DE2351157A1 - DISPLAY DEVICE TO PROTECT ELECTROMAGNETIC DEVICES FROM OVERHEATING - Google Patents

Description

Applicant: Canadian General Electric Company Limited,. Peterborough, Ontario / Canada

Display device to protect electromagnetic devices from overheating

The invention relates to a static display device to protect electromagnetic devices from overheating as a result of excessive current; in particular concerns the Invention a thermal overload indicator with a reciprocal or opposing time characteristic for an electromagnetic one Consumer in which the electrical and magnetic losses as well as the thermal properties the load or the consumer when heating and, if necessary, must be taken into account during cooling.

Overheating of the consumer due to electrical, thermal losses or as a result of losses in the IR Kind occurs in particular with engines and other consumers, since the overheating as a function of in these facilities • flowing current increases. Over the years, therefore, simulation devices have been developed which operating data have the electrical, thermal characteristics

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the consumer's same; In the following, the characteristic data are represented by curves in which the thermal damage or the safe operating time are plotted against the current is. The simulation devices are generally used to switch off the consumer or the load for all overload values used before damage has occurred (or the allowable time has passed). Here is with the term safe operating time at any overload essentially denotes the time at which a thermal stress on the consumer becomes large enough that the manufacturer is no longer ready to use the guarantee normal service life at full load; or in other words, by such adverse occurrences' the service life of the consumer is shortened to an extent that cannot be precisely calculated, but it is large it is enough that the manufacturer is not ready to guarantee its usefulness for the normal life.

Electromechanical overload relays are simulated devices which are generally used to protect a consumer. Such relays have a bimetal element to which a pair of contacts and a heating element are assigned, which is operated with the current flowing through the consumer in order to heat the bimetal element in accordance with this current. With the help of these contacts, which are connected to the supply lines to the consumer, the consumer is disconnected from the lines if the bimetal is overheated. Beneficial and enjoyable is their property in these relays, during their operating time maintain the electrical, thermal losses of previous unfavorable overloads and _to consider which have not led to a shutdown of the consumer; This storage capacity inherent in the relay is due to the thermal storage properties of the bimetal element

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as well as the environment. With short cyclical overloads, which do not lead to a disconnection of the consumer, therefore the relay works as a result of the in the device stored heat generally faster with each subsequent overload. This is particularly advantageous since this takes into account the fact that an already warm consumer is much more likely to be overloaded is thermally stressed.

Unfortunately, however, with the relays with a bimetal element, the temperature cannot be sensed as precisely as in is required in some cases. Basically, compared to the time constant, the bimetal element has one Motor has a very short time constant, so it see heats up and cools down faster than the engine; the display device created according to the invention has time ■ constants that are the same as those of the engine, and thereby precisely senses its' temperature. For engines with a long start-up time where, for example, the starting currents are large, the bimetal element is often already warmed up enough after the engine has started, so that it is switched off incorrectly. This is known as overshoot or oversteer designated; conversely, failure or failure of the bimetal element in the event of a rapid response to overloads referred to as lagging or chasing.

Although these Haehteile in some applications, for example They play only a minor subordinate role in motors with long permissible start-up times it is necessary to switch the relay for a certain part of the starting or starting period, for example up to 10 seconds. short-circuit in order to extend the operating time of the relay and thus avoid overshooting or overdriving

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To take into account. However, the relay often overflows anyway. Though it's about the overshoot or oversteer too prevent it seems possible to short-circuit the relay for as long as necessary, it should generally be stated that that short-circuiting for more than 10 sec. the motor is not permitted in the event of a blockage or standstill endangered. The watchdog device in the form of an overload relay can therefore not effectively provide adequate overload protection for all purposes both at a standstill and while running; of course it can't be preset to either to be switched on for a specific downtime and a certain running value. As a result, in has developed static overload switch tones in recent years to replace the overload relay. In a simultaneously filed application P the applicant (attorney's file 0-3351; US-SN 153 623) describes an invention in which the relay inherent storage capacity to take into account actual consumer warming as a result of the electrical, thermal loss is modeled. In this application, the static overload indicator has analog facilities in the form of resistances and capacitances to simulate the thermal behavior of copper, so that whose operating characteristic is considerably more similar to the thermal damage characteristic of the consumer. With electromagnetic However, this is not only for consumers

by the I. R loss but also by the energy loss heated in the magnetic material; in other words, heated by a consumer in the form of a motor the energy that is converted into heat both in the conductor coils and in the core material, the consumer and in particular its insulating material.

