Transformers play an indispensable role in modern electrical systems, ensuring the smooth and efficient transition of voltage levels. Among the wide variety of transformers available, the 15 kVA transformer stands out as a reliable and versatile choice for a broad spectrum of applications. Whether it’s used in industrial facilities, commercial settings, or even residential systems, this transformer is highly regarded for its balance of power, efficiency, and adaptability.
This guide explores the key features, operational principles, and applications of 15 kVA transformers. We will break down how these transformers work, their primary components, and the technical benefits they offer. Furthermore, we’ll highlight the specific scenarios where they shine and provide insights into their maintenance and safety requirements. By the end of this article, you’ll have a comprehensive understanding of what makes 15 kVA transformers an essential component in many electrical networks.
What is a 15 kVA transformer and how does it work?
A 15 kVA transformer is an electrical device designed to transfer electrical energy between circuits while altering the voltage levels. The “kVA” stands for kilovolt-amperes, which measures the transformer’s capacity, indicating it can handle up to 15,000 volt-amperes of power. These transformers operate on the principle of electromagnetic induction, where a primary coil receives alternating current (AC) to generate a magnetic field. This magnetic field induces a current in the secondary coil, effectively transforming the voltage to a higher or lower level depending on the application. They are commonly used in industrial or commercial settings to power equipment, ensuring safe and efficient voltage management.
Understanding the basics of 15 kVA transformers
15 kVA transformers are compact yet powerful devices commonly used to step up or step down voltage levels in various electrical systems. With a power rating of 15 kilovolt-amperes, these transformers are suitable for moderate energy demands in industrial, commercial, and residential use cases. Constructed with high-quality cores and efficient winding designs, their performance minimizes energy loss while ensuring reliable power transmission.
One of the distinguishing features of 15 kVA transformers is versatility. They can operate in single-phase or three-phase systems, depending on the requirements of the installation. Additionally, they are engineered to handle a wide range of input and output voltage levels, such as transforming 480V to 240V or vice versa, optimizing energy distribution for specific applications.
These transformers are designed with protective measures like robust enclosures to guard against environmental damage and overload protection systems to enhance durability. Applications include powering HVAC systems, small machinery, lighting systems, and other medium-capacity devices, ensuring safe and efficient voltage utilization. Regular maintenance is crucial to prolong their lifespan and maintain operational efficiency.
Primary and secondary windings in 15 kVA transformers
The primary and secondary windings in a 15 kVA transformer are essential components that enable voltage transformation by facilitating electromagnetic induction. The primary winding is connected to the input voltage source, where it receives electrical energy, while the secondary winding delivers the transformed voltage to the output load. The number of turns in the windings directly affects the voltage ratio, with the transformer’s turns ratio determining whether the device steps voltage up or down. For a typical 15 kVA transformer, the windings are constructed with high-quality conductive materials like copper or aluminum to ensure optimal efficiency and minimize energy loss. Proper design and insulation between these windings are critical to prevent short circuits and maintain the reliability and safety of the transformer.
Voltage transformation process in 15 kVA units
The voltage transformation process in a 15 kVA transformer operates on the principle of electromagnetic induction. When alternating current flows through the primary winding, it creates a varying magnetic field. This field induces a corresponding voltage in the secondary winding, determined by the turns ratio between the two windings. For example, if the turns ratio is 2:1, the transformer steps the voltage down by half; if it’s 1:2, it steps the voltage up to double.
The core, typically made of laminated silicon steel, plays a pivotal role by reducing energy losses and efficiently directing the magnetic flux between the windings. High-quality insulation separates the primary and secondary windings to ensure safe operation and prevent electrical breakdowns. The overall design is tailored to handle the rated power of 15 kVA, ensuring reliable voltage conversion for applications such as residential power distribution, industrial machinery, or renewable energy systems. High efficiency and durability are achieved through the use of heat-resistant materials and precise engineering standards.
What are the different types of 15 kVA transformers available?
Like other transformers, 15 kVA transformers also come in different types tailored to meet specific applications. These include:
Step-Up Transformers: Used within power plants, they serve to increase voltage levels towards the efficient power transmission across longer distances.
Step-Down Transformers: Primarily used to lower voltage levels for power supply to various types of residential, commercial, or industrial setups.
