CN109557400B - Online detection method for electric energy quality and insulation performance of three-phase IT system of microgrid - Google Patents

Abstract

An online detection method for the electric energy quality and the insulation performance of a three-phase IT system of a microgrid is realized by a device comprising a controller unit, an insulation signal sampling unit and a voltage and current sampling unit. The voltage and current sampling unit and the insulation signal sampling unit are respectively used for acquiring three-phase voltage and current signals, monitoring narrow pulse voltage signals and ground narrow pulse voltage signals and transmitting the ground narrow pulse voltage signals to the controller unit for online detection of electric energy quality and insulation performance; the controller unit controls the first electronic switch, the second electronic switch and the third electronic switch in the first signal sampling branch, the second signal sampling branch and the third signal sampling branch to be turned on and obtained according to the ground narrow pulse voltage signal. According to the method, the on-line monitoring of the power quality and the insulation performance of the three-phase three-wire system alternating current IT system can be realized without injecting an additional independent signal; the respective insulation resistance to ground of 3 generating lines can accurately be calculated, short-circuit fault can be monitored, and the degree of generating line insulation deterioration can be judged.

Description

Online detection method for electric energy quality and insulation performance of three-phase IT system of microgrid

The invention discloses a method and a device for detecting the power quality and the insulation performance of a three-phase IT system of a micro-grid on line, wherein the patent application is a divisional application, the original application number is 201610894157.2, and the application date is 2016, 10 and 13.

Technical Field

The invention relates to a method and equipment for online monitoring of power grid performance, in particular to a method for online detecting the power quality and the insulation performance of a three-phase IT system of a micro-grid.

Background

When a solar energy, wind energy and geothermal energy power generation system, a mobile power generation vehicle, a gasoline and diesel generator and other micro-grid systems supply power to loads such as mines, field medical vehicles, ships and the like, the power supply reliability is required to be high, and the safety is good. IT is a good choice to use IT systems for power supply. When the IT system has a first fault, the fault current is small, and the metal shell of the electrical equipment can not generate dangerous contact voltage, so that the electrical equipment can continuously operate without cutting off a power supply, but the power quality and the insulation performance of the electrical equipment need to be monitored on line and informed through an alarm device, and the fault is timely checked and eliminated.

In the existing insulation on-line monitoring of the IT system, a detection method based on an injection signal is widely adopted, and by collecting the voltage of a sampling resistor or the current on a phase line of the IT system when the signal is injected, when the IT system is short-circuited to the ground or the insulation is degraded, the insulation resistor to the ground is reduced, and the voltage on the sampling resistor or the fault characteristic quantity in the current on the phase line of the IT system when the signal is injected is sharply increased, so that the judgment can be carried out according to the voltage or the current. When the insulation of an IT system is monitored by adopting a signal injection method, no matter a direct current signal, a single-frequency alternating current signal or a double-frequency alternating current signal is injected, a corresponding independent signal source is needed, and the system is complex; and the effective value of the voltage of the independent signal source is not allowed to exceed 50V, which brings difficulty to the judgment of fault characteristic quantity and fault line selection and positioning.

Disclosure of Invention

In order to solve the problems in insulation online monitoring of an IT system, the invention provides an online detection method for the electric energy quality and the insulation performance of a three-phase IT system of a micro-grid, wherein the method loads a monitoring narrow pulse voltage on a loop formed by phase lines through a protective ground to form a corresponding ground narrow pulse voltage; carrying out online detection on the insulation performance according to the monitored narrow pulse voltage and the corresponding ground narrow pulse voltage; and analyzing the power quality according to the three-phase alternating current voltage and current data.

The narrow pulse voltage monitoring is formed by loading the line voltage of the three-phase IT system in a pulse conduction mode and is realized by pulse type switching on of an electronic switch. The pulse type turn-on time of the electronic switch is the zero crossing point of the line voltage of the three-phase IT system.

The monitoring narrow pulse voltage and the corresponding ground narrow pulse voltage have at least 3 groups.

The method is realized by a microgrid three-phase IT system electric energy quality and insulation performance online detection device, and the device comprises a controller unit, an insulation signal sampling unit and a voltage and current sampling unit.

The insulation signal sampling unit comprises a first signal sampling branch, a second signal sampling branch, a third signal sampling branch and a sampling resistor; the first signal sampling branch circuit comprises a first electronic switch and a first current-limiting resistor which are connected in series, the second signal sampling branch circuit comprises a second electronic switch and a second current-limiting resistor which are connected in series, and the third signal sampling branch circuit comprises a third electronic switch and a third current-limiting resistor which are connected in series; one end of the first signal sampling branch is connected to a phase line A of the three-phase alternating current IT system, one end of the second signal sampling branch is connected to a phase line B of the three-phase alternating current IT system, and one end of the third signal sampling branch is connected to a phase line C of the three-phase alternating current IT system; the other end of the first signal sampling branch circuit, the other end of the second signal sampling branch circuit and the other end of the third signal sampling branch circuit are connected with one end of a sampling resistor, and the other end of the sampling resistor is connected to a protective ground.

The ground narrow pulse voltage of the three-phase alternating current IT system comprises a phase line A ground narrow pulse voltage, a phase line B ground narrow pulse voltage and a phase line C ground narrow pulse voltage, and the controller unit respectively controls the first electronic switch, the second electronic switch and the third electronic switch to be switched on and obtained.

The method for realizing the online detection of the power quality and the insulation performance of the device comprises the following specific steps:

step 1, sampling and obtaining a phase line A to ground narrow pulse voltage, a phase line B to ground narrow pulse voltage and a phase line C to ground narrow pulse voltage; sampling to obtain three-phase alternating current voltage and current data;

step 2, analyzing three-phase alternating-current voltage and current data to obtain monitoring narrow pulse voltages corresponding to the phase line A ground narrow pulse voltage, the phase line B ground narrow pulse voltage and the phase line C ground narrow pulse voltage respectively; analyzing three-phase alternating current voltage and current data to obtain an electric energy quality index;

step 3, forming an equation set by a relational expression between the ground narrow pulse voltage of the phase line A and the corresponding monitoring narrow pulse voltage, a relational expression between the ground narrow pulse voltage of the phase line B and the corresponding monitoring narrow pulse voltage, and a relational expression between the ground narrow pulse voltage of the phase line C and the corresponding monitoring narrow pulse voltage;

solving an equation set to obtain a phase line A ground insulation resistance value, a phase line B ground insulation resistance value and a phase line C ground insulation resistance value;

and 5, processing results and returning to the step 1.

