RU2263383C1 - Electric motor and driven equipment protective device - Google Patents

Abstract

FIELD: electrical and radio engineering.

SUBSTANCE: proposed device designed for protection of electric motor and driven equipment against overcurrent and overtemperature, unwanted load shedding, and inadmissible ground fault of motor winding has overcurrent protection channel, overtemperature protection channel, driven-equipment emergency load shedding protection channel, and channel for motor protection against its starting at ground fault of its winding insulation. These channels are interconnected in parallel and connected through OR gate to final relay whose output is connected to control circuit contacts of magnetic starter whose power contacts are designed to connect motor phase leads to power line.

EFFECT: enhanced reliability of motor and driven mechanism protection.

6 cl, 6 dwg

Description

The invention relates to electrical engineering and can be used to protect the electric motor and its equipment from unacceptable current and thermal overload, abnormal load shedding and unacceptable lowering of the insulation resistance of the winding relative to the motor housing.

A device is known for protecting an electric motor from overheating and overload, comprising a current sensor of a protected electric motor, the output of which is connected to an input of an actuating element and a shunt thyristor, a key and a delay element connected in series, a first potentiometer and a zener diode connected in series. Parallel to the zener diode, a series-connected engine temperature sensor, a second potentiometer, and an ambient temperature sensor are connected. The output of the second potentiometer is connected to one of the key inputs, to the other input of which, through the logical operator OR, the output of the delay element and the current cutoff element are connected [1].

The disadvantage of this device is the low reliability of protection due to the mismatch of the time-current characteristics of the device with the thermal characteristics of the engine.

A device for protecting an electric motor with a pump drive, comprising a temperature sensor, a voltage source, a low-pass filter, a first battery, a control unit and a pulse generator [2]. The low-pass filter input is designed to connect to the zero point of the secondary winding of the power transformer. A temperature sensor installed near the stator windings of the submersible motor is connected in series with the diode between the zero point of the motor winding and its grounded housing. The control unit is made in the form of two comparison units, the outputs of which are connected to the actuators.

This device eliminates the influence of insulation resistance on the measurement of the heating temperature of the stator windings of the electric motor.

The disadvantage of this device is the lack of protection elements for the submersible motor from a disruption in the supply of the electric pump, controlled by the pressure in the well, which can lead to “dry friction” in the pump, an increase in the gas factor of the pumped liquid, and, consequently, deterioration in the cooling of the engine and power cable .

The closest in technical essence to the present invention is a device for protecting an electric motor from abnormal operating conditions, comprising a current sensor in the form of a current transformer, which is configured to be mounted on an electric motor with thermal contact with the electric motor at a temperature control point, while the current transformer core is made from a ferromagnetic material with a given Curie point, which allows you to expand the functionality of the device by providing a temperature protection of the electric motor [3]. In this case, the Curie point is equal to the maximum permissible motor temperature at the location of the current transformer.

In the prototype device, when the maximum permissible temperature is reached by the electric motor, the core of the current transformer loses its magnetic properties when the Curie point is reached, which leads to the disconnection of the magnetic starter and electric motor from the network. In the overload mode of the electric motor by current, when the permissible value is exceeded or when the phase is broken, the motor also disconnects from the network.

However, when the motor is running, the value of the permissible excess current above the nominal value largely depends on the duration of this current. So, the shorter the duration of the action, the greater the amount of current that can be skipped in the motor windings without accidental consequences, while for longer exposure times, the current should be reduced. Thus, the presence of only one value of the permissible current without taking into account its duration with short times of its flow can lead to unreasonable shutdown of the electric motor, and at significant times to delayed shutdown with emergency consequences for the electric motor.

The prototype device has limited functionality, since the motor does not turn off when the load disappears from the side of the equipment it brings, which is accompanied by a decrease in current. So, if the driven equipment is, for example, a conveyor, an elevator, etc., then unauthorized load shedding indicates its stopping or disconnection from the electric motor. The situation will be especially dangerous if the pump used is a pump for pumping liquids, such as water, because in this case the pump will operate in the “dry run” mode and inevitable damage.

In addition, when using the prototype device, it is possible to start the electric motor in motion with a reduced insulation resistance of the winding relative to the housing, which occurs when moisture or other aggressive environments in which the equipment and the electric motor are operating is hit. This device will not be able to protect the motor from the resulting emergency.

The objective of the invention is to increase the reliability of protection of the electric motor and driven equipment.

