0.4kV low-voltage distribution system solutions against voltage fluctuations: voltage fluctuation resistance modules, comprehensive motor vibration resistance devices, permanent voltage fluctuation resistance modules, motor protection against voltage fluctuations, frequency converter protection against voltage fluctuations, voltage fluctuation stabilization, contactors...

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Project Background: Due to fluctuations in the voltage of the company’s power grid, low-voltage motors and frequency converters experience unplanned shutdowns as a result of these external voltage fluctuations, which has a significant impact on the company’s normal production activities, research work, and projects. After investigating the cause, it was found that both the amplitude and duration of voltage fluctuations in the power grid exceeded the range and duration for which the contactor coil could maintain its voltage; as a result, the contactor released due to insufficient voltage. Inverters are sensitive to voltage changes, and when the voltage drops by more than 80%, their low-voltage protection mechanism activates, causing the inverter to stop operating due to a low-voltage fault. As a continuous manufacturing enterprise, it is affected by voltage fluctuations; voltage drops of more than about 80 milliseconds, associated with drops in grid voltage, can cause alarms to be triggered in various high and low voltage motors as well as frequency converter devices, leading to unplanned shutdowns. This has a significant impact on the company’s normal production activities, research efforts, and projects. Production interruptions not only result in reduced output but also affect product quality, causing substantial financial losses. Worse still, there is a possibility of personal safety accidents. Through detailed discussions with the client, the current power supply system diagram of the client was analyzed, allowing for an overall understanding of the company’s current power supply situation and requirements. Due to issues such as the high-voltage capacity on site, it is not possible to carry out a seamless switchover; therefore, solutions are being developed only for the low-voltage system to mitigate voltage fluctuations (power outages or manual switching are not covered by these solutions). Requirement analysis 1. Hazards of voltage fluctuations. During operation, power systems experience sudden and significant voltage fluctuations as a result of faults such as lightning strikes on external lines or instantaneous short circuits, which can lead to short circuits in the internal power grids of enterprises, as well as the startup of large or numerous motors. This phenomenon is commonly referred to as voltage fluctuation; it lasts from 0.5 cycles to up to 1 minute, with the voltage level dropping to 90%-10% of the nominal value. When voltage fluctuations occur, they can cause a range of problems for production processes and on-site equipment: excessive voltage drops or prolonged durations can cause devices such as motors, frequency converters, and soft starters to stop working, leading to production interruptions and resulting in losses related to safety, environmental issues, defective products, wasted raw materials, and reduced output ； During the recovery period from voltage fluctuations, restarting a large number of motors can subject them to high-current surges once again, posing a risk to the safety of both equipment and personnel ； 2. Requirement description: The low-voltage side is located on the low-voltage load side, where there are numerous motor-based loads and frequency converters. Some of these devices play a key role in the production process. Typically, in 400V low-voltage systems, the motor control circuits are operated by contactors; generally, AC relays cause the contactors to release when the voltage falls below 50% of the coil’s rated voltage for a period of more than 20 ms ； When the voltage drops to 80% or even lower and this condition persists for five cycles, the contactor also releases, causing the low-voltage motor to lose power and stop operating. Inverters generally come equipped with various protection functions such as overvoltage, undervoltage, overcurrent, and protection against sudden power outages. When there is a voltage drop to 70% of the rated voltage or a complete power loss, the low-voltage protection mechanism of the inverter activates, shutting down its output; as a result, the motor comes to a stop due to inertia. Since the relay that controls the operation of the inverter is also released due to power fluctuations, once the power supply returns to normal, the inverter cannot be activated to use its instant restart function because there is no command to operate it. A manual reset is required to resolve the low-voltage fault in order to restart the inverter, which results in the interruption of normal production. In extreme situations, when the high-voltage side fast switching scheme fails to achieve rapid switching and instead relies on synchronous or residual voltage switching, the switching time may extend to 200–300 ms, posing a risk of failure in the control circuit; therefore, appropriate supplementary measures need to be implemented to improve its reliability. To address the issue of downtime of critical equipment, the design and modification plan must take the following requirements into account: 1. When power is lost, the control circuit is released; to ensure that the production process does not stop, the electrical components that have been released must be automatically reconnected as soon as power is restored, thereby enabling prompt resumption of continuous production. 