Safe converters for the Aquaretum fountain in Lake Zurich
Since mid-May 2019, the new fountain in Zurich's lake basin has been delighting onlookers from all over the world. Since, despite the ban, people on the waterway can marvel at the structure from close up, personal protection must be fully guaranteed at all times. With the NFO sine wave inverter used, the spectacle can be reliably operated at the FI circuit breaker. No bearing currents are generated and thus safe operation without failures is guaranteed.
The water feature leads a "life of its own
The sequence of the fountains is not programmed, but maps the seismic activity of the earth's layer. An algorithm choreographs the signals from the ETH earthquake observatory in real time.
Despite the ban, people on the waterway can marvel at the construct from close up, so personal protection must be fully guaranteed at all times. For this reason, each individual pump must be protected with a residual current circuit breaker (<30mA) in the motor cable without delay. Commercially available PWM frequency converters can cause strong sources of interference and are primarily designed for industrial networks.
The making of the Aquaretum
Limitations of commercially available frequency converters
Commercial PWM frequency converters are very strong sources of interference and are designed for industrial networks. Reliable operation of the aquaretum with PWM inverters in combination with residual current circuit breakers is not possible.
Pulse width modulation (PWM) produces switching frequency harmonics with large amplitudes in higher frequency ranges. The motor cables with grounded shielding act like capacitors, through whose capacitance the high-frequency currents flow to ground. The residual current circuit breaker cannot distinguish between fault currents (high resistive component) and leakage currents (mainly capacitive). Under certain circumstances, it could repeatedly lead to the failure of individual pumps and thus to the failure of the entire system.
NFO sine wave inverter for highest requirements
Elektron AG supported the project management in its search for a suitable solution for the pump drive and found a device in the NFO sine wave frequency converter that meets and even exceeds the high requirements for personal protection.
Due to the patented sine wave inverter technology and the associated, low arrester currents (< 2mA), reliable operation at the residual current circuit breaker is easily possible without the use of additional filters and the personal protection of the aquaretum is guaranteed at all times. Since the sinusoidal frequency converters do not generate any bearing currents, failure of the system due to bearing damage can also be ruled out.
The technical room, where the entire control system and also the frequency converters are mounted, is centrally located about 175 m away from the fountain and the pumps. No shielded cables are required to operate the NFO sine wave inverters and there is no limitation in cable length. There is also no need to use sine wave and line filters that are matched to the application and are usually very expensive. Cost-efficient installation can be achieved due to the low material requirements and the additional components that are not necessary.
We would like to thank our project partners Pumpen Lechner, Fischer Architekten and all others involved for the great cooperation!
