Characteristics - Applications Calculations

1 Isolated Current andVoltage TransducersCharacteristics - ApplicationsCalculations2 The LEM Group today provides multidisciplinary know-howand solutions for power electronic measurements and tasksin key economic segments like Energy, Transportation,Industry, R&D, Engineering, Medical, Environment, TestFacilities, total commitment to the quality of our products andservices is a priority. Together with the best combination ofunderstanding and competence, is this the only way to gaincustomer confidence and to guarantee long term Current and Voltage TransducersCharacteristics - Applications - CalculationsSummaryPage1 Optimal solutions with 5 differentLEM transducer technologies42 Determining parameters fortransducer parameters need to be selection selection criteria53 hall effect to the hall loop current and principle of and Typical of the measurement loop current and principle of and Typical of calculation and of the measurement power loop voltage and principle of transducer without incorporatedresistor transducer with incorporatedresistor Typical applications174 Closed loop transducers.

2 C and principle of and CT current CD differential current CV voltage CT current CD differential current CV voltage of the measurement CT current CV voltage transducers205 Closed loop transducers, IT and principle of of the measurement accuracy22 Isolated Current and Voltage TransducersCharacteristics - Applications - CalculationsPublished byLEM Coporate Communications LEM Geneva, Switzerland 1996 All rights are reservedPrinted on non-polluting brochure has been written together by several employees:R diger B rkel, Michel Friot, Hartmut Graffert, Hans-DieterHuber, J rgen Ko , Andreas Nemitz, Alfred to change design or specifications are for protection against supply polarity dv/dt disturbances237 LEM-flex - the flexibleAC current and principle of and of the measurement accuracy258 Current and principle of and of the measurement accuracy279 Glossary A - Z28-2910 Design specification, questionnaire31 LEM International Sales Representatives3241 Optimal solutions with 5 different technologies of LEM transducersDuring its 25 years of existence (1972-1997), LEM has beenable to respond to a number of specific demands, thuscreating a wide range of galvanically isolated current andvoltage transducers, which have become standards in themeasurement field and the Characteristics of which areclearly shown in the catalogue.

3 The user may select fromnumerous models divided into 5 main groups for themeasurement of current and voltage (Table 1):- Open-loop hall effect transducers- Closed-loop hall effect transducers- C-type closed-loop transducers- IT-type closed-loop transducers- LEM-flex, flexible transducers for AC summary table hereafter and the detailed description ofthe typical Characteristics of these technologies, make iteasier to choose the most suitable transducer for though most of the Applications will find their bestsolution with a standard transducer selected out of one ofthe 5 technologies mentioned, please contact your LEMspecialist if your needs are not totally met. He will thenpropose a transducer, specific for your solutions with 5 different technologies of LEM transducersCurrent measurementHall effectHall effectC-typeIT-typeLEM-flex, flexibleopen loopclosed loopclosed loopclosed looptransducerstransducerstransducerstra nsducerstransducersfor AC currentMeasuring rangeIP0 - 18000 A0 - 15000 A0 - 150 A0 - 600 A0 - 60000 ABandwidthf0 - 25 kHz0 - 200 kHz0 - 250/500 kHz0 - 100 kHz8 Hz - 100 kHzTyp.

4 Accuracyat 25 CX 1 % % %2 ppm 1 %Linearity % % %1 ppm %Response timetr<3 - 7 s<1 s<50 sOperatingtemperatureTA-25 - +70 C-40 - +85 C-25 - +70 C-10 - +50 C-20 - +85 CTable 1. Overview of the various LEM transducer technologies with their corresponding main characteristicsVoltage measurementHall effectC-typeclosed loopclosed looptransducerstransducersMeasuring rangeVP0 - 9500 V0 - 7000 VBandwidthfseveral kHz0 - 400/700 kHzTyp. accuracyat 25 CX 1 % %Linearity 1 % %Response s0,6 sOperatingtemperatureTA-25 - +70 C-25 - +70 C5 Determining parameters for transducer selection2 Determining parameters for transducer selectionThe wide variety of the LEM transducer range is the directresult of our know-how and many years of experience. Thisenables us to respond to the specific problems of ourcustomers within the greatly diversified application fields ofpower parameters need to be considered?The selection of a transducer is linked to parameters whichare both technical as well as aspects of an application must therefore be globallyenvisioned and taken into account.

5 Among the technicalparameters the following must be mentioned in particular:- The electrical constraints- The mechanical constraints- The thermal constraints- The environmental conditionsIn the development phase of a product, when it has to becharacterised, each parameter is tested, usually individually,without being combined with several others. As regardsproduction control, a quality plan is set up, which indicatesthe tests to be carried out on each product so as to check itscompliance. These tests, which are termed routine tests,are, unless otherwise specified, generally carried out at no-minal current and within a laboratory environment, the practical application is considered, it often is thecase of a combination of several factors which must beevaluated in their totality, so as to select the example, the current to be measured is not the nominalcurrent, the environment combines with magnetic, thermaland mechanical constraints, there are phenomena oftransient overloads, , thus an assembly of parameterswhich may influence the correct operation and the quality ofthe selection criteriaFor a simple application, namely in an environment whichcan be qualified as "clean", electrically, climatically andmechanically, one must first of all refer to the generalcatalogue of LEM transducers, which shows the variousranges of available products with their main Characteristics intabular form.