Autotransformers: Protect sensitive equipment from faulty voltages at the expense of electrical signal, providing electrical isolation between circuits and enhancing safety while reducing electrical noise.”
Dry-Type Transformers: Those which operate without employing liquid coolant mediums. Suitable for Indoor application, they offer reduced maintenance with high safety standards.
Oil Filled Transformers: Employed outdoors or in industrial scenarios, these transformers utilize specialized oil for insulation and coolant. They offer durability and high load-handling capacity.
Each type serves unique functions based on the systems voltage requirements, environmental conditions, and the efficiency under consideration.
Dry type vs. liquid-filled 15 kVA transformers
When deciding between dry type and liquid-filled 15 kVA transformers, several key factors should be considered:
Cooling Mechanism: Dry type transformers use air as their cooling medium and require proper ventilation for efficient operation. Liquid-filled transformers, on the other hand, utilize a coolant for heat dissipation, enabling them to handle higher loads more effectively.
Installation Environment: Dry type transformers are ideal for indoor use due to their fire-resistant design and lack of hazardous liquids. They are often chosen for commercial buildings, hospitals, and schools. Liquid-filled transformers are better suited for outdoor or industrial environments, as they offer a higher capacity and robustness in extreme weather conditions.
Maintenance: Dry type transformers generally require less maintenance since they do not involve liquids, reducing the risk of leaks. Liquid-filled transformers, though durable, need regular inspection of fluid levels and quality to ensure optimal performance and safety.
Efficiency & Lifespan: Liquid-filled transformers are typically more efficient and have a longer lifespan due to their superior cooling capabilities, which reduce thermal stress. Dry type transformers may have slightly lower efficiency but are valued for their environmental safety and minimal maintenance needs.
Each option offers distinct advantages, and the best choice depends on factors like the operating environment, budget, and specific application requirements.
Single-phase vs. three-phase 15 kVA transformers
Single-phase and three-phase 15 kVA transformers are designed to serve different operational needs depending on the power distribution system. A single-phase transformer is ideal for smaller or residential applications where lower energy loads are sufficient, operating efficiently in areas without access to three-phase power. These transformers are simpler, compact, and often more cost-effective for limited power requirements.
On the other hand, three-phase transformers are designed for larger industrial or commercial applications, providing a more balanced and consistent power supply for heavy-load equipment. They are more efficient for high-power systems as they deliver power through three alternating currents, reducing energy losses and ensuring a smoother electrical flow. Three-phase transformers are generally bulkier and more complex but are vital for infrastructure requiring significant energy distribution.
Choosing between the two depends on your application context. Single-phase systems suit smaller, localized energy demands, while three-phase systems cater to intensive power needs in larger setups. Both options are pivotal in ensuring stable and reliable electricity, tailored to specific load, efficiency, and scale demands.
Isolation transformers: When and why to use them
Isolation transformers are essential for enhancing safety and improving performance in various electrical systems. These transformers decouple the primary and secondary circuits, providing electrical isolation that prevents the direct transfer of current, reducing the risk of electric shock. They are commonly used when sensitive equipment, such as medical devices or industrial machinery, requires protection from electrical noise and surges. Additionally, isolation transformers help mitigate ground loops, a frequent cause of interference in audio and communication systems.
When deciding to use an isolation transformer, consider scenarios requiring improved electrical safety, noise reduction, or enhanced equipment longevity. These devices are particularly valuable in environments where uninterrupted and clean power is critical, offering an added layer of reliability and security. Whether safeguarding high-value systems or meeting regulatory compliance, isolation transformers are a powerful solution tailored to modern electrical challenges.
How do I choose the right 15 kVA transformer for my needs?
When selecting a 15 kVA transformer, start by assessing your specific power requirements, including voltage levels, load type, and operating environment. Determine whether the transformer will be used for step-up or step-down purposes and ensure it meets applicable safety and compliance standards. Consider factors such as efficiency, cooling methods, and the level of insulation required for your setup. Additionally, account for future scalability and the transformer’s ability to handle potential power surges or fluctuations, ensuring long-term reliability and performance.
Assessing voltage requirements: 240V, 480V, and other options
When determining voltage requirements, consider the type of equipment being powered, the distance of transmission, and the overall energy efficiency desired. For most residential and light commercial applications, 240V is a common standard due to its compatibility with household appliances and smaller machinery. However, for industrial or larger-scale operations, 480V systems are often preferred, as they support higher power demands and reduce energy loss during transmission over long distances.