It is therefore the object of the invention to provide an overload

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To create display device for an electromagnetic consumer with the help of analog devices, their electrical resistances and capacitances are sufficient to both the resistance and the capacitance of the electrical and to represent magnetic components of the consumer, and their current inputs are sufficient to absorb the losses in the To represent consumers, so that its operating characteristic even more closely resembles the thermal damage curve of the consumer equals.

According to an embodiment of the invention for an engine the display device ^ is characterized by a Circuitry for sensing the current on the motor and generating a current which has a function thereof Current is, through a source of relatively constant current, through a thermally analog device with first and second capacitive devices which are connected to resistors in a circuit arrangement, whose electrical characteristics are the thermal resistances and capacities of the electrical and magnetic components of the consumer as well as the transmission between these elements, through first and second capacitive Devices that are connected to the circuit arrangement or to the source of constant current to this to be charged in order to take into account the thermal characteristics of the motor, and by a voltage excited Device connected to the first and / or second capacitive device for sensing the voltage applied to it and for sensing a predetermined voltage is connected, which corresponds to a certain, permissible temperature at the consumer and with which a. Display this Temperature is created.

An embodiment of the invention for a consumer in the form of a motor is based on the following description

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with reference to the accompanying drawings in detail explained. Show it:

1 shows a circuit diagram of a display device according to the invention;

FIG. 2 shows a simple graphical representation in which the operating characteristic curve of the one shown in FIG. 1 is shown Display device is reproduced; and

FIG. 3 is a further graphical illustration showing the voltage rise across a capacitor C2 in FIG Shows the circuit arrangement of FIG. 1 for different current values.

In Fig. 1, a motor 10 is connected via breakers 11 to lines L1 to L3 of a three-phase AC power source; the display device designated in its entirety by 12 are useful values for some of those designated in more detail below Components specified. The display device 12 for the motor or any other electromagnetic consumer has the following parts: a circuit arrangement with current-voltage converters T1 to T3, diodes D1 to D3, a zener diode Z1, a capacitor C1 and a resistor R1 for generating a voltage which is proportional to the maximum current in one of the lines L1 to L3, resistors E2 to R7, a transistor and diodes D4 to D6, which are connected to the DC voltage lines 13 and 14 of a further energy source and an adjustable Form voltage-current-dependent valve for generating a Stromsjam collector of the transistor Q1, which is a function of consumer current; another valve is made by resistors E8 and R9 and a transistor 02 is formed to produce a relatively constant current for the collector of this resistor; one

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thermal analog device for the engine has one Resistor R10 and a capacitor 02 to simulate the thermal resistance of the conductors of the motor for ambient conditions or for the conductor heat capacity, a resistor R 11 and a capacitor 0 3 for simulation the thermal resistance value for the magnetic core of the motor for ambient conditions or for the core heat capacity, and a resistor R 12 for replicating the thermal resistance for the conductors in the core .on; an adjustable voltage energized indicator is provided by resistors R13 and R14, a Capacitor 04 and an operational amplifier of one embodiment formed which does not adversely affect the circuit.

The display device 12 operates as follows: if the motor draws power from the AC power source the voltage at the base of transistor Q1 negative enough to turn it on so that capacitor 02 is charged; this charging constitutes the warming of the motor conductors as a result

2 of the electrical heat losses or the IR losses.

