TEMPERATURE CONTROL METHOD FOR TERMINAL CONNECTION

Abstract

A method for protecting an electrical grid against short circuits by controlling a temperature of terminal connections is disclosed, it can be used in industrial and consumer equipment to prevent fire hazardous situations. The technical result consists in the possibility of obtaining prompt and reliable information about a thermal state of terminal connections in an electrical circuit by avoiding an electrical connection between temperature sensors and a terminal connection. The metal device is used as a base for a temperature sensor. By using a triggering circuit, a voltage whose value depends on the temperature change is measured or compared or controlled with a predetermined voltage. If the temperature rises to a predetermined value or becomes higher than the predetermined value, the electrical circuit is opened or interrupted. After the temperature drops below the predetermined value, the electrical circuit is closed or restored.

Claims

1. A temperature control method for a terminal connection, comprising: installing a metal device in the terminal connection or in direct proximity to the terminal connection, using the metal device as a base for a temperature sensor, measuring temperature based on a property of changing an electrical resistance of bodies with a temperature change, by using a triggering circuit, measuring or comparing or controlling a voltage, the value of which depends on the temperature change, with a predetermined voltage, if the temperature rises to a predetermined value or becomes higher than the predetermined value, opening or interrupting an electrical circuit, and after the temperature drops below the predetermined value, closing or restoring the electrical circuit.

2. The control method of claim 1, comprising using, as the triggering circuit, an inverting comparator connection circuit which allows a low signal level to be obtained at a comparator output, or a non-inverting comparator connection circuit which allows a high signal level to be obtained at the comparator output, or a circuit having a Zener diode.

3. The control method of claim 1, wherein the metal device is made as a pin-type metal device configured to be clamped in the terminal connection, or as a terminal for a nut connection, or as pin contacts of a mains plug.

4. The control method of claim 1, wherein the metal device is installed at a distance of up to one meter from the terminal connection.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] FIG. 1 shows an inverting comparator connection circuit that implements a method according to the invention.

[0016] FIG. 2a shows a top view of a metal device involved, and FIG. 2b shows a side view of the metal device involved.

[0017] FIG. 3a shows a pin-type metal device configured to be clamped in a terminal connection, and

[0018] FIG. 3b shows a metal device made as a terminal for a nut connection.

[0019] FIG. 4 shows a non-inverting comparator connection circuit that implements the method according to the invention.

[0020] FIG. 5 shows a circuit having a controlled Zener diode, which implements the method according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0021] FIG. 1 shows an inverting comparator connection circuit that implements a temperature control method for a terminal connection according to the invention. The inverting comparator connection circuit comprises a comparator 1, both inputs of which are connected to voltage dividers. The first voltage divider connected to the inverting input (“−”) of the comparator 1 consists of a constant resistor 2 and thermistors 3, 4 which are temperature sensors and may be connected both in series and in parallel. The second voltage divider connected to the non-inverting input (“+”) of the comparator 1 consists of constant resistors 5, 6. The comparator 1 has an output connected to a transistor 7 and a relay 8. A resistor 10 is a current limiter for a light emitting diode (LED) 9 which serves as a terminal connection overheating indicator. An audible alarm 11 may be additionally used to alert users of terminal connection overheating.

[0022] As known, a resistance of a thermistor at a room temperature is very high and decreases when the thermistor is heated. According to the operational logic of the voltage divider, a voltage at the inverting input of the comparator 1 will be lower at the room temperature and will increase when the thermistors 3, 4 are heated.

[0023] To switch on the relay 8 depending on the temperature, it is necessary to set a switching threshold (switching threshold temperature). To do this, the non-inverting input of the comparator 1 is used, which is provided with a reference (constant) voltage. This reference voltage is set by the constant resistors 5, 6 which serve as the voltage divider.

[0024] The comparator compares the two voltage levels at the inverting and non-inverting inputs. If the voltage at the inverting input is greater than at the non-inverting input, then the output voltage from the comparator 1 will open the transistor 7 and cause the relay 8 to trigger. Once the voltage at the inverting input drops, due to a temperature decrease, below the voltage level at the non-inverting input, the transistor 7 will close and the relay 8 will turn off.

[0025] A metal device of any configuration is clamped in the terminal connection or arranged at a distance of up to one meter from the terminal connection, i.e. in direct proximity to the place of the potential overheating of electrical wiring, which allows one to quickly determine the occurrence of a critical situation. In the body of the metal device, there are temperature sensors—i.e. the thermistors 3, 4. The number of thermistors is determined by the number of terminal connections to be controlled. To provide the most accurate and fast heat transfer from the metal device to the temperature sensor, the latter is lubricated with a thermal grease (see FIG. 2a, FIG. 2b).

