SU1749848A1 - Device for measuring insulation resistance in networks with grounded neutral - Google Patents

Abstract

The invention relates to electrical measuring equipment and can be used to measure and control the insulation resistance and capacitance of phase conductors in networks with grounded neutral. The purpose of the invention is to improve the measurement accuracy. The device contains a voltage transformer winding 1, a generator 2, three phase windings 3 voltage transformers, three phase windings 4 current transformers, the fifth winding 5 voltage transformers, the fifth winding 6 current transformers, variable resistor 7, variable capacitor 8, winding 9 current transformers, indicator 10, three additional capacitors 11. 1 Il.

Description

The invention relates to electrical engineering and can be used to measure and control the active insulation resistance and capacitance of the phase conductors relative to the ground in networks with a grounded neutral.

A device for continuously measuring the active insulation resistance. in networks with a grounded neutral, containing a voltage transformer with five windings, three windings of which are included in the gap of the phase wires of the network with the beginnings to the power transformer, and the fourth winding is to the output of the generator, and an indicator.

The disadvantages of the device are the presence of some initial current, in this case, the open circuit current of the voltage transformer, as well as the influence of the network capacitance, resulting in reduced measurement accuracy.

The closest in technical essence to the proposed device is a device for measuring the active insulation resistance in networks with a grounded neutral, containing a voltage transformer, three windings of which are included in the gap of the phase conductors of the network with a lead to the power transformer, and the fourth winding is connected to the generator output, the current transformer with five windings, three windings of which are included in the gap of the phase wires of the network with the beginnings to the ends of the windings of the voltage transformer, and an indication unit connected to the fourth bmotke current transformer.

However, the known device has the following disadvantages. The power transformer, which is a complex, non-linear, variable resistance, will influence the measurement results. In the core of the magnetic core of the current transformer there is always an alternating magnetic flux, and consequently, hysteresis losses and eddy currents, which vary depending on the magnetic flux induced in the core by a current flowing through the changing insulation resistance. The measurement process is affected by the nonlinearity of the magnetization curve of the core of the current transformer, and the influence of fluctuations in the operating voltage reduces the accuracy of the measurements.

The purpose of the invention is to increase the accuracy of measurements.

This goal is achieved by the fact that the device for measuring insulation resistance in networks with a grounded neutral containing a voltage transformer, three windings of which are included in the gap of the phase conductors of the network with the beginning to the power transformer, and the fourth winding is to the generator output, the current transformer with five windings, three windings which are included in the rupture of the phase wires of the network with the beginnings to the ends of the voltage transformer, and the display unit connected to the fourth winding of the current transformer is equipped with a capacitor capacitor, a variable resistor, the fifth winding of the voltage transformer and three additional capacitors connected between the beginnings of the three windings of the voltage transformer and the neutral of the power transformer, the capacitor of variable capacitance and the variable resistor being connected to one end of the fifth winding of the current transformer and the other to the end of the fifth windings of the voltage transformer, the beginning of the fifth winding of the voltage transformer is connected to the beginning of the fifth winding of the current transformer.

The drawing shows a block diagram of a device.

The device comprises a winding 1 of a voltage transformer, a generator 2, three phase windings 3 of a voltage transformer, three phase windings 4 of a current transformer, a fifth winding 5 of a voltage transformer, a fifth winding 6 of a current transformer, a variable resistor 7, a capacitor 8 of variable capacitance, a winding 9 of a current transformer, indicator 10, three additional capacitors 11, Variable resistor 7 and variable capacitor 8 can be blocks containing sets of constant resistors of constant capacitors and special ialnyh switching devices. Switching devices allow you to change the values of resistor 7 and capacitor 8. '

