WO2024035250A1

WO2024035250A1 - Neutral tear protection device in low-voltage electrical installations

Info

Publication number: WO2024035250A1
Application number: PCT/MK2023/000003
Authority: WO
Inventors: Jovica VULETIK
Original assignee: Vuletik Jovica
Priority date: 2022-08-08
Filing date: 2023-07-17
Publication date: 2024-02-15

Abstract

Neutral tear protection device for equipment protection, supplied from a single or three-phase AC low-voltage grid/installation when a neutral conductor tear, disconnection and/or discontinuity occurs, intended for installation at the point of common coupling or at the customer's distribution board. The device utilizes a sensing circuit that registers measurable parameters specific to an event of neutral conductor tear/discontinuity and is connected in series with an electromagnetic trigger and disconnects the supply and/or the protected phase via mechanically coupled power switch. The same functionality can be achieved with higher sensitivity by using optocoupling circuits with integrated driver. The device protects electrical equipment permanently or occasionally connected to the power supply by means of supply disconnection /interruption when a neutral conductor tear/discontinuity occurs.

Description

NEUTRAL TEAR PROTECTION DEVICE IN LOW-VOLTAGE ELECTRICAL

INSTALLATIONS

Field of search

The current invention is from the field of electricity and refers to the class H01 H — electric switches; relays; selectors; emergency protective devices and subclass H01R. - electrically- conductive connections' structural associations of a plurality of mutually-insulated electrical connecting elements; coupling devices; current collectors.

Technical scope of the invention

The present intention solves the problem of efficient protection and disconnection of electrical devices and loads, supplied by a single or three/multi-phase low-voltage electrical installation in case of deliberate and/or arbitrary neutral conductor tear and/or its disconnection. The present im ention offers protection of electrical devices and loads supplied in pari or completely behind the installations point of common coupling (PCC).

Background of the invention fearing of the neutral conductor is one of the most insidious and tmaddressed faults that can occur in low-voltage electrical installations. Its occurrence is totally random and it’s usually more present in old electrical installations, overhead low-voltage lines, and overhead stay-wire cable bundles, though not excluded in the cable installations as well. Reasons for its occurrence vary from natural causes (wind, rain, ice, snow, trees etc.), old/aged electrical installation, to human error due to false inters ention in the installation and/or stealing of conductors with large cross sections.

Current state of the art

Nowadays there are plenty of commercially available protection devices for low-voltage electrical installations, i.e., circuit breakers, residual current protection device, arc-fault detection devices and surge protection devices. With exception of the surge protective device, all other devices operate on the principle of interrupting the supply due to a fault occurring behind them (as seen towards the supply), hence protecting the installation, its users and equipment Only the surge protecting device operates on the principle of interrupting the supply due to a fault that occurs in front of its installation location. The neutral tear protection device uses the same principle of operation as the surge protecti ve device. Its primary function is equipment protection supplied behind its installation location. To the inventors best of knowledge, the current market does not offer a commercialls available neutral tear protection device, CN 215641782 utilizes current clamps, resistors, and an additional w ire for detection of the neutral line disconnection, DE 10 2014 1 18 suggests a neutral eondaetor disconnection by means of mechanical coupling to a phase conductor disconnection dev ice EP 0069655 uses signal generators, multiwinding current transformers and operational amplifiers to detect a fault and interrupt the supply. EP 1383218 utilizes comparators, reference signals and simultaneous voltage measurement of the phase, neutral and earthing conductor to decide for potential fault and interrupt the supply. US 10288664 B2 discusses protection against protective earthing conductor in grounded and ungrounded systems. by means of measuring the conductor’s leakage capacitance.

The proposed approach utilizes the installation topology, and the load composition behind the device to cheek for potential neutral conductor tear, hence disconnecting the supply and protecting the equipment installed behind the device.

None of the technical solutions and practical realizations in the current state of the art derived for similar or identical purpose are known to the inventor of this specification.

Brief summary of the invention

Short description of Figures

For detailed illustration of the neutral tear/discontinuity problem and solution, the following figures with schematics apply along with an appropriate description. Figure 1 shows low-voltage electrical installation illustrating the nature and effects of neutral conductor tear/discontinuity . The sy mbols have the following meaning:

LV grid - low-voltage grid owned by the utility;

PCC - point of common coupling;

LV customer - low-voltage electrical installation owned by the customer supplied from the utility;

LD 1, LD2 ... - single phase low-voltage loads owned by the LV customer supplied from its low- voltage installation.

