DE1027771B - Thermal overload protection for electrical lines, apparatus and machines - Google Patents

Description

GERMAN

The invention relates to thermal overload protection for electrical systems, which depicts the thermal behavior of the equipment to be protected and at Exceeding a permissible temperature limit as a result of malfunctions or the like. The protégé switches off or there is a corresponding display. The new facility differs from the familiar of this type in that a self-balancing electrical bridge circuit with a measuring mechanism, a voltage divider and quadratic characteristic having circuit elements is provided, which is one of the thermal equation

Q = _Cl d9 \ dt + c ₂ -Θ

analog equation with electrical quantities
U ₁ = 1 / c · da / dt + U ₂ Ia ₀ · a

enough. Here, Q means the amount of heat generated; Θ the overtemperature; c, C ₁ , c ₂ are constants; U ₁ is the measurement voltage proportional to the square of the load current and thus proportional to the amount of heat generated; U ₂ is a comparison voltage, and α / α ₀ represents a ratio of the tapped partial resistance at the voltage divider to its total resistance.

On the basis of this equation, the simplifying assumptions are made that the heat storage within the protégé and the heat dissipation over the surface of the protégé takes place evenly.

The measuring mechanism adjusting the tap of the voltage divider is preferably connected between the tap of the voltage divider fed by the reference voltage U ₂ and one end of a fixed resistor influenced by the load current via the circuit elements, the other end of which is directly connected to one fixed pole of the voltage divider. Rectifiers operated in the curved part of their characteristic curve, preferably in a full-wave circuit, can be used as square-acting circuit elements, which are connected on the AC side to a current proportional to the load current and connected to a low resistance in relation to the fixed resistance. The excess temperature, i.e. the temperature difference to the coolant temperature, of the protégé can be taken from the position of the tap in the voltage divider, as this is adjusted by the measuring mechanism driven depending on _{the difference between the reference voltage and two of the measuring voltage JT 1, which is analogous to the respective amount of heat,} that the difference becomes zero. To switch off the protégé when a certain temperature is reached, a contact mechanically coupled to the voltage divider tap can be provided in a corresponding tripping circuit.

Furthermore, within the scope of the invention, for detecting the temperature of the environment and for triggering thermal overload protection
for electrical cables,
Apparatus and machines

Applicant:

Siemens-Schuckertwerke

Corporation,

Berlin and Erlangen,

Erlangen, Werner-von-Siemens-Str. 50

Dipl.-Ing. Karl Nimes, Erlangen,
has been named as the inventor

of protection, an electrical display and / or protective device can also be provided, which is arranged in the circuit of a second voltage divider, which is also connected to the reference voltage U ₂ and whose tap located in the circuit or protective device is also made dependent on the measuring mechanism. To measure the actual temperature of the protégé, z. B. a thermocouple or resistance thermometer is arranged, the resistance of which changes depending on the coolant temperature and thus influences the display or the responsiveness of the organ accordingly. In the event that the time constant of the protégé changes due to a change in the cooling conditions, a corresponding change in the analog time constant τ = a _o / U ₂ · c is possible by changing the comparison voltage U ₂ .

A change in the time constants of the protégé can be made, for example, by additional cooling (installation further fan or the like) enter. In the case of self-ventilated machines, z. B. for acquisition the influence of the self-ventilation according to the invention is the equivalent voltage of one coupled to the machine Be removed from the speedometer.

In the drawing, an embodiment of the subject matter of the invention is shown. A transducer W, which is the primary side through which the load current i of protégé, fed on the secondary side a resistor R. The voltage drop across this resistance drives by a device connected to this rectifier circuit G in Graetz circuit a current which is a to the

70S 959/326

Resistor R ₁ connected to DC poles flows. The resistors R and R ₁ and the rectifier arrangement G are dimensioned and matched to one another in such a way that the rectifier arrangement G is operated in the curved part of its characteristic curve, where R ₁ must be larger than R. This ensures that the voltage drop U ₁ across the resistor R ₁ is proportional to the square of the load current i , so that, due to the relationship ζ) ~ ϊ ^2, the amount of heat Q can be simulated by the measurement voltage U ₁ . The resistor R ₁ is on the one hand directly connected to one end of a voltage divider P ₁ and on the other hand via a measuring mechanism M to the tap A of the voltage divider, which in turn is fed by a reference voltage U ₂ . The measuring mechanism, which is used to adjust the tap of the voltage divider, consists of a small, highly sensitive and practically smoothly working direct current motor.

