RU2488129C1 - Method to measure resistance of insulation and to protect against short circuits to body in power circuits of diesel locomotives - Google Patents

Abstract

FIELD: measurement equipment.SUBSTANCE: in the method to measure resistance of insulation and to protect against short circuits to a body in power circuits of diesel locomotives, based on connection of a circuit of two serially connected resistors to poles of a DC circuit, in the place of resistor connection to each other there are some ends of two measurement circuits connected, the first measurement circuit comprises a resistor, a voltage sensor and diode. The second measurement circuit comprises the second resistor, the second voltage sensor and the second diode connected in polarity, which is reverse relative to the first measurement circuit, other ends of the first and second measurement circuits are connected to the grounding element. In process of measurement they measure voltage drops at resistors in the first and second measurement circuits. Voltage is measured at poles of the DC circuit. On the basis of these parameters they calculate resistance of insulation separately in a positive circuit and separately in a negative circuit, and if one of these resistances drops down to the specified threshold value, it is assumed there was a breakthrough of insulation in the appropriate circuit, and the decision is made to implement protection by removal of excitation off a generator, which supplies to the power circuit of the diesel locomotive.EFFECT: increased reliability and stability of the method due to monitoring of condition of insulation resistance in power circuits of diesel locomotives under continuously alternating voltage with simultaneous permanent realisation of protection against insulation breakthrough to a body.1 dwg

Description

The invention relates to the control and measurement technique of vehicles with electric traction, and in particular to microprocessor control systems and diagnostics of diesel locomotives.

There is a method of measuring the electrical insulation resistance of electrical circuits under DC voltage, which consists in changing the configuration of the measured circuit by shunting and making a series of measurements of the measured circuit, first measuring the potentials of different sections of the circuits with respect to the housing, then shunting the circuit section having a higher potential, a capacitor of known capacity, and measure the parameters of the transient at the bypass points, and these parameters calculate the values of stray capacitance and insulation resistance of the circuits with respect to the housing. (RU, patent No. 2200329, class G01R 27/16, G01R 27/18, publ. 2003).

The disadvantages of this method are the impossibility of its application in systems with rapidly changing voltage in the network, for example the power circuit of diesel locomotives, as well as the inability to simultaneously measure insulation resistance and protect the circuit from breakdown of insulation on the housing.

A known method of measuring insulation resistance in DC circuits, adopted as a prototype, based on connecting to the poles of the DC circuit of a resistor circuit consisting of two series-connected resistors, including at the connection point of the resistors between themselves the first end of the measuring circuit, consisting of a series-connected measuring source voltage and current meter, connecting the second end of the measuring circuit to the ground element, determining the measuring current in the measuring circuit, with c In order to eliminate the measurement error from the unbalance current in the resistor circuit, connect two resistors with the same resistance to the poles of the DC circuit, turn on the source of the measuring voltage in either one polarity or in the opposite polarity of the poles, determine the absolute values of the measuring current, determine the equivalent measuring current, as half the sum of two absolute values of the measuring current, measured sequentially in time at different polarity of the source Single measurement voltage, determine the equivalent circuit resistance of resistors of equal magnitude as half the value of one resistor divide value measuring voltage source by an amount equivalent to the measuring current and is subtracted from the value obtained by this division, the equivalent resistance value of the resistor chain. (RU, patent No. 2384855, class G01R 27/18, publ. 2010).

The disadvantages of this method are the unreliability and impossibility of stable operation in systems with rapidly changing voltage in the network due to the inability to simultaneously measure insulation resistance and protect the circuit from breakdown of insulation on the housing due to the lack of constant measurement.

The technical result of the invention is to increase the reliability and stability of the method by monitoring the state of the insulation resistance of the power circuits of diesel locomotives under continuously changing voltage with the simultaneous continuous implementation of protection against breakdown of insulation on the body.

The specified technical result is achieved by the fact that in the method of measuring the insulation resistance and protection against short circuits on the case of the power circuits of diesel locomotives, based on connecting to the poles of the DC circuit of a circuit of two series-connected resistors, one ends of two measuring circuits are connected to the place of connection of the resistors, the first measuring circuit includes a resistor, a voltage sensor and a diode, the second measuring circuit includes a second resistor, a second voltage sensor and a second diode included in the polar the inverse relative to the first measuring circuit, the other ends of the first and second measuring circuits are connected to the ground element, during the measurement they measure the voltage drops across the resistors in the first and second measuring circuits, measure the voltage at the poles of the DC circuit, according to these parameters calculate the resistance isolation of the positive and negative circuits separately and when one of these resistances is reduced to a predetermined threshold value, it is believed that an insulation breakdown has occurred They should decide on the implementation of protection by removing the excitation from the generator supplying the power circuit of the locomotive.

The drawing shows a schematic diagram of a device for implementing the method of measuring insulation resistance and protection against short circuits on the case of power circuits of diesel locomotives.

Two series-connected resistors R ₁ and R _{2 are} connected between the positive and negative poles of the circuit to which the DN voltage sensor is connected. To the junction of the resistors R ₁ and R ₂ connected at one end two measuring circuit. The first circuit consists of a resistor R∂ ₁ , a voltage sensor DN ₁ and a diode D ₁ connected by the anode to the ground element. The second circuit consists of a second resistor R∂ ₂ , a second voltage sensor DN ₂ and a second diode D ₂ connected by a cathode to the ground element.