The phase line A-to-ground narrow pulse voltage can comprise a first phase line A-to-ground narrow pulse voltage and a second phase line A-to-ground narrow pulse voltage, and the controller unit controls the first electronic switch to be switched on and obtained when the voltage between the phase line B and the phase line C crosses zero and the voltage between the phase line A and the phase line B crosses zero respectively; the phase line B ground narrow pulse voltage can comprise a phase line B first ground narrow pulse voltage and a phase line B second ground narrow pulse voltage, and the controller unit controls the second electronic switch to be switched on and obtained when the voltage of the phase line C and the phase line A crosses zero and the voltage of the phase line B and the phase line C crosses zero respectively; the phase line C ground narrow pulse voltage may include a phase line C first ground narrow pulse voltage, a phase line C second ground narrow pulse voltage, and the controller unit controls the third electronic switch to be turned on and obtained when the voltage between the phase line a and the phase line B crosses zero, and the voltage between the phase line C and the phase line a crosses zero, respectively. At the moment, the specific steps of the device for realizing the online detection of the power quality and the insulation performance comprise:

sampling to obtain narrow pulse voltage to ground; sampling to obtain three-phase alternating voltage and current data;

analyzing three-phase alternating-current voltage and current data to obtain monitoring narrow pulse voltages corresponding to a first ground narrow pulse voltage pair of a phase line A, a second ground narrow pulse voltage pair of the phase line A, a first ground narrow pulse voltage pair of a phase line B, a second ground narrow pulse voltage pair of the phase line B, a first ground narrow pulse voltage pair of a phase line C and a second ground narrow pulse voltage pair of the phase line C respectively; analyzing three-phase alternating current voltage and current data to obtain an electric energy quality index;

step three, judging according to the narrow pulse voltage signal to the ground, and returning to the step one if the ground insulation of the phase line A, the phase line B and the phase line C is normal;

step four, judging according to the narrow pulse voltage signal to the ground, and if one of the phase lines A, B and C is short-circuited to the ground, going to step seven;

judging according to the ground narrow pulse voltage signals, and respectively judging whether the phase lines A, B and C are poor in ground insulation;

step six, calculating the earth insulation resistance value of the phase line when the earth insulation of 1 phase line is poor, or calculating the earth insulation resistance value of each of 2 phase lines when the earth insulation of 2 phase lines is poor, or calculating the earth insulation resistance value of each of 3 phase lines when the earth insulation of 3 phase lines is poor;

and step seven, processing the result and returning to the step one.

The first signal sampling branch circuit further comprises a first diode connected in series, the second signal sampling branch circuit further comprises a second diode connected in series, and the third signal sampling branch circuit further comprises a third diode connected in series;

the first signal sampling branch circuit further comprises a fourth diode, the second signal sampling branch circuit further comprises a fifth diode, and the third signal sampling branch circuit further comprises a sixth diode; the fourth diode is reversely connected in parallel with the first electronic switch, the fifth diode is reversely connected in parallel with the second electronic switch, and the sixth diode is reversely connected in parallel with the third electronic switch. The diode is connected in reverse parallel with the electronic switch, and means that the cathode of the diode is connected to the current inflow end of the electronic switch, and the anode of the diode is connected to the current outflow end of the electronic switch.

The first diode enables the current on the first electronic switch to flow to the protective ground only from the phase line A, the second diode enables the current on the second electronic switch to flow to the protective ground only from the phase line B, and the third diode enables the current on the third electronic switch to flow to the protective ground only from the phase line C; alternatively, the first diode allows the current on the first electronic switch to flow only from the protected ground to phase a, the second diode allows the current on the second electronic switch to flow only from the protected ground to phase B, and the third diode allows the current on the third electronic switch to flow only from the protected ground to phase C.

The device can also comprise one or more units of an alarm unit, a man-machine interaction unit and a verification unit.

The invention has the beneficial effects that: (1) meanwhile, online detection of the electric energy quality and the insulating property of the three-phase IT system of the micro-grid is realized; (2) the insulation performance of the three-phase three-wire system alternating current IT system can be monitored on line without injecting an additional independent signal; (3) the monitoring signal is a direct-current narrow pulse voltage, so that the influence of the phase line to ground capacitance on the insulation resistance monitoring can be eliminated; (4) the respective ground insulation resistance values of the 3 phase lines of the three-phase three-wire system alternating current IT system can be accurately calculated, and besides the short-circuit fault can be monitored, the degree of insulation degradation of the phase lines can be judged.

Drawings

FIG. 1 is a block diagram of an embodiment of an online detection device for power quality and insulation performance;

FIG. 2 is a schematic circuit diagram of an embodiment of an isolated signal sampling unit;

FIG. 3 is an equivalent circuit diagram of the insulated signal sampling unit according to the embodiment when the first electronic switch is turned on;

FIG. 4 is an equivalent circuit diagram of the second electronic switch of the embodiment of the insulation signal sampling unit when it is turned on;

FIG. 5 is an equivalent circuit diagram of the insulated signal sampling unit according to the embodiment when the third electronic switch is turned on;

FIG. 6 is a diagram of the phase line AC voltage waveform and the narrow pulse voltage signal to ground.

Detailed Description

The invention is further described below with reference to the accompanying drawings.

Fig. 1 is a block diagram illustrating an embodiment of an online detection device for power quality and insulation performance. The embodiment of fig. 1 comprises a controller unit 100, an insulation signal sampling unit 200, a voltage and current sampling unit 300, a verification unit 400, an alarm unit 500 and a human-computer interaction unit 600. A. B, C are phase line A, phase line B and phase line C of a three-phase AC IT system, which is a three-wire system without neutral line; the PE is a protection conductor or a protection ground of the IT system.

FIG. 2 is a schematic circuit diagram of an embodiment of an insulation signal sampling unit, which includes a first electronic switch M1, a second electronic switch M2, a third electronic switch M3, and a first current limiting resistor R_E1A second current limiting resistor R_E2A third current limiting resistor R_E3Sampling resistor R_SA first diode D1, a second diode D2, a third diode D3, a fourth diode D4, a fifth diode D5, and a sixth diode D6; a first electronic switch M1 and a first current limiting resistor R_E1A first signal sampling branch consisting of a first diode D1 and a fourth diode D4, and a second electronic switchM2, second current limiting resistor R_E2A second signal sampling branch consisting of a second diode D2 and a fifth diode D5, a third electronic switch M3, and a third current limiting resistor R_E3The third diode D3 and the sixth diode D6 form a third signal sampling branch. In FIG. 2, R_F1、R_F2、R_F3The ground insulation resistors of the phase line A, the phase line B and the phase line C are respectively; k1, K2, K3 are control signals for the first electronic switch M1, the second electronic switch M2, the third electronic switch M3, respectively, and K1, K2, K3 come from the controller unit. The first electronic switch, the second electronic switch and the third electronic switch are all controlled electronic switches, and in the embodiment of fig. 2, triode type photo-couplers are adopted as M1, M2 and M3. The first electronic switch, the second electronic switch and the third electronic switch can be replaced by a direct current solid-state relay or other fully-controlled electronic switches.

