A DC bus-to-ground resistance detection and early warning system

Abstract

The present invention detects the insulation resistance value of the positive power supply or the negative power supply to the ground by setting a DC busbar-to-ground resistance detection and early warning system, and uses the detection of the use environment and use time of the insulation resistance to determine whether the insulation resistance is normal. If it is normal, the unbalanced bridge method in the prior art is used to detect the resistance value. If it is not normal, the leakage current of the insulation resistance is detected by an external detection circuit. When an abnormality is detected, a corresponding balanced bridge method detection is performed, thereby solving the problems of inaccurate detection results caused by changes in the ground voltage and a long detection time when detecting the insulation resistance by the unbalanced bridge method in the prior art, and inaccurate double-wire grounding detection results by the balanced bridge method.

Description

Technical Field

[0001] The invention relates to the field of direct current bus protection, and in particular to a direct current bus ground resistance detection and early warning system. Background Art

[0002] The DC power supply is used as the power supply system for the secondary control circuit and the relay protection device. Its failure may cause the malfunction of the primary system, thus leading to a major power accident. The DC bus is the most important transmission line for the DC system of the power plant or substation to supply power to the power system. The stability of its power transmission is crucial. The detection of the insulation resistance of the DC bus to the ground is an important research direction for power equipment monitoring and fault diagnosis. With years of research, many methods have emerged. The traditional DC system insulation detection device adopts the bridge balance principle. The bridge balance principle is to set two ground-dividing resistors with the same resistance value inside the host of the bus monitoring device, and measure the bus voltage to the ground through them, so as to obtain the insulation resistance value of the bus to the ground. The attachment of the instruction manual Figure 1 This is a circuit diagram for testing the insulation resistance to ground based on the bridge balance principle. However, the bridge balance principle has its own shortcomings. The biggest shortcoming is that when the insulation resistance of the positive and negative electrodes decreases at the same time, the bridge still maintains balance and cannot make a correct judgment. Later, there was an unbalanced bridge method. The unbalanced bridge detection is to connect two equal-resistance ground resistors inside the host to the positive and negative ground terminals respectively to test the insulation resistance to ground. The instruction manual is attached. Figure 2 This is a circuit diagram of the unbalanced bridge detection principle. However, the unbalanced bridge method also has its disadvantages. During the measurement process, the positive and negative busbars need to respectively cast resistance to the ground. The busbar-to-ground voltage is changing, and the detection speed is very slow each time the measurement is performed, resulting in inaccurate insulation resistance measurements due to changes in the busbar-to-ground voltage. The insulation resistance to ground usually decreases rapidly due to environmental problems or aging problems. For good insulation, the relationship curve between the leakage current and the applied voltage is usually an approximate straight line. If the insulation resistance decreases by more than a critical value, the leakage current will increase sharply as the voltage increases. In the prior art, neither the bridge balance principle nor the bridge unbalance principle can monitor the insulation resistance when such a sharp decrease in resistance occurs.

[0003] 1. Technical issues to be resolved

[0004] In order to solve the above technical problems, the present invention provides a DC bus ground resistance detection and early warning system

[0005] (I) Technical solution

[0006] A DC busbar ground resistance detection and early warning system comprises a ground resistance use condition detection system, a ground resistance value detection switching system, and a ground resistance value detection system; the ground resistance use condition detection system detects and evaluates the use environment and use time of the insulation resistance.

[0007] Furthermore, the ground resistance value detection switching system switches the ground resistance detection system.

[0008] Furthermore, the ground resistance detection system includes a positive pole of a power generation system and a negative pole of a power generation system. A busbar I is connected between the positive pole of the power generation system and the negative pole of the power generation system. A switch K1 and a switch K2 are provided on the busbar I. A controller is also provided. The switches K1 and K2 are connected to the controller to control their opening and closing.

[0009] Furthermore, a ground connection I is connected in the middle of bus I, and the ground connection I connects bus I to the ground. Bus II is also connected between the positive pole of the power generation system and the negative pole of the power generation system. Switches K3 and K4 are provided on bus II, and a sampling resistor balancing bridge is provided on bus II, and resistors R1 and R2 are provided on the sampling resistor balancing bridge.

[0010] Furthermore, the ground connection I connects the busbar I and the busbar II.

