Case Studies
Voltage Transducers Used in Solar Panel Arrays
Designed & Assembled in the USA
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Challenge
Solar Panels (photovoltaic arrays) are used primarily in two ways:
1. To charge batteries that are used to power remote loads where installing a connection to the utility grid would be cost prohibitive, and
2. To energize installations where the DC power is converted to 60 Hz AC power through a solid-state inverter. Monitoring and/or measuring of solar panel output voltage contributes to an efficient solar system output.
Solution
NK Technologies voltage transducers play a critical role in ensuring the efficient operation, safety, and performance optimization of solar panel systems by providing accurate and real-time voltage measurements.
Solar panels generate DC electricity which can vary based on a variety of factors such as sunlight intensity, temperature, and shading. A voltage transducer can be connected to the output terminals of the solar panels to continuously monitor the voltage level. By monitoring the voltage output, system optimization can be achieved. For example, if the voltage drops below a certain threshold, it can indicate a problem is affecting the system like a malfunctioning panel or shading. Detection of these issues allows corrective action to be taken to ensure the energy yield of the system is maximized.
Additionally, monitoring voltage levels can improve the overall safety of the system. If the voltage exceeds the safe threshold limit, it could increase the risk of electrical hazards or even damage the system or equipment connected to it. An NK Technologies voltage transducer can provide real-time monitoring to help prevent unsafe and costly events.
Solar panels may be used to power an inverter and convert the DC input into AC output. Alternatively, the DC input may be used to charge a battery array for later use. In both cases, monitoring the input and output voltages over time will ensure maximum system uptime and efficiency and provide the needed feedback for ongoing system maintenance.
Battery Charging System
Designed & Assembled in the USA
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Challenge
Voltage Sensing, Charging Control, Overcharge Protection, Under Voltage Protection, Fault Detection
Solution
Battery charging systems are utilized in many applications including renewable energy storage, cell towers, electric grid support, and rail transportation. In each of these applications, voltage transducers are a critical component as they allow you to monitor and control the battery charging process. NK Technologies’ line of voltage transducers ensures your implementation is running optimally by providing solutions for voltage sensing, charging control, overcharge and undervoltage protection, and fault detection.
At its most basic function, voltage transducers can be used to measure the voltage of the battery charging system when the voltage transducer is connected to the terminals of the battery being charged. It continuously measures and monitors the voltage across the battery terminals, providing real-time feedback on the battery's state of charge and voltage level. This allows for charging control. Based on the voltage readings from the transducer, the charging system can adjust the current or voltage to ensure optimal charging conditions. For example, if the voltage transducer detects that the battery voltage is low, it signals the charger to increase the charging current until the desired voltage level is reached.
One crucial function of a voltage transducer in a battery charging system is to prevent overcharging. Once the battery reaches its full charge, the voltage transducer signals the charger to either reduce the charging current or switch to a trickle charging mode. This avoids overcharging, which can damage the battery. Conversely, the voltage transducer can also detect an under-voltage condition. This occurs when the battery voltage drops below a certain threshold, indicating that the battery is discharged. In such cases, the charging system can adjust the charging parameters to provide the necessary current and voltage to recharge the battery safely.
Voltage transducers can also be used to detect faults in the charging system or the battery itself. For example, if the voltage transducer detects an unusually high or low voltage reading, it may indicate a problem such as a short circuit, a faulty battery cell, or a malfunctioning charger.
Data logging and analysis can be enabled by feeding the voltage transducer’s analog output to an analog input card of a process control device, such as a Programmable Logic Controller (PLC), Distributed Control System (DCS), or a digital display capable of accepting an analog input. System operators can then track the charging process over time, identify trends, and diagnose potential issues with the battery or charging system. For example, in larger battery charging systems or applications where multiple batteries are being charged simultaneously, a voltage transducer paired with a PLC integration enables automated monitoring, control, and management of the charging process for each individual battery. A properly designed system can then remain online while individual battery cells can be evaluated and scheduled for maintenance or replacement.