Figure 2 shows the block diagram (monolith/integrated solution) for single phase neutral tear protection device (NTPD-1 p), The symbols and markings have the following meaning: 2.1 - preset values sensing circuit;

2.2 - electromagnetic trigger for protection of phase L1;

2.3 - single-phase power contact switch. Preset value sensing circuit 2.1 is connected in scries with the electromagnetic trigger 2.2. that is mechanically coupled to the single-phase power contact switch 2.3 that disconnects the supply when a neutral conductor tear occurs.

Figure 3 shows the block diagram (monolith/integrated solution) for three phase neutral tear protection device (NTPD-3p). The symbols and markings have the following meaning:

3.1 - preset values sensing circuits, one for each phase, identical to 2.1 ;

3.2 - dedicated electromagnetic trigger for protection of each phase, identical to 2.2;

3.3 - three-phase power contact switch for simultaneous disconnection of all three phases. Preset values sensing circuits 3.1 (three in total, one for each phase, all identical) are connected in series with dedicated electromagnetic triggers 3.2 (also three in total, identical and one for each phase). All three electromagnetic triggers 3.2 are mechanically coupled to the three-phase power contact switch 3.3 that disconnects the supply in all three phases when a neutral conductor tear occurs. Figure 4 shows the block diagram (monolith/integrated solution) of single-phase neutral tear protection device with increased sensitivity (NTPDi-lp). The symbols and markings have the folIowing meaning:

4.1 - preset values sensing circuit, identical to 2.1 ;

4.2 - electromagnetic trigger for protection of phase L1 , identical to 2.2; 4.3 - single phase power contact switch, identical to 2.3;

4.5 - dual-channel optocoupler with integrated drive unit (HCPL 2730);

4.6 - dedicated power supply for the optocoupler unit;

Preset values sensing circuit 4.1 is connected in series with the optocoupler unit 4.5 inputs that are connected in antiparallel. Optocouplers output i.e., its drive unit is connected in series with the electromagnetic trigger 4.2. The latter connection of elements is supplied from the DC output of the dedicated power supply 4.6. Dedicated supply’s 4.6 AC input is connected to the other two phases not subject to protection (L2 and L3). The electromagnetic trigger 4.2 is mechanically coupled to the single-phase power contact switch 4.3 that disconnects the supply in the protected phase L1 when a neutral conductor tear occurs. Figure 5 shows the block diagram (monolith/integrated solution) for three phase neutral tear protection device with increased sensitivity (NTPDi-3p). The symbols and markings have the folIowing meaning:

5.1 - preset values sensing circuits, one for each phase, identical to 3.1;

5.2 - electromagnetic trigger, identical to 2.2; 5.3 - three-phase power contact switch for simultaneous disconnection of all three phases, identical to 3.3;

5.5 dual-channel optocoupler with Integrated drive unit (HCPL 2730). one for each phase, identical to 4.5; 5.7 - dedicated power supply for the optocoupling units, can be Identical to 4,6.

Preset values sensing circuits 5.1 (three in total, one for each phase, all identical) are connected in series with the optocoupling units 5.5 inputs (also three in total, identical and one for each phase) that are connected in antiparallel. Optocoupler outputs, i.e., drive units from all three optocouplers are connected in parallel and then in series with the electromagnetic trigger 5.2. The latter connection of elements is supplied from the DC output of the dedicated power supply

5.7. Dedicated supply’s AC input is connected to all three phases or if the power supply is identical to 4.6 to any two phases. The electromagnetic trigger 5.2 is mechanically coupled to the three-phase power contact switch 5.3 that disconnects the supply in all three phases when a neutral conductor tear occurs. Detailed description of the invention

Neutral conductor tear/discontinuity usually if not exclusively occurs on the grid side of the supply (LV grid), owned by the uti lity supplier. Figure 1 shows the nature and the eftects from this type of fault. If a neutral conductor tear/discontinuity happens for some reason, and there are no single-phase loads connected behind the point of common coupling (PCC), or at the customer side of the low-voltage installation (LV customer), nothing wifi happen. Also. nothing happens if a three-phase sy mmetrical load is connected at the customer side of the low- voltage installation.

