SU1233242A1 - Device for overload protection of electric motor - Google Patents

Abstract

This invention relates to electrical engineering - protection of an electric motor against overload - and can be used for passenger elevator electric motors. The purpose of the invention is to improve the accuracy of protection. The device contains a motor current sensor 1 with a square converter 3 and a constant setting device 5, which are connected to the first comparator (K) 6 through the aperiodic link (A3) 4 to the key 6 and to the key 13. The sensor of the end of cycle (DOC) 9 and output 6 through the element And 8, amplifiers (Y) 10 are connected to the executive relay 11, acting on the shutdown of the electric motor. The introduction of a second comparator 14, connected between sensor 1 and 10 in dot-lift modes to the next floor, with a single phase break or an elevator movement with unloaded brake pads, without waiting for a signal from DOC 9, gives a signal to turn off the engine with a fixed delay for detuning from rated starting currents. 1 h. N. f-ly. 3 il. a c k o: o: k 4 k

Description

The invention relates to devices for protecting an electric motor from overheating and can be used in particular to protect electric motors of passenger elevators.

- The purpose of the invention is to increase the accuracy and reliability of protection.

FIG. 1 shows a block diagram of the proposed device; Fig. 2 shows a thermal model of an electric motor that implements a differential equation; in fig. 3 shows an embodiment of the device.

The device for protecting the motor against overload contains the sensor 1 of the current of the motor 2, quadratic converter 3j, aperiodic link 4, constant setting device 5, first comparator 6, maximum permissible temperature setting device 7, element 8, cycle end sensor 9, amplifier 10, actuator relay 11, switch 12, key 13, the second comparator 14.-

The device works as follows.

From the current sensor 1 of a three-phase asynchronous motor 2, the voltage proportional to the current of the electric motor e 2 is fed to the input of a quadratic converter 3, from the output of which a signal proportional to the square of the current of the motor

AT

(a + DlH

 const.

I .. is the rated current of the electric motor

the gate arrives at the first input of the aperiodic link 4, and the second summing input of the last from the output of the gate 5 of the constant is given a signal proportional to

one

1000 r.

A (a +

a (1+ g)

D) T7

but

And the loss factor; engine rated power;

Engine efficiency at rated load;

heat transfer, i.e. the amount of heat the engine emits to the environment in

time unit at separation. About, ti temperatures in 1 C.

At the output of the aperiodic link, a signal is formed that is proportional to

0

s

thirty

five

0

five

The actual motor temperature that is fed to the first input of the comparator 6, to the second input of which comes from the output of the dial 7, the maximum allowable temperature of the electric motor is proportional to the specified maximum allowable temperature max of the electric motor. When the actual temperature C exceeds a predetermined G, the comparator 6 is activated and from its output a signal is sent to the first input of element 8. At the end of the cycle (in our case, when the elevator reaches the next floor) from the output of sensor 9, the cycle ends to the second input of element 8 And the element B is triggered and a signal appears at its output, which is amplified by amplifier 10. From the output of amplifier 10, the signal is applied to the executive relay 11, which with its contacts acts on the control circuits of the switch 12, and the latter AET motor 2 from the mains. In addition, the executive relay 11 contacts the control signal to the key 13, the latter triggers and performs the following switchings: the first output changes the parameters of the RC chain of the aperiodic link (thermal model of the electric motor in stop mode), and the second reduces the maximum allowable temperature of the electric motor so that when it is turned on again after cooling down and a constant load at which the first disconnection occurred, the elevator lifted (lowered) to the next floor without overheating the electric motor 2

To build the simplest thermal protections of electric motors, models are used that describe electric motors as homogeneous with respect to heating the body.

Qdr

where Q

 Cdr + Adt,

(one)

- the total amount of heat imparted to the body;

С - body heat capacity, i.e. the amount of heat required to raise the engine temperature at

A - heat transfer, i.e. the amount of heat emitted by the engine into the environment per unit of time with the temperature difference in

с - engine temperature (winding) of the ambient temperature. From the basic equation (1) of the heating electric machine we get j

 d

-dT- S.

(2)

where t

and c..j

whose solution is: L t r 6y (1 -) .e,

where h; - the value of the initial temperature or obmgatel In these equations

Q 1000 dR, J / s,

where LR P, -R;

P - power, supplied by the body:

P - power on the engine shaft.

