JPH0322819A - Motor protective unit - Google Patents

Abstract

PURPOSE:To improve protective performance by storing temperature operation results of a motor obtained immediately before power interruption, during interruption of control power source, then operating temperature rise of motor during power interruption based on the temperature operation results and control power source interruption time obtained through a timer means. CONSTITUTION:Upon missing of control power source 7, a source monitoring means P detects power interruption and an operating means C operates temperature of a motor M which is then stored in a memory means ME. The memory means ME is a non-volatile type where data do not disappear even when the control power source 7 is missed, and the data are held until the control power source 7 is recovered. Upon recovery of the control power source 7, temperature theta2(t) of the motor M is computed based on the power interruption time DELTAT which is the difference between the power interruption time To and a time measured through a timer means T, temperature operation results of the motor M during power interruption being held in the memory means ME, and radiation time constant TD of the motor M.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a motor protection device that protects a three-phase induction motor, which is widely used in industry, from overheating and burnout due to overload, for example.

(Prior technology) Is a thermal overload joint used as a conventional motor protection device? IS device (
There is a thermal relay). Thermal relays are widely known and in practical use as the cheapest and simplest protection devices.

The principle of operation is that a heating element provided within the thermal relay generates heat due to the motor current, and the heat bends the bimetal to operate the output contact. The temperature of the heating element changes depending on the current flowing through the motor, and the degree and speed of bending of the bimetal changes. Although such a thermal relay has a simple structure, it has the following drawbacks.

l) The temperature rise of the electric motor is simulated using a heating element and a bimetal, but these characteristics are determined by their own physics and cannot be adjusted to match the actual heating conditions of the motor to be protected. be.

2) In particular, the cooling characteristics when the motor is stopped are different from the time constant of the motor, which ranges from several tens of minutes to one hour and several tens of minutes.
That of a thermal relay is a few minutes. When putting thermal relays into practical use, these drawbacks are taken into account and thermal relays with appropriate characteristics are selected and used.

recently,. In order to solve the above-mentioned drawbacks of the thermal relay, a temperature calculation type motor protection device (hereinafter referred to as a temperature calculation relay) has been put into practical use, which uses a microcomputer to calculate the temperature rise value of the motor from time to time.

Figure 4 is a block diagram showing the general outline of this temperature calculation relay, including a current flow device 1 that detects the motor current, a conversion circuit 2 that converts it into a digital signal, heat generation time constant, heat radiation time constant, and tolerance of the motor M. A setting unit 3 sets a constant specific to the motor M, such as a temperature rise value ε, a settlement circuit 4 calculates a temperature rise value using equations (1) and (2), which will be described later, and a calculation result and calculation unit 4.
Memorize the Na order Ki 1 Momme・1:・Il Road 5, When the calculated temperature rise value of the motor reaches the allowable temperature rise value, an output circuit 6 that outputs a trip output, and a transformer 8 that supplies power to each circuit. The control power source 7 transforms the voltage and supplies the power.

The temperature rise value calculated in the calculation circuit 4 is calculated by the electric motor M.
Time constant TRN Heat dissipation time constant T o f': 1: Determined by constants specific to the motor and motor current.

FIG. 5 is a diagram showing the relationship between motor current and temperature rise value to explain this.

During operation θ1 (L) 10" (It) ・( 1-ey.p"
″t/T n > ,,, (1) Here, θl(t
) : Temperature rise value θoa Bt) at time t : Saturation temperature rise value TR when motor current 1 t flows continuously : Motor heat generation time constant θ2<t) 10(o) ・exp −' TD- (
'． a Here, θ2 (t): temperature 1 at time t. Ascension θ(o): 1m! Temperature rise value TD when the motor stops (t-o): Heat radiation time constant of the electric motor (problem to be solved by the invention) Such a temperature calculation relay calculates the temperature rise value of the electric motor M from time to time. Therefore, it is not only optimal for electric motor V43, but also because it performs calculations using constants unique to electric motor M.
The protection suitable for the temperature characteristics of any electric motor M can be performed, and in particular, the heat dissipation characteristics are also simulated, so the above-mentioned drawbacks of the thermal relay are solved.

