SU877686A1

SU877686A1 - Device for protecting ac network with insulated neutral wire from single-phase earthing

Info

Publication number: SU877686A1
Application number: SU802885112A
Authority: SU
Inventors: Василий Михайлович Кутин; Леонид Петрович Любонько
Original assignee: Винницкий политехнический институт
Priority date: 1980-02-19
Filing date: 1980-02-19
Publication date: 1981-10-30

Description

объединены и подсоединены через блок питани и рези:гтор к земле; вход реагирующего органа включен параллелно резистору 2.combined and connected via a power supply and power supply unit: ground to ground; the input of the reacting body is connected in parallel to the resistor 2.

Устройство реагирует как на симметричное снижение сопротивлени изол ции трех фаз сети относительно земли, так и на однофазную утечку через большое сопротивление.The device responds both to a symmetrical reduction of the insulation resistance of the three phases of the network relative to the ground, and to a single-phase leakage through a large resistance.

Однако оно ненадежное в работе из-за частого повреждени трансформатора напр жени при перемежающихс дуговых замыкани х. Кроме этого, имеет перезащиту при возникновении Утечки ,в области больших значений сопротивлени изол ции, поскольку устройство срабатывает при одном и том же значении сопротивлени утечки независимо от значени сопротивлени изол ции. Известно, что при одном и том же значении сопрот ивлени утечки ток через нее возрастает по мере уменьшени активного сопротивлени изол ции сети относительно земли. Поскольку уставка срабатывани реле выбираетс исход из наиболее неблагопри тных условий - минимального допустимого значени сопротивлени изол ции , то в области больших значений активного сопротивлени изол ции имеет место перезащита.However, it is unreliable in operation due to frequent damage to the voltage transformer during intermittent arc closures. In addition, it has re-protection when a leak occurs, in the region of large insulation resistance values, since the device operates with the same leakage resistance value regardless of the insulation resistance value. It is known that with the same leakage resistance, the current through it increases as the active resistance of the insulation of the network relative to the ground decreases. Since the relay setpoint is selected based on the most unfavorable conditions, the minimum allowable value of the insulation resistance, in the region of large values of the active resistance of insulation, there is a re-protection.

Цель изобретени - повышение надежности и точности устройства.The purpose of the invention is to increase the reliability and accuracy of the device.

Поставленна цель достигаетс тем, что в устройство дл защиты сети переменного тока с изолированной нейтралью от однофазного заМыкани на землю, содержащее трехфазный измерительный трансформатор напр жени , первична обмотка которого соединена в звезду и заземлена через разр дник, источник питани ,первый выход которого подключен к питающе му входу исполнительного реле, разделительный конденсатор, омметр и диод, введены повышанхдий трансформатор напр жени , .сумматор напр жени - и однофазные измерительные трансформаторы напр жени , включенные между фазами защищаемой сети и первичной обмоткой указанного трехфазного измерительного трансформатора напр жени , причем, последовательно соединенные первична обмотка повышающего трансформатора напр жени и разделительный конденсатор шунтируют разр дник, сумматор напр жени первьом входом через диод подключен ко вторичной обмотке повышающего трансформатора напр жени , вторым входом - через омметр и второй выход источника питани подключен к разделительному конденсатору, а выходом к измерительному входу исполнительного реле.The goal is achieved by the fact that a device for protection of an AC mains with an insulated neutral from single-phase ground to ground contains a three-phase measuring voltage transformer, the primary winding of which is connected in a star and grounded through the arrester, the power source, the first output of which is connected to the mains To the input of the executive relay, an isolating capacitor, an ohmmeter and a diode, a voltage transformer has been introduced upstream, a voltage transformer, and single-phase instrument transformers not connected between the phases of the protected network and the primary winding of the specified three-phase measuring voltage transformer, moreover, the primary winding of the step-up voltage transformer and the isolation capacitor shunts the voltage, the voltage adder first through the diode is connected to the secondary winding of the voltage step transformer, the second input is through an ohmmeter and the second output of the power source is connected to the separation capacitor, and the output to the measuring input is used additional relay.

Кроме того, параллельно контрольному входу исполнительного реле включена кнопка возврата, а параллельноIn addition, the return button is connected in parallel with the control input of the executive relay, and in parallel

разр днику - последовательно соединенные кнопка проверки и резистор.Discharge - in series connected test button and resistor.

Принципиальна схема устройства изображена на чертеже.A schematic diagram of the device shown in the drawing.

Устройство состоит из трехфазного измерительного трансформатора 1 напр жени , кажда фаза первичной обмотки которого подсоединена через первичную обмотку однофазных измерительных трансформаторов 2 напр жени к контролируемой сети 3,а нейтральна точгка - чеоез первичную обмотку повышающего трансформатора 4 и разделительный конденсатор 5 к земле; сумматора 6 напр жений, состо щего из двух потенциометров 7 и 8, один из которых подключен через диод 9 ко вторичной обмотке повышающего трансформатора 4 а другой - между положительным полюсом источника 10 питани и омметром 11 исполнительного реле 12, вход которого подключен к выходу сумматора 6 напр жений; выходного контакта 13 исполнительного рел 12, разр дника 14, кнопки проверки исполнительного реле 15, подключенной между нейтральной точкой первичной обмотки трехфазного измерительного трансформатора 1 напр жени и землей через резистор 16, кнопки 17 .возвра та исполнительного реле 12.The device consists of a three-phase measuring transformer 1 voltage, each phase of the primary winding of which is connected through the primary winding of single-phase measuring transformers 2 voltage to the monitored network 3, and the neutral point is the primary winding of the step-up transformer 4 and separation capacitor 5 to the ground; a voltage adder 6 consisting of two potentiometers 7 and 8, one of which is connected via diode 9 to the secondary winding of the step-up transformer 4 and the other between the positive pole of the power supply 10 and ohmmeter 11 of the executive relay 12, whose input is connected to the output of the adder 6 stress; the output pin 13 of the executive relay 12, of the arrester 14, of the check button of the executive relay 15 connected between the neutral point of the primary winding of the three-phase voltage measuring transformer 1 and the ground through the resistor 16, the buttons 17 of the return of the executive relay 12.