[0011] Furthermore, the positive pole of the power generation system is also connected to a ground connection II, which is directly connected to the ground after being connected from the positive pole of the power generation system. A positive pole insulation resistor RX is arranged on the ground connection II, and the positive pole insulation resistor RX is connected in parallel to the insulation resistance outflow current detection circuit I. The insulation resistance outflow current detection circuit I is provided with an initial voltage U V The power supply is provided, and a detection switch K5 is provided on the insulation resistance outflow current detection circuit I.

[0012] Furthermore, the negative pole of the power generation system is also connected to a ground connection III, which is directly connected to the ground after being connected from the negative pole of the power generation system. A negative pole insulation resistor RY is arranged on the ground connection III, and the negative pole insulation resistor RY is connected in parallel to the insulation resistance outflow current detection circuit II. The insulation resistance outflow current detection circuit II is provided with an initial voltage U V The power supply is provided, and a detection switch K6 is provided on the insulation resistance outflow current detection circuit II.

[0013] Furthermore, when the use environment and use time of the insulation resistance are detected, the use environment influencing factor of the insulation resistance is set to A, and the use time is set to B, wherein A and B are both variable values, and the A value increases as the use environment becomes worse.

[0014] Furthermore, when When the insulation resistance is normal, the detection switches K5 and K6 are disconnected. When detecting the insulation resistance value of the positive electrode of the power generation system, the control device is used to disconnect switches K1 and K4, and switches K2 and K3 are opened. The insulation resistance value of the positive electrode of the power generation system is detected using the unbalanced bridge method.

[0015] Furthermore, when detecting the resistance value of the negative power supply resistance of the power generation system, the control device is used to disconnect switches K2 and K3, open switches K1 and K4, and the unbalanced bridge method is used to detect the insulation resistance value of the positive electrode of the power generation system.

[0016] (III) Beneficial effects

[0017] The present invention detects the insulation resistance value of the positive power supply or the negative power supply to the ground by setting a DC busbar-to-ground resistance detection and early warning system, and uses the detection of the use environment and use time of the insulation resistance to determine whether the insulation resistance is normal. If it is normal, the unbalanced bridge method in the prior art is used to detect the resistance value. If it is not normal, the leakage current of the insulation resistance is detected by an external detection circuit. When an abnormality is detected, a corresponding balanced bridge method detection is performed, thereby solving the problems of inaccurate detection results caused by changes in the ground voltage and a long detection time when detecting the insulation resistance by the unbalanced bridge method in the prior art, and inaccurate double-wire grounding detection results by the balanced bridge method. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Attached Figure 1 The circuit diagram of the unbalanced bridge detection method in the prior art

[0019] Attached Figure 2 The circuit diagram of the balanced bridge detection method in the prior art

[0020] Attached Figure 3 Circuit diagram of ground resistance detection warning system DETAILED DESCRIPTION