In the embodiment of fig. 2, the fourth diode D4, the fifth diode D5 and the sixth diode D6 protect the first electronic switch M1, the second electronic switch M2 and the third electronic switch M3 from an excessive reverse voltage, respectively; when the first electronic switch, the second electronic switch and the third electronic switch can bear the reverse voltage of the circuit, the fourth diode, the fifth diode and the sixth diode are not necessary.

The device loads the monitoring narrow pulse voltage on a loop formed between phase lines through a protective ground, and measures the corresponding narrow pulse voltage to the ground; carrying out online detection on the insulation performance according to the monitored narrow pulse voltage and the corresponding ground narrow pulse voltage; the monitoring narrow pulse voltage is formed by controlling a pulsed loading of the line voltages between the phases of the three-phase IT system. The first electronic switch, the second electronic switch and the third electronic switch are all switched on in a short-time and pulse mode, and only one of the first electronic switch, the second electronic switch and the third electronic switch is controlled to be switched on and switched off at each time. The first electronic switch can be controlled to be switched on when the potential of the phase line A is higher than or equal to the potential of the protective ground PE, and the current on the first electronic switch can only flow from the phase line A to the protective ground PE at the moment, or the first electronic switch can be controlled to be switched on when the potential of the phase line A is lower than the potential of the protective ground PE, and the current on the first electronic switch can only flow from the protective ground PE to the phase line A at the moment; similarly, the second electronic switch can be controlled to be switched on when the potential of the phase line B is higher than the potential of the protective ground PE, and the current on the second electronic switch can only flow from the phase line B to the protective ground PE at this time, or controlled to be switched on when the potential of the phase line B is lower than the potential of the protective ground PE, and the current on the second electronic switch can only flow from the protective ground PE to the phase line B at this time; the third electronic switch can be controlled to be switched on when the potential of the phase line C is higher than the potential of the protective ground PE, and the current on the third electronic switch can only flow from the phase line C to the protective ground PE at the moment, or the third electronic switch can be controlled to be switched on when the potential of the phase line C is lower than the potential of the protective ground PE, and the current on the third electronic switch can only flow from the protective ground PE to the phase line C at the moment. Since the PE potential of the protective earth is related to A, B, C three-phase potential and its insulation from earth, when the potential of a certain phase line is higher than or equal to the potentials of the other two phase lines, the potential of the phase line is definitely higher than or equal to the PE potential of the protective earth; or when the potential of a phase line is lower than or equal to the potentials of the other two phase lines, the potential of the phase line is definitely lower than or equal to the potential of the protective earth PE.

In the embodiment of fig. 2, the first diode D1 enables the current of the first electronic switch M1 to flow only from the phase line a to the protection ground PE, the second diode D2 enables the current of the second electronic switch M2 to flow only from the phase line B to the protection ground PE, and the third diode D3 enables the current of the third electronic switch M3 to flow only from the phase line C to the protection ground PE; when the first electronic switch, the second electronic switch and the third electronic switch have unidirectional conduction performance and are not connected with the fourth diode, the fifth diode and the sixth diode in parallel, the first diode, the second diode and the third diode are not necessary.

In the embodiment of fig. 2, the first diode D1, the second diode D2, the third diode D3, the fourth diode D4, the fifth diode D5 and the sixth diode D6 are connected in reverse, and the first electronic switch M1, the second electronic switch M2 and the third electronic switch M3 are connected in reverse in the current direction, so that the currents of M1, M2 and M3 only partially flow from the protection ground PE to the phase line, and the rest flows from the phase line to the protection ground PE. When the first diode D1, the second diode D2, the third diode D3, the fourth diode D4, the fifth diode D5 and the sixth diode D6 in the embodiment of fig. 2 are all connected in the reverse direction, and the current directions of the first electronic switch M1, the second electronic switch M2 and the third electronic switch M3 are all connected in the reverse direction, the first diode D1 enables the current of the first electronic switch M1 to flow only from the protected ground PE to the phase line a, the second diode D2 enables the current of the second electronic switch M2 to flow only from the protected ground PE to the phase line B, and the third diode D3 enables the current of the third electronic switch M3 to flow only from the protected ground PE to the phase line C.

FIG. 3 is an equivalent circuit diagram of the insulated signal sampling unit according to the embodiment of the present invention, wherein the phase line A is a narrow pulse voltage U to ground₁The controller unit controls M1 to turn on the acquisition. When M1 is turned on in fig. 3, the potential of phase line a should be higher than the potential of protective earth PE. 3 line voltages U of FIG. 3_AB、U_BC、U_ACOnly 2 of them are independent, and 2 of them are used to monitor the narrow pulse voltage. Let U in FIG. 3_ABIs U_AB4，U_BCIs U_BC4And let R be_E1＝R_EHaving R₄＝R_E1+R_S＝R_E+R_S. At this time have

FIG. 4 is an equivalent circuit diagram of the second electronic switch of the embodiment of the insulation signal sampling unit when it is turned on, where the phase line B is a narrow pulse voltage U to ground₂The controller unit controls M2 to turn on the acquisition. When M2 is turned on in fig. 4, the potential of phase line B should be higher than the potential of protective earth PE. 3 line voltages U of FIG. 4_BC、U_CA、U_BAOnly 2 of them are independent, and 2 of them are used to monitor the narrow pulse voltage. Let U in FIG. 4_BCIs U_BC5，U_CAIs U_CA5And let R be_E2＝R_EHaving R₄＝R_E2+R_S＝R_E+R_S. At this time have

FIG. 5 shows a third electronic switch of the embodiment of the insulation signal sampling unitEquivalent circuit diagram at power-on, phase line C to ground narrow pulse voltage U₃The controller unit controls M3 to turn on the acquisition. When M3 is turned on in fig. 5, the potential of the phase line C should be higher than the potential of the protective earth PE. 3 line voltages U of FIG. 5_CA、U_AB、U_CBOnly 2 of them are independent, and 2 of them are used to monitor the narrow pulse voltage. Let U in FIG. 5_CAIs U_CA6，U_ABIs U_AB6And let R be_E3＝R_EHaving R₄＝R_E3+R_S＝R_E+R_S. At this time have

