Recent content by testtech

Thanks for your comments. Mark-The bottom waveform is current and is acquired at line side of the main chiller breaker. It is essentially the sum of the capacitor and current waveforms. The magnitude difference between the motor and breaker currents occurs because this is a star-delta starter...

I was testing a chiller and noted substantial distortion in the current, but not the voltage. This chiller has a star delta starter and 60 kvar of capacitors connected at load side of the M1 contactor. The attached waveforms show the distortion level at the motor terminals, capacitor and source...

Here is what Trane says in one of their installation manuals: Rule 2 Size motor overload protection to account for capacitor-supplied current. Overloads are typically set to measure the total current drawn by the motor. When PFCCs are used, they become the source of part of that current. If the...

Addendum to prior thought--If the caps are on load side of the starter, the cap feeds should probably be routed through the CTs. Then, the CT's would sense the load for which the protective circuits were designed.

Here is another concern--overload protection. The presence of capacitors on load side of the starter will reduce the load sensed by the starter's CT's. The starter will probably no longer detect an overload condition, because the CT's were set up assuming no power factor correction.

I am going to propose testing to the owner. The company that sold them the "energy saving" capacitors has amended their contract, guaranteeing that no failures will result from their installation for a period of one year! Of course, after the failure occurs, it will be too late to prove that...

Thanks Bill. The issue is whether the transients are impacted by the specific location of the capacitor connection. In this case, the capacitors are terminated to load side of the M2 contactor. Thus, they become part of the circuit at the completion of the transition. This is an open...

LionelHutz-If the capacitor is on load side of 2M, then the capacitor is out of the circuit until transition is complete, as you pointed out. Would not this hook-up eliminate the capacitor's potential contribution to a high transient on start-up? It appears to me that the reason the capacitor...

It is a big motor. I measured 1200 amps at full load. The nameplate requires circuit ampacity of 1700 amps. The bus duct that powers the motor is rated 1600 amps. The story gets better--a salesman convinced them to install "energy saving devices" to reduce their energy use by up to 50%...

What is the proper method of connecting power factor correction capacitors to a star delta motor starter? Is there any NEC reference for this (I could not find anything in NEC 460)? The motor in question is 3 phase, 208V, about 500 HP.

Thanks everyone.

Marke: I posted two images of currents. One is 3 phases in a single plot. It occurs just above the one you downloaded. Let me know what you think.

waross This is the 41st harmonic. It seems to me that a rotor bar issue that produced magnetic field imbalances would show up as side bands or been seen through demodulation processing, but not as a harmonic of 60 Hz. Further, it is unclear how high frequency current distortion that is not...

HI All I don't know how many rotor bars. Voltage THD is 1.55%. 60 Hz-476V 3rd-.84 5th-6.97 7th-.76 11th- 1.63 13th-1.13 41st-.43 Motor is 2 pole, <3600 RPM. Should be single speed. It is star-delta connected. Marke--If the motor is overfluxed, does this have any implication for reliability...

waross I am attaching a vibration spectrum. The vibration amplitudes are extremely low, so I have not seen them as evidence of an electrical or mechanical problem. However, the key frequencies are all harmonics of 120 Hz. Unfortunately, I did not acquire vibration frequencies high enough to...