SU1594642A1 - Method of protecting induction motor from abnormal duties - Google Patents

Abstract

This invention relates to relay protection for electric motors. The purpose of the invention is to increase the sensitivity of protection. The goal is achieved by measuring the active power consumed by the motor and the effective mechanical power on the motor shaft. The engine consumed active power is determined in normal operation. After that, a protection signal is formed if the power loss in the protected motor exceeds the power losses of the normal mode of operation by a predetermined amount. 1 il.

Description

The invention relates to electrical engineering, namely to relay protection of electric motors, and can be used to protect an asynchronous electric motor, especially one for which, under operating conditions, it is necessary to measure the torque on the shaft and the angular velocity of rotation of the shaft against damage and dangerous abnormal operating modes .

The aim of the invention is to increase the sensitivity of the protection.

The drawing shows a diagram of the device for implementing the proposed method.

. The protection device of the asynchronous motor 1 consists of current sensors 2-4, sensors 5-7, respectively, voltage, torque and angular velocity of rotation of the rotor, as well as controller 8 with freely programmable logic and the actuator 9. The outputs of sensors 2-7 are connected to analog inputs of the controller 8, the output of which is connected to the input of the actuator 9, and the output of the latter is the output of the device as a whole.

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The current sensors are measuring current transformers, the voltage sensor is a three-phase measuring voltage transformer. The torque sensor can be made non-contact. The angular velocity sensor in the simplest case is a tachogenerator. Controller 8 is a controller with freely programmable logic, containing software for storing the engine, and the actuator is a relay device.

The essence of the method consists in comparing the actual value of active power losses in a working electric motor with a known value of power loss corresponding to the normal mode of operation of the engine and set by its operating characteristic.

The active power losses in the electric motor, determined from measurements in the current mode of operation, are equal to

LR

PI g t

(one)

where r

- power consumed by an electric motor from a network;

P - useful mechanical power on the motor shaft.

The loss of active power, given by the operating characteristic of an electric motor (at the same values of useful power on its shaft and network voltage), is equal to

LR R 9 2)

where P is a motor consumed from a network, MonipocTb is active in normal operation.

In the event of damage or abnormal abrupt work, the loss of P in the motor increases. The proximity of the current mode of operation of the electric motor to the normal mode is estimated by comparing the active power losses in both modes, from (1) and (2):

LR - LR

P - P g, f,,

(3)

Tlkim way, dp detection of damage or abnormal operation of the motor is enough

five

0

five

0

five

0

five

0

five

to estimate the value of the difference between the active power consumption values in the current mode and the consumed active power, determined from the operating characteristic of the electric motor for the measured values of useful mechanical power on its shaft and network voltage.

When satisfied

LR -,

where P is the set value, which, subject to (3), is replaced by

P - P P f, i, / t

The controller 8 generates a control signal to the executive authority 9, acting on the shutdown of the protected engine 1.

The value of power P is calculated by controller 8 from the currents and voltages measured in the power supply circuit of motor 1, and the power values P from the values of torque on the shaft and angular velocity of rotation of the rotor measured by sensors 6 and 7, respectively. P is calculated by controller 8 using a software-defined operating characteristic of the electric motor 1. for the measured value of the mains voltage, that. Eliminates false operation of the protection when the motor is operating with a reduced supply voltage, for example, under self-starting conditions or in case of a close short circuit in the network. The effective values of the powers P, and P are determined according to the measurement data over a sufficiently long time interval, which excludes the erroneous operation of the protection in transient operating modes of the protected motor.

The protection method can be used to protect any asynchronous electric motor, especially one for which, under the operating conditions, it is necessary to measure the torque on the shaft and the angular velocity of rotation of the rotor.

The use of the proposed method allows to realize universal protection of asynchronous electric motors against damage and dangerous abnormal operation modes. Under the conditions of speed, it is advisable to use such office as a backup.

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Claims (1)

Claim The method of protection of an asynchronous motor against damage and dangerous abnormal modes of operation, in which the currents and voltages at the power end of the line to which the motor is connected is measured, determine the active power at the input and output of the protected motor, which means that protection sensitivity, to determine the active power at the output of the electric motor, an additional torque is measured at ^ 0 the shaft and the angular velocity of the rotor of the electric motor, according to the working characteristic, determine the active power consumed by the electric motor in the normal mode when measuring, 5 r is the network voltage, determine the loss of active power in the engine and generate a protection signal, if these losses exceed active 20 power in normal operation.