Protecting electric drive motors and preventing excess temperatures, damage to windings, and motor fires
The high start-up currents that occur during start-stop operation can push the temperature of a motor up to critical levels, especially when starting under heavy loads.
An extreme example is a blocked armature. This can be caused by things like excessive load that prevents the motor from starting to turn. The incoming electrical energy which is normally converted into movement is dissipated in the form of heat in the stator and rotor. The temperature inside the casing quickly rises to a level that can be critical for the windings.
By building temperature sensors into the motor windings and using an INT69 motor protection relay for cable winches, slewing gear, and running gear, any such scenario is detected and the motor is shut down in the event of a fault.
What only Kriwan can achieve is to reliably detect a case of blockage by measuring temperature, before the motor’s temperature reaches critical levels. According to the Montsinger rule this significantly increases the lifespan of motor windings. Switching a motor back on again too soon after an emergency shut-down is prevented by means of a fixed re-start delay.
As well as fitting temperature sensors to the motor windings, the motor can also be monitored by means of current measurement. This method is often used, especially on large motors in which the armature plays a critical role, because in such motors the temperature of the rotor rises more quickly than the temperature in the stator windings. KRIWAN INT89 motor protection relays with current sensors possess the significant advantage of being tamper-proof and having a built-in data memory (diagnostics).
Protection against overload and heavy starting by means of current measurement
Cranes are built to transport and position goods.
It can easily happen that a crane is unable or barely able to lift goods on account of its surroundings, its previous operation, or a load which is simply too heavy.
It may be best to allow such overloads for certain periods, depending on the application, but if they persist over a longer period they can severely burden the motor and cause serious damage.
That is why the INT89 measures the electric current in windings and responds according to securely set parameters. These latter are defined beforehand to achieve an optimum balance between protection and availability.
Protecting mobile, lattice boom, and revolving tower cranes against excessive winds
In applications in which cranes are exposed to windy environments it is advisable to use sensors to record wind speeds. For example, strong winds can cause uncontrollable load movements on construction sites. This increases the risk of loads hitting buildings or high-voltage electrical cables. Cranes can also become unstable in excessive winds and even fall over. In some countries there are therefore regulations governing the use of wind sensors on cranes above certain heights or booms over certain lengths.
By permanently measuring wind speeds using KRIWAN’s high-end anemometers, cranes can be moved into a safe position before it is too late.
Various structurally adapted wind sensors can be used for different kinds of crane so as to reliably avoid incorrect measurements. For mobile cranes and crawlers whose angle of tilt and rotation can change, KRIWAN has developed pendulum vane anemometers that automatically and accurately correct themselves using gravity.
What sets KRIWAN’s anemometers apart is the special design of their casings and electronics to cope with the toughest environments, ensuring top performance for years on end. These products have been proving their worth under extreme conditions for many years. Take heavy dust loads for instance, which occur especially frequently when loading and unloading bulk materials in places such as ports, construction sites, open-cast mines, and some parts of Asia. KRIWAN’s sensors have also proven themselves thousands of times over in other highly challenging settings such as wind turbines and mountain facilities.
- High IP protection categories
- The sensors are immune to interference by mist, rain, dust, and foreign objects
- Wear-free measurement
- Top quality metal casings – ensured by corrosion-testing prior to series approval using special salt-spray tests involving harmful gases
- Alloy quality constantly assessed using x-ray spectrography
- Electronics highly resistant to electromagnetic interference caused by indirect lightning strikes
- IP protection category can easily be optionally upgraded
- Long operating life, precise, wear-free measurement, and high-grade bearings
- All bearings acoustically and mechanically routine-tested before delivery