HiTeC & Yokogawa - emitec-industrial.ch

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why an external Zeroflux tm current sensor? To maintain the unique features of the Yokogawa power meters, such as measuring accurately current and power from DC up to several kHz, it is necessary to connect special current sensors with the same features. This is of great importance for measuring conversion efficiency in situations where DC power is converted to AC power as for solar power or variable frequency drives. temPerature & Phase shift The normal connection for measuring current with power meters is the “direct current input”, which consists of a special resistor with very good AC properties, the shunt. Up to 50Arms for Yokogawa’s WT1600 (33Arms for WT3000) is no problem. Higher currents however generate too much heat in this shunt to maintain accurate measurements due to temperature drift. For this reason, measuring higher currents requires external current sensors. Current sensors (most for 50–60Hz only) are widely available, but current sensors for accurate energy and power measurements are scarce. A current sensor for electrical power measurements needs to have specifications, not only for its transfer ratio, but also for its internal phase shifts at several frequencies and it’s stability. ct anD Dcct Conventional AC measurement Current Transformers (CT’s) lack the capability to measure current at low frequencies (for example 5Hz, as found in frequency inverter drives). DC current will not be transformed at all, as it saturates the transformer. 8 Output AC with some DC might saturate a conventional transformer, or at least strongly distort the current shape. The Hitec Direct-Current Current Transformer (DCCT), based on the Zero-flux TM principle, is able to measure currents in a wide bandwidth from DC to several kHz with a very high accuracy. Hitec DCCT’s eliminate measuring errors which may arise with conventional AC-sensors. Galvanic isolation More and more users in the Industry start to appreciate the performance of the Hitec Zero-flux TM CT’s for precise current measurements related to electrical power and energy. A Zero-flux TM CT consists of a special multi-core toroidal measuring head and an electronics module. The high accuracy and stability of the Hitec Zero-flux TM CT is based on the Zero-flux TM principle that actively maintains a perfect balance between the magnetic fields of the primary and secondary windings down to the parts-per-million (ppm) level. The Zero-flux TM CT sensors are galvanic isolated from the primary circuits, similar to conventional AC-current transformers. Powerloss Dc-comPonent As most AC clamps and sensors today ignore DC current by not being able to measure DC, the Zero-flux TM CT measures the true wave shape, including the DC component. This is a great improvement for PWM inverters measurements, where any DC component at the output creates a power-loss in the drive and motor windings and therefore should be measured. aDDeD Value of zero-fl Power loss measurements on big transformers require an equals 1 MW uncertainty. Zero-flux TM sensors used in the 500 kV High Voltage Dire current measuring systems in the NORNED converter sta of 700 MW. Transfer ratio of isolated current sensor types and the Yokogawa power meter direct input.
ux TM CurrenT SenSorS extreme high accuracy: 0,1% of a 1 GW transformer ct Current transmission. Shown here are the three-phase tion in Eemshaven (NL) with a total power transmission accuracy The accuracy of the Hitec Zero-flux TM CT sensors matches perfectly with the high accuracy of the power meters from Yokogawa. The typical accuracy of a Zero-flux TM CT with a closed type sensor head is 0.01% of the rated current (50Hz). Closed AC/DC-type sensors equipped with Hall-elements do have an uncertainty of approximately 0.1% of the rated current. sPlit-core A disadvantage in using closed type current sensors is that the primary conductors temporarily have to be disconnected from the load. The load has to be switched off, eyelets of the cable connection need to be replaced if they don’t fit through the sensor hole etc. This is not always allowed and at least timeconsuming, inconvenient and costly. Often it requires the assistance of an installation engineer Therefore Hitec developed the SC1000 high precision split-core Zero-flux TM CT, with an overall accuracy of 0.1% of the rated current (for DC and AC), where as traditional clamp type accuracy normally starts with a 1% uncertainty. The SC1000 reduces the measurement uncertainty on a 4 MW motor/ generator from 40 kW to 4kW. multi-Phase anD easy connection The Hitec current sensors can be delivered as a single unit to measure single-phase current or as a multiphase system with 3 or 4 Zero-flux TM CT’s together with a junction unit, powering all Zero-flux TM CT’s. The junction unit interconnects the current sensors and directs all measuring signals to one output connector to which the Yokogawa power meter is connected. In case of multiple primary cables per phase (power generators, distribution transformers etc.) it is even possible to parallel the Zero-flux TM current sensors to measure higher currents. The standard cable length between the sensor head and the junction unit is 3 meter. Up to 50 meter of cable length is possible on request, more than 50 meter, depends on the local noise environment. The same flexibility applies for the cable length between the junction unit and power meter. measurinG ac-current incluDinG Dc-current; the Zero-flux tm current transformer ■ Measures AC + DC currents at the same time ■ Isolated from the primary circuits ■ Current output or voltage output ■ Wide bandwidth ■ Also a clamp type is available ■ Can be switched on with primary current already present ■ Long cables possible for remote operation Electrical motors easily draw 300 A or more. ■ Saturation detection circuit with automatic reset after over current ■ Very high stability and accuracy 9
Page 1: zero-flux TM CurrenT SenSorS & PreC
Page 4 and 5: eleCTroniC CurrenT SenSorS Measurin
Page 6 and 7: Power MeTerS & analYSerS reliable m
Page 10 and 11: large HaDron ColliDer aT Cern, SwiT
Page 12 and 13: zero-flux TM CurrenT SenSor DiagraM
Page 14 and 15: general SPeCifiCaTionS hitec curren
Page 16: euroPean HeaDQuarTerS Yokogawa euro

HiTeC & Yokogawa - emitec-industrial.ch

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