SU1379648A1 - Device for measuring the a.c. electric machine winding temperature - Google Patents

Abstract

The invention relates to the field of thermometry. The purpose of the invention is to improve the measurement accuracy. Accurate measurement of the DC voltage on the winding - thermal sensor 1, caused by the flow of the measuring current, is hampered by the constant component caused by the flow of the operating alternating current. To eliminate it, the voltage meter 16 is connected to the temperature sensor 1 via a compensator. The latter is a bridge circuit. A limiting inductance correction winding 14 is connected to the supply diagonal of the compensator 11 via rectifier 20. By varying the ratio of the resistance values of the shoulders of potentiometer 19, the required value and sign of the compensation voltage are provided. 1 il. (L

Description

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The invention relates to thermometry, namely to measuring the temperature of the windings of AC electric machines, which are directly under high voltage without disconnecting from the mains, and can be used in thermal protection devices of electric machines, generator-transformer blocks and other high-voltage electrical products.

The purpose of the invention is to improve the measurement accuracy.

The drawing shows a schematic diagram of a device for measuring the winding temperature of an electrical machine.

The device contains a thermal sensor 1, made in the form of one of the windings of an electric machine and connected via shunt 2 to an alternating voltage source 3. Parallel to shunt 2, the resistors 4-6 of the bridge meter 7 of the thermal sensor 1, the tr of which arms are formed by the resistors A-6, and the fourth shoulder are directly the shunt 2, and the resistor 8 is connected to the DC source 9, the measuring diagonal of the bridge The first gauge 7 is on the equilibrium gauge 10.

In parallel with the winding-temperature sensor 1, an asymmetry compensator 11 and a resistive voltage divider, made on resistors 12 and 13, inductance 14 is connected. The primary winding of the compensating transformer 15 is connected in parallel with the voltage divider 12, the secondary winding of which is connected through voltage meter 16 . parallel to the second shoulder of the voltage divider - resistor 13.

The asymmetry compensator 11 is made in the form of two series-connected resistors 17 and 18, parallel to which potentiometer 19 is connected. The connection point of resistors 17 and 18 is connected to limiting inductance 14, connected to resistor 12 of the voltage divider in the middle of the potentiometer. Parallel to the potentiometer 19, through the rectifier 2, a winding for correction of the limiting inductance 14 is connected.

The device works as follows.

A constant current is applied from source 9 along the chain formed by resistors 6 and 8 and shunt 2 to create a voltage on shunt 2. This voltage ensures that a constant current of a required current not exceeding 0.3 0.5% of the nominal value of the load current of the electric machine.

The measurement of direct current in the circuit of the winding-sensor 1 is carried out by a bridge meter 7, the equilibrium meter 10 is connected to the measuring diagonal. When the winding sensor 1 is disconnected from the alternating voltage source 3, the bridge meter 7 of the thermal sensor 1 is in a balanced state. When a source of alternating voltage 3 is connected to the winding of the thermal sensor 1 and shunt 2, a part of the current of shunt 2 flows through the thermal sensor circuit. At the same time, the voltage on the resistor 5 and shunt 2 is not equal to each other, and their difference is the unbalance voltage of the bridge meter 7 - measured by the equilibrium measuring device 10. According to the unbalance value of the bridge measuring device 7 (and „,), the amount of current flowing in the circuit of the winding-thermal sensor 1 which is equal to

I; 06 R

where Igg is the current in the winding-temperature sensor 1; Ry - shunt resistance 2.

The DC voltage drop on the winding-sensor 1 is measured by a voltage meter 16, which is connected parallel to the sensor 1 via limiting inductance 14, an unbalance compensator 11, a resistive voltage divider and a compensating transformer 15. AC voltage compensation in the meter circuit 16, the voltage is produced using a voltage divider on the resistors 12 and 13 and the compensating transformer 15, the primary winding of which is connected in parallel to the resistor 12. Using elitel voltage transformer and a compensating ensures complete compensation of the variable component of the mains voltage with the phase error of the transformer 15 which does not prevppaet 0,5 ,. In this case, the voltage measurement circuit provides maximum sensitivity, since one of the voltage divider arms — resistor 12 — is shunted by the primary winding of a transformer 15, whose resistance does not exceed 1.0 Ohm, i.e. the transmission coefficient of the useful signal is close to one.

Accurate measurement of the DC voltage on the winding-sensor 1 caused by the flow of the measuring current is hampered by the constant component caused by the flow of the alternating current and the asymmetry of the parameters of the machine under study. In order to eliminate this component, the voltage meter 16 is connected to the temperature sensor 1 via an asymmetry compensator 11.

The asymmetry compensator 11 is a bridge circuit. The power supply of the compensating inductance 14 is connected to the diagonal of the power supply of the compensator 11 through expander1; the driver 20 is connected. When the bridge circuit is completely balanced, there is no compensation voltage. By changing the ratio of the impedance of the shoulders of the potentiometer 19, the required value and sign of the compensation voltage is provided. The advantage of this circuit is an insignificant (no more than 1–2 ohms) output resistance of the compensator.

The winding temperature of the electric machine is determined by the formula

 R

and

H6

and

where Rgg is the resistance of thermal sensor 1 {

  voltage drop 1 "1 measuring current on the temperature sensor 1.

Claims (1)

The invention The device for measuring the temperature of the winding of an electric machine of alternating current, comprising a thermal sensor, made in the form of one 10 windings of an electric machine, connected through a shunt to an alternating voltage source, a bridge current meter of a thermal sensor, a DC source connected in parallel to a shunt through the shoulders of a bridge current meter of a thermal sensor, and a voltage meter and limiting inductance, characterized in that In order to improve measurement accuracy, a compensating transformer, a resistive voltage divider, an asymmetry compensator and a rectifier were introduced into it, while the inductance 25 li ne parallel to the temperature sensor, through the compensator unbalance and resistive voltage divider is formed with a winding correcting unbalance compensator is configured in the form of 30 two series-connected resistors with a potentiometer connected in parallel with them, the middle terminal of which is connected to a resistive voltage divider, the limiting inductance is connected to the common point of the asymmetry compensator resistors, the limiting inductance correction winding is connected to the potentiometer parallel to the rectifier, 40 and parallel to one of the arms of the resistive voltage divider, the primary winding of the compensating transformer is connected, the secondary winding of which through a voltage meter 45 is connected parallel to the other side of the resistive voltage divider. 35