The problem, i.e., fault occurs after the first load 1.D1 is connected. Since the neutral conductor N coming from the grid is disconnected, no current flows through LD1 and no voltage drop appears on its ends, meaning that the piece of neutral conductor behind the tear/discontinuity, N’ is going to be at the potential of L1. Now. if another load is connected across L1-N', again nothing will happen, but if a load LD2 is connected between L2-N'. then both the loads will be connected at potential L 1-L2, meaning line voltage.

Now, the current that will flow through the load’s series connection will be determined by the load with a lower power rating. At the same time, this load will be the one that will be exposed to a higher voltage compared to the other load (potential divider rule). Due to the randomness of the load composition, there is no way of knowing which load will be exposed io a voltage larger than its rated voltage. In a hot-case scenario. both the loads will have the same power rating. i.e., the line voltage will be div ided equally amongst their terminals. In a worse-case scenario, one of the loads will have a way higher power rating than the other, i.e., the line voltage will be divided so as its larger portion will drop across the load with the lower power rating, potentially the full line voltage when that load will be instantly destroyed.

One should hear in mind that no protection device currently available will trigger and disconnect the supply up until the very moment after the load’s destruction. After this moment, it is expected that a short circuit or some other type of fault will occur and some of the other protection dev ices will trigger and disconnect the supply, i.e., circuit breaker and/or residual current protection device. From this example, one can see the randomness and unpredictability of the load composition and its switching state, i.e., which load is in stand-by mode and/or fully operational and on which phase it is connected.

Neutral conductor tear/discontinuity if not treated properly, can cause serious and irreparable damage to loads that are usually connected to the supply most if not during their entire lifetime, i.e., refrigerators, consumer electronics, personal computers, air conditioners, water heaters etc.

Some of these loads can be somewhat if not extremely expensive and sensitive, and considering the nature of the fault and its potential risk of fire due to electrical hazard within those loads, the current invention offers a secondary protection from fire, additionally to its primary function i.e., disconnection of the supply in case of neutral conductor tear/discontinuity, Furthermore, since the damage occurs at the LV -customer side, the utility bears no responsibility for any compensation of damages even li the fault occurs at their side of the grid. In some oases, unclear grid codes and proprieiaiy issues regarding the grid maintenance, in some countries even stealing of neutral conductor copper bars from MV/LV transformer stations, make it difficult tor the utility to maintain a reliable supply grid, which is one of the main reasons for occurrence of this type of fault. Additionally, Insurance companies do not provide insurance policies for equipment damage originating from the supply grid. Also, equipment, manufacturers void the warranty of their sold equipment if any fault occurs from the supply grid. And finally, household’s low- voltage electrical installations are rarely if not never routine-tested. Now, if one takes all these factors into account, the randomness and unpredictabi lity of the fault and the potential risks for permanent equipment damage, fire and risk for life, the necessity for this type of protection device is more than clear.

Figure 2 shows a neutral tear protection device for protection of single-phase loads at the customer side (LV customer). Preset sensing circuit (2.1 ) detects a voltage above certain threshold that can occur between the protected phase and the discontinued piece of the neutral conductor N', and a current flow above certain threshold dictated from load/s connected to any or both of the other two phases.

The sensing circuit is comprised of commercially available electronic components connected in a way that is invention specific. These sensing circuit building components possess extremely non-linear characteristics and operation regions. They usually have two to three operation regions i.e., non-conducting region, transient region that is component specific, and conducting region. The component characteristics define the sensing circuit (2.1 ) voltage threshold that is 1 10% to 130% of the rated phase voltage. Current through the sensing circuit (2.1 ). depending on the voltage across it. ranges from few microamperes io few tens of milliamperes and is limited with an additional commercially available component. The sensing circuit (2.1 ) is self-regulated and sell-adjusted i.e., there’s no need for any adjustments for its connection. The sensing circuit (2.1) doesn’t measure any quantities, it just detects/registers their presence (abnormal voltages and currents native to the fault). .All these aspects are solved during the scusing circuit's design stage, or in other words, the sensing circuit building components determine the voltage and current threshold triggering values without any adjustment nor regulation.