However, such temperature calculation relays also have the following drawbacks.

l) Control voltage l to operate each circuit of the temperature calculation relay.
! i. 7 is necessary, and if the control power supply 7 is lost, the motor MLy) i degree rise value disappears, and after the control power supply 7 is established again, the actual temperature rise value of the motor M and the simulation result will be There may be a temporary discrepancy. Now, when the motor M is operating at full load and the control@power source '7 experiences a power outage at the point indicated as "power outage", the temperature of the motor increases as shown by the broken line and at the point indicated as "power restoration". When the control power source 7 becomes double-current, the actual increase in audience level of the electric motor M and the simulation result (solid line) become inconsistent.

2) Also, it is unthinkable to provide a backup power source within the temperature calculation relay to ensure the operation of each circuit when the control power [7] is lost.

However, in order to avoid a discrepancy between the simulation results and the actual motor temperature rise value, it is necessary to continue operating each circuit at least three times the heat dissipation time constant TD of the motor. Considering the duration of one hour and several tens of minutes, a backup power source that can operate for about 5 to 6 hours is required to preserve data, which is practically impossible from the standpoint of space, economy, and maintainability.

The purpose of the present invention is to use a temperature calculation relay, which is an ideal protection means for an electric motor, to be able to accurately simulate the heat dissipation of the electric motor even if the control power is lost and then the control power is reestablished. An object of the present invention is to provide a motor protection device that does not cause mismatch with an actual motor temperature rise value, thereby improving protection performance.

[Structure of the Invention] (Means for Solving the Problems) In order to achieve the above-mentioned object, the present invention provides a means for calculating a temperature rise value from an inherent constant of the motor and a motor current in order to protect the motor from overheating and burnout. In a temperature calculation type electric motor protection device that calculates the temperature according to storage means capable of storing temperature calculation results calculated by the calculation means during a power outage of the control power supply, and when a power failure is detected by the power supply monitoring means, the calculation means stores the temperature calculation result at the time of power failure measured by the timer means. The heat radiation temperature of the electric motor is calculated from the temperature calculation results stored in the storage means.

(Function) According to the present invention, the temperature calculation result of the motor immediately before the power outage is stored in the storage means that can be stored during a power outage of the control power supply,
Since the motor heat radiation temperature rise value during a power outage can be calculated from this temperature calculation result and the control power outage time determined by the timer means, the motor heat radiation temperature rise value during a power outage can be calculated even if the control power is lost and the control power is reestablished. can be accurately simulated, and there will be no discrepancy with the actual temperature rise value of the motor.

(Length Examples) Examples of the present invention will be described below with reference to the drawings.

Figure 1 is a block diagram showing the schematic structure of the present invention.
j Power supply monitoring technology that detects loss of power and restoration of power. A stage P, a timer means T for measuring the power outage time until the power is restored after the power outage of the control power source 7 occurs; a storage means ME capable of retaining the color temperature calculation result during a power outage; and a memory for the power outage time measured by the timer means T. The calculation means C calculates the motor heat radiation temperature increase value during timer power outage from the temperature calculation results stored in the means ME.

In such a configuration, when the control power supply 7 is lost at t2, the power supply monitoring means P detects a power failure (SL
)L, in response to this, the calculation means C can store the temperature calculation result of the electric motor M in the storage means ME (S2). This storage means ME is a storage means that does not lose data even when the control power source 7 is lost, and holds this data until the control power source 7 is established and restored again (S3). After the control power supply 7 is established by power restoration, the power outage time ΔT (S5) is determined from the difference between the IIS time T2 measured by the timer T (S4) and the power outage time To.
．． Memory means M. Based on the temperature calculation result of the electric motor M at the time of power outage held in (S2) and the heat radiation time constant To of the electric motor M, the temperature θ2(t) of the conduction @M is calculated, for example, by the above-mentioned equation (2) (S6).

FIG. 3 shows a specific embodiment of FIG. 1.