Устройство работает следующим образом.The device works as follows.

Дл непрерывного контрол изол ции и защиты от утечек устройство подключают между фазами обесточенной сети 3 и землей и подают переменное напр жение на вход источника 10 питани . При исправном состо нии исполнительного реле 12 оно срабатывает от броска тока зар да разделительного конденсатора 5 и своим контактом 13 замыкает цепь сигнализации . После проверки исправности исполнительного реле 12 путем нажати кнопки 17 возвращают его в исходное положение и подают напр жейие на контролируемую сеть 3.For continuous monitoring of the insulation and leakage protection, the device is connected between the phases of the de-energized network 3 and the ground and is supplied with alternating voltage to the input of the power supply 10. When the executive relay 12 is in good condition, it is triggered by the inrush of the charging current of the coupling capacitor 5 and by its contact 13 closes the alarm circuit. After checking the operability of the executive relay 12 by pressing the button 17, it returns to its original position and supplies voltage to the controlled network 3.

Если уровень сопротивлени изол ции выше уставки срабатывани исполнительного реле 12, то оно не возбуждаетс и по омметру 11 можно определить суммарное сопротивление изол ции всех трех фаз сети относительно земли.If the insulation resistance level is higher than the pickup value of the executive relay 12, it is not energized and the total insulation resistance of all three phases of the network relative to ground can be determined from ohmmeter 11.

Claims

In the event of a leakage, the capacitor 5 begins to discharge in a circuit: the primary windings of the step-up transformer 4, the instrument transformers 1 and 2, the leakage resistance, ground. In this case, a voltage arises on potentiometer 7, the maximum value of which will be inversely proportional to the leakage resistance and does not depend on the insulation resistance. On the other hand, at the initial moment of leakage, the current through potentiometer 8, due to the inertia of the system, does not change and will be inversely proportional to the active resistance of the insulation of all three phases of the network relative to the ground. Thus, the input of the executive relay 12 from potentiometers 7 and 8 is removed the sum of the voltages, one of which is inversely proportional to the leakage resistance only, and the other to the insulation resistance of all three phases of the network relative to ground. Relay 1 then it is activated and its output contacts 13 closes the alarm circuit. Such a method of connecting the actuating relay 12 makes it possible to vary the ratio of the voltage levels with the help of resistance potentiometers 7 and 8 and, thereby, to obtain the required protective characteristic, i.e. eliminate re-protection in the area of high insulation resistance values. In the event of the occurrence of a long intermittent earth fault through an arc, the damage to the three-dimensional measuring transformer will not occur. Since the voltage between the phases of the network and the ground will be. distributed between the primary windings of the single-phase 2 and three-phase transformer 1, and therefore the magnetic system of the three-phase transformer 1 will not be saturated. On the other hand, the active resistance to magnetizing current surges doubles. This makes it possible to increase the reliability of the device in comparison with the known RADAR 14 works automatically when the voltage rises in transient conditions and reduces it to acceptable values. Verification of the device components during operation is carried out by pressing the test button 15, while artificially creating a leak. The device is returned to its original position when the return button 17 is pressed ... The use of this device reduces the amount of damage to the three-phase voltage transformers during the long existence of an intermittent arc circuit by eliminating over-excitation of the magnetic system and. reduces the number of unjustified device triggers when a leak occurs in the region of high insulation resistance values by connecting reacting organ i: a sum of signals, one of which is proportional to the resistance of the leak that has occurred, and the other to the resistance of the insulation and choosing the level ratio of these signals. Claim 1. A device for protecting an AC mains with an insulated neutral from a single-phase earth fault, containing a three-phase voltage measuring transformer, the primary winding of which is connected in a star and grounded through a glitter, the power source, the first output of which is connected to the executive input A relay, a coupling capacitor, an ohmmeter and a diode, characterized in that, in order to increase reliability and accuracy, a step-up voltage transformer, a voltage and single-phase combiner are introduced voltage measuring transformers connected between the phases of the protected network and the primary winding of the specified three-phase voltage measuring transformer, with the primary winding of the step-up voltage transformer and the isolating capacitor shunting the voltage across the diode connected to the secondary winding of the step-up circuit voltage transformer, the second input is through an ohmmeter and the second output of the power source is connected to the separator condensate y, and the output - to the measuring input of the output relay. 2. The device according to claim 1, about the fact that in parallel with the control input of the executive relay the return button is turned on, and in parallel the discharge button is connected in series with the test button and the resistor. Sources of information taken into account in the examination 1. S. Usov. Electric part of power plants. L., Energie, 1977, e. 418.

2. Authors certificate of the USSR, cl. H 02 H 3/16, I960. + Jl C 220