CN104345218B - Three-phase reactor reactance value measuring system and method - Google Patents

Abstract

A system for measuring the reactance value of a three-phase reactor, including: the DC side of the three-phase inverter power supply unit is the DC power supply provided by the system through rectification or a battery for the inverter, and the output of the AC side is low-pass filtered by RC connected to one end of the three-phase reactor under test; the other end of the three-phase reactor under test is connected to the neutral point of the system; the three-phase electrical signal detection units are respectively connected in series to the output of the three-phase inverter power supply unit and connected to the three-phase reactor under test The collected current signals are respectively output to the first connection terminal of the calculation control unit; the composition and connection relationship of the calculation control unit are: the first connection terminal, conditioning circuit, A/D, CPLD, The dual-port RAM, DSP, and CPLD are respectively externally connected with a PWM transmission circuit and a binary input and output circuit, and the PWM transmission circuit and binary input and output circuit are externally connected through the second connection terminal. The invention has the characteristics of compact structure, advanced function, high test efficiency, convenient on-site use, and small measurement error.

Description

System and method for measuring reactance value of three-phase reactor

technical field

The invention relates to a reactance value measuring system of a three-phase reactor. The invention also relates to a method for measuring the reactance value of a three-phase reactor using the system.

Background technique

Reactor is a commonly used and important power equipment in the power grid. It is widely used in reactive power compensation, current limiting, steady current (smoothing), filtering, damping, and phase shifting in the circuit. GB/T1094.6—2011 "Power Transformer Part 6: Reactor" includes the measurement of the reactance value of the reactor as a factory test item; for the reactor that has been put into operation, the measurement of its reactance value is important to judge whether it is running normally. Indicators, included in the preventive test items; and according to national standards, the reactance measurement of the iron core reactor should be effective when it is greater than 90% of the rated current.

The traditional three-phase reactor reactance value measuring device is composed of generator, voltage regulator, compensation capacitor bank, current transformer, voltage transformer, voltmeter, ammeter, connecting cable and supporting fasteners. This kind of device has the disadvantages of large space occupation, fragmented structure, and high cost, and can only be used in manufacturers or professional testing institutions; at present, it is almost impossible to complete reactance measurement for reactors that have been put into use.

In addition, the traditional three-phase reactor reactance value measurement is based on the three-phase symmetrical voltage source measurement method, which has the following defects: (1) The inductance test results are related to the internal resistance of the power supply, and different internal resistance test results are different, so there is a system Error; (2) It is difficult to make the values of the three-phase currents closer, and the different sizes of the three-phase currents affect the induced voltage between phases through the mutual inductance, thereby affecting the measurement results. There is no regulation on the current deviation; (3) Even if the three-phase current can be achieved The values are equal, but the three-phase current is not necessarily symmetrical, which still affects the induced voltage between phases, resulting in inaccurate measurement.

Contents of the invention

The first technical problem to be solved by the present invention is to propose a system for measuring the reactance value of a three-phase reactor.

The second technical problem to be solved by the present invention is to propose a method for measuring the reactance value of a three-phase reactor using the system.

The system of the invention has the characteristics of compact structure, advanced functions, high test efficiency and convenient on-site use, and the measurement accuracy and error of the reactance value measurement method of the three-phase reactor using the system are small.

To solve the above-mentioned first technical problem, the technical solution adopted in the present invention is:

A reactance value measuring system for a three-phase reactor, characterized in that it includes a three-phase inverter power supply unit, a three-phase electrical signal detection unit, and a calculation control unit;

The DC side of the three-phase inverter power supply unit is rectified by the system or the DC power provided by the battery for the inverter, and the output of the AC side is connected to one end of the three-phase reactor to be tested after passing through a low-pass filter composed of RC ;The other end of the three-phase reactor under test is connected to the neutral point of the system;

The three-phase electrical signal detection units are respectively connected in series with the three-phase inverter power supply unit and output to the three-phase line connected to the three-phase reactor to be tested, and the current signals collected by it are respectively output to the first terminal of the calculation control unit;

The composition and connection relation of described computing control unit are: the first connecting terminal, conditioning circuit, A/D, CPLD (ComplexProgramableLogicDevice), dual-port RAM and DSP (DigitalSignalProcessing) that are connected successively, and described CPLD also externally connects PWM respectively. The transmission circuit and the binary input and output circuit, the PWM transmission circuit and the binary input and output circuit are externally connected through the second connection terminal.

The low-pass filter composed of RC is a resistor and a capacitor in series, and a Hall voltage sensor is connected in parallel at both ends of the capacitor, and outputs u _A , u _B , and u _C .

