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  • Users: MikiBg
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  1. MikiBg

    Voltage and current THD of solar inverters

    Hi all! I was dealing with manufacturer's data about THD at solar inverter's output, in order to use it for harmonic load flow calculation. It wasn't clear whether voltage or current THD is specified. I have searched for other data sheets from different manufacturers, and it looks like THD of...
  2. MikiBg

    Thermal effects of short circuit currents according to IEC standards

    Hi all! Couple of questions about the subject. Low voltage: Relatively new IEC 61439 standard defines rated short time withstand current Icw. It is the current which equipment or assembly can withstand for period of time given by manufacturer. Icw shall be equal to or higher than the prospective...
  3. MikiBg

    Thermal effects of short circuit currents according to IEC standards

    Hi all! Couple of questions about the subject. Low voltage: Relatively new IEC 61439 standard defines rated short time withstand current Icw. It is the current which equipment or assembly can withstand for period of time given by manufacturer. Icw shall be equal to or higher than the prospective...
  4. MikiBg

    Shunt trip coil controlled by electronic protection unit

    Hi all. There is ABB Sace Emax 2.2N circuit breaker with Ekip dip LI electronic protection unit. It contains a terminal for connection of control voltage to shunt trip coil via NO contact controlled by protection unit. Since protection unit must cause CB to be opened in the case of fault...
  5. MikiBg

    Altivar 630 starting torque

    Hi all! I'm currently dealing with Altivar 630 VFD and wondering how to find out starting motor torque, because no such parameter is available. Is it implicitly determined by low (starting) frequency and V/f ratio, regardless of control mode selected? Is it related to acceleration time and...
  6. MikiBg

    Altistart 48 motor leakage protection

    Hi all! Is there any leakage/residual current protection implemented in Schneider Electric ATS48 soft starter, in steady state, after start? I haven't found anything about it inside the manual. We need a protection equivalent to RCD, i.e. switch off the motor in the case of relatively small...
  7. MikiBg

    Impedance in parallel with surge arrester

    Hi all! Connection of impedance in parallel with surge arrester at 36/0.4 kV power transformer terminals is required by tender documentation. What is the purpose of this impedance and how it should be dimensioned? Regards, Miki
  8. MikiBg

    4 wire Pt100 probe to 2/3 wire temperature controller

    Hi all. We have 4 wire Pt100 probe for submersible pump motor protection and temperature controller which supports 2 or 3 wire measurement installed on the site. What is the best way to adapt the probe to controller? I have found some drawings online suggesting 2 wire connection of 4 wire probe...
  9. MikiBg

    Explosive zone around pump shaft

    Greetings to all. We have defined Ex zone 1 within inlet pumping station quadratic shaft on WWTP. Flammable gas present is methane. Since shaft cover isn't gas-tight, the Engineer requires that Ex zone 2 needs to be defined around the cover. The shaft is outside the building, i.e. open space is...
  10. MikiBg

    Line or load contactor

    Hi all! By your experience, which is a better solution for VFD controlled motor outgoing: 1. With line contactor (upstream of VFD). Some say that it's good for VFD to be disconnected from power supply if it is out of operation for long time (e.g. standby pump unit) 2. With load contactor...
  11. MikiBg

    Lightning protection of steel water tank

    Hi all. Steel tank for potable water is on the top of steel supporting structure. Early streamer emission device is planned to be installed on the top of it, in order to protect other facilities. Steel supporting structure can be used as natural down conductor. My question is should I use non...
  12. MikiBg

    Lightning protection of steel water tank

    Hi all. Steel tank for potable water is on the top of steel supporting structure. Early streamer emission device is planned to be installed on the top of it, in order to protect other facilities. Steel supporting structure can be used as natural down conductor. My question is should I use non...
  13. MikiBg

    Earthing rectangular tape in cable trench

    Hi all! I haven't found a clear recommendation about this issue, so I'm asking you about it... Earthing tape with rectangular 30x3.5mm cross section shall be laid down in cable trench, as additional earthing on WWTP. Is it better to laid it above or bellow cables? Some say that tape placed above...
  14. MikiBg

    How to determine a frequency reference for VFD

    Hi all, Mixers for flocculation in WTP need to be rotated in desired speed. Motors are driven by vector control capable VFDs, but no speed sensors or any external control loops are applied. Is there a way to calculate, at least approximate frequency reference for VFD which will result in...
  15. MikiBg

    Fixed cap bank during motor start

    Hi all! There is a 110kW motor in blower set. Manufacturer says that DOL motor start can damage the blower. Current design solution assumes star(wye)-delta starter, but there is a fixed capacitor bank connected to motor. I'm afraid that capacitor inrush current/over voltage during motor start...
  16. MikiBg

    VFD input power factor

    Hi all! I'm about to start a re-design of some pumping and compressor stations supplied via VFDs. It will be good to know input power factor for large VFD. I suppose that there is a PFC circuit, but guess that it compensates only fundamental. So, with voltage distortion neglected, there will be...
  17. MikiBg

    Gas generator vs Grid load sharing

    Hi all! Waste water treatment plant produces gas during cleaning process, and it should be use for gas generator supply, giving electric power and heat at the output. 0.4kV PCC is feed from grid via 20/0.4 distribution transformer, and from two generators. How would generator and grid share the...
  18. MikiBg

    V/Hz vs Vector control VFD

    Hi all! This thread may be considered as extension of one previous: http://www.eng-tips.com/viewthread.cfm?qid=248018&page=8 After receiving request for offer and required techical data, one potential vendor asked: "Is it neccessary to provide VFDs with vector control, wich are much more...
  19. MikiBg

    Influence of VFD on short circuit current

    Hi all! IEC defines how to estimate a influence of motor to short circuit current, but it says nothing about how motor is supplied. What about motor driven by a VFD, is it need to be taken into account? I'm asking because of often case I'm dealing with: 3 motors via VFD and one DOL, all four...
  20. MikiBg

    VFD data sheet

    Hi all! Can someone tell me what are MINIMUM NECESSARY data for valid VFD data sheet? I'm writing it for the first time and I'm not sure. 250kW motor, centrifugal pump for water intake. Besides nominal motor power/current, is it necessary to specify starting current, maximum torque and speed...

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