I have been living with my inlaws since October. I built this house in 1992, and they have been experiencing the same recurring problem since they moved in.
Everytime the geothermal system kicks on, every light in the house dims. When this first occured I called the rural electric company and had them check it out. They replaced the transformer and things were fine as far as I knew, until we moved in. After talking with my FIL I find out that the problem had started agian within three years after the first fix by the utility company.
I wired the house, so I can descibe the service from the weatherhead down:
Service drop at the weather head is 350 kcmil copper. It feeds a 200 amp main panel and is paralled to a 100 amp panel that feeds only the geothermal heat pump and backup heat. The drop from the transformer pole to the weather head is roughly 190 feet of 2/0 Triplex with one pole between the house and the transformer. That pole has an outdoor light on it. Both poles have a #4 solid copper ground wires attached. The house service is grounded per NEC with a 9 foot driven ground and #4 THHN stranded wire pluss the copper plumbing ground clamp with #6 THW.
I had the utility company check the problem out again back in Dec. They placed a recording base on the 300 amp meter base. It has taken until this Friday to get the results of thier recording. They say that each time the HVAC system comes on the amp draw peaks at around 164 amps, and the voltage goes from 124v nominal to 105v, and then returns to nominal.
They say that this is indicative of the Locked Rotor Amperage of the unit coming on. The LRA on the unit plate says it is 148 amps. My Fluke says that it is only pulling 36 amp on start up and has a running amp draw of 27.5 amp ( in line with the 28 ams listed on the plate). The only way I can get the start up amps higher is to set the T-stat. high enough to bring on the electric heat at the same time the compressor starts. I max out at 116 amp in that scenario, but this unit has very very rarely had the back up heat come on, and certinally not at all durring the recording period of the utility company.
I have checked all grund and nuetral connection on my side of the service. All of them are at the same torque lbs. that I installed them at 11 years ago.
I have also noticed that in the basement, where we live, when a coffee pot, TV, vacumn cleaner or refrigerator starts up we get the same light flicker.
My contention is that the utility company needs to set a bank of capacitors on this circuit. There have been 10 or 12 houses built here and added to the circuit since I built this house in 92.
All ideas and suggestions are welcomed. At this point I am stumped.
Bill Hartman, 4LORN, And IBEW Barry tell me what I am missing.
Sorry this is long winded.
Dave
Replies
"190 feet of 2/0 Triplex"
ir+l*di/dt,
do a Pspice anal of your circuits, power co is likely right
The 2/0 Triplex is the power companys' service drop from the transformer to my 350 kcmil cable at the weather head.
I pointed that out to the engineer at the REC that I spoke to Friday. The utility company i work for uses 1/0 for all service drops to residentials now.
Still makes it thier problem, doesn't it?
This is a little out of my area.
But I would not automatically trust Fluke. You need to get the specs on it. A lot of meters have some filtering or average circuits in them. That will cause the peak current to be flattened out.
You might check with your company to see what you can get get a meter that that has a fast peak mearurement to compare.
Also I am wonder what would happen if there was a problem with the motor such as a partially failed starting cap. That would give less starting torque and increase the time and current before it gets up to speed.
I know that they have hard start start kits for compressors, but I don't know what they are or what affect that they would have on starting current.
You ask about this over in http://www.hvac-help.com. The last time that I was look at that forum there was a number of tech types.
Also I not sure what a bank of cap's would do at the transformer. It will improve the power factor and thus reduce the secondary current throught the transformer somewhat, but I don't think that it would help your problem. A bank of caps at the compressor would have more affect. By improving the PF you will be reducing the current draw from the feed.
BTW, I graduated from Speed with a BEE back when it was a 5 year program before Ky took over UofL. And we have a full power program along with the electroncis. But that many, many moons ago and I have never done anything with power. All of my work as been with electronics and now software. While I control some multi thousand HP pumps I do it all with 5 volts and let other worry about the high power stuff.
My knowledge of AC is just from working on my own house.
Thanks Bill. The hard start kit is an option I am looking into. I called a Water Furnace dealer the other day, but he hasn't returned my call yet.
If this were only occurring when the HVAC unit started I would be a lot more suspicous of it. We get an annoying flicker of the lihgts when the TV comes on, as well as any number of other appliances. these flickers occure even when the HVAC unit is not running. I an going to call a few neighbors today and see if they are experincing any similar problems.
We have a power quality department at work, that they may loan me a recorder that I can place on just the 100 amp HVAC feed circuit.
If other people are experincing these problems it could be a circuit problem for the rural electric co. If not then the whole issue is on me, and I need to fix it. My FIL has gone through three tv's in the past 11 years. That is a pretty high rate for tv's rated as excellent by consumer report. Now we have four tv's, three PCs and a computerize sewing machine (cost more than 2 PCs), not to mention the other modern marrvals of the electronic age experiencing a 19v voltage drop the HVAC unit cycles.
Dave
First of all I would get whole house surge protect and put it on the main pannel.
On of the problem is that been in a rual area you might be at way out on a "stretchy" line. I remember some comments from my client about one of the rual water pump stations. That they had adnormaly high voltage at that location and I think that they put in a ferroresonant transformer for th electronics. It seem that it was a long line and there where a bunch of dairy farms so they boosted the voltage up so that they could maintain voltage come 4pm when they all started milking and running the feed augers.