At the same time, the transistors Q3, Q4- and Q2 turn on, so that the capacitor 03 through the transistor Q2 to a relatively constant value is loaded, whereby the heating of the engine iron as a result of the Mangetic.Wärmeoder Core losses is simulated. Some current from the transistor Q1 to charge the capacitor 02 flow, whereby the heat .transfer from the ladders to the core is shown. When the voltage across the capacitor 02 is a certain the value preset by the resistor R13 has been reached, which corresponds to a certain permissible motor temperature, an amplifier 15 is switched on, whereby a relay coil 18 is energized to operate the breaker 11 to turn on the motor. If the capacitor 02 as a result an overload is significantly overloaded, the

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Engine switched off; the resistor R13 can then simply can be set to the current value that flows for the motor when switching. Since when the motor is blocked this should be switched off in a shorter time, which is generally referred to as the blocking time, are resistors Rf? up to R7 and diodes D4- to D6 provided, whereby by adjusting the resistor R7 a certain. Blocking time for the motor can be preset.

In Fig. 3 it is shown how the voltage across the resistor R2 for different values of a fixed overload rises to a value that is determined by the setting at resistor R13, for which then, as described above, a signal is present at the amplifier output; the times T6 to T2 and indicated in the figure T *> are the operating or switching times for the in Fig. 1 shown 'display device for the corresponding Overload values on the motor used as the load. The operational characteristic shown in Fig. 2 becomes simple obtained by plotting these switching times and overloads. From this it can be seen that for the value 6XFL (six times the current at full load) the display device works or a signal at the amplifier output in a period of time 0 to T6, because at the end of this period of time the voltage across capacitor C2 is straight is slightly higher than "the tension on the grinding arm of the Resistor R13; the working curve is as required the display device naturally has an inverse or reverse curve.

If the motor does not start or locks up, how stated above, a signal at the amplifier output. Safe engine operation requires a maximum switching time for a certain current value when blocking to

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so to protect the engine in this case too. The current value during blocking is generally 6XE ¹ L (or six times the current at full load). It can be seen from FIG. 2 that the corresponding switching time in the case of blocking is then the time segment 0 to T6. Since the currents corresponding to full load as well as the switching times in the event of blocking change with the motor size, it is advisable to preset the working time interval 0 to T6 to six times the current at full load without disturbing the continuity of the working characteristic curve, which at the moment of the Engine damage line is the same. In Fig. 1, the interval 0 to T6 is preset in the display device in that the wiper arm of the resistor R7, as explained above, is set.

Safe engine operation also requires a maximum. Switching value for a certain overload level during the run so as to protect the engine from thermal damage during its run; the congestion level generally chosen with the engine running is 1.05FL (or 1.05 times of the current at full load). As can also be seen from FIG. 2, the corresponding turn-on value should be shown be adjustable to adapt to different engines, without destroying the working characteristic. Presetting the operating level for this general one Overload with the engine running will then, as well detailed above, made by means of the adjustable resistor E13. .

From Fig. 1 it can also be seen that the capacitor C2 via an electronic switch 16 and a resistor R19 associated therewith, and a capacitor C3 via a corresponding switch 17 and a resistor R20 charged will. Each switch is also connected to a simple oscillator, which switches the switches at the oscillator frequency,

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which is set by changing a resistor E 24-. can be switched on and off; by means of this arrangement can then the charging time or the time constant of the circuit be enlarged. Although these facilities need not be included, smaller ones can be used if provided Capacitors, which can be film capacitors, can be used, which then hold the charge better than large capacitors, such as electrolytic capacitors.

The above-described display device can therefore simply be calibrated, does not oscillate or oversteer, and do not rush; the display device for an engine, their switching time in the event of blocking and their overcurrent switching level can be set when the engine is running, has an electrical analog device that controls the thermal Characteristic values simulate when the motor heats up, so that its working characteristic corresponds to the actual temperature profile of the engine. The display device can also be set as follows to display when the Machine has cooled down sufficiently after the display of an excessive temperature to be started again. · Basically, only one feedback circuit on the amplifier 15 is required for this. With this simple Addition with which an indication of excess temperature takes place at a point in time at which the transistors Q1 until Q4 are turned off, the circuit operates as follows.

