RU1772858C - Overload relay - Google Patents

Abstract

Usage: the field of electrical engineering, namely, the relay protection technique of electric networks, is intended to protect electric networks, including contact networks of electric vehicles, from overload currents. SUMMARY OF THE INVENTION: An overload relay comprises a current sensor. a first adder, a first variable coefficient unit, a voltage to frequency converter, and a decoder connected to its output via a pulse counter. New and relays are the use of wind speed and ambient temperature sensors, a stable voltage source, second, third and fourth adders, a quadrature, a multiplier, a divider, a functional voltage converter, and seven variable coefficient blocks. When the climatic conditions change, the response time of the relay automatically changes, in which it is possible to independently adjust the value of the temperature long-term permissible for the forbidden line, the resistance of the wires and their temperature coefficient, the unit surface area of the conductor, and the approximating dependence of the heat transfer coefficient. 2 ill.

Description

The invention relates to the field of electrical engineering, in particular to the relay protection technique of electric networks, and is intended to protect electric networks, including contact networks of electric vehicles, from currents of prolonged overload.

With short circuits arising outside the protected network section, or with prolonged overloads, when the current in the line significantly exceeds the nominal (long-term acceptable) value, excessive heating of the wires occurs. Heating above the permissible temperature, if it continues for a sufficiently long time, leads to the loss of mechanical strength by the wires and their rupture, i.e. power outages. Overload relays are used to prevent such accidents - current relays with dependent time delay. In this case, overload relays (current relays with dependent time delay) based on counters and pulse generators are recognized as the most accurate at present.

Known overload relays with dependent time delay, made on the basis of counters and pulse generators, also containing an input unit (current sensor), an output organ, logic elements, a functional converter. Their common drawback is the inaccurate determination of the time delay during overload due to the neglect of actual cooling conditions.

h j ju 00

ate

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wires of the protected network, as well as the inability to independently adjust all parameters of the relay, with regard to the characteristics of each specific protected line (such parameters as resistance, cross-section, wire material, cooling conditions) are meant.

The closest in technical essence to the claimed device is the overload relay selected as a prototype (3). It contains a current sensor (input block), a first adder, a first variable coefficient block (scale converter), a voltage to frequency converter and a pulse counter and a decoder (output block) connected to it. A disadvantage of the known device is the inaccurate determination of the time delay from - due to the fact that the actual cooling conditions of the wires of the protected network are not taken into account and there is no independent adjustment of all parameters reflecting the features of the protected line and affecting the indicated time delay.

The time-current characteristic of the prototype is determined by the expression

T-A / O-B) (1)

where g is the response time (time delay);

A is a constant coefficient;

B - long-term permissible; the current value for this type of shielded wire, taken as a constant.

The characteristic in the indicated expression does not take into account the fact that B (long-term permissible current value) is not actually a constant value, but depends, in particular, on wind speed and ambient temperature. Calculations show that with a change in B, of the aforementioned factors, the value of A also changes. The law of change of A from B is rather complicated and it is rather difficult to take it into account by a circuit (automatically).

The proposed device uses the time current characteristic, defined (2)

expression

t A / (12-V), where 1d is the long-term permissible current value for the data of the structural design of the network and climatic conditions.

When B changes in expression (2), the value of A remains almost constant (for electric networks), therefore, taking climatic conditions into account in (2) is easier than in (1).

The aim of the invention is to improve the accuracy of operation by taking into account climatic conditions and specific parameters

protected line, affecting the conditions of heating and cooling of wires,

The goal is achieved in that in a known device containing a sensor

5 current, the first adder, the first variable coefficient unit, a voltage to frequency converter and a decoder connected to its output through a pulse counter, additionally included 10 wind speed and ambient temperature sensors, a stable voltage source, a second, third, fourth adder, a quadrator, a multiplier, a divider, a functional voltage converter 15, second, third, fourth, fifth, sixth, seventh and eighth blocks of variable coefficient, and the output of the current sensor is connected via kva drator to the first input of the first adder, the output of which through the first block of a variable coefficient is connected to the input of the voltage to frequency converter, a stable voltage source is connected to the inputs of the second, third and fourth blocks