Additionally, other voltage options may be used depending on region-specific standards or specialized applications, such as 208V in commercial three-phase systems or higher voltages for heavy-duty industries. Always evaluate safety codes, compatibility with existing infrastructure, and the potential need for step-up or step-down transformers to ensure optimal system performance.
Considering NEMA ratings and enclosure types
NEMA ratings are essential for identifying the level of protection that electrical enclosures provide against environmental factors such as dust, water, corrosion, and hazardous conditions. Common NEMA types include NEMA 1, which offers basic protection for indoor use, and NEMA 4 or 4X, providing watertight and corrosion-resistant capabilities for outdoor settings. The choice of enclosure type depends on the operating environment, with NEMA 12 being ideal for indoor industrial applications, and NEMA 3R suited for outdoor residential or light commercial installations. It is crucial to match the NEMA rating with the specific environmental challenges your equipment may encounter, ensuring longevity and operational efficiency.
Evaluating efficiency and DOE 2016 compliance
Efficiency evaluation is a critical aspect when selecting equipment to ensure optimal performance and adherence to regulatory standards. The DOE 2016 compliance standards were introduced to improve energy efficiency and reduce environmental impact for electrical equipment such as distribution transformers. This regulation mandates higher efficiency levels, minimizing energy losses and lowering operating costs over the equipment’s lifespan.
To evaluate efficiency and DOE 2016 compliance, check whether the equipment meets the applicable TP-1 or DOE 2016 energy efficiency specifications. Review the product labels, manufacturer certifications, or technical documentation to confirm compliance. Utilizing certified energy-efficient equipment ensures both regulatory adherence and cost savings. Furthermore, consider lifecycle energy consumption and operational demands, as these factors influence long-term efficiency.
What are the key specifications to look for in a 15 kVA transformer?
In evaluating the specifications for a 15 kVA transformer, the following details are critical:
Voltage Rating: The primary and secondary voltage ratings should align with application requirements.
Phase Type: Ascertain whether your system requires a single or a three-phase transformer.
Efficiency: Compliance with standards such as DOE or NEMA are important; look for models that are energy efficient.
Cooling Method: Determine if the transformer is air-cooled or oil cooled based on your operating environment.
Temperature Rise: Review the temperature rise rating against operating conditions and related loads to confirm alignment with requirements.
Enclosure Type: NEMA rated enclosures for industrial or outdoor applications will require selection of the suitable environment enclosure.
Impedance: Check impedance values to avoid creating voltage regulation difficulties or overly high short-circuit currents.
Certifications: Confirm compliance with industry requirements like UL, CSA or IEC, assuring operational safety and dependability.
Evaluating these factors will likely ensure optimal performance relative to your application.
Understanding primary and secondary voltage ratings
Primary and secondary voltage ratings are critical to the proper operation of a transformer, as they define the input and output voltages. The primary voltage corresponds to the voltage supplied to the transformer, while the secondary voltage is the transformed voltage delivered to the load. These ratings are determined by the turns ratio of the transformer, which dictates the proportional relationship between the input and output voltages. For instance, a step-down transformer reduces voltage, while a step-up transformer increases it.
When selecting a transformer, it is essential to match the primary voltage rating with the supply voltage and ensure the secondary voltage meets the requirements of the connected load. Variations or mismatches in these ratings can lead to inefficiencies or potential equipment damage. Understanding these ratings also helps maintain the performance, safety, and compatibility of electrical systems in both residential and industrial contexts.
Importance of frequency and tap settings
Frequency is a critical factor in the operation of transformers, as it directly affects their efficiency and performance. Most transformers in the United States are designed to operate at 60 Hz, aligning with the standard grid frequency. Deviations can cause overheating, increased losses, and vibrations, potentially reducing the lifespan of the transformer. Maintaining the correct frequency is crucial for ensuring the reliability and stability of the connected equipment.
Tap settings play an essential role in adjusting transformer voltages to accommodate variations in supply or load conditions. By providing the ability to modify the transformer’s output voltage, tap settings help optimize performance and ensure voltage levels remain within acceptable limits. Proper tap setting adjustments also protect sensitive equipment and support efficient energy distribution, especially in systems subjected to fluctuating electrical demands. Understanding and managing both frequency and tap settings are vital for the safe and efficient operation of transformers in diverse applications.