The problem is solved in that in the known device for protecting an electric motor and driven equipment, containing protection channels against current and thermal overload, including a current sensor made in the form of a current transformer and mounted on a phase wire, a magnetic starter, the power contacts of which are designed to be connected to the line power supply of the phases of the electric motor, controls of the magnetic starter, and an executive relay with an output contact, and the input of the executive relay is connected to the output of the current sensor, and e o the output contact is included in the control circuit of the magnetic starter, and the contact element mounted on the electric motor responding to thermal overload of the electric motor, a protection channel against current overload, containing an electronic unit for generating time-current characteristics, a protection channel against thermal overload, a protection channel against emergency load shedding of driven equipment and the channel of protection against starting the motor with insufficient insulation resistance of the winding relative to the motor housing is connected between th parallel and are connected by the logical OR operator to the actuator relay whose output is connected to the contacts of the magnetic actuator control circuit.

In addition, the current overload protection channel contains an integrator, to the input of which current sensors mounted on two phase wires are connected in parallel with an amplifier and a rectifier, and the electronic block for generating the time-current characteristic includes a unit that converts the magnitude of the current overload factor to the pulse repetition rate, for example, quadratic dependence, which is connected to the pulse counter.

The overload protection channel contains a warning indicator “CURRENT OVERLOAD”, illuminated when the pulse counter is turned on, and an alarm indicator “CURRENT OVERLOAD”, illuminated when the pulse counter is full.

The motor protection channel against thermal overload contains a contact element made in the form of a temperature sensor, and an alarm indicator "CURRENT OVERLOAD", which lights up when the temperature measured by the sensor exceeds the setpoint temperature.

The channel for protection against emergency load shedding of driven equipment contains the DRY STROKE alarm indicator, which lights up when the motor current decreases below the minimum current setting value.

The channel for protecting the motor from starting with insufficient insulation resistance of the winding relative to the motor housing contains a constant voltage source and an alarm indicator "ISOLATION", illuminated when the insulation resistance of the winding decreases below the value of the resistance setting.

The warning indicator “CURRENT OVERLOAD” is yellow, and the alarm indicators “CURRENT OVERLOAD”, “HEAT OVERLOAD”, “DRY STROKE” and “INSULATION” are red.

In the present invention, a comprehensive protection of the electric motor against:

1) unacceptable current overload caused by the breakdown of one of the phases of the stator winding or power line, phase voltage asymmetry, technological overload, jamming of the rotor or inter-turn short circuits;

2) abnormal disappearance of the load, for example, due to the operation of the pump in the "dry running" mode;

3) lowering the insulation resistance of the winding relative to the motor housing below an acceptable level;

4) unacceptable thermal overload of the engine caused by the deterioration of its cooling conditions.

The presence of a logical OR operator causes the motor to turn off when any of the above factors occurs. The presence of a unit for forming the time-current characteristic in the channel for protecting the motor from current overload allows taking into account not only the multiplicity of current overload, but also its duration. In this case, it is possible to form a real characteristic for a particular electric motor, for example, a quadratic one, according to which it will be switched off.

Parallel connection of protection channels increases the reliability of the protection device, because if one of the channels for some reason does not work, then protection will occur on the other channels.

The proposed protective device allows you to give signals about the motor overload, proportional to its current, in digital form, which is important for recording on recording devices and establishing the causes of an emergency shutdown.

The presence of a warning indicator “CURRENT OVERLOAD” and alarm indicators “CURRENT OVERLOAD”, “HEAT OVERLOAD”, “DRY STROKE” and “INSULATION”, as well as their yellow and red color familiar to many people, makes it convenient for the operator.

Figure 1 presents the General structural diagram of a protection device for an electric motor and driven equipment;

figure 2 is an expanded block diagram of a motor protection device and driven equipment;

figure 3 is a structural diagram of an electronic unit for the formation of time-current characteristics;

figure 4 - time-current characteristic generated by the electronic unit, where t is the response time of the device, K _I is the multiplicity of current overload;

figure 5 is an electrical diagram of a motor protection device and driven equipment;

figure 6 - indicator panel of the protection device.