In the formula (1), the formula (2) and the formula (3), only R is_F1、R_F2、R_F3For unknown quantities, the monitoring narrow pulse voltage U is measured when the first electronic switch is switched on_AB4、U_BC4Phase line A to ground narrow pulse voltage U₁Monitoring narrow pulse voltage U when second electronic switch is on_BC5、U_CA5Phase line B to ground narrow pulse voltage U₂Monitoring narrow pulse voltage U when third electronic switch is on_CA6、U_AB6Phase line C to ground narrow pulse voltage U₃R can be calculated by combining the vertical type (1), the formula (2) and the formula (3)_F1、R_F2、R_F3. Calculation of R_F1、R_F2、R_F3The specific steps for realizing the online detection of the power quality comprise:

step 1, sampling and obtaining a phase line A to ground narrow pulse voltage, a phase line B to ground narrow pulse voltage and a phase line C to ground narrow pulse voltage; sampling to obtain three-phase alternating current voltage and current data;

step 2, analyzing three-phase alternating-current voltage and current data to obtain monitoring narrow pulse voltages corresponding to the phase line A ground narrow pulse voltage, the phase line B ground narrow pulse voltage and the phase line C ground narrow pulse voltage respectively; analyzing three-phase alternating current voltage and current data to obtain an electric energy quality index;

step 3, forming an equation set by a relational expression between the ground narrow pulse voltage of the phase line A and the corresponding monitoring narrow pulse voltage, a relational expression between the ground narrow pulse voltage of the phase line B and the corresponding monitoring narrow pulse voltage, and a relational expression between the ground narrow pulse voltage of the phase line C and the corresponding monitoring narrow pulse voltage;

solving an equation set to obtain a phase line A ground insulation resistance value, a phase line B ground insulation resistance value and a phase line C ground insulation resistance value;

and 5, displaying the result and alarming, and returning to the step 1.

In the formula (1), when U is selected_BC40, i.e. U in fig. 3_BC0 or U_AB40, i.e. U in fig. 3_ABTurning on M1 when 0 simplifies the expression, facilitating calculation, U_BC＝0、U_ABWhen the voltage is equal to 0, the phase line A obtained by turning on M1 respectively is connected with the narrow pulse voltage U to the ground₁Respectively expressed as a first narrow pulse voltage U of phase line A₁₁Phase line A, second opposite ground narrow pulse voltage U₁₂. The same applies to equations (2) and (3), and the pulse-type turn-on time of the electronic switch is the zero-crossing point of the three-phase IT system line voltage, U in FIG. 4_CA＝0、U_BCPhase line B obtained by turning on M2 respectively at 0 to ground narrow pulse voltage U₂Respectively expressed as a first narrow pulse voltage U of phase line B₂₁Phase line A, second opposite ground narrow pulse voltage U₂₂(ii) a U in FIG. 5_AB＝0、U_CAWhen the voltage is equal to 0, the phase line C obtained by turning on M3 respectively is connected with the ground narrow pulse voltage U₃Respectively expressed as a first narrow pulse voltage U to ground of phase line C₃₁Phase line A, second opposite ground narrow pulse voltage U₃₂。

In fig. 3, phase line a is a first narrow pulse voltage U to ground₁₁Control of M1 at U by the controller unit_BCWhen the voltage is equal to 0, the narrow pulse voltage is loaded between the phase lines and monitored on a loop formed by PE_AB1I.e. U in FIG. 3_AB，U₁₁Is now U in FIG. 3₁(ii) a Phase line A second narrow pulse voltage U to ground₁₂M1 at U controlled by the controller unit_AC0 or U_ABWhen the phase line is not equal to 0, the phase line is switched on to obtain the phase lineThe monitoring narrow pulse voltage on a loop formed by PE is U_AB3Or U_BC2I.e. U in FIG. 3_ABOr U_BC，U₁₂Is now U in FIG. 3₁. Select U_BC0. Or U_AC0, or U_ABWhen M1 is turned on at zero crossing point, such as 0, the potential of the phase line a at the selected zero crossing point is higher than that of the protective earth PE, and M1 current flows from the phase line a to the protective earth PE.

In fig. 4, phase line B has a first narrow pulse voltage U to ground₂₁Control of M2 at U by the controller unit_CAWhen the voltage is equal to 0, the narrow pulse voltage is loaded between the phase lines and monitored on a loop formed by PE_BC1I.e. U in FIG. 4_BC，U₂₁Is now U in FIG. 4₂(ii) a Phase line B second ground narrow pulse voltage U₂₂M2 at U controlled by the controller unit_BA0 or U_BCWhen the voltage is equal to 0, the narrow pulse voltage is loaded between the phase lines and monitored on a loop formed by PE_BC3Or U_CA2I.e. U in FIG. 4_BCOr U_CA，U₂₂Is now U in FIG. 4₂. Select U_CA0. Or U_BA0, or U_BCWhen M2 is turned on at zero crossing point, such as 0, the potential of the phase line B at the zero crossing point is selected to be higher than that of the protection ground PE, and M2 current flows from the phase line B to the protection ground PE.

In fig. 5, phase line C has a first narrow pulse voltage U to ground₃₁Control of M3 at U by the controller unit_ABWhen the voltage is equal to 0, the narrow pulse voltage is loaded between the phase lines and monitored on a loop formed by PE_CA1I.e. U in FIG. 5_CA，U₃₁Is now U in FIG. 5₃(ii) a Phase line C second ground narrow pulse voltage U₃₂M3 at U controlled by the controller unit_CB0 or U_CAWhen the voltage is equal to 0, the narrow pulse voltage is loaded between the phase lines and monitored on a loop formed by PE_CA3Or U_AB2I.e. U in FIG. 5_CAOr U_AB，U₃₂Is now U in FIG. 5₃. Select U_AB0. Or U_CB0, or U_CAWhen M3 is turned on at a zero-crossing point equal to 0, the potential of a phase line C at the selected zero-crossing point is higher than that of the protective earth PE, and M3 current flows from the phase line C to the protective earth PE.

Under different states of the system, the first narrow pulse voltage U of the phase line A measured when M1, M2 and M3 are respectively switched on₁₁Phase line A, second opposite ground narrow pulse voltage U₁₂Phase line B first grounded narrow pulse voltage U₂₁Phase line B, second opposite ground narrow pulse voltage U₂₂Phase line C first narrow pulse voltage U₃₁Phase line C, second opposite ground narrow pulse voltage U₃₂See table 1.

Fig. 6 is a schematic diagram of the phase line ac voltage waveform and the narrow pulse voltage signal to ground. In FIG. 6, U_AB、U_BC、U_CAThe line voltage among phase lines A, B and C is the first ground narrow pulse voltage U of phase line A at the time shown by pulse 1, pulse 2, pulse 3, pulse 4, pulse 5 and pulse 6₁₁Phase line A, second opposite ground narrow pulse voltage U₁₂Phase line B first grounded narrow pulse voltage U₂₁Phase line B, second opposite ground narrow pulse voltage U₂₂Phase line C first narrow pulse voltage U₃₁Phase line C, second opposite ground narrow pulse voltage U₃₂The measurement time of (2).

