Universal tool for residual current monitoring. Smart Energy & Power Quality Solutions

Transcription

1 Smart Energy & Power Quality Solutions Universal tool for residual current monitoring

2 Janitza electronics Ethernet level (TCP/IP) Server SQL database Client 1 to... Mobile Web server Grid visualisation software ProData UMG 512-PRO UMG 509-PRO UMG 96RM-E UMG 604-PRO UMG 605-PRO Feld bus level (e. g. Modbus RTU) UMG 20CM ProData UMG 104 UMG 96RM UMG 103-CBM Analogue- / Status- / Pulse input level Water meter Status message Gas meter Alarm lamp Temperature measurement UMG 508 / UMG 604 = Janitza power analyser UMG 512 / UMG 605 = Janitza power quality analyser UMG 96RM / UMG 96RM-E / UMG 103-CBM / UMG 104 = Janitza multifunctional measurement devices for energy measrument technology UMG 20CM = Janitza Residual current monitoring (RCM) and energy data acquisition Press contact:: Janitza electronics GmbH Ms. Stefanie Hollingshaus Manager marketing communication Vor dem Polstück Lahnau Germany Phone: Fax: stefanie.hollingshaus@janitza.de Web:

3 Whitepaper AN1030/V01 Author Dipl.-Ing. (FH) Gerald Fritzen Key Account Manager Janitza electronics GmbH Increased safety, increased system availability, reduced risk of fire An insulation measurement is required for the repeat testing of fixed electrical systems per DGUV V3, for which the system must be switched off. Production processes and administration processes are interrupted. This means an increase in work and often also significant costs. In order to avoid this, the standards offer an alternative: Continuous residual current monitoring, with which it is also possible to locate faults faster. With continuous RCM monitoring, it is possible to avoid shut-downs and minimise test work. Constant checking of the system takes place, which enables the immediate detection of faults. Conventional recurrent testing is unable to guarantee this. Faults are often detected only after years have passed. Highly automated production systems, computer centres and systems with constant processes (e.g. food sector, cable fabrication, paper production) require a reliable power supply - often even high availability, i.e. an availability of at least 99.9%, frequently even %. If availability of 99% sounds extremely good then it is necessary to consider that this equates to a failure time of 87.7 hours, in comparison to 0.53 minutes with the six nines ( %). The numerous servers, automation systems, lifts, safety systems, communication devices, storage media and network components do not generally tolerate voltage interruptions or undervoltage > 10ms. A basic precondition for all further measures is a reliable installation. TN-S systems are state-of-the-art and are also prescribed in the majority of critical applications. In contrast to the previously customary TN-C systems, they exhibit more favourable EMC characteristics for example. Additionally, they enable residual current monitoring (in 3

4 checking for residual currents in TN-S systems. With a comprehensive RCM system, faults in TN-S systems are located directly. So that the user is able to react before a critical level is reached. It is also possible to avoid shut-downs due to residual current circuit breakers (RDCs). This applies in particular to quietly rising residual currents (e.g. triggered by an insulation fault), overly high operating currents or any other overloading of system parts and consumers (image 2). Image 2: Principle of residual current monitoring. short RCM), as illustrated in image 1. RCM measuring devices such as the UMG 96RM-E / UMG 509-PRO / UMG 512-PRO / UMG 20CM from Janitza are suitable for monitoring alternating currents, pulsing DC currents per IEC/TR ( ) and can be used for continuously RCM the functionality The basic functionality of the residual current principle is shown in image 3. Here, the phase and neutral conductor of the protected output are fed through the summation current transformer, the ground wire is left out. The image provides a better overview due to the highly simplified wiring. In practical terms, all three phases and the neutral conductor run through the summation current transformer. In case of systems without a neutral conductor, for example with controlled drives, only the three phases run through the summation current transformer. If the system is in fault-free condition, the summation current is zero or close to zero (within a Image 1: Modern TN-S systems exhibit more favourable EMC characteristics than the old TN-C systems. 4