The device for protecting the electric motor and the driven equipment comprises a channel 1 for protection against current overload, a channel 2 for protecting against thermal overload, a channel 3 for protecting against emergency load shedding of the driven equipment, and a channel 4 for protecting against starting the electric motor 5 with insufficient insulation resistance of the winding 6 relative to the motor casing. These channels are connected in parallel with each other and connected via an OR operator 7 to an executive relay 8, the output of which is connected to the contacts of the control circuit of the magnetic starter 9, the main contacts of which 10 are designed to be connected to the phases of the electric motor 5. The device contains an enable element 11, an auxiliary contact 12 and the shutdown element 13 of the magnetic starter.

Channel 1 protection against current overload contains installed on two phase wires 14 current sensors 15 and 16, made in the form of current transformers. Current sensors 15 and 16 by means of amplifiers 17, 18 and rectifiers 19, 20, respectively, are connected in parallel to the input of the integrator 21. The electronic unit for generating the current-time characteristic 22 includes an adjustable setpoint maximum current regulator 23, a maximum current comparator 24, a warning indicator "current overload" 25, a current-frequency block 26, which converts the magnitude of the current overload factor to the pulse repetition rate, for example, in a quadratic dependence, which is connected to the pulse counter 27. Channel 1 contains the alarm indicator "CURRENT OVERLOAD" 28.

Channel 2 of the motor protection against thermal overload contains a temperature sensor 29, made in the form of an integrated circuit mounted on a heat-conducting mounting plate with a terminal block (not shown), a temperature setpoint adjuster 30, a temperature comparator 31, and an “HEATER OVERLOAD” 32 alarm indicator.

Channel 3 of the protection against emergency load shedding of driven equipment (not shown) contains a setpoint regulator for minimum current 33, a minimum current comparator 34 and an alarm indicator “DRY DRIVE” 35.

Channel 4 of protection of the electric motor 5 from starting with insufficient insulation resistance of the winding 6 relative to the motor housing contains a setpoint adjuster for resistance 36, a constant voltage source (not shown), a resistance comparator 37 and an alarm indicator "ISOLATION" 38.

The warning indicator “CURRENT OVERLOAD” 25 is yellow, and the alarm indicators “CURRENT OVERLOAD” 28, “HEAT OVERLOAD” 32, “DRY STROKE” 35, and “INSULATION” 38 are red. These indicators are located on the indicator panel 39 of the housing 40 of the protective device.

The protection device of the electric motor and driven equipment operates as follows.

If one of the emergency factors occurs:

1) excess of the duration of the current overload of the device operating time according to the time-current characteristic;

2) the temperature measured by the sensor 29 exceeds the setpoint temperature 36;

3) a decrease in the current of the electric motor that occurs during an emergency load shedding of the driven equipment is lower than the value of the minimum current setting 33;

4) lowering the insulation resistance of the winding 6 relative to the motor housing 5, below the value of the resistance setting 36,

a logical operator or 7 generates a signal to the actuator relay 8, which, in turn, provides a signal to the control circuit of the magnetic starter 9, the main contacts 10 of which disconnect the power supply phase of the phases of the electric motor 5.

Before starting the motor, a constant voltage DC motor 5 is supplied to the winding 6. The measured insulation resistance of the winding 6 relative to the motor housing in the resistance comparator 37 is compared with the value of the setpoint for resistance 36. If the measured value of the insulation resistance is less than the setpoint 36, the IZOLATION 38 alarm indicator lights up and the power contacts 9 of the magnetic starter 8 open.

The current measured by one of the current sensors 15 and 16 is amplified by an amplifier 17 and 18, respectively, rectified by a rectifier 19 and 20, respectively, and then fed to the input of the integrator 21.

The greatest value of the signal from the current sensors after the integrator 21 goes to the electronic unit for generating the time-current characteristic 22. The value of this current in the comparator of the maximum current 24 is compared with the value of the setpoint for the maximum current 23. If the current value exceeds the value of the setpoint, the warning indicator "CURRENT OVERLOAD" 25, the signal is supplied to the “CURRENT-FREQUENCY” block 26, which converts the magnitude of the current overload factor to the pulse repetition rate, for example, in a quadratic dependence, and upaet a pulse to the counter 27. In the pulse sequence entry counter 27 lights up the alarm lamp "overcurrent" 28, and by the logical operator OR 7 signal is supplied to the output relay 8, so that the motor comes off from the supply line phases. The greater the magnitude of the overcurrent multiplicity, the higher the pulse repetition rate of block 26, the faster the pulse counter 27 is filled. Thus, a quadratic dependence of the response time of the protection device on the multiplicity of overcurrent is realized.