The sensing circuit (2.1) triggers an electromagnetic trigger (2.2) specifically designed for (his purpose which then disconnects the supply of the protected phase L1 via a mechanical coupling with the power contact switch (2.3). The electromagnetic trigger (2.2) is designed so as to safely and reliably trigger while very small currents flow through it (from several hundreds of microamperes to several milliamperes). hence protecting the load/s (regardless of type, characteristics, performance, switching state and operation regime) connected to phase L1 and behind the device (NTPD-1p). Figure 3 shows a device realization that uses three preset sensing circuits (3.1 ). one for each phase. As in the single-phase realization from Figure 2, each of the sensing circuits detects a voltage above certain threshold in any of the appropriate phases and a current flow above certain threshold dictated from the load composition connected between any or all of the three phases. The sensing circuit (3.1 ) then triggers a dedicated electromagnetic trigger (3.2) depending on the operating conditions and load composition in all three phases. Ail three electromagnetic triggers (3.2) are mechanically coupled to a power contact switch (3.4) that disconnects the supply, hence protecting the entire load connected across all three phases and behind the device (NTPD-3p). All NTPD device realizations are monolithic (single-phase and three-phase), and all their building blocks mentioned within this application present, an integrated solution placed in a suitable bousing identical to that of existing protecting devices.

All realizations within this application account for compatible and standards approved connection to conductors and/or bars i.e., DIN-rail mounting or '"clip-on” technology of connection without any other Jittering specifics.

Figure 4 shows an NTPD realization for single -phase protection with increased sensitivity. Preset sensinu circuit (4,1 ) detects a voltaoe above certain threshold and a current flow above certain threshold dictated from load/s connected to any or both of ths other two phases. The signal from the sensing circuit (4.1 ) is optocoupled through (4.5) that is supplied by a device’s dedicated supply ( 4.6). The optocoupler’s integrated driver activates the specially designed electromagnetic trigger (4.2) which then disconnects the supply of the protected phase L1 via the mechanically coupled power contact switch (4.3), hence protecting the load connected to 1.1 and behind the device (NTPDi-1p). This NTPD device is intended for increased sensitivity, contrary to that presented in Figure 2. increased sensitivity is obtained and realized through a suitable choice of optocoupling integrated circuits (4.5) and is introduced to provide protection of loads permanently connected to the supply grid for which there is no way of knowing (beforehand) their operation regime (stand-by. normal operation etc.). Loads that operate in stand-by mode and/or near zero consumption arc considered extremely critical for protection.

The optocoupling unit (4.5) inputs are connected in series with the sensing circuit (4.1 ) and its inputs are voltage limited-current excited. Optocoupling integrated drive outputs excite the electromagnetic trigger (4.2). Since now the optocoupling unit (4.5) defines the current sensitivity, ail realizations that include such a component eliminate the need of using highly sensitive electromagnetic triggers (2.2), hence providing a more unconstrained design approach, and reducing production costs.

The essential difference within this device realization contrary to those from Figure 2 and Figure 3 is the optoconpling unit connection to the sensing circuit, which is scries connected, voltage limited-current excited. Figure 5 Three preset sensing circuits (5.1 ), one for each phase, detect a voltage above certain threshold in any of the phases and a current flow- above certain threshold dictated from the load composition connected between any or all of the three phases. Each sensing circuit (5.1) is optocoupled through dedicated optocouplers (5.5) and the combined signal from all three phases, depending on the operating conditions is sent in the electromagnetic trigger (5.2). The optocouplers (5.5) are supplied by a dedicated supply (5.7), Optocoupler's integrated driver circuits then activate the specially designed electromagnetic trigger (5.2) which then disconnects the supply of all three phases via the mechanically coupled power contact switch (5.3), hence protecting the load connected across all three phases and behind the device (NTPDi-3p). This NTPD device is intended for increased sensitivity, contrary to that presented in figure 3.

The preset sensing circuits (2.1), ( 3.1 ), (4.1 ) and (5.1 ). are configured during the design stage not to conduct when the voltage at their terminals equals the rated grid phasemperational voltage including the deviations allowed by standards, grid codes and normal grid operation. When neutral conductor tear/discontinuity occurs, the sensing circuit must conduct a current dictated by the load composition from the other two phases but not from the load connected in the protected phase. The circuit is required to be discriminatory i.e., not to trigger under momentary or instantaneous voltage deviations, but rather long duration ones (voltage swells, neutral conductor tear etc.). Voltage deviations, regardless of their magnitude and duration are naturally imposed as a consequence from power system operation and exploitation. During conduction, the sensing circuit is designed to have a linear voltage-current dependance.