5 Image 3: Report prior to switching off an aim of residual current monitoring. Image 4: Defective motor insulation leads to a short circuit to ground and residual current against the PE phase. tolerable range), meaning that the current induced in the secondary circuit is also zero or close to zero. If, however, residual current flows away to ground due to a fault, the current differential in the secondary circuit will result in a current being logged and evaluated by the RCM measuring device (image 4). Modern RCM measuring devices accept different threshold value settings here (image 5). A static threshold value has the disadvantage that it is either too high with a part load, or too low with a full load, i.e. either insufficient protection is provided or erroneous alarms are issued, which may have negative effects on the attentiveness of the monitoring personnel over time. For this reason it is advisable to use RCM measuring devices with dynamic threshold value formation. In this case the residual current threshold value is formed on the basis of the actual load conditions and is therefore optimally aligned with the respective applicable load (image 6). Through parameterisation (i.e. stipulation of the typical residual current in "GOOD" condition) of the system in new condition and constant monitoring, all changes to the system state after the point of start-up can be detected. This also enables detection of creeping residual currents. On the basis of historic progressions of the load and residual current, it is possible to determine the GOOD condition and define an expedient residual current threshold value. Integrated measuring device storage and superimposed SCADA systems or the energy data acquisition software GridVis facilitate chronological statements and analyses. Image 5: Comprehensive configuration options for RCM threshold value formation (e.g. dynamic threshold value formation) in the energy data acquisition software GridVis. Image 6: Parameters of residual and operating current monitoring. 5

6 Source EMC manual: Wilhelm Rudolph Table A2 per IEC 64/1120/CDV: Orientation aid: Examples for maximum ground wire / residual currents with AC voltage Equipment (devices) from protection class I: Current consumer for connection via connector devices up to and including 32 A: For rated currents I_n of devices: Maximum threshold values of the ground wire currents: < = 4 A 2 ma > 4 to > = 10 A 0.5 ma / A > 10 A 5 ma Current consumer with fixed connection, without special precautions for the ground wire or current consumer with connection via connector device for over 32 A For rated currents I_n of devices: Maximum threshold values of the ground wire currents: < = 7 A 3.5 ma > 7 A to < = 20 A 0.5 ma / A > 20 A 10 ma Image 7: Threshold values are empirical values, and must be stipulated depending on the type of consumer. Orientation aids are provided by works such as the EMC manual from Wilhelm Rudolph. RCM in practice Listing every standard and specification that has been written in relation to RCM would go beyond the purpose of this contribution. However, a number of general rules do serve as starting points: For example, work with individual current circuits should continue to take place with fixed threshold values such as 30 ma, or with a fire protection objective with 300 ma. With frequency converters, the maximum residual currents in the datasheets should not be exceeded. The following always applies: Threshold values are empirical values, and must be stipulated depending on the type of consumer. Orientation aids are provided by works such as the EMC manual from Wilhelm Rudolph (image 7). It is also necessary to select the right residual current acquisition equipment. The table in image 8 provides an overview. The challenge of high availability A typical application for RCM systems is the computer centre. IT technology itself places high demands on the supply, frequently even requiring high availability, i.e. an availability of at least 99.9 %. However, particularly critical are applications in which the loss of data simply cannot be allowed to occur. BITKOM therefore writes the following in its guidelines for "Operationally reliable computer centres": In computer centres the maximum availability requirements apply. The energy supply must therefore be permanently guaranteed. Therefore comprehensible is the requirement that the power supply to the computer centre itself, and to all areas in the same building to which data cables run, must be designed as a TN-S system. Essential for assured operation is permanent self-monitoring of a clean TN-S system and the issue of signals to a permanently manned desk, e.g. in the control centre. The electrician then ascertains the action requirement based on the respective signals, and is able to prevent damage through targeted service measures. With the Janitza complete solution, it is possible to realise the safety criterion "RCM residual current monitoring" of this type of EMC-optimised TN-S system (image 9). Reduced testing costs with RCM RCMs not only ensure the maximum in safety, they also help to reduce costs. Recurrent testing, as prescribed for example in DGUV V3 Electrical systems and operating equipment, is time-intensive and therefore costly. RCM monitoring systems reduce test costs and save time, whilst also ensuring increased safety. Fixed electrical systems and operating equipment are considered to be monitored constantly if they are permanently maintained by electrical engineers and tested by measuring equipment within the framework of operations (e.g. monitoring of the insulation resistance). Through permanent RCM measurement, monitoring systems are able to deliver the required degree of constant testing. 6