If the protégé is not in operation and therefore its temperature corresponds to that of the coolant temperature, tap A, which can be adjusted by the measuring mechanism, should be in the lowest position. In this position, the measuring mechanism M is de-energized. When the protégé is put into operation, a measuring voltage U ₁ corresponding to the load current occurs, which activates the measuring mechanism so that it adjusts tap A until the counteracting voltage part a / a ₀ · U ₂ becomes effective. The operating temperature in question can then be read from the position of the tap A using a correspondingly calibrated scale (not shown). To switch off the protégé when a certain dangerous temperature is reached, a contact, not shown, can be coupled to the tap, the z. B. closes the trip circuit, also not shown, for a protective device so that it switches off the protégé. When the temperature decreases, the differential voltage acts in the opposite direction and the measuring mechanism is actuated in the opposite direction. In addition to the outside temperature, ie the ambient temperature of the protégé, z. B. the room temperature, to take into account, a second voltage divider P _{2 can be connected} to the DC voltage U ₂ within the scope of the invention, and the tap B of the voltage divider P ₂ can itself be brought into adjustment dependency of the measuring mechanism M. Between the tap B and the one end of the voltage divider P _{2 there} is a series circuit of an electrical display and / or protection element T with a resistance thermometer Th , the resistance value of which changes as a function of the coolant temperature. With the help of this arrangement, with appropriate calibration of the organ T, the entire temperature of the protégé can be read immediately, or a contact device (not shown) can be activated by a contact (not shown) of this organ when a certain temperature difference between the coolant temperature and the temperature is reached of the protégé. The invention is of course not limited to the specified embodiment, but it can be modified in many ways. For example, instead of a rectifier as a square-acting circuit element, a Hall generator arrangement or the like can also be provided. Furthermore, instead of a resistance thermometer, as mentioned, a thermocouple can also be provided.

Claims (7)

Patent claims: 1. Thermal overload protection for electrical lines, apparatus and machines, characterized in that that a self-balancing electrical bridge circuit with a measuring mechanism, a voltage divider and circuit elements having quadratic characteristics are provided which are one the heat equation Q = c ₁ deidt + c ₂ -0 analog equation with electrical quantities U ₁ = 1 / c ■ iajdt + UYes ₀ ■ a enough; herein means Q = amount of heat generated, Θ = temperature,
c, C ₁ , c ₂ = constant, U ₁ = proportional to the square of the load current Tension, U ₂ = equivalent voltage, α / α ₀ = ratio of the tapped partial resistance of the voltage divider to the total resistance. 2. Thermal overload protection according to claim 1, characterized in that the tap of the voltage divider (P ₁ ) adjusting the measuring mechanism (M) between the tap of the voltage divider fed by the reference voltage U ₂ and one end of a circuit elements with a quadratic characteristic (G ) is connected by the load current influenced fixed resistor (R ₁ ) , the other end of which is directly connected to the one fixed pole of the voltage divider. 3. Thermal overload protection according to claims 1 and 2, characterized in that as square-acting circuit elements in the curved part of their characteristic operated rectifiers are preferably used in full-wave circuit, the AC side to a current flowing through a current proportional to the load current, in relation to the fixed resistance (R ₁ ) small resistor (R) are connected. 4. Thermal overload protection according to claims 1 to 3, characterized in that an electrical display and / or protective element is arranged in the circuit of a second voltage divider (P ₂ ) which is fed by the reference voltage U ₂ and which is located in the circuit of the organ Pickup is brought into adjustment dependency from the measuring mechanism (M). 5. Thermal overload protection according to claim 4, characterized in that for consideration the coolant temperature in series with the display and / or protective device a thermocouple, resistance thermometer Od. Like. Is arranged. 6. Thermal overload protection according to the preceding claims, characterized in that the reference voltage can be changed to adapt the time constants r = & olU ₂ · c, analogous to the thermal time constants of the protégé, to the respective cooling conditions. 7. Thermal overload protection according to claim 6 for self-ventilated machines, characterized in that that to record the influence of self-ventilation as a reference voltage, the voltage of one with the Machine coupled speedometer is used. 1 sheet of drawings © 709 959/326 4.58