TABLE 1

Phase line A first narrow pulse voltage U₁₁Phase line A, second opposite ground narrow pulse voltage U₁₂Measured when M1 was on, U in Table 1₁₁Is U_BCU measured when 0₁Value U₂₁Is U_ABU measured when 0₁The value is obtained.

When A, B, C insulation to ground is normal, R_F1、R_F2、R_F3Is very large, so no matter in U_BCU measured when 0₁₁Value is also in U_ABU measured when 0₁₂Values are all equal to orWhich is close to a value of 0.

When A is short-circuited to ground, the potential of the protective ground PE is equal to the potential of the A phase, and therefore, no matter in U_BCU measured when 0₁₁Value is also in U_ABU measured when 0₁₂The values are all equal to or close to a value of 0.

When B is short-circuited to ground, the potential of the protective ground PE is equal to the potential of the B phase, and therefore, at U_BCMeasure U when equal to 0₁Having U₁₁≈U_AB1(ii) a At U_ABMeasure U when equal to 0₁Having U₁₂≈0。

When C is short-circuited to ground, the potential of the protective earth PE is equal to the potential of the C phase, and therefore, at U_BCMeasure U when equal to 0₁Having U₁₁≈U_AB1(ii) a At U_ABMeasure U when equal to 0₁Having U₁₂≈U_BC2。

When insulation of only A to ground is poor, R_F2、R_F3A large value of (A), R_F1Is a resistance value of poor insulation to ground, therefore, in U_BCU measured when 0₁₁A value of R₄And R_F1Parallel connection and R_F2And R_F3After parallel connection, narrow pulse voltage U is monitored_AB1A partial pressure value of approximately 0; at U_ABU measured when 0₁₂A value of R₄、R_F1、R_F2After parallel connection with R_F3For monitoring narrow pulse voltage U_BC2The partial pressure value of (2) is close to a value of 0.

When only B is poorly insulated from ground, R_F1、R_F3A large value of (A), R_F2B is a resistance value of poor insulation to ground, and therefore, in U_BCU measured when 0₁₁A value of R₄And R_F1After parallel connection with R_F2And R_F3After parallel connection, narrow pulse voltage U is monitored_AB1A partial pressure value of approximately R₄And R_F2For U at this time_AB1The partial pressure value of (a); at U_ABU measured when 0₁₂A value of R₄、R_F1、R_F2After parallel connection with R_F3At this time, the narrow pulse voltage U is monitored_BC2The partial pressure value of (2) is close to a value of 0.

When insulation of only C to ground is poor, R_F1、R_F2A large value of (A), R_F3The resistance value of C poor insulation to ground is set, so that the resistance value of U_BCU measured when 0₁₁A value of R₄And R_F1After parallel connection with R_F2And R_F3After parallel connection, narrow pulse voltage U is monitored_AB1A partial pressure value of approximately R₄And R_F3For U at this time_AB1The partial pressure value of (a); at U_ABU measured when 0₁₂A value of R₄、R_F1、R_F2After parallel connection with R_F3At this time, the narrow pulse voltage U is monitored_BC2A partial pressure value of approximately R₄And R_F3For U at this time_BC2The partial pressure value of (a).

When there is poor insulation of A, B to ground, R_F3A large value of (A), R_F1、R_F2A, B resistance values of poor insulation to ground, so U_BCU measured when 0₁₁A value of R₄And R_F1After parallel connection with R_F2And R_F3After parallel connection, narrow pulse voltage U is monitored_AB1A partial pressure value of approximately R₄And R_F1After parallel connection with R_F2For U at this time_AB1The partial pressure value of (a); at U_ABU measured when 0₁₂A value of R₄、R_F1、R_F2After parallel connection with R_F3At this time, the narrow pulse voltage U is monitored_BC2The partial pressure value of (2) is close to a value of 0.

When there is poor insulation of B, C to ground, R_F1A large value of (A), R_F2、R_F3B, C resistance values of poor insulation to ground, so U_BCU measured when 0₁₁A value of R₄And R_F1After parallel connection with R_F2And R_F3After parallel connection, narrow pulse voltage U is monitored_AB1A partial pressure value of approximately R₄And R_F2And R_F3After parallel connection, the current is aligned with the time U_AB1The partial pressure value of (a); at U_ABU measured when 0₁₂A value of R₄、R_F1、R_F2After parallel connection with R_F3At this time, the narrow pulse voltage U is monitored_BC2A partial pressure value of approximately R₄And R_F2After parallel connection with R_F3For U at this time_BC2The partial pressure value of (a).

When there is poor insulation of C, A to ground, R_F2A large value of (A), R_F1、R_F3A, C resistance values of poor insulation to ground, so U_BCU measured when 0₁₁A value of R₄And R_F1After parallel connection with R_F2And R_F3After parallel connection, narrow pulse voltage U is monitored_AB1A partial pressure value of approximately R₄And R_F1After parallel connection with R_F3For U at this time_AB1The partial pressure value of (a); at U_ABU measured when 0₁₂A value of R₄、R_F1、R_F2After parallel connection with R_F3At this time, the narrow pulse voltage U is monitored_BC2A partial pressure value of approximately R₄、R_F1After parallel connection with R_F3For U at this time_BC2The partial pressure value of (a).

When A, B, C are all poorly insulated from ground, R_F1、R_F2、R_F3A, B, C resistance values of poor insulation to ground, so U_BCU measured when 0₁₁A value of R₄And R_F1After parallel connection with R_F2And R_F3After parallel connection, narrow pulse voltage U is monitored_AB1The partial pressure value of (a); at U_ABU measured when 0₁₂A value of R₄、R_F1、R_F2After parallel connection with R_F3At this time, the narrow pulse voltage U is monitored_BC2The partial pressure value of (a).

Phase line B first ground narrow pulse voltage U₂₁Phase line B, second opposite ground narrow pulse voltage U₂₂Measured when M2 was on, U in Table 1₂₁Is U_CAU measured when 0₂Value U₂₂Is U_BCU measured when 0₂The value is obtained. Phase line C first ground narrow pulse voltage U₃₁Phase line C, second opposite ground narrow pulse voltage U₃₂Measured when M3 was on, U in Table 1₃₁Is U_ABU measured when 0₃Value U₃₂Is U_CAU measured when 0₃The value is obtained. U shape₂₁、U₂₂And U₃₁、U₃₂Are all equal to U₁₁、U₁₂The measurement method is the same, and the measurement results are shown in Table 1.

From the data in Table 1, it can be concluded that when U is present₁₁、U₁₂、U₂₁、U₂₂、U₃₁、U₃₂When the phase line A, the phase line B and the phase line C are all close to and equal to 0, the ground insulation of the phase line A, the phase line B and the phase line C is normal; when U is turned₁₁≈U_AB1、U₁₂When the current is approximately equal to 0, the phase line B is short-circuited to the ground; when U is turned₂₁≈U_BC1、U₂₂When the current is approximately equal to 0, the phase line C is short-circuited to the ground; when U is turned₃₁≈U_CA、U₃₂When 0, phase line a is shorted to ground.