2. The entire production process is controlled by a DCS distributed control system, with interconnections between various equipment units. Even when a device stops operating, it is still necessary to maintain normal communication with the DCS in order to prevent cascading shutdowns. 3. Supplementary measures for critical equipment fall under the category of distributed governance solutions; a large number of such devices are installed on-site, so it is necessary to take into account factors such as cost, installation space, and ease of installation. 4. When a large number of motors are restarted simultaneously, there is a risk of inrush current during startup; the modification plan should take into account the addition of appropriate functions to avoid this risk. 5. The modification plan should ensure that no new risk of failure is introduced and that the existing control circuits remain unchanged. Overview of the solution: The concept behind this solution is to consider the entire distribution network system as a whole and to address problems at their source. There are two ways to deal with voltage fluctuations in the power grid; one involves addressing the issue at the power supply side, that is, by providing a stable power source with continuous output when external power supplies experience fluctuations, thereby ensuring that the loads connected to it receive a proper operating voltage. It is solved at the load control side: when the external power supply experiences voltage fluctuations and sensitive electrical components are released, these components are automatically reconnected as soon as the power supply returns to normal, thereby enabling rapid resumption of continuous production. For now, the issue is addressed at the load control level; that is, when there are voltage fluctuations in the power supply, the configured solution ensures the continuous operation of the equipment by maintaining and restarting the load control circuit, or by compensating for the voltage in the power circuit. Such as UPS power supplies, low-voltage ride-through, motor protector auxiliary functions, and voltage fluctuation resistance modules. l UPS power supply: By connecting UPS power supplies in series, it ensures continuous power supply to the load during power fluctuations, allowing it to operate normally. Online UPS units have a short switching time, which meets the requirements. Due to the series connection approach, it first increases the risk of failures. Additionally, the capacity of the power support devices must match the actual load capacity; this is especially true for high-power equipment. The cost associated with such equipment is high, their installation locations are scattered, and there are many of them, resulting in extremely high total costs. Moreover, the batteries used for energy storage have high environmental requirements, need to be replaced regularly, and incur high maintenance costs over time. L Low-voltage ride-through device: Designed primarily for frequency converter equipment; when voltage fluctuations occur, this device uses its internal BOOST voltage-raising module to compensate the DC bus of the frequency converter, thereby ensuring its normal operation. This solution is also costly, as it applies only to the key frequency converter nodes in the production process. l Auxiliary functions of the motor protector: The device is primarily designed for protection purposes, with voltage fluctuation resistance serving as an auxiliary function; it operates solely through relay signals. There is no energy storage source within the motor protection system, and thus the device cannot function properly in the event of voltage fluctuations. In such situations, transmission signals to the DCS (such as signals indicating operation or faults) are likely to be lost. When power is restored to the control circuit, motor protection needs to determine the operating conditions prior to the power outage in order to decide whether the motor can be started again. The time required for this determination is too long, making it impossible to control the timing of the motor’s restart. The inverter cannot be restarted. l Anti-surge power module: When a surge occurs, the internal supercapacitor ensures the normal operation of the module; once power is restored, the internal relay activates to automatically restart the motor in stages, as well as enable frequency conversion and soft start. Compact in size, with a magnetic design for easy installation. Taking into account the actual needs of customers, and through comprehensive evaluation from various aspects such as anti-interference performance, safety and reliability, investment cost, product structure, and ease of modification, an overall solution for the DCM-621KH anti-interference module has been proposed. There are two types of anti-surge modules available on the market: those with energy storage for maintenance and those with energy storage for restart. The principle of energy storage maintenance is to supply a DC or AC auxiliary power source to the contactor; when there are voltage fluctuations in the power grid, this ensures that a continuous holding voltage is available for the contactor coil, preventing it from releasing. Once the voltage returns to normal, the main circuit of the contactor remains connected, and thus the motor continues to operate as it receives power from the energized contactor coil. The principle behind the restart of energy storage is to maintain the start command for the contactor during voltage fluctuations, while not keeping the contactor’s coil energized. As a result, the contactor releases due to the low voltage caused by those fluctuations. When the voltage returns momentarily, since the contactor’s start circuit is in a locked state, the contactor’s coil becomes energized and the contactor