SU1758592A1 - Method of measuring insulation resistance and capacitance of electric networks - Google Patents

Abstract

The invention relates to electrical measuring equipment and can be used to measure insulation resistance and the capacity of an electrical network. The purpose of the invention is to improve the accuracy, especially in networks with large capacities relative to the ground, while simultaneously increasing the speed and dynamic range of the measured parameters. The device implementing the method comprises measuring voltage sources 1.2, analog switches 3-6, memory elements 7-9, resistances 10 and 11, comparison element 12, threshold element, time meter 14, time settings 15 and 16, calculator 17, indicators 18 and 19, emergency indicator 20, decoupling unit 21, one-shot 22, pause-forming unit 23, artificial zero-point unit 24, delay element 25. Applying simultaneously two jumps of measuring voltage of different amplitude provide an accelerated charge to the network capacity up to a voltage equal to the amplitude of the jump of measuring voltage. 2 Il. cl

Description

There is no doubt that the left side of equation (4) is larger than the left side of the equation

(5), since - 1. Therefore

The expression for determining the current instantaneous values of the measuring voltage during the discharge of the capacitance is written as

t

12 ti.

those. the time to reach in the transient process of the same predetermined level of network capacity charge (other things being equal) for the transient from the high voltage source is less than for the transient from the lower voltage source.

Thus, the tangent of the slope of the curve describing the transient at the quasilinear, initial portion of the network capacity charge for the transient from the higher voltage source will be

U (t) UA-e

(7)

0

five

0

where UA is the voltage on the capacitance Cx at the initial instant of discharge, which is fixed at the moment when the measuring voltage is interrupted by the impedance of the insulation.

Equations TB) and (7) when fixing the first and second instantaneous values take the form (for the case in question):

lh UA nU0 (1 - e

tt

and 2(,

j.

 JU3 Uie

..1 A a

(8) (9)

It is difficult to show that solving the jointly indicated equations for the measured values of n and Oz and a priori given values of Ui, Uz. t2, the expressions Rx and Cx will appear as follows:

  t2-ln (1--)

-And, (y)

t2

-.(eleven)

ShP-UM-ln U3 ln V T i „) m TTG

U2

Ui

Since the ratio of the values of Ui and U2 is chosen by the developer in advance, for specific applications formulas (10) and (11) can be simplified. For example, if U2 10Ui, then expression (10) and (11) will be written as follows:

Ri

v.2 In 0.9

ti In

U3 Ui

-P.

(12)

Cx t2

JL., NO, 9-.n-

(13)

The sign (-) in expressions (11) and (13) disappears when performing calculations, since the logarithm of a number less than one is always negative.

FIG. Figure 1 shows the measuring circuit of the device proposed; in fig. 2 - one of the variants of the device that implements the proposed method.

An apparatus for measuring insulation resistance and capacitance of electrical networks, implementing the proposed method, contains sources 1 and 2 of measuring DC voltage, analog switches 3-6, memory elements (for example, static triggers) 7-9, resistances (resistors) 10 and 11, comparison element 12, threshold element 13, time interval meter 14, time setting devices 15 and 16 time intervals, calculator 17, insulation and capacitance indicators 18 and 19, respectively, alarm indicator 20, isolating unit 21, one-shot op22, pause forming unit 23 (for example, a one-shot), artificial zero-point block 24, delay element 25, OR 26 switch, switch 27, capacitor 28, terminals 29-32.

In addition, in FIG. 2 depicts a three-phase network section 33, the insulation resistances and the capacitances of the phases of the network RXA, RxB, RxC and ShA, ShV and ShC. parallel connection which gives equivalent insulation resistance of the network Rx and equivalent capacitance

Cx network, the values of which are of interest.

The first output of the source 1 measuring voltage DC through

serially connected normally open analog switch and resistance 10 is connected to the input of block 24 of an artificial zero point, the outputs of which are connected to terminals 30.31 and 32. Second

The output of the DC measuring voltage source 1 is connected to ground.

The first output of the source 2 of the measuring voltage of direct current through

The normally open analog switch 4 in series and the resistance 0 are connected to the input of the artificial zero point block 24 and the input of the decoupling block 21. The second input of the source 2 of the measuring voltage of the constant goke is connected to ground.