The method is as follows: The voltage U, available at the time of measurement in the power circuit, is monitored by a voltage sensor connected between the positive and negative poles of the circuit. The voltage sensor DN ₁ in the first measuring circuit monitors the voltage drop U ⁺ on the resistor R∂ ₁ , due to the leakage of the positive pole insulation leakage current through this circuit. The voltage sensor DN ₂ in the second measuring circuit monitors the voltage drop U on the resistor R∂ ₂ , due to the leakage of the minus pole insulation leakage current through this circuit. Calculation of insulation resistance separately plus R ⁺ and separately minus R ^- poles is carried out in accordance with the following expressions:

$$R^{+}=\frac{U^{-}{R}_{\mathrm{one}}{R}_{2}R{\partial }_{\mathrm{one}}-U^{+}{R}_{\mathrm{one}}{R}_{2}R{\partial }_2+U{R}_{\mathrm{one}}R{\partial }_{\mathrm{one}}R{\partial }_2-U^{+}{R}_{2}R{\partial }_{\mathrm{one}}R{\partial }_2-U^{+}{R}_{\mathrm{one}}R{\partial }_{\mathrm{one}}R{\partial }_2}{U^{+}R{\partial }_2\left(R_{\mathrm{one}}+R_2\right)}$$

$$R^{-}=\frac{U^{+}{R}_{\mathrm{one}}{R}_{2}R{\partial }_2-U^{-}{R}_{\mathrm{one}}{R}_{2}R{\partial }_{\mathrm{one}}+U{R}_{2}R{\partial }_{\mathrm{one}}R{\partial }_2-U^{-}{R}_{2}R{\partial }_{\mathrm{one}}R{\partial }_2-U^{-}{R}_{\mathrm{one}}R{\partial }_{\mathrm{one}}R{\partial }_2}{U^{-}R{\partial }_{\mathrm{one}}\left(R_{\mathrm{one}}+R_2\right)}$$

The protective function is performed by removing excitation from the traction generator (not shown), a power supply circuit in the event of any decrease of the calculated resistances R ⁺ or R ^- below predetermined thresholds. The ratio of the values of the resistors R ₁ to R _{2 is} chosen to be greater than or equal to two in order to ensure that the protection is triggered while the positive and negative circuits are broken through to the case.

The introduction of a constant measurement of the insulation resistance of the power circuits of diesel locomotives under a continuously changing voltage with the simultaneous continuous implementation of protection against breakdown of insulation on the casing improves the reliability and stability of the power equipment of diesel locomotives with electric traction.

Claims (1)

A method of measuring insulation resistance and protection against short circuits on the case of power circuits of diesel locomotives, based on connecting to the poles of the DC circuit of a circuit of two series-connected resistors, characterized in that at the connection point of the resistors are connected the ends of two measuring circuits, the first measuring circuit includes a resistor, a voltage sensor and a diode, the second measuring circuit includes a second resistor, a second voltage sensor and a second diode connected in polarity inverse to the first and the measuring circuit, the other ends of the first and second measuring circuits are connected to the grounding element, during the measurement they measure the voltage drops across the resistors in the first and second measuring circuits, measure the voltage at the poles of the DC circuit, using these parameters calculate the insulation resistance separately positive and negative chains in accordance with the following expressions:
$$R^{+}=\frac{U^{-}{R}_{\mathrm{one}}{R}_{2}R{\partial }_{\mathrm{one}}-U^{+}{R}_{\mathrm{one}}{R}_{2}R{\partial }_2+U{R}_{\mathrm{one}}R{\partial }_{\mathrm{one}}R{\partial }_2-U^{+}{R}_{2}R{\partial }_{\mathrm{one}}R{\partial }_2-U^{+}{R}_{\mathrm{one}}R{\partial }_{\mathrm{one}}R{\partial }_2}{U^{+}R{\partial }_2\left(R_{\mathrm{one}}+R_2\right)},$$

$$R^{-}=\frac{U^{+}{R}_{\mathrm{one}}{R}_{2}R{\partial }_2-U^{-}{R}_{\mathrm{one}}{R}_{2}R{\partial }_{\mathrm{one}}+U{R}_{2}R{\partial }_{\mathrm{one}}R{\partial }_2-U^{-}{R}_{2}R{\partial }_{\mathrm{one}}R{\partial }_2-U^{-}{R}_{\mathrm{one}}R{\partial }_{\mathrm{one}}R{\partial }_2}{U^{-}R{\partial }_{\mathrm{one}}\left(R_{\mathrm{one}}+R_2\right)},$$

where R ⁺ is the insulation resistance of the plus pole;
R ^- is the insulation resistance of the negative pole;
R∂ ₁ , R∂ ₂ - resistance of the resistors of the first and second measuring circuits, respectively;
R ₁ , R ₂ - resistance of the resistors of the divider;
U is the voltage in the power circuit;
U ⁺ is the voltage drop across the resistor R∂ ₁ ;
U ^- is the voltage drop across the resistor R∂ ₂ ,
and when one of these resistances is reduced to a predetermined threshold value, it is believed that a breakdown of the insulation of the corresponding circuit has occurred and a decision is made to protect by removing the excitation from the generator supplying the locomotive power circuit.