When U is turned₁₁Has a value of U_AB1Partial pressure values of (i.e. 0 < U)₁₁＜U_AB1And U is₁₂When the insulation is approximately equal to 0, the phase line B has poor insulation to the ground; when U is turned₂₁Has a value of U_BC1Partial pressure values of (i.e. 0 < U)₂₁＜U_BC1And U is₂₂When the insulation is approximately equal to 0, the phase line C has poor insulation to the ground; when U is turned₃₁Has a value of U_CA1Partial pressure values of (i.e. 0 < U)₃₁＜U_CA1And U is₃₂When the insulation is approximately equal to 0, the phase line A has poor insulation to the ground.

If none of the above conditions are met, phase line A, B, C is poorly insulated from ground.

When the insulation of the phase line A to the ground is poor, the U is measured and calculated at will₂₁、U₂₂、U₃₂Any one or more of the three measured partial pressure ratios, e.g. measuring and calculating U₃₁Partial pressure ratio of, i.e. in U_ABWhen M3 is on at 0, U is measured₃₁And monitoring narrow pulse voltage U corresponding thereto_CAI.e. by

R can be calculated_F1。

When only the phase line B has poor insulation to the ground, the U is measured and calculated arbitrarily₁₁、U₃₁、U₃₂Any one or more of the three measured partial pressure ratios, e.g. measuring and calculating U₁₁Partial pressure ratio of, i.e. in U_BCWhen M1 is on at 0, U is measured₁₁And monitoring narrow pulse voltage U corresponding thereto_AB1I.e. by

R can be calculated_F2。

When only the phase line C has poor insulation to the ground, the U is measured and calculated arbitrarily₁₁、U₁₂、U₂₁Any one or more of the three measured partial pressure ratios, e.g. measuring and calculating U₂₁Partial pressure ratio of, i.e. in U_CAWhen M2 is on at 0, U is measured₂₁And monitoring narrow pulse voltage U corresponding thereto_BC1I.e. by

R can be calculated_F3。

When multiple measurement values are obtained by measuring the monitoring narrow pulse voltage and the ground narrow pulse voltage for multiple times, and multiple voltage division ratios are measured and calculated, or multiple calculation results are obtained by measuring and calculating the same voltage division ratio and the multiple voltage division ratios for multiple times, and the insulation resistance value of the same phase line has multiple calculation results, the multiple measurement values and the multiple calculation results should be subjected to arithmetic mean, median, sliding mean and median average, or other data processing methods to obtain corresponding measurement values or final calculation results.

When there is poor insulation of A, B to ground, U is arbitrarily measured and calculated₁₁、U₁₂、U₂₁、U₂₂、U₃₁、U₃₂2 of non-0 values and non-linearly relatedPartial pressure ratios, i.e. measuring and calculating U arbitrarily₁₁Or U₃₂、U₂₁Or U₂₂、U₃₁The R can be calculated by connecting 2 voltage division ratios and corresponding monitoring narrow pulse voltages with expressions which are correlated immediately_F1、R_F2。U₁₁、U₂₁、U₂₂、U₃₁、U₃₂The partial pressure ratio expressions of the same are respectively

Wherein, the formula (4) is linearly related to the formula (8), and the formula (5) is linearly related to the formula (6). For example, measure and calculate U₁₁、U₂₁The partial pressure ratio of (4) and (5) in combination can be used to calculate R_F1、R_F2。

Similarly, when there is poor insulation of B, C to ground, U is arbitrarily measured and calculated₁₁、U₁₂、U₂₁、U₂₂、U₃₁、U₃2 non-0 values and non-linear correlation voltage division ratios in the system are connected with a vertically correlated expression, and R can be calculated_F2、R_F3(ii) a When there is poor insulation of A, C to ground, U is arbitrarily measured and calculated₁₁、U₁₂、U₂₁、U₂₂、U₃₁、U₃₂2 non-0 values and non-linear correlation voltage division ratios in the system are connected with a vertically correlated expression, and R can be calculated_F1、R_F3。

When A, B, C are all poorly insulated from ground, U is arbitrarily measured and calculated₁₁、U₁₂、U₂₁、U₂₂、U₃₁、U₃₂The three (3) voltage division ratios and the corresponding monitoring narrow pulse voltage are connected with expressions which are correlated immediately, and R can be calculated_F1、R_F2、R_F3. The expression of the relative voltage division ratio is

For example, measure and calculate U₁₂、U₂₂、U₃₂Corresponding to the monitored narrow pulse voltage U_BC2、U_CA2、U_AB2The partial pressure ratio of (1), the joint type (10), the formula (12) and the formula (14) can be calculated_F1、R_F2、R_F3。

When the monitoring narrow pulse voltage and the ground narrow pulse voltage are measured for multiple times, a plurality of measured values are obtained; calculating a plurality of calculation results of the insulation resistance value of the same phase line by simultaneous multi-group expressions; or when the same voltage division ratio or multiple voltage division ratios are measured and calculated for multiple times to obtain multiple calculation results of the insulation resistance value of the same phase line, the multiple measurement values or the multiple calculation results should be subjected to data processing including arithmetic mean, median, sliding mean and median average, or other manners to obtain corresponding measurement values or final calculation results.

Phase line A first narrow pulse voltage U₁₁Phase line A, second opposite ground narrow pulse voltage U₁₂By collecting the first electronic switches M1 at U respectively_BC＝0、U_ABSampling resistor R when being opened 0_SVoltage U on_C1Obtained by

Or

Phase line B first ground narrow pulse voltage U₂₁Phase line B, second opposite ground narrow pulse voltage U₂₂By collecting the second electronic switches M2 at U respectively_CA＝0、U_BCSampling resistor R when being opened 0_SVoltage U on_C2Obtained by

Or

Phase line C first ground narrow pulse voltage U₃₁Phase line C, second opposite ground narrow pulse voltage U₃₂By collecting the third electronic switches M3 at U respectively_AB＝0、U_CASampling resistor R when being opened 0_SVoltage U on_C3Obtained by

Or

In order to limit the ground current of the phase line A, B, C when the first electronic switch, the second electronic switch and the third electronic switch are switched on, a first current limiting resistor R_E1A second current limiting resistor R_E2A third current limiting resistor R_E3The resistance value of (a) is preferably more than 500 k.OMEGA.and particularly preferably more than 2 M.OMEGA..