That is, a microprocessor (CPU) 10 is used as the calculation means C in FIG. sexual memory (
Using the RAMSNOV-RAM 12, a real time counter (RC) (IC) is used as a timer means T.
13 and a battery 14 for this RTC, and a power supply monitoring circuit 1 as a power supply monitoring means P.
5 was used. Each circuit is connected by a bus line and a control signal line.

The above-mentioned points are different from conventional temperature calculation relays.

Now, in such a configuration, when the control power supply 7 is lost, the power supply monitoring circuit 15 detects a power outage and sends a power outage signal to c p u 1 . Send to Q. cpulo is electric motor M
The temperature calculation result θ(o) and the time To indicated by R T C 1 '3 are stored in the nonvolatile memory 12, and a store signal is sent to the nonvolatile memory 12 to hold the data. When the non-volatile memory 12 receives the store signal, it saves the data to the non-volatile memory cell and retains its contents even if the control power supply 7 is no longer supplied. During this time, the control power supply 7 continues to supply the power necessary for each circuit to operate. The time required to save this data is approximately 10 msec.

After this, each circuit stops operating, but l? Tc13
Only the dedicated battery 14 continues the timekeeping operation.

Next, when the control power supply 7 is established, each circuit starts operating. First, cpulO performs necessary initialization processing and then reads time T1 from the RTC 13. Next, the time To at the time of power loss saved in the non-volatile memory 12
is read, power outage time t-TI-To is calculated from this, and power outage n. The motor temperature calculation result θ(0) of ') and the electric conductor heat radiation time constant TD of the setting unit 3 are read, and the above-mentioned equation (2) is calculated to obtain the current motor temperature calculation result.

Hereafter, the temperature calculation of the motor is continued using the motor current.

According to the embodiment of the present invention described above, if the control heavy source 7
Even if the motor is lost, the heat dissipation calculation of the motor can be performed, and there will be no discrepancy with the actual temperature rise value of the motor. The backup battery 14 may also be an RTC battery 14 with a capacity that can operate each circuit for about 10 wsec during a power outage, which is not only feasible but also space-saving, economical, and maintainable compared to the conventional technology. It is not significantly inferior to.

The present invention is not limited to the above-mentioned embodiments, and it goes without saying that the present invention can be made into a bag-like shape or length without departing from the scope of the invention. For example, instead of the microprocessor 10, a logic circuit may be used as the calculation means C;
As the storage means ME, a static RAM may be used instead of the nonvolatile memory 12, and data may be retained by a dedicated battery during a power outage. Furthermore, as a timer means T, RTC
It goes without saying that 13 may be replaced by an RC timer using a simple resistive capacitor, or any combination thereof.

[Effects of the Invention] According to the present invention described above, even if one monme of control power is lost and the control power is re-established, the heat dissipation of the motor can be accurately simulated, and the heat dissipation from the actual motor It is possible to provide a motor protection device that does not cause mismatch with the temperature rise value, thereby improving protection performance.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing a schematic configuration of the motor protection device of the present invention, Fig. 2 is a flowchart for explaining the operation of Fig. 1, and Fig. 3 is a concrete example of the fire protection device of Fig. 1. FIG. 4 is a block diagram showing the configuration of the conventional device, and FIG. 5 is a diagram showing the relationship between the current of the electric conductor and the temperature rise value. C...Calculating means, ME...Storing means, 7...Control power supply, P...Power supervising means.

Claims (1)

[Claims] In order to protect the motor from overheating and burnout, a temperature calculation type motor protection device that uses a calculation means to calculate the temperature rise value from the motor's individual constants and the motor current is designed to prevent power outage and restoration of the control power source of the protection device. A power supply monitoring means for detecting a power supply, a timer means for measuring a power outage time from a power failure to a power restoration of the control power supply, and a storage means capable of storing a temperature calculation result calculated by the calculation means during a power outage of the control power supply. ,
When a power outage is detected by the power supply monitoring means, the calculating means calculates the heat radiation temperature of the electric motor from the power outage time measured by the timer means and the temperature calculation result stored in the storage means. motor protection device.