JPH03230781A - Condensation-proof device for alternating current motor - Google Patents

Abstract

PURPOSE:To realize condensation-preventing without using a space heater, an exclusive main circuit, and a control circuit by building in a safety stop mode for generating no output and stopping a motor, and a heating mode for generating voltage on specific one phase and single-phase-heating the motor under stopping. CONSTITUTION:A perfect stop mode for generating no AC output as a motor stopping mode, and a single-phase heating mode for single-phase-operating an inverter and generating single-phase voltage just on specific one phase are built in, and each of the two modes is selected by a mode change-over switch 17. When single-phase AC voltage is applied to an AC motor 1 under stopping, then open-phase voltage is to be applied to the motor. Accordingly, rotational torque is not generated on the motor and it is set in a stopped state, and by heat generated from the winding of phase with voltage applied to, the interior section of the motor is heated.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a dew condensation prevention device for an AC motor that heats a stopped AC motor using its drive power source.

(Prior Art) Conventional examples of dew condensation prevention devices for AC motors are shown in FIGS. 2 and 3, respectively.

Figure 2 shows the case where a space heater is used.
is an AC motor, 2 is an overload relay that protects the motor, and 3 is an overload relay that protects the motor.
4 is a main circuit electromagnetic contactor for starting and stopping the electric motor, 4 is a space heater, and 5 is an electromagnetic contactor for turning on and off the electric motor.

Traditionally, space heaters have been used in cold regions or in motors that are stopped for long periods of time to prevent condensation inside the motor while the motor is stopped, but in this case, a special motor with a space heater installed inside is required, and the space is A main circuit dedicated to the heater, an electromagnetic contactor for the space heater, and a control circuit are required.

Fig. 3 shows a case where the motor is heated in a single phase in order to omit this dedicated circuit, and when the motor is stopped, the magnetic contactor 6 for single-phase heating is closed, and the motor 1 is supplied with a voltage lowered by the autotransformer 7. Apply phase AC voltage.

In this case, the input of the motor 1 is in an open-phase state, so no rotating torque is generated and the motor 1 remains stopped, and the winding RT of the phase to which the single-phase AC voltage ■ is applied has a heat amount determined by the winding resistance r V2/r is generated, and the other phase windings R-5 and ST each heat the inside of the calorific motor.

(Problem to be Solved by the Invention) In this way, both the space heater and single-phase heating heat the inside of the motor while the motor is stopped to prevent condensation.
Single-phase heating requires a dedicated circuit consisting of a single-phase heating magnetic contactor 6 that supplies only one phase to the power supply side, and since the applied voltage V is constant, the amount of heat generated W is uniquely determined by the above formula, The winding resistance r of the motor is also determined without regard to the required amount of heat for single-phase heating, so it may generate more heat than necessary while the motor is stopped, causing the motor to overheat, or the required amount of heat may not reach the required amount of heat. There are problems such as not being able to get it.

The present invention was made in consideration of such problems, and
The purpose is to provide a dew condensation prevention device for an AC motor that can prevent condensation while the AC motor is stopped, driven at variable speed by an inverter device, without using a space heater or a dedicated main circuit or control circuit. be.

[Structure of the Invention] (Means and Effects for Solving the Problems) The dew condensation prevention device for an AC motor according to the present invention stops the motor without generating any output as a stop mode for an inverter that generates three-phase AC output. Complete stop mode and certain 1
It has a built-in heating mode that heats a stopped motor by generating a voltage in one phase, and is characterized by the ability to select between these two modes. In contrast to conventional methods, the interior of the motor was heated by installing a dedicated circuit and heating the motor in a single phase.

By controlling the switching of the inverter, which is the output part of the inverter, and generating voltage only in one specific phase, a dedicated circuit is installed, and by controlling the pulse width of this voltage, the amount of heat required for heating is adjusted. I'm trying to be able to do that.

(Example) An embodiment of the present invention is shown in FIG.

In FIG. 1, 8 is an inverter device, and when the operation switch 10 is turned on, a frequency setting signal 9 is sent to the A/D converter 1.
1 is converted into a digital signal and sent to the microprocessor 1.
2, the microprocessor 12 outputs a signal with a voltage and frequency corresponding to this signal to the PWM processor 13, and upon receiving this signal, the base drive circuit 14 converts an inverter section composed of main circuit switching elements U-Z. A signal is generated to drive each of the 15 switching elements.

The commercial AC voltage is rectified into a DC voltage by the converter section 16, and converted again to an arbitrary frequency and voltage by switching of the switching elements U to Z of the inverter section 15, thereby driving the AC motor 1 at a variable speed.

The present invention incorporates a complete stop mode in which no AC output is generated as a motor stop mode, and a single-phase heating mode in which the inverter is operated in a single phase to generate single-phase voltage only in one specific phase. Mode changeover switch 1
7, and the latter mote performs single-phase heating of the motor to prevent condensation.

When a single-phase AC voltage is applied to a stopped AC motor, it means that an open-phase voltage is applied to the motor, and the motor remains stopped without generating rotational torque. The heat generated from the windings heats up the inside of the motor.

By using an inverter, you can obtain any voltage by controlling the pulse width of this voltage.

You can easily obtain the optimal amount of heat for heating.

Furthermore, by sequentially switching the phases to which voltage is applied, voltage is applied only to one specific phase, and thermal stress is not intensively applied to the windings of that phase.

〔Effect of the invention〕

As explained above, according to the present invention, the amount of heat required to prevent condensation can be easily obtained by switching the main circuit of the inverter to single-phase operation, and the electric motor can be specified by sequentially switching the phases of single-phase operation. Thermal stress on the windings is eliminated.

It is also economically advantageous because a standard motor can be used without the need for a special circuit or a special motor.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing an embodiment of the present invention, Fig. 2 is a circuit diagram showing an example of a conventional condensation prevention device when a space heater is applied, and Fig. 3 is an example of a conventional condensation prevention device. FIG. 3 is a circuit diagram of the electric motor shown in FIG. 1 when single-phase heating is applied. 1... AC motor 2... Overload relay 3
...Main circuit electromagnetic contactor 4...Space heater 5...Magnetic contactor for space heater 6...Magnetic contactor for single-phase heating 7..Auto transformer 8.
...Inverter device 9...Frequency setting signal 1
0... Operation switch 11... A/D converter 12... Microprocessor 13... PWM processor 14... Base drive circuit 15... Inverter section 16... Converter section 17...
Mode selector switch (8733) Agent Patent attorney
Yoshiaki Inomata (and 1 other person) Diagram

Claims (1)

[Claims] A dew condensation prevention device for an AC motor driven by a three-phase inverter is characterized by a single-phase heating control circuit that causes the three-phase inverter to operate in a single phase when the AC motor is stopped and applies the single-phase output to the AC motor. A dew condensation prevention device for AC motors.