Island power question asked of me by Renaldi

[itsmoked]

If possible I would like some feed back if you can assist.

I am in The Bahamas and work in oil storage. For some reason, they've increased their input voltage. It breaks down eventually from 480 volts 3 phase 60 Hz to 500 volts 3 phase 58.5-61.3 Hz. Their single phase voltage has also been affected by this. Since being there I have heard about and noticed fluorescent bulbs, photo cells, motors and even starter coils demonstrating shortened lifespans. To combat some of this, they have gone to replacing their lighting with lamps which have a wide voltage span.

My question is, how much affect will the increase in voltage/frequency have on these types of equipment?

What sort of testing can be done to show this?

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

Anecdote on.
Reminds me of the time I was with a small island utility.
The general manager came to me wondering about a billing trend.
The consumption on one circuit had taken a jump of several percent.
The distribution transformer had recently been replaced on that circuit.
I checked the voltage and discovered that the taps were set too high.
The percentage of overvoltage closely matched the percentage of increased consumption.
I did not have direct control of the line crews. The manager was so happy to see increased billing that he resisted my strong suggestions to set the transformer taps properly.
He was unswayed by the argument that the increased billing was offset by increased fuel consmption, and that there was also the possibility that at times we were running at reducd efficiency, and the gain was much less than he imagined.
Anecdote off.
Frequency; I'd guess that they are running about 5% droop with a swing set.
RESULTS:
Overvoltage; Increased billing. Equipment damage: Incandescent lamp loads, about 4% increased consumption, other resistive loads, about 8% increased consumption, motors and coils, initially a small increase in consumption. The percentage increase will increase with the percentage of over voltage.
Frequency excursions; Generally not an issue. BUT
Overvoltage combined with frequency excursions; If a high voltage coincides with a low frequency you are more likely to exceed the Volts per Hertz ration of inductive equipment such as motors, contactor coils, transformers and lighting ballasts.
Costs: In residential use, expect a small increase in billing and lamp replacement.
In an industrial setting the cost of parts and labour combined with possible downtime will often greatly exceed the increase in billing.
Remedies:
1. Contact the utility and request that the voltage be lowered.
2. Install a bank of autotransformers to reduce the voltage.
If you are able to share with us some details of your plant load, we can suggest a size of autotransformer bank to lower the voltage.
Anecdote on.
We were installing some highlight lighting for a department store chain. This was directed lighting above a furniture display area.
Installation was easy with an open floor area, however once the displays were in place relamping was difficult and time consuming.
The store had us install an autotransformer bank to reduce the voltage by 10%. The result was three fold; Reduced consumption, greatly increased lamp life, and a softer light.
We also did new installations and repairs for an industrial plant with a 600 Volt incoming supply and a mix of 575 Volt motors and 460 Volt motors. The main service was a unit construction that included a 600 Volt MCC for 575 Volt motors and an autotransformer bank feeding a 480 Volt MCC for the 460 Volt motors.
Worked well.
Anecdote off.



Bill
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"Why not the best?"
Jimmy Carter