2/2018 | MONITOR | 11 NEWSWORTHY | BUI LDING TECHNOLOGY To evaluate the power quality of a shopping centre, you need to have a true r.m.s. measuring device (True RMS) that is capable of recording, analysing and evaluating several parallel measurements such as currents, har- monic voltage, interharmonic voltages, asymmetry of the power supply, power frequency, flicker severity and voltage fluctuations over extended periods of time and to very high levels of precision. In this investigation of power quality to DIN EN 50160 (measurement to IEC 61000-4-30 Class A), a Bender PEM735 measuring case was used. The shopping centre is supplied with power by three local network transformers, each with the same power rating. A PEN bridge can be seen between the PE and N bus bars on all low-voltage main distribution boards (LVMD). The system type from the transformers to the LVMD is a TN-C system and it was established from the LVMD to all outgoing circuits in the form of a TN-S system. For this reason, the entire system type of the shopping centre is a TN-C-S system. “Nowadays, this system type is not suitable because it no longer satisfies the current standards or specifications of modern protective measures against electric shock”, explains Jörg Steffen, the proprietor of Jörg Steffen Ingenieurgesellschaft mbH. FIRE AFFECTING the safety lighting of a shopping centre It is not uncommon for old existing low-voltage networks in office or busi- ness buildings to be subjected to extra loads from additional consumers. There is a great need for action to investigate this because fires can occur easily. Safety can be achieved by retrofitting Bender’s power quality and residual current monitoring systems to the mains power monitoring system in existing distribution systems. Jörg Steffen Ingenieurgesellschaft, a German engi- neering company in the building technology and facility management business, recently experienced a fire in the safety lighting system of a shopping centre. A short while before, as the subject of a Masters dis- sertation entitled ‘Investigation of a low-voltage network in a shopping centre with reference to: power quality, load flow and short circuit’ [translation], the low-voltage network of this building complex was subjected to close scrutiny. Jörg Steffen