[0026] The most common types of metal devices are a pin-type device configured to be clamped in a terminal connection (see FIG. 3a) and a device made as a terminal for a nut connection (see FIG. 3b). Additionally, as the metal device, one can use pin contacts of a mains plug and control temperature in a socket which receives the mains plug with any triggering circuit implementing the method according to the invention (not shown).

[0027] FIG. 4 shows a non-inverting comparator connection circuit that implements the method according to the invention. The non-inverting comparator connection circuit comprises a comparator 12, both inputs of which are connected to voltage dividers. The first voltage divider connected to the non-inverting input (“+”) of the comparator 12 consists of a constant resistor 13 and thermistors 14, 15 which are temperature sensors and may be connected both in series and in parallel. The second voltage divider connected to the inverting input (“−”) of the comparator 12 consists of constant resistors 16, 17. The comparator 12 has an output connected to a transistor 18 and a relay 19. A LED 20 having a current limiter implemented as a resistor 21 may serve as a terminal connection overheating indicator. An audible alarm 22 may also be additionally used to alert users of terminal connection overheating.

[0028] In this case, the voltage at the non-inverting input of the comparator 12 is lower at the room temperature and rises when the thermistors 14, 15 are heated. The switching threshold (switching threshold temperature) is defined by the inverting input of the comparator 12, which is provided with a reference (constant) voltage set by the voltage divider based on the constant resistors 16, 17.

[0029] If the voltage at the non-inverting input is greater than at the inverting input, the output voltage from the comparator 12 will open the transistor 18 and cause the relay 19 to trigger. Once the voltage at the non-inverting input drops, due to a temperature decrease, below the voltage level at the inverting input, the transistor 18 will close and the relay 19 will turn off.

[0030] FIG. 5 shows a circuit having a controlled Zener diode, which implements the method according to the invention. The circuit comprises a controlled Zener diode 23 having a control input 24 connected to a voltage divider consisting of a constant resistor 25 and a thermistor 26 having a negative temperature coefficient of resistance. The Zener diode has a cathode connected to a relay coil 27, a shunt diode 28, and a LED 29 having a current limiter implemented as a resistor 30. The LED may serve as a terminal connection overheating indicator.

[0031] The controlled Zener diode 23 is a key element of this temperature control device for the terminal connection. Once the voltage at the control electrode 24 reaches a threshold operation level, the controlled Zener diode 23 opens, and current flows from the positive terminal of the power supply through the relay coil 27, the cathode-anode of the controlled Zener diode 23 and further—to the negative terminal of the power supply. The voltage at the control electrode 24 is set by the voltage divider consisting of the constant resistor 25 and the thermistor 26 with the negative temperature coefficient of resistance. When the temperature of the terminal connection rises, the resistance of the resistor 25 remains constant, while the resistance of the thermistor 26 decreases.

[0032] Accordingly, as the resistance of the thermistor 26 drops, the voltage at the control electrode 24 of the controlled Zener diode 23 rises. Once this voltage becomes greater than the threshold operation level, the controlled Zener diode 23 opens, and the relay coil 27 is triggered, thereby disconnecting a load (consumer). After a while, the temperature of the terminal connection decreases. At the same time, the temperature of the thermistor 26 begins to drop, thereby leading to an increase in its resistance. Once the ratio of the resistance set by the constant resistor 25 to the resistance of the thermistor 26 which increases as a result of cooling ensures an appropriate voltage balance at which the voltage at the control electrode 24 of the controlled Zener diode 23 becomes less than the threshold operation level, the controlled Zener diode 23 will close again and turn off the relay coil 27. The cycle will repeat itself.

[0033] In this case, the switch-on and switch-off temperatures of the temperature control device for the terminal connection are defined by the constant resistor 25. Since the thermistor 26 has a certain thermal inertia due to its mass and protective coating, its switch-on temperature will slightly differ from its switch-off temperature. The diode 28 shunts the EMF arising in the coil-relay 27 and caused by the abrupt closing of the controlled Zener diode 23 and current interruption. The voltage appearing at the terminals of the relay coil 27 at this moment may exceed the supply voltage several times and make the controlled Zener diode 23 inoperative. The LED 29 with the limiting resistor 30 is configured to monitor the state of the relay coil 27 (on/off).

[0034] The invention makes it possible to prevent the overheating of electrical wiring and to avoid fires which spread from the clamps of switching equipment and are caused by the ignition of electrical wiring in power supply systems for providing residential, administrative and industrial facilities with voltage up to 0.4 kV.