- -.

ai

e P is the nominal power of the engine;

a is the loss coefficient; JQ 2c - engine efficiency at rated load; I is the current in the motor windings;

I. - motor rated current, n

R.

a + 1

(V) ha + (td) 1-1000; (6) h5

 n L C J

. Q 1000 Р, 1 у-д-1000 р.

A (a + 1)

AT . but

a + 1

a + 1

The loss factor a can be determined analytically from two values of efficiency and power.

 RI

 R

l-gn

I

1- H

n. k k

+ its eggs (a + 1) 1 + and „(I) (a + x2) T

l-uJ

from where

DR - DRi x Pu-4R

(ten)

j

to

15

20

Jq

h5

40

. Approximately (for a nominal load) the following values of the loss coefficient can be taken; for DC motors of independent excitation 1-1.5; for sequential motors, 0.5-0.9; for asynchronous motors of common industrial type 0.5-1.0; for asynchronous, crane-type motors 0.4-1.0; for synchronous motors 1 -2.

FIG. Figure 2 shows the thermal model of the electric motor (aperiodic link 4), which implements differential control (2), where R.C .Xj is the constant heating of the electric motor (in the operating mode of the electric motor);

() C T is the motor cooling constant (in the stop mode);

Until key 13 is triggered, the time of the aperiodic link is constant.

T, R, C ..

After actuation of the key 13 (the engine stops), the contact of the key 13 is opened and the constant time of the aperiodic link increases

H f The transfer function of the aperiodic link at the first input

ij (-0 «3 1 P 1)

 R, Cp +1 /

at the second entrance

4S

SO

W, (P)

RI / R4

R, Cp +1

(12)

LA

T P + 1

Similarly, with engine cooling, R, -t-R2

JiL.

W, (P)

W, (P)

R.

(R, + Rj) Cp + 1 1

-; (13)

R + R,

() Cp +1 T P + 1

(14)

During the operation of electric motors of elevators, situations arise when the lift-up of the elevator to the next stage is possible: an unacceptable overheating of the electric motor, for example

at break of one phase or at movement of the elevator with not released brake shoes. In these cases, the engine must be disconnected (Zez waiting for a signal from the cycle sensor.

In order to realize the motor protection in this situation, the proposed device additionally includes (FIG. 3) a second comparator 14 with a fixed delay (for tuning out from normal starting modes), the input of the second comparator 14 being connected to the second output of current sensor 1, and the output of the second comparator 14 connected to the second input of the amplifier 10.

The operation of this protection channel is as follows. With a motor current equal to the starting one, with a given time delay, the output of the second comparator 14 is a signal that goes to the second input of the amplifier 10, then the executive relay 11 is activated, the switch 12 and the engine 2 are disconnected from the network. The time delay in the comparator 14 is set longer than the duration of the normal start-up modes in order to eliminate false alarms of protection,

The advantage of the proposed device in comparison with the known one is in the protection accuracy.

Claims (2)

1. Device to protect the motor against overload, containing a series-connected sensor about s 0 5 o five motor current, quadratic converter, aperiodic link, first comparator and series-connected amplifier, actuating relay and switch, due to the fact that, in order to increase the protection accuracy, a constant setpoint adjuster is added to it, a key, an element And an end-of-cycle sensor, the second newly introduced regulating input of an aperiodic element, made with a tunable time constant, is connected to the output of sensor constant, and the third newly introduced control input aperiodic link - with the first key output, the second key output is connected to the set point input of the maximum allowable temperature of the electric motor, the output of which is connected to the second input of the first comparator, the last output is connected to the first input of the And element, the second input which is connected to the output of the end of cycle sensor, the output of the element I is connected to the input of the amplifier, and the second output of the executive relay is connected to the input of the key. 2. The device according to claim 1, characterized in that, in order to increase the reliability of protection of the motor, a second comparator is additionally introduced with a delay, the input of which is connected to the second output of the current sensor and the output to the second input of the amplifier. at kblonub Aperiodized link Figure 2 Editor O. Bugir Compiled by O. Muratov Tehred M. Khodanich Proofreader A. Ferenc Order 2779/55 Circulation 612 Subscription VNIIPI USSR State Committee for inventions and discoveries 113035, Moscow, Zh-35, Raushsk nab., 4/5 Production and printing company, Uzhgorod, st. Project, 4