Protecting electrical pump motors and preventing excessive temperatures, damage to windings, and motor fires
During normal, long-term operation, the temperature of a pump’s motor remains very constant and generally does not present a problem. However, there are a range of factors outside of the normal scenario that can cause damage to a pump and even its environment (process or plant).
During start-stop operation, the high (start-up) currents that occur when the pump is being switched on can increase the temperature in its motor. If it is switched on and off frequently, this temperature can rise to a critical level and endanger the windings.
An extreme example is a blocked armature. This can happen because of things like foreign objects in the fluid. The electrical energy fed into the motor, which is usually converted into motion, is dissipated as heat in the stator and rotor – and the temperature can quickly reach critical levels.
Overheating can also be caused by insufficient cooling in the pump due to a lack of fluid (running dry) or reduced ventilation, and problems with thermal discharge.
All of these scenarios are reliably detected by temperature sensors embedded in the motor windings. The INT69 motor protection relay evaluates these sensors and the pump’s motor is quickly and reliably shut down in the event of a fault.
KRIWAN possesses the unique ability to quickly and reliably detect a blockage by means of thermal measurement – and can do so long before the windings reach the temperatures defined as critical. This significantly and effectively reduces any overshooting of the temperature in the windings. It is a function which, in compliance with the Montsinger rule, allows the motor windings to last many times longer.
Protecting pumps against running dry by means of current measurement, fluid sensors, and conductivity measurement
Pumps are designed to convey fluids. The cooling and lubricating effect of these fluids is taken into consideration when designing the mechanical components.
If unintended situations arise such as running dry, this can damage the system if it is not protected and can have a very negative impact on reliability and operating life.
Running dry can be detected in three different ways, depending on the protective relays used. In many instances it can be detected by measuring electric current in the motor windings, or by integrating a level sensor into the suction side which can differentiate between gas and liquid.
Optical sensors for single-point measurement of the fluid level offer very high resistance to temperature, pressure, and media. They are available in various different versions with signal outputs allowing them to be integrated into the INT69 protective relay or a PLC, or switching outputs for use as stand-alone solutions which autonomously switch off and protect pumps if they run dry.
The third way of detecting running dry is to measure conductivity in electrically conductive fluids (such as water). This too differentiates between liquid and gas (air) at the pump’s suction inlet.
Reliable phase monitoring of pumps
Pumps cannot work without electric current. But the quality of electrical power supplies in different countries can vary a lot. Pumps intended for global use should therefore be protected against the dangers that can be caused by electrical network problems.
Risks include undervoltage, asymmetries in the network, and phase failure. These can cause unwanted heating in the motor and irregular operation, and can reduce a pump’s operating life. The motor’s direction of rotation is also very important in many pumps. Depending on the design, incorrect rotation can reduce conveying performance or even destroy machinery.
With its INT69 Y platform, KRIWAN has created a solution for any pump fitted with a three-phase motor and connected to a three-phase supply network. The INT69 reliably monitors all three phases, immediately shutting down and protecting the pump in the event of phase asymmetry, failure, or fault.
KRIWAN phase monitors also monitor direction of rotation, phase asymmetry, and undervoltage. Past readings are documented in the protective relay and can be downloaded as statistics to more easily identify the causes of problems on site.
Sensors for the continuous measurement of the temperature of liquids, gases, and components
Motors in pumps have to be protected against overheating. To achieve this, temperature sensors are embedded in their enameled copper wire windings and evaluated by protective relays or PLCs.
Another critical component that is worth monitoring are the bearings, because an increase in temperature caused by increased friction or mechanical wear can be an early sign of damage as it happens.
It can also be expedient to measure the temperature of liquids and gases in order to protect downstream components, ensure operational safety, and avoid unwanted thermal reactions. For this purpose the actual measuring element, such as a Pt100 or PTC, is encapsulated in a pressure-proof metal casing. This unit can then be immersed in the medium to measure its temperature directly.
KRIWAN offers a wide range of PTC, NTC, Pt100, and Pt1000 sensors with which to continuously measure temperatures. Fully automated quality control at each stage of production combined with documentation of results help these sensors to set quality standards that place them among the best products available. Our PTC sensors are produced in a globally unique fully automated production facility operating at the highest level. That is the reason why many leading electric motor manufacturers have been relying on KRIWAN sensors for decades.