[0021] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0022] A DC busbar ground resistance detection and early warning system includes a ground resistance use condition detection system, a ground resistance value detection switching system, and a ground resistance value detection system; the ground resistance use condition detection system detects and evaluates the use environment and use time of the insulation resistance, the ground resistance value detection switching system switches the ground resistance detection system, and the ground resistance value detection system includes a positive pole of a power generation system and a negative pole of a power generation system, a busbar I is connected between the positive pole of the power generation system and the negative pole of the power generation system, a switch K1 and a switch K2 are arranged on the busbar I, and a controller is also arranged, the switch K1 and the switch K2 are connected to the controller to control their opening and closing, and the middle of the busbar I A ground connection I is connected between the bus I and the negative pole of the power generation system, and the ground connection I connects the bus I to the ground. A bus II is also connected between the positive pole of the power generation system and the negative pole of the power generation system. Switches K3 and K4 are arranged on the bus II, and a sampling resistor balancing bridge is arranged on the bus II. The sampling resistor balancing bridge is provided with resistors R1 and R2. The ground connection I connects the bus I and the bus II. The positive pole of the power generation system is also connected to the ground connection II. The ground connection II is directly connected to the ground after being connected from the positive pole of the power generation system. A positive pole insulation resistor RX is arranged on the ground connection II. The positive pole insulation resistor RX is connected in parallel to the insulation resistance outflow current detection circuit I. The insulation resistance outflow current detection circuit I is provided with an initial voltage U V The power supply is provided, and the insulation resistance outflow current detection circuit Ⅰ is provided with a detection switch K5. The negative pole of the power generation system is also connected to the ground connection Ⅲ. The ground connection Ⅲ is directly connected to the ground after being connected from the negative pole of the power generation system. The negative pole insulation resistor RY is provided on the ground connection Ⅲ. The negative pole insulation resistor RY is connected in parallel to the insulation resistance outflow current detection circuit Ⅱ. The insulation resistance outflow current detection circuit Ⅱ is provided with an initial voltage U V The power supply is provided, and the insulation resistance outflow current detection circuit II is provided with a detection switch K6. When the use environment and use time of the insulation resistance are detected, the use environment influencing factor of the insulation resistance is set to A, and the use time is set to B, wherein A and B are both variable values, and the worse the use environment, the larger the A value. When the condition is satisfied, When the insulation resistance is normal, the detection switches K5 and K6 are disconnected. When detecting the insulation resistance value of the positive electrode of the power generation system, the control device is used to disconnect switches K1 and K4, and switches K2 and K3 are opened. The insulation resistance value of the positive electrode of the power generation system is detected by the unbalanced bridge method. When detecting the insulation resistance value of the negative electrode of the power generation system, the control device is used to disconnect switches K2 and K3, and switches K1 and K4 are opened. The insulation resistance value of the positive electrode of the power generation system is detected by the unbalanced bridge method. When the insulation resistance value of the negative electrode of the power generation system is satisfied, When the insulation resistance is judged to be abnormal, the controller is used to close the detection switches K5 and K6 respectively. Initially, the initial voltage built into the insulation resistance outflow current detection circuit is U V , set U in normal state VAs the unit time increases by the same value, as U V Increase, set U V Value is U (v+1) , U (V+2) , U (V+3) ....U (V+N) ; Insulation resistance leakage current I v and U V The relationship is Where K is a constant, if I v and U V If the relationship is met, the unbalanced bridge method is used to detect the insulation resistance of the positive or negative pole of the power generation system. When the insulation resistance leakage current I v and U V The relationship is When the leakage current I v The positive or negative side that meets this relationship is regarded as a short-circuited wire that is directly grounded. The insulation resistance of the corresponding side is detected by the balanced bridge method. When the leakage current I v and U V The relationship is When , it is considered that the ground connections of the positive power supply and the negative power supply are short-circuited wires, and the K1-K6 switches are directly disconnected.

[0023] When the insulation resistance of the positive power supply or negative power supply to the ground is tested by the unbalanced bridge method, the K2 and K3 switches are turned on and the K1 and K4 switches are turned off; or the K1 and K4 switches are turned on and the K2 and K3 switches are turned off, where R1 and R2 are known resistances, and the bus voltage between the positive and negative poles is measured as U, and the positive voltage to the ground is U + , the negative voltage to ground is U － ,but

[0024]

[0025] Thus, the values ​​of RX and RY can be obtained by detecting the values ​​of U+ and U-.

[0026] When the resistance of the positive or negative power supply is tested by the balanced bridge method, the K1 and K2 switches are disconnected, the K3 and K4 switches are opened, and the bus voltage between the positive and negative poles is measured as U, and the positive voltage to ground is measured as U. + , the negative voltage to ground is U －， but

[0027] The RX and RY values ​​are determined by the measured values. If a short-circuited wire is identified, the corresponding RX value or RY value is considered non-existent.