7 Application Type of residual current Form of residual current Installation location Correct function with 1 Ohmic consumers, resistance heaters, electric bulbs, purely inductive and capacitive consumers, lighting systems with conventional ballast and transformer, direct-start motors with no electronic control and regulation, etc. Sinus-form alternating current No longer topical because systems with such equipment are now rare Type AC Alternating current-sensitive Single-phase electronic devices, and devices with electronic control and regulation, such as: Power units, computers, TV, printers, UPS, lighting systems with electronic ballast or electronic transformer, dishwashers, washing machines, microwaves, single-phase drives, heat pumps, circulation pumps, etc. Single-phase dimmers and devices with phase angle or trailing phase control Single-phase electronic devices operated in a three-phase network, split into phases (2 + 3) (a low DC component arises due to a superimposing of pulsing residual currents) Pulsing alternating current (positive or negative half-wave) Phase angle-controlled half-wave currents Phase angle from 90 el Phase angle from 135 el Pulsing alternating current superimposed with smooth DC current of max. 6 ma All areas, in particular single-phase e.g. apartments, small offices, etc Standard switch for modern household Type A Alternating current + pulse current-sensitive 5 6 Devices with three-phase current bridge circuits and pure DC current systems, e.g. photovoltaic systems (on the collector side) Regulated three-phase drives (FC), e.g. regulated three-phase motors (heat pumps, circulating pumps, etc.), three-phase UPS systems, three-phase dimmers, medical three-phase devices (computed tomography, X-rays, etc.), etc. Smooth DC current High frequency up to 1000 Hz and higher Industry, in particular 4-pole, with PV systems also 2-pole DC and in all systems in which pure DC residual currents may arise, e.g. construction site Type B Alternating current + pulse current + DC current = All-currentsensitive Image 8: Overview of types of residual current circuit breaker and their application. 7

8 Under certain preconditions, it is also possible to avoid RCDs with continuous RCM monitoring. These are: Signal connection and immediate reaction in case of a fault Function testing of the signalling equipment Electrician on site Plugs inaccessible to laypersons The following always applies: Residual current monitoring devices (RCMs) are not protective devices, however they may be used to monitor residual currents in electrical systems. Residual current monitoring devices (RCMs) emit an audible or an audible and visible signal if the predefined residual current value is exceeded. Image 9: Constant 3-in-1 monitoring (EnMS + PQ + RCM) of an EMC-optimised TN-S system. New draft standard for recurrent testing DIN VDE : / IEC Low voltage electrical installations Part 6: Verification Extract: Recurrent testing Where circuit is permanently monitored by an RCM in accordance with IEC or an IMD in accordance with IEC , it is not necessary to measure the insulation resistance if the functioning of the IMD or RCM is correct. Potential savings: Reduction in the test costs due to omission of the insulation measurement Avoiding a system shut-down enables constant operation No shut-down of sensitive consumers, which could be damaged by a high test voltage No high personnel costs and administration work due to shut-downs Permanent testing for residual currents = improvement in EMC and minimisation of faults in controls and data lines (See: VDE and / VDS2349 and 2046 / TRBS1201 / DGUV V3 / New draft standard for recurrent testing DIN VDE : / IEC ) Particularly noteworthy here is that RCM renders the cost-intensive measurement of insulation resistances at least partially superfluous, whilst constant testing of the insulation characteristics takes place. In order to carry out conventional insulation measurements, fixed systems and consumers must be switched off. Furthermore, there is a risk that the high test voltage used for the insulation measurement may damage sensitive electronic components. The test accuracy and scope can be significantly reduced by constant monitoring. However, this must be determined on an applicationspecific basis. Acceptance and risk evaluation of comprehensive RCM monitoring by an expert or the employers' liability insurance association is advisable, although not mandatory. It is also explicitly noted at this point that the following work must be carried out despite constant RCM measurement: Visual inspection for externally visible defects Protective measures and switch-off conditions Loop resistances and testing of the continuity of ground wires Function tests 8