6 The individual data sheet of each product willthen inform you in greater detail of its following parameters will guide you to a first sample ofproducts which, among the various existing technologies,may prove satisfactory for selection criteriaFor an application of higher complexity, involving acombination of various environmental elements, such as:- Disturbed magnetic environment;- Electro-magnetic interference;- Fast transitory fronts generating important common modevoltage variations (dv/dt);- Disturbances of mechanical origin (vibrations, shocks, )- Specific requests relative to a desired level of partialdischarges;- Compliance with specific standards;- information may be necessary to carry out yourdefinitive is therefore generally useful to supply us with a set-updiagram of your installation and the most detailed possibledescription of the operating conditions of your application ( graph of the waveform of the signal to be measured,nearby disturbing elements such as inductances, othercurrent carrying conductors, or other environmentalconditions).

7 In this instance we have a standard specification sheet (seepage 31), which you should fill out as well as othernecessary information which would allow us to analyse yourneeds in greater parameters for transducer selection Current transducers Electrical parametersSelection criterialType of current to be measured:lAdapted technology (see table 1)DC, AC or complex waveform currentlDefine the thermal or IPN current to be measuredlRange of current to be measuredlDefine the permanent peak current to be measured: IplTransient overloads to be measured:- Maximum peak value- DurationlRequired output signallType: current, voltagelValue at IPN , at Ipk max: define the necessarymeasuring resistor (for current output).lMeasurement accuracylRequired accuracy at 25 CTake into account the offset current or voltage (DC) + accuracy within the operating temperature into account the accuracy at 25 C + the offset drift+ the gain variation (if applicable).lAvailable power supplylPower supply voltagelMaximum allowable current consumptionlIsolation voltagelWorking voltagelApplicable standards defining either:- The necessary dielectric test voltage;- The rated voltage according to the specifiedpollution class.

8 Dynamic operating parametersSelection criterialFrequency rangelDefine the operating frequency range- Fundamental operating frequency- Superimposed switching frequency (if applicable)lDecide on the appropriate transducer technologyldi/dt correctly followedlDefine the response time and rise time in relation to theapplied current slope (di/dt)lDefine the di/dt overloads applied but not measurablewhich the transducer has to on the appropriate transducer technology Environmental parametersSelection criterialOperating, storage temperatureslDefine the effective temperature range for which thespecified performances are the storage temperature range Mechanical parametersSelection criterialElectrical connection of the primary circuitlWith through-hole: define the appropriate aperturedepending on the conductor bar dimensionslOther connections (screw terminals, )lElectrical connection of the secondary circuitlType of secondary circuit connectionlExternal dimensionslDefine the maximum dimensions requiredlFasteninglType of appropriate fastening (printed circuit, on frontpanel)7 Determining parameters for transducer selection Voltage transducersClosed loop hall effect transducersSelection criteria are in their great majority identical tocurrent transducers.

9 Two types of design are available:Without built-in resistor R1- These models are chosen when response time is the fun-damental criteria to consider. Indeed the primary windingshall be designed with a minimum number of turns in orderto reduce its primary inductance. On the other hand inorder to obtain an optimum accuracy, the primary currentwill be higher in order to keep the nominal primaryampere-turns (IP NP) as specified for the model. Forinstance, LV100 model has 100 ampere-turns and LV 200model has 200 Adjustment of the output signal value:Calibration of the output signal value can either be carriedout via the external resistor R1 or by adjusting themeasuring built-in primary resistor R1 The transducer is composed of a complete unit together withR1 + transducer:Choice is made according to the nominal voltage to bemeasured and the measuring range which, for these devicesof generally is times the specified nominal voltage. Electrical parametersSelection criterialMeasurement accuracylConsider value of the primary winding resistance and itsvariation with temperature, relative to the value ofresistance R1 (built-in or external).

10 LMaximum power allowed to dissipate in R1lRelated to resistance R1 and the primary current tobe supplied to the primary winding. Dynamic operating parametersSelection criterialFrequency bandwidth or response timelDepends on the L/R time constant of the primary circuit(Primary winding LP and Primary resistance R1).Voltage transducers, C typeBy principle the construction integrates the primary number of primary amperes-turns is lower than for Halleffect closed loop transducers (for example: CV3 - ..means 3 ampere-turns).Criteria leading to the choice of these transducers are:lHigher frequency bandwidth or faster low sensitivity to common mode voltage accuracy of low power dissipation in the primary low sensitivity to external magnetic effect open loop current to the hall effectBoth the open loop and the closed loop transducers use theHall effect , which was discovered in 1879 by the Americanphysicist Edwin Herbert hall , at the John Hopkins Universityin Baltimore. The hall effect is caused by the Lorentz force,which acts on the mobile electrical charge carriers in theconductor, when they are exposed to a magnetic field that isperpendicular to the current thin sheet of semiconductor material is traversed length-wise by a control current IC (Fig.)