These requirements are realized using a series connection of chain of diacs and resistor. The chain of diacs determines the voltage threshold for device triggering, while the resistor limits the current and guarantees a linear volt-amp dependance when the circuit is conducting. The chain of series connected diacs must account for possible false triggering due to dU/dt effect, hence they should be placed in a manner that reduces stray capacitances between the diacs in the chain. This should potentially alleviate issues with false triggering due to rapid voltage changes. The same requirements from the sensing circuit are realized using a series connection of sidac and resistor as an altemate/better solution. The sidac is a commercially available component that’s equivalent to the chain of diacs. It's more reliable, cheaper and it alleviates all negative aspects introduced from the chain of diacs.

Sensing circuit discriminatory capabilities are guaranteed with die diacs/sidac characteristic region of tunneling, i.e,. negative resistance. This is considered a transient region in the diacs/sidac transfer characteristics (between conduction and non-conduction and vice versa). It is useful tn this application since it enables discrimination between voltage deviations that are intended to be registered (slow, such as the neutral conductor tear) versus those that are supposed to be ignored (last and instantaneous). Utilizing this diacs/sidac feature enables supplementary action to conventional overvoltage protection that utilizes surge arresters. W hen the sensing circuit starts to conduct, the chain of diacs or sidac, drops a certain voltage across it that is known as holding voltage and is constant, This is when the series resistor starts to act in a way that it forms a linear volt-amp dependance between the so called residual voltage (voltage difference between the holding voltage od the diaes/sidac and the neutral conductor piece that’s teared/discontinued from the grid) and current through the sensing circuit, while simultaneously limiting its value. The resistor's role is to protect the sensing circuit from large currents, to enable a linear volt-amp characteristic while the sensing circuit conducts, and to introduce a safety margin when an overvoltage occurs, whether it's from grid element switching /commutation or atmospheric origin, when it is expected that the overvoltage protection should take over absorbing the energy carried from the overvoltage. This action is supplementary to conventional overvoltage protection rather than competitive,

The special electromagnetic trigger (2,2), (3.2), (4.2) and (5.2) is actually a modified electropermanent magnetic trigger. These devices are utilized as triggers in RCCB’s (residual current circuit breakers). These are commercially available components with predefined characteristics but in very large quantities. Therefore, for the purposes of this invention, a modification in the trigger’s winding is made from what was commercially available to the inventor, so as to reduce the triggering threshold from several tens of milliamperes to a few hundred microamperes.

'The optocoupling units (4.5) and (5.5) are commercially available monolithic integrated circuits. Their selection is limited by the necessity for highly sensitive input units and a low output resistance drive output units. The present invention uses two-channel, high currenttransfer ratio (CTR) monolithic integrated circuits commercially labeled HCPL 2730. The optocoupler inputs are antiparallel connected hence limiting their input voltage and protecting them. Optocoupler’s current sensitivity (current transfer ratio - CTR) is determined from its manufacturer specifications.

Dedicated supplies (4.6) and (5.7) are realized as two~pha.se and three-phase bridge rectifiers accordingly and as such are known technical solutions. They can safely and reliably supply the optocoupler outputs and the electromagnetic trigger without a connection to the neutral conductor or filtering capacitors at its DC terminals.

The use of bridge configuration supply is especially important here since if there’s a neutral conductor tear/discontinuity and the supply is connected to it. one risks an outage or a total disability of the NTPD’s protective action. Also, the use of multi-pulse supplies alleviates the need for using filtering capacitors at their DC terminals. This might be important in order to eliminate the residual charge from the capacitors, that could false-trigger the device after an initial fault detection and supply disconnection. All other elements such as the power switch (single-phase and three-phase) and their mechanical couplings to the electromagnetic trigger are known technical solutions and as such they are utilized in this invention.

The modular/hlock representation of elements within the NTPD is made lor the purposes of deriving different configurations with identical characteristics. All modules/blocks are integrated within a compact device that can be installed at the PCC right after the metering point or as part of the users/household’s standard distribution board before the other protective devices.

