above, values are given to the measurement error 8 _re f of the reference transformers H0, H4 and H8 (one for each phase) to make the largest number of transformers their calculated measurement error be as close as possible to the calculated load level.

H0 -> £ _ref = 0.10

H4 -> £ _ref = 0.10

H8 -> £ _re f = 0.05

By means of the aforementioned procedure, once the measurement error z _{re \} of the reference transformer has been determined, the absolute measurement errors of the voltage transformers measured accurately enough to apply predictive maintenance to said transformers are determined, since You can determine which transformers are a certain number of times (4xCI or 7xCI, for example) out of accuracy class.

After the measurements made, it is seen that in this second substation there are several transformers that have an error greater than 0.8 (4xClass), and even a couple of them with an error greater than 1, 4 (7xClass), which can be indicative of a short-term predictive maintenance than the rest.

In addition, of those with an error greater than 0.8 there are four cases -A0, C8, E8 and K8- of which the data from a previous campaign indicated that they had no problem; that is, the error obtained is indicative that the deterioration of these transformers is very fast, and that they should be monitored.

On the other hand, in this case two other transformers that have an out-of-class error and that are 2008 and 2009 transformers are also striking: A8 and G0.

As it has been possible to verify in the two cases of measurements carried out in two substations by means of the process of the invention, without the need for a standard transformer, the measurement error of the substation measurement transformers can be determined, and based on The values obtained establish preventive maintenance of them.

In this text, the word "understand" and its variants (such as "understanding", etc.) should not be interpreted in an exclusive manner, that is, they do not exclude the possibility that what has been described includes other elements, steps, etc.

On the other hand, the invention is not limited to the specific embodiments that have been described but also covers, for example, the variants that can be made by the average person skilled in the art (for example, in terms of the choice of dimensions, components , configuration, etc.), within what follows from the claims.

Claims

one . Procedure for calibrating a measurement error 8 _re f of a first measuring transformer (10) connected to a phase (30) of a high voltage line; The procedure includes the following steps:

a) establishing said first measurement transformer as reference measurement transformer (20) and initially establishing that said measurement error 8 _re f is zero;

b) measure a first voltage value V _ref of said reference measurement transformer (20) at a given time for load conditions; c) at that same time measure a second voltage value V _med of a second measuring transformer (10) connected to said same phase (30), this second measuring transformer (10) being working according to certain load conditions ;

d) calculate a relative measurement error ε of the second measurement transformer (10) according to the following expression:

£ med = (Vmed- V _re f) / V _re f; [one ]

e) calculate the absolute measurement error ε of the second measurement transformer (10) according to the following expression:

ε = 8med + 6 _re f [2]

f) reiterate steps b) -e) for a plurality i of second measurement transformers (10);

g) giving values to said measurement error 8 _re f of the reference measurement transformer (20) to minimize the difference between said absolute measurement error ε of each second measurement transformer (10) and an expected error for each second transformer of measure in your loading conditions.

2. The method according to claim 1, wherein said expected NC error for each measuring transformer (10, 20) under its load conditions is calculated according to the following expression:

NC = x1 - (x1 -x2) ^* C1 - (x2-x3) ^* (C2 + C3) / (n ^e sec-1)

being:

- n ^e sec: number of secondary of the measuring transformer (10, 20); - x1: accuracy of the corresponding measurement transformer (10, 20) when working with its secondary in vacuum;

- x2: precision of the measuring transformer (10, 20) corresponding to working with its secondary of measurement at 100% load and the rest of secondary in empty;

- x3: precision of the measuring transformer (10, 20) corresponding to work with all its secondary ones at 100% load; Y

- C1, C2 and C3: percentage of load of each secondary of the measuring transformer (10, 20) with respect to the maximum permissible load.

3. The method according to claim 1, wherein said expected error for each measuring transformer in its load conditions is obtained from previously recorded information of each measuring transformer.

4. The method according to any of claims 1 -3, wherein said first and second voltage values V _ref , V _med are obtained by means of a measuring bridge simultaneously connected to said first and second measuring transformers (10, 20), respectively.

5. Method according to any of claims 1 -3, wherein said first and second voltage values V _ref , V _med are obtained by a modular measuring bridge (100) comprising a first element (1 10) and a second element (120) separated from each other and connected, respectively, to said first and second measurement transformers (10, 20), and these first and second voltage values being sent V _ref , V _med to an electronic comparator (130) which also It is part of the modular measuring bridge (100) that receives these values and voltage and performs step d).

Method according to any one of claims 1-5, in which the load conditions of the measuring transformers (10, 20) are calculated using a current measuring element.