In addition, the phase wires 12, the power transformer 13, the resistance 14 of the grounding system of the neutral point of the power transformer, the complex resistance 15 of the insulation of the phase wires relative to the ground are indicated. The winding 1 of the voltage transformer is connected to the output of the generator 2, three phase windings 3 of the voltage transformer beginnings are connected to the power transformer 13, and the ends are connected to the beginnings of the three phase windings 4 of the current transformer, the ends of the three phase windings 4 of the current transformer are connected to the phase wires 12, the fifth winding 5 the voltage transformer is connected at the beginning to the beginning of the fifth winding 6 of the current transformer, the fifth winding 6 of the current transformer is connected end to one terminal of the resistor 7 and capacitor 8, the other terminals are a source 7 and a capacitor 8 are connected to the end of the fifth winding 5 of the voltage transformer, an indicator 10 is connected to the winding 9 of the current transformer, three additional capacitors 11 are connected between the beginnings of the three windings 3 of the voltage transformer and the neutral of the power transformer 13. phase wires 12 are connected to earth through resistance isolation 15, the neutral point of the power transformer 13 is connected to earth through a resistance 14.

The device operates as follows.

Generator 2 supplies operational voltage ϋι to the controlled network. Under the action of the operating voltage, the operating current flows And along the following chain: the beginning of the windings 3 of the voltage transformer, additional capacitors 11, resistance 14, ground, insulation resistance 15, phase wires 12, ends-beginning of the windings 4 of the transformer to.ka, ends. windings 3 voltage transformer. Under the action of the operating voltage of the winding 5 of the voltage transformer, the operating current! G flows along the following circuit: the beginning of the winding 5 of the voltage transformer. the beginning-end of the winding 6 of the current transformer, one or the other terminals of the resistor 7 and the capacitor 8. the end of the winding 5 of the voltage transformer. Current N is directed counter current 1g. The geometric sum of the currents N and 1g creates a current I flowing through the indicator 10. By changing, manually or automatically, the resistance values of the resistor 7 and the capacitor 8, it is possible to completely compensate the current I. The absence of current I in the circuit of the indicator 10 indicates that the resistance values pre-calibrated, the resistor 7 and the capacitor 8 correspond to the values of the insulation resistance 15 of the phase wires 12 relative to the ground. Thus, the values of the insulation components are determined.

Generator 2 delivers an operating current of the order of 1000 to 5000 Hz to the controlled network, for which additional capacitors 11 represent a small capacitive resistance, which reduces the effect of the power transformer. It is possible to eliminate the influence of loss of inconstancy in the steel of the current transformer by compensating for the alternating magnetic flux induced by current Ιι by changing the magnetic flux induced by current 1g, changing the capacitance of the variable capacitor 8 and the resistance of the variable resistor 7.

The influence of the nonlinearity of the magnetization curve of the core of the current transformer can be eliminated if the measurement results are taken at the moments of complete compensation of the magnetic flux induced by the currents h and 1 g.

Elimination of the influence of instability of operational voltage is as follows. Suppose that the voltage ϋι decreases, therefore the voltage Og decreases, since the voltages Οι and иг are removed from the windings of one transformer.Currently, the currents Д and и directed towards each other will decrease, and the geometric sum of currents 1ι and 12 will remain constant.

Claims (1)

Claim A device for measuring insulation resistance in networks with a grounded neutral, containing a voltage transformer, three windings of which are included in the gap of the phase wires of the network with a lead to the power transformer, and the fourth winding .- to the output of the generator, a current transformer with five windings, three windings of which are included in the gap phase wires of the network with the beginnings to the ends of the windings of the voltage transformer, and an indication unit connected to the fourth winding of the current transformer, characterized in that, in order to improve the measurement accuracy , it is equipped with a capacitor of variable capacitance, a variable resistor, a fifth winding of a voltage transformer and three additional capacitors connected between the beginnings of the three 'windings of the voltage transformer and the neutral of the power transformer, the capacitor of variable capacitance and a variable resistor being connected to one end of the fifth winding of the current transformer, and the other conclusions - to the end of the fifth winding of the voltage transformer, the beginning of the fifth winding of the trans, voltage formatter is connected to the beginning of the fifth current transformer slots.