All presented variations of the NTPD include components that are known to the inventor and can be replaced by compatible and adequate components and realizations, and while the specification does not explicitly state them, they can be assumed and/or reproduced.

Claims

PATENT CLAIMS

1. Neutral tear protection device connected at a point of common coupling or at a consumer’s distribution board between a phase and neutral conductor, comprised of preset sensing circuit (2.1 ) connected in series to an electromagnetic trigger (2.2) that is mechanically coupled to a single-phase power switch (2.3) connected in a way that enables a supply interruption of the protected phase, is distinguished with the detection of voltages above a certain threshold between the phase and neutral conductor by the preset sensing circuit (2.1) that occurs when the neutral conductor is teared/discontinued from the utility’s side of the grid, hence using the current that flows through it to excite the electromagnetic trigger (2.2) which in turn activates the singlephase power switch (2.3).

2. Neutral tear protection device connected at a point of common coupling or at a consumer’s distribution board between a phase and neutral conductor, comprised of three identical preset sensing circuits (3.1 ) connected in series to three dedicated electromagnetic triggers (3.2) that are mechanically coupled to a three-phase power switch (3.3) connected in a way that enables a supply interruption of all three phases, is distinguished with the detection of voltages above a certain threshold between any of the phases and neutral conductor by the any of the preset sensing circuits (3.1) that occurs when the neutral conductor is teared/discontinued from the utility’s side of the grid, hence using the current that flows through it to excite the electromagnetic trigger (3.2) which in turn activates the three-phase power switch (3.3).

3. Neutral tear protection device connected at a point of common coupling or at a consumer's distribution board between a phase and neutral conductor, comprised of preset sensing circuit (4.1) that detects voltages above a certain threshold and current flow above certain value depending on load composition in any of the other two phases and passes the output signal front it through an integrated optocoupler unit with output drive (4.5) supplied by a dedicated power supply (4.6), integrated optocoupler drive unit activates the electromagnetic trigger (4.2) that is mechanically coupled to a singlephase power switch (4.3 ), is distinguished with an activation of the electromagnetic trigger by the integrated optocoupler drive unit that disconnects the supply via a mechanically coupled single-phase power switch (4.3).

4. Neutral tear protection device connected at a point of common coupling or at a consumer's distribution board in a three-phase sy stem, between all three phases and the neutral conductor, comprised of three preset sensing circuits (5.1 ) connected to dedicated integrated optocoupler units with driver outputs (5.5) supplied from a dedicated supply (5.7) and connected to an electromagnetic trigger (5.3), is distinguished with an optocoupling drive units (5.5) activation as a consequence of increased voltage detection and current flow within the preset sensing circuits owed to a neutral conductor tear/discontinuity, of the electromagnetic trigger (5.2) that disconnects the supply in al l three phases via a mechanically coupled three-phase power switch (5.3).

5. Neutral tear protection device in compliance with any of the above claims is distinguished by means that preset sensing circuits (2.1 ). (3.1). (4.1) and (5.1) are configured and designed appropriately not to conduct when the voltage at their terminals equals the grid rated/operational voltage and is comprised of series connection (chain) of diacs or a sidac and a resistor that operate in their non-conductive region, geometrically placed in a way that reduces stray capacitances for the chain of diacs, not critical for the sidac, when the sensing circuit conducts, a holding voltage occurs at the end of the diac chain or the sidac and the series connected resistor limits the current flow through the sensing circuit, enables for linear voltage-current dependency between the residual voltage and sensing circuit's current flow.

6. Neutral tear protection device in compliance with any of the claims from 1 to 4 is distinguished by an electro permanent magnetic trigger (2.2), (3.2), (4.2) and (5.2) that incorporates a specially designed winding coil that shifts the triggering threshold from several tens of milliamperes to a few hundred microamperes.

7. Neutral tear protection device in compliance with the claims 3 and 4 is distinguished by dual channel optocoupling units with an integrated driver (4.5) and (5.5) that, possess highly sensitive inputs connected in antiparallel and low resistance drive outputs connected in parallel.

8. Neutral tear protection device in compliance with claims 3 and 4 is distinguished by dedicated supply units (4.6) and (5.7) derived as two-phase and three-phase bridge supply units with or without filtering capacitors.