The three-phase inverter power unit is composed of three single-phase inverters, the three-phase inverter power unit adopts PWM (pulse width modulation) technology, the frequency of PWM is 2-12kHz, the command cycle is 40us, and the device outputs a sine wave frequency The range is 0.5~50Hz;

The three-phase electrical signal detection unit uses a Hall current sensor to measure the three-phase currents i _A , i _B , and i _C , uses an RC filter circuit (see Fig. 3 conditioning circuit) and a Hall voltage sensor to measure the three-phase voltages u _A , u _B , u _C ;

The computing control unit CPU adopts TI's high-speed floating-point DSP chip TMS320C6713, and the core frequency can reach 225MHz. The logic chip uses CPLD to control the external 8-channel 14-bit AD and issue PWM instructions. There are a certain number of digital input and output modules inside the controller, which are used to control the external AC contactor.

To solve the above-mentioned second technical problem, the technical solution adopted in the present invention is:

A method for measuring the reactance value of a three-phase reactor using the system comprises the following steps:

The first step is to calculate the maximum frequency that the system can withstand according to the rated inductance value, rated current of the three-phase reactor to be tested and the capacity of the system;

The second step is to calculate the phase shift and amplitude coefficient of the sampling voltage caused by the RC filter according to the output frequency of the system, and reverse the voltage zero-crossing point;

The third step is to find the voltage zero-crossing point according to the detected voltage value, and establish sinωt and cosωt;

In the formula, ω is the angular frequency of the power supply; t is the time;

The fourth step is to calculate the active and reactive currents of the output current according to sinωt and cosωt:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}\mathrm{<span\; class="notranslate">\; sin</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}}\underset{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 1</span>}}{\overset{\mathrm{<span\; class="notranslate">\; N</span>}}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; k</span>}}\mathrm{<span\; class="notranslate">\; cos</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

In the formula, I _M1 and I _M2 are the peak value of active current and reactive current respectively; N is the number of discrete points of a cycle; i _k is the detected current discrete signal; sin(k) and cos(k) are the values of sinωt and cosωt respectively Discrete quantity;

The fifth step is to calculate the inductance value of the reactor according to the voltage and reactive current:

$\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; u</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}}$

Since the capacity formula of the three-phase reactor is P _N =3ωL _N I ² , that is, the capacity of the reactor is proportional to the frequency of the applied current, therefore, under the same test current, reducing ω can effectively reduce the test capacity, which can also Reduce the required test equipment capacity.

Therefore, the idea of the present invention is to reduce the measurement equipment capacity by reducing the frequency of the measurement power supply to meet the requirements of on-site measurement; to make a three-phase frequency-controlled and current-controlled current source instead of a three-phase voltage source to improve the three-phase inductance measurement accuracy.

Compared with the prior art, the present invention has the following advantages:

1. The sine wave frequency range of the system output of the present invention is 0.5～50Hz, and the capacity formula of the three-phase reactor is P _N =3ωL _N I ² Therefore, under the same test current, the reduction The capacity of required test equipment can be effectively reduced.

2. The three-phase inverter power supply unit of the present invention adopts the current tracking PWM technology, and the output three-phase current values are symmetrical and equal, which eliminates the adverse effects of current deviation on the mutual inductance voltage, improves the measurement accuracy, and eliminates the internal resistance of the power supply There is no systematic error in the measurement results.

Description of drawings

Fig. 1 a is one of structural representations (wiring diagram) of the present invention;

Fig. 1 b is the second (three-phase inverter circuit) of structural representation of the present invention;

Fig. 2 is a schematic diagram of wiring of a three-phase electrical signal detection unit;

Fig. 3 is a schematic diagram of the composition and connection relationship of the computing control unit.

detailed description

The present invention will be further described below in conjunction with accompanying drawing.

Refer to Fig. 1-Fig. 3 for four years, the embodiment of the reactance value measurement system of the three-phase reactor of the present invention includes a three-phase inverter power supply unit, a three-phase electric signal detection unit and a calculation control unit.

The DC side of the three-phase inverter power supply unit is the DC power supply provided by the system through rectification or the battery for the inverter, and the output of the AC side is passed through a low-pass filter composed of RC (A, B, and C external connection circuits in Figure 1a). Connect one end of the three-phase reactor to be tested, and the other end of the three-phase reactor to be tested is connected to the neutral point of the system; the three-phase electrical signal detection units are respectively connected in series with the three-phase inverter power unit output to the three-phase reactor connected to the three-phase reactor to be tested. On the phase line, the current signals collected by it are respectively output to the first connection terminal of the calculation control unit; the composition and connection relationship of the calculation control unit are: first connection terminal, conditioning circuit, A/D, CPLD, dual-port The RAM, DSP, and CPLD are respectively externally connected with a PWM transmission circuit and a binary input and output circuit, and the PWM transmission circuit and binary input and output circuit are externally connected through the second connection terminal.

