Location: Ahaus, Germany

Segment: Machine building

Challenge: Generate mobile power whilst simultaneously ensuring secure supply for agricultural operations in the event of an outage.

Solution: The NZMN2-VE250 generator circuit breaker effectively measures the generator’s actual power consumption, which limits the period during which it can run at a load capacity of up 110 % to one hour.

Results: The generator circuit breaker protects the generator and thus the connected equipment from physical and financial damage. By adjusting the tripping current and time lag, this circuit breaker can be used to safely start and operate high-performance systems until they are switched off.

The circuit breaker not only protects our generator against overloads and short-circuits, it also prevents harm to humans or the farm’s electrical systems.

Hermann Kemper, Zapfwellenaggregatebau Kemper.


A power outage may have devastating effects for livestock farmers, with considerable financial implications. In the event of a power outage, they need to make sure that their automatic milking, heating, feeding and ventilation systems continue to operate. As such, the German Animal Welfare and Livestock Regulation [Tierschutz-Nutztierverordnung] stipulates that farms must be equipped with alarm systems for power outages. Additionally, they should also have a stationary or mobile emergency power generator at the ready.

In agricultural operations, tractors have to be constantly available, which is why power take-off units powered by emergency generators are widely used. Given their mobility, power take-off units can ensure emergency power supply for the farm in the event of a grid outage, in addition to their availability at any location. Zapfwellenaggregatebau Hermann Kemper (Kemper) is a German company that specialises in manufacturing mobile emergency power generators.


The process of starting up a conventional emergency power generator is not always smooth, which may cause irreparable damage to the electronic devices used to control and regulate agricultural operations. For instance, malfunctions may be caused by frequency fluctuations in the emergency power generator. And while the miniature circuit breakers used in domestic power lines can handle overloading by a factor of 5 to 10, in an emergency power generator, this is limited to double the nominal power supply.

The conventional overload protection systems for domestic service lines (for instance, safety fuses and B- or C-type circuit breakers) do not provide sufficient overload and short-circuit protection when connecting the emergency power generator to systems with high energy consumption, such as slurry mixers or hammer mills. In the event of a short circuit caused by overloading, the generator housing can become live. In this case, the installed miniature circuit breakers would not be able to respond quickly enough due to the rapid voltage drop. In order to prevent thermal and mechanical overloading of the generator, which may even cause a fatal electric shock, emergency power generators require a special safeguard that will also secure safe power for the farm in the event of a power outage.


Kemper has made it its mission to develop especially durable emergency power generators. These must be forgiving of any operating errors and, most importantly, need to protect agricultural operations against damage from short circuits and overloads. To this end, the company has developed two special generators (with 75 kVA and 150 kVA, respectively), each with its own gearbox aligned to the specifications of modern tractors. This means that the engine will have no trouble compensating for higher loads produced by other connected systems.

To ensure that the generator starts up reliably and safely, Kemper has equipped its power take-off unit with the NZMN2-VE250, a generator circuit breaker from Eaton's Moeller series. With this circuit breaker, high-performance systems can be safely started up by adjusting the tripping current and time lag. During this process, the setting range for the overload trip units is specified at between 125 A and 250 A. The short-circuit trip with short-time delay can be set between 2 and 10 times the value of the overload trip unit, with the short-circuit trip responding instantly at 3,000 A. For the Kemper emergency power take-off unit, the overload trip units were set to the generator's nominal voltage of 220 A. The short-time delay trip is used to suppress short-time current peaks, such as those that occur when starting up an engine. Kemper programmes the circuit breakers in such a way that they trip within 20 ms if the load reaches double the nominal power output of the emergency power generator.

In addition, the devices are able to recognise the generator's actual power consumption by continuously measuring the relevant values. Together with the thermal memory provided by the electronic trip unit, this ensures that the generator can only be run at a load of up to 110 % for a maximum of one hour. Should the generator heat up due to overloading, it then has to run in normal operating mode for at least five hours in order to cool down again. Should the current-time values and therefore the temperature reach unsustainable levels, the generator circuit breaker will trip to protect the system against damage. Since the circuit breaker responds even if minor short-circuit currents occur, the wires to the terminal point are also protected. This effectively prevents fires due to overloading.

In principle, after tripping, the circuit breaker can immediately be put back into service by performing a reset. If, however, the overload persists for a longer period of time, the thermal memory will prevent the circuit breaker from being reset straight away. The circuit breaker will then trip to allow the machine to cool down. The thermal memory will trigger this cool-down phase based on the duration and intensity of the overload, in order to protect the machine components.

Kemper commissions its emergency power generators on site to ensure that they operate reliably and fault-free. It also checks their compatibility with existing tractors, the readiness of the switching and protection devices, and the ability of the power take-off unit to operate the entire agricultural machine at full load.


The generators are equipped with an Eaton generator circuit breaker as standard, which provides a broad and versatile setting range. It protects not only the generator, but also any connected electrical systems and all electronic control systems against overloads and short-circuits. In the event of any fault, this reduces the risk of fires and the build-up of dangerous contact voltages.

"Safety is our utmost priority," says Hermann Kemper, the company's managing director. "From our perspective, this means providing maximum protection for humans, animals and infrastructure. In this, Eaton’s established generator circuit breakers play an important part, and we have therefore incorporated them as standard in our emergency power generators for many years. And it is not just the product itself that convinced us: Eaton also offers outstanding advice and service."