Terminal 27, to which the DC voltage is connected, through a series-connected switch 27,

the capacitor 28 and the first input of the element OR 26 are connected to the first inputs of the storage elements (static triggers) 7 and 8, the first input of the meter 14 time intervals and the input of the sensor

16 time interval. The second inputs of the memory elements (static triggers) 7 and 8 are connected to the output of the threshold element 13, the second meter input 14 time intervals, the input of the time interval master 15 and the first input of the memory element (static trigger) 9. The input of the threshold element 13 is connected to the output of the element 12 comparison, the first input of which is connected to the output

analog key 3, and the second input - to the input of the block 24 artificial zero point. The outputs of the memorization (static triggers) 7-9 are connected to the second (controlled) inputs of the analogue keys 3, 4 and O

respectively. The output of the time interval meter 14 is connected to the first input of the calculator 17, the second input of which through the serially connected analog switch 5 and the decoupling unit 21 is connected to the input of the block 24 of the artificial zero point. The first and second outputs of the calculator 17 are connected to the inputs of the insulation resistance indicator 18 and the network capacity indicator 19, respectively. The output of the setter 15 time interval is connected to the input of the block 23 forming pauses directly and through the one-shot 22 with the second (controlled) input of the analog key 5 and the input

the delay element 25, the output of which is connected to the third input of the calculator 17,

The output of the pause forming unit 23 is connected to the second input of the OR element 26 and the second input of the memory element (static trigger) 9, the output of which is also connected to the second input of the time interval setting device 16, the output of which is connected to the input of the alarm indicator 20 via the normally closed analog switch 6.

The operation of the device is as follows.

When the switch 27 is closed, the voltage drop comes from terminal 29 through the capacitor 28 and the OR element 26 to the first inputs of the static trigger 7 and 8, transfer them to state 2, at which the analog switches 3 and 4 are closed, respectively, and to the first input of the meter 14 time slots in which the time begins. The closure of the analog switches 3 and 4 leads to the fact that in the controlled network 33 single jumps of two measuring voltages Ui and 1) 2 will simultaneously begin to flow. which will cause a transient to establish a measuring voltage on the impedance of the network insulation (parallel connection of the insulation resistance Rx and the capacitance of the network Cx) associated with the charge of the capacitance of the network Cx.

Due to the fact that the voltage level U2 is many times, for example, an order of magnitude higher than the voltage Ui, then practically the charge rate of the capacity of the network Cx will be determined by this voltage and the voltage level Ui at the impedance of the isolator It will be reached in time, many times less than in the case when the second measuring voltage is absent.

At this moment, the voltage levels at the inputs of the comparison element 12 will become equal, and at its output, a signal will occur that will cause the signal at the output of the threshold element 13. This signal will go to the second inputs of the memory elements (static triggers) 7 and 8. translation them in the initial state 1, which will cause the opening of the analog switches 3 and 4 and the termination of the arrival of the measuring voltage of both single jumps on the insulation impedance.

At the same time, the signal from the output of the threshold element 13 will go to the first input of the memory element (static trigger) 9, transferring it to state 2. in which the analog key 6 is opened. This prevents the entry of

the signal from the unit 16 time interval on the indicator 20 of the accident rate. The signal from the output of the memory element (static trigger) 9 is fed to the second input of the time interval setting unit 16, translating it into the initial state.

If the insulation resistance value of the RX network is much lower than the permissible level and, naturally, much less than the value of the charging resistance 10, for example, in the short circuit to earth mode, charge the network capacity to the value of the voltage of the source 1 of the DC voltage ( a lower level is not possible because the capacitor is shunted (almost shorted) by a low impedance. Therefore, for this case, an accident control line is provided, consisting of a setpoint

0 16 time interval, normally closed analog key 6 and alarm indicator 20. If, after the time interval a priori set in the setter 16 expires, the signal from the output of the threshold element 13 to the first memory input (static trigger) 9 does not arrive and the key 6 does not open, then the signal from the output of the setter 16 of the time interval will go to the alarm indicator 20, which will This means inexpediency and incorrectness of further measuring operations.

A priori, the preset time in the setter 16 is chosen so that it exceeds the maximum possible (based on the network capacity and charge resistance 10 values) equalization time of the specified levels.