The three-phase inverter power supply unit is composed of three single-phase inverters. The three-phase inverter power supply unit adopts PWM (pulse width modulation) technology. The frequency of PWM is 2-12kHz, the command cycle is 40us, and the output sine wave frequency range of the device is 0.5～50Hz; the three-phase electric signal detection unit uses Hall current sensor to measure three-phase current i _A , i _B , i _C , uses RC filter circuit and Hall voltage sensor to measure three-phase voltage u _A , u _B , u _C ; The computing control unit CPU adopts TI's high-speed floating-point DSP chip TMS320C6713, and the core frequency can reach 225MHz. The logic chip uses CPLD to control the external 8-channel 14-bit AD and issue PWM instructions. There are a certain number of digital input and output modules inside the controller, which are used to control the external AC contactor.

The current signal collected by the Hall current sensor enters the A/D converter through the RC filter of the control board, the CPLD controls the AD sampling time, and writes the collected signal into the dual-port RAM; value and the capacity of the test equipment to calculate the amplitude and frequency of the command current, and write it back to the CPLD through the dual-port RAM. Optical fiber communication is used to improve the anti-interference performance of the test equipment calculation and the controller unit.

The method for measuring the reactance value of a three-phase reactor by using the above system includes the following steps:

The first step is to calculate the maximum frequency that the system can withstand according to the rated inductance value, rated current of the three-phase reactor to be tested and the capacity of the system;

The second step is to calculate the phase shift and amplitude coefficient of the sampling voltage caused by the RC filter according to the output frequency of the system, and reverse the voltage zero-crossing point;

The third step is to find the voltage zero-crossing point according to the detected voltage signal, and establish sinωt and cosωt;

The fourth step is to calculate the active and reactive currents of the output current according to sinωt and cosωt;

The fifth step is to calculate the inductance value of the reactor according to the voltage and reactive current.

Claims (3)

1. a reactance value measuring system for three-phase reactor, is characterized in that: comprise three phase inverter unit, three-phase electricity detecting signal unit and calculation control unit;

The dc source that the DC side of described three phase inverter unit provides for inverter through rectification or with battery for system, the output of AC connect respectively tested three-phase reactor one end after the low pass filter of RC composition; Tested three-phase reactor other end welding system neutral point;

Described three-phase electricity detecting signal unit is connected on respectively that three phase inverter unit exports in the triple line that connects tested three-phase reactor, the current signal of its collection exports respectively the first binding post of calculation control unit to;

The composition of described calculation control unit with annexation is: the first binding post, modulate circuit, A/D, CPLD (ComplexProgramableLogicDevice), dual port RAM and the DSP (DigitalSignalProcessing) that are connected successively, described CPLD also distinguishes external PWM transmission circuit and input and output circuit, and described PWM transmission circuit and input and output circuit outreach by the second binding post.

2. the reactance value measuring system of three-phase reactor according to claim 1, is characterized in that: the low pass filter of described RC composition is resistance and the electric capacity of series connection, the Hall voltage sensor in parallel at electric capacity two ends, and it exports u_A、u_B、u_C。

3. the method that the system of employing as described in claim 1-2 any one carried out the measurement of three-phase reactor reactance value, is characterized in that comprising the following steps:

The first step, calculates according to the volumeter of specified inductance value, rated current and the native system of tested three-phase reactor the peak frequency that native system can bear;

Second step, calculates sampled voltage phase shift and the amplitude coefficient that RC wave filter causes, the anti-voltage over zero that pushes away according to native system output frequency;

The 3rd step, finds voltage over zero according to detecting magnitude of voltage, and sets up sin ω t and cos ω t;

In formula, ω is power supply angular frequency; T is the time;

The 4th step, calculate gaining merit and reactive current of output current according to sin ω t and cos ω t:

In formula, I_M1、I_M2Be respectively watt current, peak value of idle current; N is a cycle discrete point number; i_kIt is the electric current discrete signal detecting; Sin (k), cos (k) are respectively the discrete magnitudes of sin ω t and cos ω t;

The 5th step, the inductance value according to voltage and reactive current calculating reactor:

Because the capacity formula of three-phase reactor is P_N＝3ωL_NI²The capacity that is reactor is directly proportional to the frequency that applies electric current, therefore, under same test current, reduces ω and can effectively reduce capacity of experiment, also just can reduce required testing equipment capacity.