25 of a variable coefficient, the wind speed sensor is connected to the first input of the second adder through a series-connected functional converter and the fifth variable coefficient block, the second input of which is connected to the output of the second variable coefficient block, and the output is connected to the first input of the multiplier through the sixth variable coefficient block, sensor

35 temperature is connected to the first input of the third adder, to the second input of which the output of the third and the input of the seventh variable coefficient block are connected, and its output through the eighth block of the forged coefficient is connected to the first input of the divider, to the second input of which the output of the fourth adder is connected, to the first and second the input of which is connected to the outputs of the fourth and seventh blocks of a variable coefficient, respectively, and the output of the divider is connected to the second input of the multiplier, the output of which is connected to rum input of the first adder.

50 Comparative analysis with the prototype shows that the claimed device is distinguished by the presence of new block sensors of wind speed and ambient temperature, a source of stable voltage,

55 three adders, a quadrator, a multiplier, a divider, a functional converter, seven variable coefficient blocks.

Constructive execution of all units is known, however, the proposed connection

between them, a new property is shown that is not available with known devices of a similar purpose. This property consists in a more accurate consideration of the determining climatic and structural features of the protected line, on which the time delay and the ability to configure relays for each of these signs independently of others depend. This ensures the achievement of the main goal - improving the accuracy of work.

Fig. 1 is a functional diagram of an inventive device; Figure 2 shows experimentally measured dependences of the heat transfer coefficient on wind speed for different types of wires.

The overload relay (figure 1) contains the following blocks: 1 - wind speed sensor; 2 - functional voltage converter; 3, 5, 6, 9, 13. 14, 15, 20 - blocks of variable coefficients; 4, 8, 16, 19 - adders; 7-ambient temperature sensor; 10 - divider, 11 - multiplier; 12 is a source of stable voltage; 17 - current sensor; 18 - a quadrator; 21 is a voltage to frequency converter. Its peculiarity lies in the fact that the voltage is converted only one voltage polarity, for example, positive; 22 - pulse counter; 23 - decoder (output unit).

Elements 17,19,20,21,22,23 relate to the prototype and are known. The remaining elements are new.

. The device operates as follows.

A signal is generated at the output of the functional converter 2, where V is the wind speed; q is an exponent. A voltage is generated at the output of the variable coefficient block 3, where K3 is a constant adjustable coefficient. A voltage is generated at the output of block 5. At the output of adder 4, the voltage is U Ks + KsV 1, and at the output of block 6 it is (K5 + K3Vq). The voltage UT toicp is supplied to one output of adder 8, where bcr is the ambient temperature, and voltage is applied to its second input. The voltage at the output of adder 8 is U8 Ki3-toicp. and at the output of block 9 (Ki3-toicp). At the first input of adder 16, voltage Ki4 is supplied, and voltage is applied to its second input. At the output of adder 16, the voltage is Ui6 Kis + Ki3 Ki4, and at the output of the divider 10, the voltage is (Ki3-toicp} / (+ К ™ К1з).

The voltage at the output of multiplier 11 is respectively Un U6Uio K6 {K5j + K3Vq) K9 (Ki3-toKP) / (Ki5 + Ki3Ki4). This voltage is supplied to one of the inputs of the adder 19, the second input of which receives the voltage, where I is the current of the protected

lines. At the output of adder 19, the voltage is Ui9 Uie-Uii, and at the output of block 20, the voltage is U20 K2oUi9 K2o (Ui8-Uii}. At the output of the voltage-to-frequency converter 21, the frequency is f KfU20 KfK2o (Ui8-Uii),

where Kf is constant or

| kgk20 to K5 + IU; s-p). (h)

M5 t K.13M4

When the current of the protected network changes, the temperature of the surrounding network of the wind speed, the voltage at the output of block 20 changes according to the law U20 K2o02-Uii) and can be positive or negative.

The voltage Un corresponds to the square of the long-term permissible current d. If overload starts in the protected line, i.e. , then the voltage Lteo becomes positive and the converter 21 it

is converted to the frequency of the pulses that fill the counter 22. The relay is activated when there are N pulses in the drive counter. This state is determined by the decoder 23. which in this case gives a signal to disconnect the line.

