High Performance Current Sensing for Automation Applications
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Power Factor Correction Control

With ever increasing demands for electrical power the power generating Power Factor Correction Controlcompanies are beginning to penalize customers with low Power Factors. Low PFs can be considered very inefficient use of electrical energy. A low PF can be corrected by the installation of PF Correction capacitors. Although this can be achieved at the main feeder most facilities, due to multiple varying loads, choose to install PF correction on individual pieces of equipment (like a large motor) or area of plant. When a load is switched off, unless the PF correction capacitors are removed, undesirable over-correction occurs. Sophisticated automatic control systems are available but are very expensive. A simple way to switch a PF correction capacitor bank is to use an NK Technologies’ Current Operated Switch. When the load goes down, for example at night when equipment is not used, the PF correction capacitor is switched out. Then when load returns it is switched back in.

Power Transformer Monitoring

Installing an NK Technologies’ Current Transducer over the conductors on the Power Transfomer Monitoringsecondary of a transformer can be used to alarm if the current draw reaches a critical level. Action can then be taken to reduce the load before the transformer overheats.

Most large power transformers utilize auxiliary cooling fans, drawing cooler air from a distance away from the transformer. NK Technologies’ Current Transducers or Current Operated Switches are used to monitor these fans for overload from bearing failure, under loads from drive component breakage or slippage, and to just be sure that the fan is energized and doing its required job.

Generator Installations

The need for back-up power for critical loads is becoming more and more Generator Installationsapparent to operating and maintenance personnel. Many existing factories and facilities are also adding generators to assist the grid connection supply during times of excessive consumption, or to help the plant ride through periods of peak usage when the utility charges a premium for power. Monitoring the current demand provided from a generator allows for load shedding of non-critical loads when the generator is nearing its capacity. NK Technologies’ Current Operated Switches close when the demand, measured by current, is too high, and by connecting to a controller (like a PLC), less critical loads can be disconnected from the system.

Current Transformer Monitoring

C.T.s (Current Transformers) have been used for many years to measure AC Current Transformer Monitoringamperage. There are many C.T.s installed throughout Electric Utilities, Process Plants and Manufacturing facilities. Typically a C.T. provides either a 1A, or more commonly a 5 Amp AC output on the secondary side. In order to use this signal for a modern control system (DCS, PLC or DDC) or Data Logging System a signal conversion or conditioner device is required to provide an analog DC signal.

C.T.s step down current and the secondary has to feed into a very low impedance to maintain accuracy. In the event that the secondary is open-circuited during operation the device operates as a step-up voltage transformer since there is nowhere for the current to flow and voltages of several kV appear on the secondary, overheating occurs and combustion or explosion often results. NK Technologies’ Split-Core Current Transducers are simply and safely snapped over the shorted secondary of a C.T. to provide a fully isolated analog 4-20mA DC signal proportional to the current in the secondary, which in turn is proportional to the measured (primary) current.

NK’s Split-core Current Transducers are used to safely monitor the secondary of high voltage C.T.s used in power generation and distribution in the low voltage cubicles.

Vacuum Pump Monitor

Vacuum pumps are used in a variety of applications in the semiconductor industry, Vacuum Pump Monitorheat treatment, plastics and packaging industries. By adding an NK Technologies’ Current Transducer over the lead feeding a vacuum pump, it can easily be determined when all the air has been removed from a vessel or envelope. The analog output can signal the vacuum or equipment controller that it is time for the next step in the process. In the case of an automated packaging machine, a drop in current will signal that the package is ready for sealing.

Moisture Ingress on a Submersible Pump Motor

An NK Technologies’ Ground Fault Sensor installed on a submersible pump motor provides Submersible-Pump-Motoran easy to install replacement or addition to moisture sensors housed in the motor casing. Unlike moisture sensors that have to be wired back to the motor control center, the GF sensor is installed in the motor control center. By detecting the ground fault current resulting from moisture ingress or other potentially dangerous condition remedial action can be taken prior to catastrophic failure. Either the pump can be replaced at the next convenient time or switched off and a back-up pump started.

Pump Load Monitoring

NK Technologies’ Current Transducers are used to monitor motor current and Pump Load Monitoringtherefore motor load. The output from the transducer may be fed to an analog or digital indicator or a Programmable Logic Controller (PLC) for more sophisticated monitoring and control.

NK Technologies’ Power Transducers provide load monitoring in more critical applications where the addition of voltage measurement and the determination of the phase relationship between current and voltage (power factor) provides more control.

NK Technologies’ Ground Fault Sensors keep the pumps safe by measuring ground leakage currents as low as 5mA. This also provides an alternative to moisture sensors used with submersible pump motors.

Also see these other articles:
Pump Jam & Suction Loss
Moisture Ingress on a Submersible Pump Motor

Status Alarming

The auxiliary contacts in a motor starter are commonly used to indicate when the Status-Alarmingmotor is running. However, auxiliary contacts only indicate the position of the contactor, not the actual load status. If a downstream disconnect is open (for example, for maintenance) or the contact fails (either sticks or dirt build-up) there can be serious consequences.

At a large fish farm, failed aerator pumps resulted in massive stock losses. Because the auxiliary contacts remained closed when the pump failed, the alarm was never activated, the back-up pumps were not switched on and the fish suffocated due to lack of oxygen. Now NK Technologies’ Current Operated Switches have been installed to provide an alarm signal and a signal to automatically switch over to the back-up aerator pumps.

Closed Loop Control

Normal linear AC induction motors have a current characteristic that increases with Closed Loop Controlload. Thus a measurement of current is proportional to the motor load. NK Technologies’ True RMS Current Transducers are designed to work in conjunction with variable frequency drives (VFD) and measure the current in the leg of the motor.

At an engine block manufacturing facility NK Technologies’ Current Transducers provide the input to a PLC used to position the rotating wire brushes in order to clean away burrs and debris after machining. As the current, and thus the load, changes so the brushes are positioned for optimal clean-up. Similarly Power Transducers are used to control the position of wheel wash brushes in a carwash. Power measurement provides a more linear relationship for motors and other loads with non-linear current characteristics. Current Operated Switches are used to co-ordinate operations between conveyor, washing and drying systems.

DC Motor Installations

Many applications requiring high torque at low speeds, like bridge cranes and log DC Motor Installationscarriages, use DC shunt wound motors. Since it is relatively easy to control the speed of a DC motor by adjusting the voltage to the field windings, precise regulation is afforded to applications like printing press paper feeds or web control of multiple motors in the paper making process. Using an NK Technologies’ DC Current Transducer will provide an analog signal that can be used to keep the motor from over-current situations. Using an NK Technologies’ DC Current Operated Switch will insure that if the motor field supply is lost, the motor will not over-speed to the point of self-destruction.

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