Since the signal from the threshold element 13 is supplied to the second input of the meter 14

0 time intervals, then a voltage appears at its output, the value of which carries information about the time elapsed from the beginning of single jumps to the moment of equalization of the charge capacity of the network with

5 is the voltage level at the output of the source 1. This voltage from the output of the meter 14 time intervals is fed to the first input of the calculator 17. The signal from the output of the threshold element 13 on

0 an input of the setpoint generator 15 of the time interval provides a reference point for an a priori specified time interval during which a partial discharge of the capacitance of the network Cx occurs through the insulation resistance Rx. Upon expiration of this predetermined time, the signal at the output of the setpoint generator 15 will translate the one-oscillator 22 into an unstable position, in which the analog switch 5 closes and the instantaneous value of the voltage in the transient process of discharging the network capacitance Cx will go through to the second input of the evaluator 17.

Since the calculator 17 previously introduced constants characterizing the voltage values of sources 1 and 2 of the DC voltage Ui and U2 and the a priori specified time interval t2, after a time due to delay element 25, the signal from the one-shot 22 The third input of the calculator 17 is a command to determine the values of RX and Cx using the expressions entered into the memory of the calculator 17 and outputting these determined values to indicators 18 and 19, respectively.

The delay time of the element 25 is chosen to be less than the residence time of the one-shot 22 in an unstable position.

A signal from the output of the time interval setting unit 15 is also fed to the input of the pause-forming unit 23, which can also be implemented as a one-shot. The time interval set by the pause-forming unit 23 ensures that the network capacity returns to zero initial conditions (relative to the measurement signal).

The signal from the output of the pause shaping unit 23 is fed to the second input of the storage element (static trigger) 9, its transfer to the initial state, which ensures the closure of the analog switch 6 and the reset of the 16 time intervals to the initial state, and through the second input of the logical element OR 26 to the first inputs of the memory elements (static triggers) 7 and 8, transferring them to state 2, the first inputs of the time meter 14 time intervals and the time interval setting unit 16, thereby starting a new measurement cycle.

Claims (2)

Claim 1, A method for measuring the insulation resistance and the capacity of electrical networks, in which a single step of measuring DC voltage is fed into a monitored network, starting to charge the network capacity, and during the discharge of the network capacity, the instantaneous value is measured after a predetermined a priori time. measuring voltage on the impedance of the network insulation, characterized in that, in order to increase the accuracy of the measurement of the insulation resistance and capacity of electrical networks, especially those having large capacitances relative to earth , while improving speed and expansion dynamic range of measured parameters, additionally simultaneously with the specified first single step of measuring voltage, the second single step of measuring voltage is many times greater, for example, order, amplitude, continuously monitored at the same time, both different-sized single jumps of the measuring voltage and fix the moment of termination of the network capacity from a single jump of smaller amplitude, measure the time elapsed from the supply of both different-sized single jumps of the measuring voltage to the specified time, and interrupt the flow of both single ones into the monitored network. measuring jumps voltage, which ensures the beginning of the network capacity discharge to the network insulation resistance, and the network capacity charging time measured before the specified fixation moment, as well as the instantaneous value of the measurement voltage measured during the network capacity discharge through the a priori time specified from the beginning of the discharge used to determine the magnitude of the insulation resistance and network capacity by expressions Ui Cx where Ui and Ua amplitude of a single jump measuring voltage less level and higher levels, respectively; 1) s - measured (recorded) the instantaneous value of the measuring voltage in the process of discharging the network capacity after an a priori specified time; . ti - measured time of reaching the moment of termination of charge of network capacity a single step of measuring voltage of smaller amplitude; t2 - a priori specified time in the period of discharge of the network capacity from the beginning of the discharge; RT is the resistance value through which a single jump of the measuring voltage of higher amplitude goes to the insulation impedance (to the charge of the network capacitance). 2. Method pop.1, characterized in that the moment of termination of charge of the network capacity from a single jump of measuring voltage of lower amplitude is fixed upon reaching the moment of equality of the drop of measuring voltage on the series connection of the resistance of the connection unit, for example, an artificial zero point, for three-phase AC mains and impedance network isolation amplitude of a smaller unit jump in the measuring voltage, i.e. the voltage at the output of its voltage source. RI -CZr BUT U +