Analyzing amperage and low voltage requirements
Understanding amperage and low voltage requirements is essential for designing and operating efficient electrical systems. Amperage, or the measure of electrical current flow, directly influences the system’s capacity and the sizing of components such as wires, circuit breakers, and transformers. Properly sizing these elements ensures safety and prevents overheating or system failures. Low voltage requirements, on the other hand, focus on maintaining adequate power delivery for devices operating under 1000 volts. This involves calculating voltage drops across circuits and ensuring loads receive sufficient power for consistent performance, particularly in long-distance electrical installations. Addressing these factors effectively reduces energy loss, improves system safety, and enhances overall reliability in a variety of residential, commercial, and industrial applications.
How do I install and maintain a 15 kVA transformer?
To install a 15 kVA transformer, first ensure you have the correct specifications and location prepared. Begin by securely mounting the transformer on a stable platform or wall bracket, ensuring proper ventilation around the unit. Follow local electrical codes and regulations while connecting the primary and secondary wiring. Double-check all connections to ensure they are tight and use appropriate protective equipment such as fuses or circuit breakers.
For maintenance, regularly inspect the transformer for signs of damage, overheating, or unusual noise. Keep the area surrounding the transformer clean and free from obstructions. Check connections to ensure they remain secure over time, and test the insulation resistance periodically. Oil-cooled transformers may require oil level and quality assessments to prevent electrical failure. Always de-energize the unit before conducting maintenance and consult a licensed electrician for complex issues.
Proper installation techniques for 15 kVA units
Installing a 15 kVA transformer requires adherence to strict guidelines to ensure safety, durability, and performance. Begin by selecting an appropriate location that is well-ventilated, free from excessive moisture or dust, and compliant with local codes. The transformer should be mounted on a sturdy foundation that can support its weight and minimize vibration, such as a concrete pad. Ensure proper clearance around the unit for ventilation and maintenance access, as per manufacturer specifications.
The electrical connections must be carried out precisely, following the wiring diagrams provided by the manufacturer. Use appropriately rated cables and verify that all connections are secure to prevent overheating or electrical faults. A reliable grounding system is critical to safeguard the transformer and connected systems from electrical surges or faults.
Before energizing the transformer, conduct thorough inspections and testing. This includes checking for loose connections, measuring insulation resistance, and verifying voltage levels. If applicable, confirm the proper oil levels for oil-cooled units and ensure no leaks are present. Once the system is powered, monitor initial operation for any abnormalities. All installation steps should comply with National Electrical Code (NEC) standards and involve certified professionals to ensure safety and reliability.
Regular maintenance and cooling considerations
Proper maintenance of electrical systems is vital to ensure longevity and efficiency. Regularly inspect components for wear and tear, including wiring, connectors, and protective devices. Clean equipment to prevent dust accumulation, as it can lead to overheating. For cooling systems, verify that fans, vents, and ductwork are unobstructed and functioning efficiently. Oil-cooled units require periodic oil sampling and analysis to prevent deterioration or contamination.
Temperature management is also crucial. Monitor system heat levels and maintain consistent airflow. Consider installing temperature sensors to detect overheating and automate cooling adjustments. Ensure that any system upgrades or repairs align with the original manufacturer’s recommendations and comply with industry standards for safety and performance. Proactive maintenance not only prevents breakdowns but also minimizes energy loss and extends the equipment’s life.
What are the safety considerations when working with 15 kVA transformers?
In the case of 15 kVA transformers, the main safety concern is the potential for accidents during operation. Always remember to turn off the system prior to installing, maintaining or inspecting it. Basic safety measures should be taken, such as using insulated gloves and eye protection, to reduce the risk of electrocution. To minimize the risk of electric shock and damage to the equipment, the transformer must be grounded. Repairs and installations must be completed following the manufacturer’s instructions, electrical codes, and relevant guidelines. Prevent overheating by ensuring cooling systems for the transformer are functioning properly and that there is adequate airflow. Last, conduct periodic maintenance checks for worn-out parts and take steps to mitigate the more severe consequences of these issues.
