RU2016453C1 - Equipment for protection of electric installations of three-phase network in case of fault of neutral wire - Google Patents

Abstract

FIELD: electrical engineering. SUBSTANCE: equipment is meant for three-phase electric power supply systems. Operational properties of equipment are improved by way of automatic disconnection of electric installation with fault of neutral wire thanks to connection of two relays 1, 2 with make and break contacts 3 and 4 and command button 5 with make contacts placed into electric circuit between common point of connection of relay contacts and common point of connection of relay windings. EFFECT: improved efficiency of protection. 1 dwg

Description

 The invention relates to electrical automation and can be used in three-phase electric power supply networks with a zero wire to protect electrical installations, for example electric motors of domestic refrigeration units, in case of damage to the neutral wire.

 A device for protecting electrical installations from abnormal values of the parameters of the electrical circuit, containing a series-connected valve, a current transformer, a two-input measuring unit, a forming unit, a single vibrator and an actuator, the output of which is connected to the input of the operation signaling device and to the control input of the valve [1]. The second input of the measuring unit is connected via a voltage transformer to the bus of a controlled electrical circuit. Using the AND, NOT elements and the delay line, the operational state of the measurement and formation units is monitored, and the automatic restart of the device is also prohibited. A disadvantage of the known device is the complexity of its design and operation due to the presence of a large number of functional blocks in its composition and the need to control the on state of several signaling devices at once.

 The closest technical solution is a device for protecting three-phase electrical installations from abnormal operating conditions, containing a three-phase load, a three-phase current transformer, three rectifiers, the outputs of which are connected to the corresponding three relays with a working and brake winding each, the breaking contacts of which are included one in each corresponding phase [2]. When abnormal operation occurs in any of the three phases of electrical installations, the corresponding relay is activated, the opening contacts of which disconnect this phase.

 The disadvantage of the prototype is low performance, because executive relays are triggered when only extremely extreme abnormal operating modes of electrical installations that are associated with a short circuit or an open circuit in any of the phases appear. Intermediate variations in the supply voltage of a three-phase network in a range not exceeding the extreme limit values can occur for an arbitrarily long time during which the electrical installation can fail. For example, if the neutral wire is damaged for a long time, the load of the three-phase network can be balanced through the common connection bus of this load independently. In this case, the values of phase voltages change randomly, disabling one or the other electrical installation of the corresponding phase load, which may be household refrigeration units of the compressor type. The electric motor of such a household refrigerator with a low voltage does not start reliably with its start relay, causing a dangerous overheating of its working windings, and with an increased phase voltage, either the starting relay or the starting winding of the compressor motor of the domestic refrigerator is damaged.

 The aim of the invention is to improve the operational properties of the device by automatically shutting down electrical installations when the supply phase voltage changes in excess of the specified tolerance values with a working zero wire.

+ U_o + U_o, а уровень cрабатывания второго реле имеет значение U U

-U_o - U_o, размыкающие контакты второго реле имеют задержку на размыкание, а замыкающие контакты первого реле имеют задержку на размыкание, где U - фазное напряжение, а U_o - допустимое отклонение напряжения от номинального для электроустановок. В результате сопоставительного анализа известных и предложенных признаков можно сделать вывод, что предложенный объект изобретения обладает существенной новизной, за счет которой достигается новый положительный эффект, а именно: улучшаются эксплуатационные свойства устройства для защиты электроустановок трехфазной сети при повреждении нулевого провода.The essence of the invention lies in the fact that, in addition to the well-known and common nodes and blocks, namely: the first and second relays of each phase, the common connection bus of the three-phase load and the phase line bus, the first terminals of the windings of the first and second relays have a common connection point, proposed the device comprises a command button, the make contacts of which are included in the electric circuit between the common point of connection of the second terminals of the windings of the first and second relays and the common point of connection of the make contacts of the second relay and make contacts o the first relay, the extreme contacts of which are connected respectively to the phase line bus and to the common connection point of the second terminals of the relay windings connected to one terminal of the phase load, the other terminal of which is connected to the common connection point of the first terminals of the relay windings and to the common connection bus of the three-phase load, moreover, the level of operation of the first relay is

+ U _o + U _o , and the level of operation of the second relay is UU

-U _o - U _o , the opening contacts of the second relay have an opening delay, and the closing contacts of the first relay have an opening delay, where U is the phase voltage and U _o is the permissible voltage deviation from the nominal voltage for electrical installations. As a result of a comparative analysis of the known and proposed features, it can be concluded that the proposed object of the invention has a significant novelty, due to which a new positive effect is achieved, namely: the operational properties of the device for protecting electrical installations of a three-phase network are improved if the neutral wire is damaged.