9 Association of insurers requires RCM The VdS has said the following on the subject of power supply systems: "In the case of power supply systems with PEN phase, operational currents - which may cause damage - flow through the entire ground and potential equalisation system (see section 3.3). With new electrical system installations it is therefore necessary to plan TN systems as TN-S systems. In the case of existing TN-C systems, modification to a TS-S system is advised. TN-S systems must be realised from the supply (handover) point where possible. In order to guarantee the functionality of a TN-S system on a permanent basis (no conductor short between the N and PE phase, interchanging of the N and PE phase) this must be monitored by a residual current measurement device (RCM). If the set trigger value is reached, a perceivable optical and acoustic error signal must be issued, in order that the defect can be eliminated immediately. In order that signal issuance is successful, this should be sent to a manned desk where applicable. If signalling is dispensed with then the forced shut-down of the faulty current circuit is required..." Planning residual current monitoring Planning can be roughly divided into the following steps: Risk estimation Stipulate measuring points (with residual currents, it must be possible to quickly locate fault sources) Construct measurable distribution systems Label CGP and test points clearly Stipulate, document and set threshold values Stipulate two autonomous signal routes (signal on site, signal in a permanently manned control centre) Test signal routes by imprinting faults (function testing) Train personnel on site (actions in case of a fault) Acceptance by an expert is advisable Image 10: Comprehensive RCM monitoring of the power supply takes place at all levels: From CGP and outputs requiring monitoring in the LVDS, subdistribution systems, right through to individual critical loads. 9

10 Summary and outlook Comprehensive RCM monitoring of the power supply takes place at all levels: From CGP and outputs requiring monitoring in the LVDS and sub-distribution systems, right through to individual critical loads (image 10). However, RCM is a monitoring measure through which to ensure a reliable power supply. Janitza has its UMG 512- PRO (image 11), UMG 96RM-E and UMG 20CM series for this. Together with the GridVis energy data acquisition software and the integrated alarm management, solutions for three areas are united within a common system environment and just one measuring device per measurement point: Energy management according to ISO (acquisition of V, A, Hz, kwh, kw, kvarh, kvar ) Power quality monitoring (harmonics, flicker, voltage dips, transients, etc.) Residual current monitoring RCM This consolidation of the three different functions within a single measuring device brings with it the major advantage that both the assembly and installation, as well as the remaining infrastructure (current transformer, communication lines and equipment, database, software, analysis tools and reporting software, etc.) are only Image 11: The 3-in-1 power quality analyser from Janitza: UMG 512-PRO. required once. Furthermore, all data is logged centrally in a database and can be conveniently processed with a single software application, which in turn significantly increases the acceptance among users. Source references: VdS (Association of Insurers) DIN VDE standards BG: DGUV Specification 3 Electrical systems and operating equipment (BGV A 3) ((Image Source)) Janitza electronics GmbH 10

11 Smart Energy & Power Quality Solutions Janitza electronics GmbH Vor dem Polstück 6 D Lahnau Germany Tel.: Fax: info@janitza.de Document no.: Edition 07/2017 All rights to technical changes are reserved. Important Message Janitza electronics GmbH offers a collection of application reports addressed with in-depth expertise on the topics of Power Quality Monitoring (PQM), Power Management (PM), Power Quality Solutions (PQS), Residual Current Monitoring (RCM) and Energy Management Systems (EnMS). Furthermore, case studies and reference projects are treated. These application notes are meant to our worldwide distributors and agents, as well as its own sales people to train and provide the necessary basic knowledge. On the other hand, they should serve to answer repetitive questions quickly and new trends technically to be transmitted. Each issue covers a self-contained application theme, a specific solution or a technical topic of general interest. It is to share the broad application know-how of Janitza electronics GmbH and its experts, which was established with partners from the PQM, PM, PQS, RCM and EnMSover a long-term period around the world. Some parts of this publication may make statements on the application, use or availability in certain fields or applications. These statements are based on our experience, typical uses and typical requirements associated with specific applications. However, it is the customer or the user to check whether a product of Janitza electronics GmbH with its specifications and standards specified for the particular use is applicable. This application report may be amended by us without further information and brought up to date. This is indicated by the document number. Our products are specified in detail in our catalogues and manuals.