Electrical safety precautions for transformer handling
De-energize Equipment
Always ensure the transformer is completely powered down and isolated from the electrical supply before performing any maintenance, inspection, or repair work. Use proper lockout/tagout procedures to safeguard against accidental re-energization.
Check for Residual Voltage
Use a reliable voltage-testing device to verify that no residual or stored energy remains in the transformer before starting work. Capacitors and other components can retain charge even after disconnection.
Surge Protection
Install appropriate surge protection devices to shield the transformer and associated equipment from damage caused by transient overvoltages or lightning strikes.
Work Zone Safety
Maintain a clean and organized work area around the transformer. Ensure that tools and electrical conductors are stored securely, avoiding clutter that may lead to accidental contact with live components.
Adequate Training and Supervision
Personnel required to handle transformers must be properly trained in electrical safety practices and possess relevant qualifications. Complex or high-voltage operations should always involve supervision by experienced technicians or engineers.
Fire Hazard Management
Have fire suppression systems or extinguishers rated for electrical fires accessible near the transformer site. Be aware of the risks posed by transformer oil leaks, which can amplify fire hazards.
By implementing these precautions alongside the foundational safety measures, operators can significantly reduce the likelihood of accidents and equipment malfunctions.
Importance of proper grounding and shielding
Proper grounding and shielding are critical to ensuring the safety and performance of electrical systems. Grounding provides a clear path for excess electrical energy, protecting both individuals and equipment from electrical shocks or damage. It stabilizes voltage levels, especially during power surges or faults, reducing the risk of operational disruptions. Shielding, on the other hand, minimizes electromagnetic interference (EMI) by enclosing electrical components with conductive materials. This is particularly important in areas with sensitive equipment, as EMI can compromise functionality and data integrity. Together, grounding and shielding safeguard systems, enhance reliability, and prevent costly failures or hazards in high-voltage environments.
Compliance with UL standards and electrical equipment regulations
Ensuring compliance with UL (Underwriters Laboratories) standards and electrical equipment regulations is essential for safety, reliability, and market acceptance. UL standards are globally recognized benchmarks that evaluate the safety and performance of electrical components. These standards address critical aspects such as fire hazards, electrical shocks, and mechanical risks, ensuring that equipment operates safely under normal and fault conditions.
Meeting compliance often involves rigorous testing and certification processes to verify products meet UL criteria. This not only protects users but also ensures adherence to local and international regulatory requirements, such as OSHA in the United States or IEC standards globally. Manufacturers should perform regular inspections, maintain accurate documentation, and stay updated with evolving standards to remain compliant. Ultimately, UL certification fosters trust with consumers and stakeholders, solidifying a company’s reputation in the industry.
How do 15 kVA transformers compare to other transformer sizes?
Fifteen kVA transformers are typically regarded as medium capacity units with an adequate degree of power output tempered with physical size. They present vastly more capacity than smaller units, such as 5 kVA transformers, which makes them better suited for at least small commercial operations or for more extensive residential systems. On the other hand, larger 50 kVA or 100 kVA transformers are used for more energydemanding industrial facilities or entire buildings. For users that need moderate power, the 15 kVA size is optimal as it comes at a reasonable cost, avoiding the bulk size and high pricing of larger transformers. This makes 15 kVA units versatile and efficient.
Comparing 15 kVA to 10 kVA and 25 kVA transformers
When comparing 15 kVA transformers to 10 kVA and 25 kVA transformers, the differences primarily lie in capacity, application suitability, and cost. A 10 kVA transformer offers lower capacity, making it best suited for smaller-scale applications, such as powering individual machines or small houses. It is more compact and budget-friendly but may not handle heavier loads that exceed its capacity.
On the other hand, a 25 kVA transformer is designed to deliver higher power, making it ideal for larger commercial operations or systems with greater energy demands. While this increased capacity provides versatility for more intensive use, the larger size and cost may not justify the investment for applications where 15 kVA would suffice.
The 15 kVA transformer strikes a balance, offering greater capacity than 10 kVA while maintaining a more compact and affordable profile compared to 25 kVA. This middle-ground option is particularly suitable for moderate energy needs, ensuring efficiency and cost-effectiveness without overloading or underutilizing resources.