^{+ U}o + U_o и U U

-U_o - U_o соответственно; 3 - командная кнопка с замыкающими контактами; 6 - нагрузка одной из трех фаз, например электроустановка в виде бытового холодильника компрессорного типа; 7 и 8 - общая и фазная шины трехфазной системы энергоснабжения с нулевым проводом соответственно.The drawing shows an electrical diagram of the proposed device for one of the three phase loads, where it is indicated: 1 and 2 - threshold relays with closing 3 and opening 4 contacts, respectively, and trip levels equal to

^{+ U} o + U _o and UU

-U _o - U _o respectively; 3 - command button with make contacts; 6 - load of one of the three phases, for example, an electrical installation in the form of a compressor-type domestic refrigerator; 7 and 8 are the common and phase buses of a three-phase power supply system with a zero wire, respectively.

 The drawing shows that in the statistics in the initial state, the common bus 7 is connected to one winding of the relay 1 and 2 and to one output of the load 6 directly, and the phase bus 8 is connected to the other output of the load 6 and other terminals of the relay windings 1 and 2 through series-connected interconnecting and closing contacts of relays 2 and 1, respectively. The common point of connection of the relay contacts is connected via the make contacts of the command button 5 to the common point of connection of the other terminals of the relay windings 1 and 2. The making contact 3 has a delay for opening, and the making contact 4 has a delay for opening.

 The proposed device operates as follows.

When the nominal value of the phase voltage U is within the tolerance of ± U _o, after pressing the command button 5, relay 1 is activated with a low level of tripping along a circuit composed of elements: 8-4-5-1-7. Relay 1 is self-locking using its NO contacts 3 in a circuit: 8-4-3-1-7 and connects the phase 8 bus to one terminal of electrical installation 6 through contacts 4 and 3, to the other terminal of which the common bus 7 is directly connected.

-U_o - U_o срабатывает реле 2, которое, спустя время задержки, своим размыкающим контактом 4 отключит электроустановку 6 от поражающего действия фазного напряжения. Время задержки на размыкание контактов 4 предназначено для исключения ложных срабатываний реле 2 при появлении кратковременных безопасных пиков и всплесков фазного напряжения, которые обычно выравнивает нулевой провод.When the neutral wire is broken, the phase voltage at the terminals of the electrical installation 6 of any of the three phases changes randomly, which leads to the breakdown of these electrical installations 6. The proposed device protects the electrical installation 6 from switching on the three-phase network with its neutral wire disconnected. For example, when the phase voltage increases above the threshold UU

-U _o - U _o relay 2 is activated, which, after a delay time, with its NC contact 4 disconnects the electrical installation 6 from the damaging effect of the phase voltage. The delay time for opening the contacts 4 is designed to eliminate false alarms of relay 2 when short-term safe peaks and surges of phase voltage appear, which are usually balanced by the neutral wire.

+ U_o + U_o реле 1 отключается и контакты 3, спустя время задержки на размыкание, отключают нагрузку 6 от нежелательного воздействия пониженного фазного напряжения и разблокируют реле 1. Время задержки на размыкание контактов 3 реле 1 предназначено для исключения ложного отключения электроустановки 6 при случайных кратковременных пропаданиях фазного напряжения, которые обычно выравнивал нулевой провод.With a decrease in phase voltage below the threshold

+ U _o + U _o relay 1 is disconnected and contacts 3, after a time delay for opening, disconnect load 6 from the undesirable effects of reduced phase voltage and unlock relay 1. The time delay for opening contacts 3 of relay 1 is designed to prevent false shutdown of electrical installation 6 in case of accidental short-term loss of phase voltage, which usually neutralized the neutral wire.

 The device can be turned on again only when the command button 5 is pressed again and the damage to the neutral wire is repaired.

 The positive effect of the use of the invention is that simple technical means improve the operational properties of the protection device of expensive electrical installations of a three-phase power supply network in case of damage to the neutral wire.

Claims (1)

DEVICE FOR PROTECTING ELECTRICAL INSTALLATIONS OF A THREE-PHASE NETWORK DURING ZERO WIRING DAMAGE, containing the first and second relays of each phase, a common three-phase load connection bus in the form of electrical installations and a phase line bus, the first terminals of the relay windings having a common connection point, characterized in that it contains a command button the closing contacts of which are included in the electric circuit between the common point of connection of the second terminals of the relay windings and the common point of connecting the opening contacts of the second relay and the making contacts the first relay, the extreme contacts of which are connected respectively to the phase line bus and to the common connection point of the second terminals of the relay windings connected to one terminal of the phase load, the other terminal of which is connected to the common connection point of the first terminals of the relay windings and to the common connection bus of the three-phase load, the threshold of the first relay is U /

+ U _o , and the threshold of the second relay is U /

- U _o , the contacts of the first and second relays have an opening delay, where U is the phase voltage, and U _o is the permissible voltage deviation from the nominal voltage for the electrical installation.