The capacitor C2 is discharged via a pendulum switch 16 and ^v the resistors R10 and RI2, which represent the cooling of the motor current conductors when it is switched off. The capacitor discharging via the resistor R12 then again represents the heat transfer from the current conductors to the core. The capacitor C3 discharges in a similar way

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via switch 17 and resistor RI1. Once the Capacitor G2 is set to a certain lower voltage has discharged, which is determined by the setting of a resistor R22 in the feedback loop and which represents a safe starting temperature for the engine, the amplifier 15 is in its original or display state switched back, which it occupies before an excessive temperature, thereby indicating that the engine is sufficiently cooled and can be started again. If the motor is switched off for a long time, the capacitors will of course be completely discharged, and thus represent a future cold engine.

In practice, the engine cooling times for engines from 100 to 1000 hp are 2,000 to 50,000 seconds. consequently is it is generally expedient to use the oscillator switching arrangement described above to use in order to reduce the time constants to further increase the circuit and thus also a very large increase in the time constant of the motor when it cools down without turning. A possibility this is shown in FIG. 1. Here, an oscillator control 21 is added and to the arrangement of the transistors Q3 and 04, which have previously been used to monitor the state of transistor Q2 and oscillator 20 to control; The latter has then also been provided with a further resistor R25 and an electronic switch 19, which has the same design as the switches 16 and 1 ?. The oscillator control 21 can be any device which can feel the different voltage levels at the collector of the transistor 04 and the switch 19 as a function before, the voltage level can switch on and off.

The display device modified in this way operates as follows. When the engine is switched off, the

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Transistors Q1 to Q4 off and the voltage on the collector of transistor Q4- rises from a low voltage to a higher voltage. In order to use the oscillator control 21, the switch 19 when the To connect higher voltage, resistors R24 · and R25 connected in parallel whereby the oscillator pulse width is made narrow in order to further slow down the discharge of the capacitors 02 and 03 and thus the time constants to enlarge the circuit. The same result could be achieved by maintaining the pulse width and the frequency is decreased by means of the same control circuit.

The display device shown in FIG. 1 is therefore only a display device excited by a voltage shown. In practice, however, it can be useful to connect a second device to the capacitor 03. The first display device can then be set to operate when the temperature of the motor current conductors for example, exceeds 180 ° - with a heating of the conductors when starting the engine is allowed while the second device can be set to work if the core temperature is 180 °, for example maximum permissible temperature for the insulation generally used - exceeds. The exits of the two Facilities would then be monitored to indicate when the temperature of either facility was exceeded.

In particular, a device indicating an engine overload has thus been described above, which device accordingly the actual temperature of the engine working; the characteristic of the display device can be set and the Indicator itself can be adapted to indicate when the engine has cooled sufficiently after being overloaded in order to apply energy to him again the display device can also be used for other electromagnetic loads, such as a transformer etc. be applied.

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Claims (9)