The first electronic switch, the second electronic switch and the third electronic switch are all short in turn-on time, at the moment, the monitoring narrow pulse voltage loaded between the phase lines and on a loop formed by PE is equivalent to direct current narrow pulse voltage, and due to the fact that the ground capacitance of the phase lines is small, the sampling resistor R is connected with the ground capacitor_SWhen the voltage is sampled, the charging and discharging of the ground capacitor are finished by the direct-current narrow pulse voltage, so that the influence of the phase line to ground capacitor on insulation monitoring can be avoided.

When the phase line a ground narrow pulse voltage comprises a phase line a first ground narrow pulse voltage and a phase line a second ground narrow pulse voltage, the phase line B ground narrow pulse voltage comprises a phase line B first ground narrow pulse voltage and a phase line B second ground narrow pulse voltage, and the phase line C ground narrow pulse voltage comprises a phase line C first ground narrow pulse voltage and a phase line C second ground narrow pulse voltage, the specific steps of the device for realizing the on-line detection of the electric energy quality and the insulation performance include:

sampling to obtain narrow pulse voltage to ground; sampling to obtain three-phase alternating current voltage and current data;

analyzing three-phase alternating-current voltage and current data to obtain monitoring narrow pulse voltages corresponding to a first ground narrow pulse voltage pair of a phase line A, a second ground narrow pulse voltage pair of the phase line A, a first ground narrow pulse voltage pair of a phase line B, a second ground narrow pulse voltage pair of the phase line B, a first ground narrow pulse voltage pair of a phase line C and a second ground narrow pulse voltage pair of the phase line C respectively; analyzing three-phase alternating current voltage and current data to obtain an electric energy quality index;

step three, judging according to the narrow pulse voltage signal to the ground, and returning to the step one if the ground insulation of the phase line A, the phase line B and the phase line C is normal;

step four, judging according to the narrow pulse voltage signal to the ground, and if one of the phase lines A, B and C is short-circuited to the ground, going to step seven;

judging according to the ground narrow pulse voltage signals, and respectively judging whether the phase lines A, B and C are poor in ground insulation;

step six, calculating the earth insulation resistance value of the phase line when the earth insulation of 1 phase line is poor, or calculating the earth insulation resistance value of each of 2 phase lines when the earth insulation of 2 phase lines is poor, or calculating the earth insulation resistance value of each of 3 phase lines when the earth insulation of 3 phase lines is poor;

and step seven, displaying results and alarming, and returning to the step one.

The voltage and current sampling unit is used for acquiring three-phase line voltage signals and A, B, C three-phase line current signals of a three-phase IT system A, B, C. The controller unit needs to control the voltage and current sampling unit to continuously sample the three-phase alternating current voltage and current so as to analyze the quality of the electric energy. The zero crossing point of the phase line alternating voltage and the monitoring narrow pulse voltage signal corresponding to the zero crossing point are obtained by analyzing the voltage continuous sampling data of the voltage and current sampling unit by the controller unit. The method comprises the steps of analyzing three-phase alternating-current voltage and current data to obtain an electric energy quality index, and mainly obtaining indexes such as voltage deviation, frequency deviation, harmonic waves, voltage fluctuation and flicker of a three-phase IT system of the micro-grid through FFT calculation and other calculation and analysis. How to design a voltage and current sampling unit, realize continuous sampling of three-phase alternating voltage and current signals through a controller unit, analyze continuous sampling data to obtain a zero crossing point of phase line alternating voltage and a monitoring narrow pulse voltage signal corresponding to the zero crossing point, and obtain indexes such as voltage deviation, frequency deviation, harmonic wave, voltage fluctuation, flicker and the like of a three-phase IT system of a micro-grid through FFT (fast Fourier transform) calculation and other calculation and analysis.

When the insulation to ground of the three-phase alternating current IT system is degraded or the short-circuit to ground fault exists, and the insulation resistance of the phase line to ground is smaller than the set threshold resistance, the controller unit gives an alarm through the alarm unit. The man-machine interaction unit is used for realizing functions of setting threshold resistance, displaying ground insulation resistance values of all the phases and the like. The design of the alarm unit and the human-computer interaction unit and the implementation of the required functions are conventional techniques known to the person skilled in the art.

And the checking unit is used for carrying out function checking on the monitoring of the insulation performance. In the embodiment shown in fig. 1, the verification unit 400 is controlled by the human-computer interaction unit via the controller unit. The checking unit can also be directly controlled by the man-machine interaction unit, namely directly controlled by a switch and a button. When the function is verified, the verifying unit is connected with a verifying resistor between the phase line A and a protective ground, or between the phase line B and the protective ground, or between the phase line C and the protective ground, or between a plurality of phase lines and the protective ground, and whether the device can work normally is observed. The control is directly performed by a switch and a button, or the control is performed by a human-computer interaction unit through a controller unit, and a check resistor is connected between the phase line a and a protected ground, or between the phase line B and the protected ground, or between the phase line C and the protected ground, or between a plurality of phase lines and the protected ground at the same time, which is the conventional technology known by those skilled in the art.

The controller unit comprises a MCU, an A/D converter, a signal conditioning circuit and other functional modules and circuits. The phase line alternating voltage signal output by the voltage and current sampling unit and the ground narrow pulse voltage signal output by the insulation signal sampling unit are processed by the signal conditioning circuit and then sent to the A/D converter, and the output data of the A/D converter is processed by the MCU. The MCU is electrically connected with the insulation signal sampling unit, the calibration unit, the alarm unit, the human-computer interaction unit and the like so as to transmit related information. The control core MCU can select microcontrollers such as a DSP, an ARM, a singlechip and the like. It is a conventional technique known to those skilled in the art how to select and use the a/D converter and how to design the signal conditioning circuit such that the signals output by the voltage-current sampling unit and the isolated signal sampling unit meet the requirements of the a/D converter for signal input.

The device also comprises a direct current power supply unit. The direct-current power supply unit can adopt an external power supply, and can also be obtained by three-phase alternating-current voltage reduction, rectification, filtering and voltage stabilization.