Claims

1. A DC busbar ground resistance detection and early warning system, comprising a ground resistance use condition detection system, a ground resistance value detection switching system, and a ground resistance value detection system; the ground resistance use condition detection system detects and evaluates the use environment and use time of the insulation resistance, the ground resistance value detection switching system switches the ground resistance detection system, and the ground resistance value detection system comprises a positive pole of a power generation system and a negative pole of a power generation system; a busbar I is connected between the positive pole of the power generation system and the negative pole of the power generation system, a switch K1 and a switch K2 are arranged on the busbar I, and a controller is also arranged, the switch K1 and the switch K2 are connected to the controller to control their opening and closing, and the busbar I A ground connection I is connected in the middle, and the ground connection I connects the bus I to the ground. A bus II is also connected between the positive pole of the power generation system and the negative pole of the power generation system. Switches K3 and K4 are provided on the bus II, and a sampling resistor balancing bridge is provided on the bus II. The sampling resistor balancing bridge is provided with resistors R1 and R2. The ground connection I connects the bus I and the bus II. The positive pole of the power generation system is also connected to the ground connection II. The ground connection II is directly connected to the ground after being connected from the positive pole of the power generation system. A positive insulation resistor RX is provided on the ground connection II. The positive insulation resistor RX is connected in parallel to the insulation resistance outflow current detection circuit I. The insulation resistance outflow current detection circuit I is provided with an initial voltage U V The power supply is provided, and the insulation resistance outflow current detection circuit Ⅰ is provided with a detection switch K5. The negative pole of the power generation system is also connected to the ground connection Ⅲ. The ground connection Ⅲ is directly connected to the ground after being connected from the negative pole of the power generation system. The negative pole insulation resistor RY is provided on the ground connection Ⅲ. The negative pole insulation resistor RY is connected in parallel to the insulation resistance outflow current detection circuit Ⅱ. The insulation resistance outflow current detection circuit Ⅱ is provided with an initial voltage U V The power supply is provided, and a detection switch K6 is provided on the insulation resistance outflow current detection circuit II.

2. The DC bus-to-ground resistance detection and early warning system according to claim 1 is characterized in that: The negative pole of the power generation system is also connected to the ground connection III, which is directly connected to the ground after being connected from the negative pole of the power generation system. A negative pole insulation resistor RY is set on the ground connection III, and the negative pole insulation resistor RY is connected in parallel to the insulation resistance outflow current detection circuit II. The insulation resistance outflow current detection circuit II is set with an initial voltage U V The power supply is provided, and a detection switch K6 is provided on the insulation resistance outflow current detection circuit II.

3. The DC bus ground resistance detection and early warning system according to claim 2 is characterized in that: When testing the use environment and use time of the insulation resistance, the use environment influencing factor of the insulation resistance is set to A, and the use time is set to B, where A and B are both variable values, and the worse the use environment, the larger the A value.

4. The DC bus ground resistance detection and early warning system according to claim 3 is characterized in that: It is determined that the insulation resistance is in a normal state, and the detection switches K5 and K6 are disconnected. When detecting the insulation resistance value of the positive electrode of the power generation system, the control device is used to disconnect switches K1 and K4, and switches K2 and K3 are opened. The insulation resistance value of the positive electrode of the power generation system is detected using the unbalanced bridge method.

5. The DC bus ground resistance detection and early warning system according to claim 4 is characterized in that: When detecting the negative power supply resistance of the power generation system, the control device is used to disconnect switches K2 and K3, open switches K1 and K4, and the positive insulation resistance of the power generation system is detected using the unbalanced bridge method to determine that the insulation resistance is in an abnormal state.

6. The DC bus-to-ground resistance detection and early warning system according to claim 5 is characterized in that: The controller is used to close the detection switches K5 and K6 respectively. Initially, the initial voltage built into the insulation resistance outflow current detection circuit is U V , set U in normal state V As the unit time increases by the same value, as U V Increase, set U V Value is U (v+1) , U (V+2) , U (V+3) ....U (V+N) ; Insulation resistance leakage current I v and U V The relationship is Where K is a constant, if I v and U V If the relationship is met, the unbalanced bridge method is used to detect the insulation resistance of the positive or negative electrode of the power generation system.

7. The DC bus-to-ground resistance detection and warning system according to claim 6 is characterized in that: When the insulation resistance leakage current I of the positive power supply or negative power supply to ground v and U V The relationship is When the leakage current I v The positive or negative side that meets this relationship is regarded as a short-circuited wire that is directly grounded. The insulation resistance on the corresponding side is tested by the balanced bridge method.

8. The DC bus-to-ground resistance detection and warning system according to claim 7 is characterized in that: When the insulation resistance of the positive power supply and the negative power supply to the ground leaks, it is considered that the connections of the positive power supply and the negative power supply to the ground are short-circuited wires, and the K1-K6 switches are directly disconnected.

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