Patent claims 1. [Static display device to protect against electromagnetic ^v ' see devices. from overheating as a result of too high a current, characterized by circuitry for sensing the current of the device (10) and generating a current which is a function of the device current; by a source of relatively constant current; by thermal analog devices with first and second capacitive devices (C2, C3) »which are connected to resistors (R10, R11) in a circuit arrangement, the electrical characteristics of which are the thermal resistance and capacitive values of the electrical and magnetic components of the device and the heat transfer between them components represent the first and second capacitive means (C2, C3) are connected to the circuit arrangement and the constant current source to its charging, the thermal characteristics to consider the device and by an energized by voltage means _(R13? R14 , C4, 15), which creates a temperature display on at least one of the two capacitive devices (C2, C3) for sensing the voltage applied to them and at a predetermined voltage corresponding to the respectively permissible device temperature. 2. Display device according to claim 1, characterized in that the analog device has a first circuit with a first capacitor (C2) and a first resistor (R10) connected in parallel thereto, a second circuit with a second capacitor (C3) and a second resistor connected in parallel thereto (R11) and a third resistor (R12) connected between the first and second circuits, the circuit arrangement and the voltage-excited device (R13, R14 ·, C5 _S 15) being connected to the first capacitor (C2) and the source - 14 409816/0946 constant current connected to the second capacitor (C3) is. 3. Display device according to claim 2, characterized characterized in that each electronic switch (16, 17) in series with one of the capacitors (C2, C3) are connected, and that an oscillator (20) is connected to the switches (16,17) to their To control switch-on and switch-off time, the charging times of the capacitors (C2, C3) by the Switches (16,17) j which interrupt their charging intermittently are extended. 4. Display device according to claim 3 »to display when the device has cooled down sufficiently after an excess temperature display to start again, characterized in that the device excited by a voltage (R13 »R14-, 04,15) has two initial states and at a predetermined Voltage switches from one state to the other to indicate an excessive device temperature, and at much lower temperature switches back to one state to indicate that the device (10) has cooled down sufficiently. 5- display device according to claim 4 · ,. marked by an oscillator control circuit (21) which is responsive to the device current so that the oscillator (20) with a Pulse width when current flows into the device and with a The narrower pulse width oscillates when no current flows, whereby the discharge times of the capacitors (C2, C3) are extended are to enable cooling of the device (10). 6. Thermal overload display device, in particular according to one of the preceding claims, to protect a motor connected to an energy source, whereby the inverse or reciprocal operating characteristic of the display 409816/0946 - 15 - installation of the thermal damage curve for the motor is largely the same and operating times for the time of a motor standstill as well as a current switching value with the motor running are preset, geke η η is characterized by two direct voltage lines connected to another energy source (14,15)} through a device (T1 to T3 ; D1 to DJ; Z1, R1, C1) for generating a voltage proportional to the current at the motor; by a voltage-current-dependent valve (E2 to E7, QI, D4 to D6), which is connected between the lines (14,15) and to the voltage generating device, the current from the valve being a function of the Current to the motor (10) is through a flow valve connected between the lines (14,15) with a constant current, through a first resistor (R10) and a capacitor (02) which is parallel to this and to the voltage-current-dependent valve to take account of the electrical heat loss the current to the motor (10) is connected in parallel; through a second resistor (R11) and a capacitor (05) _{s of} the constant current in parallel and to the valve, taking into account the. magnetic heat loss of the power is turned on to the motor (10); by a drivcer .. resistor connected between the first and second resistors (R10, R11) and the capacitors (C2,05) to take into account the energy transfer occurring between the elements; and by a display device (R13, R14, 04, 15) excited by a voltage, which is connected to at least one of the two capacitors (G2, C5X for cooling the voltage and a display at a predetermined voltage corresponding to a specific, respectively permissible motor temperature generated, the voltage-current-dependent valve and the display device for presetting the operating time for the standstill time or for the current switching value can be set while the engine is running. 409816/0946 7 »Display device according to claim 6, characterized ge ke η η ζ e i chne 1; that each one switch (16,17) in series with one capacitor (C2, C3) is switched, and that an oscillator (20) is connected to the switches (16,17) to switch them on and to control switch-off time, whereby the time constants of the circuits are lengthened. 8. Display device according to claim 7, in order to indicate when the engine has cooled down sufficiently after an over temperature display to let it start from ®uem, characterized in that the device excited by a voltage (K13, R14-, 04,15) having two output states and to switch at a predetermined voltage from one state to the other state to an excessive! display temperature, and at a much lower temperature switches back to a state of _t to indicate that the motor has cooled sufficiently, and that the oscillator (20) oscillates at a narrower pulse width, when the motor (10) receives no current _t than when it receives a, thereby the time constant corresponding to the larger time constant of the motor (10) to. extend when it cools down without turning. 9. Display device according to one of claims 6, 7 or 8, characterized in that a another device excited by a voltage. to the second capacitor (GJ) is turned on and that facilities are provided to indicate when one of the two devices generates an advertisement; » by. which the indicator indicates that either electrical or magnetic heat loss is about to occur is high. 409818/0948 Lee r side