If the cause of the current overload is eliminated before filling the counter 27, which occurs, for example, at the time of starting the electric motor, the counter is reset to zero with the cessation of the warning indicator “CURRENT OVERLOAD” 25.

The signal value from the current sensors 15 and 16 after the integrator 21, arriving at the minimum current comparator 34, is compared with the minimum current setting value 33. If the current value after the integrator 21 turns out to be lower, the DRY STROKE 35 alarm indicator lights up with the subsequent opening of the main contacts 10 of the magnetic starter 9.

The temperature value measured by the sensor 29 in the temperature comparator 31 is compared with the temperature setpoint value 30, and if it exceeds it, the “HEATER OVERLOAD” alarm indicator 32 lights up with the subsequent opening of the main contacts 10 of the magnetic starter 9.

Using the “TOK-FREQUENCY” electronic unit 26, it is possible to generate a time-current characteristic of the device according to any necessary law. This allows the protection of electric motors of various types under various operating conditions and the nature of the load.

The proposed device provides comprehensive protection against various heterogeneous factors (unacceptable current and thermal overload, emergency load shedding, lowering the insulation resistance of the winding relative to the motor housing below the acceptable level), which guarantees high reliability of protection. The protection device is implemented in a housing 40, on the outer surface of which there is a display panel 39 with indicators 25, 28, 32, 35 and 38, as well as behind a protective cover (not shown) - regulators of the settings for the maximum current 23, minimum current 33, temperature 30 and resistance 36. Using the setpoint regulators, you can set the appropriate value of the monitored parameter, taking into account the actual working conditions, type of electric motor and driven equipment.

The protection device was manufactured, passed an experimental test in various conditions, showing high reliability.

Sources of information

1. A.S. USSR No. 600654, MKI N 02 N 7/08, 1978

2. A.S. USSR No. 1302369, MKI N 02 N 7/08, 1985

3. A.S. USSR No. 1764118, MKI N 02 N 7/08, 1992 (prototype).

Claims (6)

1. The protection device of the electric motor and driven equipment, containing protection channels against current and thermal overload, including a current sensor made in the form of a current transformer and mounted on a phase wire, a magnetic starter, the power contacts of which are designed to be included in the power supply line of the phases of the motor, the control circuit a magnetic starter and an executive relay with an output contact, and the output contact of the executive relay is included in the control circuit of the magnetic starter, and mounted on an electric motor contactor element, responsive to thermal overload of the electric motor, characterized in that the channel for protection against current overload, comprising an electronic unit for generating a time-current characteristic, a channel for protection against thermal overload, a channel for protection against emergency load shedding of the driven equipment and a channel for protection against starting the motor with insufficient resistance winding insulation relative to the motor housing are interconnected in parallel and connected via a logical operator OR to tional relay. 2. The protection device of the electric motor and driven equipment according to claim 1, characterized in that the current overload protection channel comprises an integrator, to the input of which current sensors installed on two phase wires are connected in parallel with an amplifier and a rectifier, the electronic block for generating the time-current characteristic includes a block, converting the magnitude of the current overload factor to the pulse repetition rate, for example, in a quadratic dependence, which is connected to the pulse counter, illuminated when when operating the pulse counter, the “CURRENT OVERLOAD” warning indicator and the “CURRENT OVERLOAD” alarm indicator illuminated when the pulse counter is full. 3. The protection device of the electric motor and driven equipment according to claim 1, characterized in that the channel for protecting the electric motor from thermal overload contains a contact element made in the form of a temperature sensor and an alarm indicator “HEAT OVERLOAD”, which lights up when the temperature setpoint is exceeded . 4. The protection device of the electric motor and driven equipment according to claim 1, characterized in that the channel for protection against emergency load shedding of the driven equipment contains an alarm indicator “DRY DRIVE”, illuminated when the motor current decreases below the minimum current setting value. 5. The protection device of the electric motor and the driven equipment according to claim 1, characterized in that the channel for protecting the motor from starting with insufficient insulation resistance of the winding relative to the motor housing contains a constant voltage source and an alarm indicator "ISOLATION", illuminated when the insulation resistance of the winding decreases below the set value resistance. 6. The protection device of the electric motor and driven equipment according to claim 2, 3, 4 or 5, characterized in that the warning indicator "CURRENT OVERLOAD" is yellow, and the alarm indicators "CURRENT OVERLOAD", "HEAT OVERLOAD", " DRY STROKE ”and“ INSULATION ”are made in red.

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