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If you have ABC rotation then Vab = V at 0 , Vbc = V at -120, Vca = V at 120 if the meter measures voltages to neutral then Van = Va - Vn Vbn = Vb - Vn Vcn = Vc - Vn now if you ground B phase as is done on open delta PT Vb = Vn then Van = Va - Vb = Vab Vbn = Vb - Vb = 0 Vcn = Vc - Vb = Vcb =...

If there are only three leads coming out of the motor than how the motor is wound makes no difference since you can't hook it up wrong. Have you looked at the CT ratio of the first transformer and compared it to the meter scale. I would try primary current injection on the CT's to verify the...

Delta-Delta or Delta wye connected transformer makes no difference to the motor if the voltage and installation are correct. But,how many leads does the motor have? If the motor has more than three leads than each motor may have been wired incorrectly when it was put on the first transformer...

Rem76: I understand the issue of capacitive charging, however, the very large plant I work at has been using 10 amp high resistance grounding at 13.8KV and 6.9KV for over 40 years. The plant has had many faults over the years and is alarm only on a ground fault. In this time there has not been...

The 6.6kv systems at my plant are limited to 10A. The Multilin 469 with the 50:.025 zero sequence CT does fine at tripping at only 2-3 amps.

If you have a high starting torque load, voltage drop associated with a long cable run can also be a problem on a VFD. As an example, at a starting frequency of 4 hz a VFD may only provide ~30 volts but the motor may draw up to 150% of the motors full load amps. So in order to keep voltage drop...

The Copper Development Association has a very good write up on this. See http://www.cda.org.uk/megab2/elecapps/pub22/sec7.htm "Galvanised steel bolts are normally used but brass or bronze bolts have been used because their coefficients of expansion closely match the copper conductor and hence...

Unfortunatley, the capacitor bank was installed around 1960. So it is unlikely I will get any technical support from the manufacturer. The caps were replaced about 15 years ago to get rid of PCB's. My job is to replace the old oil filled dashpot breaker with a new breaker.

I am installing an electronic trip unit on a 480 volt Circuit Breaker that is protecting a 240 KVAR capacitor bank. The cap bank is made up of 12 modules. Each 20KVAR module consists of 3 delta connected capacitors (each cap is 6.66 KVAR). The substation is a typical 1500KVA solidly grounded...

If you have not tested the cable for absence of voltage you need to consider it energized. When you are making the test for the absence of voltage you need to wear the same PPE as if it is energized, because it may be energized. Grounding switches can fail, the wrong circuit could be locked out...

The motor is started across the line and there are no capacitors. There are actually three of these motors in service and the problem is from time to time these motors blow a 9R fuse in the starter. Usually, but not always, the fuse blows when the motor is started. I talked about this in thread...

How long do you need to wait to restart an induction motor that is still coasting? I have a 1000HP 4160V motor for a large blower that will coast for 10+ minutes after it is shutdown. In this case, if the motor is off for more than 5 minutes the plant must go through a very lengthy startup...

Thank all of you for the prompt responses. I am modernizing the motor protection relay and this information will be helpful in my settings.

A 750KW, 4000V European motor at my plantsite in the US lists three parameters that I am not familiar with and I have not been able to find a reference on: Ma/Mn = .7 Ia/In = 5.3 Te = 16s The Ia/In looks like the ratio of locked rotor current to full load current (maybe Iaccel./Inormal) but I...

Dan, You can find the reference in the Allen-Bradley Centerline Instruction Manual on Page 9-2. See http://literature.rockwellautomation.com/idc/groups/literature/documents/in/2100-in012_-en-p.pdf NOTE: The factory-made power bus connections are tightened by a computer-controlled torquing...

The very large industrial plant I am at has been using HRG at 13.8KV for approximately 40 years. The current is limited to 10 amps. We make many types of plastic and continuity of service is critical so that the plastic does not solidify in the pipes. The plant uses a primary selective system so...

The NEC in section 110.14 (A) says "Terminals for more than one conductor and terminals used to connect aluminum shall be so identified."

Harmonics will raise the temperature of the coil through skin effect heating.

I think your problem is probably due to harmonics and negative sequence currents caused by the severe voltage imbalance on your system. See: http://www.icrepq.com/PONENCIAS/4.279.QUISPE.pdf and http://www.ssac.com/catalog/0807S.pdf

After the overloads tripped I did put a monitor on each of the overloads and watched the motor current as the motor came up to speed and it was picture perfect. If the blower was spinning slowly from process pressure before the motor was started could we draw more than LRA?