Preventative Maintenance Using Ground Fault Monitors
Challenge: There are many industrial applications where monitoring electrical heating elements for leakage to earth is needed. Insulation of electrical apparatus may degrade over time contributing to leakage. When a heating process should not be interrupted until the process is completed, disconnecting power through a ground fault circuit interrupter is not an ideal approach. For example, if the heating process is stopped before annealing parts are brought to the target temperature, they will not be properly hardened and must be scrapped. While letting the process complete is not as safe as disconnecting the offending circuit supply source power, it is certainly better and more cost effective than scrapping the parts.
Solution: NK Technologies provides a smart way to control premature process interruptions utilizing the AGT-FD series ground fault relay. Producing an output signal proportional to this current to earth is a way to monitor deteriorating insulation or direct shorts to ground. The sensor produces a signal which can be read with a panel meter or a programmable logic controller. If the fault current exceeds an allowable level, a limit alarm contact or an output from the PLC can be used to control a signal (audible or visual) letting the equipment operator know a problem is imminent or a hard fault to earth has occurred. The operator can then initiate procedures preventing shutdown of the entire system. With an analog sensor output, there can be multiple alarm points. For example, one alarm would trip if fault current exceeds 10 or 20 mA, while another alarm can trigger when the fault exceeds 50 mA. This allows more extensive action if a higher fault current is detected.
This solution is also ideal for enhancing a preventative maintenance program. Using the same monitoring approach, leakage levels can be established at the point at which preventative maintenance occurs, allowing the offending element to be removed and replaced or another corrective action taken in a cost-effective manner. Additional applications that benefit from this approach include monitoring electric heating processes, semiconductor wafer fabrication, AC motor loads, plastic molding processes, heat trace cable systems, and snow melt protection.
Electrical Heating System Protection
Challenge: The National Electric Code requires that all (with few exceptions) electric heating sources be protected against faults to ground. Combinations of electrical heating systems and moisture can present a challenge in ground fault protection. Insulation systems of heating elements can degrade over time in the face of wide temperature variations, constant expansion and contraction, and wet conditions. In heating applications it is important to balance protecting personnel while minimizing nuisance trips. Disconnecting the circuit is the best protection in both instances, and the faster the circuit can be de-energized the safer the installation.
Typical Electric Heating Applications:
- Heat Trace Cable
- Snow Melt Mats
- Fuel Preheaters
- Plastic Injection Molding
- Drying
- Finish Curing
- Water Heating
- Baking
Solution: NK Technologies has a wide assortment of ground fault relays to achieve an optimal solution based on the application needs. AG series ground fault relays are ideal for lower current applications where a quick disconnect is desired. If there is any current over five milliamps f lowing to ground, the sensor can actuate a contact to close a shunt trip breaker solenoid, or in applications where turning off the offending circuit would create a major problem, the contact can be used to alarm an operator or controller. The AGL and AG-LC series relays makes it possible to monitor conductors carrying over 200 amps (or even larger circuits) for applications with larger heating requirements. NK Technologies also manufactures ground fault sensors designed to produce an analog signal directly proportional to the fault current. This output can to identify areas where insulation is failing, allowing the user to take corrective measures before equipment is damaged. This range of product allows the designer to optimize the solution that best fits the application requirements.
How to Detect DC Current Leakage to Earth
Challenge: Detecting low level AC current without adding a physical connection and added burden to the circuit is relatively easy and quite common. In North America, all electrical outlets mounted in wet environments are required by codes to be protected with ground fault relays to save lives by cutting the power when a very small fault to earth is detected. If an AC current of 5 to 7mA passes to the ground, a circuit breaker or the contacts in the power receptacle open before electrocution can occur. Most electrical heating elements must also be protected to keep equipment from damage in the event of a ground fault.