closes, thereby allowing the motor to accelerate again once it receives power. Through our in-depth understanding of customer preferences and market usage patterns, we conducted a comparison and analysis of the two methods. We concluded that the energy storage restart method is safer, more reliable, and more practical, for the following reasons: Comparison of the two different energy storage methods for preventing voltage fluctuations – Parameter: Energy storage restart method vs. Energy storage retention method; Control mechanism: Connected in parallel to the contactor’s start-up and self-holding circuit vs. Connected in series to the contactor’s coil main circuit; Behavior during voltage fluctuations: The contactor releases and then re-engages after the fluctuation passes, whereas in the retention method the contactor remains engaged throughout the fluctuation; Reliability: There is no series connection between the main circuit and the control circuit, so a failure in one module does not affect the operation of the contactor. The energy storage capacitor is connected in series with the contactor coil circuit; a failure of this capacitor can affect the proper operation of the contactor. It features a detachable installation structure, making replacement convenient without affecting the normal operation of the circuit. The terminal-fixing wiring structure makes replacement more troublesome and can disrupt the normal operation of the existing circuit. It has a small size and volume, is magnetically attached, making it easy to install in drawer cabinets. Those with a larger volume use rails, which makes installation in drawer cabinets more difficult. The control targets include contactors, frequency converters, and soft starter contactors. Since the duration of power fluctuations is generally around 100 ms, the loads that need to be protected against such fluctuations are mainly variable-torque loads such as fans and pumps, which possess a certain degree of inertia. When the contactors or frequency converters release due to these power fluctuations, the fans and pumps continue to operate at high speeds due to their inertia. Once the power supply is restored momentarily, an energy-storage-based anti-fluctuation device causes the contactors to close automatically. The motor then accelerates again at high speed, with little impact on the manufacturing process. Additionally, this control method does not require any changes to the existing system’s wiring or control scheme. Thanks to the parallel control approach, even if there is a fault in the equipment itself, it does not affect the normal operation of the system. This is the biggest advantage of this approach: it avoids disrupting the existing stable system just because of dealing with a low-probability transient event. The energy-storage-based method for preventing voltage fluctuations relies on a series connection setup, using the discharge of energy storage capacitors to maintain the holding voltage of the contactor; this increases the likelihood of failures. Should the device designed to prevent voltage fluctuations fail, it can also cause the original equipment to shut down unexpectedly. Also, keeping the contactor coil engaged during voltage fluctuations can affect the physical structure of the contactor, as well as its lifespan due to the frequent opening and closing of the contactor’s moving and stationary contacts. Based on the analysis and research of the above circumstances, adopting energy storage restart-based anti-flicker technology is more appropriate and practical. Implementation of the solution: 1. The working principle of the straight-type motor module is to establish a composite criterion by monitoring the voltage of the load’s power supply, the voltage of the contactor coil, and the voltage in the control circuit. After startup, the system enters an anti-fluctuation standby mode after a 5-second delay. When there is a change in the contactor’s position signal, the internal supercapacitor system is activated automatically, and the system begins timing. If power supply is restored automatically within the set maximum fluctuation time, the motor is started again after a delay, thereby restoring normal operation prior to the power fluctuations and ensuring uninterrupted production. Based on extensive previous experience in modifications, and taking into account the actual secondary circuit of the customer’s motor, the DCM621KH anti-vibration module is used; the schematic diagram is as follows: Terminals 1 and 4 represent the control power supplies L and N, which are taken from the control circuit of the contactor ； Power supply for the motor restart controller and input for the detection voltage. Terminals 2 and 3 are the contactor status feedback signal and restart output, and are connected in parallel in the start-up circuit ； Detect and determine the different operating states of the contactor – stopped or running – as well as its restart after power fluctuations. Terminals 7 and 8 are operation signals, connected in parallel to the operation signal circuit monitored by the DCS. When voltage fluctuations occur, the signal output closes to provide feedback to the DCS, preventing it from tripping due to these fluctuations; once the circuit resumes normal operation, the signal output returns to its normal state. The low-voltage motor circuits are upgraded in phases, following the approach of \"continuous production with phased transformation\". Estimated renovation time: about 30 minutes per drawer for straight-type motors. The expected outcomes after the modification are as follows: During normal operation, when the motor is started manually or remotely, the KM coil is energized, causing the KM contactor to close. The DCM621KH detects this closed state of KM and begins charging. Once 5 seconds of charging have passed, the system enters a mode designed to resist voltage fluctuations. When such fluctuations occur and the voltage drops, KM releases automatically, causing the motor to stop. The supercapacitor built into the DCM621KH then takes over to supply power to the module responsible for resisting voltage fluctuations. The system starts timing; if power is restored automatically within the specified maximum time limit (up to 9 seconds), after a delay, the RS relay activates and restarts the motor, restoring normal operation as it was before the voltage fluctuations occurred. 