Claims (7)

1. A method for detecting the electric energy quality and the insulation performance of a three-phase IT system of a micro-grid on line is characterized in that monitoring narrow pulse voltage is loaded on a loop formed by protection grounds among phase lines to form corresponding narrow pulse voltage to the ground; carrying out online detection on the insulation performance according to the monitored narrow pulse voltage and the corresponding ground narrow pulse voltage; analyzing the quality of the electric energy according to the three-phase alternating current voltage and current data;

the online detection method for the electric energy quality and the insulation performance of the three-phase IT system of the micro-grid is realized by a device comprising a controller unit, an insulation signal sampling unit and a voltage and current sampling unit;

the insulation signal sampling unit comprises a first signal sampling branch, a second signal sampling branch, a third signal sampling branch and a sampling resistor; the first signal sampling branch circuit comprises a first electronic switch and a first current-limiting resistor which are connected in series, the second signal sampling branch circuit comprises a second electronic switch and a second current-limiting resistor which are connected in series, and the third signal sampling branch circuit comprises a third electronic switch and a third current-limiting resistor which are connected in series; one end of the first signal sampling branch is connected to a phase line A of the three-phase alternating current IT system, one end of the second signal sampling branch is connected to a phase line B of the three-phase alternating current IT system, and one end of the third signal sampling branch is connected to a phase line C of the three-phase alternating current IT system; the other end of the first signal sampling branch, the other end of the second signal sampling branch and the other end of the third signal sampling branch are connected with one end of a sampling resistor, and the other end of the sampling resistor is connected to a protective ground;

the ground narrow pulse voltage of the three-phase alternating current IT system comprises a phase line A ground narrow pulse voltage, a phase line B ground narrow pulse voltage and a phase line C ground narrow pulse voltage, and the controller unit respectively controls the first electronic switch, the second electronic switch and the third electronic switch to be switched on and obtained;

the phase line A-to-ground narrow pulse voltage comprises a first phase line A-to-ground narrow pulse voltage and a second phase line A-to-ground narrow pulse voltage, and the controller unit controls the first electronic switch to be respectively switched on and obtained when the line voltage between the phase line B and the phase line C crosses zero and the line voltage between the phase line A and the phase line B crosses zero; the phase line B ground narrow pulse voltage comprises a phase line B first ground narrow pulse voltage and a phase line B second ground narrow pulse voltage, and the controller unit controls the second electronic switch to be respectively switched on and obtained when the line voltage between the phase line C and the phase line A crosses zero and the line voltage between the phase line B and the phase line C crosses zero; the phase line C ground narrow pulse voltage comprises a phase line C first ground narrow pulse voltage and a phase line C second ground narrow pulse voltage, and the controller unit controls the third electronic switch to be switched on and obtained when the line voltage between the phase line A and the phase line B crosses zero and the line voltage between the phase line C and the phase line A crosses zero respectively.

2. The method for detecting the electric energy quality and the insulation performance of the three-phase IT system of the microgrid according to claim 1, characterized in that the monitoring of the narrow pulse voltage is realized by loading the line voltage of the three-phase IT system in a pulse conduction mode and performing pulse type switching on through an electronic switch.

3. The method for detecting the electric energy quality and the insulation performance of the three-phase IT system of the microgrid according to claim 2, characterized in that the pulse-type turn-on time of the electronic switch is the zero crossing point of the line voltage of the three-phase IT system.

4. The method for on-line detection of electric energy quality and insulation performance of a microgrid three-phase IT system, characterized in that at least 3 groups of monitoring narrow pulse voltages and corresponding ground narrow pulse voltages are provided.

5. The microgrid three-phase IT system power quality and insulation performance online detection method according to any one of claims 1 to 4, characterized in that the specific steps of realizing online detection of power quality and insulation performance include:

sampling to obtain narrow pulse voltage to ground; sampling to obtain three-phase alternating voltage and current data;

analyzing three-phase alternating-current voltage and current data to obtain monitoring narrow pulse voltages corresponding to a first ground narrow pulse voltage pair of a phase line A, a second ground narrow pulse voltage pair of the phase line A, a first ground narrow pulse voltage pair of a phase line B, a second ground narrow pulse voltage pair of the phase line B, a first ground narrow pulse voltage pair of a phase line C and a second ground narrow pulse voltage pair of the phase line C respectively; analyzing three-phase alternating current voltage and current data to obtain an electric energy quality index;

step three, judging according to the narrow pulse voltage signal to the ground, and returning to the step one if the ground insulation of the phase line A, the phase line B and the phase line C is normal;

step four, judging according to the narrow pulse voltage signal to the ground, and if one of the phase lines A, B and C is short-circuited to the ground, going to step seven;

judging according to the ground narrow pulse voltage signals, and respectively judging whether the phase lines A, B and C are poor in ground insulation;

step six, calculating the earth insulation resistance value of the phase line when the earth insulation of 1 phase line is poor, or calculating the earth insulation resistance value of each of 2 phase lines when the earth insulation of 2 phase lines is poor, or calculating the earth insulation resistance value of each of 3 phase lines when the earth insulation of 3 phase lines is poor;

and step seven, processing the result and returning to the step one.

6. The microgrid three-phase IT system electric energy quality and insulation performance online detection method of claim 1, characterized in that the first signal sampling branch further comprises a first diode connected in series, the second signal sampling branch further comprises a second diode connected in series, and the third signal sampling branch further comprises a third diode connected in series;

the first signal sampling branch circuit further comprises a fourth diode, the second signal sampling branch circuit further comprises a fifth diode, and the third signal sampling branch circuit further comprises a sixth diode; the fourth diode is reversely connected in parallel with the first electronic switch, the fifth diode is reversely connected in parallel with the second electronic switch, and the sixth diode is reversely connected in parallel with the third electronic switch;

the first diode enables the current on the first electronic switch to flow to the protective ground only from the phase line A, the second diode enables the current on the second electronic switch to flow to the protective ground only from the phase line B, and the third diode enables the current on the third electronic switch to flow to the protective ground only from the phase line C; alternatively, the first diode allows the current on the first electronic switch to flow only from the protected ground to phase a, the second diode allows the current on the second electronic switch to flow only from the protected ground to phase B, and the third diode allows the current on the third electronic switch to flow only from the protected ground to phase C.

7. The method for the online detection of the electric energy quality and the insulation performance of the microgrid three-phase IT system according to claim 1, characterized in that the specific steps for realizing the online detection of the electric energy quality and the insulation performance comprise:

step 1, sampling and obtaining a phase line A to ground narrow pulse voltage, a phase line B to ground narrow pulse voltage and a phase line C to ground narrow pulse voltage; sampling to obtain three-phase alternating current voltage and current data;

step 2, analyzing three-phase alternating-current voltage and current data to obtain monitoring narrow pulse voltages corresponding to the phase line A ground narrow pulse voltage, the phase line B ground narrow pulse voltage and the phase line C ground narrow pulse voltage respectively; analyzing three-phase alternating current voltage and current data to obtain an electric energy quality index;

step 3, forming an equation set by a relational expression between the ground narrow pulse voltage of the phase line A and the corresponding monitoring narrow pulse voltage, a relational expression between the ground narrow pulse voltage of the phase line B and the corresponding monitoring narrow pulse voltage, and a relational expression between the ground narrow pulse voltage of the phase line C and the corresponding monitoring narrow pulse voltage;

solving an equation set to obtain a phase line A ground insulation resistance value, a phase line B ground insulation resistance value and a phase line C ground insulation resistance value;

and 5, processing results and returning to the step 1.

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