When to choose a 15 kVA transformer over other options
A 15 kVA transformer is an optimal choice when your energy needs fall between light and heavy usage, making it suitable for small to medium-sized facilities such as workshops, small-scale industries, or residential complexes. This transformer is ideal when you require more power than what a 10 kVA transformer can provide but do not need the larger capacity or higher cost associated with a 25 kVA transformer. It is particularly effective in scenarios where the connected load is steady and within the transformer’s capacity limits, ensuring reliable performance without risking overloading. Additionally, its compact size and affordability make it a practical solution for businesses looking to achieve cost-efficiency without compromising on power requirements.
Cost considerations and energy efficiency comparisons
When assessing the cost and energy efficiency of a 15 kVA transformer, several factors come into play, including upfront purchase price, installation costs, and ongoing operational expenses. Generally, these transformers offer a balance between affordability and performance, making them a cost-effective option for small to medium-scale operations. Compared to smaller transformers, a 15 kVA unit may have a slightly higher initial investment but provides greater capacity at a reasonably efficient energy output, which offsets the upfront cost over time.
Energy efficiency is a critical aspect, as it determines operational costs and sustainability. Modern 15 kVA transformers are designed with low-loss cores and advanced insulation, reducing energy wastage and improving efficiency under steady load conditions. They often comply with energy efficiency standards such as DOE or EcoDesign, ensuring minimal power loss during operation. When compared to larger transformers like 25 kVA units, the 15 kVA option generally offers better energy efficiency for applications requiring moderate power, as larger units can become underutilized in such scenarios, leading to unnecessary energy losses.
Ultimately, choosing a 15 kVA transformer involves balancing your budget with your power requirements. Businesses and facilities aiming to achieve long-term savings should focus on models designed for maximum efficiency under the expected load conditions.
References
Frequently Asked Questions (FAQ)
Q: What is a 15 kVA transformer and how does it work?
A: A 15 kVA transformer is a power transformer designed to transfer electrical energy between two or more circuits through electromagnetic induction. It typically converts high voltage electricity to a lower voltage, or vice versa, to suit the needs of various applications.
Q: Can a 15 kVA transformer handle both 480 volt and 240 volt applications?
A: Yes, a 15 kVA transformer can be designed to handle both 480 volt and 240 volt applications, depending on the specific configuration and wiring of the transformer. It can be set up to either step down from 480 volt to 240 volt or step up from 240 volt to 480 volt.
Q: What are the differences between single phase and 3-phase transformers?
A: A single phase transformer operates with one phase of alternating current (AC), while a 3-phase transformer uses three phases of AC. 3-phase transformers are generally more efficient and can carry more power over long distances compared to single phase transformers, making them suitable for industrial applications.
Q: How does a delta configuration affect a 15 kVA transformer?
A: In a delta configuration, the transformer windings are connected in a triangle formation. This setup is often used in 3-phase systems to provide a stable and balanced voltage supply, allowing for efficient distribution of electrical power.
Q: Is a 15 kVA transformer suitable for general purpose applications?
A: Yes, a 15 kVA transformer is often used for general purpose applications such as supplying power to small businesses, residential areas, and certain industrial settings. Its size and power rating make it versatile for various uses.
Q: What is the significance of a NEMA 3R rating for transformers?
A: A NEMA 3R rating indicates that the transformer enclosure is designed for outdoor use, providing protection against falling rain, sleet, and external ice formation. This makes it suitable for outdoor installations.
Q: How does a phase isolation transformer differ from a regular transformer?
A: A phase isolation transformer provides galvanic isolation between the input and output, which helps in reducing electrical noise and preventing ground loops. This is particularly useful in sensitive electronic applications.
Q: What is the manufacturer’s warranty period for a typical 15 kVA transformer?
A: The warranty period for a 15 kVA transformer can vary by manufacturer, but it is commonly between 1 to 5 years. It’s important to consult the specific manufacturer’s warranty terms for details.
Q: What should be considered when shipping a 15 kVA transformer?
A: When shipping a 15 kVA transformer, consider the weight, dimensions, and any specific handling instructions from the manufacturer. Proper packaging is essential to prevent damage during transit.
Q: What is the typical amp rating for a 15 kVA transformer with a 480 primary voltage?
A: The amp rating of a 15 kVA transformer with a 480 primary voltage depends on the secondary voltage. For example, if the secondary voltage is 240 volts, the current would be approximately 62.5 amps. Calculations should be based on the formula: Power (VA) = Voltage (V) x Current (A).