4.2 The variable-frequency motor is equipped with a DCM621KH anti-vibration module; the schematic diagram is as follows: Terminal 1 and Terminal 4 represent the control power supplies L and N, which are taken from the control circuit of the inverter ； Power supply for the motor restart controller and input for the detection voltage. Terminals 2 and 3 are the contactor status feedback signal and restart output, and are connected in parallel in the start-up circuit ； Detect and determine the different operating states of the contactor – stopped or running – as well as its restart after power fluctuations. Terminals 7 and 8 are operation signals that are connected in parallel to the operation signal circuit monitored by the DCS. When a voltage fluctuation occurs, the signal output closes, providing feedback to the DCS; this prevents the DCS from issuing a shutdown command due to the detection of a disconnected contactor. Once the circuit resumes normal operation, the signal output returns to its normal state. Terminals 9 and 10 serve as reset signals and are connected in parallel to the DCS reset signal circuit. When a power fluctuation occurs, the frequency converter triggers an alarm due to this fluctuation; at such times, it is necessary to reset the frequency converter first before it can be started again. Terminals 11 and 12 serve as alarm signals and are connected in series within the alarm signal circuit monitored by the DCS. When a power fluctuation occurs, the signal output is disconnected, preventing the DCS from issuing a shutdown command due to the detection of a fault signal from the inverter; once the circuit resumes normal operation, the signal output is re-established. Estimated renovation time: about 1 hour per circuit for the frequency converter. The expected outcomes after the modification are as follows: During normal operation, when the inverter is started manually or remotely, the 1KA1 coil is energized, causing the 1KA1 contactor to close. The DCM621KH detects this closed state of 1KA1 and begins charging. Once 5 seconds of charging have passed, the system enters a mode designed to resist voltage fluctuations. When such fluctuations occur and the voltage drops, 1KA1 releases automatically, the inverter stops operating, and the AL relay of the DCM621KH activates, preventing the “inverter fault signal” from being sent out. The supercapacitor built into the DCM621KH then takes over to supply power to the module designed to counter voltage fluctuations. The system starts timing; if power is restored automatically within the specified maximum time frame (up to 9 seconds), the RE reset relay closes, thereby resolving the inverter fault. After a delay period, the RS relay activates, causing the inverter to restart automatically and returning it to its normal operating condition prior to the voltage fluctuations. Main features and basic parameters 1. Main features u The starting motor is in automatic standby mode; it discharges automatically when stopped manually ； U-magnetic mounting, reliable and flexible ； U-type plug terminal for easy maintenance ； Starts with a U pulse – energy-efficient and reliable ； The flash duration can reach up to 10 seconds, and it is easy to modify ； The restart delay can be modified, which is useful in environments with multiple motors operating in batches ； The voltage fluctuations did not cause the contactor to release, and thus they have no impact on the anti-vibration module. 2. Basic parameters:
u System power consumption: 1W
u Installation method: Magnetic attachment
u Dimensions: 64mm*47mm*96mm (width*height*depth)
u Net weight of the product: Approximately 300 grams
u Applicable voltage: AC220V (customizable)
u Operating current capacity: Normally open, 5A at 440Vac/300Vdc
u RUN signal capacity: Normally open, returns upon timeout, 5A at 250Vac/30Vdc
u Maximum power fluctuation tolerance: Adjustable from 0 to 9 seconds, in 1-second increments; the module shuts down when set to 0. Additional delay time: adjustable continuously from 0 to 1 second, in steps of 0.1S. Applicable circuits: direct start, frequency converters, soft starters. The appearance and installation method require on-site assessment to examine the operating conditions of the motors on site, ensuring the effectiveness of the anti-vibration modifications. The DCM621KH model is compact, with a magnetic mounting method (as shown in Figures 1 and 2), making it easy to install on-site. Figures 1 and 2 Material List 1. Basic Materials Serial Number Material Name Quantity Check 1 DCM621KH Motor Vibration Tester – several 2 Intermediate relays – several 3 Signal cables – several 2. Tools and Auxiliary Materials Serial Number Name Quantity Check 1 Multimeter – 1 2 Flat-head screwdrivers – 2 3 Cross-head screwdrivers – 2 4 Tool box – 1 set 5 Pliers with beveled tips – 1 set 6 Crimping pliers – 1 set 7 Stripping pliers – 1 set 8 Drill and drill bits – 1 set 9 Handheld cutting machine – 1 set 10 Zip ties – 1 pack 11 Numbering tubes – 1 roll 12 Oil-based pen – 1 13 Wiring tape – 1 roll 14 Insulating tape – 1 roll 15 Safety helmet – 1 per person 16 Work ID badge – 1 per person