The Reflected Wave Phenomenon

1. Good Q so why anonymous... it just winds people up.

2. Not my field of expertise, but shouldn't any line should be matched at each end for optimum performance?

3. Who won the FA cup in 2008?

Del

Not my field either, but a couple of queries.

Was the VSD giving 50Hz when voltage measured?

Why "only" 510V? If the RMS voltage (phase-phase) is 220, peak is root2*220 = 311V.

To be pedantic, should be 380V star/220V delta or 415V star/240V delta.

In my opinion, if the motor is rated 415 V star then each one of phase windings will be 240 V supplied. The same in delta connection. The difference it is on supply side, only: 415 V phase-to-phase or 240 V phase-to-phase. So if the voltage peak is 510 V then this it could be only phase-to-phase voltage [360 V] peak -in my opinion. Does it?

So 360 V it is less 13.1% than 415 V-motor rated [or 208V compared with 240 V].

Are you sure motor is not 220 V star or 415 V delta? For three phase voltage, phase to phase is 1.732 times the phase voltage. Your supply voltage needs to be 220 VAC phase or 415 V phase to phase.

AC voltages are rms values, so your peak value is 1.414 times that.

Make sure your wiring is of appropriate size for that length run.

Yes, see #2!

You are correct, a little brain fade there. The motor is connected as the diagram on the left (delta). The voltage source is 220 volts (rms) phase to phase or 127 volts phase voltage (rms) or 180 phase volts peak.

I'm confused where the OP measured "peak voltage of only 510 volts" unless it is a voltage spike.

Your comment 3 was correct. measuring in star will always measure RMS per phase with reference to a 0V artificial Neutral point. Measuring in Delta will measure one phase starting to move up the positive 'sine' wave to +160 odd volt while the other phase 'sine' wave is at maximum negative -308V (220V RMS) voltage 120 Deg apart = 380V RMS, and that will always be a higher voltage than 0V to positive peak or negative peak which is 308V and that is 220V RMS or effective 220V. The next Delta measurement will be one phase already 160V in the negative wave while the other phase 120 deg apart will be at 308V (220V RMS) positive, 308V peak (220 RMS)+160V = 380V RMS. Adding the two voltages to get to an RMS reading will be RMS of 308V + 160 full voltage and that is 220+160 =380V. Full sine wave always have an effective value while a rising or falling voltage does not have a RMS value as they are real values.

3. is opposite to 2. and 3. is right.

A recent post, relative to harmonics with VSD motor drive:

Medium Voltage Variable Speed Drive Harmonics

There are several comments and links of very useful information (see JRaef #7, and others).

I think its the same Guy "fishing" for the same data......

Why? Who the hell knows......but that is why he is Anonymous....

Generally, you don't need to be terribly concerned with rejected wave issues at 230V, the insulation used on the magnet wire inside of the motor is the same if you connect it for 400V, so it's peak voltage rating is based on that and thereby well above any possible refuel he'd save peak voltages you will get, even at that distance. You might still get problems with your bearings being damaged by EDM effects, especially if the motor was not designed as inverter duty. If you are concerned and/or the motor is critical or hard to replace, I would invest in a sine wave filter to wire on the output of the drive.

It's better to use a filter if your distance between vsd and motor is above 150 m. With out filter pwm output of vsd on a 280 m is enough to create voltage transients and it may lead to insulation failure in motor. This condition will be more critical even in elicited temperatures.

I would say yes. Filter and suitable VSD cable. Try other VSD manufacturer's literature (Lenze, ABB, etc) and see what their application literature says (the drives are all very similar and Lenze do 220V phase to phase drives).

If in doubt contact the drive manufacturer directly.

Beware of thinking the scope is telling you everything. If your 510V is a "spike" it may be mostly beyond the bandwidth of the scope, but it still shows an impulse response - with a peak amplitude much less than the true value. Also, if you have horizontal scan showing one cycle, a spike may appear too faint to see, except with screen "in the dark". If the scope is "digital", it will reveal little of what happens beyond its bandwidth.

Regarding the possible effect of a spark discharge at the end of a long cable, note that 380m of cable could have a substantial fraction of microfarad capacitance. Together with hundreds of volts at breakdown, the possible spark energy is motor car spark ignition level.

A technique for pulse operation of radar was to discharge a transmission line into a magnetron, pulse length was proportional to line length while the line voltage and characteristic line resistance set the operating current.

Both of these viewpoints make the energy proportional to cable length.

A filter design should incorporate the cable as an element. Also, filters made of capacitors and inductors do not absorb stop band energy, they just reflect it back to the source. Unless the filter has at least a source resistance of matched value, the filter may become a resonator. Note that a cable becomes a resonator when its length is 1/4 wavelength (about 200 kHz for 380m), notably a short at one end makes it behave as a parallel resonance at the open end. Since cable characteristic impedancies are about 100 ohm, a few ohms qualifies as a "short". A few volts at the "short" end can be multiplied many times at the "open" end.

Note that a low voltage across the ends [motor terminals?] of a series L-C resonator can conceal a high current and high resonance voltages across the L & C. When C is the bearing and its insulating oil film, breakdown can occur.

In my opinion, if your motor rated star voltage is 415 V the delta voltage has to be 415/sqrt(3)=240V.

If the peak voltage measured with the scope is 510 V then voltage to neutral it is only 510/sqrt(2)/sqrt(3)=208 V. It seems to me 208 V it is more than 13% dip so your motor works undervoltage [10% has to be the maximum allowable-see IEC 60034-1 Figure 12].It is recommended not more than 5% voltage drop- if the frequency is 50 Hz-for good performances.

In my opinion, if you are using the scope you may check the harmonics also.

208 volts phase to neutral is not a problem (apart maybe from being too high). The motor is connected 220 volt delta, so phase to neutral should be 220/√3 = 127 volt. That's why I queried the 510 volt peak.