The time delay (response time G.s. 3) is determined by the accumulation time in the pulse counter 22, i.e.

sz:

N

m / g | 2 KeCKs + KaU KBCKia-toup), N / UK, 5 + Yi3Ki4

(4)

The process of heating a conductor by the current passing through it is described by the expression 6M 0 6 Be (). where 0 is the conductor overheating, i.e. excess of its temperature over ambient temperature;

in - initial overheating at t 0:

& f - steady-state temperature rise at t oo; T is constant heating time;

g - current time.

When m «we have 8 wu, and it is calculated by the formula (ibid.)

„- I l2ro (1 + fft) ar

(5)

B-af

where I is the line current;

g-conductor resistance:

r0-resistance of the conductor at a temperature of 0 ° C;

/ is the temperature coefficient of resistance;

t is the temperature of the conductor;

a - heat transfer coefficient;

F is the surface area of the conductor.

Assuming that the long-term permissible temperature, etc. corresponds to the long-term permissible current 1D, we obtain

2 (tg - toxp) a F J r0 (1 + / h)

(6)

The heat transfer coefficient a varies insignificantly in the range of operating temperatures of the long-term mode and its value can be approximately calculated as a function of temperature independent. The experimental dependence of this coefficient on the wind for different passages is shown in Fig. 2. It is well approximated by the expression

a a + bVq

(7)

So, for example, for the MF100 wire, we have 5, 5, 6, and the design points for these conditions are shown in Fig. 2.

Substituting (7) into (6). we get

Ofl-toupKa + bVQF r0 (1 + / 3t)

(8)

Denote; / Kg; t- Ki5; / 3 Ki4. In this case, expression (8) becomes identical to the voltage Un, whence it follows. We denote A N / KfK20, in this case, instead of (4), we obtain expression (2) defining the characteristic of the relay. This characteristic automatically takes into account the climatic conditions of the cooling of the wire and can be adjusted to the factors determining these conditions independently of each other. Such factors are the long-term permissible temperature rd, the resistance of the conductor r0 and v its temperature coefficient D, the surface area of the conductor F, the parameters a, b, and q of the heat transfer coefficient.

The positive effect is to increase the accuracy of the relay by taking into account the climatic and cooling conditions of a particular wire, for each of which the relay is configured independently of other factors. More accurate operation compared to the prototype provides advantages such as more reliable overload protection and increased stability of power supply to consumers.

Claims (1)

The claims An overload relay comprising a current sensor, a first adder, a first variable coefficient unit, a voltage to frequency converter, and connected to its output through the counter of the number of pulses is a decoder, characterized in that, in order to improve the accuracy of operation by taking into account the climatic conditions and specific parameters of the protected line, affecting under the conditions of heating and cooling wires, it additionally includes sensors for wind speed and ambient temperature, a source of stable voltage, the second, third and fourth adders, a quadrator, a multiplier, a divider, a functional voltage converter, from the second to eighth variable coefficient blocks, while the output of the current sensor is connected via a quadrator to the first input of the first adder, the output of which is connected through the first variable coefficient block to the input of the voltage to frequency converter , the voltage source is connected to the inputs of the second, third and fourth variable coefficient blocks, the wind speed sensor is connected to the first input of the second adder through a series-connected functional converter and the fifth variable coefficient block, to the second input of which the output of the second variable coefficient block is connected, and its output is connected to the first input multiplier through the sixth a variable coefficient unit, a temperature sensor is connected to the first input of the third adder, to the second input of which the output of the third and the input of the seventh variable coefficient unit is connected, and its output through the eighth variable coefficient unit is connected to the first input of the divider, to the second input of which the output of the fourth adder is connected, to the first and second inputs of which the outputs of the fourth and seventh blocks of a variable coefficient are connected, and the output of the divider is connected to the second input of the multiplier, whose output is connected to the second input of the first adder. g j -SY i-ch 5 by ipn ynShda m by cC ; FIG 10