Trying to detect the same fault condition in a DC circuit with a floating ground is not as simple. With the proliferation of photovoltaic panels and other alternative power sources, the need for ground fault relays in DC powered systems is critical. With solar panels or battery-operated systems, the positive and negative conductors are insulated to contain the voltage potential between each and also to earth. When connections get wet, this insulation becomes compromised and current can pass to earth. Water is the most common cause of DC fault current, while deteriorating insulation and contaminants on battery housings are additional factors. Since DC current leakage to earth presents a dangerous situation, detecting a fault before it causes harm is essential. Ground fault detection without adding impedance to the monitored circuit is the safest approach.
Solution: NK Technologies developed an innovative solution to DC ground faults that employs the same zero-sum principles as its AC offerings. The DG Series DC ground fault relay, used with loads drawing 50 amps or less, can be incorporated at a fraction of the cost of the typical and cumbersome hardwired installations.
How to Detect Ground Faults in Semiconductor Fabrication Equipment
Challenge: Fabricating silicon wafers into semiconductor chips involves many hazardous chemicals and extreme heat that must be precisely controlled. The SEMI standard S22-071b provides guidelines regarding the safety of semiconductor processing equipment, including Emergency Mains Off (EMO) circuitry design. This requires that if any problem occurs during processing, the operator can easily disconnect main power. With electrical heating elements used throughout the fabrication equipment, ground fault protection is paramount. As the elements are monitored in each process segment, ground fault relays are set at a fairly low trip point. As a fault to earth through the heating element occurs, relays will selectively shut down only that part of the process. During a situation where several heating processes short at once, a relay with a bit of delay and higher trip point will shut off the main power feed.
Solution: NK Technologies wide range of ground fault relays are ideal for the semiconductor manufacturer, allowing optimization of each portion of the fabrication process while protecting machine operators and minimizing or eliminating potential damage to expensive materials. AG ground fault relays and AGL ground fault relays with adjustable setpoint and delay will help manage the controlled shut down of the system in case of critical failures.
Adjustable Ground Fault Circuit Interrupter Solutions for Commercial Kitchens
Challenge: The NFPA NEC 2017 Sec. 210.8 requires electrically operated commercial kitchen equipment with “single-phase receptacles rated 150 volts to ground or less, 50 amperes or less, and three phase receptacles rated 150 volts to ground or less, 100 amperes or less” to have GFCI for personnel protection installed. Prior to this change, only 15- and 20-Amp single phase circuits of 125 volts or less needed this level of ground fault protection, with circuit breakers and receptacles meeting this requirement being readily available and quite common. Requirements above 20 amps or needing three-phase protection is a more difficult issue.
Additionally, commercial kitchen steamers and grills sometimes retain humidity while stored prior to installation. To address this issue, units must be “burned in” or energized for a minimum of two hours prior to normal use. The additional moisture present during this process increases the ground fault leakage to a point above the 5-mA desired trip level. To avoid nuisance tripping during the burn in cycle, a ground fault relay needs to allow a temporary increase in the setpoint.
Solution: The NK Technologies Tri-Set relays offer adjustable capabilities as a standard feature. A factory placed range jumper is installed at the highest setpoint (30 mA) allowing the equipment to operate as required during the initial burn-in period. Once the burn in cycle is completed, the relay can be readjusted to accommodate the desired ongoing 5 mA setpoint. Because of their rugged solid core design and wide operating temperature range capabilities, AG and AGL ground fault relays work well in this environment.
Ground Fault Detection for High Current Circuits at Marina Docking Facilities
Challenge:
Recent updates to NEC Code 555 require Marina owners to consider ground fault protection at both the individual slips and at the power distribution center feeding the separate branches to each slip’s power pedestal. Typical power feeds now require relays that can handle conductors carrying more than 300 amps necessitating the solution to involve additional components.
Solution:
To address this problem, NK design engineers developed a relay with an aperture measuring four inches in diameter allowing conductors (carrying 800 amps or more) to easily pass through the relay. These large aperture AG-LC relays can be used to monitor the main feeding circuit to the pedestals and to energize a shunt trip breaker protecting the entire docking facility. Additionally, the smaller aperture NK Technologies AG Series relays can be used to monitor individual power pedestals at each slip, with the relay output energizing a shunt trip breaker circuit at the pedestal.