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7/4/2011 7:38 AM | |
Posts: 1 Rating: (0) |
My customer has come back with the following response (in red) - do you have a reply? All `current-dependent` functions ( e.g. overload protection, current measurement and monitoring) of SIMOCODE are not useable, if SIMOCODE is operated together with a converter. (whether for the operation on the load side of a frequency convertors nor an the main side).The reasons for that are following : - For current evaluations only frequencies of 50/60 Hz and multiples thereof are allowed.Harmonics ARE multiples of 50/60Hz! I presume Support mean multiples of 50/60Hz but only sinusoidal, not a combination harmonic currentsOther frequencies (or a high part of harmonics) will result in inaccurate measurements. - it is not guarantueed, that the overload tripping characteristic of SIMOCODE (according IEC 947-4)) is suitable to protect motors, when they are operated with slow speed. Problem is there, that the naturally, own convection of the motor is reduced. That effect is not considered in the SIMOCODE overload tripping characteristic Not sure what Support is saying here – that the Simocode cannot measure current accurately if it is high in harmonics, or that the problem is only on slower speeds?? The two are separate issues.1. Nearly all new electronic protection relays (like ETU’s) can measure harmonic currents accurately and then compare this to the protection that is set. If the harmonic current exceeds the set protection, it will trip within the period.I don’t see why the Simocode cannot do the same (ie. compare harmonic current with motor class protection setting), unless of course it does not have the computational brain power like the new relays have? Can you find out if that is the reason?2. Slow speeds are always a problem and to my knowledge no electronic relay can accurately protect a motor at speeds <20% when running at full current (ie. VSD controlled). That is why we specify external forced fan cooling for the motor when running <50% speed on VSD; with additional thermistor or RTD protection. If the Simocode is used with the VSD, it would only be for overload current protection per standard DOL, not at low speeds.Please note also, that the nuisance impacts of a converter are very high, especially when it is installed very close to the SIMOCODEs. Therefore the whole installation (earthing of all parts, electromagnetic shielding ...) have to be done very carefully. So I can only recommend : - do not connect the main lines to the internal CT`s of SIMOCODEThis is the best answer yet why Simocodes should not be connected load side of the VSD – electromagnetic interference or EMI. Because the cables will not be individually shielded when connected through the Simocode CTs, the EMI may affect the Simocode electronics (same discussion as electronic relays affected by EMI). So for dual drive application, it will not work…However, this does not stop us from connecting at the line side of the VSDs where an application requires, where the harmonics are of much lower frequency and not considered to have EMI issues?- Runtime anfd Check-Back Time (these are internal current monitoring functions of SIMOCODE) have to be set to `0` (= deactivated). - the feed-back, that the motor is on or off, has to be done by auxiliary contacts of the main contactor via inputs of the SIMOCODE - nevertheless, the thermistor protection of SIMOCODE can be used for the motor protection. With other words: the use of SIMOCODE in connection with converters is not very comfortable and only with reduced functionality possible.
Splitted from Simocode Pro V Current reading. |
Last edited by: O_Moderator at: 7/6/2011 2:32 PMnew subject after splitting |
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